Sample records for andesites

  1. Thermodynamic and rheological properties of rhyolite and andesite melts


    Neuville, Daniel R.; Courtial, Philippe; DINGWELL, Donald B.; Richet, Pascal


    The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measur...

  2. Thermoelastic properties of the Rotokawa Andesite: A geothermal reservoir constraint (United States)

    Siratovich, P. A.; von Aulock, F. W.; Lavallée, Y.; Cole, J. W.; Kennedy, B. M.; Villeneuve, M. C.


    Knowledge of the thermal properties of geothermal reservoir rocks is essential to constraining important engineering concerns such as wellbore stability, reservoir forecasting and stimulation procedures. The thermo-mechanical evolution of geological material is also important to assess when considering natural processes such as magmatic dyke propagation, contact metamorphism and magma/lava emplacement and cooling effects. To better constrain these properties in the geothermal reservoir, thermal measurements were carried out on core samples from production wells drilled in the Rotokawa Andesite geothermal reservoir, located in the Taupo Volcanic Zone, New Zealand. Linear thermal expansion testing, thermogravimetric analysis, and differential scanning calorimetry were used, employing experimental heating rates of 2, 5 and 20 °C/min. Thermal property analyses can elucidate whether thermal expansion values measured under varied heating (and cooling) rates are rate dependent and if thermo-chemical reactions influence the resultant expansivity. Measured thermal expansion coefficients of the Rotokawa Andesite are shown not to be heating rate dependent. We have also found that significant thermochemical reactions occur during heating above 500 °C resulting in non-reversible changes to the thermomechanical properties. The combined thermogravimetric, calorimetric and thermomechanical analysis allows insight to the reactions occurring and how the thermomechanical properties are affected at high temperature. We incorporated results of tensile strength testing on the Rotokawa Andesite to apply our thermal property measurements to a one-dimensional thermal stress model. The developed model provides a failure criterion for the Rotokawa Andesite under thermal stress. The importance of this study is to further understand the critical heating and cooling rates at which thermal stress may cause cracking within the Rotokawa reservoir. Thermal cracking in the reservoir can be

  3. Exploring the scale-dependent permeability of fractured andesite (United States)

    Heap, Michael J.; Kennedy, Ben M.


    Extension fractures in volcanic systems exist on all scales, from microscopic fractures to large fissures. They play a fundamental role in the movement of fluids and distribution of pore pressure, and therefore exert considerable influence over volcanic eruption recurrence. We present here laboratory permeability measurements for porous (porosity = 0.03-0.6) andesites before (i.e., intact) and after failure in tension (i.e., the samples host a throughgoing tensile fracture). The permeability of the intact andesites increases with increasing porosity, from 2 ×10-17 to 5 ×10-11 m2. Following fracture formation, the permeability of the samples (the equivalent permeability) falls within a narrow range, 2- 6 ×10-11 m2, regardless of their initial porosity. However, laboratory measurements on fractured samples likely overestimate the equivalent permeability due to the inherent scale-dependence of permeability. To explore this scale-dependence, we first determined the permeability of the tensile fractures using a two-dimensional model that considers flow in parallel layers. Our calculations highlight that tensile fractures in low-porosity samples are more permeable (as high as 3.5 ×10-9 m2) than those in high-porosity samples (as low as 4.1 ×10-10 m2), a difference that can be explained by an increase in fracture tortuosity with porosity. We then use our fracture permeability data to model the equivalent permeability of fractured rock (with different host rock permeabilities, from 10-17 to 10-11 m2) with increasing lengthscale. We highlight that our modelling approach can be used to estimate the equivalent permeability of numerous scenarios at andesitic stratovolcanoes in which the fracture density and width and host rock porosity or permeability are known. The model shows that the equivalent permeability of fractured andesite depends heavily on the initial host rock permeability and the scale of interest. At a given lengthscale, the equivalent permeability of high

  4. Origin of High-Alumina Basalt, Andesite, and Dacite Magmas. (United States)

    Hamilton, W


    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it.

  5. Magma heating by decompression-driven crystallization beneath andesite volcanoes. (United States)

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine


    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

  6. Correlation between aggregate quality and compressive strength of andesite from Hungary (United States)

    Czinder, Balázs; Török, Ákos


    Andesite is one of the most common lithology that is used as aggregate. Testing of aggregate quality traditionally includes Los Angeles, micro-Deval tests and the quality of the stone is assessed according to these values. In the present paper both aggregate properties and strength properties of andesites are compared in order to find correlation between aggregate strength, durability and compressive and tensile strength as well as frost resistance. Tests were made from andesite types obtained from two operating quarries of Nógrádkövesd and Gyöngyössolymos. Uniaxial compressive strength (UCS) values were compared with aggregate test results obtained from the same block. Air dry, water saturated and freeze-thaw subjected specimens were tested. According to lithological description and fabric analyses samples were grouped into 4 main lithotypes: one from Nógrádkövesd and three from Gyöngyössolymos. Fine porphyric andesite from Gyöngyössolymos provided the best micro-Deval values. In terms of uniaxial compressive strength the same trend was found, fine porphyric andesite from Gyöngyössolymos had the highest UCS under laboratory conditions, while coarser porphyritic andesite from the same quarry had lower strength. Water saturation decreased UCS as it was expected. Tensile strength values show a gradual deceases from air dry to water saturated and finally subjected to freeze-thaw cycles. Mean micro-Deval value of fine porphyric Gyöngyössolymos andesite was about 7, while that of the coarser porphyritic andesite was app. 16. These values are still higher than the mean micro-Deval test result of Nógrádkövesd andesite; which was 20. A good correlation was found in between Los Angeles and micro-Deval values, but there was no indication that micro-Deval values correlate well with UCS.

  7. Rare-earth element geochemistry and the origin of andesites and basalts of the Taupo Volcanic Zone, New Zealand (United States)

    Cole, J.W.; Cashman, K.V.; Rankin, P.C.


    Two types of basalt (a high-Al basalt associated with the rhyolitic centres north of Taupo and a "low-Al" basalt erupted from Red Crater, Tongariro Volcanic Centre) and five types of andesite (labradorite andesite, labradorite-pyroxene andesite, hornblende andesite, pyroxene low-Si andesite and olivine andesite/low-Si andesite) occur in the Taupo Volcanic Zone (TVZ), North Island, New Zealand. Rare-earth abundances for both basalts and andesites are particularly enriched in light rare-earth elements. High-Al basalts are more enriched than the "low-Al" basalt and have values comparable to the andesites. Labradorite and labradorite-pyroxene andesites all have negative Eu anomalies and hornblende andesites all have negative Ce anomalies. The former is probably due to changing plagioclase composition during fractionation and the latter to late-stage hydration of the magma. Least-squares mixing models indicate that neither high-Al nor "low-Al" basalts are likely sources for labradorite/labradorite-pyroxene andesites. High-Al basalts are considered to result from fractionation of olivine and clinopyroxene from a garnet-free peridotite at the top of the mantle wedge. Labradorite/labradorite-pyroxene andesites are mainly associated with an older NW-trending arc. The source is likely to be garnet-free but it is not certain whether the andesites result from partial melting of the top of the subducting plate or a hydrated lower portion of the mantle wedge. Pyroxene low-Si andesites probably result from cumulation of pyroxene and calcic plagioclase within labradorite-pyroxene andesites, and hornblende andesites by late-stage hydration of labradorite-pyroxene andesite magma. Olivine andesites, low-Si andesites and "low-Al" basalts are related to the NNE-trending Taupo-Hikurangi arc structure. Although the initial source material is different for these lavas they have probably undergone a similar history to the labradorite/labradorite-pyroxene andesites. All lavas show evidence

  8. A dearth of intermediate melts at subduction zone volcanoes and the petrogenesis of arc andesites. (United States)

    Reubi, Olivier; Blundy, Jon


    Andesites represent a large proportion of the magmas erupted at continental arc volcanoes and are regarded as a major component in the formation of continental crust. Andesite petrogenesis is therefore fundamental in terms of both volcanic hazard and differentiation of the Earth. Andesites typically contain a significant proportion of crystals showing disequilibrium petrographic characteristics indicative of mixing or mingling between silicic and mafic magmas, which fuels a long-standing debate regarding the significance of these processes in andesite petrogenesis and ultimately questions the abundance of true liquids with andesitic composition. Central to this debate is the distinction between liquids (or melts) and magmas, mixtures of liquids with crystals, which may or may not be co-genetic. With this distinction comes the realization that bulk-rock chemical analyses of petrologically complex andesites can lead to a blurred picture of the fundamental processes behind arc magmatism. Here we present an alternative view of andesite petrogenesis, based on a review of quenched glassy melt inclusions trapped in phenocrysts, whole-rock chemistry, and high-pressure and high-temperature experiments. We argue that true liquids of intermediate composition (59 to 66 wt% SiO(2)) are far less common in the sub-volcanic reservoirs of arc volcanoes than is suggested by the abundance of erupted magma within this compositional range. Effective mingling within upper crustal magmatic reservoirs obscures a compositional bimodality of melts ascending from the lower crust, and masks the fundamental role of silicic melts (>/=66 wt% SiO(2)) beneath intermediate arc volcanoes. This alternative view resolves several puzzling aspects of arc volcanism and provides important clues to the integration of plutonic and volcanic records.

  9. Lead isotope constraints on the origin of andesite and dacite magmas at Tungurahua volcano (Ecuador) (United States)

    Nauret, Francois; Ancellin, Marie-Anne; Vlastelic, Ivan; Tournigand, Pierre-Yves; Samaniego, Pablo; Le Pennec, Jean Luc; Gannoun, Mouhcine; Hidalgo, Silvana; Schiano, Pierre


    Understanding the occurrence of large explosive eruptions involving silica-rich magmas at mostly andesitic volcanoes is crucial for volcanic hazard assessment Here we focus on the well-known active Tungurahua volcano (Ecuador), specifically its eruptive sequence for the last 3000 years BP, which are characterized by VEI 3 explosive events involving mostly homogeneous andesitic compositions (56-59 wt.% SiO2). However, some large eruptions (VEI ≥ 4) involving andesitic and dacitic magmas (up to 66 wt.% SiO2) also occur at 3000 BP, 1250 BP and 1886 AD. An additional outburst of siliceous magmas occurred during the last eruptive eruption of this volcano in 2006 [1]. Volcanic products at Tungurahua are described as been generated by a binary mixing between a silica-rich and a silica-poor end-member, but the origin of these components was not discussed [2]. Major, trace elements and Sr-Nd-Pb isotopes were used to investigate the genesis of the andesites and dacites. Andesites are heterogeneous in terms of Pb isotopes (206Pb/204Pb: 18.189-19.154, 207Pb/204Pb:15.658-15.696, 208Pb/204Pb: 38.752-38.918, 207Pb/206Pb: 0.8240-0.8275) but homogeneous in terms of major-trace element. Dacite are characterized by homogenous and low 207Pb/206Pb (0.8235±0.0001), very low Nb/U (1.97 to 4.49) and Ce/Pb (2.52-2.99) and high Th/La ratios (0.24 to 0.49). Triangular distribution of data in major element or trace element ratio vs. Pb isotopes plots suggests that at least three components control geochemical variability at Tungurahua. We interpret andesite compositions as reflecting mainly a deep mixture of two mantle components, with small addition of crustal material. We suggest that dacite results from a mixing between various andesite compositions and a larger amount of a contaminant derived from the volcanic basement of the Tungurahua made of late Cretaceous to Palaeogene oceanic plateau basalts and volcano-sedimentary rocks volcanic. Since andesite and dacite occur during the same

  10. Spectral evidence for weathered basalt as an alternative to andesite in the northern lowlands of Mars. (United States)

    Wyatt, Michael B; McSween, Harry Y


    Mineral abundances derived from the analysis of remotely sensed thermal emission data from Mars have been interpreted to indicate that the surface is composed of basalt (Surface Type 1) and andesite (Surface Type 2). The global distribution of these rock types is divided roughly along the planetary dichotomy which separates ancient, heavily cratered crust in the southern hemisphere (basalt) from younger lowland plains in the north (andesite). But the existence of such a large volume of andesite is difficult to reconcile with our present understanding of the geological evolution of Mars. Here we reinterpret martian surface rock lithologies using mineral abundances from previous work and new mineralogies derived from a spectral end-member set representing minerals common in unaltered and low-temperature aqueously altered basalts. Our results continue to indicate the dominance of unaltered basalt in the southern highlands, but reveal that the northern lowlands can be interpreted as weathered basalt as an alternative to andesite. The coincidence between locations of such altered basalt and a suggested northern ocean basin implies that lowland plains material may be composed of basalts weathered under submarine conditions or weathered basaltic sediments transported into this depocentre.

  11. The anatomy of an andesite volcano: A time-stratigraphic study of andesite petrogenesis and crustal evolution at Ruapehu volcano, New Zealand

    DEFF Research Database (Denmark)

    Price, R.C.; Gamble, J.A.; Smith, I.E.M.;


    Ruapehu, New Zealand’s largest active andesite volcano is located at the southern tip of the Taupo Volcanic Zone (TVZ), the main locus of subduction-related volcanism in the North Island. Geophysical data indicate that crustal thickness transitions from ... Ruapehu. The volcano is built on a basement of Mesozoic metagreywacke and geophysical evidence together with xenoliths contained in lavas indicates that this is underlain by oceanic, meta-igneous lower crust. The present-day Ruapehu edifice has been constructed by a series of eruptive events that produced...

  12. Soils derived from Pieniny andesite, Wdżar hill, Outer Carpathians (Poland) (United States)

    Kajdas, Bartlomiej; Zaleski, Tomasz; Mazurek, Ryszard


    Tertiary andesite occurs in only few places in Polish part of the Outer Carpatians. The biggest andesitic body is observed at the Wdżar hill (676 m a.s.l), SE from Kluszkowce village. To the beginning of the 1970s active quarry were located at the hill slope, and from the end of 1990s Wdżar is used as a ski resort. Because Wdżar is the culmination protruding over sandstones and shales of Magura Unit of Outer Carpatians, it gives opportunity to investigate soils derived directly from the andesite. Primary, unaltered andesite contain mainly plagioclase (An28-62), amphibole (hornblende group), clinopiroxene (pigeonite group) and Fe-Ti oxides (Michalik et al., 2004). Quartz in those type of rocks is absent. Andesites from Pieniny Mts. contain low amount of silica (ca. 52-55% wt. in fresh and about 62% wt. in hydrothermally altered rocks), and high amount of CaO (5,5-9,2% wt.) and MgO (0,8-5,5% wt.) (Nejbert et al., 2012). Soils cover on Wdżar hill represents different stages of soil development. Shallow, ca. 15 cm deep, Eutric Leptosols and deeper, 60 cm and over 200 cm deep, Eutric Skeleti Cambisols (Colluvic, Humic) were distinguished. There are significant differences both between the soil groups as well as inside them. Investigated soils have sandy loam, loam and silt loam texture. Surface, organic horizons show acid reaction, but cambic and parent material horizons show neutral reaction. Cation exchange capacity ranges between 526.9 and 298.2 mmol(+)ṡkg-1 in humus horizons and between 451.4 and 225.8 mmol(+)ṡkg-1in cambic and parent material horizons. The amount of exchangeable Ca2+ ranges between 386.8 and 175.8 mmol(+)ṡkg-1 and is about 6 times higher than sum of Mg2+, Na+ and K+ in the soil horizon. Despite of the high amount of Ca2+, there were no active carbonates in investigated soil. The soils, that are developed from the andesite, usualy contain high amount of clays and very low amount of primary quartz. Andesite from Wdżar reveals minor degree


    Directory of Open Access Journals (Sweden)

    - Munaji


    Full Text Available Telah dilakukan penelitian untuk menentukan nilai resistivitas dan kedalaman batuan andesit di Desa Polosiri. Prinsip kerja metode geolistrik adalah mempelajari aliran listrik di dalam bumi dan cara mendeteksi di permukaan bumi. Metode tahanan jenis didasari oleh hukum Ohm, untuk mengetahui jenis lapisan batuan didasarkan pada distribusi nilai resistivitas pada tiap lapisan. Variasi harga tahanan jenis akan didapatkan jika jarak masing-masing elektroda diubah, sesuai konfigurasi alat yang dipakai (konfigurasi Schlumberger. Data hasil pengukuran di lapangan berupa beda potensial dan arus yang dapat digunakan untuk menghitung resistivitas semu. Penelitian ini dilakukan sebanyak tiga lintasan. Data hasil pengukuran diolah menggunakan software IPI2Win. Berdasarkan hasil penelitian diperoleh bahwa batuan andesit di Desa Polisiri memiliki resistivitas 212 Ωm – 300 Ωm dengan kedalaman 1.3 m - 1.86 m.

  14. Production of ferroan andesites by the experimental partial melting of an LL chondrite (United States)

    Mcguire, J. C.; Jurewicz, A. J. G.; Jones, J. H.


    A partial melting experiment on the St. Severin (LL) chondrite produced a melt that was andesitic, having 54-60 wt% silica, at 1200 C and an oxygen fugacity of IW+2, two log units above the iron-wustite (IW) buffer. Under these same conditions, CV, CM, and L chondrites produced low-silica melts resembling angrites. This experimental study attempts to reproduce and explain this unusual result.

  15. Isotopic composition of strontium in three basalt-andesite centers along the Lesser Antilles arc (United States)

    Hedge, C.E.; Lewis, J.F.


    Si87/Sr86 ratios have been determined for lavas and py lastic rocks from three basalt-andesite centers along the Lesser Antilles arc-Mt. Misery on the island of St. Kitts, Soufriere on the island of St. Vincent, and Carriacou, an island of The Grenadines. The average Si87/Sr86 content of these rocks is 0.7038 for Mt. Misery, 0.7041 for Soufriere, and 0.7053 for Carriacou. All the Sr87/Sr86 values from each center are the same within analytical uncertainty (??0.0002). The constancy of strontium isotopic data within each center supports the hypothesis that basalts and andesites for each specific center investigated are generated from the same source - in agreement with petrographic and major- and minor-element data. Strontium isotopic compositions and elemental concentrations, particularly of strontium and nickel, indicate that this source was mantle peridotite and that the relationship between the respective basalts and andesites is probably fractional crystallization. ?? 1971 Springer-Verlag.

  16. The Petrographical-Geochemical Properties and Industrial Availability of the Karadeniz Eregli Andesites (Zonguldak

    Directory of Open Access Journals (Sweden)

    Gürkan Bacak


    Full Text Available Aim of this study is to determine the geological properties (lithology, petrography, geochemistry and industrial usibility of the Upper Cretaceous volcanics, seperated on the area, among Kozlu-Krd. Ereğli and Ormanlı, westside of Zonguldak. Volcanics, described as andesite, basaltic andesite and trachy-andesite by petrographically and geochemically, have subduction zone calk-alkaline character. Firstly, in laboratuary studies the aggregate tests (grading, specific gravity, water absorption, organic impurity, flakiness index, Los Angeles test for resistance to wear, peeling test, freezing resistance and UCS were realized on the 5 selected fresh patterns, match with the standarts (TS, ASTM, AASHO. Secondly, concrete tests (grading of the concrete aggregates, concrete preperation, slump test, specific density of concrete and UCS of the concrete were made on the concrete patterns with volcanic aggregate additive.Statistical relationships were determined between values of the agreggate and concrete tests results. Both petrographical, chemical, physical and mechanical tests values of the agreggates and concretes are also match with the standarts, given above.As a conclusion, realized that volcanic aggregates for superstructure materials and C 25/30 concrete which made with volcanic aggregate (by using the specimen of N-4 aggregate for rainforcement buildings, bridges, foundation walls can be used.

  17. Manupulation of microstructure, phase evolution and mechanical properties by devitrification of andesite for use as proppant (United States)

    Koseski, Ryan P.

    Small, roughly spherical ceramic particles, approximately 1mm in size are used for a number of applications including casting sands, catalysts, and cement fillers. The oil and natural gas industry utilizes such materials in tonnage quantities yearly as extraction aids. Particles intended for this application are referred to as proppants. Proppants are composed of materials that differ by density, strength and cost, and are selected on a site by site basis. Recently, competing usage and depletion of reserves of one of the most popular category of proppant materials, sintered aluminosilicates (e.g. kaolinite, bauxite) have driven the need for alternative raw materials for proppant manufacturing. Andesite, a by-product of mining operations in the south-west United States was identified as an abundant, readily available, and low cost alternative proppant material that can be fused and net-shaped into a glass which when crystallized results in microstructures which may offer substantial toughening and fracture characteristics which may serve to their advantage for use as proppants that do not decrease the permeability ("blind") the particle bed. This study addressed the devitrification behavior and its role on the mechanical properties of andesite-based glass-ceramic spheres for use as proppants. Timetemperature- transformation studies were performed to evaluate the devitrification behavior of andesite glass. Crystalline phase evolution and microstructural development were evaluated using quantitative x-ray diffraction, scanning electron microscopy, differential thermal analysis, and spectrophotometry. The andesite glass devitrification commenced with the precipitation of iron oxides (magnetite) which served as seeds for the epitaxial growth of dendritic pyroxenes. Mechanical properties, such as diametral compressive strength, fracture toughness, hardness, and fracture morphology were correlated with crystalline phase evolution. Selected heat treatments resulting in the

  18. Andesite petrogenesis in a hybrid arc-rift setting: the Western Trans-Mexican Volcanic Belt (United States)

    Gómez-Tuena, A.; Vázquez-Duarte, A.; Díaz-Bravo, B.; Mori, L.


    The western sector of the Mexican subduction zone is characterized by the steep subduction of one of the youngest slabs on the planet (Rivera plate), and by the existence of a continental rift at ~230 km to the north from the trench (the so-called Tepic-Zacoalco rift, TZR), under which the subducted slab is either extremely deep or even absent (>250 km). The volcanic front is located at ~170 km from the trench and contains abundant potassic-alkaline lamprophyres with strong subduction (Ba/Ta= 1600-6000) and garnet signatures (Gd/Yb= 2-8), that have been recently interpreted as influenced by deep K2O-rich slab melts or supercritical fluids (Gómez-Tuena et al., 2011, GCA). In contrast, the most mafic rocks within the TZR are high-Nb, intraplate-like basalts that appear to derive from low extents of melting of a dryer (Ba/Ta= 800-60) and shallower (Gd/Yb= 2-2.5) mantle source. Even though a simple transition from an arc environment to an extensional tectonic regime is apparent when only the most primitive volcanic rocks are taken into account, the scenario becomes more complicated since at least five stratovolcanoes have been erupting typical arc andesites within the TZR over the last million years (San Juan, Sanganguey, Tepetiltic, Ceboruco and Tequila). Surprisingly, true calc-alkaline basalts that could be parental to andesites have not been found, indicating that andesites may have a direct mantle origin. Indeed, mayor and trace element compositions of volcanic rocks from western Mexico arrange in discrete suites with linear trends that are indicative of mixing, but they form sub-parallel arrays that do not converge to a common primitive basaltic melt, and often follow diverging trends in trace element-ratio plots. Melt-crust interactions likely occurred during magma ascent, since the volcanic rocks frequently include xenoliths and disequilibrium textures, but correlations among isotopic compositions and indexes of fractionation are not clearly observed in the

  19. Contrasting andesitic magmatic systems in adjacent North Island volcanoes, New Zealand: implications for predicting eruptions (United States)

    Price, R. C.; Smith, I. E.; Gamble, J. A.; Moebis, A.; Cronin, S. J.


    For active or dormant andesite volcanoes, detailed, stratigraphically controlled, geochemical and petrological information enables an understanding of the magma supply and plumbing system feeding eruptions at the surface. This can establish a basis for predictive eruption models and thus for hazard prediction and management. The potential for petrography to inform volcanic hazard management is demonstrated by comparing two andesitic volcanoes located at the southern end of the Taupo Volcanic Zone in New Zealand's North Island. Ngauruhoe has been constructed over the past 3-5 ka and last erupted in 1975. Nearby Ruapehu has a much longer eruptive history extending back beyond 230 ka B.P. Despite their close spatial proximity, the two volcanoes show geochemical contrasts suggesting that each magmatic system has operated separately. The petrology and geochemistry (major and trace element chemistry, U-series isotopes, Sr and Nd isotopes) of eruptives from each volcano reflect magma evolution in a complex magma storage and plumbing system with magma chemistry strongly influenced by fractional crystallisation and crustal assimilation but in the case of Ngauruhoe there is evidence for cyclicity in the evolution of magma batches and this appears to be driven by periodic replenishment of the magmatic system from the mantle. In contrast, the past 2 ka of eruptive history at Ruapehu reflects random tapping of shallow, volume magma reservoirs.

  20. Wide-angle seismic reflections as direct indictors of partial melt beneath an andesite arc (United States)

    Stern, T. A.; Benson, A.; Stratford, W. R.; Gamble, J. A.


    Quasi-linear arcs of andesite volcanoes that erupt above 120 ± 40 km deep Waditi-Benioff zones are one of the most striking surface manifestations of plate tectonics. The prevailing view is that andesite magma that feed these arcs are an end-product of fluid-assisted melting in the mantle wedge1. Two key questions remain unresolved: why is the line of an active arc so sharply defined? and where do parental mantle-derived melts pool and differentiate into mafic restite and more felsic magma components that are so distinctive of continental magmatic arc systems ? Here we present seismic evidence from the MORC (mantle or crust?) project for a focused zone of melt below the andesite arc within northern New Zealand. Nine ~ 0.4 - 1.3 tonne dynamite shots were recorded on ~ 700 seismographs spaced along a 120 km long array across, and normal to the axis of the Taupo Volcanic Zone (TVZ). Two important features of the ray tracing solution are: (i) a lower-crustal, 10 km thick, "rift-pillow" of rocks where the P-wave seismic velocities (Vp) are ~ 6.8-7.1 km/s. Seismic reflections from top and bottom of the pillow are termed R1 and R2 respectively. (ii) Strong seismic reflections (termed R3 reflector) are recorded from a relatively short (12 -18 km-long) reflector at a depth of ~ 32 ± 2 km. An analysis of interval velocities between the R2 and R3 reflectors show a P-wave speed of 7.6 +/- 0.2 km/s, which is interpreted as anomalous upper mantle. Thus R3 is regarded as being a reflector within the upper mantle. Ray-tracing locates R3 beneath the eastern margin of the TVZ and directly beneath the active volcanic (andesite) front and geothermal fields. A causal relationship between the R3 reflector and the andesite arc is therefore implied. The amplitude ratio of the R3/R2 reflections along common traces is as high as 4-6 for incidence angles of reflection of 45-60 degrees. These data suggest R3 is best explained with numerical methods by an interface across which there is a

  1. Thermal properties of andesite from Popocatepetl and Volcán de Colima, México. (United States)

    Cardenas-Sanchez, Enrique; De la Cruz-Reina, Servando; Varley, Nick


    The thermal conductivity (K), specific heat (Cp) and the coefficient of heat transfer surface (H) are the basic parameters to describe the process of cooling a volcanic rock fragment released in an explosive event. The analysis of the cooling process by conduction, convection and radiation of heat in volcanic rock fragments, has been limited to basalts, and various minerals such as olivine, pyroxene, quartz, etc. (Miao & Chen, 2014; Branlund & Hofmeister, 2012; Romine et al, 2012;. Schön, 2011; Stroberg et al, 2010;. Schatz & Simmons, 1972). There are no detailed studies on the thermal properties of the andesites, abundant in continental stratovolcanoes, and particularly susceptible from lava domes with frequent destruction processes, such as Popocatepetl and Volcan de Colima. Previously, we developed an algorithm for calculation of the grain-size distribution, degree of fragmentation, the thermal energy released and its possible correlation with Volcanic Explosive Index (VEI) from the cooling curves of fragments from vulcanian and strombolian explosions. These curves were obtained from sequences of time over incandescent deposits recorded at selected pixel thermal images of vulcanian activity in the Popocatepetl and Volcan de Colima, Mexico. However, the model was limited by the lack of thermal parameters of the andesites, forcing a first approximation using basalts data. We present a simple model for the cooling process using andesites samples from Popocatépetl and Volcan de Colima. First, the samples were subjected to a rounding process to minimize surface effects. Then, heated to 800 ° C were extracted from the muffle and cooling rate is measured. The thermal conductivity and coefficient of surface heat are determined using a thermal camera and three thermocouples embedded at various depths within the sample. An inversion method was implemented to determine the thermal properties parameters , by comparing the observed data regarding cooling model for a solid

  2. Paleoproterozoic andesitic volcanism in the southern Amazonian craton (northern Brazil); lithofacies analysis and geodynamic setting (United States)

    Roverato, Matteo; Juliani, Caetano; Capra, Lucia; Dias Fernandes, Carlos Marcelo


    Precambrian volcanism played an important role in geological evolution and formation of new crust. Most of the literature on Precambrian volcanic rocks describes settings belonging to subaqueous volcanic systems. This is likely because subaerial volcanic rocks in Proterozoic and Archean volcano-sedimentary succession are poorly preserved due to erosive/weathering processes. The late Paleoproterozoic Sobreiro Formation (SF) here described, seems to be one of the rare exceptions to the rule and deserves particular attention. SF represents the subaerial expression of an andesitic magmatism that, linked with the upper felsic Santa Rosa F., composes the Uatumã Group. Uatumã Group is an extensive magmatic event located in the Xingú region, southwestern of Pará state, Amazonian Craton (northern Brazil). The Sobreiro volcanism is thought to be related to an ocean-continent convergent margin. It is characterized by ~1880 Ma well-preserved calc-alkaline basaltic/andesitic to andesitic lava flows, pyroclastic rocks and associated reworked successions. The superb preservation of its rock-textures allowed us to describe in detail a large variety of volcaniclastic deposits. We divided them into primary and secondary, depending if they result from a direct volcanic activity (pyroclastic) or reworked processes. Our study reinforces the importance of ancient volcanic arcs and rocks contribution to the terrestrial volcaniclastic sedimentation and evolution of plate tectonics. The volcanic activity that produced pyroclastic rocks influenced the amount of detritus shed into sedimentary basins and played a major role in the control of sedimentary dispersal patterns. This study aims to provide, for the first time, an analysis of the physical volcanic processes for the subaerial SF, based in field observation, lithofacies analysis, thin section petrography and less geochemical data. The modern volcanological approach here used can serve as a model about the evolution of Precambrian

  3. Treatment of ammonium-rich swine waste in modified porphyritic andesite fixed-bed anaerobic bioreactor. (United States)

    Wang, Qinghong; Yang, Yingnan; Li, Dawei; Feng, Chuanping; Zhang, Zhenya


    In this study, a modified porphyritic andesite (WRS) was developed as ammonium adsorbent and bed material for the anaerobic digestion of ammonium-rich swine waste. The performance in bioreactors with modified WRS, natural WRS, calcium chloride and no additives was investigated. The bioreactor with modified WRS exhibited the best performance, with start-up time on the 7th day, methane yield of 359.71 ml/g-VS, and COD removal of 67.99% during all 44 days of the experiment at 35°C. The effective ammonium adsorption and essential ions dissociation for microorganisms by modified WRS, as well as the immobilization of microbial on the surface of the modified WRS play a great role on the high efficiency anaerobic digestion of ammonium-rich swine waste. PMID:22366608

  4. Andesitic Plinian eruptions at Mt. Ruapehu: quantifying the uppermost limits of eruptive parameters (United States)

    Pardo, Natalia; Cronin, Shane; Palmer, Alan; Procter, Jonathan; Smith, Ian


    New tephro-stratigraphic studies of the Tongariro Volcanic Centre (TgVC) on the North Island (New Zealand) allowed reconstruction of some of the largest, andesitic, explosive eruptions of Mt. Ruapehu. Large eruptions were common in the Late Pleistocene, before a transition to strombolian-vulcanian and phreatomagmatic eruptive styles that have predominated over the past 10,000 years. Considering this is the most active volcano in North Island of New Zealand and the uppermost hazard limits are unknown, we identified and mapped the pyroclastic deposits corresponding to the five largest eruptions since ~27 ka. The selected eruptive units are also characterised by distinctive lithofacies associations correlated to different behaviours of the eruptive column. In addition, we clarify the source of the ~10-9.7 ka Pahoka Tephra, identified by previous authors as the product of one of the largest eruptions of the TgVC. The most common explosive eruptions taking place between ~13.6 and ~10 ka cal years BP involved strongly oscillating, partially collapsing eruptive columns up to 37 km high, at mass discharge rates up to 6 × 108 kg/s and magnitudes of 4.9, ejecting minimum estimated volumes of 0.6 km3. Our results indicate that this volcano (as well as the neighbouring andesitic Mt. Tongariro) can generate Plinian eruptions similar in magnitude to the Chaitén 2008 and Askja 1875 events. Such eruptions would mainly produce pyroclastic fallout covering a minimum area of 1,700 km2 ESE of the volcano, where important touristic, agricultural and military activities are based. As for the 1995/1996 eruption, our field data indicate that complex wind patterns were critical in controlling the dispersion of the eruptive clouds, developing sheared, commonly bilobate plumes.

  5. H 2O in basalt and basaltic andesite glass inclusions from four subduction-related volcanoes (United States)

    Sisson, T. W.; Layne, G. D.


    Total dissolved H 2O and major element abundances were measured in basalt and basaltic andesite glass inclusions in olivine phenocrysts from Quaternary eruptions of four subduction-related volcanoes to test the hypothesis that low-MgO high-alumina basalts contain high H 2O at depth [1] and to reveal any petrogenetically significant correlations between arc basalt compositions and H 2O contents. Total dissolved H 2O (combined molecular H 2O and OH groups) measured by ion microprobe in mafic glass inclusions from the 1974 eruption of Fuego, Guatemala, reaches 6.2 wt.%. Dissolved H 2O contents decrease in more evolved Fuego glasses. Correlations of H 2O with MgO, Na 2O, K 2O, S and Cl indicate that aqueous fluid exsolution during magma ascent forced crystallization and differentiation of residual liquids. Low-K 2O magnesian high-alumina basalt glass inclusions from the 3 ka eruption of Black Crater (Medicine Lake volcano, California) have low H 2O contents, near 0.2 wt.%, which are consistent with the MORB-like character of these and other primitive lavas of the Medicine Lake region. Basalt and basaltic andesite glass inclusions from Copco Cone and Goosenest volcano on the Cascade volcanic front north of Mt. Shasta have H 2O contents of up to 3.3 wt.%. The range of H 2O contents in Cascade mafic magmas is too large to have resulted solely from enrichment by crystallization and indicates the participation of an H 2O-rich component in magma generation or crustal-level modification. Whereas fluid-absent melting of amphibole-bearing peridotite can account for the H 2O in most mafic arc liquids, the very high H 2O/alkali ratios of the 1974 Fuego eruptives suggest that an aqueous fluid was involved in the generation of Fuego basalts.

  6. The Bowen-Fenner Debate Revisited: A Review of Basalt Crystal Fractionation and the Generation of Andesite (United States)

    Conrey, R. M.


    The Bowen-Fenner debate over the nature of basalt crystal fractionation is still unresolved. Bowen's classic 1928 book detailed his basalt-andesite-rhyolite fractionation scheme, whereas Fenner emphasized the evidence for Fe-enrichment during most basalt crystallization, thus anticipating discovery of the Skaergaard. In the 1940's Bowen suggested only wet basalt generates common andesite. To address this debate MELTS simulations were performed with near-constant parents but varied water contents from 0-4 wt per cent. For comparison, data were compiled from mid-ocean ridge (MORB), back-arc basin (BABB), and arc basalts. There is a strong correlation between empirical fractionation patterns and the simulations. Dry basaltic magma exemplified by MORB shows fractionation patterns controlled by early plagioclase crystallization, whereas nearly all wet arc basaltic magmas have patterns controlled by crystallization of mafic minerals, with the later onset of highly calcic plagioclase. BABB have fractionation patterns between those two extremes. The fundamental antithetic behavior of Al and Fe during basalt crystal fractionation due to the sensitive control over plagioclase crystallization by water is completely obscured by the use of Harker and AFM diagrams. Mafic arc basalts which show evidence for significant crystallization of magnetite are largely lacking - most arc basalt fractionation patterns are consistent with 2-3 per cent H2O in the primitive melt and oxygen fugacity near the NNO buffer. A few mafic arc volcanoes have steep increases in Al content or slightly declining Fe content with only slight increases in FeO*/MgO suggestive of significant magnetite crystallization. Magma at these centers must be somewhat more hydrous and/or oxidized than is the normal case. Arc basalt clinopyroxene compositions support the inference that common high-alumina basalt (HAB) is a derivative magma, as empirical and experimental data, and MELTS simulations, all show coupled

  7. Paleoproterozoic crustal evolution in the East Sarmatian Orogen: Petrology, geochemistry, Sr-Nd isotopes and zircon U-Pb geochronology of andesites from the Voronezh massif, Western Russia (United States)

    Terentiev, R. A.; Savko, K. A.; Santosh, M.


    Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr-Nd isotopes, and zircon U-Pb geochronological data from andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe-Ti oxides, we estimate a temperature range of 1179 to 1262 °C, pressures of 11.3 to 13.0 kbar, H2O content of 1-5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) andesites. Our zircon U-Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for andesite and dacite-porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic andesite of the KG. The andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive εNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in the

  8. Petrographic and Geochemical Investigation of Andesitic Arc Volcanism: Mount Kerinci, Sunda Arc, Indonesia (United States)

    Tully, M.; Saunders, K.; Troll, V. R.; Jolis, E.; Muir, D. D.; Deegan, F. M.; Budd, D. A.; Astbury, R.; Bromiley, G. D.


    Present knowledge of the chain of dominantly andesitic volcanoes, which span the Sumatran portion of the Sunda Arc is extremely limited. Previous studies have focused on Toba and Krakatau, although over 13 further volcanic edifices are known. Several recent explosive eruptions in Sumatra such as that of Mt. Sinabung, 2014, have highlighted the potential hazard that these volcanoes pose to the local and regional communities. Mount Kerinci, is one of the most active of the volcanoes in this region, yet little is known about the petrogenesis of the magma by which it is fed. Kerinci is located approximately mid-way between Toba in the North and Krakatau in the south. Along arc variations are observed in the major, minor and trace elements of whole rock analyses. However, bulk rock approaches produce an average chemical composition for a sample, potentially masking important chemical signatures. In-situ micro-analytical analysis of individual components of samples such as melt inclusions, crystals and groundmass provides chemical signatures of individual components allowing the evolution of volcanic centres to be deciphered in considerably more detail. Examination of whole rock chemistry indicates its location may be key to unravelling the petrogenesis of the arc as significant chemical changes occur between Kerinci and Kaba, 250 km to the south. Kerinci samples are dominantly porphyritic with large crystals of plagioclase, pyroxene and Fe-Ti oxides, rare olivine crystals are observed. Plagioclase and pyroxene crystals are chemically zoned and host melt inclusions. Multiple plagioclase populations are observed. A combination of in-situ micro-analysis techniques will be used to characterise the chemical composition of melt inclusions and crystals. These data can be used along with extant geothermobarometric models to help determine the magma source, storage conditions and composition of the evolving melt. Integration of the findings from this study with existing data for

  9. Subaqueous cryptodome eruption, hydrothermal activity and related seafloor morphologies on the andesitic North Su volcano (United States)

    Thal, Janis; Tivey, Maurice; Yoerger, Dana R.; Bach, Wolfgang


    North Su is a double-peaked active andesite submarine volcano located in the eastern Manus Basin of the Bismarck Sea that reaches a depth of 1154 m. It hosts a vigorous and varied hydrothermal system with black and white smoker vents along with several areas of diffuse venting and deposits of native sulfur. Geologic mapping based on ROV observations from 2006 and 2011 combined with morphologic features identified from repeated bathymetric surveys in 2002 and 2011 documents the emplacement of a volcanic cryptodome between 2006 and 2011. We use our observations and rock analyses to interpret an eruption scenario where highly viscous, crystal-rich andesitic magma erupted slowly into the water-saturated, gravel-dominated slope of North Su. An intense fragmentation process produced abundant blocky clasts of a heterogeneous magma (olivine crystals within a rhyolitic groundmass) that only rarely breached through the clastic cover onto the seafloor. Phreatic and phreatomagmatic explosions beneath the seafloor cause mixing of juvenile and pre-existing lithic clasts and produce a volcaniclastic deposit. This volcaniclastic deposit consists of blocky, non-altered clasts next, variably (1-100%) altered clasts, hydrothermal precipitates and crystal fragments. The usually applied parameters to identify juvenile subaqueous lava fragments, i.e. fluidal shape or chilled margin, were not applicable to distinguish between pre-existing non-altered clasts and juvenile clasts. This deposit is updomed during further injection of magma and mechanical disruption. Gas-propelled turbulent clast-recycling causes clasts to develop variably rounded shapes. An abundance of blocky clasts and the lack of clasts typical for the contact of liquid lava with water is interpreted to be the result of a cooled, high-viscosity, crystal-rich magma that failed as a brittle solid upon stress. The high viscosity allows the lava to form blocky and short lobes. The pervasive volcaniclastic cover on North Su is

  10. Controls on long-term low explosivity at andesitic arc volcanoes: Insights from Mount Hood, Oregon (United States)

    Koleszar, Alison M.; Kent, Adam J. R.; Wallace, Paul J.; Scott, William E.


    The factors that control the explosivity of silicic volcanoes are critical for hazard assessment, but are often poorly constrained for specific volcanic systems. Mount Hood, Oregon, is a somewhat atypical arc volcano in that it is characterized by a lack of large explosive eruptions over the entire lifetime of the current edifice (~ 500,000 years). Erupted Mount Hood lavas are also compositionally homogeneous, with ~ 95% having SiO2 contents between 58 and 66 wt.%. The last three eruptive periods in particular have produced compositionally homogeneous andesite-dacite lava domes and flows. In this paper we report major element and volatile (H2O, CO2, Cl, S, F) contents of melt inclusions and selected phenocrysts from these three most recent eruptive phases, and use these and other data to consider possible origins for the low explosivity of Mount Hood. Measured volatile concentrations of melt inclusions in plagioclase, pyroxene, and amphibole from pumice indicate that the volatile contents of Mount Hood magmas are comparable to those in more explosive silicic arc volcanoes, including Mount St. Helens, Mount Mazama, and others, suggesting that the lack of explosive activity is unlikely to result solely from low intrinsic volatile concentrations or from substantial degassing prior to magma ascent and eruption. We instead argue that an important control over explosivity is the increased temperature and decreased magma viscosity that results from mafic recharge and magma mixing prior to eruption, similar to a model recently proposed by Ruprecht and Bachmann (2010). Erupted Mount Hood magmas show extensive evidence for mixing between magmas of broadly basaltic and dacitic-rhyolitic compositions, and mineral zoning studies show that mixing occurred immediately prior to eruption. Amphibole chemistry and thermobarometry also reveal the presence of multiple amphibole populations and indicate that the mixed andesites and dacites are at least 100 °C hotter than the high-SiO2

  11. Geochemistry and petrology of andesites from the north rift zone of Axial Seamount, Juan de Fuca Ridge (United States)

    Smithka, I. N.; Perfit, M. R.; Clague, D. A.; Wanless, V. D.


    In 2013, the ROV Doc Ricketts onboard R/V Western Flyer explored ~4 km of an elongate pillow ridge up to ~300 m high along the eastern edge of the north rift zone of Axial Seamount. The steep-sided volcanic ridge is constructed of large pillow lavas up to 2-3 m in diameter and smaller elongated pillow tubes. Of the 27 samples collected during dive D526, all but one are andesites making it one of the largest confirmed high-silica exposures along a mid-ocean ridge (MOR). Based on radiocarbon ages of sediment on top of flows, the mounds are at least ~1390 years old. This minimum age is much younger than the 56 Ka age calculated based on distance from the rift axis, indicating eruption off-axis through older, colder crust and supporting the hypothesis and model calculations that extensive fractional crystallization (>85%) caused the high silica content. The andesitic lavas are primarily glassy, highly vesicular, crusty, and sparsely phyric with small (~1 mm) plagioclase crystals and olivine, clinopyroxene, and Fe-Ti oxide microphenocrysts. Microprobe analyses of glasses are similar to wax-core samples previously collected from this area but are more compositionally variable. Excluding one basalt (7.7 wt% MgO) sampled between mounds, the lavas are basaltic andesites and andesites (53-59 wt% SiO2) with <3 wt% MgO and 12.8-15.7 wt% FeO concentrations. Incompatible trace element abundances are ~4-6 times more enriched than in Axial Seamount T-MORB. Primitive mantle-normalized patterns are similar to those of high-silica lavas from other MORs (southern Juan de Fuca Ridge, 9N East Pacific Rise) with significant positive U anomalies, large negative Sr anomalies, small negative Eu anomalies, and slight positive Zr-Hf anomalies. The andesites are more enriched in light rare earth elements than basalts from Axial Seamount ((La/Yb)N 1.35-1.4 vs. 0.7-1.27) and N-MORB from the southern Juan de Fuca Ridge. The andesites also have high Cl (~0.3-0.6 wt%) and H2O (~1.60-1.71 wt

  12. The Origin of Voluminous Dacite (vs. Andesite) at Mature, Thick Continental Arcs: A Reflection of Processes in the Deep Crust (United States)

    Lange, R. A.


    An outstanding question is why some continental arc segments are characterized by voluminous eruptions of dacite (65-70 wt% SiO2), whereas others erupt more andesite (58-64 wt% SiO2) than any other magma type. An example of the former is the Altiplano-Puna region of the central Andean arc, which has erupted a predominance of dacite over all magma types 10-1 Ma (de Silva, 1989). In contrast, a 200-km arc segment of the Mexican volcanic arc (Michoacán-Guanajuato arc segment) has erupted ~75% andesite, ~26% basaltic andesite and 20%) of hornblende-rich (~40%) gabbronorite in the deep crust, driven by mantle-derived basalt intrusions at depths of 30-40 km. The absence of any dacite or rhyolite along this arc segment indicates that interstitial liquid from crystal-rich andesites never segregated to form eruptible magma. Thus, little upper-crust differentiation occurred along this arc segment. On the basis of phase-equilibrium experiments in the literature (e.g., Sisson et al., 2005), it is proposed that rhyolite and dacite did form during partial melting of the lower arc crust, but at melt fractions too low (≤15%) to permit efficient transport to the upper crust (Vigneresse and Tikoff, 1999). It is further proposed that the reason why dacite is so abundant at mature thick continental arcs (e.g., Altiplano-Puno complex) may be because mantle-derived basalts are primarily emplaced at similar depths (~30-40 km) in continental arc crustal columns. If so, in the central Andean arc, a depth of 30-40 km is within the middle dioritic crust (Graeber and Asch, 1999). Partial melts of hornblende diorite (vs. hornblende gabbro) are predicted to be dacitic (vs. andesitic) at melt fractions of 20-25%, which permits transport to the upper crust. It is therefore proposed that it is deep crustal processes that determine whether andesite or dacite is the most voluminous magma type emplaced into the upper crust and erupted at arcs.

  13. Petrogenesis of Mount Rainier andesite: magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades (United States)

    Sisson, Thomas W.; Salters, V.J.M.; Larson, P.B.


    Quaternary Mount Rainier (Washington, USA) of the Cascades magmatic arc consists of porphyritic calc-alkaline andesites and subordinate dacites, with common evidence for mingling and mixing with less evolved magmas encompassing andesites, basaltic andesites, and rarely, basalts. Basaltic andesites and amphibole andesites (spessartites) that erupted from vents at the north foot of the volcano represent some of Mount Rainier's immediate parents and overlap in composition with regional basalts and basaltic andesites. Geochemical (major and trace elements) and isotopic (Sr, Nd, Pb, O) compositions of Mount Rainier andesites and dacites are consistent with modest assimilation (typically ≤20 wt%) of evolved sediment or sediment partial melt. Sandstones and shales of the Eocene Puget Group, derived from the continental interior, are exposed in regional anticlines flanking the volcano, and probably underlie it in the middle to lower crust, accounting for their assimilation. Mesozoic and Cenozoic igneous basement rocks are unsuitable as assimilants due to their high 143Nd/144Nd, diverse206Pb/204Pb, and generally high δ18O.

  14. The Cerro Bitiche Andesitic Field: petrological diversity and implications for magmatic evolution of mafic volcanic centers from the northern Puna (United States)

    Maro, Guadalupe; Caffe, Pablo J.


    The Cerro Bitiche Andesitic Field (CBAF) is one of the two largest mafic volcanic fields in northern Puna (22-24° S) and is spatially and temporally associated with ignimbrites erupted from some central Andean Altiplano-Puna Volcanic Complex calderas. The CBAF comprises seven scoria cones and widespread high-K calcalkaline lava flows that cover an area of 200 km2. Although all erupted rocks have a relatively narrow chemical range (56-62 % SiO2, 3-6 % MgO), there is a broad diversity of mineral compositions and textures. The least evolved lavas (˜58-61 % SiO2) are high-Mg andesites with scarce (<10 %) microphenocrysts of either olivine or orthopyroxene. The small compositional range and low phenocryst content indicate evolution controlled by low percentages (<10 %) of fractional crystallization of olivine and clinopyroxene of magmas similar to the least evolved rocks from the field, accompanied by assimilation during rapid ascent through the crust. Evolved andesites (˜62 wt% SiO2), on the other hand, are porphyritic rocks with plagioclase + orthopyroxene + biotite and ubiquitous phenocryst disequilibrium textures. These magmas were likely stored in crustal reservoirs, where they experienced convection caused by mafic magma underplating, magma mixing, and/or assimilation. Trace element and mineral compositions of CBAF lavas provide evidence for complex evolution of distinct magma batches.

  15. Natural analogues: Alamosa River monzonite intrusive into tuffaceous and andesitic rocks

    International Nuclear Information System (INIS)

    This project encompasses investigations of selected natural analogues of minerals and rocks containing radioelements and fission-product elements, to ascertain how radionuclides and their daughter elements may migrate from sites or origin in response to long-term natural processes such as heating due to an igneous intrusion, circulating hydrothermal systems, diffusion through the rock matrix, weathering and erosion. Comparison of natural occurrences with conceptual models based on laboratory data will furnish a test of such models over time periods comparable to or longer than those expected for a repository. For this study, we have examined large-scale intrusions of igneous rocks which have profoundly affected the thermal and hydrologic settings of large masses of surrounding country rock, and occurrences where migration of elements has occurred after intrusion and subsequent cooling. Specifically, we have investigated the Alamosa River stock, intrusive into tuffaceous rocks and andesites of the Platoro Caldera in the San Juan Mountains of southern Colorado. The oxygen isotopic studies show the effect of extensive hydrothermal activity on the intruded rocks, as well as the host tuffaceous and flow rocks. Convective cooling has been demonstrated for the Alamosa River Stock. The distribution of U, Th, REE, V, K, Ti, in each rock is apparently unaffected by the intrusion. This is true also for Rb, Sr, Ta, Na, and others, although for some of these elements there is no strong chemical gradient between the rocks. Some elements show some evidence for contact zone mobility, but only within ten meters or so of the contact (Cs, Cr, Co). Both the mozonite and tuff have retained their bulk chemistry during and after intrusion. The absence of elemental migration between the tuffs and monzonites, even in a convective system, supports continued assessment of such rocks for radwaste repository consideration

  16. Controls on rind thickness on basaltic andesite clasts weathering in Guadeloupe (United States)

    Sak, P.B.; Navarre-Sitchler, A. K.; Miller, C.E.; Daniel, C.C.; Gaillardet, J.; Buss, H.L.; Lebedeva, M.I.; Brantley, S.L.


    A clast of low porosity basaltic andesite collected from the B horizon of a soil developed on a late Quaternary volcaniclastic debris flow in the Bras David watershed on Basse-Terre Island, Guadeloupe, exhibits weathering like that observed in many weathered clasts of similar composition in other tropical locations. Specifically, elemental profiles measured across the core-rind interface document that primary minerals and glass weather to Fe oxyhydroxides, gibbsite and minor kaolinite in the rind. The earliest reaction identified in the core is oxidation of Fe in pyroxene but the earliest reaction that creates significant porosity is plagioclase dissolution. Elemental loss varies in the order Ca???Na>K???Mg>Si>Al>Fe???P??Ti, consistent with the relative reactivity of phases in the clast from plagioclase???pyroxene???glass>apatite>ilmenite. The rind surrounds a core of unaltered material that is more spherical than the original clast. The distance from the core-rind boundary to a visually prominent rind layer, L, was measured as a proxy for the rind thickness at 36 locations on a slab cut vertically through the nominal center of the clast. This distance averaged 24.4??3.1mm. Maximum and minimum values for L, 35.8 and 20.6mm, were observed where curvature of the core-rind boundary is greatest (0.12mm-1) and smallest (0.018mm-1) respectively. Extrapolating from other rinds in other locations, the rate of rind formation is estimated to vary by a factor of about 2 (from ~4 to 7??10-14ms-1) from low to high curvature. The observation of a higher rate of rind formation for a higher curvature interface is consistent with a diffusion-limited model for weathering rind formation. The diffusion-limited model predicts that, like rind thickness, values of the thickness of the reaction front (h) for a given reaction, defined as the zone over which a parent mineral such as plagioclase completely weathers to rind material, should also increase with curvature. Values of h were

  17. Phenocryst complexity in andesites and dacites from the Tequila volcanic field, Mexico: resolving the effects of degassing vs. magma mixing (United States)

    Frey, Holli M.; Lange, Rebecca A.


    The petrology of five phenocryst-poor (2-5%) andesites and dacites, all of which were erupted from different short-lived, monogenetic vents, is compared to that of phenocryst-rich (10-25%) andesites erupted from the adjacent stratovolcano, Volcán Tequila, in the Mexican arc. Despite differences in phenocryst abundances, these magmas have comparable phase assemblages (plagioclase + orthopyroxene + titanomagnetite + ilmenite + apatite ± augite ± hornblende), and similarly wide variations in phenocryst compositions, coupled to complex zoning patterns. For the phenocryst-poor lavas, equilibrium pairs of two Fe-Ti oxides lead to a narrow range of calculated temperatures for each sample that range from 934 (±24) to 1,073 (±6)°C and oxygen fugacities that range from +0.1 to +0.7 log units relative to the Ni-NiO buffer. Application of the plagioclase-liquid hygrometer to each sample at these calculated temperatures leads to maximum melt water concentrations of 4.6-3.1 wt% during plagioclase crystallization, indicating that the magmas were fluid saturated at depths ≥6.4-4.5 km. There is a wide, continuous range in the composition of plagioclase (≤44 mol% An) and orthopyroxene (≤16% Mg#) phenocrysts in each sample, which is consistent with a loss of dissolved water (≤2.8 wt%) from the melt phase during degassing as the magmas ascended rapidly to the surface. Evidence is presented that shows the effect of dissolved water is to reduce the activity of MgO relative to FeO in the melt phase, which indicates that degassing will also affect the Mg# of pyroxene phenocrysts, with higher melt water concentrations favoring Fe-rich pyroxene. Both plagioclase and orthopyroxene commonly display diffusion-limited growth textures (e.g., skeletal and hopper crystals, large interior melt hollows, and swallow tails), which are consistent with large undercoolings produced by degassing-induced crystallization. Therefore, degassing is proposed as a possible cause for the phenocryst

  18. Geochemistry of the high-Mg andesites at Zhangwu, western Liaoning: Implication for delamination of newly formed lower crust

    Institute of Scientific and Technical Information of China (English)

    HUANG; Hua; GAO; Shan; HU; ZhaoChu; LIU; XiaoMing; YUAN; HongLing


    Ten volcanic samples at Zhangwu, western Liaoning Province, North China were selected for a systematic geochemical, mineralogical and geochronological study, which provides an opportunity to explore the interaction between the continental crust and mantle beneath the north margin of the North China craton. Except one basalt sample (SiO2= 50.23%), the other nine samples are andesitic with SiO2 contents ranging from 53% to 59%. They have relatively high MgO (3.4%-6.1%, Mg#=50-64) and Ni and Cr contents (Ni 27×10-6-197×10-6, Cr 51×10-6-478×10-6). Other geochemical characteristics of Zhangwu high-Mg andesites (HMAs) include strong fractionation of light rare earth elements (LREE) from heavy rare earth elements (HREE), and Sr from Y, with La/Yb greater than 15, and high Sr/Y (34-115). Zircons of andesite YX270 yield three age groups with no Precambrian age, which precludes origin of the Zhangwu HMAs from the partial melting of the Precambrian crust. The oldest age group peaking at 253 Ma is interpreted to represent the collision of the Siberia block and the North China block, resulting in formation of the Central Asian orogenic belt by closure of the Mongol-Okhotsk Ocean. The intermediate age group corresponds to the basalt underplating which caused the widespread coeval granitoids in the North China craton with a peak 206Pb/238U age of 172 Ma. The youngest age group gives a 206Pb/238U age of 126±2 Ma, which is interpreted as the eruption age of the Zhangwu HMAs. The high 87Sr/86Sri(126 Ma)>0.706 and low -Nd(t)= -6.36--13.99 of the Zhangwu HMAs are distinct from slab melts. The common presence of reversely zoned clinopyroxene phenocrysts in the Zhangwu HMAs argues against the origin of the Zhangwu HMAs either from melting of the water saturated mantle or melting of the lower crust. In light of the evidence mentioned above, the envisaged scenario for the formation of the Zhangwu HMAs is related to the basaltic underplating at the base of the crust, which led to

  19. Contemporaneous trachyandesitic and calc-alkaline volcanism of the Huerto Andesite, San Juan Volcanic Field, Colorado, USA (United States)

    Parat, F.; Dungan, M.A.; Lipman, P.W.


    Locally, voluminous andesitic volcanism both preceded and followed large eruptions of silicic ash-flow tuff from many calderas in the San Juan volcanic field. The most voluminous post-collapse lava suite of the central San Juan caldera cluster is the 28 Ma Huerto Andesite, a diverse assemblage erupted from at least 5-6 volcanic centres that were active around the southern margins of the La Garita caldera shortly after eruption of the Fish Canyon Tuff. These andesitic centres are inferred, in part, to represent eruptions of magma that ponded and differentiated within the crust below the La Garita caldera, thereby providing the thermal energy necessary for rejuvenation and remobilization of the Fish Canyon magma body. The multiple Huerto eruptive centres produced two magmatic series that differ in phenocryst mineralogy (hydrous vs anhydrous assemblages), whole-rock major and trace element chemistry and isotopic compositions. Hornblende-bearing lavas from three volcanic centres located close to the southeastern margin of the La Garita caldera (Eagle Mountain - Fourmile Creek, West Fork of the San Juan River, Table Mountain) define a high-K calc-alkaline series (57-65 wt % SiO2) that is oxidized, hydrous and sulphur rich. Trachyandesitic lavas from widely separated centres at Baldy Mountain-Red Lake (western margin), Sugarloaf Mountain (southern margin) and Ribbon Mesa (20 km east of the La Garita caldera) are mutually indistinguishable (55-61 wt % SiO2); they are characterized by higher and more variable concentrations of alkalis and many incompatible trace elements (e.g. Zr, Nb, heavy rare earth elements), and they contain anhydrous phenocryst assemblages (including olivine). These mildly alkaline magmas were less water rich and oxidized than the hornblende-bearing calc-alkaline suite. The same distinctions characterize the voluminous precaldera andesitic lavas of the Conejos Formation, indicating that these contrasting suites are long-term manifestations of San Juan

  20. Soluble iron inputs to the Southern Ocean through recent andesitic to rhyolitic volcanic ash eruptions from the Patagonian Andes (United States)

    Simonella, L. E.; Palomeque, M. E.; Croot, P. L.; Stein, A.; Kupczewski, M.; Rosales, A.; Montes, M. L.; Colombo, F.; García, M. G.; Villarosa, G.; Gaiero, D. M.


    Patagonia, due to its geographic position and the dominance of westerly winds, is a key area that contributes to the supply of nutrients to the Southern Ocean, both through mineral dust and through the periodic deposits of volcanic ash. Here we evaluate the characteristics of Fe dissolved (into soluble and colloidal species) from volcanic ash for three recent southern Andes volcanic eruptions having contrasting features and chemical compositions. Contact between cloud waters (wet deposition) and end-members of andesitic (Hudson volcano) and rhyolitic (Chaitén volcano) materials was simulated. Results indicate higher Fe release and faster liberation rates in the andesitic material. Fe release during particle-seawater interaction (dry deposition) has higher rates in rhyolitic-type ashes. Rhyolitic ashes under acidic conditions release Fe in higher amounts and at a slower rate, while in those samples containing mostly glass shards, Fe release was lower and faster. The 2011 Puyehue eruption was observed by a dust monitoring station. Puyehue-type eruptions can contribute soluble Fe to the ocean via dry or wet deposition, nearly reaching the limit required for phytoplankton growth. In contrast, the input of Fe after processing by an acidic eruption plume could raise the amount of dissolved Fe in surface ocean waters several times, above the threshold required to initiate phytoplankton blooms. A single eruption like the Puyehue one represents more than half of the yearly Fe flux contributed by dust.

  1. Engineering geological research of andesite alteration related to the revitalization of the Šášov Castle (central Slovakia

    Directory of Open Access Journals (Sweden)

    Renáta Adamcová


    Full Text Available An architectural study of the revitalization of the Šášov castle in the neovolcanic Štiavnické vrchy Mts. initiated a revision of the castle buildings. The building stone showed high post-volcanic alteration (hydrothermal and/or by weathering or total disintegration in some parts of the walls. It must be replaced, because the safety of the ruins determines a sustainable development of this historical site. The castle hill rocks and the main building stone are both Neogene andesites, but not necessarily identical – the building stone came probably from several sources and the original source of the building stone was not the question. Suitable replacement material was searched for in a local quarry. Andesites at different weathering levels were taken to test the impact of alteration upon the rock properties and their suitability for the castle remediation. Expandable clay minerals were considered important for the rock weakening and weathering resistivity. Mineral composition was analysed by X-ray diffractometry. Powdered samples were used for the determination of the particle density and Enslin-Neff tests. The dry bulk density, total porosity, He-effective porosity, and the uniaxial compressive strength (UCS were determined only on cylindrical rock cores of the quarry andesite. The “sound” building stone consists of feldspars (andesine > orthoclase, amorphous phases and a small amount of augite and quartz. Its alteration is manifested by the falling content of amorphous phases, augite and feldspars, by increasing smectite (up to 28% and secondary carbonates (up to 22 %, as well as by the color change due to increasing iron oxyhydroxides. Mineralogical composition showed acceptable differences compared to the sound quarry rock. There, higher alteration levels show higher water adsorption and increasing macroporosity, as well, which could be explained by a hypothesis: the basic macroporosity is of syngenetic origin, but, cyclic wetting

  2. Crystallization of oxidized, moderately hydrous arc basalt at mid- to lower-crustal pressures: Implications for andesite genesis (United States)

    Blatter, Dawnika L.; Sisson, Thomas W.; Hankins, W. Ben


    This study focuses on the production of convergent margin calc-alkaline andesites by crystallization–differentiation of basaltic magmas in the lower to middle crust. Previous experimental studies show that dry, reduced, subalkaline basalts differentiate to tholeiitic (high Fe/Mg) daughter liquids, but the influences of H2O and oxidation on differentiation are less well established. Accordingly, we performed crystallization experiments at controlled oxidized fO2 (Re–ReO2 ≈ ΔNi–NiO + 2) on a relatively magnesian basalt (8.7 wt% MgO) typical of mafic magmas erupted in the Cascades near Mount Rainier, Washington. The basalt was synthesized with 2 wt% H2O and run at 900, 700, and 400 MPa and 1,200 to 950 °C. A broadly clinopyroxenitic crystallization interval dominates near the liquidus at 900 and 700 MPa, consisting of augite + olivine + orthopyroxene + Cr-spinel (in decreasing abundance). With decreasing temperature, plagioclase crystallizes, Fe–Ti-oxide replaces spinel, olivine dissolves, and finally amphibole appears, producing gabbroic and then amphibole gabbroic crystallization stages. Enhanced plagioclase stability at lower pressure narrows the clinopyroxenitic interval and brings the gabbroic interval toward the liquidus. Liquids at 900 MPa track along Miyashiro’s (Am J Sci 274(4):321–355, 1974) tholeiitic versus calc-alkaline boundary, whereas those at 700 and 400 MPa become calc-alkaline at silica contents ≥56 wt%. This difference is chiefly due to higher temperature appearance of magnetite (versus spinel) at lower pressures. Although the evolved liquids are similar in many respects to common calc-alkaline andesites, the 900 and 700 MPa liquids differ in having low CaO concentrations due to early and abundant crystallization of augite, with the result that those liquids become peraluminous (ASI: molar Al/(Na + K + 2Ca) > 1) at ≥61 wt% SiO2, similar to liquids reported in other studies of the high-pressure crystallization of hydrous basalts

  3. Analysis of noise pollution in an andesite quarry with the use of simulation studies and evaluation indices. (United States)

    Kosała, Krzysztof; Stępień, Bartłomiej


    This paper presents the verification of two partial indices proposed for the evaluation of continuous and impulse noise pollution in quarries. These indices, together with the sound power of machines index and the noise hazard index at the workstation, are components of the global index of assessment of noise hazard in the working environment of a quarry. This paper shows the results of acoustic tests carried out in an andesite quarry. Noise generated by machines and from performed blasting works was investigated. On the basis of acoustic measurements carried out in real conditions, the sound power levels of machines and the phenomenon of explosion were determined and, based on the results, three-dimensional models of acoustic noise propagation in the quarry were developed. To assess the degree of noise pollution in the area of the quarry, the continuous and impulse noise indices were used.

  4. Analysis of noise pollution in an andesite quarry with the use of simulation studies and evaluation indices. (United States)

    Kosała, Krzysztof; Stępień, Bartłomiej


    This paper presents the verification of two partial indices proposed for the evaluation of continuous and impulse noise pollution in quarries. These indices, together with the sound power of machines index and the noise hazard index at the workstation, are components of the global index of assessment of noise hazard in the working environment of a quarry. This paper shows the results of acoustic tests carried out in an andesite quarry. Noise generated by machines and from performed blasting works was investigated. On the basis of acoustic measurements carried out in real conditions, the sound power levels of machines and the phenomenon of explosion were determined and, based on the results, three-dimensional models of acoustic noise propagation in the quarry were developed. To assess the degree of noise pollution in the area of the quarry, the continuous and impulse noise indices were used. PMID:26652503

  5. A chilled margin of komatiite and Mg-rich basaltic andesite in the western Bushveld Complex, South Africa (United States)

    Maier, W. D.; Barnes, S.-J.; Karykowski, B. T.


    A chill sequence at the base of the Lower Zone of the western Bushveld Complex at Union Section, South Africa, contains aphanitic Mg-rich basaltic andesite and spinifex-textured komatiite. The basaltic andesite has an average composition of 15.2 % MgO, 52.8 % SiO2, 1205 ppm Cr, and 361 ppm Ni, whereas the komatiite has 18.7 % MgO, 1515 ppm Cr, and 410 ppm Ni. Both rock types have very low concentrations of immobile incompatible elements (0.14-0.72 ppm Nb, 7-31 ppm Zr, 0.34-0.69 ppm Th, 0.23-0.27 wt% TiO2), but high PGE contents (19-23 ppb Pt, 15-16 ppb Pd) and Pt/Pd ratios (Pt/Pd 1.4). Strontium and S isotopes show enriched signatures relative to most other Lower Zone rocks. The rocks could represent a ~20 % partial melt of subcontinental lithospheric mantle. This would match the PGE content of the rocks. However, this model is inconsistent with the high SiO2, Fe, and Na2O contents and, in particular, the low K2O, Zr, Hf, Nb, Ta, Th, LREE, Rb, and Ba contents of the rocks. Alternatively, the chills could represent a komatiitic magma derived from the asthenosphere that underwent assimilation of the quartzitic floor accompanied by crystallization of olivine and chromite. This model is consistent with the lithophile elements and the elevated Sr and S isotopic signatures of the rocks. However, in order to account for the high Pt and Pd contents of the magma, the mantle must have been twice as rich in PGE as the current estimate for PUM, possibly due to a component of incompletely equilibrated late veneer.

  6. Origin of co-existing basalts, high-Mg andesites, and adakites in the SW Japan hot subduction system (United States)

    Kimura, J.; Kunikiyo, T.; Osaka, I.; Shimoshioiri, Y.; Katakuse, M.; Kakubuchi, S.; Nagao, T.; Furuyama, K.; Kamei, A.; Nakajima, J.; Stern, R. J.; Gill, J. B.


    In response to subduction of the young, hot Shikoku Basin of the Philippine Sea Plate (PSP) slab, arc magmas have been active throughout the late Cenozoic (arc. Extremely variable magma types occurred including oceanic island-type basalt (OIB), shoshonitc to mildly alkalic to sub-alkalic basalts with arc signatures, high-Mg andesites (HMAs), and adakitic andesites and dacites. The OIB-type basalts preceded the arc-type magmas. Therefore, the transition from OIB- to arc-types was related to opening of the Japan of Sea back-arc basin and subsequent re-initiation of PSP subduction. However, both the origin and tectonic implications of this magmatism are debated. Consequently, we analyzed the bulk rock geochemistry of 340 lava samples from seven Quaternary volcanoes and investigated their sources and melting conditions using a geochemical mass balance model, Arc Basalt Simulator version 4 (ABS4). Comparison to basement granitoids precludes adakite genesis in the lower crust. Instead, the ABS4 model suggests that the adakites are mostly slab melts plus minor interaction with mantle wedge peridotite (PERID). Increasing involvement of PERID during slab melt-fluxed mantle melting explains fairly well the geochemical variations of the shoshonites, mildly alkalic to sub-alkalic basalts, and HMAs. We propose that the generation of various magma types in the late Cenozoic SW Japan arc originated simply by "slab melt-fluxed mantle melting" with large variations in melting conditions including depth, temperature, degree of melting, and flux fractions. Such volcanism has been continuous from 13 Ma (Setouchi HMA) to the present, so that the hot subduction system, involving subduction of the Shikoku Basin spreading ridge, should be continuous since 13 Ma beneath the SW Japan arc. Our results further suggest that this atypically hot system generated diverse primary arc magmas from various degrees of flux melting even though the slab source components and sub-arc mantle are fairly

  7. Peninsular terrane basement ages recorded by Paleozoic and Paleoproterozoic zircon in gabbro xenoliths and andesite from Redoubt volcano, Alaska (United States)

    Bacon, Charles R.; Vazquez, Jorge A.; Wooden, Joseph L.


    Historically Sactive Redoubt volcano is an Aleutian arc basalt-to-dacite cone constructed upon the Jurassic–Early Tertiary Alaska–Aleutian Range batholith. The batholith intrudes the Peninsular tectonostratigraphic terrane, which is considered to have developed on oceanic basement and to have accreted to North America, possibly in Late Jurassic time. Xenoliths in Redoubt magmas have been thought to be modern cumulate gabbros and fragments of the batholith. However, new sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages for zircon from gabbro xenoliths from a late Pleistocene pyroclastic deposit are dominated by much older, ca. 310 Ma Pennsylvanian and ca. 1865 Ma Paleoproterozoic grains. Zircon age distributions and trace-element concentrations indicate that the ca. 310 Ma zircons date gabbroic intrusive rocks, and the ca. 1865 Ma zircons also are likely from igneous rocks in or beneath Peninsular terrane basement. The trace-element data imply that four of five Cretaceous–Paleocene zircons, and Pennsylvanian low-U, low-Th zircons in one sample, grew from metamorphic or hydrothermal fluids. Textural evidence of xenocrysts and a dominant population of ca. 1865 Ma zircon in juvenile crystal-rich andesite from the same pyroclastic deposit show that this basement has been assimilated by Redoubt magma. Equilibration temperatures and oxygen fugacities indicated by Fe-Ti–oxide minerals in the gabbros and crystal-rich andesite suggest sources near the margins of the Redoubt magmatic system, most likely in the magma accumulation and storage region currently outlined by seismicity and magma petrology at ∼4–10 km below sea level. Additionally, a partially melted gabbro from the 1990 eruption contains zircon with U-Pb ages between ca. 620 Ma and ca. 1705 Ma, as well as one zircon with a U-Th disequilibrium model age of 0 ka. The zircon ages demonstrate that Pennsylvanian, and probably Paleoproterozoic, igneous rocks exist in, or possibly beneath, Peninsular

  8. Origin of Permian andesites from Xi Ujimqin, the Hinggan Mountains: Contributions of lower crust North China Carton (United States)

    Gao, X.


    Andesite magmas at convergent margins are enriched in silica compared to magmas erupting at mid-ocean ridges and intra-plate volcanoes. Determining the cause (s) of silica enrichment is fundamental for models of continental crust formation, arc growth rates and across-arc mass balances (Plank and Langmuir, 1993; Rudnick, 1995; White et al., 2006).The Xi-Ujimqin is located the eastern segment of the Central Asian Orogenic Belt , the CAOB is composed of mainly subduction-accretion complexes, intruded by vast plutons of mainly magmatic arc origin and covered in places by their volcanic derivatives (Sengor et al. 1993; Sengor and Natalin 1996). As the most important site for Phanerozoic crustal growth in the world, the subduction-accretion complexes added ~ 5.3 million km2of material to Asia, half of which may be of juvenile origin (Sengor et al. 1993).The andesitic lavas of Daotenuoer Fms. at Xi-Ujimqin have different trace and Sr-Nd-Pb isotopic characteristic from them, these rocks span a SiO2 range of 56.83 ~ 59.17% and MgO of range of 1.21~2.91%, characterized by obviously LREE/HREE fractionation (Ce/YbCN = 11.6 ~ 16.8), strong LILE enrichment and variable Nb-Ta and Sr depletion. They have more radiogenic Sr and less radiogenic Nd and Pb isotopic composition (87Sr/86Sr(i) = 0.7063 ~ 0.7066, eNd(t) = -10.5 ~ -6.3,TDM = 1.22 ~ 1.51Ga, 206Pb / 204Pb(i) = 17.29 ~ 17.33, D7/4 = 3.7 ~ 6.9, D 8/4 = 94 ~ 104) than the contemporaneous intermediate-felsic volcanic lavas. Zircon U-Pb dating results give an emplacement age of ~253 Ma for the these rocks by LA-ICP-MS, corresponding to the Late Permian. The features of major, trace and Sr-Nd-Pb isotope of These rocks imply its sources are of attributes of lower crust North China Carton (NCC) during Paleozoic subduction and collision related to the closure of the Chinese segment of the Paleo-Asian Ocean between the NCC and south Mongolia Block (Sengor et al., 1993).

  9. The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations (United States)

    Zajacz, Zoltán; Candela, Philip A.; Piccoli, Philip M.; Sanchez-Valle, Carmen


    Andesite melts were equilibrated with an H-O-S-bearing volatile phase to determine the partition coefficients for S and Cl as a function of melt composition and oxygen fugacity. The experiments were conducted in rapid-quench MHC vessel assemblies at 200 MPa and 1000 °C, and over a range of imposed fO2 between NNO-1.2 and NNO+1.8. High fluid/melt mass ratios (∼15) were employed, allowing precise and accurate partition coefficients to be obtained by mass balance calculations. Chlorine exhibits Henrian behavior at ClO-0.5 activities typical for arc magmas, with D Cl volatile/melt = 1.36 ± 0.06 (1σ) below 0.2 wt.% Cl in the melt; at higher ClO-0.5 activities, D Cl volatile/melt increases linearly to 2.11 ± 0.02 at 1 wt.% Cl in the melt. In the volatile phase: FeCl2 ∼ NaCl > KCl ∼ HCl. The determination of cation exchange coefficients for major cations yielded: K K,Na volatile/melt = 1.23 ± 0.10 (1σ) and ∗K Fe,Na volatile/melt = D Fe volatile/melt / D Na volatile/melt = 1.08 ± 0.16 (1σ). Under these conditions, the concentration of HCl in the vapor is negatively correlated with the (Na + K)/(Al + Fe3+) ratio in the melt. Reduced sulfur (S2-) appears to obey Henry's law in andesite melt-volatile system at fH2S below pyrrhotite saturation. The partition coefficient for S at fO2 = NNO-0.5 correlates negatively with the FeO concentration in the melt, changing from 254 ± 25 at 4.0 wt.% FeO to 88 ± 6 at 7.5 wt.% FeO. Pyrrhotite saturation is reached when approximately 3.2 mol% S is present in the volatile phase at fO2 = NNO-0.5. At the sulfide/sulfate transition, the partition coefficient of S drops from 171 ± 23 to 21 ± 1 at a constant FeO content of ∼6 wt.% in the melt. At fO2 = NNO+1.8, anhydrite saturation is reached at ∼3.3 mol% S present in the volatile phase. Aqueous volatiles exsolving from intermediate to mafic magmas can efficiently extract S, and effect its transfer to sites of magmatic-hydrothermal ore deposit formation.

  10. Origin of Miocene andesite and dacite in the Goldfield-Superstition volcanic province, central Arizona: Hybrids of mafic and silicic magma mixing (United States)

    Fodor, R. V.; Johnson, Kelly G.


    The Miocene Goldfield-Superstition volcanic province (G-SVP), ∼8000 km2 in central Arizona, is composed largely of silicic pyroclastic rocks and lavas, and smaller volumes of alkalic basalt and intermediate-composition lavas. Volcanism began ∼20.5 Ma as sparse rhyolitic and mainly basaltic lavas followed by intermediate lavas, lasting until ∼19 Ma. At that time, ∼1 m.y. of silicic eruptions began, creating most of the G-SVP. Petrologic studies are available for basalts and some for silicic rocks, but petrologic/geochemical information is sparse for intermediate-composition lavas. These latter, andesites and dacites, are the focus of this study, in which we present the processes and sources responsible for their origins. Goldfield-Superstition andesites and dacites have SiO2 ∼56-70 wt.% and Na2O + K2O that qualifies some as trachy-andesite and -dacite. A prominent petrographic feature is plagioclase-phyric texture (∼11-30 vol% plagioclase), where oligoclase-andesine phenocrysts have cores surrounded by corroded, or reacted, zones, mantled by higher An% plagioclase. Where corroded zones are absent, margins are etched, curved, or embayed. Groundmass plagioclase is labradorite, also more calcic than the phenocrysts. Other minerals are quartz (subrounded; embayed), clinopyroxene, amphibole, biotite, and rare titanite and zircon. A salient compositional characteristic that provides insight to andesite-dacite origins with respect to other G-SVP rocks is revealed when using SiO2 as an index. Namely, abundances of many incompatible elements, mainly HFSE and REE, decrease over the low to high SiO2 range (i.e., abundances are lower in dacites than in co-eruptive andesites and underlying alkalic basalts). As examples: G-SVP basalts have ∼50-70 ppm La, and andesites-dacites have ∼59-22 ppm La; for Zr, basalts have ∼225-170 ppm, but most andesites-dacites have ∼180-50; for Y, basalts >20 ppm, andesites-dacites ∼18-9 ppm. To understand these trends of lower

  11. Potential reactivity of the andesitic rocks from Cabo de Gata (SE Spain); Reactividad potencial de las rocas andesiticas de Cabo de Gata (SE de Espana)

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    Soriano, J.; Iglesia, A. la; Garcia Calleja, M. A.; Lopez-Ruiz, J.


    Andesitic rocks produce an alkali-silica reaction with the components of the interstitial phase of concrete. This reaction can be considered as belonging to the slow-kinetic type, since the incongruent dissolution of the rock-forming minerals leads to the late formation of siliceous calc-alkaline gel. As a conquence, the conventional mortar-bar method does not detect such reaction until 90 days later. (Author) 9 refs.

  12. The role of slab melting in the petrogenesis of high-Mg andesites: evidence from Simbo Volcano, Solomon Islands (United States)

    König, S.; Schuth, S.; Münker, C.; Qopoto, C.


    The petrogenesis of high-Mg andesites (HMA) in subduction zones involves shallow melting of refractory mantle sources or, alternatively, the interaction of ascending slab-derived melts with mantle peridotite. To unravel the petrogenesis of HMA, we report major, trace element and Sr-Nd-Hf-Pb isotope data for a newly found occurrence of HMA in the New Georgia group, Solomon Islands, SW-Pacific. Volcanism in the Solomon Islands was initiated by subduction of the Pacific plate beneath the Indian-Australian plate until a reversal of subduction polarity occurred ca. 10 Ma ago. Currently, the Indian-Australian plate is subducted northeastwards along the San Cristobál trench, forming the younger and still active southwestern Solomon island arc. However, a fossil slab of Pacific crust is still present beneath the arc. The edifice of the active volcano Simbo is located directly in the San Cristobál trench on top of the subducting Indian-Australian plate. Simbo Island lies on top of a strike-slip fault of the adjacent Woodlark spreading centre that is subducted beneath the Pacific plate. Geochemical and petrological compositions of volcanic rocks from Simbo are in marked contrast to those of volcanic rocks from islands north of the trench (mostly arc basalts). Simbo-type rocks are opx-bearing HMA, displaying 60-62 wt% SiO2 but rather primitive Mg-Ni-Cr characteristics with 4-6 wt% MgO, up to 65 ppm Ni, up to 264 ppm Cr and Mg# from 67 to 75. The compositions of the Simbo andesites are explained by a binary mixture of silicic and basaltic melts. Relict olivine phenocrysts with Fo88-90 and reaction-rims of opx also support a mixing model. The basaltic endmember is similar to back-arc basalts from the Woodlark Ridge. A slab melt affinity of the silicic mixing component is indicated by Gd(N)/Yb(N) of up to 2.2 that is higher if compared to MORB and other arc basalts from the Solomon Islands. 87Sr/86Sr, ɛNd and ɛHf values in the analysed rocks range from 0.7035 to 0.7040, +6

  13. The Multiphase Rheology of Andesitic Magmas from the 1.9ka Eruption of Turrialba Volcano (Costa Rica) (United States)

    Vona, A.; Di Piazza, A.; Romano, C.; De Astis, G.; Soto, G. J.


    We present a study of high-temperature, uniaxial deformation experiments of natural magma from an andesitic eruption of Turrialba volcano (1.9ka Plinian eruption). The aim of this work is to investigate the multiphase rheology (liquid+vesicles+crystals) of natural samples and the effect of vesicles and crystals on the magma viscosity. The experiments were performed using a high-temperature uniaxial Geocomp LoadTrac II press at dry atmospheric conditions and controlled deformation rates. Cores of natural sample (with Φcrys=0.20-0.30 and Φves=0.41-0.58) were deformed isothermally (790-870°C) at variable strain rates (VSR, from 10-6 to 10-4 s-1) and constant strain rate (CSR, 10-5 s-1). VSR were performed at low total amount of strain (eflow behavior of these complex natural materials. The stress-strain rate relationships under flow conditions showed a linear trend between the applied stress and strain rate in the temperature interval investigated. All the samples display a steep linear trend, typical of Newtonian fluids (n index ~ 1), with a very small shear thinning behavior. CSR tests were performed at different total amount of strain (e=0.15-0.25-0.35). Strain hardening was observed with increasing deformation, resulting in an increase of apparent viscosity (up to 100.5 Pa s). This increase is related to the loss of total porosity (up to ΔΦves=0.15) due to compaction of the sample as indicated by post-run analyses . The measured multiphase rheology of Turrialba magmas was compared with literature models for both crystal- and bubble-bearing suspension. We calculate a difference of ~101 Pa s in magma apparent viscosity between high and low density samples, that coupled with a lateral temperature gradient inside the conduit of the volcano, could increase up to ~103 Pa s. The large difference in viscosity could be responsible of significant rheological contrasts, possibly resulting in strain localization and brittle fragmentation of magma.

  14. On progress and rate of the peritectic reaction Fo + SiO2 → En in natural andesitic arc magmas (United States)

    Zellmer, Georg F.; Sakamoto, Naoya; Matsuda, Nozomi; Iizuka, Yoshiyuki; Moebis, Anja; Yurimoto, Hisayoshi


    Using a high resolution ion microprobe with SCAPS imaging, the peritectic reaction of forsterite + silica to enstatite was studied down to submicron level in a natural andesitic tephra from the Central Plateau of North Island, New Zealand. The fayalitic component of natural olivines is stable in high-silica melts, and therefore the reaction is in fact a two-step progress: 1. Dissolution of Mg-rich olivine, rate-limited by Fe-Mg interdiffusion at the crystal rim, results in enrichment of Fe in the crystal rim and of Mg in the c. 1 μm wide melt boundary layer around the crystal. 2. Magnesian pyroxenes preferentially but not exclusively nucleate in the melt boundary layer and grow; as soon as these microlites touch the rim of the dissolving olivine, they shield the crystals from the silica-rich melt, thereby preventing further olivine dissolution. At this point, Fe-Mg interdiffusion begins to destroy the Fe-enrichment of the olivine rim. The reaction is completed when the dissolving olivine crystal is completely mantled by magnesian pyroxene microlites. Thick pyroxene mantles are likely the result of pyroxene overgrowth rather than due to peritectic transformation. The morphology of the olivine rim preserves information about the reaction history of the grain. Modeling of Fe-Mg interdiffusion in the olivine rim following its shielding from the melt by pyroxene overgrowth may yield the rates of olivine dissolution and the rates of pyroxene growth if temperature is known. For the tephra we have studied, microlite thermometry yields a temperature of 1137 (±41) °C, indicating an olivine dissolution rate of 3-6 × 10-11 ms-1 and an initially volumetric pyroxene growth rate of 2.2-5.6 × 10-21 m3 s-1. This points to timescales between olivine crystal uptake into the SiO2-rich melt and explosive eruption at the surface of a few hours to at most a day.

  15. Melt inclusions are not reliable proxies for magmatic liquid composition: evidence from crystal-poor andesites and dacites in the Tequila volcanic field, Mexico (United States)

    Frey, H. M.; Lange, R. A.


    A compositional study of >200 melt inclusions in plagioclase and orthopyroxene phenocrysts from six crystal-poor (2-5 vol%) andesite and dacite lavas (60-68 wt% SiO2) from the Tequila volcanic field in the Mexico arc is used to evaluate whether melt inclusions in phenocrysts accurately record magmatic liquid compositions. The crystal-poor andesites and dacites were erupted contemporaneously with crystal-poor rhyolites, and there is a continuum in the SiO2 concentration of the erupted magmas. The liquid line of descent defined by the whole-rock compositions ranges from andesite to rhyolite (60-77 wt% SiO2), as illustrated on Harker diagrams. The crystal-poor andesites and dacites are multiply saturated with five to seven mineral phases (plagioclase + orthopyroxene + titanomagnetite + ilmenite + apatite ± augite ± hornblende), most of which crystallized via degassing during magma ascent (Frey and Lange, 2009). By comparison with phase equilibrium experiments from the literature, it is shown that the vast majority of crystals are phenocrysts and not xenocrysts. Textural evidence of rapid crystal growth includes skeletal, hopper, and swallow-tail morphologies and abundant melt inclusions. The inclusions range in size from a few microns to > 50 μm and occur as isolated pockets and extensive channels that mimic the crystal morphology. Inclusions are typically brown glass, with occasional microphenocrysts of titanomagnetite and/or apatite within or adjacent to the melt inclusions. The compositions of the melt inclusions in the plagioclase and orthopyroxene phenocrysts, when plotted on Harker diagrams, vary systematically from one another and from the liquid line of descent defined by the whole rock compositions of erupted magmas. For example, melt inclusions in plagioclase are systematically depleted in Al2O3 relative to the whole rock samples, whereas those in coexisting orthopyroxenes are systematically enriched in Al2O3. The opposite trend is found for FeO, where it

  16. Microgranular enclaves in island-arc andesites: A possible link between known epithermal Au and potential porphyry Cu-Au deposits in the Tulasu ore cluster, western Tianshan, Xinjiang, China (United States)

    Zhao, Xiaobo; Xue, Chunji; Symons, David T. A.; Zhang, Zhaochong; Wang, Honggang


    The successful exploration for porphyry copper deposit in western Tianshan, Xinjiang, faces great challenge. Tulasu basin is an important epithermal gold ore cluster in western Tianshan, which was formed in a southwest-Pacific-type island-arc setting during the late Paleozoic by the southward subduction of the North Tianshan ocean beneath the Yili plate. Porphyry Cu-Au deposits are possibly to be found at depth or adjacent to these epithermal gold deposits. Some sulfide-mineralized microgranular enclaves of monzonite porphyry and microdiorite were found in andesites of the Tawuerbieke gold district, Tulasu basin. The enclaves are randomly distributed, with generally round or subangular shape and commonly clearly defined within their host andesite, and have a chilled surrounding margin of andesite. The monzonite porphyry enclaves (MPE) exhibit porphyritic texture with the phenocrysts of plagioclase and K-feldspar. The microdiorite enclaves (MDE) are mainly composed of plagioclase and hornblende with an aplitic texture and massive structure. The host andesites show porphyritic texture, with the phenocrysts major of plagioclase, minor of hornblende and clinopyroxene. The groundmass consists of short-column plagioclase and minor clinopyroxene with a hyalopilitic texture. Zircon grains from a MPE sample yield a weighted 206Pb/238U age of 356.2 ± 4.3 Ma (n = 13, MSWD = 1.11), which is effectively coincident with the 360.5 ± 3.4 Ma (n = 20, MSWD = 0.61) of an andesite sample within analytical error, indicating that they were coeval. In addition, the MPE, MDE and the andesite samples share similar normalized incompatible element and rare earth element patterns that are characterized by a pronounced enrichment of large ion lithophile elements and a deficit of high field strength elements. Moreover, the samples show similar Nd isotope compositions to the contemporary andesites and basaltic andesites. Detailed petrology, geochronology and geochemistry studies suggest that

  17. Zircon LA-ICP MS U-Pb Dating of the Longkang Andesitic Ignimbrites from Jiuzhaigou: Evidence of the Mianlue Suture Westward Extension

    Institute of Scientific and Technical Information of China (English)

    Qin Jiangfeng; Lai Shaocong; Zhang Guowei; Diwu Chunrong; Li Yongfei


    Genesis of metasedimentary-volcanics outcroped in Kangxian-Pipasi-Nanping (康县-琵琶寺-南坪) tectonic zone is closely related with tectonic evolution of the Mianlue (勉略) Ocean. In the west end of Kangxian-Pipasi-Nanping tectonic zone, there are hundred meters of andesitic ignimbrites and tuffites. Zircon U-Ph dating on these volcanies has great significance to the tectonic implication of zircons from Longkang andesitic ignimbrites are magmatic genesis with oscillatory zoning and high U ((35-750) ppm), Th ((311-717) ppm) contents with high Th/U (0.44-1.30) ratios. The measured 206pb/238U ratios are in good analytical precision, yielding a weighted mean age of (246±3) Ma (MSWD=2.6, n=12, 2σ). Some detrital zircons have also been observed, they have maximal concordia area. Combined with regional geology and the volcanic rocks in the studied area, the (246±3) Ma zircon U-Pb age suggests a Late Permian orogenic volcanism and provides important geochronology evidence for the Mianlue suture westward extension.

  18. Manganese mineralization in andesites of Brestovačka Banja, Serbia: evidence of sea-floor exhalations in the Timok Magmatic Complex (United States)

    Pačevski, Aleksandar; Cvetković, Vladica; Šarić, Kristina; Banješević, Miodrag; Hoefer, Heidi Eva; Kremenović, Aleksandar


    Andesites near Brestovačka Banja belong to the Late Cretaceous Timok Magmatic Complex (TMC), which hosts the world-class Bor metallogenic zone including numerous porphyry-copper and epithermal deposits. Two main volcanic phases are recognized in the TMC. The newly discovered Mn mineralization reported here is associated with the second volcanic phase of Turonian-Campanian age. Manganese mineralization containing 58 % MnO on average, occurs as black veins, lumps and nests filling cracks and cavities within an autoclastic andesite, which was deposited in a subaqueous environment. This rock also contains minor Fe mineralization, which is contemporaneous with the manganese mineralization. Manganese mineralization predominantly consists of Mn-Ca silicates (macfallite, pumpellyite-Mn, orientite, bustamite) and Mn oxides (pyrolusite, manganite). Micrometer-scale mineral intergrowths and locally preserved botryoidal and colloform textures are characteristic features of this uncommon mineral assemblage. The features could indicate that the mineralization was formed by deposition from a primary colloidal assemblage and is of sub-marine hydrothermal origin. Orientite is the only Mn mineral with grain size reaching several tenths of micrometers and showing prismatic crystal habit. Scarce to rare associated minerals are hollandite, crednerite, an unknown REE mineral, powellite, pyrite, barite and galena, in decreasing abundance. Trace element analyses of the Mn mineralization show different element contents and REE patterns compared to those of the volcanic host-rock. Manganese mineralization shows relatively high contents of Cu - 1784 ppm, Mo - 20 ppm and As - 268 ppm. These elements are commonly enriched in the Cu deposits of the Bor zone and their relatively high contents in the studied Mn crusts indicate sea-floor hydrothermal vents as a source of the metals.

  19. Mixing and mingling in the evolution of andesite dacite magmas; evidence from co-magmatic plutonic enclaves, Taupo Volcanic Zone, New Zealand (United States)

    Cole, J. W.; Gamble, J. A.; Burt, R. M.; Carroll, L. D.; Shelley, D.


    The southeastern side of the Taupo Volcanic Zone, New Zealand is marked by a line of andesite/dacite/low-silica rhyolite complexes. Co-magmatic plutonic enclaves occur within the lavas of the four youngest complexes: White Island, Motuhora (Whale Island), Edgecumbe and Tauhara. The enclaves range from coarse-grained gabbros, diorites, granodiorites and a syenite to finer-grained dolerites and microdiorites. The more mafic types are generally porphyritic with large phenocrysts of plagioclase, usually with extensive sieve textures in the cores and corroded margins. Most of these enclaves, including the coarser-grained plutonic examples, contain glass and many are miarolitic. Diorites and microdiorites/dolerites predominate at White Island, Motuhora and Edgecumbe; many are porphyritic. Enclaves at Tauhara are more variable; those collected from Hipaua Dome include a range from microdiorites to quartz microdiorites and those from Rubbish Tip Dome include microdiorites, a granodiorite, and a syenite. Most enclaves show textural evidence for disequilibrium with multiple populations of plagioclase and pyroxene. They also show considerable textural variation, even within a thin section, with coarse-grained gabbros/diorites intimately mixed with finer-grained dolerites/microdiorites. Geochemically and isotopically, most enclaves have a similar composition with their host lavas, although some have lower silica contents. Enclaves at Motuhora and Tauhara are isotopically more variable, indicating multiple sources and a more complex petrogenesis. Most diorite/microdiorite enclaves are interpreted to represent parts of a crystal mush formed during fractionation of andesite/dacite magma, and entrained during later rise of magma to the surface. The granodiorite from Rubbish Tip Dome, Tauhara, probably represents part of a silicic magma chamber within the crust that fed the host low-silica rhyolite lava dome. Variability within the enclaves indicates the complexity likely to occur

  20. Chemical and isotopic fractionation of wet andesite in a temperature gradient: Experiments and models suggesting a new mechanism of magma differentiation (United States)

    Huang, F.; Lundstrom, C. C.; Glessner, J.; Ianno, A.; Boudreau, A.; Li, J.; Ferré, E. C.; Marshak, S.; DeFrates, J.


    Piston-cylinder experiments were conducted to investigate the behavior of partially molten wet andesite held within an imposed temperature gradient at 0.5 GPa. In one experiment, homogenous andesite powder (USGS rock standard AGV-1) with 4 wt.% H 2O was sealed in a double capsule assembly for 66 days. The temperature at one end of this charge was held at 950 °C, and the temperature at the other end was kept at 350 °C. During the experiment, thermal migration (i.e., diffusion in a thermal gradient) took place, and the andesite underwent compositional and mineralogical differentiation. The run product can be broadly divided into three portions: (1) the top third, at the hot end, contained 100% melt; (2) the middle-third contained crystalline phases plus progressively less melt; and (3) the bottom third, at the cold end, consisted of a fine-grained, almost entirely crystalline solid of granitic composition. Bulk major- and trace-element compositions change down temperature gradient, reflecting the systematic change in modal mineralogy. These changes mimic differentiation trends produced by fractional crystallization. The change in composition throughout the run product indicates that a fully connected hydrous silicate melt existed throughout the charge, even in the crystalline, cold bottom region. Electron Backscatter Diffraction analysis of the run product indicates that no preferred crystallographic orientation of minerals developed in the run product. However, a significant anisotropy of magnetic susceptibility was observed, suggesting that new crystals of magnetite were elongated in the direction of the thermal gradient. Further, petrographic observation reveals alignment of hornblende parallel to the thermal gradient. Finally, the upper half of the run product shows large systematic variations in Fe-Mg isotopic composition reflecting thermal diffusion, with the hot end systematically enriched in light isotopes. The overall δ 56Fe IRMM-14 and δ 26Mg DSM-3

  1. Using mineral geochemistry to decipher slab, mantle, and crustal inputs to the generation of high-Mg andesites from Mount Baker and Glacier Peak, northern Cascade arc (United States)

    Sas, M.; DeBari, S. M.; Clynne, M. A.; Rusk, B. G.


    A fundamental question in geology is whether subducting plates get hot enough to generate melt that contributes to magmatic output in volcanic arcs. Because the subducting plate beneath the Cascade arc is relatively young and hot, slab melt generation is considered possible. To better understand the role of slab melt in north Cascades magmas, this study focused on petrogenesis of high-Mg andesites (HMA) and basaltic andesites (HMBA) from Mt. Baker and Glacier Peak, Washington. HMA have unusually high Mg# relative to their SiO2 contents, as well as elevated La/Yb and Dy/Yb ratios that are interpreted to result from separation of melt from a garnet-bearing residuum. Debate centers on the garnet's origin as it could be present in mineral assemblages from the subducting slab, deep mantle, thick lower crust, or basalt fractionated at high pressure. Whole rock analyses were combined with major, minor, and trace element analyses to understand the origin of these HMA. In the Tarn Plateau (Mt. Baker) flow unit (51.8-54.0 wt.% SiO2, Mg# 68-70) Mg#s correlate positively with high La/Yb in clinopyroxene equilibrium liquids, suggesting an origin similar to that of Aleutian adakites, where slab-derived melts interact with the overlying mantle to become Mg-rich and subsequently mix with mantle-derived basalts. The source for high La/Yb in the Glacier Creek (Mt. Baker) flow unit (58.3-58.7 wt.% SiO2, Mg# 63-64) is more ambiguous. High whole rock Sr/P imply origin from a mantle that was hydrated by an enriched slab component (fluid ± melt). In the Lightning Creek (Glacier Peak) flow unit (54.8-57.9 SiO2, Mg# 69-72) Cr and Mg contents in Cr-spinel and olivine pairs suggest a depleted mantle source, and high whole rock Sr/P indicate hydration-induced mantle melting. Hence Lightning Creek is interpreted have originated from a refractory mantle source that interacted with a hydrous slab component (fluid ± melt). Our results indicate that in addition to slab-derived fluids, slab

  2. Effect of fO2 on phase relationship in basaltic andesites during magmatic differentiation: Control of fO2 and sulphur speciation in piston cylinder experiments. (United States)

    Matjuschkin, Vladimir; Tattitch, Brian; Blundy, Jonathan D.; Skora, Susanne


    Within the mantle wedge above subduction zones, oxidation reaction take place by interaction of reduced mantle rocks with more oxidized, hydrous fluids, which can cause a local drop of the solidus, resulting in partial melting (2,6,7). The resultant melts are more oxidized that their ocean floor counterparts, which has implications for their subsequent differentiation paths, the speciation of multivalent elements and the solubility and transport of chemical compounds in magmatic systems (1,4,5). We present a series of sulphur-doped high-pressure experiments conducted to investigate the effect of oxygen fugacity on phase relationships and the behaviour of sulphur in silicate melts. Natural aphyric andesite (FM37) erupted from Laguna del Maule volcano, Chile (3) was selected as a starting composition. Experiments were carried out at 5kbar, 950-1150° C and variable oxygen fugacity conditions. New experiments buffered at Co-CoO and Ni-NiO buffer conditions have been performed using a new "MTB capsule design" developed in order to accurately control fO2 by means of a double capsule containing metal-oxide buffers and a pyrex sleeve to minimise H2 diffusion. This new design constrains oxygen fugacity to within ±0.1-0.2logfO2 units of the target value. Before conducting these experiments, the assemblage was tested multiple times at 10kbar, 1000° C over 24-48 hours and demonstrated consistent, accurate fO2 control. Analyses of the preliminary experimental run products, from a related Chilean basaltic andesite starting composition, demonstrate a clear effect of fO2 on phase relationships and the proportion of melt generated during experiments. Under oxidized conditions, as temperature decreased from 1150° C to 1050° C, the amount of melt decreased from 100% to ~80%, due to the formation of orthopyroxene, anhydrite and plagioclase. In contrast, in reduced runs the system remains nearly liquid (~5% crystals) down to 950° C due to the change in sulphur speciation and

  3. Genesis of andesitic boninitic magmas at mid-ocean ridges by melting of hydrated peridotites: Geochemical evidence from DSDP Site 334 gabbronorites (United States)

    Nonnotte, Philippe; Ceuleneer, Georges; Benoit, Mathieu


    account for part of the variability in the Sr isotopic signature of oceanic basalts, among other to the short wavelength isotopic "noise" superimposed on regional trends. We conclude that seawater introduction into residual peridotite at shallow depth beneath mid-ocean ridges can lead mantle rocks and their melts to follow complex P-T-f H2O paths that mimic petrogenetic contexts classically attributed to subduction zone environments, like the production of boninitic-andesitic magmas.

  4. High-K andesite petrogenesis and crustal evolution: Evidence from mafic and ultramafic xenoliths, Egmont Volcano (Mt. Taranaki) and comparisons with Ruapehu Volcano, North Island, New Zealand (United States)

    Price, Richard C.; Smith, Ian E. M.; Stewart, Robert B.; Gamble, John A.; Gruender, Kerstin; Maas, Roland


    This study uses the geochemistry and petrology of xenoliths to constrain the evolutionary pathways of host magmas at two adjacent andesitic volcanoes in New Zealand's North Island. Egmont (Mt. Taranaki) is located on the west coast of the North Island and Ruapehu lies 140 km to the east at the southern end of the Taupo Volcanic Zone, the principal locus of subduction-related magmatism in New Zealand. Xenoliths are common in the eruptives of both volcanoes but the xenoliths suites are petrographically and geochemically different. Ruapehu xenoliths are predominantly pyroxene-plagioclase granulites derived from Mesozoic meta-greywacke basement and the underlying oceanic crust. The xenolith population of Egmont Volcano is more complex. It includes sedimentary, metamorphic and plutonic rocks from the underlying basement but is dominated by coarse grained, mafic and ultramafic igneous rocks. Gabbroic xenoliths (Group 1) are composed of plagioclase, clinopyroxene and amphibole whereas ultramafic xenoliths are dominated by amphibole (Group 2) or pyroxene (Group 3) or, in very rare cases, olivine (Group 4). In Group 1 xenoliths plagioclase and clinopyroxene and in some cases amphibole show cumulate textures. Amphibole also occurs as intercumulate poikilitic crystals or as blebs or laminae replacing pyroxene. Some Group 2 xenoliths have cumulate textures but near monomineralic amphibole xenoliths are coarse grained with bladed or comb textures. Pyroxene in Group 3 xenoliths has a polygonal granoblastic texture that is commonly overprinted by veining and amphibole replacement. Group 1 and most Group 2 xenoliths have major, trace element and Sr, Nd and Pb isotope compositions indicating affinity with the host volcanic rocks. Geochemical variation can be modelled by assimilation fractional crystallisation (AFC) and fractional crystallisation (FC) of basaltic parents assuming an assimilant with the composition of average crystalline basement and Group 1 xenoliths have

  5. Etude de l’activité pouzzolanique d’une roche andésitique en Algérie Study of the pozzolanic activity of an andesitic rock in Algeria

    Directory of Open Access Journals (Sweden)

    Clastres P.


    Full Text Available Ce travail s’inscrit dans le cadre de l’accord programme Tassili N° 09 MDU 773 entre le Laboratoire de Physicochimie des Matériaux, USTO-Oran et le Laboratoire des Matériaux et Durabilité des Constructions (LMDC, INSA-UPS-Toulouse, France. La présente étude est une contribution aux travaux de la recherche de nouvelles sources d’approvisionnement en ajouts et en matières premières et la valorisation des matériaux naturels locaux utilisés dans la fabrication du ciment. Cette étude porte sur l’activité pouzzolanique des roches volcaniques, elle a pour but de comparer les caractéristiques physiques et mécaniques d’un mortier témoin à ciment de type CEMI 52,5R fourni par la firme Lafarge et d’un mortier à ciment du même type avec ajout dont les taux de substitution de la roche Andésitique est de 0- 40%. Dans notre travail, nous avons utilisé des roches volcaniques appartenant à la famille des Andésites, provenant de la région de Tipaza, Nord Ouest Algérois. L’étude des caractéristiques mécaniques et de l’indice de pouzzolanicité ont montré que les ciments fabriqués sont capables de remplacer certains ciments Portland pour une éventuelle utilisation dans le domaine de construction. This work is a part of the agreement programs Tassili N° 09 MDU 773 between Laboratory of Physic-chemistry Materials, USTO-Oran and Laboratory of Materials and Durability of Constructions (LMDC, INSA-UPS-Toulouse, France. The present study is an attempt to the research of new supply sources in admixtures and raw materials and the evaluation of local natural materials used in the manufacture of cement. It deals with the pozzolanic activity of the volcanic rocks and aims to compare the physical and mechanical characteristics of a mortar control made with cement CEMI 52,5R provided by Lafarge firm and of a mortar made with the same cement incorporated by different replacement rate of andesitic rock in a range of 0 – 40

  6. Mid infrared throughput with 5 mu m aperture for H sub 2 O determination of an andesitic glass. Comparison of synchrotron radiation source at SPring-8 with conventional light sources

    CERN Document Server

    Kawamoto, T; Kagi, H; Handa, T; Yamashita, S; Ikemoto, Y; Moriwaki, T; Kimura, H


    Mid infrared throughput using 5 mu m apertures was investigate using micro-FTIR spectrometers with conventional light sources at two laboratories and the synchrotron radiation infrared (SR-IR) light source at SPring-8. With both the light sources micro-FTIR microscopy can analyze the fundamental O-H vibration in andesitic glass with 1 weight % H sub 2 O through 5 mu m apertures. Spectra obtained at SPring-8 show better relative standard deviations due to the brighter and more highly collimated nature of SR-IR compared to conventional light sources. The spectra with 100 and 1000 scans at SPring-8 have similar relative standard deviations to those with 1000 and 10200 scans, respectively, at laboratories. The successful analysis with 5 mu m apertures using both light sources shows the potential for an improvement in the spatial resolution of micro-FTIR analyses. (author)

  7. Late Permian high-Mg andesite and basalt association from northern Liaoning, North China: Insights into the final closure of the Paleo-Asian ocean and the orogen-craton boundary (United States)

    Yuan, Lingling; Zhang, Xiaohui; Xue, Fuhong; Lu, Yinghuai; Zong, Keqing


    High-Mg andesites (HMAs) and related basalts constitute a volumetrically minor, but genetically important occurrence along most convergent plate margins of various ages on Earth. The details of their petrogenesis can contain critical information for resolving essential geodynamic and crustal evolutionary issues. This zircon U-Pb dating and geochemical study documents the late Permian metamorphosed high-Mg basaltic to andesitic suite from Kaiyuan of northern Liaoning, North China. These rocks feature SiO2 contents ranging from 48.7 to 63.2 wt.%, high Mg# values of 63-75, an enrichment in large-ion lithophile elements (LILE), and depletion in high field strength elements (HFSE). They possess whole-rock initial 87Sr/86Sr ratios of 0.70417-0.70457, εNd(t) values from - 0.4 to 5.0, and εHf(t) values from 5.1 to 11, as well as zircon εHf(t) values from - 9.4 to 0.4. These features indicate that their petrogenesis most likely involved precursory metasomatism of mantle peridotites by melts from subduction-related sediments, and subsequent partial melting. With a depleted mantle source and possible tectonic link to post-subduction slab break-off, the Kaiyuan suite could present a spatial reference not only for defining the demarcation line between the North China craton (NCC) and the Central Asian Orogenic belt (CAOB) in the region, but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean. Synthesizing the suite with coeval igneous episodes as well as concomitant metamorphic events along the Solonker-Xra Moron-Changchun zone leads to the characterization of the eventual closure of the Paleo-Asian Ocean within a double-sided subduction system during late Permian-Early Triassic.

  8. Post-collisional volcanism in a sinking slab setting—crustal anatectic origin of pyroxene-andesite magma, Caldear Volcanic Group, Neogene Alborán volcanic province, southeastern Spain (United States)

    Zeck, H. P.; Kristensen, A. B.; Williams, I. S.


    Caldear Volcanic Group (CVG), a stratigraphically well defined, calc-alkaline rock complex within S a de Gata in the eastern part of the Alpine Betic mountain chain, S Spain, consists of three distinct formations: Hernández pyroxene andesites, Bujo hornblende-bearing pyroxene andesites and Viuda hornblende-bearing pyroxene dacites-rhyolites. The letter rock formation may have developed through crystal fractionation of mainly plagioclase and pyroxenes, however there is no direct relation between two formations. CVG has a domainal structure with a northeastern domain where Hernández formation is overlain by Bujo formation while Viuda formation is absent, and a southwestern domain where Viuda formation forms the only fractionate after Hernández formation. Hernández parent magma is thought generated through crustal anatexis by dehydration melting of a predominantly amphibolitic source rock complex which was formed by metamorphism from c. 500 Ma volcano-sedimentary parent material. The domainal structure of CVG is explained by compositional variation within this protogenetic complex. Single crystal U-Pb ages of c. 500 Ma to 1800 Ma for inherited zircon support the presence of clastic material of Proterozoic derivation within the original volcano-sedimentary complex. Regional study of syn-collisional rock formations (Alpine nappe complexes) indicate that the collisional tectonic stage in the Betic-Rif orogenic belt took place rather early (25-30 Ma?) and was followed by a stage of rapid regional rock uplift, fast cooling (c. 500°C/my) and extensional tectonics in the period 22-17 Ma. This later tectonic stage was set into motion by slab break-off which set the stage for a high temperature regime in the overlying lithosphere, providing the framework for the crustal melting and magma production responsible for the calc-alkaline rocks of Alborán volcanic province. Miocene zircon with ages ranging from c. 17 to 11 Ma indicate a rather protracted magmatic development

  9. Devonian Nb-enriched basalts and andesites of north-central Tibet: Evidence for the early subduction of the Paleo-Tethyan oceanic crust beneath the North Qiangtang Block (United States)

    Zhang, Hongrui; Yang, Tiannan; Hou, Zengqian; Bian, Yeke


    The early evolution of the Tethyan Ocean in north-central Tibet is currently poorly constrained. A sequence of volcanic rocks ranging from basic to intermediate in composition has been identified in the Zaduo area of the North Qiangtang Block. SHRIMP U-Pb dating of zircons from a sample of Zaduo andesite suggests an eruption age of Late Devonian (~ 380 Ma). The Zaduo volcanic rocks exhibit geochemical characteristics similar to those of typical Nb-enriched basalts, with relatively high Nb, Ta, and Zr contents, resulting in high Nb/La ratios (0.70-1.08) and Nb/U ratios (10.57-34.37). The relative enrichment in high field strength elements, together with positive εNd(t) values of + 4.6 to + 5.8 and low (87Sr/86Sr)i ratios of 0.70367-0.70532, indicates the Zaduo volcanic rocks were derived from a depleted mantle source metasomatized by silicate melts of a subducted oceanic slab. The occurrence of Nb-enriched volcanic rocks in the North Qiangtang Block suggests that the subduction of Paleo-Tethyan oceanic crust was initiated in the Late Devonian. Available geochronological data from ophiolites surrounding the North Qiangtang Block suggest that the subducted slab is most likely the Longmucuo-Shuanghu Paleo-Tethyan oceanic crust.

  10. Geochemistry, age and strontium isotope composition of late tertiary and quaternary basalts and andesites in western Nevada and their relation to geothermal potential. Final report, October 1, 1982-December 31, 1983

    Energy Technology Data Exchange (ETDEWEB)

    Fultz, L.A.; Bell, E.J.; Trexler, D.T.


    This research was undertaken to characterize the late Cenozoic volcanic rocks associated with active geothermal systems in west-central Nevada. Petrographic and microprobe, geochemical and isotopic analysis and age dating techniques were used to characterize these young volcanic rocks. These data were combined with the limited data previously reported in the literature on these same volcanic areas to interpret their petrogenesis. The overall characterization resulted from integrating the petrogenesis with a structural-tectonic model of the region. Potassium-argon isotopic ages ranging up to 14 million years were determined for eight localities within the Reno 1 x 2/sup 0/ study region. These ages are consistent with the morphology of the volcanic landforms, the active geothermal systems associated with them, and with other isotopic ages reported in the literature for these and similar rocks within the study region. Petrographic analysis of hand specimens and thin-sections indicated mineralogic assemblages of the respective rock types and specific mineral textures and phenocryst compositions and characteristics. These identifications were further substantiated by microprobe analysis of selected phenocrysts and groundmass phases. Classification of the respective rock types was also based on chemical composition and normative calculations using the program PETCAL. Basaltic andesites are identified and described for Steamboat Hills, Table Mountain, Silver Springs, Churchill Butte, Cleaver Peak, Desert Peak and Carson City sites.

  11. Las Andesitas Estrechura del Complejo Volcánico Piroclástico del Río Chubut Medio (Paleoceno-Eoceno Medio The Estrechura Andesites from the Middle Rio Chubut Volcanic-Pyroclastic Complex (Paleocene-Middle Eocene

    Directory of Open Access Journals (Sweden)

    E. Aragón


    Full Text Available Las Andesitas Estrechura muestran una tendencia evolutiva basalto-traquita del tipo toleítico transicional. En esta secuencia la inmisciblidad líquida está presente desde los basaltos hasta las traquitas. Esto permite establecer que: los basaltos y traquibasaltos representan el magma que se está fraccionando; las traquiandesitas son la mezcla de magma basáltico enriquecido con líquido inmiscible y las traquitas son el líquido inmiscible alojado en el techo de la cámara magmática. Aunque estos basaltos toleíticos transicionales sean pobres en agua, el enriquecimiento en volátiles por fraccionamiento en una de las fases inmiscibles permite la extrusión esporádica de ignimbritas que arrastran restos de magma sin vesicular y perliticos en los núcleos de los pómez. La profundidad de emplazamiento de la cámara magmática se estima próxima a los 4,5 kilómetros.The Estrechura Andesites show a basalt-trachyte tholeiitic transitional trend. Liquid immiscibility is present from basalts to trachytes. Thus, basalts and trachybasalts are interpreted as the fractionating magmas; the trachyandesites are the enriched (mix residual magma - immiscible liquid; and the trachytes are the segregated immiscible liquid at the magma chamber top. Even though it is a water poor system, the concentration of volatile in one of the immiscible liquids enables few ignimbrite extrusions that carry non-vesiculated perlitic magma blebs in pumice core. The depth of the magma chamber emplacement is estimated to be close to the 4,5 kilometers.

  12. Andesita Cerro Bola: Nueva unidad vinculada al magmatismo mioceno de la Cordillera de Olivares, San Juan, Argentina (30°35´S; 69°30´O Cerro Bola Andesite: New unit linked to the Miocene magmatism of the Olivares Cordillera, San Juan (30°35' S ; 68°30' W

    Directory of Open Access Journals (Sweden)

    A.F. Wetten


    properly in the regional stratigraphic context. The main outcrops were recognized in the Bola Hill and surroundings, where they are irregularly distributed, covering an area greater than 5 km². Dome and lava flow structures are present with the light gray andesite - phenoandesite rock. These outcrops can be correlated with the Pircas volcanic unit (Miocene, to the west, and could be further related to other porphyry bodies of different composition, situated both in Chita Creek and in Divisadero Hill. The extension of the area, lithological uniformity, the low alteration and a K/Ar radiometric age were considered, in order to propose these subvolcanic and volcanic bodies as a new lithostratigraphic unit, Upper Miocene in age, denominated "Cerro Bola Andesite".

  13. The Petrographic Distinction between Basalt and Andesite Based upon the Arrested Fractionation of Plagioclase Phenocrysts. (United States)

    Garlick, G. Donald; Garlick, Benjamin J.


    Discusses the need to take into account the effects of arrested fractional crystallization in the petrographic classification of volcanic rocks containing plagioclase phenocrysts. Describes the development and use of a computer program to accomplish this task graphically. (TW)

  14. Sulfur metabolizing microbes dominate microbial communities in Andesite-hosted shallow-sea hydrothermal systems. (United States)

    Zhang, Yao; Zhao, Zihao; Chen, Chen-Tung Arthur; Tang, Kai; Su, Jianqiang; Jiao, Nianzhi


    To determine microbial community composition, community spatial structure and possible key microbial processes in the shallow-sea hydrothermal vent systems off NE Taiwan's coast, we examined the bacterial and archaeal communities of four samples collected from the water column extending over a redoxocline gradient of a yellow and four from a white hydrothermal vent. Ribosomal tag pyrosequencing based on DNA and RNA showed statistically significant differences between the bacterial and archaeal communities of the different hydrothermal plumes. The bacterial and archaeal communities from the white hydrothermal plume were dominated by sulfur-reducing Nautilia and Thermococcus, whereas the yellow hydrothermal plume and the surface water were dominated by sulfide-oxidizing Thiomicrospira and Euryarchaeota Marine Group II, respectively. Canonical correspondence analyses indicate that methane (CH(4)) concentration was the only statistically significant variable that explains all community cluster patterns. However, the results of pyrosequencing showed an essential absence of methanogens and methanotrophs at the two vent fields, suggesting that CH(4) was less tied to microbial processes in this shallow-sea hydrothermal system. We speculated that mixing between hydrothermal fluids and the sea or meteoric water leads to distinctly different CH(4) concentrations and redox niches between the yellow and white vents, consequently influencing the distribution patterns of the free-living Bacteria and Archaea. We concluded that sulfur-reducing and sulfide-oxidizing chemolithoautotrophs accounted for most of the primary biomass synthesis and that microbial sulfur metabolism fueled microbial energy flow and element cycling in the shallow hydrothermal systems off the coast of NE Taiwan.

  15. Sulfur metabolizing microbes dominate microbial communities in Andesite-hosted shallow-sea hydrothermal systems.

    Directory of Open Access Journals (Sweden)

    Yao Zhang

    Full Text Available To determine microbial community composition, community spatial structure and possible key microbial processes in the shallow-sea hydrothermal vent systems off NE Taiwan's coast, we examined the bacterial and archaeal communities of four samples collected from the water column extending over a redoxocline gradient of a yellow and four from a white hydrothermal vent. Ribosomal tag pyrosequencing based on DNA and RNA showed statistically significant differences between the bacterial and archaeal communities of the different hydrothermal plumes. The bacterial and archaeal communities from the white hydrothermal plume were dominated by sulfur-reducing Nautilia and Thermococcus, whereas the yellow hydrothermal plume and the surface water were dominated by sulfide-oxidizing Thiomicrospira and Euryarchaeota Marine Group II, respectively. Canonical correspondence analyses indicate that methane (CH(4 concentration was the only statistically significant variable that explains all community cluster patterns. However, the results of pyrosequencing showed an essential absence of methanogens and methanotrophs at the two vent fields, suggesting that CH(4 was less tied to microbial processes in this shallow-sea hydrothermal system. We speculated that mixing between hydrothermal fluids and the sea or meteoric water leads to distinctly different CH(4 concentrations and redox niches between the yellow and white vents, consequently influencing the distribution patterns of the free-living Bacteria and Archaea. We concluded that sulfur-reducing and sulfide-oxidizing chemolithoautotrophs accounted for most of the primary biomass synthesis and that microbial sulfur metabolism fueled microbial energy flow and element cycling in the shallow hydrothermal systems off the coast of NE Taiwan.

  16. Posteruptive impacts of pyroclastic deposits from basaltic andesite stratovolcanoes on surface water composition (United States)

    Genareau, K.; Cronin, S. J.; Stewart, C.; Bhattacharyya, S.; Donahoe, R.


    Volcanic ash deposition following explosive eruptions can pose significant hazards for water quality, human health, agriculture, and infrastructure functionality. Many studies have examined how fresh ash deposition may lower the pH of, and introduce a range of potentially toxic elements into, exposed surface waters. However, no study has yet determined the effects on water composition as a result of mechanical pyroclast disaggregation and production of new fresh particle surfaces and increasingly fine grained particles. Such disaggregation could result from natural posteruptive processes such as debris avalanches, lahars, or fluvial/aeolian transport and human activities such as cleanup efforts or mining of pyroclastic deposits. The posteruption time scales of pyroclast disaggregation may vary from months in moist tropical or temperate environments to years or decades in arid settings. Here we show, for the first time in experimental studies, that mechanical milling of pyroclasts will introduce a range of elements into exposed waters, including Al, which can be toxic at elevated levels, and Na, which increases the electrical conductivity of solutions. The pH of leaching solutions also increases by several log units. Such dramatic changes on the experimental scale may have implications for surface water composition in posteruptive settings, necessitating longer-term risk assessments for ecosystem health and consideration of the role of pyroclastic deposits in element cycling in volcanically active regions.

  17. Groundwater circulations within a tropical humid andesitic volcanic watershed using the temperature as a tracer (United States)

    Selles, Adrien; Violette, Sophie; Hendrayana, Heru


    Groundwater flow within volcano-detritic environment, is of prime importance to many human needs and activities, from the supply of clean drinking water to the extraction of hydrocarbons or geothermal energy. However, the heterogeneity of the geological formations makes difficult to quantify the groundwater spatial distribution. Moreover, its temporal variation in tropical humid regions is sometimes poorly known. For instance, the surronding of the Merapi volcano, in Central Java, Indonesia, is an area of high but seasonal rainfall, and extensive crop irrigation. It has a large population and a need to increase food and potable water supplies depending upon exploiting groundwater ressources. The stress on these resources increases with the intensification of the demography, the agricultural practices and the industrial exploitations. In order to implement a sustainable management of the water resources, the description of the groundwater circulations and the quantification of the resources is needed. A mutidisciplinary approach has been performed at the watershed scale, including geology, hydrogeochemistry and long term hydrogeological monitoring. The data synthesis and constisency have been confirm with a numerical model of physical processes. Based on a geological and geomorphological study, the hydrogeological watershed on the Eastern flank of the Merapi volcano is composed by an alternation of aquitards (mainly ashes, tuffs and clay) and aquifers (sand, gravel and boulders). The deep aquifers are agenced in conduit following the burried channel of the paleo-rivers. The eastern flank of Merapi provides excellent example of a volcanic-sedimentary environment. From 20 cold springs of 3 spring zones, sampled on 2 hydrological years (2011 to 2013), the study of the transfer into the saturated zone from upstream to downstream, given the geological context and topography, allows to estimate the role of supply from high and low altitudes to the recharge processes. The water temperature has been used as a tracer to understand the pattern of groundwater flow and to determine the mean recharge elevation for springs. Inferences from standard oxygen and hydrogen isotopic measurements are compared with temperature measurements made at the springs to confirm the recharge elevation estimation and whether groundwater circulates to shallow or deeper depths. The METIS model, coupling groundwater flow and heat transport simulations in 2D steady flow regime, has been used in order to confirm the findings of the temperature and mean flow rate analysis and to characterize the regional flow of the multi-layered aquifer system. This approach provides methodological insights into characterization of the groundwater pathway within complex porous media in tropical humid regions. This study enable us to provide guidance on the required level of model complexity as well as on the amount and type of observations data required.

  18. Wastewater Phosphorus Removal by Two Different Types of Andesitic Volcanic Tephra (United States)

    Liesch, Amanda M.


    Phosphorus (P) is the limiting nutrient controlling productivity in most inland freshwater systems. Several materials have been proposed for use to remove excess P from wastewater treatment, including volcanic lapilli and ash (tephra). There is limited data in using tephra as a P filter. There were two objectives of this study: (1) to determine…

  19. Geochemical discrimination of the geotectonic environment of basaltic-andesitic volcanic rocks associated with the Laochang polymetallic ore deposit at Lancang, Yunnan

    Institute of Scientific and Technical Information of China (English)

    GAO Jianguo


    The Laochang polymetallic ore deposit at Lancang is one of the well known ancient ore deposits associated with volcanic rocks in the Sanjiang (Tri-river) region of Southwest China. Volcanic rocks are dominated by alkali basalt and trachyte basalt. There has long been a controversy on the environment of formation of basalts. Some scholars hold that the basalts were formed in a continental environment, some thought they were formed in an oceanic environment and others considered that the basalts were emplaced in a back-arc basin. This study focuses on the geochemical characteristics of the basalts on the basis of their major elements, REEs and trace elements. At the same time, strongly incompatible elements such as Ta, Th and Hf and their ratios were used to differentiate the geotectonic settings of basalts. The results showed that the basalts in the region studied were formed in a continental rift environment.

  20. New insights into the evolution of the magmatic system of a composite andesite volcano revealed by clasts from distal mass-flow deposits: Ruapehu volcano, New Zealand (United States)

    Tost, M.; Price, R. C.; Cronin, S. J.; Smith, I. E. M.


    Stratovolcanoes characteristically build large composite edifices over long periods with stacked lavas intercalated with pyroclastic deposits. In most cases, only the most recent volcanic products are exposed on the flanks of the volcano, and consequently the search for deposits recording an older eruptive and magmatic history is typically focussed far from the cone, within distal tephra deposits. Clasts within lahar and debris avalanche deposits may also provide unique insights into the earliest eruptive and magmatic history of long-lived volcanoes, especially when widespread fallout is absent. Careful sampling and subsequent petrological and geochemical analyses of lava and pumice clasts from six distal mass-flow deposit sequences (hyperconcentrated flow, debris flows and debris avalanche deposits) from Mt. Ruapehu (New Zealand), combined with detailed stratigraphic studies and radiometric age dating, give new perspectives on the pre-50 ka magmatic system of this complex volcano. A conglomerate emplaced between 340 and 310 ka contains evidence for the oldest episode of Mt. Ruapehu volcanism, and unusually for the composite cone, pumice clasts from this unit contain amphibole-bearing xenoliths. Chemical and petrological data for these oldest Ruapehu clasts indicate that a deep (˜40 km) crustal storage system had already developed under Mt. Ruapehu before ˜340 ka. From the very earliest stages, evolution was largely controlled by magma mixing, along with decoupled assimilation and fractional crystallization within numerous isolated small-scale magma batches stored throughout the crust. From around 340 to 160 ka, there was a progressive shift towards more primitive compositions, suggesting that during this period large-scale replenishment events involving mantle-derived basaltic magmas occurred within the mid- to upper crustal storage system. Subsequent magmas became progressively more evolved due to decoupled fractional crystallization and assimilation processes accompanied by magma recharge events, which triggered major phases of eruptive activity.

  1. The effect of kauri (Agathis australis) on grain size distribution and clay mineralogy of andesitic soils in the Waitakere Ranges, New Zealand

    NARCIS (Netherlands)

    Jongkind, A.G.; Buurman, P.


    Kauri (Agathis australis) is generally associated with intense podzolisation, but little research has been carried out to substantiate this. We studied soil profiles, grain size distribution patterns and clay mineralogy under kauri and broadleaf/tree fern vegetation in the Waitakere Ranges, North Is

  2. Mineralization model for Chahar Gonbad copper-gold deposit (Sirjan), using mineralogical, alteration and geochemical data and multivariate statistical methods


    Seayed Jaber Yousefi; Abas Moradian


    The study area is located in southeastern Iran, about 110 km southwest of Kerman. Geologically, the area is composed of ophiolitic rocks, volcanic rocks, intrusive bodies and sedimentary rocks. Vein mineralization within andesite, andesitic basalt, andesitic tuffs occurred along the Chahar Gonbad fault. Sulfide mineralization in the ore deposit has taken place as dissemination, veins and veinlets in which pyrite and chalcopyrite are the most important ores. In this area, argillic, phyllic and...

  3. Research on isotope geology: Isotopes ages of volcanic rocks from Ryeongnam Massif, Korea

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Seong Cheon; Chi, Se Jung; Kim, Yoo Sook [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)


    Chronostratigraphy of most volcanic rocks in the Ryeongnam Massif have been undefined or mis-classified in different geological maps due to total absence of reported isotope ages. Twenty-four new isotope ages are given for age-undefined volcanic units and some related igneous bodies. Most of volcanic rocks show high [La/Yb]n ratios and LREE enrichments which are characteristics of subduction-related high-K calc-alkali volcanic rocks occurred in the active continental margin. Preliminary results on carbon and oxygen stable isotope ratios({delta}{sup 13}C=-1.7{approx}-6.2 per mil; {delta}{sup 18} O=-21.6{approx}-24.7 per mil) of druse- or phenocryst-calcite from andesitic and basaltic rocks in the southern coastal region indicate a magmatic origin. Based on new K-Ar whole-rock ages, chronological guidelines are established as follows: 1) Gayasan andesite (78{+-}4Ma) - Gurye andesitic tuff (81{+-}4Ma); 2) Gurye andesite (68{+-}4Ma) - Suncheon andesitic tuff (67{+-}3Ma) - Yeosu basaltic andesite (67{+-}3Ma) - Narodo andesite (70{+-}3Ma); 3) Taebaeg Baegbyeongsan basaltic andesite (62{+-}3Ma) - Gurye Obongsan andesite (64{+-}3Ma) - Yeosu dacite (63{+-}3Ma) - Dolsando andesite (62{+-}3Ma) - Jangheung Buyongsan andesite (65{+-}3Ma); 4) Suncheon Joryedong andesite (55{+-}2Ma) - Goheung andesite (56{+-}3Ma); 5) Taebaeg Baegbyeonsan basaltic andesite (48{+-}2Ma) - Yeosu basalt (51{+-}3Ma). Resetted age (49{+-}2Ma) of an intrusive rhyolite implies the timing of thermal alteration in the Wondong Fe-Mine of the Taebaegsan Mineralized Belt. K-Ar hornblende ages of two hornblendite stocks in the southern Jangsu suggests apparent emplacement-ages of late Triassic (210{+-}9Ma) and early Permian (274{+-}10Ma), independently. K-Ar hornblende age (1023{+-}37Ma) of the Ogbang amphibolite implies a reduction of original age due to later thermal effect probably attributed to either later intrusion or regional metamorphism. (author). 56 refs., 19 tabs., 14 figs.

  4. Magmatic controls on eruption dynamics of the 1950 yr B.P. eruption of San Antonio Volcano, Tacaná Volcanic Complex, Mexico-Guatemala (United States)

    Mora, Juan Carlos; Gardner, James Edward; Macías, José Luis; Meriggi, Lorenzo; Santo, Alba Patrizia


    San Antonio Volcano, in the Tacaná Volcanic Complex, erupted ~ 1950 yr. B.P., with a Pelean type eruption that produced andesitic pyroclastic surges and block-and-ash flows destroying part of the volcano summit and producing a horse-shoe shaped crater open to the SW. Between 1950 and 800 yr B.P. the eruption continued with effusive andesites followed by a dacite lava flow and a summit dome, all from a single magma batch. All products consist of phenocrysts and microphenocrysts of zoned plagioclase, amphibole, pyroxene, magnetite ± ilmenite, set in partially crystallized groundmass of glass and microlites of the same mineral phases, except for the lack of amphibole. Included in the andesitic blocks of the block-and-ash flow deposit are basaltic andesite enclaves with elongated and ellipsoidal forms and chilled margins. The enclaves have intersertal textures with brown glass between microphenocrysts of plagioclase, hornblende, pyroxene, and olivine, and minor proportions of phenocrysts of plagioclase, hornblende, and pyroxene. A compositional range obtained of blocks and enclaves resulted from mixing between andesite (866 °C ± 22) and basaltic andesite (enclaves, 932 °C ± 22), which may have triggered the explosive Pelean eruption. Vestiges of that mixing are preserved as complex compositional zones in plagioclase and clinopyroxene-rich reaction rims in amphibole in the andesite. Whole-rock chemistry, geothermometry, experimental petrology and modeling results suggest that after the mixing event the eruption tapped hybrid andesitic magma (≤ 900 °C) and ended with effusive dacitic magma (~ 825 °C), all of which were stored at ~ 200 MPa water pressure. A complex open-system evolution that involved crustal end-members best explains the generation of effusive dacite from the hybrid andesite. Amphibole in the dacite is rimmed by reaction products of plagioclase, orthopyroxene, and Fe-Ti oxides produced by decompression during ascent. Amphibole in the andesite

  5. Mount Pinatubo, Philippines: June 1991 Eruptions (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Mount Pinatubo is an andesitic island arc volcano, located on the southern Luzon Island, Philippines. Prior to 1991 it had been dormant for more than 635 years. On...

  6. The geology of the Rosas-Terreseo area (Sulcis, South Sardinia)

    NARCIS (Netherlands)

    Poll, J.J.K.


    Cambrian sandstones, limestones and slates, unconformably overlain by Ordovician and Silurian slates, intruded by Hercynian granodiorite and dolerite, and Alpine andesite, occur. The traditional rock stratigraphic subdivisions of the sequences below the Ordovician unconformity are here proposed as f

  7. 長崎県に分布する赤黄色土の粘土鉱物組成


    江頭, 和彦; 中島, 康夫; 秋山, 美保子; 林, 由紀子; 和仁, 佳子


    Red-Yellow soils are widely distributed on the mountains, hills, and plateaus in Nagasaki Prefecture, located at the most western part of Japan, and used as an important agricultural land. They are derived from various kinds of parent rock including basalt, andesite, andesitic tuff breccia, welded tuff, Tertiary sedimentary rock, and crystalline schist. The purpose of the present study is to investigate the clay mineralogical composition of the Red-Yellow soils in relation to their parent roc...

  8. Spatial variations in the frequency-magnitude distribution of earthquakes in the southwestern Okinawa Trough


    Lin, Jing-yi; Sibuet, Jean-claude; Lee, Chao-Shing; Hsu, Shu-kun; Klingelhoefer, Frauke


    The relations between the frequency of occurrence and the magnitude of earthquakes are established in the southern Okinawa Trough for 2823 relocated earthquakes recorded during a passive ocean bottom seismometer experiment. Three high b-values areas are identified: (1) for an area offshore of the Ilan Plain, south of the andesitic Kueishantao Island from a depth of 50 km to the surface, thereby confirming the subduction component of the island andesites; (2) for a body lying along the 123.3 d...

  9. Neogene volcanism in Gutai Mts. (Eastern Carpathains: a review

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    Marinel Kovacs


    Full Text Available Two types of volcanism developed in Gutâi Mts. (inner volcanic chain of Eastern Carpathians: a felsic, extensional/“back-arc” type and an intermediate, arc type. The felsic volcanism of explosive origin, consisting of caldera-related rhyolitic ignimbrites and resedimented volcaniclastics, had taken place during Early-Middle Badenian and Early Sarmatian. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The geochemical study on the volcanic rocks shows the calc-alkaline character of both felsic and intermediate volcanism and typical subduction zones geochemical signatures for the intermediate one. The felsic volcanism shows affinities with subduction-related rocks as well. The main petrogenetic process in Gutâi Mts. was crustal assimilation, strongly constrained by trace element and isotope geochemistry.

  10. Geologic and chemical evolution of volcan tepetiltic, Nayarit, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Deremer, L.A.; Nelson, S.A.


    Volcan Tepetiltic is located in the northwestern segment of the Mexican Volcanic Belt, about 40 km SW of the city of Tepic. The structure is a calc-alkaline stratovolcano composed primarily of andesite and dacite lava flows topped by an elliptical caldera measuring approximately 5 by 2.5 km. At least two cycles of andesite volcanism followed by rapid differentiation into volumetrically subordinate dacite flows and dikes built the majority of the complex. The second pulse of andesitic lavas were more basic than the first and appear to have been the result of reinjection of mafic magma into the shallow andesitic magma chamber. This was closely followed by the emplacement of two rhyolite domes and associated ash deposits on the eastern flank of the volcano. Finally, two small hornblende andesite domes were erupted on the floor of the caldera, and a lake formed in the northeastern corner of the caldera. Cinder cones on the flanks of the volcano have erupted alkaline lavas of mugearitic affinity. These are chemically unrelated to the calc-alkaline lavas erupted from Tepetiltic itself. The latest activity of Tepetiltic was the emplacement of a crystal rich rhyolite domes on the southern flank, which has blocked stream drainages to form a coulee lake. This last event has occurred within the last several thousand years. The rocks erupted from Tepetiltic form a chemically continuous suite which could have been derived through crystal fractionation of andesitic magma. No basic parental magmas, however, have erupted throughout the area.

  11. Experimental and textural constraints on mafic enclave formation in volcanic rocks (United States)

    Coombs, M.L.; Eichelberger, J.C.; Rutherford, M.J.


    We have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at Southwest Trident volcano, Alaska. Andesite enclaves are present throughout the four dacite lava flows produced by the eruption, and resemble mafic enclaves commonly found in other volcanic rocks. Our experiments replicate the pressure-temperature-time path taken by enclave-forming andesite magma as it is engulfed in dacite during magma mixing. Pressure and temperature information for the andesite and dacite are from [Coombs et al., Contrib. Mineral. Petrol. 140 (2000) 99-118]. The andesite was annealed at 1000??C, and then cooled to 890??C at rates of 110??C h1, 10??C h1 and 2??C h1. Once cooled to 890??C, andesite was held at this lower temperature from times ranging from 1 to 40 h. The andesite that was cooled at the slower rates of 2??C h1 and 10??C h1 most resembles enclave groundmass texturally and compositionally. Based on simple thermal calculations, these rates are more consistent with cooling of the andesite groundmass below an andesite-dacite interface than with cooling of enclave-sized spheres. If enclaves do crystallize as spheres, post-crystallization disaggregation must occur. Calculations using the MELTS algorithm [Ghiorso and Sack, Contrib. Mineral. Petrol. 119 (1995) 197-212] show that for incoming andesite to become less dense than the dacite to become less dense ???34 volume % of its groundmass must crystallize to undergo~18 volume % vesiculation; these values are similar to those determined for Southwest Trident enclaves. Thus such crystallization may lead to 'flotation' of enclaves and be a viable mechanism for enclave formation and dispersal. The residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments. Decompression experiments on Southwest Trident dacite suggest an average ascent rate for the eruption of ???2

  12. The production of intermediate magmas through magma mixing and commingling: Evidence from the Hoover Dam Volcanics, Mohave County, Arizona and Clark County, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Mills, J.G. Jr. (Univ. of Nevada, Las Vegas, NV (United States). Dept. of Geoscience)


    The Hoover Dam Volcanic section ([approximately]14 Ma) is composed of the reversely-zoned dacitic tuff of Hoover Dam, Switchyard basaltic andesite, Sugarloaf dacite, Black Canyon dacite and Kingman Wash basaltic andesite (Mills, 1985). The origin of this suite is best explained by the commingling and mixing of end-member mafic and felsic magmas. These end-member magmas were most likely formed by partial melting of the mantle and subsequent advective heating and melting of the crust respectively. Textural evidence for these processes is observed in the Black Canyon dacite which contains enclaves of basaltic andesite, and, in the Paint Pots pluton which contains commingled basaltic andesite and monzonite. The Black Canyon dacite is a biotite (4%), homblende (1%) and plagioclase 10% phyric dacite flow which contains up to 5% enclaves of basaltic andesite. The enclaves contain 54 wt% SiO[sub 2], 7.22 ppm Tl, 65 ppm Rb, 1,274 ppm Sr and 1,810 ppm Ba. The gray to purplish-red enclaves have crenulate margins, are commonly vesiculated and contain phenocrysts of biotite (< 1%), hornblende ([much lt]1%), plagioclase (1%) and clinopyroxene( ) (2%). Chemically, the enclaves are distinct from the Switchyard and Kingman Wash basaltic andesites. The enclaves most likely represent a more primitive magma from which the Switchyard and Kingman Wash basaltic andesites were derived. These two units were subsequently chemically modified by mixing with crustal melt and/or crystal fractionation. The presence of a small, clinopyroxenite xenolith (clinopyroxene 90%, garnet 5%, plagioclase 4%) within one of the enclaves indicates an upper mantle source for the enclave magma.

  13. The eruptive history of the Tequila volcanic field, western Mexico: ages, volumes, and relative proportions of lava types (United States)

    Lewis-Kenedi, Catherine B.; Lange, Rebecca A.; Hall, Chris M.; Delgado-Granados, Hugo


    The eruptive history of the Tequila volcanic field (1600 km2) in the western Trans-Mexican Volcanic Belt is based on 40Ar/39Ar chronology and volume estimates for eruptive units younger than 1 Ma. Ages are reported for 49 volcanic units, including Volcán Tequila (an andesitic stratovolcano) and peripheral domes, flows, and scoria cones. Volumes of volcanic units ≤1 Ma were obtained with the aid of field mapping, ortho aerial photographs, digital elevation models (DEMs), and ArcGIS software. Between 1120 and 200 kyrs ago, a bimodal distribution of rhyolite (~35 km3) and high-Ti basalt (~39 km3) dominated the volcanic field. Between 685 and 225 kyrs ago, less than 3 km3 of andesite and dacite erupted from more than 15 isolated vents; these lavas are crystal-poor and show little evidence of storage in an upper crustal chamber. Approximately 200 kyr ago, ~31 km3 of andesite erupted to form the stratocone of Volcán Tequila. The phenocryst assemblage of these lavas suggests storage within a chamber at ~2 3 km depth. After a hiatus of ~110 kyrs, ~15 km3 of andesite erupted along the W and SE flanks of Volcán Tequila at ~90 ka, most likely from a second, discrete magma chamber located at ~5 6 km depth. The youngest volcanic feature (~60 ka) is the small andesitic volcano Cerro Tomasillo (~2 km3). Over the last 1 Myr, a total of 128±22 km3 of lava erupted in the Tequila volcanic field, leading to an average eruption rate of ~0.13 km3/kyr. This volume erupted over ~1600 km2, leading to an average lava accumulation rate of ~8 cm/kyr. The relative proportions of lava types are ~22 43% basalt, ~0.4 1% basaltic andesite, ~29 54% andesite, ~2 3% dacite, and ~18 40% rhyolite. On the basis of eruptive sequence, proportions of lava types, phenocryst assemblages, textures, and chemical composition, the lavas do not reflect the differentiation of a single (or only a few) parental liquids in a long-lived magma chamber. The rhyolites are geochemically diverse and were likely

  14. Composition of plagioclases in volcanic rocks of King George Island, Antarctica with reference to the petrogenetic significance

    Institute of Scientific and Technical Information of China (English)


    Plagioclases occur mainly as phenocrysts in volcanic rocks of King George Island, South Shetland Islands, West Antarctica. In basaltic andesites and andesites of Keller Peninsula and Ullman Spur (Admiralty Bay), they are high structure state labradorite-andesines; and in high-A1 basalts and basaltic andesites of Barton and Weaver peninsulas (Maxwell Bay), they are high structure state bytownite-anorthites.∑REE, La/Yb ratios and δEu values of plagioclases from Admiralty Bay are higher than those from Maxwell Bay. All plagioclases have rather identical chondritenormalized transitional element distribution patterns, probably reflecting that crystal structure rather than composition of plagioclase controls their diversity. Compositions of plagioclases depend chiefly on those of their host rocks, compositional differences of plagioclases reveal that basaltic magmas in the Admiralty Bay area are more evolved than in the Maxwell Bay area.


    Directory of Open Access Journals (Sweden)

    Dragomir Jovičić


    Full Text Available Andesite agregate, due to its suitable physical-mechanical properties, is known on market primarily of asphalt mixtures production for wear covers of roads, regardles to traffic intensity and impedance. The economic importance of the andesite Fužinski Benkovac (Gorski kotar is presented on the basis of the geological, genetic, technical-exploitable, technological, regional, marketing, and social-economic factors. Petrographic structure and tectonic fabric of the deposit have been separately elaborated. On the basis of these researches, quality, hydro-geological characteristics, natural and factors of evaluation, the deposit is economically evaluated as prosperous (the paper is published in Croatian.



    Karatepe, Yasin


    In this study, total N (Nt) and organic C of soils; and total N and organic matter of forest floor were compared in black pine (Pinus nigra Arn. supsp. pallasiana (Lamb.) Holmboe) stands developed on four different growing sites in Golcuk, Isparta. Average of total N reserves was greatest in soils on andesite parent material (8.568 ton/ha) while it was lowest in soils on Golcuk Formation (0.614 ton/ha). Average of organic carbon reserves was greatest in soils on andesite parent material (79.0...

  17. The evolution of young silicic lavas at Medicine Lake Volcano, California: Implications for the origin of compositional gaps in calc-alkaline series lavas (United States)

    Grove, T.L.; Donnelly-Nolan, J. M.


    At Medicine Lake Volcano, California, the compositional gap between andesite (57-62 wt.% SiO2) and rhyolite (73-74 wt.% SiO2) has been generated by fractional crystallization. Assimilation of silicic crust has also occurred along with fractionation. Two varieties of inclusions found in Holocene rhyolite flows, hornblende gabbros and aphyric andesites, provide information on the crystallization path followed by lavas parental to the rhyolite. The hornblende gabbros are magmatic cumulate residues and their mineral assemblages are preserved evidence of the phases that crystallized from an andesitic precursor lava to generate the rhyolite lavas. The andesitic inclusions represent samples of a parental andesite and record the early part of the differentiation history. Olivine, plagioclase and augite crystallization begins the differentiation history, followed by the disappearance of olivine and augite through reaction with the liquid to form orthopyroxene and amphibole. Further crystallization of the assemblage plagioclase, amphibole, orthopyroxene, magnetite, and apatite from a high-SiO2 andesite leads to rhyolite. This final crystallization process occurs on a cotectic that is nearly horizontal in temperature-composition space. Since a large amount of crystallization occurs over a limited temperature interval, a compositional gap develops between rhyolite and high SiO2 andesite. Liquidus surfaces with shallow slopes in temperature-composition space are characteristic of several late-stage crystallization assemblages in the andesite to rhyolite compositional range. Experimentally produced plagioclase+ amphibole+orthopyroxene+magnetite and plagioclase+ augite+low-Ca pyroxene+magnetite cotectics have liquidus slopes that are nearly flat. At other calc-alkaline volcanic centers crystallization processes involving large compositional changes over small temperature intervals may also be important in the development of bimodal volcanism (i.e. the existence of a composition

  18. K-Ar dating of the magmatic activity in the Momchilgrad volcanotectonic depression

    International Nuclear Information System (INIS)

    The Momchilgrad volcanotectonic depression originated in the Southern parts of Eastern Rhodopes during the paleocene. The earliest products of the magmatic activity in the area are the rocks of the Kalabak andesite complex of Priabonian age (35 - 39 MA). The pyroclastic rocks and lavas of Beli Plast rhyodacite, Majarovo latite, Perperek trachyrhyolite, Zvezdel basaltic - andesite, Ustra rhyolite, Sveti Ilia trachyriodacite, Momchilgrad trachydacite complexes (28-34 MA) and Pcheloyad dyke complex (26.5-32.2 MA) formed lately during Rupelian and Rupelian-Chatian respectively. Obtained K-Ar age ranges for the different complexes overlap significantly indicating that the magmatic activity might have occurred during quite short period of time. (authors)

  19. The rotation of Spain: Palaeomagnetic evidence from the Spanish meseta

    NARCIS (Netherlands)

    Voo, R. van der


    The magnetic properties of 39 oriented samples of Triassic siltstones and of 43 oriented samples of Silurian andesites and basalts from the Spanish Meseta were investigated. After a.c. magnetic field demagnetization up to 3,000 Oe, peak value, and after correction for the dip of the geological stra

  20. Inca Volcanic Stone Provenance in the Cuzco Province, Peru

    Directory of Open Access Journals (Sweden)

    Patrick N. Hunt


    Full Text Available The use of andesite and basalt as architectual ashlars by Inca stonemasons has been widely discussed throughout the literature. Most of these archaeological or architectural studies are in agreement that that primary Inca quarrying centers in the Cuzco area are in the Rio Huatanay valley at Rumiqolqa and Huaccoto, both to the southeast of Cuzco.

  1. Origin of lead in andean calc-alkaline lavas, southern peru. (United States)

    Tilton, G R; Barreiro, B A


    Lead isotope data from Quaternary andesitic lavas of the Arequipa and Barroso groups of southern Peru and from regional Precambrian granulitic gneisses reveal a lead component in the lavas from the gneisses. The lava leads can be accounted for by two-component mixtures of lead from mantle and lower crustal sources, although the mixing process need not have occurred in the lower crust.

  2. Geologic and preliminary reservoir data on the Los Humeros Geothermal System, Puebla, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Ferriz, H.


    Exploratory drilling has confirmed the existence of a geothermal system in the Los Humeros volcanic center, located 180 km east of Mexico City. Volcanic activity in the area began with the eruption of andesites, followed by two major caldera-forming pyroclastic eruptions. The younger Los Potreros caldera is nested inside the older Los Humeros caldera. At later stages, basaltic andesite, dacite, and olivine basalt lavas erupted along the ring-fracture zones of both calderas. Geologic interpretation of structural, geophysical, and drilling data suggests that: (1) the water-dominated geothermal reservoir is hosted by the earliest andesitic volcanic pile, is bounded by the ring-fracture zone of the Los Potreros caldera, and is capped by the products of the oldest caldera-forming eruption; (2) permeability within the andesitic pile is provided by faults and fractures related to intracaldera uplift; (3) the geothermal system has potential for a large influx of meteoric water through portions of the ring-fracture zones of both calderas; and (4) volcanic centers with similar magmatic and structural conditions can be found in the eastern Cascades, USA.

  3. Petrology and geochemistry of igneous inclusions in recent Merapi deposits

    DEFF Research Database (Denmark)

    Chadwick, J.P.; Troll, V.R.; Waight, Tod Earle;


    Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography, ge...

  4. Estimating heat capacity and heat content of rocks (United States)

    Robertson, Eugene C.; Hemingway, Bruch S.


    New heat-capacity measurements are reported for four rock types; Westerly granite from Bradford, RI, andesite from Lake County, OR, peridotite from Sonoma County, CA, and basalt from the Columbia River Group. Measurements were made on powders of the rocks in the temperature range of 340 to about 1000 K.

  5. 蛍光X線分析装置(XRF)による1:5希釈ガラスビードを用いた全岩主成分・微量成分元素の定量分析


    新城, 竜一; 宮本, 正雪; Shinjo, Ryuichi; Miyamoto, Masayuki


    Analytical results of major and trace elements(Ba, Co, Cr, Nb, Ni, Rb, Sr, V, Y, and Zr) for bulk rocks by XRF using 1:5 dilution glass bead were evaluated. Analytical conditions and protocol are also reported. The results show relatively good accuracy and precision for major and trace elements. This method could be suitable to basalts to andesites, with error

  6. Geochronology and magmatic evolution of the Dieng Volcanic Complex, Central Java, Indonesia and their relationships to geothermal resources (United States)

    Harijoko, Agung; Uruma, Ryusuke; Wibowo, Haryo Edi; Setijadji, Lucas Doni; Imai, Akira; Yonezu, Kotaro; Watanabe, Koichiro


    We analyzed new radiometric dating and petrological data of DVC in an attempt to reconstruct volcanic history as groundwork to understand magmatic temporal and spatial evolution. The magma of DVC can be divided on the basis of mineral composition into three types: olivine bearing basalt-basaltic andesite, pyroxene basaltic andesite-andesite, and biotite andesite-dacite, which coincide with three volcanic episodes of DVC: pre-caldera, second, and youngest episode, respectively. The pre-caldera episode was active no later than 1 Ma, the second episode occurred between 0.3 and 0.4 Ma, and the youngest occurred after 0.27 Ma. Plots of CaO, K2O, Al2O3, and Rb/Sr against FeO*/MgO and/or MgO suggest that each volcanic episode has distinct differentiation trends, indicating the presence of multiple shallow magma chambers. The close spatial relationship between the geothermal manifestation, geophysical anomalies, geothermal production zones and volcanic edifices supports the presence of multiple shallow magma chambers beneath DVC, which act as a heat source for the existing geothermal system.

  7. Nematodes from rocky grassland in Börzsöny Mountains, Hungary

    Directory of Open Access Journals (Sweden)

    Kiss, M.


    Full Text Available This paper reports on investigations carried out on soil inhabiting nematodes living in andesitic rock regions ofBörzsöny Mountains. Seventeen species are listed. Heterodorus arcuatus (Thorne, 1939, new to the fauna of Hungary, isdescribed and illustrated in detail.

  8. Nematodes from rocky grassland in Börzsöny Mountains, Hungary


    Kiss, M


    This paper reports on investigations carried out on soil inhabiting nematodes living in andesitic rock regions ofBörzsöny Mountains. Seventeen species are listed. Heterodorus arcuatus (Thorne, 1939), new to the fauna of Hungary, isdescribed and illustrated in detail.

  9. Chemical trends in a perhumid soil catena on the Turrialba volcano (Costa Rica)

    NARCIS (Netherlands)

    Meijer, E.L.; Buurman, P.


    The variation in chemical composition of soil samples (XRFS data) from a soil catena of 14 soil profiles on the northern slope and foot slope of the andesitic Turrialba volcano (3300 m) has been analysed to test the two hypotheses, which underlie our interpretation that this catena is a weathering s

  10. Carbonate assimilation at Merapi volcano, Java Indonesia

    DEFF Research Database (Denmark)

    Chadwick, J.P; Troll, V.R; Ginibre,, C.;


    Recent basaltic andesite lavas from Merapi volcano contain abundant, complexly zoned, plagioclase phenocrysts, analysed here for their petrographic textures, major element composition and Sr isotope composition. Anorthite (An) content in individual crystals can vary by as much as 55 mol% (An40...

  11. Long-distance lava correlation in the Paraná volcanic province along the Serra Geral cuesta, southeastern Brazil (United States)

    Hartmann, L. A.; Arena, K. R.; Duarte, S. K.; Pertille, J.


    The capability of determining the flow-by-flow stratigraphy and the long-distance correlation of lava flows in large continental volcanic provinces leads to a considerable advance in the understanding of processes related to generation and evolution of the lavas. The Paraná volcanic province is exposed along the Serra Geral cuesta of southern Brazil in a steeply inclined, 1,000-m-high section starting 40-m above sea level. Each of the 10-20 pahoehoe flows and rhyodacite flow units has a unique chemical composition. Integrated with field stratigraphy and gamma-spectrometric measurements, this leads to the establishment of the correct stratigraphic sequence in each of three different vertical sections. The number of flows integrating the three serras is 26 ("serra" is a mountain range in Portuguese). Each serra has basaltic andesites at the base, whereas rhyodacites are intercalated with basaltic andesites at the top. Three basaltic andesite flows and one rhyodacite flow unit are correlated between Serra Umbu and Serra Boa Vista (10 km). In the Serra Faxinal, a thick (170 m) sill at the base correlates with flow 13F, whereas a dike-sill in the Graxaim quarry (24 km distance) correlates with flow 3F. One basaltic andesite and two rhyodacite flow units correlate between Serra Faxinal and Serra Umbu (50 km). The results are most significant for the understanding of large tracts of continental volcanic provinces with use of common geochemical and gamma-spectrometric techniques.

  12. Stratigraphy, petrology, and geochemistry of the Spurr Volcanic Complex, eastern Aleutian Arc, Alaska. [(Appendix for geothermal fluid chemistry)

    Energy Technology Data Exchange (ETDEWEB)

    Nye, C.J.


    The Spurr Volcanic Complex (SVC) is a calcalkaline, medium-K, sequence of andesites erupted over the last quarter of a million years by the easternmost currently active volcanic center in the Aleutian Arc. The ancestral Mt. Spurr was built mostly of andesites of uniform composition (58 to 60% SiO/sub 2/), although andesite production was episodically interrupted by the introduction of new batches of more mafic magma. Near the end of the Pleistocene the ancestral Mt. Spurr underwent Bezyianny-type avalanche caldera formation, resulting in the production of a volcanic debris avalanche with overlying ashflows. Immediately afterward, a large dome (the present Mt. Spurr) was emplaced in the caldera. Both the ashflows and dome are made of acid andesite more silicic than any analyzed lavas from the ancestral Mt. Spurr (60 to 63% SiO/sub 2/), yet contain olivine and amphibole xenocrysts derived from more mafic magma. The mafic magma (53 to 57% SiO/sub 2/) erupted during and after dome emplacement, forming proto-Crater Peak and Crater Peak. Hybrid pyroclastic flows and lavas were also produced. Proto-Crater Peak underwent glacial dissection prior to the formation of Crater Peak in approximately the same location. Appendices II through VIII contain a summary of mineral compositions; Appendix I contains geochemical data. Appendix IX by R.J. Motyka and C.J. Nye describes the chemistry of geothermal fluids. 78 refs., 16 figs., 3 tabs.

  13. The End of Sluiter’s Coral Reef at Krakatoa

    NARCIS (Netherlands)

    Umbgrove, J.H.F.


    It is well known that before the famous eruption of August 1883 took place, the island Krakatoa consisted of three volcanoes, the basaltic volcano Rakata and the andesitic volcanoes Danan and Perbuwatan. With the great explosion of August 28th of that year Danan, Perbuwatan and the northwestern part

  14. Formation of redox gradients during magma-magma mixing (United States)

    Ruprecht, P.; Fiege, A.; Simon, A. C.


    Magma-mixing is a key process that controls mass transfer in magmatic systems. The variations in melt compositions near the magma-magma interface potentially change the Fe oxidation state [1] and, thus, affect the solubility and transport of metals. To test this hypothesis, diffusion-couple experiments were performed at 1000 °C, 150 MPa and QFM+4. Synthesized crystal-bearing cylinders of hydrous dacite and hydrous basaltic andesite were equilibrated for up to 80 h. The run products show that mafic components (Fe, Mg, etc.) were transported from the andesite into the dacite, while Si, Na and K diffused from the dacite into the andesite. A crystal dissolution sequence in the order of cpx, opx, plag, and spl/il was observed for the andesite. We combined μ-XANES spectroscopy at Fe K-edge [2] with two-oxide oxybarometry [3] to measure redox profiles within our experiments. Here, fO2 decreased towards the interface within the dacite and increased towards the interface within the andesite. This discontinuous fO2 evolution, with a sharp redox gradient of ~1.8 log fO2 units at the interface was maintained throughout the time-series despite the externally imposed fO2 of the vessel. We propose a combination of two mechanisms that create and sustain this redox gradient: 1) The dissolution of cpx and opx in the andesite mainly introduced Fe2+ into the melt, which diffused towards the dacite, lowering Fe3+/SFe near the interface. 2) Charge balance calculations in the melt during diffusive exchange suggest net positive charge excess in the andesite near the interface (i.e., oxidation) and net negative charge excess in the dacite near the interface (i.e., reduction). We suggest that this (metastable) redox layer can help to explain the contrasting Au/Cu ratios observed for arc-related porphyry-type ore deposits. [1] Moretti (2005), Ann. Geophys. 48, 583-608. [2] Cottrell et al. (2009), Chem. Geol. 268, 167-179. [3] Ghiorso and Evans (2008), Am. J. Sci. 308, 957-1039.

  15. 39Ar/40Ar Chronology and Volumes of Eruptive Products Over the Last 1 Myr in the Tequila Volcanic Field, Jalisco, Mexico (United States)

    Lewis-Kenedi, C. B.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.


    The Tequila volcanic field, located within the western Trans-Mexican arc, covers an area of 1036 km2 and includes a central, andesitic stratocone, Volc\\­_{a}n Tequila, as well as cinder cones, domes, and fissure-fed flows. Sixty-nine high precision 39Ar-40Ar dates reveal that major activity in the Tequila volcanic field began at approximately 1 Ma. From 1 Ma to 200 ka, rhyolite (> 73 wt. % SiO2) and alkali basalt (­š 51 wt. % SiO2) were the only compositions erupted in significant volumes (29 +/- 5.7 km3 and 12 +/- 1.2 km3, respectively). At approximately 200 ka, the andesite comprising Volc\\­_{a}n Tequila erupted within 30-40 kyr, producing a volume of 30 +/- 2.0 km3. Additional andesitic flows (11 +/- 1.4 km3) erupted to the northwest and southeast of the stratocone between 140 and 20 ka. The total volume of dacite that erupted at the Tequila volcanic field is small (1.3 +/- 0.03 km3) and occurred largely (88%) within the last 70 kyrs. Unlike the andesites and dacites, the basalts and rhyolites did not erupt within narrow time intervals, but extruded over the entire last 1 Myr, producing a total volume of 12.6 +/- 1.2 km3 and 32 +/- 6.1 km3, respectively. This detailed eruptive history, combined with the observed phenocryst assemblages (0-10 vol. %) in the small-volume andesite, dacite, and alkali basalt flows, suggest that they were erupted directly from the lower (or middle) crust, without prior storage in an upper crustal chamber. In contrast, the voluminous burst of andesitic volcanism that produced the phenocryst-rich (35-45 vol. %) lavas of Volc\\­_{a}n Tequila was likely fed from a short-lived (­š 40 kyrs) upper crustal chamber. This scenario is supported by the complex, disequilibrium textures seen in the phenocryst assemblage of the Volc\\­_{a}n Tequila lavas, indicative of magma mingling within an upper crustal chamber (Wallace and Carmichael, 1994). The total volume of erupted material at the Tequila volcanic field is 89 +/- 12 km3, of which

  16. Analisis stratigrafi awal kegiatan Gunung Api Gajahdangak di daerah Bulu, Sukoharjo; Implikasinya terhadap stratigrafi batuan gunung api di Pegunungan Selatan, Jawa Tengah

    Directory of Open Access Journals (Sweden)

    Hill Gendoet Hartono


    Full Text Available, Tertiary volcanisms in the Southern Mountains, Central Jawa were started with the formation of pillow lavas having basalt to basaltic andesite in composition. This initial stage volcanism developed into a  construction period of composite volcanoes that consist of alternating basaltic to andesitic lava flows, breccias, and tuffs. The construction period could be followed by a destructive phase, producing pumice-rich pyroclastic breccias, lapillistones, and tuffs of high silica andesite to dacite, or even rhyolite in composition. A stratigraphic measuring section at Bulu area, Sukoharjo Regency, presents an alternat- ing fine-grained andesitic volcaniclastic material and some limestones, with the total thickness is 143.33 m. The thickness of bedded volcaniclastic material tends to be thickening upward from 35 m until 90 m. The grain size of the volcaniclastic material also tends to be coarsening upward from clay size through silt and fine sand to coarse sand and granules. Paleontological analysis on fossils contained in the lime- stone gives an age of Early Miocene (N7 - N9. The volcaniclastic rocks is conformably overlain by the Mandalika Formation, comprising alternating andesitic breccias, lavas, and tuffs. These data imply that the fine-grained volcaniclastic material is an initial product of the construction period of Gajahdangak Volcano in the area, that formed the Mandalika Formation. This Formation is overlain by the Semilir Formation, composed of pumice-rich pyroclastic breccias and tuffs with dacitic composition. This as- sociated volcanic rock reflects a product of a caldera explosion or a destructive phase. Based on the characteristics of lithology of volcanic products from the initial stage, to a construction and destruction period, and compiled age data, the Southern Mountains represent formal volcanic rock units that are able to be divided into many formations.  

  17. Evidencia textural y geoquímica de mezcla de magmas en el volcán Chimpa, Puna Salteña Textural and geochemical evidence for magma mixing in the Chimpa Volcano, Puna Salteña

    Directory of Open Access Journals (Sweden)

    Marcelo Arnosio


    Full Text Available La historia eruptiva del volcán Chimpa (24º00´S-66º08´O comprende un ciclo explosivo que eruptó ignimbritas y depósitos de flujos de bloques y ceniza de composición andesítica, y un ciclo efusivo, representado por lavas andesíticas y andesíticas basálticas. Los primeros materiales emitidos durante el ciclo explosivo corresponden a ignimbritas, las cuales no poseen evidencias de interacción con magmas básicos. Por el contrario, en los depósitos de flujos de bloques y ceniza quedó registrada la interacción con un magma básico (mingling representado por inclusiones máficas y el desarrollo de texturas de desequilibrio en plagioclasa y biotita. Sin embargo, la composición del magma andesítico no se modificó durante la mezcla. En el ciclo efusivo se generó un nuevo magma, por mezcla y homogeneización (magma mixing entre el magma andesítico y un magma más básico. Este magma híbrido posee una asociación mineral en desequilibrio, que incluye olivino y cuarzo con corona de clinopiroxeno, hornblenda y biotita con coronas formadas por plagioclasa + ortopiroxeno + magnetita, así como ortopiroxeno con coronas de clinopiroxeno. Estas fases en desequilibrio coexisten junto a otros cristales de las mismas fases, pero en aparente equilibrio. En diagramas geoquímicos, las lavas híbridas ocupan una posición intermedia en la tendencia lineal definida por el extremo andesítico y andesítico basáltico. La proporción del magma básico involucrado en la mezcla es de 44%. Los datos petrográficos y geoquímicos indican un proceso creciente de interacción de magmas básicos con el magma andesítico residente en la cámara magmática a lo largo del tiempo.The eruptive history of the Chimpa volcano (24º00´S-66º08´O comprises an explosive cycle that erupted andesitic ignimbrites and blocks and ash flow deposits, and an effusive cycle, represented by the discharge of andesitic and basaltic andesite lava flows. The first material

  18. Origin of rhyolite by crustal melting and the nature of parental magmas in the Oligocene Conejos Formation, San Juan Mountains, Colorado, USA (United States)

    Parker, D. F.; Ghosh, A.; Price, C. W.; Rinard, B. D.; Cullers, R. L.; Ren, M.


    Four closely spaced volcanoes (Summer Coon; Twin Mountains; Del Norte; Carnero Creek) form the east-central cluster of Conejos volcanic centers. These Conejos rocks range from high-K basaltic andesite to rhyolite, with andesite volumetrically the most abundant. Summer Coon and Twin Mountains are composite volcanoes. The Del Norte and Carnero Creek volcanoes are deeply eroded dacite shields. Rhyolite (10% of our Conejos analyses but a much smaller percentage by volume) is only known from Summer Coon and Twin Mountains volcanoes, although high-SiO 2 dacite occurs in the Del Norte volcano. The younger Hinsdale Formation contains a related series ranging from transitional basalt to high-K andesite; we use Hinsdale Formation analyses to represent Conejos parental magmas. Conejos and Hinsdale magmas evolved through AFC processes: Basalt, after interacting with lower crust, assimilated low K/Rb crust, similar in some ways to Taylor and McLennan (Taylor, S.R., and McLennan, S.M., 1985, The continental crust: its composition and evolution. Oxford, Blackwell Scientific.) model upper crust; main series basaltic andesite fractionated to high-K andesite; rhyolite was produced by melting of high K/Ba upper crustal rocks similar to granite gneiss known from inclusions and basement outcrops. Some rhyolite may have been back-mixed into fractionating andesite and dacite. Field evidence for assimilation includes sanidinite-facies, partially melted, gneiss blocks up to 1 m in diameter. Temperature estimates (1100-900 ° C) from two-pyroxene equilibria are consistent with this interpretation, as are the sparsely porphyritic nature of the most-evolved rhyolites and the absence of phenocrystic alkali feldspar. Our study supports the conclusions of previous workers on AFC processes in similar, but generally more mafic, Conejos magmas of the southeastern San Juan Mountains. Our results, however, emphasize the importance of crustal melting in the generation of Conejos rhyolite. We further

  19. Late Cenozoic volcanism in the western Woodlark Basin area, SW Pacific: the sources of marine volcanic ash layers based on their elemental and Sr-Nd isotope compositions (United States)

    Lackschewitz, K. S.; Mertz, D. F.; Devey, C. W.; Garbe-Schönberg, C.-D.


    Tephra fallout layers and volcaniclastic deposits, derived from volcanic sources around and on the Papuan Peninsula, form a substantial part of the Woodlark Basin marine sedimentary succession. Sampling by the Ocean Drilling Program Leg 180 in the western Woodlark Basin provides the opportunity to document the distribution of the volcanically-derived components as well as to evaluate their chronology, chemistry, and isotope compositions in order to gain information on the volcanic sources and original magmatic systems. Glass shards selected from 57 volcanogenic layers within the sampled Pliocene-Pleistocene sedimentary sequence show predominantly rhyolitic compositions, with subordinate basaltic andesites, basaltic trachy-andesites, andesites, trachy-andesites, dacites, and phonolites. It was possible to correlate only a few of the volcanogenic layers between sites using geochemical and age information apparently because of the formation of strongly compartmentalised sedimentary realms on this actively rifting margin. In many cases it was possible to correlate Leg 180 volcanic components with their eruption source areas based on chemical and isotope compositions. Likely sources for a considerable number of the volcanogenic deposits are Moresby and Dawson Strait volcanoes (D'Entrecasteaux Islands region) for high-K calc-alkaline glasses. The Dawson Strait volcanoes appear to represent the source for five peralkaline tephra layers. One basaltic andesitic volcaniclastic layer shows affinities to basaltic andesites from the Woodlark spreading tip and Cheshire Seamount. For other layers, a clear identification of the sources proved impossible, although their isotope and chemical signatures suggest similarities to south-west Pacific subduction volcanism, e.g. New Britain and Tonga-Kermadec island arcs. Volcanic islands in the Trobriand Arc (for example, Woodlark Island Amphlett Islands and/or Egum Atoll) are probable sources for several volcaniclastic layers with ages

  20. Magma hybridisation at Soufriere Hills Volcano, Montserrat (United States)

    Humphreys, Madeleine; Edmonds, Marie; Christopher, Thomas; Hards, Vicky


    Arc volcanoes commonly show evidence of mingling between mafic and silicic magma. For example, the Soufrière Hills Volcano, Montserrat typically erupts andesitic magma containing basaltic to basaltic-andesite inclusions. However, the andesite also contains a wide variety of phenocryst textures as well as strongly zoned microlites, suggesting that more intimate physical mixing also occurs. Analysis of minor elements in both phenocrysts and microlites allows the discrimination of different crystal populations, and provides insight into their origins. Microlites of plagioclase and orthopyroxene are chemically distinct from the phenocrysts, being enriched in Fe and Mg, and Al and Ca respectively. However, they are indistinguishable from the compositions of these phases in the mafic inclusions. Microlite compositions also give anomalously high temperatures using standard geothermometry techniques, similar to those of the mafic inclusions. Compositions of clinopyroxene from overgrowth rims on quartz and orthopyroxene and coarse-grained breakdown rims on hornblende, are identical to those from the mafic inclusions, indicating that these rims form during interaction with mafic magma. We infer that the inclusions disaggregated under conditions of high shear stress during ascent in the conduit, transferring mafic material into the andesite groundmass. This implies that the mafic component of the system is greater than previously determined from the volume proportion of mafic enclaves. The presence of mafic-derived microlites in the andesite groundmass also means that care must be taken when using this as a starting material for phase equilibrium experiments. Melt inclusions and matrix glasses in the erupted include an anomalously K2O-rich population which overlaps with residual (high-K2O, high-TiO2) mafic inclusion glass. These glasses represent the effects of physical mixing with mafic magma, both during ascent and by diffusive exchange during the formation of mafic

  1. Genesis of hydrothermal alterations using stable isotope geochemistry in Takestan area (Tarom zone

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    Batool Taghipou


    Full Text Available Hydrothermal alteration processes are extensively took place on volcanic and pyroclstics of Takestan area. Existence of abundant, deep fracturing and subvolcanic intrusions are enhanced extend hydrothermal alteration zones. The following alteration zones are determined: propylitic, argillic, advanced argillic and sillicic. There are outcropped and widespread in different size and limit. Formation of siliceous sinter, silicified tuffs with preserved primary sedimentary layering including pure mineralized alunite patches are most outstanding. Quartz, sussoritic plagioclase, chlorite, sericite and alunite are main mineral constituents in the volcanics. On the basis of geochemical data volcanic rocks are rhyolite, dacite, andesite, andesitic-basalt and basalt in composition. Acid-sulfate zone is the type of alteration in Tarom area and alunite is an index mineral of this zone. Results of 18O, D and 34S stable isotope geochemistry on altered minerals (muscovite, kaolinite and alunite, revealed that alteration fluids are magmatic in origin.


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    Jakob Pamić


    Full Text Available In the paper are presented basic geological, petrologieca1, geochemi-cal and mineral deposit data for five main magmatic-metallogenic formations of the northwestern and central Dinarides: (lThe Permo Triassic rifting related andesite-diorite formations; (2 The Jurassic-Lower Cretaceous accretionary (ophiolite formations; (3 The Upper Cretaceous-Paleogene subduction related basalt-rhyohite formations; (4 The Paleogene collisional granite formations, and (5 The Oligo-cene-Neogene postsubduction andesite formations. All these magmatic-metallogenic formations originated in different geotectonic settings during the Alpine evolution of the Dinaridic parts of thc Tethys and the postorogenic evolution of the Paratethys and the Pannonian Basin, respectively.

  3. Repetitive mixing events and Holocene pyroclastic activity at Pico de Orizaba and Popocatepetl, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Cantagrel, J.M.; Gourgaud, A.; Robin, C.


    The Holocene volcanic activity which built up the present terminal cones of Pico de Orizaba and Popocatepetl in eastern Mexico, was characterized by repeated pyroclastic Saint-Vincent type eruptions. Radiocarbon data show that these paroxysmal events occurred at more or less regular intervals, and were followed by moderate activity producing ash and pumice falls and andesitic lava flows from the summit craters. Typical ash and scoria pyroclastic flows exhibit a heterogeneous composition given by the interaction of a dacitic component with a more basic andesitic one. Scoria bombs are characterized by banded to emulsified textures, mineralogical disequilibrium assemblages and linear chemical variations on element-element plots as exemplified by the Loma Grande flow at Pico. Periodic replenishments of the magmatic reservoir could be the major phenomenon that started mixing and consequently triggered the pyroclastic eruptions. 22 references.

  4. Eruptive history and petrology of Mount Drum volcano, Wrangell Mountains, Alaska (United States)

    Richter, D.H.; Moll-Stalcup, E. J.; Miller, T.P.; Lanphere, M.A.; Dalrymple, G.B.; Smith, R.L.


    Mount Drum is one of the youngest volcanoes in the subduction-related Wrangell volcanic field (80x200 km) of southcentral Alaska. It lies at the northwest end of a series of large, andesite-dominated shield volcanoes that show a northwesterly progression of age from 26 Ma near the Alaska-Yukon border to about 0.2 Ma at Mount Drum. The volcano was constructed between 750 and 250 ka during at least two cycles of cone building and ring-dome emplacement and was partially destroyed by violent explosive activity probably after 250 ka. Cone lavas range from basaltic andesite to dacite in composition; ring-domes are dacite to rhyolite. The last constructional activity occured in the vicinity of Snider Peak, on the south flank of the volcano, where extensive dacite flows and a dacite dome erupted at about 250 ka. The climactic explosive eruption, that destroyed the top and a part of the south flank of the volcano, produced more than 7 km3 of proximal hot and cold avalanche deposits and distal mudflows. The Mount Drum rocks have medium-K, calc-alkaline affinities and are generally plagioclase phyric. Silica contents range from 55.8 to 74.0 wt%, with a compositional gap between 66.8 and 72.8 wt%. All the rocks are enriched in alkali elements and depleted in Ta relative to the LREE, typical of volcanic arc rocks, but have higher MgO contents at a given SiO2, than typical orogenic medium-K andesites. Strontium-isotope ratios vary from 0.70292 to 0.70353. The compositional range of Mount Drum lavas is best explained by a combination of diverse parental magmas, magma mixing, and fractionation. The small, but significant, range in 87Sr/86Sr ratios in the basaltic andesites and the wide range of incompatible-element ratios exhibited by the basaltic andesites and andesites suggests the presence of compositionally diverse parent magmas. The lavas show abundant petrographic evidence of magma mixing, such as bimodal phenocryst size, resorbed phenocrysts, reaction rims, and

  5. Early Archean sialic crust of the Siberian craton: Its composition and origin of magmatic protoliths (United States)

    Vovna, G. M.; Mishkin, M. A.; Sakhno, V. G.; Zarubina, N. V.


    This study demonstrates that the base of the Archean deep-seated granulite complexes within the Siberian craton consists of a metabasite-enderbite association. The major and trace element distribution patterns revealed that the protoliths of this association are represented by calc-alkaline andesites and dacites, containing several minor sequences of komatiitic-tholeiitic volcanic rocks. The origin of the primary volcanic rocks of the metabasite-enderbite association is inferred on the basis of a model of mantle plume magmatism, which postulates that both andesitic and dacitic melts were derived from the primary basitic crust at the expense of heat generated by ascending mantle plumes. The formation of the protoliths of the Archen metabasite-enderbite association of the Siberian craton began at 3.4 Ga and continued until the late Archean.

  6. Andosols of Georgia (United States)

    Urushadze, T. F.; Blum, W. E. H.; Sanadze, E. V.; Kvrivishvili, T. O.


    Andosols formed on andesite-basalts, andesite, diabase, and dolerite in the central part of the Adzhar-Trialet Ridge are studied. Their morphological features and some chemical properties are characterized. The soils are diagnosed according to the World Reference Base for Soil Resources (WRB). The soil bulk density, the contents of oxalate-soluble R2O3, adsorbed phosphates, and organic carbon are determined. It is shown that vitric and andic diagnostic features predominate in the investigated soils. According to the adopted classification, these soils are classified as mountain meadow soils. Their morphological features and chemical characteristics correspond to those of Andosols, one of the soil groups in the WRB. It can be expected that these soils are developed in some other regions of volcanic activity in Georgia.

  7. Late Holocene tephrochronology of the northern Antarctic Peninsula (United States)

    Björck, Svante; Sandgren, Per; Zale, Rolf


    Andesitic and basaltic andesitic tephra layers are abundant in Holocene deposits from the Antarctic Peninsula. Visually discernible tephra horizons occur in three lakes on Livingston Island. Tephra in two other lakes and in a moss bank on Elephant Island, with very low ash concentrations, were detected magnetically. Deception Island is the most likely volcanic source for the tephra. With direct 14C dating, age/depth curves, and cross-correlations at least 14 tephra horizons dating to between ca. 4700 and 250 yr B.P. were identified and now form the basis for a preliminary regional tephrochronology that will be a valuable dating tool for investigating the Holocene climatic history of Antarctica.

  8. Isparta' da Çıkarılan Andezit Ve Bazalt Kayaçlarının Radyasyon Soğurma Özelliklerinin İncelenmesi

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    Kadir GÜNOĞLU


    Full Text Available Natural stones are generally igneous, metamorphic and sedimentary are divided into 3 classes including. A region of Isparta volcanic magmatic origin andesite and basalt stones which are classified as an area where there are plenty of rocks. These rocks are used as coating materials, especially in buildings. Therefore it is important to determine stones radiation absorbing properties. In this study, in Isparta andesite and basalt rocks extracted 137Cs and 60Co radiation absorbing properties obtained from the radioactive source 662, 1173, and 1332 keV gamma energy was measured for. Gamma Spectroscopy Laboratory measurements of Suleyman Demirel University, located in the 3 "x3" size NaI (Tl detector containing gamma spectroscopy was performed using the system

  9. Multiple plagioclase crystal populations identified by crystal size distribution and in situ chemical data: Implications for timescales of magma chamber processes associated with the 1915 eruption of Lassen Peak, CA (United States)

    Salisbury, M.J.; Bohrson, W.A.; Clynne, M.A.; Ramos, F.C.; Hoskin, P.


    Products of the 1915 Lassen Peak eruption reveal evidence for a magma recharge-magma mixing event that may have catalyzed the eruption and from which four compositional members were identified: light dacite, black dacite, andesitic inclusion, and dark andesite. Crystal size distribution, textural, and in situ chemical (major and trace element and Sr isotope) data for plagioclase from these compositional products define three crystal populations that have distinct origins: phenocrysts (long axis > 0??5 mm) that typically have core An contents between 34 and 36 mol %, microphenocrysts (long axis between 0??1 and 0??5 mm) that have core An contents of 66-69, and microlites (long axis Author 2008. Published by Oxford University Press. All rights reserved.

  10. New Insights to the Mid Miocene Calc-alkaline Lavas of the Strawberry Volcanics, NE Oregon Surrounded by the Coeval Tholeiitic Columbia River Basalt Province (United States)

    Steiner, A. R.; Streck, M. J.


    The Strawberry Volcanics (SV) of NE Oregon were distributed over 3,400 km2 during the mid-Miocene and comprise a diverse volcanic suite, which span the range of compositions from basalt to rhyolite. The predominant composition of this volcanic suite is calc-alkaline (CA) basaltic andesite and andesite, although tholeiitic (TH) lavas of basalt to andesite occur as well. The coeval flood basalts of the Columbia River province surround the SV. Here we will discuss new ages and geochemical data, and present a new geologic map and stratigraphy of the SV. The SV are emplaced on top of pre-Tertiary accreted terranes of the Blue Mountain Province, Mesozoic plutonic rocks, and older Tertiary volcanic rocks thought to be mostly Oligocene of age. Massive rhyolites (~300 m thick) are exposed mainly along the western flank and underlie the intermediate composition lavas. In the southern portion of this study area, alkali basaltic lavas, thought to be late Miocene to early Pliocene in age, erupted and overlie the SV. In addition, several regional ignimbrites reach into the area. The 9.7 Ma Devine Canyon Tuff and the 7.1 Ma Rattlesnake Tuff also overlie the SV. The 15.9-15.4 Ma Dinner Creek Tuff is mid-Miocene, and clear stratigraphic relationships are found in areas where the tuff is intercalated between thick SV lava flows. All of the basalts of the SV are TH and are dominated by phenocryst-poor (≤2%) lithologies. These basalts have an ophitic texture dominated by plagioclase, clinopyroxene and olivine (often weathered to iddingsite). Basalts and basaltic andesites have olivine Fo #'s ranging from 44 at the rims (where weathered to iddingsite) and as high as 88 at cores. Pyroxene Mg #'s range from 65 to 85. Andesites of the SV are sub-alkaline, and like the basalts, are exceedingly phenocryst-poor (≤3%) with microphenocrysts of plagioclase and lesser pyroxene and olivine, which occasionally occur as crystal clots of ~1-3 mm instead of single crystals. In addition, minimal

  11. Investigation into Variations of Saw Rotation and Noise Level in Cutting by Circular Saw

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    Nazmi Şengün


    Full Text Available In natural stone technology, to cut rocks circular diamond saws are widely being used. With these saws some variations are seen on pre-set peripheral speed and occurring noise level according to the rock type during cutting. In this study, in rock cutting experiment by circular saw, spindle speed and noise level measurements were made both when cutting and standing idle. About 1% decrease was showed saw spindle speed when cutting according to idle at rocks having low porosity, high strength, hardness and specific energy value. While the highest decrease value was measured at limestone, a lower speed reduction values was determined in travertine, lymra and andesite. The highest noise level increases approximately 6.46% was occurred in andesite and basalt.

  12. Submarine silicic volcanism: Processes and products

    Digital Repository Service at National Institute of Oceanography (India)

    Kalangutkar, N.G.; Iyer, S.D.

    and these are supported by several experimental studies (Annen et al., 2006). A silicic calc-alkalic magma can form by differentiation from a more mafic parent magma and by crustal anatexis. Several evidences show the origin of some rhyolitic and andesitic magma... to be related due to similar tectonic settings. Fractional crystallisation: This process produces a series of residual liquids of variable compositions as compared to their parental magmas and is best explained by the Bowen’s reaction principle (Bowen, 1922...

  13. The delicate balance between soil production and erosion, and its role on landscape evolution


    Dosseto, Anthony; Buss, Heather L; Suresh, P O


    The diversity in landscapes at the Earth’s surface is the result, amongst other things, of the balance (or imbalance) between soil production and erosion. While erosion rates are well constrained, it is only recently that we have been able to quantify rates of soil production. Uranium-series isotopes have been useful to provide such estimates independently of erosion rates. In this study, new U-series isotope are presented data from weathering profiles developed over andesitic parent rock in ...

  14. Late Neoproterozoic Nuqara Dokhan Volcanics, Central Eastern Desert, Egypt: Geochemistery and petrogenesis (United States)

    Hassan, Tharwat; Asran, Asran; Amron, Taha; Natflos, Theo


    The Nuqara volcanic is one of the northernmost outcrops of the Arabian-Nubian Shield Dokhan volcanics. The origin and tectonic setting of the late Neoproterozoic Dokhan volcanics (ca. 610-560 Ma) in the Egyptian Eastern Desert is highly debated. The debate concerns the tectonic setting where they formed during transition between convergent to extensional regime or after the East- and the West-Gondwana collision (~600Ma). In order to solve this problem, lavas from Nuqara area were studied geologically and geochemically. Nuqara Dokhan volcanics comprises two main rock suites: (a) an intermediate volcanic suite, consisting of basaltic andesite, andesite and their associated pyroclastics rocks; and (b) a felsic volcanic suite composed of dacite, rhyolite and ignimbrites. The two suites display well-defined major and trace element trends and continuum in composition with wide ranges in SiO2 (52-75.73%), CaO (9.19-0.22%), MgO (5.29-0.05%), Sr (1367-7.4 ppm), Zr (688.5-172.7 ppm), Cr (207-0.4 ppm), and Ni (94.3-0.2 ppm). The Nuqara Dokhan volcanics are characterized by strong enrichment in LILE relative to HFSE and affiliated to the calc-alkaline subducted - related magmatism. Geochemical Modeling displays that the evolution of these rocks was governed by fractional crystallization of plagioclase, amphiboles, pyroxene, magnetite and apatite in the intermediate varieties and plagioclase, amphibole, magnetite, apatite and zircon in the felsic varieties. The obtained mineral chemistry of these volcanics reveals: (a) Plagioclase range in composition from An55 to An40 in basaltic andesite and from An39 to An24 in andesite. (b) Alkali feldspars have sanidine composition. (c) Clinopyroxenes have augite composition. The low Al2O3 contents (1.94-5.588 wt %) indicate that clinopyroxene crystallized at low - pressure conditions. (d) Amphiboles have magnesio- hornblende composition.

  15. Eocene volcanism during the incipient stage of Izu–Ogasawara Arc: Geology and petrology of the Mukojima Island Group, the Ogasawara Islands.


    Kanayama, Kyoko; Umino, Susumu; Ishizuka, Osamu


    The Ogasawara Islands mainly comprise Eocene volcanic strata formed when the Izu-Ogasawara-Mariana Arc began. We present the first detailed volcanic geology, petrography and geochemistry of the Mukojima Island Group, northernmost of the Ogasawara Islands, and show that the volcanic stratigraphy consists of arc tholeiitic rocks, ultra-depleted boninite-series rocks, and less-depleted boninitic andesites, which are correlatable to the Maruberiwan, Asahiyama and Mikazukiyama Formations on the Ch...

  16. Micromorphological Characterization of Some Volcanic Soil In West Java


    Mahfud Arifin; Rina Devnita

    2014-01-01 characterization has been studied on six pedons of soils developing in volcanic materials in West Java. The pedons represent deposits of different volcanoes (Mount Tangkuban Perahu, Mount Patuha and Mount Papandayan) with different ages (Pleistocene, Holocene) within two types of volcanisms (andesitic, basaltic), and three agroclimatic zones (A, B1, B2). Undisturbed soil samples were taken from each identifiable horizon for thin ...

  17. Giant magmatic water reservoir beneath Uturuncu volcano and Altiplano-Puna region (Central Andes) (United States)

    Laumonier, Mickael; Gaillard, Fabrice; Muir, Duncan; Blundy, Jon; Unsworth, Martyn


    Volcanism at continental arcs is the surface manifestation of long-lived crustal magmatic processes whereby mantle-derived hydrous basalt magma differentiates to more silica-rich magmas by a combination of crystallization and crustal melting. What erupts is just a fraction of the total volume of magma produced by these processes; the unerupted, plutonic residues solidify and are inaccessible to direct study until millions of years of uplift and erosion bring them to the surface. In contrast, geophysical surveys, using electromagnetic and seismic waves, can provide real-time images of subduction zone magmatic systems. Several such studies have revealed that arc volcanoes are underlain by large partially molten regions at depths of >10 km, the largest known example being the Altiplano-Puna magma body (APMB) in central Andes. Interpreting such geophysical images in terms of amount, composition and distribution of partial melts is limited by our lack of knowledge of the physical properties of silicate melts at elevated pressures and temperatures. Here we present high-pressure, in situ experimental data showing that the electrical conductivity of andesitic melts is primarily controlled by their dissolved water contents. Linking our new measurements to petrological constraints from andesites erupted on the Altiplano, we show that the APMB is composed of 10-20% of an andesitic melt containing 8-10 wt% dissolved water. This implies that the APMB is a giant water anomaly in the global subduction system, with a total mass of dissolved magmatic water about half of the water contained within the Adriatic Sea. In addition to the controls on the physical properties of the melts, the abundance of dissolved water governs the structural levels of magma ponding, equivalent to the depth of water saturation, where degassing and crystallisation promote partial melting and weakening of the upper crust. Unexpectedly, very high concentrations of water in andesite magmas shall impede their

  18. The age and constitution of Cerro Campanario, a mafic stratovolcano in the Andes of central Chile (United States)

    Hildreth, W.; Singer, B.; Godoy, E.; Munizaga, F.


    Cerro Campanario, a towering landmark on the continental divide near Paso Pehuenche, is a glacially eroded remnant of a mafic stratovolcano that is much younger than previously supposed. Consisting of fairly uniform basaltic andesite, rich in olivine and plagioclase, the 10-15 km3 edifice grew rapidly near the end of the middle Pleistocene, about 150-160 ka, as indicated by 40Ar/39Ar and unspiked K-Ar analyses of its lavas.

  19. Significado de fábricas magnéticas en rocas volcánicas cuaternarias de la Isla Decepción (Shetland del Sur, Antártida)


    Gil Imaz, Andrés; Gil Peña, Inmaculada; Galindo Zaldívar, Jesús; Rey Salgado, Jorge; Maestro González, Adolfo; Pueyo Anchuela, Óscar; Soto Marín, Ruth; Oliva Urcia, Belén; López Martínez, Jerónimo


    This work deals with the magnetic fabric (AMS technique) of different lithotypes related to quaternary volcanism of Deception Island (South Shetland Islands). The studied rocks include lava flows from basaltic to basaltic-andesitic composition, mafic dykes and several types of pyroclastic deposits. By combining the analysis of parametric aspects of the magnetic ellipsoids and their directional pattern, four types of magnetic fabrics have been recognized. Type I fabrics are related...

  20. Tree-mould caves in Slovakia.


    Gaal Ludovit


    Four tube-shaped caves are described in this work, which origined in consequence of weathering the trees. Their length ranges from 5.8 to 17 m. All of them occur in neovolcanic rocks of Middle Slovakia, in epiclastic andesite conglomerates, breccias or in the tuffs. Some other caverns are close to the entrance of this caves, however they are inaccessible for a man. Thin rim of silicates (opal or chalcedony) occurs in some of them.

  1. 水田,畑,樹園地土壌化学性の因子分析による対比 : 佐賀県と熊本県農耕地土壌の事例


    江頭, 和彦


    Soil chemical properties of the surface horizon were compared between paddy, upland and orchard fields by conducting factor analysis on analytical data for agricultural lands of Saga and Kumamoto prefectures. Soils of Saga prefecture were mainly derived from alluvial marine or fluvial sediment in the paddy field and from granite or andesite in the orchard field. Factor analysis for agricultural lands of Saga prefecture reduced 11 variables (pH, total carbon and nitrogen, cation exchange capac...

  2. Bulk rock composition and geochemistry of olivine-hosted melt inclusions in the Grey Porri Tuff and selected lavas of the Monte dei Porri volcano, Salina, Aeolian Islands, southern Italy (United States)

    Doherty, Angela L.; Bodnar, Robert J.; De Vivo, Benedetto; Bohrson, Wendy A.; Belkin, Harvey E.; Messina, Antonia; Tracy, Robert J.


    The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72−84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57−78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma.

  3. Petrology, mineral chemistry and tectono-magmatic setting of volcanic rocks from northeast Farmahin, north of Arak


    Reza Zarei Sahamieh; Sara Ebrahimi


    Introduction The study area is a small part of the Urumieh-Dokhtar structural zone in the Markazi province, located in the northeastern part of the Farmahin, north of Arak (Hajian, 1970). The volcanic rocks studied from the area include andesite, dacite, rhyodacite, ignimbrite and tuff of Middle to Late Eocene age (middle Lutetian to upper Lutetian) (Ameri et al., 2009). It seems that folding and faulting is caused in sedimentary basin and volcanic activities. On the other hand, except of ...

  4. International Uranium Resources Evaluation Project (IUREP) national favourability studies: Taiwan

    International Nuclear Information System (INIS)

    Taiwan is an island of 36,000 sq km located 160 km east of mainland China. Geologically, the oldest rocks are Tertiary, and the only igneous rocks on the island are Quaternary andesites and basalts. Copper, gold, and silver are the only known metallic minerals produced. Uranium occurrences and exploration efforts are unknown. The potential uranium resource of Taiwan is considered a category 1 resource. (author)

  5. Tree-mould caves in Slovakia.

    Directory of Open Access Journals (Sweden)

    Gaal Ludovit


    Full Text Available Four tube-shaped caves are described in this work, which origined in consequence of weathering the trees. Their length ranges from 5.8 to 17 m. All of them occur in neovolcanic rocks of Middle Slovakia, in epiclastic andesite conglomerates, breccias or in the tuffs. Some other caverns are close to the entrance of this caves, however they are inaccessible for a man. Thin rim of silicates (opal or chalcedony occurs in some of them.

  6. A Preliminary Study of Seismicity at Ceboruco, Volcano, Nayarit, Mexico (United States)

    Sanchez, J. J.; Nunez-Cornu, F. J.; Suarez-Plascencia, C.; Trejo-Gomez, E.


    Ceboruco Volcano is located northwestern of Tepic-Zacoalco graben (Jalisco, Mexico). Its volcanic activity can be divided in four eruptive cycles differentiated by their volcano explosivity index (VEI) and chemical variations as well. As a result of andesitic effusive activity, during the first cycle the "paleo-Ceboruco" edifice was constructed. The end of this cycle is defined by a plinian eruption (VEI is estimated between 3 and 4) which occurred some 1020 years ago and formed the external caldera. During the second cycle an andesitic dome extruded in the interior of the caldera. The dome, called Dos Equis, collapsed and formed the internal caldera. The third cycle is represented by andesitic lava flows which partially cover the northern and south-southwestern part of the edifice. The last cycle is represented by historic andesitic lava flows located in the southwestern flank of the volcano. In February 2003 as part of an agreement with Nayarit Civil Defense a seismic station was installed in the SW flank of the volcano. The station is equipped with a Marslite (lennartz) digitizer with a 3DLe 1Hz. seismic sensor. Detection system is based on a STA/LTA recording algorithm. More than 2000 small earthquakes have been attributed to various local sources, and some of this earthquakes are possibly located beneath Ceboruco volcano. A preliminary classification separates high frequency and low frequency seismic events. The sources of high frequency earthquakes appear to be distributed as evidenced from waveforms variety and changing S-P arrivals separations. The low frequency seismic events also show varying signatures and some of them exhibit extended coda, including some monochromatic character.

  7. Airborne dust transport to the eastern Pacific Ocean off southern California: Evidence from San Clemente Island (United States)

    Muhs, D.R.; Budahn, J.; Reheis, M.; Beann, J.; Skipp, G.; Fisher, E.


    Islands are natural dust traps, and San Clemente Island, California, is a good example. Soils on marine terraces cut into Miocene andesite on this island are clay-rich Vertisols or Alfisols with vertic properties. These soils are overlain by silt-rich mantles, 5-20 cm thick, that contrast sharply with the underlying clay-rich subsoils. The silt mantles have a mineralogy that is distinct from the island bedrock. Silt mantles are rich in quartz, which is rare in the island andesite. The clay fraction of the silt mantles is dominated by mica, also absent from local andesite, and contrasts with the subsoils, dominated by smectite. Ternary plots of immobile trace elements (Sc-Th-La and Ta-Nd-Cr) show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust. In contrast, the silt and, to a lesser extent, clay fractions of the silt mantles have compositions closer to average upper continental crust. The silt mantles have particle size distributions similar to loess and Mojave Desert dust, but are coarser than long-range-transported Asian dust. We infer from these observations that the silt mantles are derived from airborne dust from the North American mainland, probably river valleys in the coastal mountains of southern California and/or the Mojave Desert. Although average winds are from the northwest in coastal California, easterly winds occur numerous times of the year when "Santa Ana" conditions prevail, caused by a high-pressure cell centered over the Great Basin. Examination of satellite imagery shows that easterly Santa Ana winds carry abundant dust to the eastern Pacific Ocean and the California Channel Islands. Airborne dust from mainland North America may be an important component of the offshore sediment budget in the easternmost Pacific Ocean, a finding of potential biogeochemical and climatic significance.

  8. Behaviour of major, minor and trace elements (including REEs) during kaolinization processes at Zonouz deposit, northeast of Marand, East Azarbaidjan province


    Vahideh Alipour; Ali Abedini


    The Zonouz kaolin deposit is located ~15 km northeast of Marand, East-Azarbaidjan province. Based on physical features in field investigations, such as color, five distinct kaolin types including (1) white, (2) lemon, (3) gray, (4) brown, and (5) yellow are distinguished in the deposit. Field evidence and petrographic studies indicate that the deposit is genetically close to trachy-andesite rocks. According to mineralogical data, the deposit contains quartz, kaolinite, montmorillonite, calcit...

  9. Strontium isotope systematics of experimentally produced melts: understanding magma-carbonate interaction at Merapi volcano, Indonesia


    DEEGAN, F.M.; Uppsala University, Uppsala, Sweden; Troll, V. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Freda, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; MCLEOD, C.; Durham University, Durham, United Kingdom; MALARKEY, J.; Durham University, Durham, United Kingdom; DAVIDSON, J.P.; Durham University, Durham, United Kingdom; CHADWICK, J.P.; Vrije Universiteit, Amsterdam, Netherlands


    There is considerable evidence for ongoing, late-stage interaction between the magmatic system at Merapi volcano, Indonesia, and local crustal carbonate. In order to resolve the interaction processes in detail, we have performed a series of time-variable carbonate dissolution experiments in silicate melt using Merapi basaltic-andesite and local limestone as starting materials, at magmatic pressure and temperature. Major element profiling of the experimental products has identified strongly co...

  10. 水蒸気圧下の岩石の強度特性


    鄭, 海植; 尾原, 祐三; 菅原, 勝彦; オバラ, ユウゾウ; スギワラ, カツヒコ; Jeong, Hae-Sik; Obara, Yuzo; Sugiwara, Katsuhiko


    In order to investigate the environmental dependence on strength of rock, uniaxial compression test and Brazilian test under water vapor environment were conducted on Kumamoto andesite and Kitagishima granite. Tests were carried out under various water vapor pressures, which are controlled in special chambers, at a constant strain rate. The results obtained by the uniaxial compression test and Brazilian test are follows:The Young's moduli are almost constant with the change of water vapor pre...

  11. 非大気環境下における熊本安山岩の強度特性


    鄭, 海植; 尾原, 祐三; オバラ, ユウゾウ; Jeong, Hae-Sik; Obara, Yuzo


    The uniaxial compression tests and Brazil tests in non-atmospheric environments were conducted on Kumamoto andesite to investigate the environmental dependence on strength of rock. The environments used in the experiment were organic vapor environments as methanol, ethanol and acetone, inorganic gas environments as argon, nitrogen and oxygen and water vapor environment.The obtained results are as follows:1. From the uniaxial compression test, it was clear that the uniaxial compressive strengt...

  12. Composition and origin of aeolian and fluvial sands of Gavkhuni playa lake (southeast of Isfahan)


    H.R., Pakzad,; Van, M. A.; M., Pasandi,; Z., Aliniaie,


    Gavkhuni playa lake, located 130 km southeast of Isfahan, comprises of sand, mud and salt flats. This playa includes two environments as delta and playa lake. Sand dunes, 45 kilometers long, extend in the west of the playa. Rock fragments of andesite, dacite, tuff, granite, schist, gneiss, fossil bearing limestone, sandstone and also quartz and feldspar minerals form the alluvial and aeolian sediments. Heavy minerals including idocrase, tourmaline, biotite, wollastonite, magnetite, hematite, ...

  13. Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

    Indian Academy of Sciences (India)

    Ashima Saikia; Bibhuti Gogoi; Mansoor Ahmad; Talat Ahmad


    The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, crosscutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

  14. Low-K Tholeiitic Signatures in Calayan Island (Northern Luzon, Philippines)


    Pendón, R. R.; Corretgé, Luis Guillermo; Ordaz, J.


    The Calayan island is a Tertiary (7-4 Ma) volcanic island situated in the northern portion of the Philippine archipelago, a part of Babuyan segment of the Luzon arc. It is a product of subduction of South China Sea oceanic crust underneath the Philippine terrane. Rock spectrum in the island ranges from basalt to rhyolite with andesite as the most predominating lava. Geochemical signatures are characterized by low concentrations of large-ion lithophile and flat behavior of rare-earth elements,...

  15. Geological and Petrological Characteristics of Oligocene Magmatic Rocks in The Biga Peninsula, NW Turkey (United States)

    Erenoglu, Oya


    Oligocene magmatic activity in the Biga Peninsula (NW-Anatolia) produced widespread volcano-plutonic complexes. The study region, where in north of the Evciler village in the middle of Biga Peninsula includes these igneous assemblages. In this study, the petrographic and geochemical characteristics of igneous rocks in the region were investigated as well as the geological locations. The magmatic rocks are classified as 6 different units using their lithostratigraphical properties. The volcanism in the region starts with basaltic andesite lava including basalt dykes in the Lower Oligocene. In the Upper Oligocene, the evolved magma by crustal contamination produced commonly dacitic and andesitic lavas. The volcanism continued with andesitic lavas which had significant alterations in the region during this period. Evciler pluton including granite and granodiorite composition with shallow intrusive, was located with the related volcanism at the same time. The volcanic products, i.e. andesitic and trachydacitic lavas, was completed in the interval between Upper Oligocene and Lower Miocene. The post-collisional Oligocene sequence is associated with calc-alkaline composition and it has middle, high-K. Trace and rare earth elements (REE) diagrams show the enrichment in both large-ion lithophile elements (LILE) and light rare earth elements (LREE) with respect to the high field strength elements (HFSE), and a significant increment in heavy rare earth element consumption (HREE). The features of major, trace and rare earth elements of plutonic and volcanic rocks and the compositional variations of Oligocene volcanic group indicate increasing amounts of partial melting, crustal contamination and/or assimilation. The Oligocene post-collisional volcanism in Biga Peninsula points out the lithospheric mantle source enriched by subduction which controlled by slab break-off and lithospheric delamination. Acknowledgement. This study was supported by Canakkale Onsekiz Mart University

  16. Mineralization model for Chahar Gonbad copper-gold deposit (Sirjan, using mineralogical, alteration and geochemical data and multivariate statistical methods

    Directory of Open Access Journals (Sweden)

    Seayed Jaber Yousefi


    Full Text Available The study area is located in southeastern Iran, about 110 km southwest of Kerman. Geologically, the area is composed of ophiolitic rocks, volcanic rocks, intrusive bodies and sedimentary rocks. Vein mineralization within andesite, andesitic basalt, andesitic tuffs occurred along the Chahar Gonbad fault. Sulfide mineralization in the ore deposit has taken place as dissemination, veins and veinlets in which pyrite and chalcopyrite are the most important ores. In this area, argillic, phyllic and propylitic alteration types are observed. Such elements as Au, Bi, Cu, S and Se are more enriched than others and the enrichment factors for these elements in comparison with background concentration are 321, 503, 393, 703 and 208, and with respect to Clark concentration are 401, 222, 532, 101 and 156, respectively. According to multivariate analysis, three major mineralization phases are recognized in the deposit. During the first phase, hydrothermal calcite veins are enriched in As, Cd, Pb, Zn and Ca, the second phase is manifested by the enrichment of sulfide veins in Cu, Au, Ag, Bi, Fe and S and the third phase mineralization includes Ni, Mn, Se and Sb as an intermediate level between the two previous phases.

  17. Timing and geochemical characters of the Sanchazi magmatic arc in Mianlüe tectonic zone, South Qinling

    Institute of Scientific and Technical Information of China (English)


    The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (<25Ma) and hot.

  18. Synergetic use of lignite fly ash and metallurgical converter slag in geopolymer concrete

    Directory of Open Access Journals (Sweden)

    Gábor Mucsi


    Full Text Available The application and utilization of the industrial wastes and by-products in the construction industry is a key issue from an environmental and economic point of view. The increased use of lignite has substantially increased the available quantities of lignite fired power plant fly ash, which can be mainly classified as class C fly ash. The utilization of such raw material however has some difficulties. In the present paper lignite fired power station fly ash and metallurgical converter slag were used for the production of geopolymer concrete. The fly ash was used as a geopolymer based binder material, and a converter slag as aggregate, thus created a geopolymer concrete which contains mainly industrial wastes. As preliminary test experimental series were carried out using andesite as aggregate. The optimal aggregate/binder ratio was determined. The effect of the amount of alkaline activator solution in the binder, the aggregate type on the geopolymer concretes’ compressive strength and density was investigated. Furthermore, the physical properties - freeze-thaw resistance and particle size distribution - of the applied aggregates were measured as well. As a result of the experiments it was found that physical properties of the andesite and converter slag aggregate was close. Therefore andesite can be replaced by converter slag in the concrete mixture. Additionally, geopolymer concrete with nearly 20 MPa compressive strength was produced from class C fly ash and converter slag.

  19. Microtextural and mineral chemical analyses of andesite–dacite from Barren and Narcondam islands: Evidences for magma mixing and petrological implications

    Indian Academy of Sciences (India)

    Dwijesh Ray; S Rajan; Rasik Ravindra; Ashim Jana


    Andesite and dacite from Barren and Narcondam volcanic islands of Andaman subduction zone are composed of plagioclase, orthopyroxene, clinopyroxene, olivine, titanomagnetite, magnesio-hornblende and rare quartz grains. In this study, we use the results of mineral chemical analyses of the calc-alkaline rock suite of rocks as proxies for magma mixing and mingling processes. Plagioclase, the most dominant mineral, shows zoning which includes oscillatory, patchy, multiple and repetitive zonation and ‘fritted’ or ‘sieve’ textures. Zoning patterns in plagioclase phenocrysts and abrupt fluctuations in An content record different melt conditions in a dynamic magma chamber. ‘Fritted’ zones (An55) are frequently overgrown by thin calcic (An72) plagioclase rims over well-developed dissolution surfaces. These features have probably resulted from mixing of a more silicic magma with the host andesite. Olivine and orthopyroxene with reaction and overgrowth rims (corona) suggest magma mixing processes. We conclude that hybrid magma formed from the mixing of mafic and felsic magma by two-stage processes initial intrusion of hotter mafic melt (andesitic) followed by cooler acidic melt at later stage.

  20. Subaqueous environment and volcanic evolution of the Late Cretaceous Chelopech Au-Cu epithermal deposit, Bulgaria (United States)

    Chambefort, Isabelle; Moritz, Robert


    A detailed field and petrographic study constrains the volcanic evolution and environment setting of the volcano-sedimentary-hosted Chelopech Cu-Au epithermal deposit, Bulgaria. Magmatic activity and associated high-sulfidation epithermal mineralization occurred at about 91 Ma in the Panagyurishte ore district of the Eastern European Banat-Timok-Srednogorie metallogenic belt. Volcanic and hydrothermal activity took place in a complex subaqueous setting, resulting in the intercalation of quartz sandstone with andesitic volcanic and volcaniclastic breccia. There are also hypabyssal andesite intrusion, phreatomagmatic breccia and interbeds of pyroclastic, oolithic and bioclastic rocks. The presence of altered cerebroid ooid-bearing sedimentary units characteristic of salty environment is in accordance with a lagoon environment predating the mineralization at Chelopech. Four principal stages of evolution for the Chelopech district are proposed based on field and petrographic observations. Initial volcanism occurred in a lake or in a coastal, shallow lagoon environment above crystalline basement. The Chelopech "phreatomagmatic" breccia and subsurface andesites were emplaced at this time. Subsequent hydrothermal activity produced the different hydrothermal breccia types, advanced argillic and quartz-phyllic alteration, and Au-Cu vein and replacement mineralization. The end of volcanism and hydrothermal activity was associated with opening of a pull-apart basin that covered the Chelopech environment with a sedimentary flysch. Tertiary compression faulting juxtaposed various rocks and tilted the ore deposit during the Alpine orogeny.

  1. SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications

    Institute of Scientific and Technical Information of China (English)

    XIE Guiqing; MAO Jingwen; LI Ruiling; ZHOU Shaodong; YE Huishou; YAN Quanren; ZHANG Zusong


    The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower valley of the Yangtze River, is one of the important volcanic basins in East China. Volcanic rocks in the Jinniu Basin are distributed mainly in the Majiashan Formation, the Lingxiang Formation and the Dasi Formation, consisting of rhyolite, basalt and basaltic andesite, (trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively, in which the Dasi volcanism is volumetrically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indicate that there exist a large amount of magmatic zircons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128±1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios, this age is considered to represent the crystallization time of the Dasi volcanism. The volcanic rocks in the Dasi, Majiashan and Lingxiang Formations share similar trace element and REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geology, it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Cretaceous, just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also suggested for tectonic regime in this region in the Cretaceous Period.

  2. The crust role at Paramillos Altos intrusive belt: Sr and Pb isotope evidence

    International Nuclear Information System (INIS)

    Paramillos Altos Intrusive Belt (PAIB) (Ostera, 1996) is located in the thick skinned folded-thrust belt of Malargue, southwestern Mendoza, Argentina. Geochemical, geochronologic and isotopic studies were carried out in it (Ostera 1996, 1997, Ostera et al. 1999; Ostera et al. 2000) and these previous papers suggested a minor involvement of the crust in the genesis of the PAIB. According with Ostera et al. (2000) it is composed by stocks, laccoliths, dykes and sills which range in composition from diorites to granodiorites, and from andesites to rhyolites, and divided in five Members, which range in age from Middle Miocene to Early Miocene: a- Calle del Yeso Dyke Complex (CYDC), with sills and dykes of andesitic composition (age: 20±2 Ma). b- Puchenque-Atravesadas Intrusive Complex (PAIC), composed by dykes and stocks ranging from diorites to granodiorites (age: 12.5±1 Ma). c- Arroyo Serrucho Stock (SAS), an epizonal and zoned stock, with four facies, with K/Ar and Ar/Ar dates of 10±1 and 9.5±0.5 Ma. d- Portezuelo de los Cerros Bayos (PCB), that includes porphyritic rocks of rhyolitic composition, of 7.5±0.5 Ma. e- Cerro Bayo Vitrophyres (CBV), with andesitic sills and dykes (age: 4.8±0.2 Ma). We present in this paper new Sr and Pb isotopes data that constrain the evolution of the PAIB (au)

  3. Upper cretaceous magmatic suites of the Timok magmatic complex

    Directory of Open Access Journals (Sweden)

    Banješević Miodrag


    Full Text Available The Upper Cretaceous Timok Magmatic Complex (TMC developed on a continental crust composed of different types of Proterozoic to Lower Cretaceous rocks. The TMC consists of the magmatic suites: Timok andesite (AT - Turonian-Santonian, Metovnica epiclastite (EM - Coniacian-Campanian, Osnić basaltic andesite (AO and Ježevica andesite (AJ - Santonian-Campanian, Valja Strž plutonite (PVS - Campanian and Boljevac latite (LB. The sedimentary processes and volcanic activity of the TMC lasted nearly continuously throughout nearly the whole Late Cretaceous. The sedimentation lasted from the Albian to the Maastrichtian and the magmatism lasted for 10 million years, from the Upper Turonian to the Upper Campanian. The volcanic front migrated from East to West. The volcanic processes were characterized by the domination of extrusive volcanic facies, a great amount of volcanic material, a change in the depositional environment during the volcanic cycle, sharp facial transitions and a huge deposition of syn- and post-eruptive resedimented volcaniclastics.

  4. The `Strawberry Volcanic Field' of Northeastern Oregon: Another Piece of the CRB Puzzle? (United States)

    Steiner, A. R.; Streck, M. J.


    The Mid to Late Miocene Strawberry Volcanics field (SVF) located along the southern margin of the John Day valley of NE Oregon, comprise a diverse group of volcanic rocks ranging from basalt to rhyolite. The main outcrop area of the SVF (3,400 km2) is bordered by units from the Columbia River Basalt Group (CRBG), with the main CRB units to the north, the Picture Gorge Basalt to the east and Steens Basalt to the south. The geographic position and age of the Strawberry Volcanics make a genetic relationship to CRB volcanism likely, yet little is known about this diverse volcanic field. This research aims at refining the stratigraphic and age relationships as well as the petrology and geochemistry of magmas associated with the SVF. Previous investigations (e.g. Robyn, 1977) found that the SVF was active between 20 to 10 Ma with the main pulse largely being coeval with the 15 Ma CRBG eruptions. Lavas and tuffs from the SVF are calc-alkaline with low FeO*/MgO (~ 2.56 wt. %), high Al2O3 (~ 16.4 wt. %), low TiO2 (~ 1.12 wt.%), and span the entire compositional range from basalt to rhyolite (47-78 wt. % SiO2) with andesite as the dominant lithology. Basaltic lavas from the SVF have compositional affinities to earlier Steens Basalt, and some trace element concentrations and ratios are indistinguishable from those of CRBG lavas (e.g. Zr, Ba, Sr, and Ce/Y). Andesites are calc-alkaline, but contrary to typical arc (orogenic) andesites, SVF andesites are exceedingly phenocryst poor (Strawberry Volcanics are largely the product of hot-spot related basaltic magmas interacting with the continental crust. The range in compositions from calc-alkaline andesite to rhyolite may be attributed to the hybridization of mantle-derived and crustal melts, with the more evolved compositions reflecting greater proportions of crustally derived material and/or higher degrees of differentiation. Furthermore, since the earliest SVF eruption is 3 Ma older than the proposed onset of the CRBG (~ 17 Ma

  5. Petrological analysis of the pre-eruptive magmatic process prior to the 2006 explosive eruptions at Tungurahua volcano (Ecuador) (United States)

    Samaniego, Pablo; Le Pennec, Jean-Luc; Robin, Claude; Hidalgo, Silvana


    Understanding the processes at the origin of explosive events is crucial for volcanic hazard mitigation, especially during long-lasting eruptions at andesitic volcanoes. This work exposes the case of Tungurahua volcano, whose unrest occurred in 1999. Since this date, the eruptive activity was characterized by low-to moderate explosiveness, including phases with stronger canon-like explosions and regional ash fallout. However, in 2006, a sudden increase of the explosiveness led to pyroclastic flow-forming eruptions on July 14th (VEI 2) and August 16-17th (VEI 3). All magmas emitted from 1999 to 2005, as well as the samples from the 2006 eruptions, have homogeneous bulk-rock andesitic compositions (58-59 wt.% SiO 2), and contain the same mineral assemblage consisting of pl + cpx + opx + mag ± ol. However, during the August 16-17th event, the erupted tephra comprise two types of magmas: a dominant, brown andesitic scoria; and scarce, light-grey pumice representing a subordinate, silica-rich juvenile component. For the andesitic magma, thermobarometric data point to magmatic temperatures ranging from 950 to 1015 °C and pressures in the range of 200 to 250 MPa, which corresponds to 7.5-9.5 km below the summit. Disequilibrium textures in plagioclase and pyroxene phenocrysts, particularly thin overgrowth rims, indicate the recharge of this magma body by mafic magma. Between 1999 and 2005, repeated injections from depth fed the intermittent eruptive activity observed while silica-rich melts were produced by in-situ crystallization in the peripheral parts of the reservoir. In April 2006, the recharge of a primitive magma produced strong convection and homogenisation in the reservoir, as well as pressure increase and higher magma ascent rate after seven years of only moderately explosive activity. This work emphasizes the importance of petrological studies in constraining the pre-eruptive magmatic conditions and processes, as a tool for understanding the fundamental causes

  6. Eruptive History of Volcán Tepetiltic, Mexico: Evidence for Remelting of Silicic Ashflows Revealed by 40Ar/39Ar Geochronology (United States)

    Frey, H. M.; Lange, R. A.; Hall, C. M.; Nelson, S. A.; Granados, H. D.


    Volcán Tepetiltic (VT) is located in the northwestern part of the Trans-Mexican Volcanic Belt and features an elliptical caldera (5 x 2.5 km). Previous detailed 40Ar/39Ar geochronology studies at V. Tequila and V. Ceboruco, showed that cone-building events occur within narrow time intervals (200 kyr between cone building episodes along the southern flank of the volcano. Following construction of the main stratocone (dominated by andesitic effusive activity), there was a clustering of rhyolite eruptions, including the caldera forming event which produced rhyolitic ashflow and airfall deposits. The age of the eruption is constrained by stratigraphic and cross-cutting relations. The eruption must be younger than 231 ± 36 kyr, based on the uppermost andesite dated from the caldera rim. The minimum age of the eruption is constrained by the occurrence of airfall from VT found underneath lava flows from the Amado Nervo shield volcano (220 ± 30 ka). Given these results, the Plinian eruption likely occurred ˜225 ± 40 kyrs ago. The two rhyolite obsidian domes on the eastern flanks of VT were dated at 307 ± 34 ka and 274 ± 52 ka and are thus similar in age or slightly older than the Plinian eruption. The >200 kyr hiatus between the construction of the andesite/dacite stratocone and the rhyolitic activity argues against crystal fractionation of the andesite to form the rhyolite. The upper crustal magma chamber feeding the main edifice ˜524 kyrs ago was likely short-lived (tens of kyrs), and may have crystallized to a granitoid. We suggest that the rhyolites formed ˜230 kyrs ago by partial melting of older shallow basement rhyolitic ashflows prevalent in the area. Evidence for this process is found in an unconsolidated pyroclastic flow from VT with pumiceous rhyolitic blocks and andesitic lithic fragments. Anorthoclase crystals in this deposit yield ages of 4.5 ± 0.34 Ma and 25.9 ± 0.24 Ma. Thus the rhyolites were likely produced by refusing of 4-5 Ma silicic

  7. Oligocene and Miocene arc volcanism in northeastern California: evidence for post-Eocene segmentation of the subducting Farallon plate (United States)

    Colgan, J.P.; Egger, A.E.; John, D.A.; Cousens, B.; Fleck, R.J.; Henry, C.D.


    The Warner Range in northeastern California exposes a section of Tertiary rocks over 3 km thick, offering a unique opportunity to study the long-term history of Cascade arc volcanism in an area otherwise covered by younger volcanic rocks. The oldest locally sourced volcanic rocks in the Warner Range are Oligocene (28–24 Ma) and include a sequence of basalt and basaltic andesite lava flows overlain by hornblende and pyroxene andesite pyroclastic flows and minor lava flows. Both sequences vary in thickness (0–2 km) along strike and are inferred to be the erosional remnants of one or more large, partly overlapping composite volcanoes. No volcanic rocks were erupted in the Warner Range between ca. 24 and 16 Ma, although minor distally sourced silicic tuffs were deposited during this time. Arc volcanism resumed ca. 16 Ma with eruption of basalt and basaltic andesite lavas sourced from eruptive centers 5–10 km south of the relict Oligocene centers. Post–16 Ma arc volcanism continued until ca. 8 Ma, forming numerous eroded but well-preserved shield volcanoes to the south of the Warner Range. Oligocene to Late Miocene volcanic rocks in and around the Warner Range are calc-alkaline basalts to andesites (48%–61% SiO2) that display negative Ti, Nb, and Ta anomalies in trace element spider diagrams, consistent with an arc setting. Middle Miocene lavas in the Warner Range are distinctly different in age, composition, and eruptive style from the nearby Steens Basalt, with which they were previously correlated. Middle to Late Miocene shield volcanoes south of the Warner Range consist of homogeneous basaltic andesites (53%–57% SiO2) that are compositionally similar to Oligocene rocks in the Warner Range. They are distinctly different from younger (Late Miocene to Pliocene) high-Al, low-K olivine tholeiites, which are more mafic (46%–49% SiO2), did not build large edifices, and are thought to be related to backarc extension. The Warner Range is ∼100 km east of the

  8. The geology and petrology of Volcán San Juan (Nayarit, México) and the compositionally zoned Tepic Pumice (United States)

    Luhr, James F.


    Volcán San Juan is the westernmost Quaternary composite volcano in the Mexican Volcanic Belt. Its activity is divided into three stages of decreasing eruptive volume. During stage-1 activity, the main cone of San Juan and the adjacent Cerro Alto grew to a combined volume of ˜60 km 3 through eruption of hornblende-bearing andesites, dacites, and rhyodacites. Stage 1 included explosive eruptions of hornblende-dacite and an andesite dated at 33,750 a (years ago) and 23,010 a. Stage-2 activity involved a major Plinian eruption 14,770 a that produced the hypersthene-hornblende-bearing, compositionally zoned, rhyodacitic-andesitic Tepic Pumice and led to formation of an oval-shaped caldera 4×1 km in diameter. Tepic, the capital city of Nayarit State, with a population of ˜250,000, lies at the NE foot of Volcán San Juan. This location was buried under 2-9 m of rhyodacitic pumice-fall deposits from the Tepic Pumice eruption. Erosion has since removed virtually all exposures of Tepic Pumice >15 km from the caldera. The estimated volume of erupted tephra is 5.6 km 3, equivalent to 1.2 km 3 of magma. Modeling of the eruption dynamics indicates that as the eruption evolved the column height increased from ˜15 km to ˜24 km and maximum mass discharge rate increased from ˜3×10 6 kg/s to ˜6×10 7 kg/s. During stage-3 activity, a hornblende-andesitic lava dome partially filled the caldera and sent block lava flows down the north slope of the cone; total erupted volume was ˜0.55 km 3. Compared to other composite volcanoes of the western Mexican Volcanic Belt, the products from San Juan have the highest Sr contents and the lowest Rb, Y, Yb, and Lu contents, resulting in high La/Yb and Sr/Y, with low Rb/Sr. These observations indicate a strong slab-melt component at San Juan, consistent with its proximity to the Middle America Trench where young, hot lithosphere is subducting. The San Juan andesites, dacites, and rhyodacites also have relatively high 87Sr/ 86Sr, 206Pb/ 204

  9. Hybridisation during magma ascent at Soufrière Hills Volcano, Montserrat (United States)

    Humphreys, M.; Edmonds, M.; Christopher, T. E.; Hards, V.


    Intermediate arc magmas commonly contain magmatic inclusions that demonstrate mingling between mafic and silicic magma. These magmas also typically contain a wide variety of disequilibrium phenocryst textures as well as strongly zoned microlites, suggesting that smaller-scale interactions also occur. Minor-element analysis of phenocrysts and microlites in andesites erupted from Soufrière Hills volcano shows that different crystal populations can be distinguished chemically, providing insights into their origins. For plagioclase and orthopyroxene, the microlites are enriched in Fe and Mg (pl) and Al and Ca (opx) relative to the phenocrysts. However, the microlites (including cpx) are indistinguishable chemically from these phases in the mafic inclusions. The microlites also give anomalously high temperatures, similar to those given by the mafic inclusions. Clinopyroxene overgrowth rims on quartz and orthopyroxene phenocrysts and coarse-grained breakdown rims on hornblende are identical in composition to cpx from the mafic inclusions. This indicates that these rims formed during interaction with mafic magma. We infer that the mafic inclusions disaggregated under conditions of high shear stress during ascent in the conduit, transferring mafic material into the groundmass of the andesite. This implies that the mafic component of the system is greater than previously determined from the volume proportion of macroscopic mafic enclaves, and that the amount of decompression-driven microlite crystallisation may be lower than previousl thought. The presence of mafic-derived microlites in the andesite groundmass may also affect phase equilibrium studies that use this as a starting material. Melt inclusions and matrix glasses from the erupted andesites include a K-rich population which overlaps with residual mafic inclusion glass (high-K2O, high-TiO2). These glasses are affected by physical mixing with mafic magma during ascent and/or by diffusive exchange during the

  10. Eruptive Productivity of the Ceboruco-San Pedro Volcanic Field, Nayarit, Mexico (United States)

    Frey, H. M.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.


    High-precision 40Ar/39Ar geochronology coupled with GIS spatial analysis provides constraints on magma eruption rates over the past 1 Myr of the Ceboruco-San Pedro volcanic field (1870 km2), located in the Tepic-Zacoalco rift in western Mexico. The volcanic field is part of the Trans Mexican Volcanic arc and is dominated by the andesitic-dacitic stratocone of Volcan Ceboruco and includes peripheral fissure-fed flows, domes, and monogenetic cinder cones. The ages of these volcanic features were determined using 40Ar/39Ar laser step-heating techniques on groundmass or mineral separates, with 78% of the 52 analyses yielding plateau ages with a 2 sigma error < 50 kyrs. The volumes were determined using high resolution (1:50,000) digital elevation models, orthophotos, and GIS software, which allowed for the delineation of individual volcanic features, reconstruction of the pre-eruptive topography, and volume calculations by linear interpolation. The relative proportions of the 80 km3 erupted over the past 1 Myr are 14.5% basaltic andesite, 64.5% andesite, 20% dacite, and 1% rhyolite, demonstrating the dominance of intermediate magma types (in terms of silica content). Overall, there appears to be no systematic progression in the eruption of different magma types (e.g., basalt, andesite, dacite, etc.) with time. However, more than 75% of the total volume of lava within the Ceboruco-San Pedro volcanic field erupted in the last 100 kyrs. This reflects the youthfulness of Volcan Ceboruco, which was constructed during the last 50 kyrs and has a present day volume of 50 +/- 2.5 km3, accounting for 81% of the andesite and 50% of the dacite within the volcanic field. Eleven cinder cones, ranging from the Holocene to 0.37 Ma, display a narrow compositional range, with 52-58 wt% SiO2, 3-5.5 wt% MgO, and relatively high TiO2 concentrations (0.9-1.8 wt%). The total volume of the cinder cones is 0.83 km3. No lavas with < 51 wt% SiO2 have erupted in the past 1 Myr. Peripheral

  11. Reconstructing multiple arc-basin systems in the Altai-Junggar area (NW China): Implications for the architecture and evolution of the western Central Asian Orogenic Belt (United States)

    Li, Di; He, Dengfa; Tang, Yong


    The Altai-Junggar area in northwestern China is a critical region to gain insights on the tectonic framework and geological evolution of the western Central Asian Orogenic Belt (CAOB). In this study, we report results from integrated geological, geochemical and geophysical investigations on the Wulungu Depression of the Junggar Basin to determine the basement nature of the basin and understand its amalgamation history with the Chinese Altai, within the broad tectonic evolution of the Altai-Junggar area. Based on borehole and seismic data, the Wulungu Depression is subdivided into two NW-trending tectonic units (Suosuoquan Sag and Hongyan High) by southward-vergent thrust faults. The Suosuoquan Sag consists of the Middle-Late Devonian basaltic andesite, andesite, dacite, tuff, tuffaceous sandstone and tuffite, and the overlying Early Carboniferous volcano-sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance (zircon εHf(t) = 6.0-14.9), compared to the Late Carboniferous andesite and rhyolite in the Hongyan High. Zircon SIMS U-Pb ages for dacites and andesites indicate that these volcanics in the Suosuoquan Sag and Hongyan High erupted at 376.3 Ma and 313.4 Ma, respectively. The Middle-Late Devonian basaltic andesites from well LC1 are calc-alkaline and exhibit primitive magma-like MgO contents (7.9-8.6%) and Mg# values (66-68), with low initial 87Sr/86Sr (0.703269-0.704808) and positive εNd(t) values (6.6-7.6), and relatively high Zr abundance (98.2-116.0 ppm) and Zr/Y ratios (5.1-5.4), enrichment in LREEs and LILEs (e.g., Th and U) and depletion in Nb, Ta and Ti, suggesting that they were probably derived from a metasomatized depleted mantle in a retro-arc extensional setting. The well LC1 andesitic tuffs, well L8 dacites, well WL1 dacitic tuffs and well L5 andesites belong to calc-alkaline and metaluminous to peraluminous (A/CNK = 0.8-1.7) series, and display low Mg# values (35-46) and variably positive εNd(t) (4

  12. Evolution and genesis of volcanic rocks from Mutnovsky Volcano, Kamchatka (United States)

    Simon, A.; Yogodzinski, G. M.; Robertson, K.; Smith, E.; Selyangin, O.; Kiryukhin, A.; Mulcahy, S. R.; Walker, J. D.


    This study presents new geochemical data for Mutnovsky Volcano, located on the volcanic front of the southern portion of the Kamchatka arc. Field relationships show that Mutnovsky Volcano is comprised of four distinct stratocones, which have grown over that past 80 ka. The youngest center, Mutnovsky IV, has produced basalts and basaltic andesites only. The three older centers (Mutnovsky I, II, III) are dominated by basalt and basaltic andesite (60-80% by volume), but each has also produced small volumes of andesite and dacite. Across centers of all ages, Mutnovsky lavas define a tholeiitic igneous series, from 48-70% SiO2. Basalts and basaltic andesites have relatively low K2O and Na2O, and high FeO* and Al2O3 compared to volcanic rocks throughout Kamchatka. The mafic lavas are also depleted in the light rare earth elements (REEs), with chondrite-normalized La/Sm arc volcanic rocks worldwide. Radiogenic isotope ratios (Sr, Nd, Pb, Hf) are similar for samples from all four eruptive centers, and indicate that all samples were produced by melting of a similar source mixture. No clear age-progressive changes are evident in the compositions of Mutnovsky lavas. Mass balance and assimilation-fractional crystallization (AFC) modeling of major and rare earth elements (REEs) indicate that basaltic andesites were produced by FC of plagioclase, clinopyroxene and olivine from a parental basalt, combined with assimilation of a melt composition similar to dacite lavas present at Mutnovsky. This modeling also indicates that andesites were produced by FC of plagioclase from basaltic andesite, combined with assimilation of dacite. Dacites erupted from Mutnovsky I and II have low abundances of REEs, and do not appear to be related to mafic magmas by FC or AFC processes. These dacites are modeled as the products of dehydration partial melting at mid-crustal levels of a garnet-free, amphibole-bearing basaltic rock, which itself formed in the mid-crust by emplacement of magma that

  13. Igneous Petrogenesis of Tequila Volcano, Western Mexico (United States)

    Vázquez-Duarte, A.; Gómez-Tuena, A.; Díaz-Bravo, B.


    Tequila volcano belongs to a Quaternary volcanic chain that runs in parallel to the Middle American Trench, but that have been constructed within the so-called Tepic-Zacoalco rift: an extensional tectonic structure that has been active for the past 3.5 Ma. This unusual tectonic setting, and the existence of a high-resolution stratigraphy for the Tequila Volcanic Field (Lewis-Kenedi, 2005, Bull Volcanol), provide an excellent opportunity to study andesite petrogenesis. New comprehensive geochemical data allow the recognition of at least four different magmatic series around Tequila: 1) The Santa Rosa intraplate basalts (1.0 - 0.2 Ma), a volcanic plateau constructed along the Santiago River Fault north of Tequila volcano. These Na-alkaline basalts are olivine-phyric, have negligible subduction signatures (Ba/Nb= 11.75 - 49.36), and display Sr-Nd-Pb isotopic compositions that correlate with fractionation indexes, probably indicating melt-crust interactions. 2) A group of vitreous domes and flows of dacitic to rhyolitic compositions, mostly contemporaneous to the Santa Rosa basalts, that were emplaced on the periphery of Tequila volcano. These rocks can have very low Sr and Eu contents but their isotopic compositions are remarkably constant and similar to the Santa Rosa basalts, probably indicating a genetic link through low pressure fractionation in the stability field of plagioclase. 3) The main edifice of Tequila volcano (~0.2 Ma) is made of two pyroxene andesites and dacites with strong subduction signatures (Ba/Nb= 53-112), that inversely correlate with MgO contents, but that follow a diverging evolutionary trend as the rest of the sequences. The isotopic compositions of Tequila main edifice can extend to slightly more enriched values, but do not correlate with fractionation indexes, thus indicating provenance from a different source. 4) The youngest activity on Tequila volcano (~0.09 Ma) is represented by amphibole bearing andesites that erupted through the

  14. Collision zone magmatism aids continental crustal growth (United States)

    Savov, Ivan; Meliksetian, Khachatur; Ralf, Halama; Gevorg, Navasardian; Chuck, Connor; Massimo, D'Antonio; Samuele, Agostini; Osamu, Ishizuka; Sergei, Karapetian; Arkadi, Karakhanian


    The continental crust has a broadly andesitic bulk composition and is predominantly generated at convergent margins. However, estimates of the bulk composition of oceanic arcs indicate a bulk composition closer to basalt than to andesite. Hence, reworking processes that transform basaltic island arc crust into andesitic continental crust are essential[1] and explaining growth of andesitic continental crust via accretion of arc crustal fragments remains problematic. Recent studies of magmatism in the Great Tibetan Plateau[2], as site of multiple and still active continent-continent collisions, have proposed that andesitic CC is generated via amalgamation of large volumes of collision-related felsic magmas generated by melting of hydrated oceanic crust with mantle geochemical signatures. We aim to test this hypothesis by evaluating geochemical data from the volcanically and tectonically active Lesser Caucasus region (Armenia, Azerbaijan, Georgia and E. Turkey), as the only other region where active continent-continent collision takes place. We will benefit from the newly compiled volcano-tectonic database of collision-related volcanic and plutonic rocks of Armenia that is comparable in quality and detail to the one available on Tibet. Our dataset combines several detailed studies from the large Aragats shield volcano[3] and associated monogenetic volcanic fields (near the capital city of Yerevan), as well as > 500 Quaternary to Holocene volcanoes from Gegham, Vardenis and Syunik volcanic highlands (toward Armenia-Nagorno-Karabakh-Azerbaijan-Iran border). The Armenian collision-related magmatism is diverse in volume, composition, eruption style and volatile contents. Interestingly, the majority of exposed volcanics are andesitic in composition. Nearly all collision-related volcanic rocks, even the highly differentiated dacite and rhyolite ignimbrites, have elevated Sr concentrations and 87Sr/86Sr and 143Nd/144Nd ratios varying only little (average ~ 0.7043 and ~ 0

  15. Miocene magmatism and tectonics within the Peri-Alboran orogen (western Mediterranean) (United States)

    El Azzouzi, M.; Bellon, H.; Coutelle, A.; Réhault, J.-P.


    The aim of this paper concerns Miocene igneous activity in the Alboran Sea and Peri-Alboran area (northern Morocco, western Algeria and Betic Cordilleras in Spain), considering its age and its location with regard to major tectonics structures. We have compiled previous K-Ar isotopic ages of lavas and plutonic boulders and intrusives with an error of ±1σ and completed this set by a new K-Ar isotopic age for andesitic tuffites from Alboran Island. Geochemistry of most of these samples has been considered after previous analyses completed with new data for Spain magmatism. These two sets of data allow us to place the magmatic activity within the regional stratigraphy and tectonics and their chronological framework of the three major tectonic phases of the Maghrebian orogen, at 17 Ma (Burdigalian), 15 Ma (Langhian) and 9 Ma (Tortonian). Petro-geochemical characteristics are compared through time and geographical locations. A major goal of this coupled approach is to help the elaboration of possible geodynamical processes. As an application, we present the case study of the Dellys, Djinet and Thenia region (east of Algiers) where the successive magmatic events between 19.4 ± 1 and 11.6 ± 0.5 Ma are closely related to the local tectonics and sedimentation. The Peri-Alboran igneous activity is placed in a multidisciplinary framework. Timing of activity is defined according to the ages of the neighbouring sedimentary units and the K-Ar ages of igneous rocks. In Spain, the Cabo de Gata-Carboneras magmatic province displays late Oligocene and early Miocene leucogranitic dikes, dated from 24.8 ± 1.3 to 18.1 ± 1.2 Ma; three following andesitic to rhyolitic events took place around 15.1 ± 0.8 to 14.0 ± 0.7 Ma, 11.8 ± 0.6 to 9.4 ± 0.4 Ma, 8.8 ± 0.4 to 7.9 ± 0.4 Ma; this last event displays also granitic rocks. Lamproitic magmas dated between 8.4 ± 0.4 and 6.76 ± 0.04 Ma were emplaced after the Tortonian phase. In Morocco, after the complex building of the Ras Tarf

  16. Geochemistry and Tectonic Setting of Marine Volcanic Rocks of Elashan Area in Qinghai%青海鄂拉山地区三叠系洪水川组火山岩地球化学特征及构造环境

    Institute of Scientific and Technical Information of China (English)

    李善平; 李永祥; 潘彤; 白宗海; 王瑾; 舒树兰; 李小雪; 张志青; 赵海霞


    Elashan magmatic belt, an intersection location for East Kunlun, West Qinling and South Qilian orogenic belt, has complex internal structure and is an important junction in western China and ore concen-tration area in Qinghai. Marine volcanic widely outcrops in Elashan area and the rock types are ainly amyg-daloidal basaltic andesite, amygdaloidal andesite, andesitic volcanic breccia, andesitic crystal-vitric tuff debris, andesitic breccia tuff lava, dacite and rhyolite. Marine volcanic rocks occurs by the volcanic strata, or laminated and lenticular shapes in the Suolaqu sandstone, Xingfucun fine-turbidite and Hekashan coarse-turbidite of the Hongshuichuan Formation, which is the product of a marine environment eruption. Chemical composition of volcanic rocks similar with the average chemical composition of island arc calc-al-kaline andesite, The average SEu value is 0. 75 indicating a weak negative anomalies, (La/Sm)N, (Gd/ Yb)N values of the average were 5. 09, 1. 76, and There are significantly fractionated between light and heavy rare earth elements and enrich in LREE. The trace elements such as Ba, Rb and Th are strongly enriched and Ti, Cr and other elements are depleted. The Th× Ta/Hf2 value is between 0. 029 to 0. 162, shows volcanic arc character. From the above, volcanic rocks of the Hongchuichuan Formation produced in stretching after the collision environment.%鄂拉山岩浆岩地处东昆仑、西秦岭、南祁连造山带交汇部位,内部结构复杂,是中国西部重要的构造结和矿集区之一.海相火山岩出露广泛,岩石类型主要由杏仁状玄武安山岩、杏仁状安山岩、安山质火山角砾岩、安山质晶屑岩屑凝灰岩、安山质角砾凝灰熔岩及英安岩、流纹岩等组成,以火山地层、夹层状、透镜状等形式赋存于洪水川组索拉曲砂岩、幸福村细浊积岩、河卡山粗浊积岩中,属海相喷发环境的产物.火山岩岩石化学成分与岛弧钙碱性安山岩平均化

  17. An overview of the 2009 eruption of Redoubt Volcano, Alaska (United States)

    Bull, Katharine F.; Buurman, Helena


    In March 2009, Redoubt Volcano, Alaska erupted for the first time since 1990. Explosions ejected plumes that disrupted international and domestic airspace, sent lahars more than 35 km down the Drift River to the coast, and resulted in tephra fall on communities over 100 km away. Geodetic data suggest that magma began to ascend slowly from deep in the crust and reached mid- to shallow-crustal levels as early as May, 2008. Heat flux at the volcano during the precursory phase melted ~ 4% of the Drift glacier atop Redoubt's summit. Petrologic data indicate the deeply sourced magma, low-silica andesite, temporarily arrested at 9-11 km and/or at 4-6 km depth, where it encountered and mixed with segregated stored high-silica andesite bodies. The two magma compositions mixed to form intermediate-silica andesite, and all three magma types erupted during the earliest 2009 events. Only intermediate- and high-silica andesites were produced throughout the explosive and effusive phases of the eruption. The explosive phase began with a phreatic explosion followed by a seismic swarm, which signaled the start of lava effusion on March 22, shortly prior to the first magmatic explosion early on March 23, 2009 (UTC). More than 19 explosions (or “Events”) were produced over 13 days from a single vent immediately south of the 1989-90 lava domes. During that period multiple small pyroclastic density currents flowed primarily to the north and into glacial ravines, three major lahars flooded the Drift River Terminal over 35 km down-river on the coast, tephra fall deposited on all aspects of the edifice and on several communities north and east of the volcano, and at least two, and possibly three lava domes were emplaced. Lightning accompanied almost all the explosions. A shift in the eruptive character took place following Event 9 on March 27 in terms of infrasound signal onsets, the character of repeating earthquakes, and the nature of tephra ejecta. More than nine additional

  18. An experimental study of permeability development as a function of crystal-free melt viscosity (United States)

    Lindoo, A.; Larsen, J. F.; Cashman, K. V.; Dunn, A. L.; Neill, O. K.


    Permeability development in magmas controls gas escape and, as a consequence, modulates eruptive activity. To date, there are few experimental controls on bubble growth and permeability development, particularly in low viscosity melts. To address this knowledge gap, we have run controlled decompression experiments on crystal-free rhyolite (76 wt.% SiO2), rhyodacite (70 wt.% SiO2), K-phonolite (55 wt.% SiO2) and basaltic andesite (54 wt.% SiO2) melts. This suite of experiments allows us to examine controls on the critical porosity at which vesiculating melts become permeable. As starting materials we used both fine powders and solid slabs of pumice, obsidian and annealed starting materials with viscosities of ˜102 to ˜106 Pas. We saturated the experiments with water at 900° (rhyolite, rhyodacite, and phonolite) and 1025 °C (basaltic andesite) at 150 MPa for 2-72 hrs and decompressed samples isothermally to final pressures of 125 to 10 MPa at rates of 0.25-4.11 MPa/s. Sample porosity was calculated from reflected light images of polished charges and permeability was measured using a bench-top gas permeameter and application of the Forchheimer equation to estimate both viscous (k1) and inertial (k2) permeabilities. Degassing conditions were assessed by measuring dissolved water contents using micro-Fourier-Transform Infrared (μ-FTIR) techniques. All experiment charges are impermeable below a critical porosity (ϕc) that varies among melt compositions. For experiments decompressed at 0.25 MPa/s, we find the percolation threshold for rhyolite is 68.3 ± 2.2 vol.%; for rhyodacite is 77.3 ± 3.8 vol.%; and for K-phonolite is 75.6 ± 1.9 vol.%. Rhyolite decompressed at 3-4 MPa/s has a percolation threshold of 74 ± 1.8 vol.%. These results are similar to previous experiments on silicic melts and to high permeability thresholds inferred for silicic pumice. All basaltic andesite melts decompressed at 0.25 MPa/s, in contrast, have permeabilities below the detection limit

  19. Water-rich and volatile-undersaturated magmas at Hekla volcano, Iceland (United States)

    Lucic, Gregor; Berg, Anne-Sophie; Stix, John


    Olivine-hosted melt inclusions from four eruptions at Hekla volcano in Iceland were analyzed for their dissolved H2O, CO2, S, and Cl contents. A positive correlation among the repose interval, magmatic evolution, and volatile contents of magmas is revealed. H2O is the dominant volatile species; it behaves as an incompatible component, increasing in concentration over time as a result of fractional crystallization in the magma. The full suite of H2O contents ranges from a low of 0.80 wt % in basaltic andesites to a maximum of 5.67 wt % in rhyolites. Decreasing H2O/K2O at fixed major element compositions suggests that syneruptive degassing reduces H2O contents significantly. Hekla magmas are CO2 poor, with very low concentrations present only in the most evolved compositions (˜20-30 ppm or less). The decrease in S content from basaltic andesite to rhyolite demonstrates that sulfide saturation is attained when the melt composition reaches basaltic andesite, resulting in the precipitation of pyrrhotite. Low CO2/Nb ratios suggest that vapor saturation is most likely reached during an early period of cooling and solidification in the crust. Fresh injections of mafic magma interact with previously solidified intrusives, producing new melts that are volatile undersaturated. Vapor saturation pressures obtained using the most volatile-rich melt inclusions suggest the presence of a magma chamber at a minimum depth of ˜7 km. This is in agreement with geophysical observations from recent small-volume eruptions, but given the possibility of volatile-undersaturated melts, some of the magmas may reside at greater depths.

  20. Ignimbrite Analyses of Batur Caldera, Bali, based on 14C Dating

    Directory of Open Access Journals (Sweden)

    Igan S. Sutawidjaja


    Full Text Available Batur Caldera, in the northeastern part of Bali Island, is an elliptical collapse structure 13.8 by 10 km in size and another circular composite collapse structure with a diameter of 7.5 km in its centre. Two stages of the collapse were interrupted by silicic andesite lavas and domes. The first collapse was initiated by the eruption of about 84 km3 of the dacitic "Ubud Ignimbrite", about 29,300 years B.P., which caused a steep-walled depression about 1 km deep. The second ignimbrite was erupted from a large crater about the present lake, and it  produced about 19 km3 of a similar voluminous dacitic ignimbrite, called the "Gunungkawi Ignimbrite" about 20,150 years B.P. This second eruption trig- gered a second collapse, which created the central circular caldera, and formed a basin structure. Both the Ubud and Gunungkawi Ignimbrites consist of a similar dacitic composition, white to red (the most abundant nearly 90 % and dark grey to black dacitic pumice clasts. The large clasts, up to 20 cm in diameter, are in the non-welded ignimbrite, particularly in the upper part of the Gunungkawi Ignimbrite. The intracaldera ignimbrite, called the "Batur Ignimbrite" about 5 km3  in volume is a densely welded ignimbrite and generally shows typical welded features. The ignimbrite comprises at least five different flow units, separated by thin (15 - 40 cm welded pumiceous airfall deposits, with flattened pumice clasts. Another large eruption occurred about 5,500 years B.P., producing around 0.09 km3  andesitic ignimbrite. This was initiated by phreatomagmatic eruptions, indicated by thick phreatomagmatic and surge deposits, underlying the ignimbrite. The caldera and its vicinity are partly filled, and variably mantled by later eruptive products of dacitic and andesitic phreatomagmatic and airfall deposits.  

  1. Carboniferous arc magmatism in the Qiangtang area, northern Tibet: Zircon U-Pb ages, geochemical and Lu-Hf isotopic characteristics, and tectonic implications (United States)

    Jiang, Qing-yuan; Li, Cai; Su, Li; Hu, Pei-yuan; Xie, Chao-ming; Wu, Hao


    The Longmu Co-Shuanghu suture zone (LSSZ), which lies between the southern Qiangtang-Baoshan block and northern Qiangtang-Qamdo block on the Tibetan Plateau, represents remnants of the Paleo-Tethys Ocean. Previous investigations have focused on the ophiolite, high-pressure zone, and metamorphic belt in this zone, whereas few studies have considered the arc magmatism. The present study examines a suite of Carboniferous arc-magmatic rocks in the western region of the LSSZ that consist of acidic to basic volcanic rocks, including rhyolite, dacite, andesite, basaltic andesite, basalt, and pyroclastics. Zircon U-Pb dating of three samples (two andesites and one dacite) by laser ablation-inductively coupled plasma-mass spectrometry demonstrates that these rocks were emplaced at ca. 351-346 Ma. The basalts have low Cr and Ni abundances, indicating that they were generated by varying degrees of partial melting of an enriched lithospheric mantle that was metasomatized by subduction-derived components. Zircons in the felsic rocks have positive εHf(t) values of 0.8-14.8, indicating an origin by varying degrees of partial melting of juvenile basaltic lower crust, consisting mainly of underplated magmas with similar compositions to the basalts. Geochemical data show that the volcanic rocks are enriched in light rare earth elements and large ion lithophile elements (e.g., Th, U, and Pb) but are strongly depleted in high field strength elements (e.g., Nb, Ta, and Ti), have high Al2O3 and low Zr concentrations, and are calc-alkaline. These magmas are therefore subduction-related volcanic arc rocks, indicating that Paleo-Tethys subduction began in the early Carboniferous.

  2. Microbiology of Low Temperature Seafloor Deposits Along a Geochemical Gradient in Lau Basin (United States)

    sylvan, J. B.; Sia, T. Y.; Haddad, A.; Briscoe, L. J.; Girguis, P. R.; Edwards, K. J.


    The East Lau Spreading Center (ELSC) and Valu Fa Ridge comprise a ridge segment in the southwest Pacific Ocean where rapid transitions in the underlying mantle lenses manifest themselves by gradients in seafloor rock geochemistry. At the spreading center in the north, basaltic host rock extrudes while the influence of subduction in the south creates mainly basaltic andesite host rock. A contuous gradient between these two end members exists along the spreading center. We studied the geology and microbial diversity of three silicate rock samples and three inactive sulfide chimney samples collected along the ELSC and Valu Fa Ridge by X-ray diffraction, elemental analysis, thin section analysis and construction of bacterial 16S rRNA clone libraries. Here, we discuss the geological and biological differences between the collected rocks. We found that the bacterial community composition changed as the host rock mineralogy and chemistry changed from north to south. Also, the bacterial community composition on the silicates is distinct from those on the inactive chimneys, and the interior conduit of an inactive chimney hosts a very different community from the exterior. Basalt from the northern end of the ELSC had high proportions of Alphaproteobacteria and Bacteroidetes. These proportions decreased on the silicates collected further south. Epsilonproteobacteria were also present on the basalt, decreased further south and were absent on the basaltic andesite. Conversely, basaltic andesite rocks from the southern end had high proportions of Chloroflexi, which decreased further north and were absent on basalt. The exterior of inactive sulfide structures were dominated by lineages of sulfur oxidizing Gammaproteobacteria and Epsilonproteobacteria and were less diverse than those on the silicates. The interior of one chimney was dominated by sulfate-reducing Deltaproteobacteria and was the least diverse of all samples. These results support the Mantle to Microbe hypothesis in

  3. Origin of a native sulfur chimney in the Kueishantao hydrothermal field, offshore northeast Taiwan

    Institute of Scientific and Technical Information of China (English)

    ZENG; ZhiGang; LIU; ChangHua; CHEN; ChenTung; A; YIN; XueBo; CHEN; DaiGeng; WANG; XiaoYuan; WANG; XiaoMei; ZHANG; GuoLiang


    Analyses of rare earth and trace element concentrations of native sulfur samples from the Kueishantao hydrothermal field were performed at the Seafloor Hydrothermal Activity Laboratory of the Key Laboratory of Marine Geology and Environment,Institute of Oceanology,Chinese Academy of Sciences.Using an Elan DRC II ICP-MS,and combining the sulfur isotopic compositions of native sulfur samples,we studied the sources and formation of a native sulfur chimney.The results show,when comparing them with native sulfur from crater lakes and other volcanic areas,that the native sulfur content of this chimney is very high (99.96%),the rare earth element (REE) and trace element constituents of the chimney are very low (ΣREE<21×10-9),and the chondrite-normalized REE patterns of the native sulfur samples are similar to those of the Kueishantao andesite,implying that the interaction of subseafloor fluid-andesite at the Kueishantao hydrothermal field was of short duration.The sulfur isotopic compositions of the native sulfur samples reveal that the sulfur of the chimney,from H2S and SO2,originated by magmatic degassing and that the REEs and trace elements are mostly from the Kueishantao andesite and partly from seawater.Combining these results with an analysis of the thermodynamics,it is clear that from the relatively low temperature (<116℃),the oxygenated and acidic environment is favorable for formation of this native sulfur chimney in the Kueishantao hydrothermal field.

  4. Zircon U-Pb Age Determination of Volcanic Eruptions in Lutao and Lanyu in the Northern Luzon Magmatic Arc

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    Wen-Yu Shao


    Full Text Available This paper reports for the first time zircon U-Pb ages of volcanic rocks and sands from Lutao and Lanyu, two islets off SE Taiwan in the north Luzon arc. The samples include (1 seven andesites from four volcanic units and three river/beach sands from Lutao and (2 five basaltic andesites from four volcanic units and two river/beach sands from Lanyu. The Lutao andesites contain abundant magmatic zircons, aging from ~1.54 to ~1.24 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 1.31 ±± 0.03 Ma (n = 190, MSWD = 2.6. This is slightly older than, or broadly coincident with, a mean 206Pb/238U age of 1.23 ±± 0.03 Ma (n = 103, MSWD = 1.9 given by detrital zircons from the three sands. The Lanyu volcanics appear to have less abundant magmatic zircons, aging from ~2.72 to ~2.35 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 2.61 ±± 0.13 Ma (n = 11, MSWD = 1.8. This accords with a mean 206Pb/238U age of 2.69 ±± 0.11 Ma (n = 34, MSWD = 4.7 obtained by detrital zircons from the two sands. The age data suggest that in Lutao and Lanyu the major volcanic eruptions occurred at ~1.3 and ~2.6 Ma, respectively. Moreover, volcanic samples from both islets contain various amounts of older inherited zircons, ~11% in Lutao and up to ~82% in Lanyu, which together with detrital zircons from the sands show main age peaks at ~150 Ma and ~1.9 and ~2.5 Ga, consistent with the notion for a _ continental crust involved in the genesis of the northern Luzon magmatic arc.

  5. Chronology and Geochemistry of Volcanic Rocks in the Cretaceous Suifenhe Formation in Eastern Heilongjiang, China

    Institute of Scientific and Technical Information of China (English)

    JI Weiqiang; XU Wenliang; YANG Debin; PEI Fuping; JIN Ke; LIU Xiaoming


    Zircon U-Pb ages and geochemical data of volcanic rocks in the Suifenhe Formation in eastern Heilongjiang Province are reported, and their petrogenesis is discussed in this paper. The Suifenhe Formation mainly consists of basalt, andesite, and dacite. Zircon from andesite and dacite are euhedral in shape and show typical oscillatory zoning with high Th/U ratios (0.18-0.57), implying its magmatic origin. Zircon U-Pb dating results by laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) indicate that the 206Pb/238U ages of zircons from andesite range within 105-106 Ma, yielding a weighted mean age of 105.5±0.8 Ma (n=14), and that 206Pb/238U ages of zircons from dacite are between 90-96 Ma, yielding a weighted mean age of 93.2±1.3 Ma (n =13). The volcanic rocks from the Suifenhe Formation are subalkaline series and show a calc-alkaline evolutionary trend with SiO2 content of 47.69%-65.47%, MgO contents of 1.42%-6.80% (Mg#= 45-53), and Na2O/K2O ratios of 1.83-3.63. They are characterized by enrichment in large ion lithophile elements (LILE) and lightrare-earth elements (LREE), depletion in heavy rare earth elements (HREE) and high field strength elements (HFSE) (e.g., Nb, Ta, Ti), and low initial 87Sr/86Sr ratios (0.7041-0.7057) and positive εNd(t)values (0.39-4.08), implying that they could be derived from a depleted magma source. Taken together,these results suggest that the primary magma of the volcanic rocks might originate from partial melting of the mantle wedge metasomatized by fluids derived from subducted slab under a tectonic setting of active continental margin.

  6. 238U sbnd 230Th sbnd 226Ra disequilibria in young Mount St. Helens rocks: time constraint for magma formation and crystallization (United States)

    Volpe, Alan M.; Hammond, Paul E.


    We use 238U-series nuclides and 230Th/ 232Th ratios measured by mass spectrometry to constrain processes and time scales of calc-alkaline magma genesis at Mount St. Helens, Washington. Olivine basalt, pyroxene andesites and dacites that erupted 10-2 ka ago show 3-14% ( 230Th) sbnd ( 238U) and 6-54% 226Ra sbnd 230Th disequilibria. Mineral phases exhibit robust ( 226Ra) sbnd ( 230Th) fractionation. Plagioclase has large 65-280% ( 226Ra) excesses, and magnetite has large 65% ( 226Ra) deficits relative to ( 230Th). Calculated partition coefficients for Ba, Th, and U in mineral-groundmass pairs, except Ba in plagioclase, are low (⩽ 0.04). Correlation between ( 226Ra/ 230Th ) activity ratios and rm/BaTh element ratios in the minerals suggests that 226Ra partitions similar to Ba during crystallization. Internal ( 230Th) sbnd ( 238U) isochrons for 1982 summit and East Dome dacites and Goat Rocks and Kalama andesites show that closed Th sbnd U system fractionation occurred 2-6 ka ago. Apparent internal isochrons for Castle Creek basalt (34 ka) and andesite (27 ka) suggest longer magma chamber residence times and mixing of old crystals and young melt. Mineral ( 226Ra) sbnd ( 230Th) disequilibrium on Ba-normalized internal isochron diagrams suggests average magma chamber residence times of 500-3000 years. In addition, radioactive ( 226Ra/ 230Th ) heterogeneity between minerals and groundmass or whole rock is evidence for open-system Ra sbnd Th behavior. This heterogeneity suggests there has been recent, post-crystallization, changes in melt chemical composition that affected 226Ra more than 230Th. Clearly, magma fractionation, residence and transport of crystal-melt before eruption of chemically diverse lavas at Mount St. Helens occurs over geologically short periods.

  7. Geochemical variability of MORBs along slow to intermediate spreading Carlsberg-Central Indian Ridge, Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Ray, D.; Misra, S.; Banerjee, R.

    spreading ridge segment of the northern MAR. The CR has a NW–SE trend, after then the gradual bend in the ridge axis is accommodated by non-transform discontinuities and along-axis bathymetric deeps. 3. Sampling and analytical technique During... 2404) technique on fused pellets. The accuracy and precision of analyses observed for the International rock standards MO-12 [Andesite-Basalt; IGEM] and W2 [Diabase; USGS] were better than 5% and ±2% respectively. In total 18 CR MORB samples (12 from...

  8. Fading characteristics of martian analogue materials and the applicability of a correction procedure

    DEFF Research Database (Denmark)

    Morthekai, P.; Jain, Mayank; Murray, A.S.;


    The anomalous fading of trapped charge in martian analogue materials such as basalt and andesite rock samples is measured. Optically stimulated luminescence (OSL) signals show rapid fading (of between 4% and 27% per decade). Fading rates obtained using high temperature thermoluminescence signals...... are smaller. The importance of knowing whether a standard fading correction method is applicable to samples of unknown age is illustrated by application to an 'infinitely old' known-age basalt, for which both the uncorrected and fading-corrected natural signals lie within the approximately linear region...

  9. Emanation Study of Gas Radon on the Ancient Cuexcomate Geyser in Puebla City, Mexico

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    J. A. Monarca Serrano


    Full Text Available Radon measurements were collected over a period of nine months in the area of the ancient Cuexcomate geyser, in Puebla City. For measuring radon, the passive method of nuclear tracks in solids was used, using polycarbonate CR-39 as radiation sensitive material. Radon concentrations varied in strong anti-correlation with the rainfall intensity. And are lower compared to other locations, in concordance with the stratigraphic composition, as travertine and deposits of volcanic origin, corresponding to the geyser chemical composition and the active environment in the north part of the Trans-Mexican Volcanic Belt with an andesitic and basalt composition.

  10. Complete Analytical Data for Samples of Jurassic Igneous Rocks in the Bald Mountain Mining District, Nevada (United States)

    du Bray, Edward A.


    This report presents all petrographic, major oxide, and trace element data for a set of 109 samples collected during an investigation of Jurassic igneous rocks in the Bald Mountain mining district, Nevada. Igneous rocks in the district include the Bald Mountain stock, quartz-feldspar porphyry dikes, basaltic andesite dikes, aplite sills, and rare lamprophyre dikes. These rocks, although variably altered near intrusion-related mineral deposits, are fresh in many parts of the district. Igneous rocks in the district are hosted by Paleozoic sedimentary rocks.

  11. On plate tectonics and the geologic evolution of southwestern North America (United States)

    Ward, P.L.


    Very rapid subduction of the Farallon plate under southwestern North America between 60 and 40 Ma was accompanied by a relatively low volume of magmatism throughout the southwestern United States and northern Mexico. Between 40 and 20 Ma, when subduction slowed significantly and in one area may have even stopped, magmatism became widespread and voluminous from Nevada and Utah to central Mexico. This correlation of rapid subduction with a relatively low volume of magmatism can be explained by the observation that subduction-related andesitic arc volcanism, often formed in a Laramide-style compressional regime, is relatively low volume compared to continental volcanism. -from Author


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    Rayo Lorena


    Full Text Available The contact between the unit Porphyry Andesite and the Cajamarca Group is observed in the "Túnel de la Linea" section. The integration of petrographic, geochemical and textural (crystal size distribution, CSD analysis allows description of physical and chemical processes that took place in the contact zone in order to propose a model for the intrusion. Material assimilation produced quartz enrichment towards pluton's boundaries associated to a simple process of melt injection. The difference between host rock and hot melt rheologies causedshear stress that produced crystal breaking, folding and foliation rotation.

  13. Bi-directional subduction of the South Tianshan Ocean during the Late Silurian: Magmatic records from both the southern Central Tianshan Block and northern Tarim Craton (United States)

    Wang, Meng; Zhang, Jinjiang; Zhang, Bo; Liu, Kai; Ge, Maohui


    The subduction polarity of the South Tianshan Ocean (STO) is a matter of debate, primarily in that the Paleozoic structures of Tianshan orogenic belt have been strongly overprinted by the Cenozoic intra-continental deformation. Indentifying the arc-related magmatic rocks may provide a convincible clue for understanding the closure process of the STO. In this study, whole-rock geochemistry, zircon U-Pb dating and Hf isotope were presented on the andesite and monzonite from the Bayanbulak area of the southern Central Tianshan Block (CTB) and on the quartz diorite from the Ouxidaban area of the northern Tarim Craton. Geochemically, all the samples are Na-rich, enriched in light rare earth elements and large ion lithophile elements (Rb, Ba, U, K and Pb), and depleted in high strength field elements (Nb, Ta and Ti), like most arc-type igneous rocks. The Bayanbulak andesite samples display high MgO, Fe2O3T, TiO2 and Mg# values, and positive εHf(t) values, indicating magma source from the wedge mantle. But the existence of xenocrystic zircons implies that continental crust material were involved during magma ascend, suggesting a continental arc setting for the Bayanbulak andesite. The Bayanbulak monzonite and the Ouxidaban quartz diorite samples display relatively higher SiO2 contents, and lower MgO, Fe2O3T and TiO2 concentrations, indicating crustal sources. But the Mg# values of the Bayanbulak monzonite and the Ouxidaban quartz diorite are 48.76-51.85 and 50.31-53.73, and the εHf(t) values are -2.5 to 8.7 and -1.7 to 4.1, indicating that their magma sources were also mixed by mantle-derived components. LA-ICP-MS zircon U-Pb dating results reveal that the Bayanbulak andesite, the Bayanbulak monzonite and the Ouxidaban quartz diorite were formed at 423, 424 Ma, and 421 Ma, respectively. The age and geochemical data indicate that both the southern CTB and northern Tarim Craton were active continental margins during the Late Silurian, favoring a bi-directional subduction

  14. Mineralogy and fluid inclusion studies in kalchoye Copper- gold deposit, East of Esfahan

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    Rezvan Mehvary


    Full Text Available Kalchoye Copper-gold deposit is located about 110 kilometers east of Esfahan province and within the Eocene volcano sedimentary rocks. Sandy tuff and andesite lava are important members of this complex.The form of mineralization in area is vein and veinlet and quartz as the main gangue phase. The main ore minerals are chalcopyrite, chalcocite, galena and weathered minerals such as goethite, iron oxides, malachite and azurite. Studies in area indicate that ore mineralization Kalchoye is low sulfide, quartz type of hydrothermal ore deposits and results of thermometry studies on quartz minerals low- medium fluid with low potential mineralization is responsible for mineralization in this area.

  15. H2O-driven generation of picritic melts in the Middle to Late Triassic Stuhini arc of the Stikine terrane, British Columbia, Canada (United States)

    Milidragovic, Dejan; Chapman, John B.; Bichlmaier, Sebastian; Canil, Dante; Zagorevski, Alex


    Basaltic to andesitic compositions predominate island arc magmatism; ultramafic magmas are rare. Ultramafic (MgO = 21-33 wt.%) tuff breccia, lapilli tuff, and ash tuff of the Middle to Upper Triassic Stuhini Group were erupted in the Stikine arc of the North American Cordillera shortly preceding an episode of prolific porphyry Cu-Mo(-Au) mineralization. The ultramafic tuff shows accumulation (20-65%) of olivine (Fo91) and minor chromite into a subalkaline picritic parental magma with MgO ∼16 wt.%. Despite the inferred high MgO content of the parental liquid, chromite phenocrysts record relatively low liquidus temperatures (mineralization.

  16. The age and constitution of Cerro Campanario, a mafic stratovolcano in the Andes of Central Chile


    Wes Hildreth; Brad Singer; Estanislao Godoy; Francisco Munizaga


    ABSTRACT Cerro Campanario, a towering landmark on the continental divide near Paso Pehuenche, is a glacially eroded remnant of a mafic stratovolcano that is much younger than previously supposed. Consisting of fairly uniform basaltic andesite, rich in olivine and plagioclase, the 10-15 km³ edifice grew rapidly near the end of the middle Pleistocene, about 150-160 ka, as indicated by 40Ar/39Ar and unspiked K-Ar analyses of its lavas.La edad y formación del cerro Campanario, un estratovolcán má...

  17. The zircon SHRIMP chronology and trace element geochemistry of the Carboniferous volcanic rocks in western Tianshan Mountains

    Institute of Scientific and Technical Information of China (English)

    ZHU Yongfeng; ZHANG Lifei; GU Libing; GUO Xuan; ZHOU Jing


    The genesis of the Carboniferous volcanic rocks in the Dahalajunshan group, mainly consisting of trachytes and trachy-andesites and distributing widely in western Tianshan Mountains, remains to be controversial. It has been proposed to be relevant to "rift" or "plume". Detailed petrology and geochemical data presented in this paper show that these volcanic rocks represent typical continental arc magmatism. The volcanic rocks are mainly trachy-andesitic, and the magma source is enriched in LILE, Th and Pb, and depleted in HFSE and Ce. Trace element geochemical study suggests that the basalts could be modeled by 7%-11% partial melt of garnet lherzolite. The volcanic rocks in the Dahalajunshan group are neither the products of "rift" nor so-called "plume" but represent the continental island arc of the Paleo-Southern Tianshan Ocean. The mantle wedge had been modified by the melt generating in subduction zone during a long evolution history of this island arc. The continental crust materials (i.e. mainly sediment on ocean floor) had been added into island arc through melt in subduction zone. Volcanic rocks occurring in different regions might represent magma eruption in different time. The zircon SHRIMP dating indicates that the ages of the basalt varies between 334.0 Ma and 394.9 Ma. The 13 analyses give an average age of 353.7 (4.5 Ma (MSWD = 1.7). The apparent ages of zircons in trachy-andesite vary between 293.0 Ma and 465.4 Ma. All analyses fall on the U-Pb concordant line and are divided into two groups. 8 analyses produce an average age of 312.8(4.2 Ma (MSWD = 1.7), which represents the crystallizing age of zircon rims in trachy-andesite. The acquired two ages (i.e. 354 and 313 Ma) belong to the Early Carboniferous and Late Carboniferous epochs, respectively. Thus, the Dahalajunshan group would be separated into several groups with the accumulation of high-quality age dating and data of trace element and isotopic geochemistry, in our opinion.

  18. Mineralogy and Geochemistry of Clay Rich Volcano-Sedimentary Units from South of Elazıǧ Basin (Eastern Turkey) (United States)

    Akkoca, Dicle Bal; Bakır, Zülfü


    The investigated area covers Upper Cretaeous Elazıǧ Magmatics and Middle Eocene Maden Group in the southern of Elazıǧ. X-ray powder diffraction (XRD), ICP-AES, ICP-MS were performed on three sections samples belonging to Elazıǧ Magmatics (Yemişlik and Kavallı sections) and Maden Group (Alıncık section), to investigate the depositional environment of volcano-sediments. The Elazıǧ magmatic rocks are composed of diorites, monzodiorites, quartz-diorites, and tonalites, basaltic pillow-lavas, andesitic lavas, and andesitic pyroclastic rocks. The Maden Group has a complex lithology consisting of limestones, red-green clayey limestones, sandstone, agglomerate, tuffs, reddish mudstone and basaltic-andesitic pillow lavas. Yemişlik section is composed mainly of altered grey tuffites, Kavallı section is represented by brown altered sediments, intercalated with basaltic, andesitic lava flows. Reddish mudstones constiture the Alıncık section. All samples consist of clay minerals (chlorite, illite), quartz, and feldspar. Yemişlik and Kavallı sections also contain calcite. Chlorite is the dominant clay in three sections. SiO2, Al2O3, Fe2O3, K2O contents show that Kavallı, Yemişlik and Alıncık samples are convenient with Fe shales and shales. The ratios of TiO2, Zr, Th/Sc, Zr/Sc, Y/Ni-Cr/V, Al/(Al+Fe+Mn) show dominance of neutral-basic volcanism in the area. REE concentrations of samples are normalized to chondrite values. It is determined that low light rare earth elements (LREEs) are enriched in comparison to high rare earth elements (HREEs), and the absence of Eu anomalies shows that our samples are generally mafic in composition. Rare earth elements (REE) of samples were compared with North American shale composite (NASC), European shale (ES) and Post-Archean Australian shale (PAAS). Elements are not in concurrence with these compositions. Th-Hf/3-Nb/16 tectono-magmatic discrimination diagram for samples in the study area indicate that all samples were

  19. Physical volcanology of the mafic segment of the subaqueous New Senator caldera, Abitibi greenstone belt, Quebec, Canada

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Lyndsay N; Mueller, Wulf U [Universite du Quebec a Chicoutimi, 555 boul. du l' Universite, Chicoutimi, Quebec, G7H2B1 (Canada)], E-mail:


    Archean calderas provide valuable insight into internal geometries of subaqueous calderas. The New Senator caldera, Abitibi greenstone belt, Canada, is an Archean example of a subaqueous nested caldera with a basal stratigraphy dominated by gabbro-diorite dykes and sills, ponded magmas and basalt and andesite lava flows. The aim of our study is to focus on the use of physical volcanology to differentiate between the various mafic units found at the base of the New Senator caldera. Differentiation between these various mafic units is important from an exploration point of view because in modern subaqueous summit calders (e.g. Axial Seamount) margins of ponded magmas are often sites of VMS formation.


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    Arief Mustofa Nur


    Full Text Available Diabas Parang hill is one of location which conservated in area conservation of geological Karangsambung.Now, it is threatened, because there are many mines at surrounding it. Activities of mining not care science andenvironmental conservation.Impact of mining so cause change of topography/morphology, slope become more steep, and mining locationbecome potentially accure rock fall and landslide. Pursuant to result of laboratory analysis, engineeringproperties diabas Parang hill strongless than andesit so it is only fulfil for trotoir.For diabas conservation which is protected so need affort to stop activity of mining. The effort can do seekingaltenative location for mine and/or to change mine activities.

  1. Palaeoenvironment reconstruction, volcanic evolution and geochronology of the Cerro Blanco subcomplex, Nevados de Chillan volcanic complex, Central Chile


    Mee, Katy; Gilbert, Jennie S.; McGarvie, David W.; Naranjo, Jose A.; Pringle, Malcolm S.


    Nevados de Chillán Volcanic Complex, central Chile, has been active for at least 640 ka—a period spanning a number of glacial and interglacial periods. Geologic mapping, radiometric dating and geochemical analysis have identified six new volcanic units and produced four new 40Ar/39Ar ages for Cerro Blanco, the northern subcomplex of Nevados de Chillán volcano. Compositions range from dacite to basaltic-andesite and a new geologic map is presented. Examination of lava fracture structures on bo...

  2. Geochemistry and tectonic setting of the Paleoproterozoic metavolcanic rocks from the Chirano Gold District, Sefwi belt, Ghana (United States)

    Senyah, Gloria A.; Dampare, Samuel B.; Asiedu, Daniel K.


    Major and trace elements, including rare earth elements (REEs) data are presented for metavolcanic rocks of the Paleoproterozoic Birimian Sefwi belt to determine the geochemical characteristics as well as the possible tectonic setting of emplacement of these rocks. In order to accomplish the aim of the study, the petrographical characteristics of the rocks were examined coupled with analysis of the rocks for their whole-rock major and trace elements contents by ICP-AES and ICP-MS methods respectively. The rocks have been classified as basalt/basaltic andesites and dolerites based on their textural and mineralogical compositions. It is observed that the rocks have suffered various degrees of alteration evident in the overprinting of primary minerals such as pyroxenes and plagioclase by chlorite, epidote, sericite and others. Generally, the rocks are moderately deformed and may have experienced at least greenschist metamorphism. The basalt/basaltic andesites are derivative magmas [Mg# (20-51), Cr (10-220 ppm) and Ni (5-137 ppm)], and show flat REE to fractionated REE patterns with (La/Sm)N = 1.36-3.90, (La/Yb)N = 1.17-5.32 and strong negative to non-existent Eu anomalies (Eu/Eu* = 0.51-1.03). N-MORB-normalised multi-element diagrams show that the rocks have geochemical patterns characterised by enrichment in LILE relative to HFSE and in LREE relative to HREE. The basalt/basaltic andesites exhibit characteristics of subduction zone-related magmas, such as pronounced negative Nb-Ta anomalies, slightly negative Hf and variable negative Ti anomalies. The dolerites do not vary much from the basalts and basaltic andesites. The MgO and Fe2O3 values of the dolerite range from 2.97 to 6.93 and 5.98 to 14.35 wt.% respectively, corresponding to Mg#s of 38-62. LREEs enrichment over HREEs with (La/Sm)N ranging from 0.61 to 4.61 and (Gd/Yb)N ranging from 0.99 to 2.91 is also typical of these rocks. The dolerites also exhibit quite invariable Eu anomalies (Eu/Eu* = 0.81-1.00) and

  3. Trace Element Abundance Relationships in the Multi—stage Comagmatic Fractional Crystallization and Their Applications

    Institute of Scientific and Technical Information of China (English)

    汪云亮; 李巨初


    In this study a mathematical expression of trace element abundance relationship for the mul-ti-stage comagmatic fractional crystallization has been established ,based on geochemical studies of the Emeishan basalt-trachyte series and adjacent mafic-ultramafic layered intrusions, as well as on the avail-able data for basalt, andesite, dacite and rhyolite series in southern Andes,Chile ,which have been well documented.It is demonstrated that the abundance constant (R) for a given trace element at dif-ferent stages of fractional crystallization of a parental magma is highly variable,which can be used as a criterion to divide fractional crystallization stages.

  4. A Neogene back-arc origin for the Banda Sea basins: geochemical and geochronological constraints from the Banda ridges (East Indonesia) (United States)

    Honthaas, Christian; Réhault, Jean-Pierre; Maury, René C.; Bellon, Hervé; Hémond, Christophe; Malod, Jacques-André; Cornée, Jean-Jacques; Villeneuve, Michel; Cotten, Joseph; Burhanuddin, Safri; Guillou, Hervé; Arnaud, Nicolas


    Dredgings conducted during the French-Indonesian cruises Banda Sea II and III collected volcanic rocks from several ridges of the Banda Sea area (Tukang Besi ridge, site 218; Lucipara ridge, sites 214 and 305; Nieuwerkerk-Emperor of China, sites 219 and 220). With the exception of one 46-Ma-old N-MORB type basalt, thought to belong to an ophiolitic complex, K-Ar and Ar-Ar datings indicate that all the dredged volcanics are Neogene. They range in age from ca. 10 Ma (Tukang Besi back-arc basalts) to 8-7 Ma (Nieuwerkerk-Emperor of China calc-alkaline andesites) and to 7-3 Ma (Lucipara OIB-type transitional basalts and cordierite-bearing andesites). Radiogenic isotopic signatures of andesites are consistent with an AFC (Assimilation coupled with Fractional Crystallization) process involving assimilation of continental crust. 8-3-Ma-old calc-alkaline volcanic activity is also recorded on the Wetar segment, an inactive part of the East Sunda arc, and corresponding isotopic compositions are also consistent with an AFC process involving continental crust. These features suggest that Lucipara-Nieuwerkerk-Emperor of China ridges and the Wetar segment were representing a single volcanic arc 8-7 Ma ago. The corresponding calc-alkaline activity was related to the subduction of the Indian oceanic lithosphere beneath continental blocks of Australian origin. Back-arc opening processes occurred from 6 to 3 Ma as a multi-rift opening for the Wetar basin and as a single-rift opening for the Damar basin while subduction-related magmatism was still active in the Wetar segment. Volcanic activity stopped at 7 Ma in the Nieuwerkerk-Emperor of China ridge. On Lucipara ridge, 6-3 Ma volcanic activity emplaced concomitantly transitional basalts and cordierite-bearing andesites. The mineralogical and chemical features of the latter are consistent with an AFC process involving assimilation of continental crust by mantle-derived basaltic magmas. The end of magmatic activity on both volcanic

  5. Melting features along the Ryukyu slab tear, beneath the southwestern Okinawa Trough - art. no. L19607


    Lin, Jing-yi; Hsu, Sk; Sibuet, Jean-claude


    The present-day active volcanic front associated with the Ryukyu subduction zone extends from Japan to the Ilan plain (northern Taiwan) and is located within the Okinawa Trough, 80-100 km above the Ryukyu slab. An abnormal amount of arc volcanism, which consists of basalt, andesite and rhyolite occurs within the southwestern Okinawa Trough, above a slab tear of the Ryukyu subduction zone (CBVT). The power spectrum analysis of magnetic data shows the occurrence of a thin crust above the slab t...

  6. Zeolites replacing plant fossils in the Denver formation, Lakewood, Colorado. (United States)

    Modreski, P.J.; Verbeek, E.R.; Grout, M.A.


    Well-developed crystals of heulandite and stilbite, within fossil wood, occur in sedimentary rocks in Lakewood, Jefferson County. The rocks belong to the Denver formation, a locally fossiliferous deposit of fluvial claystone, siltstone, sandstone and conglomerate, containing some volcanic mudflows (andesitic) of late Cretaceous to Palaeocene age. Altered volcanic glass released Na and Ca into the ground-water and subsequently zeolites were crystallized in the open spaces between grains and within fossil plant structures. Minor pyrite, quartz (jasper), calcite and apatite also occur as replacements of fossil wood. Similar zeolite occurrences in other areas are reviewed.-R.S.M.

  7. The Records of the Tectonic Evolution From the Volcanics in Qiangtang Basin, Tibet

    Institute of Scientific and Technical Information of China (English)

    He Zhonghua; Yang Deming; Li Cai; Pu Zhongyu


    The volcanism in Qiangtang Basin is very frequent due to the divergence and subduction of the various plates. The study indicates that these volcanics are formed in different tectonic settings: 1 )Hercynian volcanics are mainly basalts and are formed in the intraplate and intercontinental rift. 2 ) Indosinian volcanics markedly vary in the distribution and composition and reflect transitional MORB and island are environments respectively. 3) Yanshanian volcanics consist predominantly of basalts, andesites, dacites and rhyolites and are characterized by calc- alkaline volcanic suite, indicating island arc setting. 4)Himalayan volcanics are complicated and associated with intraplate orogency. The volcanism provides important tectonic information for recognizing the evolution of Qiangtang Basin.

  8. Photograph of the month (United States)


    Dykes in the Bidkhan strato-volcano located in the south eastern part of the Urumieh - Dokhtar magmatic arc, south west of Kerman, Iran. Repetitive dykes intrude through Oligo-Miocene Bidkhan pyroclastic sediments. A light dacitic dyke grew syntaxially within a gray andesitic dyke. The dykes trend NE and cross Oligo- Miocene lahar and pyroclastic sediments of the south west part of Bidkhan volcano caldera. Width of view appr. 10m. South of Bardsir city, SW Kerman, Iran. 29° 33.267≠ N, 056°, 27.25≠ E. Photograph © Reihaneh Keihanizadeh, Kerman, Iran. (

  9. Petrology, mineral chemistry and tectono-magmatic setting of volcanic rocks from northeast Farmahin, north of Arak

    Directory of Open Access Journals (Sweden)

    Reza Zarei Sahamieh


    Full Text Available Introduction The study area is a small part of the Urumieh-Dokhtar structural zone in the Markazi province, located in the northeastern part of the Farmahin, north of Arak (Hajian, 1970. The volcanic rocks studied from the area include andesite, dacite, rhyodacite, ignimbrite and tuff of Middle to Late Eocene age (middle Lutetian to upper Lutetian (Ameri et al., 2009. It seems that folding and faulting is caused in sedimentary basin and volcanic activities. On the other hand, except of orogeny maybe rifting had rule in eruption so that this case has seen in the other area such as Taft and Khezrabad in central Iran (Zarei Sahamieh et al., 2008. The oldest formation in the studied area is Triassic limestones. The dominant textures of these rocks are porphyritic, microlite porphyritic, microlitic and rarely sieve-texture. Sieve texture and dusty texture (dusty plagioclases indicates magma mixing. Mineralogically, they contain plagioclases, clinopyroxenes, amphiboles, quartz and biotite as the main constituents and zircon, apatite, and opaque minerals as accessories. Plagioclases in the andesitic and basaltic- andesite rocks are labradorite, bytownite and anorthite (based on electron microprobe .Moreover, plagioclases in andesitic rocks show that H2O is lesser than 2.5 precent. Amphibole is found in both plagioclases and groundmass. Materials and methods In this article are used different analyses methods such as XRF, ICP-MS and EPMA. Whole-rock major and trace element analyses were determined with ICP-MS method. The major and trace element composition of some rock was determined by electron probe micro-analysis (EPMA using a Cameca SX100 instrument in Iran Mineral Processing Research Center (IMPRC. Moreover, whole-rock major and some trace element analyses for some samples were obtained by X-ray fluorescence (XRF, using an ARL Advant-XP automated X-ray spectrometer. Results Chemical data based on electron micro probe studies of minerals indicate

  10. SCB試験による水蒸気環境下における岩石の破壊靱性の評価


    尾原, 祐三; 佐々木, 一裕; 吉永, 徹; オバラ, ユウゾウ; ササキ, カズヒロ; ヨシナガ, トオル; Obara, Yuzo; Sasaki, Kazuhiro; Yoshinaga, Toru


    The influence of water vapor pressure of surrounding environment on fracture toughness of rock is clarified, based on the results of a series of semi-circular bend (SCB) test under various water vapor pressures. The rocks used in the test are Kumamoto andesite and Kunnum basalt, and the range of water vapor pressure is from 10-3 to 103 Pa. The results obtained in this paper are summarized as follows:1) Elastic modulus at 60% of maximum load depends on water vapor pressure, and decreases with ...

  11. Update of map the volcanic hazard in the Ceboruco volcano, Nayarit, Mexico (United States)

    Suarez-Plascencia, C.; Camarena-Garcia, M. A.; Nunez-Cornu, F. J.


    The Ceboruco Volcano (21° 7.688 N, 104° 30.773 W) is located in the northwestern part of the Tepic-Zacoalco graben. Its volcanic activity can be divided in four eruptive cycles differentiated by their VEI and chemical variations as well. As a result of andesitic effusive activity, the "paleo-Ceboruco" edifice was constructed during the first cycle. The end of this cycle is defined by a plinian eruption (VEI between 3 and 4) which occurred some 1020 years ago and formed the external caldera. During the second cycle an andesitic dome built up in the interior of the caldera. The dome collapsed and formed the internal caldera. The third cycle is represented by andesitic lava flows which partially cover the northern and south-southwestern part of the edifice. The last cycle is represented by the andesitic lava flows of the nineteenth century located in the southwestern flank of the volcano. Actually, moderate fumarolic activity occurs in the upper part of the volcano showing temperatures ranging between 20° and 120°C. Some volcanic high frequency tremors have also been registered near the edifice. Shows the updating of the volcanic hazard maps published in 1998, where we identify with SPOT satellite imagery and Google Earth, change in the land use on the slope of volcano, the expansion of the agricultural frontier on the east sides of the Ceboruco volcano. The population inhabiting the area is 70,224 people in 2010, concentrated in 107 localities and growing at an annual rate of 0.37%, also the region that has shown an increased in the vulnerability for the development of economic activities, supported by highway, high road, railroad, and the construction of new highway to Puerto Vallarta, which is built in the southeast sector of the volcano and electrical infrastructure that connect the Cajon and Yesca Dams to Guadalajara city. The most important economic activity in the area is agriculture, with crops of sugar cane (Saccharum officinarum), corn, and jamaica

  12. Subsurface geology of Los Humeros geothermal field, Puebla, Mexico; Geologia del subsuelo del campo geotermico de Los Humeros, Puebla, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Cedillo Rodriguez, Fidel [Comision federal de Electricidad, Perote, Veracruz, Mexico(Mexico)


    In the 1980s, most geologists correlated subsurface geology at Los Humeros geothermal field using penetrated by faults, as interpreted by photogeology. These were structural objectives for geothermal drilling programs. Recent petrology reinterpretation of data from well cutting lets us identify nine lithologic units, with the Toba Vitrea Humeros as the index horizon. The study of the subsurface geology allows us to demonstrate- based on the distribution, depth, and thickness of the lithologic units- that the augite andesites, the Toba Vitrea Humeros, the hornblende andesites, the basalt, and the metamorphosed limestone are affected by system of hidden faults (with no surface evidence) replaced by major fracture zones able to contain steam. Thus these hidden faults are the structural objectives controlling design and sitting of new wells. We conclude that the lithologic unit of augite andesites forms the upper geothermal reservoir, and the hornblende andesites and basalt comprise the lower reservoir- separated from each other by the Toba Vitrea Humeros lithologic unit. Based on the subsurface geologic model, we propose drilling 40 new wells, a long and parallel the north-south faults system. [Spanish] En la decada de los 80s se agrupo la geologia del subsuelo de Los Humeros en cuatro unidades litologicas afectadas por fallas interpretadas por fotogeologia. Estas fallas eran el objetivo estructural para programar la perforacion de pozos geotermicos. La reinterpretacion de los datos de petrologia de las muestras de canal permite identificar nueve unidades litologicas, de las cuales la unidad Toba Vietrea Humeros se comporta como horizonte indice. El estudio de la geologia del subsuelo permite demostrar, con base en la distribucion, profundidades y espesores de las unidades litologicas, que las andesitas de augita, la Toba Vitrea Humeros, las andesitas de hornblenda, los basaltos, y las calizasmetamorfizadas estan afectadas por sistemas de fallas ocultas (sin


    Directory of Open Access Journals (Sweden)

    Sz. Fischer


    Full Text Available Purpose. Using adequate granular materials and layer structures in the railway super- and substructure is able to stabilise railway track geometry. For this purpose special behaviour of above materials has to be determined, e.g. inner shear resistance. Inner shear resistance of granular media with and without geogrid reinforcement in different depths is not known yet. Methodology. The author developed a special laboratory method to measure and define inner shear resistance of granular materials, it is called «multi-level shear box test». This method is adequate to determine inner shear resistance (pushing force vs. depth (distance from the «zero» surface. Two different granular materials: andesite railway ballast (31.5/63 mm and andesite railway protection layer material (0/56 mm, and seven different types of geogrids (GG1…GG7 were used during the tests. Findings. Values of inner shear resistance functions of andesite railway ballast without geogrid reinforcement and reinforced with different types of geogrids and andesite granular protection layer in function of the vertical distance from the geogrid plane were determined with multi-layer shear box tests when the material aggregation is uncompacted and compacted. Only the compacted sample was tested in case of the 0/56 mm protection layer. Cubic polynomial regression functions fitted on the mean values of the measurements are described graphically. Determination coefficients with values of R2>0.97 were resulted in all the cases of regression functions. Based on the polynomial regression functions fitted on the mean values of the test results, three increasing factors were determined in function of the distance measured from the geogrid. Increasing factor «A», «B» and «D». Originality. Multi-level shear box test, developed by the author, is certified unequivocally adequate for determining inner shear resistance of reinforced and unreinforced granular materials, e.g. railway ballast

  14. Geochemical and Sr-Nd-Pb Isotopic Insights of the Low-Ti basalts from Paraná-Etendeka Igneous Province, Southern Brazil: Constraints on Petrogenesis and the Role of Crustal Contamination (United States)

    Raposo, I.; Barreto, C. J.; Lima, E. F. D.; Lafon, J. M.; Sommer, C. A.; Waichel, B. L.


    The south hinge of the Torres Syncline in southernmost Brazil hosts a volcanic succession of pahoehoe and rubbly Gramado-type lavas belonging to the ~132 Ma Paraná-Etendeka Igneous Province. We employ local-scale stratigraphy in three distinct profiles (Santa Cruz do Sul-Herveiras, Morro da Cruz and Lajeado geologic sections) as guidelines for geochemical and Sr-Nd-Pb isotope studies in order to discuss the petrogenesis of lava flows in a single magma type and to quantitatively evaluate the role of crustal contamination and the potential contaminants involved. In all profiles, the lava flows exhibit compositions ranging from basalt to andesite with tholeiitic affinity. The compositional and isotopic variations are not systematic according to stratigraphy, implying that the magma chamber could have undergone periodic replenishments or distinct magma pulses through time or multiple plumbling systems may have existed. The andesites (SiO2 55-58 wt.%) with ponded pahoehoe morphology represent evolved melts at early stages of volcanism with strong susceptibility to crustal contamination as they established pathways to the surface. The olivine basalts (SiO2 47-50 wt.%) and basaltic andesites (SiO2 51-56 wt.%) showing compound morphology and simple pahoehoe morphology, respectively, could be explained by longer time residence of liquids in the crust with higher degrees of crustal assimilation than the ponded pahoehoe lavas. The basaltic andesites (SiO2 52-56 wt. %) with rubbly morphology are related to late differentiation process in shallow magma chambers. Crustal assimilation process accounts for the high initial 87Sr/86Sr ratios at 0.707798-0.715751, very low ɛNd between -8.36 and -5.41, high 206Pb/204Pb ratios at 18.424-18.865, with intermediate 207Pb/204Pb and 208Pb/204Pb ratios at 15.649-15.710 and 38.618-39.369, respectively. The isotopic variations require assimilation of both Paleoproterozoic and Neoproterozoic contaminants at variable degrees.

  15. Magmas and their sources: A special issue honoring Frederick A. Frey (United States)

    Garcia, Michael O.; Rhodes, J. Michael; Huang, Shichun; Hickey-Vargas, Rosemary


    This special issue is dedicated to Frederick A. Frey (Fig. 1), a pioneer in the use of trace element geochemistry (especially the rare-earth elements, REE) to interpret the origin and evolution of basalts and andesites, peridotites, granites, meteorites, tektites and even sediments. Fred's remarkable career spans more than 5 decades starting in 1964 with his seminal paper with advisor Larry Haskin entitled "rare earths in oceanic basalts" (Frey and Haskin, 1964). Given that Fred was an Associate Editor of Geochimica et Cosmochimica Acta (GCA) for 20 years, GCA is a highly appropriate venue for this collection of twenty-seven new scientific papers in his honor.

  16. 40Ar/39Ar geochronology and geochemical reconnaissance of the Eocene Lowland Creek volcanic field, west-central Montana (United States)

    Dudas, F.O.; Ispolatov, V.O.; Harlan, S.S.; Snee, L.W.


    We report geochronological and geochemical data for the calc-alkalic Lowland Creek volcanic field (LCVF) in westcentral Montana. 40Ar/ 39Ar age determinations show that the LCVF was active from 52.9 to 48.6 Ma, with tuff-forming eruptions at 52.9 ?? 0.14 and 51.8 ?? 0.14 Ma. These dates span the age range of vigorous Eocene igneous activity in the Kamloops-Absaroka-Challis belt. The LCVF evolved upward from basal rhyolites (SiO 2>71 wt%) to dacites and andesites (SiO 2 > 62 wt%). Compositional change parallels a transition from early explosive volcanism to late effusive activity. Four geochemical components can be detected in the rocks. A component with 206Pb/204Pb 18.3 and epsilon;Nd>-9 contain a third component; and an andesite with low Nd content and epsilon;Nd near-9 probably contains a fourth component. The first three components probably derive from the lower and middle crust, whereas the fourth is probably from the lithospheric mantle. ?? 2010 by The University of Chicago.

  17. Multivariate Analysis, Mass Balance Techniques, and Statistical Tests as Tools in Igneous Petrology: Application to the Sierra de las Cruces Volcanic Range (Mexican Volcanic Belt) (United States)

    Velasco-Tapia, Fernando


    Magmatic processes have usually been identified and evaluated using qualitative or semiquantitative geochemical or isotopic tools based on a restricted number of variables. However, a more complete and quantitative view could be reached applying multivariate analysis, mass balance techniques, and statistical tests. As an example, in this work a statistical and quantitative scheme is applied to analyze the geochemical features for the Sierra de las Cruces (SC) volcanic range (Mexican Volcanic Belt). In this locality, the volcanic activity (3.7 to 0.5 Ma) was dominantly dacitic, but the presence of spheroidal andesitic enclaves and/or diverse disequilibrium features in majority of lavas confirms the operation of magma mixing/mingling. New discriminant-function-based multidimensional diagrams were used to discriminate tectonic setting. Statistical tests of discordancy and significance were applied to evaluate the influence of the subducting Cocos plate, which seems to be rather negligible for the SC magmas in relation to several major and trace elements. A cluster analysis following Ward's linkage rule was carried out to classify the SC volcanic rocks geochemical groups. Finally, two mass-balance schemes were applied for the quantitative evaluation of the proportion of the end-member components (dacitic and andesitic magmas) in the comingled lavas (binary mixtures). PMID:24737994

  18. Tectonic setting of Late Cenozoic gold mineralization in the gold belt of Costa Rica

    Energy Technology Data Exchange (ETDEWEB)

    Deruyter, V.D.


    The Gold Belt of Costa Rica is a northwest-elongated zone 15 km wide by 120 km long containing numerous auriferous quartz veins and pyritic silicified patterns upon which abundant small mines are developed. Gold veins are related principally to northeast-southwest and north-south striking, steeply dipping faults. Higher grade ore and thicker veins invariably occur at intersections of these fracture orientations, indicating simultaneous opening at the time of gold introduction. Restriction of gold veins to the northwest-trending arc of Miocene Aguacate Group andesite volcanic rocks, a product of Cocos Plate subduction, suggested approximately coeval formation, but recognition by the writer of the important role played by 2-5 m.y. old altered, gold mineralized rhyolite dikes intruded along north-south gold vein structures and intimately involved with high grade ores at the Esperanza Mine and Rio Chiquito prospect, for example, suggest a much younger period of fracturing and gold introduction. The rhyolite intrusions are more brittle and stockwork mineralized than andesite host rocks and form bulk tonnage gold targets. Initiation of right-lateral movement along the north-south Panama Fracture Zone at 5 m.y.a. within the pattern of northeastward Cocos Plate subduction may have tapped rhyolites from subvolcanic magma chambers into new faults.

  19. Geochemistry, geochronology and structural geology of the Birimian formations of the Katiola-Marabadiassa region (north-center of Ivory Coast). Magmatic evolution and geodynamical context of palaeo-Proterozoic

    International Nuclear Information System (INIS)

    Birimian (palaeo-Proterozoic) formations from western Africa are known from being of juvenile origin and dated of 2.1 Ga. However, few studies have been carried out so far on the nature, petrogenesis, and tectonic-metamorphic evolution of these formations, and the geodynamical evolution of the Birimian crust remains an open question. The Katiola-Marabadiassa region offers a clear litho-stratigraphy where the main units and their structural relationships can be recognized (green rocks, andesites, granitoids, sediments). Two generations of granitoids separated by the opening of a sedimentary basin are identified thanks to the petrographic, geochemical, geochronological and structural data. The first, of Archean type, is dated at 2123-2108 Ma and cuts the green rock belts in a diapiric way. The second, dated at about 2097 Ma comprises leucogranite batholites which cut the discordant overlying sedimentary formations. Thus, 3 volcanism phases can be recognized: a T-MORB type tholeiitic volcanism (the green rock belts), a rhyodacitic calc-alkaline volcanism with granitoid plutons, and an andesitic volcanism interstratified with the basin sediments. The general metamorphism is of green-schist facies. An intermediate model between the archaic Archean processes and the modern collision processes is proposed for the formation of the Birimian crust. (J.S.)

  20. The off-crust origin of granite batholiths

    Institute of Scientific and Technical Information of China (English)

    Antonio Castro


    Granitod batholiths of I-type features (mostly granodiorites and tonalites), and particularly those forming the large plutonic associations of active continental margins and intracontinental collisional belts, represent the most outstanding magmatic episodes occurred in the continental crust. The origin of magmas, however, remains controversial. The application of principles from phase equilibria is crucial to understand the problem of granitoid magma generation. An adequate comparison between rock com-positions and experimental liquids has been addressed by using a projected compositional space in the plane F(Fe þ Mg)eAnorthiteeOrthoclase. Many calc-alkaline granitoid trends can be considered cotectic liquids. Assimilation of country rocks and other not-cotectic processes are identified in the projected diagram. The identification of cotectic patterns in batholith implies high temperatures of magma segregation and fractionation (or partial melting) from an intermediate (andesitic) source. The com-parison of batholiths with lower crust granulites, in terms of major-element geochemistry, yields that both represent liquids and solid residues respectively from a common andesitic system. This is compatible with magmas being formed by melting, and eventual reaction with the peridotite mantle, of subducted mélanges that are finally relaminated as magmas to the lower crust. Thus, the off-crust generation of granitoids batholiths constitutes a new paradigm in which important geological implica-tions can be satisfactorily explained. Geochemical features of Cordilleran-type batholiths are totally compatible with this new conception.

  1. Multivariate analysis, mass balance techniques, and statistical tests as tools in igneous petrology: application to the Sierra de las Cruces volcanic range (Mexican Volcanic Belt). (United States)

    Velasco-Tapia, Fernando


    Magmatic processes have usually been identified and evaluated using qualitative or semiquantitative geochemical or isotopic tools based on a restricted number of variables. However, a more complete and quantitative view could be reached applying multivariate analysis, mass balance techniques, and statistical tests. As an example, in this work a statistical and quantitative scheme is applied to analyze the geochemical features for the Sierra de las Cruces (SC) volcanic range (Mexican Volcanic Belt). In this locality, the volcanic activity (3.7 to 0.5 Ma) was dominantly dacitic, but the presence of spheroidal andesitic enclaves and/or diverse disequilibrium features in majority of lavas confirms the operation of magma mixing/mingling. New discriminant-function-based multidimensional diagrams were used to discriminate tectonic setting. Statistical tests of discordancy and significance were applied to evaluate the influence of the subducting Cocos plate, which seems to be rather negligible for the SC magmas in relation to several major and trace elements. A cluster analysis following Ward's linkage rule was carried out to classify the SC volcanic rocks geochemical groups. Finally, two mass-balance schemes were applied for the quantitative evaluation of the proportion of the end-member components (dacitic and andesitic magmas) in the comingled lavas (binary mixtures). PMID:24737994

  2. Triassic alluvial braidplain and braided river deposits of the La Ternera Formation, Atacama region, northern Chile (United States)

    Bell, C. M.; Suárez, M.


    The La Ternera Formation is a thick (>2,100 m) succession of terrigenous clastic sediments, with andesitic and basaltic intercalations, exposed in the Quebrada de Paipote area of the Atacama Region, northern Chile. The strata were deposited in an active rift basin during Late Triassic to (?) Early Jurassic times. The lower 1,000 m of the studied elastic succession comprises pebbly granule paraconglomerates, unconformably overlying Upper Paleozoic sedimentary successions, volcanics, and granitoids. These sediments were derived from the east and are interpreted as braid-plain deposits. The upper 800 m of the succession comprises interbedded orthoconglomerates, sandstones and mudstones. Abundant plant fossils include trees in growth position and carbonaceous horizons. Small scale depositional cycles were the product of migrating braided-river channel systems. Larger scale successions resulted from tectonic uplift. The sediments of the La Ternera Formation were derived predominantly from a tectonically uplifted area of Upper Paleozoic acidic volcanic and plutonic rocks (Pantanoso Formation, Choiyoi Group). Active uplift on the eastern margin of the sedimentary basin probably occurred along north-south trending faults. Continued subsidence of the basin resulted in a Sinemurian to Bajocian marine transgression. Occurrences of Triassic andesitic and basaltic volcanic rocks both to the west and the east of the La Ternera formation suggest deposition in an intea-volcanic graben or half-graben.

  3. Characterization and zircon SHRIMP U-Pb geochronology of the subvolcanic rocks from Yarumalito Porphyry System, Marmato District, Colombia; Caracterizacao e geocronologia SHRIMP U-Pb em zircao das rochas subvulcanicas do sistema porfiro Yarumalito, Distrito de Marmato, Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Henrichs, Isadora A.; Frantz, Jose Carlos; Marques, Juliana C.; Castoldi, Marco S., E-mail:, E-mail:, E-mail: [Universidade Federal do Rio Grande do Sul (UFRS), Porto Alegre, RS (Brazil). Instituto de Geociencias; Ordonez-Carmona, Oswaldo, E-mail: [Universidad Nacional de Colombia, Medellin (Colombia). Facultad de Minas; Sato, Kei, E-mail: [Universidade de Sao Paulo (USP), Sao Paulo, SP (Brazil). Centro de Pesquisas Geocronologicas


    The mining District of Marmato, located in the Central Cordillera, is considered one of the oldest gold districts in Colombia and its exploration dates back to the Inca’s times, being exploited regularly for more than a thousand years. Inserted in this context lies the Yarumalito porphyry system (YPS), characterized to concentrate ore in structure related veins and stockworks. The YPS is related to the Miocene magmatism of the Combia Formation. In this paper, the subvolcanic rocks directly associated with the mineralized zones were described in order to obtain U-Pb ages in zircon to the intrusions. Selected samples from two fertile intrusions, one andesitic (more abundant in the area) and other dioritic (more restricted), were carefully described and dated by SHRIMP. The results points to a very restricted interval for the ages, with weighted average {sup 206}Pb/{sup 238}U varying from 7,00 ± 0,15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results constrain the Yarumalito system to the final stages of the Combia magmatism and suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and in the Marmato District. (author)

  4. Rb–Sr and Sm–Nd isotope systematics and geochemical studies on metavolcanic rocks from Peddavura greenstone belt: Evidence for presence of Mesoarchean continental crust in easternmost part of Dharwar Craton, India

    Indian Academy of Sciences (India)

    M Rajamanickam; S Balakrishnan; R Bhutani


    Linear, north–south trending Peddavura greenstone belt occurs in easternmost part of the Dharwar Craton. It consists of pillowed basalts, basaltic andesites, andesites (BBA) and rhyolites interlayered with ferruginous chert that were formed under submarine condition. Rhyolites were divided into type-I and II based on their REE abundances and HREE fractionation. Rb–Sr and Sm–Nd isotope studies were carried out on the rock types to understand the evolution of the Dharwar Craton. Due to source heterogeneity Sm–Nd isotope system has not yielded any precise age. Rb–Sr whole-rock isochron age of 2551 ± 19 (MSWD = 1.16) Ma for BBA group could represent time of seafloor metamorphism after the formation of basaltic rocks. Magmas representing BBA group of samples do not show evidence for crustal contamination while magmas representing type-II rhyolites had undergone variable extents of assimilation of Mesoarchean continental crust (< 3.3 Ga) as evident from their initial Nd isotope values. Trace element and Nd isotope characteristics of type I rhyolites are consistent with model of generation of their magmas by partial melting of mixed sources consisting of basalt and oceanic sediments with continental crustal components. Thus this study shows evidence for presence of Mesoarchean continental crust in Peddavura area in eastern part of Dharwar Craton.

  5. Early formation of evolved asteroidal crust. (United States)

    Day, James M D; Ash, Richard D; Liu, Yang; Bellucci, Jeremy J; Rumble, Douglas; McDonough, William F; Walker, Richard J; Taylor, Lawrence A


    Mechanisms for the formation of crust on planetary bodies remain poorly understood. It is generally accepted that Earth's andesitic continental crust is the product of plate tectonics, whereas the Moon acquired its feldspar-rich crust by way of plagioclase flotation in a magma ocean. Basaltic meteorites provide evidence that, like the terrestrial planets, some asteroids generated crust and underwent large-scale differentiation processes. Until now, however, no evolved felsic asteroidal crust has been sampled or observed. Here we report age and compositional data for the newly discovered, paired and differentiated meteorites Graves Nunatak (GRA) 06128 and GRA 06129. These meteorites are feldspar-rich, with andesite bulk compositions. Their age of 4.52 +/- 0.06 Gyr demonstrates formation early in Solar System history. The isotopic and elemental compositions, degree of metamorphic re-equilibration and sulphide-rich nature of the meteorites are most consistent with an origin as partial melts from a volatile-rich, oxidized asteroid. GRA 06128 and 06129 are the result of a newly recognized style of evolved crust formation, bearing witness to incomplete differentiation of their parent asteroid and to previously unrecognized diversity of early-formed materials in the Solar System. PMID:19129845

  6. Eclogite-melt/peridotite reaction: Experimental constrains on the destruction mechanism of the North China Craton

    Institute of Scientific and Technical Information of China (English)


    To study the mechanism of melt-peridotite reaction pertinent to the destruction of the North China Craton (NCC) lithosphere, a series of experiments were performed at a pressure of 2.0 GPa and temperatures from 1250 to 1400°C using Bixiling eclogite and Damaping peridotite as starting materials. The experimental results show that the reaction between eclogite melt and peridotite causes dissolution of olivine and orthopyroxene and precipitation of clinopyroxene in the melt. The experimental run products, characterized by a lherzolite/pyroxenite/garnet-pyroxenite sequence, are consistent with the mantle xenoliths in the Neogene Hannuoba basalt of the NCC found by Liu et al. (2005). It suggests that the mafic lower continental crust was probably recycled into the mantle during the Mesozoic Era. In the experiments conducted at 1300 and 1350°C, the resulting melts have a high Mg# andesite signature, indicating that the melt-peridotite reaction may have played a major role in the generation of high Mg# andesite. Our experimental results support the hypothesis that melts derived from foundered eclogite in the asthenosphere will consume the lithospheric peridotites. Therefore, melt-peridotite reaction is an important mechanism for the destruction/thinning of the lithosphere.

  7. Unmasking Sinkings Zones Caused by Subsidence-Creep Processes in Morelia, MICHOACÁN, Using Insar and GIS (United States)

    Alejandro, Avila-Olivera Jorge; Paolo, Farina; Hugo, Garduño-Monroy Victor


    In Morelia City since the beginning of the 1980s, problems of differential sinkings, crackings and superficial faults affecting natural and anthropogenic structures have been observed. At the present time the city is being affected by nine faults, eight of which are related to Subsidence-Creep-Fault Processes (SCFP) and display a preferential direction ENE-WSW, identical to the Tula-Chapala regional faulting system. As part of the SCFP studies, GDPS and InSAR monitoring have been carried out; both showed that the maximum sinkings (3. 5 cm/year, summer 2003-summer 2007) are located in the NW part of the city, considered stable (in the past) due to the coverage of Pleistocene-Holocene basaltic-andesitic materials of Quinceo volcano. In order to resolve the enigma, all the available information related to the SCFP in the city have been integrated in a GIS; as well as two analysis of lithology columns were carried out to obtain a surface of the spatial distribution of the thickness of compressible materials in the city. The first analysis just increased the doubts, but the second one showed that the subsoil in the NW portion of Morelia consists of an interleave between basaltic-andesitic products of Quinceo volcano and lacustrine and/or fluviolacustrine sediments able to suffer deformations induced by groundwater withdrawal, which have been masked by the superficial volcanic products, that in addition are responsible of accelerating the process of land subsidence (sinkings) in function of weight these represent.

  8. Mineralogy and geochemistry of xenoliths in the Eocene volcanic rocks from southwest of Jandaq

    Directory of Open Access Journals (Sweden)

    Samineh Rajabi


    Full Text Available The Eocene volcanic rocks from the southwest of the Jandaq (Kuh-e-Godar-e-Siah, Central-East Iran micro-continent are andesitic basalt and andesite in composition. These rocks contain xenoliths with granulitic mineralogy. Mineral assemblage of these xenoliths is plagioclase + phlogopite + corundum + sillimanite + chlorite + phengite with granublastic, poiklioblastic and foliated textures in the pick metamorphic condition. Thermometry of phlogopite in these xenoliths suggests the average temperature 782oC. The characteristics of the xenoliths are consistent with the granolitic facies metamorphism of the Al-saturated Si-undersaturated crustal sediments at the lower crust condition. Melting of these granulites forms the magma which crystallized the S-type granitoids. Differentiation and crystallization of this magma causes the S-type granite formation. Therefore, the S-type granites in the study area are probably generated from melting of the granulites parts of which brought to the surface as xenoliths by Eocene magmatism in south of the Jandaq (Kuh-e-Godar-e-Siah. S-type granites in the study area are located along the Doruneh, Chupanan and Aeirakan faults in the Aeirakan area and Jandaq ophiolite. These granites are the source of uranium, thorium and uranium ore in southwest of the Aeirakan mountain.

  9. The compositionally zoned eruption of 1912 in the Valley of Ten Thousand Smokes, Katmai National Park, Alaska (United States)

    Hildreth, Wes


    On June 6-8, 1912, ˜ 15 km 3 of magma erupted from the Novarupta caldera at the head of the Valley of Ten Thousand Smokes (VTTS), producing ˜ 20 km 3 of air-fall tephra and 11-15 km 3 of ash-flow tuff within ˜ 60 hours. Three discrete periods of ash-fall at Kodiak correlate, respectively, with Plinian tephra layers designated A, CD, and FG by Curtis (1968) in the VTTS. The ash-flow sequence overlapped with but outlasted pumice fall A, terminating within 20 hours of the initial outbreak and prior to pumice fall C. Layers E and H consist mostly of vitric dust that settled during lulls, and Layer B is the feather edge of the ash flow. The fall units filled and obscured the caldera, but arcuate and radial fissures outline a 6-km 2 depression. The Novarupta lava dome and its ejecta ring were emplaced later within the depression. At Mt. Katmai, 10 km east of the 1912 vent, a 600-m-deep caldera of similar area also collapsed at about this time, probably owing to hydraulic connection with the venting magma system; but all known ejecta are thought to have erupted at Novarupta. Mingling of three distinctive magmas during the eruption produced an abundance of banded pumice, and mechanical mixing of chilled ejecta resulted in deposits with a wide range of bulk composition. Pumice in the initial fall unit (A) is 100% rhyolite, but fall units atop the ash flow are > 98% dacite; black andesitic scoria is common only in the ash flows and in near-vent air-fall tephra. Pumice counts show the first half of the ash-flow deposit to be 91-98% rhyolite, but progressive increases of dacite and andesite eventually reduced the rhyolitic component to welded tuff and vapor-indurated sillar. The main ash flow was too deflated and sluggish 16 km from the vent to surmount a 25-m-high moraine in its path but was diverted around it and continued 5 km down-valley, engulfing and charring trees but not toppling all of them. Thin ash-flow veneers feather 30-40 m up the enclosing valley walls

  10. Geochemistry and geochronology of late Mesozoic volcanic rocks in the northern part of the Eastern Pontide Orogenic Belt (NE Turkey): Implications for the closure of the Neo-Tethys Ocean (United States)

    Özdamar, Şenel


    This paper presents 40Ar/39Ar and U-Pb age data, Sr-Nd isotopes, whole-rock and mineral compositions of Upper Cretaceous volcanic rocks from the Ordu area of the Eastern Pontide Orogenic Belt (EPOB) in northeastern Turkey. The volcanic rocks exhibit a wide compositional range: basalt, basaltic-andesites, andesites and a rhyodacite suite; they are characterized by subparallel light rare earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with Eu anomalies and moderate fractionation [average (La/Yb)N = 8.55]. The geochemical results show that the volcanic rocks have calc-alkaline affinity consistent with arc volcanic rocks erupted in an active continental margin. Initial 87Sr/86Sr values vary between 0.70569 and 0.70606, while initial 143Nd/144Nd values lie between 0.51244 and 0.51249. Crustal contamination affected the mantle-originated primary magma, as indicated by increased 87Sr/86Sr and decreased 143Nd/144Nd ratios with increasing SiO2. New precise laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) 206Pb-238U age analyses of zircon and 40Ar/39Ar age data of plagioclase from the volcanics enable a more precise reconstruction of the EBOP. The ages provide insight into the timing of arc formation in this region, constrain the volcanic activity between 86 My (Coniacian) and 75 My (Campanian) and constrain the timing of closure of the Neo-Tethys.

  11. K-Ar dating of lavas from Zao volcano, North-eastern Japan

    International Nuclear Information System (INIS)

    The K-Ar age was determined for the lava samples collected in North Zao, Central Zao and South Zao Volcanoes, and compared with the volcano stratigraphy and rock magnetism. Except a few cases, the K-Ar age was compatible with the stratigraphic and magnetic data. From the K-Ar age and geological data, the growth history of the Zao Volcano group was deduced as follows. In Central Zao Volcano, the first stage of volcanism started about 1 Ma ago. In the second stage of activity, there were many lava flows distinguished both in the K-Ar age ranging from 0.32 to 0.12 Ma and in the geological succession. The voluminous effusion of andesitic lavas in this stage formed most part of the volcanoes. This is in contrast to Ryuzan Volcano which was action from 0.94 to 1.13 Ma ago, accompanied by the effusion of tholeititic basalt and andesite lavas, and has been dormant since then. The age of 0.01 Ma of Furikosawa lava indicates that the third stage of volcanism involved a lava flow. The K-Ar age which was corrected for the mass fractionation was in agreement with the volcano stratigraphic data. The peak comparison method enables to measure the age and to check the mass fractionation by analyzing Ar with only one sample, and the error of determining radiogenic Ar in a young rock with large atomospheric Ar contamination is small. (Kako, I.)

  12. Eruptive parameters and dynamics of the April 2015 sub-Plinian eruptions of Calbuco volcano (southern Chile) (United States)

    Castruccio, Angelo; Clavero, Jorge; Segura, Andrea; Samaniego, Pablo; Roche, Olivier; Le Pennec, Jean-Luc; Droguett, Bárbara


    We conducted geological and petrological analyses of the tephra fallout and pyroclastic density current (PDC) products of the 22-23 April 2015 Calbuco eruptions. The eruptive cycle consisted of two sub-Plinian phases that generated > 15 km height columns and PDCs that travelled up to 6 km from the vent. The erupted volume is estimated at 0.38 km3 (non-DRE), with approximately 90% corresponding to tephra fall deposits and the other 10% to PDC deposits. The erupted products are basaltic-andesite, 54-55 wt.% SiO2, with minor amounts of andesite (58 wt.% SiO2). Despite the uniform composition of the products, there are at least four types of textures in juvenile clasts, with different degrees of vesicularity and types and content of crystals. We propose that the eruption triggering mechanism was either exsolution of volatiles due to crystallization, or a small intrusion into the base of the magma chamber, without significant magma mixing or with a magma compositionally similar to that of the residing magma. In either case the triggering mechanism generated convection and sufficient overpressure to promote the first eruptive phase. The start of the eruption decompressed the chamber, promoting intense vesiculation of the remaining magma and an increase in eruption rate towards the end of the eruption.

  13. The Ahuachapan geothermal field, El Salvador: Reservoir analysis

    Energy Technology Data Exchange (ETDEWEB)

    Aunzo, Z.; Bodvarsson, G.S.; Laky, C.; Lippmann, M.J.; Steingrimsson, B.; Truesdell, A.H.; Witherspoon, P.A. (Lawrence Berkeley Lab., CA (USA); Icelandic National Energy Authority, Reykjavik (Iceland); Geological Survey, Menlo Park, CA (USA); Lawrence Berkeley Lab., CA (USA))


    The Earth Sciences Division of Lawrence Berkeley Laboratory (LBL) is conducting a reservoir evaluation study of the Ahuachapan geothermal field in El Salvador. This work is being performed in cooperation with the Comision Ejecutiva Hidroelectrica del Rio Lempa (CEL) and the Los Alamos National Laboratory (LANL). This report describes the work done during the first year of the study (FY 1988--89), and includes the (1) development of geological and conceptual models of the field, (2) evaluation of the initial thermodynamic and chemical conditions and their changes during exploitation, (3) evaluation of interference test data and the observed reservoir pressure decline, and (4) the development of a natural state model for the field. The geological model of the field indicates that there are seven (7) major and five (5) minor faults that control the fluid movement in the Ahuachapan area. Some of the faults act as a barrier to flow as indicated by large temperature declines towards the north and west. Other faults act as preferential pathways to flow. The Ahuachapan Andesites provide good horizontal permeability to flow and provide most of the fluids to the wells. The underlying Older Agglomerates also contribute to well production, but considerably less than the Andesites. 84 refs.

  14. New ages and chemical analysis on Lower Jurassic volcanism close to the dorsal de Huincul, Neuquén

    Directory of Open Access Journals (Sweden)

    Mario SCHIUMA


    Full Text Available New single zircon ages from hydrocarbon well cores in the A-1 Norte de la Dorsal and Anticlinal Campamento area of the Neuquén basin indicate that 199.0 ± 1.5 Ma andesite lava flow and 203.75 ± 0.26 Ma dacite breccia overlie a 286.5 ± 2.3 Ma granodiorite and 284.0 ± 1.3 Ma andesite dike. The Lower Jurassic volcanics were deposited on a regional erosion surface affecting the Permian rocks. In the studied area there is no record of Middle to Upper Triassic volcanics as in other areas of the basin. Exotic zircon crystals gave ages of Mesoproterozoic, Middle Cambian, Early Devonian and Early Carboniferous, suggesting a poliphasic basement. Chemical analyses of three selected samples show a calc-alkaline signature, supporting the existence of a volcanic arc at the Early Jurassic as it has been proposed for the center of the basin.

  15. Dyke Swarms of the Paraná Triple Junction, Southern Brazil

    Directory of Open Access Journals (Sweden)

    José Moacyr Vianna Coutinho


    Full Text Available This work intends primarily to survey the field, mineralogical and petrographic characters of the mafic dykes which occuron a stretch of 650 km along the Southeastern coast of Brazil, between the city of São Sebastião, and the island of SantaCatarina. New chemical and geochronological data are also presented. The coastal dyke swarms are envisaged as the northernand southern arms of a plume-generated triple junction system centered on the Paraná State coast, and related to the initialopening of the South Atlantic. Mafic magma intruded as dyke swarms along three directions: N-S (the southern arm, along theParaná-Santa Catarina coast, NW-SE (Ponta Grossa arch and NE-SW (the northern arm along the São Paulo coast. Fiftytwo dykes, almost all tholeiitic diabases, were mapped and sampled along the south arm coast. The Ponta Grossa arch dykes are chiefly composed of tholeiitic diabases and lesser intrusions of andesitic to rhyolitic composition. Over 240 dykes were sampled and identified along the north arm west of São Sebastião. Lamprophyres are here abundant, followed by diabases, microdiorite porphyries and lesser amounts of trachy-andesite, carbonatite and Precambrian dykes. Special attention was given to the study of lamprophyres, their field appearance relative abundance, mineral and chemical composition, enclaves and relations to neighboring alkaline intrusions.

  16. Gabbroic xenoliths in alkaline lavas in the region of Sanganguey Volcano, Nayarit, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Giosa, T.A.; Nelson, S.A.


    Gabbroic xenoliths occur in alkaline cinder cones and lava flows erupted from vents along five parallel lines trending through the calc-alkaline volcano, Sanganguey in the northwestern portion of the Mexican Volcanic Belt. The xenoliths consist of varying proportions of olivine, clinopyroxene, orthopyroxene, and plagioclase. The complete lack of hydrous phases indicates that the gabbros crystallized under conditions of low PH/sub 2/O. Many xenoliths show textures indicative of a cumulate origin and others exhibit recrystallization indicative of subsolidus reactions prior to incorporation in the host liquids. Reaction between xenolithic minerals and host liquids are also observed. The range of Mg numbers calculated for liquids that would have been in equilibrium with olivines in the xenoliths suggests that these olivines crystallized from magmas such as those represented by either calc-alkaline basaltic andesites and andesites or the more evolved alkalic rocks which occur throughout the area. Crystal fractionation models show that the xenoliths may be related to such magmas. The fact that xenoliths occur most commonly in the alkaline rocks suggests that alkaline magmas rise to the surface more rapidly than the more chemically evolved calc-alkaline and alkaline magmas. Alternatively the lack of xenoliths in the more evolved magmas produced by high level crystal fractionation may indicate that the xenoliths are derived from zones below that from which the differentiated magmas begin their final ascent to the surface.

  17. Thermophysical properties of the Lipari lavas (Southern Tyrrhenian Sea

    Directory of Open Access Journals (Sweden)

    D. Russo


    Full Text Available Results of thermophysical investigations into the lavas of the island of Lipari (Southern Tyrrhenian Sea are presented. Samples selected for laboratory measurements belong to four main magmatic cycles, which produced basaltic-andesitic, andesitic and rhyolitic lavas. The wet-bulk density and the thermal conductivity measured on 69 specimens range from 1900 to 2760 kg m-3 and from 1.02 to 2.88 W m-1 K-1, respectively. Porosity is never negligible and its influence on density is maximum in rhyolites of the third cycle. The thermal conductivity is also influenced by the amount of glass. Rhyolitic obsidians show values lower than other rhyolites, although the latter rocks have a larger average porosity. The radioactive heat production determined on 36 specimens varies with the rock type, depending on the amount of U, Th and K. In basic lavas of the first cycle its value is 0.95°± 0.30 mW m-3, while in rhyolites of the fourth cycle it attains 6.68°±0.61 mW m-3. A comparison between results of g-ray spectrometry and X-ray fluorescence points out that the assumption of equilibrium in the decay series of the isotopic elements seems fulfilled. The information obtained is useful not only for the interpretation of geophysical surveys but also for the understanding of the geochemical characteristics of lavas.

  18. Petrologi - geokimia batuan Gunung Api Tampomas dan sekitarnya

    Directory of Open Access Journals (Sweden)

    Mesker H. Dirk


    Full Text Available rocks of Mount Tampomas and its surroundings belong to low–K, calc–alkaline, and high–K series of basalt, basaltic andesite, and andesite suites containing 48.59 – 60.49 wt% of SiO and 0.31-1.67 wt% of K O. The rocks are typically formed in an island arc environment characterized by the high content of Al O (16.47 – 21.76 wt%, low to moderate content of MgO (2.37 – 8.84 wt%, low content of both titanium TiO (< 1 wt% and high field strength elements (HFSEs, negative anomaly of Nb relative to K and La. The light rare earth elements (LREEs enrichment but low abundances of heavy rare earth elements (HREEs indicate fractionation process. The parent magma was an extensive removal of olivine and clino-pyroxene, plagioclase, apatite, and titanoferrousmagnetite from a basalt olivine magma of N-MORB character that was firstly enriched by LILEs such as Ba, Rb, Th, K, and LREE (La. The differentiation lasted, and the magma became water undersaturated at the crystallization phase of hornblende. The high content of incompatible elements such as Ba, Th, La, Ce, may indicate contamination by liquid derived from the subducted slab.   

  19. Petrogenesis of subvolcanic rocks from the Khunik prospecting area, south of Birjand, Iran: Geochemical, Sr-Nd isotopic and U-Pb zircon constraints (United States)

    Samiee, Somayeh; Karimpour, Mohammad Hassan; Ghaderi, Majid; Haidarian Shahri, Mohammad Reza; Klöetzli, Urs; Santos, José Francisco


    The Khunik prospecting area is located 106 km south of Birjand in eastern Iran, and is considered as an epithermal gold prospecting area. The mineralization is related to subvolcanic rocks. There are several outcrops of subvolcanic intrusions in the area which intruded into Paleocene-Eocene volcanic rocks (andesite, trachy-andesite and pyroclastic rocks). Petrographic studies indicate that subvolcanic rocks consist mainly of diorite, monzonite, quartz-monzonite, monzodiorite and quartz-monzodiorite. Mineralogically, these rocks contain plagioclase, K-feldspar, amphibole, pyroxene, biotite and quartz. Geochemically, they have features typical of high-K calk-alkaline to shoshonitic and are metaluminous, and also belong to magnetite granitoid series (I-type). Primitive mantle normalized trace element spider diagrams display enrichment in LILE, such as Rb, Ba, and Cs, compared to HFSE. Chondrite-normalized REE plots show moderately LREE enriched patterns (7.45 magmatic activity in the area, with an age of 31 ± 1 Ma (early Oligocene). The represented dates are interpreted as magmatic crystallization ages of subvolcanic intrusions.

  20. Spatial variations in the frequency-magnitude distribution of earthquakes in the southwestern Okinawa Trough (United States)

    Lin, J.-Y.; Sibuet, J.-C.; Lee, C.-S.; Hsu, S.-K.; Klingelhoefer, F.


    The relations between the frequency of occurrence and the magnitude of earthquakes are established in the southern Okinawa Trough for 2823 relocated earthquakes recorded during a passive ocean bottom seismometer experiment. Three high b-values areas are identified: (1) for an area offshore of the Ilan Plain, south of the andesitic Kueishantao Island from a depth of 50 km to the surface, thereby confirming the subduction component of the island andesites; (2) for a body lying along the 123.3°E meridian at depths ranging from 0 to 50 km that may reflect the high temperature inflow rising up from a slab tear; (3) for a third cylindrical body about 15 km in diameter beneath the Cross Backarc Volcanic Trail, at depths ranging from 0 to 15 km. This anomaly might be related to the presence of a magma chamber at the base of the crust already evidenced by tomographic and geochemical results. The high b-values are generally linked to magmatic and geothermal activities, although most of the seismicity is linked to normal faulting processes in the southern Okinawa Trough.

  1. Radiogenic Heat Production in the Gölcük Caldera and Direkli, Isparta Angle (Southwest Anatolia) (United States)

    Ayten Uyanık, Nurten; Öncü, Ziya; Akkurt, İskender


    The radiogenic heat is one of the important parameter due to the radioactivity has existed since beginning of universe as prediction of Big-Bang theory. In this study the radiogenic heat production of the Gölcük caldera and Direkli fields of the Isparta-Turkey, has been investigated. Total of 1390 data were obtained in the study area. The study area is included of the Gölcük volcanism and its around that is located in Isparta province of Turkey's Mediterranean region. The Gölcük volcanism is a young volcanism. Around this volcanism the andesite, trachy andesite, tuff, pumice and such a geological units is available. The data were collected using in-situ measurements with gamm-ray spectrometer. These measurements were covered natural radioactive elements (Uranium U, Thorium Th and Potassium K). Radiogenic heat production values were calculated using the literature relationships and in-situ measurement values of these radioactive elements. Radiogenic heat map of study area were obtained using radiogenic heat production values. In the map the red zone areas shows highest heat values while green zones areas of the map presents lowest heat values. Key words: Radioactive elements, radiogenic heat, map, Gölcük-Direkli(Isparta), Turkey

  2. Geochemistry of the subduction-related magmatic rocks in the Dahong Mountains, northern Hubei Province--Constraint on the existence and subduction of the eastern Mianlüe oceanic basin

    Institute of Scientific and Technical Information of China (English)


    The existence and subduction of the eastern Mianlue oceanic basin in the south Qinling belt are keys to understand the Qinling orogen. Based on geological mapping, several volcanic slices have been identified in Tumen, Zhoujiawan, Xiaofu and Yuantan areas, which distribute in the northern margin of the Dahong Mountains (DHM), and thrust into the Sanligang-Sanyang fault. These slices consist mainly of diabases, basaltic-andesitic lavas, pyroclastic rocks and a minor tuff. The geochemistry of the basalts, andesites, and diabases is characterized by depleting in Nb and Ta, enriching in Th and LILE (e.g.K, Rb, Ba), and undifferentiating in HFSE. These geochemical characteristics suggest that the original magma of these rocks was derived from a mantle wedge above a subduction zone, and formed in an island-arc setting in Carboniferous-early Triassic. Comparing with the ophiolites and island-arc volcanic rocks in Mianxian-Lueyang area to the west, it is reasonable to consider that there had been an oceanic basin connecting with the Mianlue ancient ocean to the westward, distributing along the south edge of the Tongbai-Dabie block. In view of the ophiolite in Huashan area and these island-arc volcanic rocks along the north of the Dahong Mountains, it is suggested that there had been a plate tectonic evolutionary history with oceanic basin rifting and subduction in this region.

  3. Newly developed evidence for the original Tethysan island-arc volcanic rocks in the southern segment of the South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)


    This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.

  4. The Chahnaly low sulfidation epithermal gold deposit, western Makran volcanic arc, southeastern Iran (United States)

    Sholeh, Ali; Rastad, Ebrahim; Huston, David L.; Gemmell, J. Bruce; Taylor, Ryan D.


    The Chahnaly low-sulfidation epithermal Au deposit and nearby Au prospects are located northwest of the intermittently active Bazman stratovolcano on the western end of the Makran volcanic arc, which formed as the result of subduction of the remnant Neo-Tethyan oceanic crust beneath the Lut block. The arc hosts the Siah Jangal epithermal and Kharestan porphyry prospects, near Taftan volcano, as well as the Saindak Cu-Au porphyry deposit and world-class Reko Diq Cu-Au porphyry deposit, near Koh-i-Sultan volcano to the east-northeast in Pakistan. The host rocks for the Chahnaly deposit include early Miocene andesite and andesitic volcaniclastic rocks that are intruded by younger dacitic domes. Unaltered late Miocene dacitic ignimbrites overlie these rocks. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology data yield ages between 21.8 and 9.9 Ma for the acidic-intermediate regional volcanism. The most recent volcanic activity of the Bazman stratovolcano involved extrusion of an olivine basalt during Pliocene to Quaternary times. Interpretation of geochemical data indicate that the volcanic rocks are synsubduction and calc-alkaline to subalkaline. The lack of a significant negative Eu anomaly, a listric-shaped rare earth element pattern, and moderate La/Yb ratios of host suites indicate a high water content of the source magma.

  5. Geochemical Characteristics and Metallogenesis of Volcanic Rocks as Exemplified by Volcanic Rocks in Ertix,Xinjiang

    Institute of Scientific and Technical Information of China (English)

    刘铁庚; 叶霖


    Volcanic rocks in Ertix,Xinjiang,occurring in the collision zone between the Siberia Plate and the Junggar Plate,are distributed along the Eritix River Valley in northern Xinjiang.The volcanic rocks were dated at Late Paleozoic and can be divided into the spilite-keratophyre series and the basalt-andesite series.The spilite-keratophyre series volcanic rocks occur in the Altay orogenic belt at the southwest margin of the Siberia Plate.In addition to sodic volcanic rocks.There are also associated potassic-sodic volcanic rocks and potassic volcanic rocks.The potassic-sodic volcanic rocks occur at the bottom of the eruption cycle and control the distribution of Pb and Zn deposits.The potassic volcanic rocks occur at the top of the eruption cycle and are associated with Au and Cu mineralizations.The sodic volcanic rocks occur in the middle stage of eruption cycle and control the occurrence of Cu(Zn) deposits.The basalt-andesite series volcanic rocks distributed in the North Junggar orogenic belt at the north margin of the Junggar-Kazakstan Plate belong to the potassic sodic volcain rocks.The volcanic rocks distributed along the Ulungur fault are relatively rich in sodium and poor in potassium and are predominated by Cu mineralization and associated with Au mineralization.Those volcanic rocks distributed along the Ertix fault are relatively rich in K and poor in Na,with Au mineralization being dominant.

  6. Zircon U-Pb and molybdenite Re-Os dating of the Chalukou porphyry Mo deposit in the northern Great Xing'an Range, China and its geological significance (United States)

    Liu, Jun; Mao, Jingwen; Wu, Guang; Wang, Feng; Luo, Dafeng; Hu, Yanqing


    The newly discovered Chalukou giant porphyry Mo deposit, located in the northern Great Xing'an Range, is the biggest Mo deposit in northeast China. The Chalukou Mo deposit occurs in an intermediate-acid complex and Jurassic volcano-sedimentary rocks, of which granite porphyry, quartz porphyry, and fine-grained granite are closely associated with Mo mineralization. However, the ages of the igneous rocks and Mo mineralization are poorly constrained. In this paper, we report precise in situ LA-ICP-MS zircon U-Pb dates for the monzogranite, granite porphyry, quartz porphyry, fine grained granite, rhyolite porphyry, diorite porphyry, and andesite porphyry in the Chalukou deposit, corresponding with ages of 162 ± 2 Ma, 149 ± 5 Ma, 148 ± 2 Ma, 148 ± 1 Ma, 137 ± 3 Ma, 133 ± 2 Ma, and 132 ± 2 Ma, respectively. Analyses of six molybdenite samples yielded a Re-Os isochron age of 148 ± 1 Ma. These data indicate that the sequence of the magmatic activity in the Chalukou deposit ranges from Jurassic volcano-sedimentary rocks and monzogranite, through late Jurassic granite porphyry, quartz porphyry, and fine-grained granite, to early Cretaceous rhyolite porphyry, diorite porphyry, and andesite porphyry. The Chalukou porphyry Mo deposit was formed in the late Jurassic, and occurred in a transitional tectonic setting from compression to extension caused by subduction of the Paleo-Pacific oceanic plate.

  7. Geochemistry, geochronology and structural geology of the Birimian formations of the Katiola-Marabadiassa region (north-center of Ivory Coast). Magmatic evolution and geodynamical context of palaeo-Proterozoic; Geochimie, geochronologie et geologie structurale des formations birimiennes de la region de Katiola-Marabadiassa (centre-Nord de la Cote-d`Ivoire). Evolution magmatique et contexte geodynamique du paleoproterozoique

    Energy Technology Data Exchange (ETDEWEB)

    Doumbia, S


    Birimian (palaeo-Proterozoic) formations from western Africa are known from being of juvenile origin and dated of 2.1 Ga. However, few studies have been carried out so far on the nature, petrogenesis, and tectonic-metamorphic evolution of these formations, and the geodynamical evolution of the Birimian crust remains an open question. The Katiola-Marabadiassa region offers a clear litho-stratigraphy where the main units and their structural relationships can be recognized (green rocks, andesites, granitoids, sediments). Two generations of granitoids separated by the opening of a sedimentary basin are identified thanks to the petrographic, geochemical, geochronological and structural data. The first, of Archean type, is dated at 2123-2108 Ma and cuts the green rock belts in a diapiric way. The second, dated at about 2097 Ma comprises leucogranite batholites which cut the discordant overlying sedimentary formations. Thus, 3 volcanism phases can be recognized: a T-MORB type tholeiitic volcanism (the green rock belts), a rhyodacitic calc-alkaline volcanism with granitoid plutons, and an andesitic volcanism interstratified with the basin sediments. The general metamorphism is of green-schist facies. An intermediate model between the archaic Archean processes and the modern collision processes is proposed for the formation of the Birimian crust. (J.S.) 220 refs.

  8. Geology of the Rincon de Garcia gold deposit, Nicaragua

    International Nuclear Information System (INIS)

    The Rincon de Garcia gold deposit is located in the El Limon Mining District in north-western Nicaragua. The gold mineralization is hosted in quartz veins in tertiary volcanic rocks of andesitic composition. The gold occurs in quartzose bands as free electrum grains at grain boundaries or in poly phase mineral aggregates of jalpaite, achantite, native silver and chalcopyrite. The size of the electrum particles is generally in the range of 10-25 microns. The vein system is structurally complex and comprises both sub vertical and moderately dipping veins. The veins are associated with zones of hydrothermal alternation and spatially related to dykes of intermediate to basic composition. Regionally, the deposit is situated in the eastern part of the Nicaragua depression, a zone of extensional tectonics which can be traced from the Atlantic coast in Costa Rica to the Fonseca gulf between Nicaragua and El Salvador. The area surrounding the deposit is dominated by a sequence of volcanic rocks ranging from rhyolites to basaltic andesite in composition. (author)

  9. Zircon U-Pb geochronology and Sr-Nd isotopes of volcanic rocks from the Dahalajunshan Formation: implications for Late Devonian-Middle Carboniferous tectonic evolution of the Chinese Western Tianshan (United States)

    Yu, Xinqi; Wang, Zongxiu; Zhou, Xiang; Xiao, Weifeng; Yang, Xinpeng


    The widespread Late Devonian-Middle Carboniferous volcanic rocks in the Chinese Western Tianshan provide important constraints on the subduction history of the South Tianshan oceanic lithosphere. Here, we investigate the basalt, basaltic andesite, andesite, trachyandesite, and rhyolite from the Dahalajunshan Formation from Western Tianshan. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon geochronology constrains their age of formation to between 376 and 333 Ma (i.e., Late Devonian-Middle Carboniferous) with distinct variation in space (from west to east) and time (from early to late). Based on geochemical, zircon geochronological, and Sr-Nd isotopic data, we demonstrate that the Dahalajunshan volcanic was generated in a continental arc setting associated with the subduction of the south Tianshan Ocean during Late Devonian to Middle Carboniferous. The volcanic rocks belonging to Dahalajunshan Formation in the northwestern part of the Yili Block suggest that the northward subduction of the south Tianshan Ocean was initiated in the Early Devonian; those in the southern and eastern part of the Yili Block were probably produced by a northward subduction of South Tianshan Ocean during Late Devonian to Middle Carboniferous.

  10. Mineral Chemistry and Geochemistry of Volcanic Rocks in The North of Pasinler (Erzurum

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    Oktay KILIÇ


    Full Text Available In the north of Pasinler (Erzurum, Upper Miocene-Pliocene volcanic rocks crop out. These volcanites are composed of basaltic andesite, andesite, dacite, rhyolite lavas and rhyolitic pyroclastics. The rocks show porphyritic, microlitic porphyritic, hyalo-microlitic porphyritic, vitrophyric, glomeroporphyritic, pilotaxitic and hyalopilitic textures. The investigated volcanites contain plagioclase (An29-80, olivine (Fo65-82, clinopyroxene (augite, orthopyroxene (enstatite, amphibole (Mg#: 0.57-0.71, biotite (phlogopite: 0.44-0.47, annite: 0.33-0.37, sanidine, quartz and opaque mineral (titano-magnetite and ilmenite. The volcanic rocks are calc-alkaline in character and have medium to high-K contents. Major oxide and trace element variations point out open-system magmatic differentiation in the evolution of rocks. Geochemical data indicate an important role of fractionation of phenocryst phases in the rocks during differentiation process. However, it is considered that assimilation±magma mixing might have accompanied to the process. High LILE (K, Rb, Ba, Th and relatively low HFSE (Nb, Ta, Hf, Zr contents of the rocks indicate that these rocks derived from parental magmas carrying subduction signature.

  11. The Relationship Between Lithology and Slope Morphology in the Tucson Mountains, Arizona.

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    Kamel Khanchoul


    Full Text Available The relationship between lithology and slope morphology is investigated at eight sites on granitic, andesitic, andsedimentary hillslopes in the Tucson Mountains, Arizona. Several methods are used in the study. Topographic profi lesare constructed. Skewness indices, slope length, and mean slope angles of the different slope profi les are computed andcompared with each other. Debris size analysis has permitted for some profi les, the determination of hillfront/piedmontjunctions. The nature and structural characteristics of the bedrock are the ones that determine the hillslope morphologyin this semi-arid region. There are, as a matter of fact, variations in profi les on the same bedrock nature but differentlyexposed. More precise morphologic studies have been also done in comparing the different lithologic pairs. They havepermitted to show some similarities in shapes. The granitic-andesitic slopes and andesiic-sedimentary slopes are thebest comparisons which show the relationship between lithology and slope morphology. The granitic-sedimentary sloperelationship is shown in the hillfront concavities, mountain front and piedmont mean slope angles.

  12. Probe Drilling Ahead of Two TBMs in Difficult Ground Conditions in Turkey (United States)

    Bilgin, Nuh; Ates, Ugur


    This paper summarizes the results of probe drilling carried out ahead of TBMs in two difficult tunneling projects in Turkey. The tunnels have completely different geological characteristics which necessitated two different methods of data analysis. Melen Water Tunnel was excavated under Istanbul Bosphorus within sedimentary rocks which are cut frequently by andesitic dykes, fracturing the surrounding rocks and creating a potential risk for water ingress into the tunnel. At the beginning of Melen Project, pioneering probe drillings with petrographic analysis and strength tests were performed on samples collected from TBM muck. This analysis allowed identifying some critical normalized probe drilling rate values for predicting potential weak zones created by andesitic dykes. These studies gave a sound basis for further interpretation of TBM and geologic data for the same tunnel. The second set of probe drilling analysis was from Kargi Tunnel. The North Anatolian Fault highly affected the tunnel excavation by fractured rock formations. Although the change in normalized probe drilling data was a good indicator of fractured zones, the diversity of rock formations made it difficult to interpret the data.

  13. Olivine and chromian spinel in primitive calc-alkaline and tholeiitic lavas from the southernmost cascade range, California: A reflection of relative fertility of the source (United States)

    Clynne, M.A.; Borg, L.E.


    Chromian spinel and coexisting olivine phenocrysts from a geochemically diverse suite of primitive tholeiitic and calc-alkaline basalts and magnesian andesites from the Lassen region, in the southernmost Cascade Range, in California, show that the sub-arc mantle is zoned. Depleted calc-alkaline basalts and magnesian andesites erupt in the forearc region, and calc-alkaline basalts contain increasing abundances of incompatible elements toward the backarc. High-alumina olivine tholeiites erupt from the arc and backarc areas. Olivine from all these lavas displays a limited compositional range, from Fo86 to Fo91, and crystallized at high temperature, generally 1225-1275??C. Chromian spinel trapped in the olivine phenocrysts displays a large range of composition: Cr# values span the range 9-76. Excess Al in the spinel relative to that in 1-atm spinel suggests that it crystallized at elevated pressure. The phenocrysts in these lavas are in equilibrium with their host liquids. The full range of Cr# of the spinel compositions cannot be explained by differentiation or variable pressure, variations in f(O2), subsolidus equilibration or variations in degree of partial melting of a single peridotitic source. Rather, the systematic compositional differences among phenocrysts in these primitive lavas result from bulk chemical variability in their mantle sources. Correlations between spinel and host-rock compositions support the assertion that the geochemical diversity of Lassen basalts reflects the relative fertility of their mantle sources.

  14. Geochemical provenance of anomalous metal concentrations in stream sediments in the Ashton 1:250,000 quadrangle, Idaho/Montana/Wyoming

    International Nuclear Information System (INIS)

    Stream-sediment samples from 1500 sites in the Ashton, Idaho/Montana/Wyoming 1:250,000 quadrangle were analyzed for 45 elements. Almost all samples containing anomalous concentrations (exceeding one standard deviation above the mean value of any element) were derived from drainage basins underlain by Quaternary rhyolite, Tertiary andesite or Precambrian gneiss and schist. Aluminum, barium, calcium, cobalt, iron, nickel, magnesium, scandium, sodium, strontium, and vanadium have no andesite provenance. Most anomalous manganese, europium, hafnium, and zirconium values were derived from Precambrian rocks. All other anomalous elemental concentrations are related to Quaternary rhyolite. This study demonstrates that multielemental stream-sediment analyses can be used to infer the provenance of stream sediments. Such data are available for many parts of the country as a result of the National Uranium Resource Evaluation. This study suggests that stream-sediment samples collected in the Rocky Mountains can be used either as pathfinders or as direct indicators to select targets for mineral exploration for a host of metals

  15. Ancient seismic record of the Tarascan (Purhepecha) Empire. Preclasic Period (3000 Yr B.P.). Jaracuaro Island, Patzcuaro Lake. Michoacan, Mexico (United States)

    Rodriguez Pascua, Miguel Angel; Garduño-Monroy, Victor Hugo; Perez-Lopez, Raul; Israde-Alcantara, Isabel


    The Pátzcuaro lake is located in the Mexican State of Michoacán in the Transmexican Volcanic Belt. The Jarácuaro island is formed by Holocene lake sediments highly deformed by active faults (Morelia-Acambay Fault System, MAFS, more than 200 km long). MAFS is an E-W strike-slip fault with a transtensive component in the Pázcuaro Lake zone. Several paleoseismic studies were carried out in the island. Four trenches were made in the active faults that cross the island and it is possible observe that there are two andesitic blocks (>4 m3) over two different faults with surface rupture. The archaeological evidences (pottery, idols, etc), founded in the soils affected by the fault, implies that the age of the events concern to the Pre - Classic period (3.000 years B.P.).The Tarascan (or Purhépecha) Empire supported this earthquakes and put the blocks close both faults on the hanging wall block. The andesitic blocks are carved and polished and the quarry where this blocks were extracted is 1.5 km long out the lake. This cultural behaviour was profusely used by the Tarascan related to natural disasters but not documented before related to earthquakes. Maybe this is ones of the oldest human seismic manifestation, and is the first time that is connected a fault with a seismic movement.

  16. Lead and strontium isotopic evidence for crustal interaction and compositional zonation in the source regions of Pleistocene basaltic and rhyolitic magmas of the Coso volcanic field, California (United States)

    Bacon, C.R.; Kurasawa, H.; Delevaux, M.H.; Kistler, R.W.; Doe, B.R.


    The isotopic compositions of Pb and Sr in Pleistocene basalt, high-silica rhyolite, and andesitic inclusions in rhyolite of the Coso volcanic field indicate that these rocks were derived from different levels of compositionally zoned magmatic systems. The 2 earliest rhyolites probably were tapped from short-lived silicic reservoirs, in contrast to the other 36 rhyolite domes and lava flows which the isotopic data suggest may have been leaked from the top of a single, long-lived magmatic system. Most Coso basalts show isotopic, geochemical, and mineralogic evidence of interaction with crustal rocks, but one analyzed flow has isotopic ratios that may represent mantle values (87Sr/86Sr=0.7036,206Pb/204Pb=19.05,207Pb/204Pb=15.62,208Pb/204Pb= 38.63). The (initial) isotopic composition of typical rhyolite (87Sr/86Sr=0.7053,206Pb/204Pb=19.29,207Pb/204Pb= 15.68,208Pb/204Pb=39.00) is representative of the middle or upper crust. Andesitic inclusions in the rhyolites are evidently samples of hybrid magmas from the silicic/mafic interface in vertically zoned magma reservoirs. Silicic end-member compositions inferred for these mixed magmas, however, are not those of erupted rhyolite but reflect the zonation within the silicic part of the magma reservoir. The compositional contrast at the interface between mafic and silicic parts of these systems apparently was greater for the earlier, smaller reservoirs. ?? 1984 Springer-Verlag.

  17. Sr isotope chemistry of the magmatism from Momchilgrad depression (Eastern Rhodopes)

    International Nuclear Information System (INIS)

    The (87Sr/86Sr)i of Zvezdel basaltic-andesite complex ranges between 0.705087 and 0.708613. Acid complexes have lower values of these ratios: Perperek trachyrhyolite - 0.69534, Ursula rhyolite - 0.70119, Sveti Ilia trachyrhyodacite - 0.70270 and Momchilgrad trachydacite - 0.70589. Considering all acid complexes the (87Sr/86Sr)i of Sveti Ilia trachyrhyodacite and Sveti Ilia trachyrhyodacite complexes are comparable with these of Zvezdel basaltic-andesite complex. The outcrops of their products associate spatially with the intermediate complexes as both acid and intermediate varieties have similar petrochemical features and trace element abundance. These complexes might have been produced by one magma reservoir of intermediate composition. Obtained (87Sr/86Sr)i values are typical of continental tectonic settings. The occurrences of Ustra rhyolite and Perperek trachyrhyolite complexes are located apart from the intermediate volcanics. The have significantly lower Sr contents, lower (87Sr/86Sr)i and specific petrochemical features and trace element distribution patterns and probably resulted from the evolution of separate and not large magma reservoirs of acid composition. Calculated (87Sr/86Sr)i for Perperek and Ustra complexes are typical of the island-arc or even mid-oceanic ridge tectonic settings. These data indirectly confirm the idea of involving both oceanic and continental crust during a process of 'continental subduction'. (authors)

  18. Determination of Mineralization Zones Using Interpretation of IP and RS Data in The GarmabCopper Deposit (South Khorasan province

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    Mansour Adelpour


    Full Text Available Introduction The Garmab copper deposit is located northeast of Qaen (South Khorasan province in the1:100,000 scale map of Abiz in the eastern tectonic zone of Iran. It is hosted by Late Paleocene-Eocene lava flows consisting mainly of andesite, trachy¬andesite, andesite-basalt and basalt lavas, as well as pyroclastic rocks, including tuffs and ignimbrites. The Lut Block has undergone intense magmatic activitywith a variety of geochemical characteristics due to changing tectonic conditions (e.g., compression during subduction followed by tensional conditions; Karimpour et al., 2012; Zarrinkoub et al., 2012. The Lut Block has a great potential for the discovery of new mineral deposits, like the Mahrabad and Khonik porphyry copper-gold deposits (Malekzadeh shafarodi, 2009, the Dehsalam porphyry copper deposit (Arjmandzadeh, 2011, high sulfidation epithermal gold deposits such as Chah Shalghami (Karimpour, 2005 and IOCG deposits such as Kuh-E-Zar and Qaleh Zari (Mazlomi et al., 2008. Materials and methods After field studies of the Garmab area, 32 thin sections and 21 polished sections were prepared for petrological and mineralogical studies.In addition, 10 least-altered and fractured samples of volcanic rocks were selected for geochemical studies. Major oxides were determined using XRF analyses at the Zarazma laboratory. Induced polarization and resistivity geophysical data were collected and correlated with geological and alteration maps. The geophysical datawere collectedfrom 420 individual points, using a dipole-dipole arrangement along five profiles separated 60m apart.This covered the study area entirely. After a change in the mineralization trend was observed,additional profileswere designed, twoon bearings of 25º and three on 75º. Results The Garmab volcanic rocks exhibit typical geochemical characteristics of subduction zone magmas including strong enrichment in LILE and depletion in HFSE. Based on the discrimination plot of Irvine and

  19. Geologic Map and Eruptive History of Veniaminof Volcano Record Aleutian Arc Processing of Mantle-Derived Melts (United States)

    Bacon, C. R.; Sisson, T. W.; Calvert, A. T.; Nye, C. J.


    Mount Veniaminof, one of the largest volcanoes in the Aleutian arc, has a basal diameter of ~40 km, a volume of ~350 km3, an 8-km-diameter ice-filled caldera, and an active intracaldera cone. The geology of this tholeiitic basalt-to-dacite volcano has been mapped at 1:50,000 scale. Over 100 Quaternary volcanic map units are characterized by 600 chemical analyses of rocks and nearly 100 40Ar/39Ar and K-Ar ages. Throughout its history, lava flows from Veniaminof recorded alternately ice/melt-water chilling or ice-free conditions that are consistent with independent paleoclimatic records. Exposures from deep glacial valleys to the caldera rim reveal a long history dominated by basalt and basaltic andesite from ≥260 ka to 150 ka that includes compositions as primitive as 9.4% MgO and 130 ppm Ni at 50% SiO2. Basaltic andesite, common throughout Veniaminof's history, has low compatible-element contents that indicate an origin by fractionation of basaltic magma. Repeated eruption of more differentiated melts from a shallow intrusive complex, represented by granodiorite (crystallized dacitic magma) and cumulate gabbro and diorite xenoliths in pyroclastic deposits, has featured virtually aphyric andesite since 150 ka and dacite (to 69.5% SiO2) beginning ~110 ka. These variably differentiated liquids segregated from crystal mush, possibly by gas-driven filter pressing, and commonly vented but also solidified at depth. A large composite cone was present at least as early as 200 ka. Although asymmetric edifice morphology hints at early sector collapse to the southeast, coeval vents on northwest and southeast flanks and the distribution of extensive lava units indicate that a large cone (again) was present by 120 ka. Flank eruption of a wide variety of Veniaminof magmas was common from plate-convergence-parallel northwest-trending fissures from at least as early as ca. 80 ka. At 56 ka and at 46 ka, voluminous dacite lava erupted on both northwest and southeast flanks. A

  20. Petrology, geochemistry and U-Pb geochronology of magmatic rocks from the high-sulfidation epithermal Au-Cu Chelopech deposit, Srednogorie zone, Bulgaria (United States)

    Chambefort, Isabelle; Moritz, Robert; von Quadt, Albrecht


    The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern part of the Panagyurishte mineral district. It lies within the Banat-Srednegorie metallogenic belt, which extends from Romania through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech deposit have been affected by propylitic, quartz-sericite, and advanced argillic alteration, but the igneous textures have been preserved. Alteration processes have resulted in leaching of Na2O, CaO, P2O5, and Sr and enrichment in K2O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the Chelopech magmatism, were dated by high-precision U-Pb geochronology. Zircons of an altered andesitic body, which has been thrust over the deposit, yield a concordant 206Pb/238U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech. Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean 206Pb/238U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted by hydrothermal alteration give a concordant 206Pb/238U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech epithermal high-sulfidation deposit. 176Hf/177Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the

  1. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events (United States)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena


    A high-grade metamorphic sequence in the Sünnice Mountains, Bolu, NW Turkey, is represented by migmatitic quartzo-feldspathic gneisses in amphibolite facies called the Demirci metamorphics/paragneisses, and a sequence of low-grade meta-volcanics containing meta-andesites with minor meta-rhyolites and meta-sedimentary rocks called the Yellice meta-volcanics. They are intruded by the Dirgine granite with an age of Upper Ediacaran (576-565 Ma) and are considered a part of the İstanbul-Zonguldak Tectonic Unit. The Demirci paragneisses are also intruded by a number of dykes in various directions, traditionally considered without radiometric dating to have been emplaced in a single magmatic phase in the Eocene related to post-collision regime of the Anatolide-Tauride platform. Mafic-intermediate-felsic dykes cross-cutting the Demirci paragneisses have been investigated in maps of 1/1000 scale, and their U-Pb zircon age, major-trace element and kinematic data have been obtained. The mafics dykes cross-cutting the Yellice meta-volcanics, equivalents of those in the Demirci paragneisses, occur in N400-500E orientations and have calc-alkaline basalt compositions with a subduction signature. The intermediate dykes occur in N650W, N800W orientations and have calc-alkaline basaltic andesite to andesitic compositions with a subduction signature. Some felsics occur in N150W and N800E orientations and have calc-alkaline dacitic compositions with a collisional tectonic setting. Other calc-alkaline granitic dykes occur in N750E orientation and calc-alkaline granitic compositions with a subduction signature. U-Pb LA-ICP-MS dating of zircons yield ages from 485.7±3.6 Ma (i.e. Cambro-Ordovician) for N800E trending dacite dykes; 443.0±5.4 Ma (i.e. Ordovician-Silurian) for N150W trending dacite dykes; 301.0±1.6 Ma (i.e. Upper Pennsylvanian-Carboniferous) for N650W trending basaltic andesite dykes; 268.2±2.4 Ma (i.e. Guadalupian-Permian) for N40-500E trending basalt dykes; 262.9±3

  2. Suprasubduction volcanic rocks of the Char ophiolite belt, East Kazakhstan: new geochemical and first geochronological data (United States)

    Safonova, Inna; Simonov, Vladimir; Seltmann, Reimar; Yamamoto, Shinji; Xiao, Wenjiao


    The Char ophiolite belt is located in the western Central Asian Orogenic Belt, a world largest accretionary orogen, which has evolved during more than 800 Ma. The Char belt formed during Kazakhstan - Siberia collision. It has been known for hosting fragments of Late Devonian-Early Carboniferous oceanic crust, MORB, OPB and OIB, of the Paleo-Asian Ocean (Safonova et al., 2012). The Char is surrounded by two Paleozoic island-arc terranes: Zharma-Saur in the west and Rudny Altai in the east, however, until recent times, no island-arc units have been found within it. We were the first to find island-arc units as tectonic sheets occurring adjacent to those consisting of oceanic rocks. In places, island-arc andesites cut oceanic basalts. The Char volcanic and subvolcanic rocks of a probable suprasubduction origin are basalt, microgabbro, dolerite, andesite, tonalite and dacite. The mafic to andesitic volcanics possessing low TiO2 (0.85 wt.%av.) and show MgO vs. major elements crystallization trends suggesting two magma series: tholeiitic and calc-alkaline. The tholeiitic varieties are less enriched in incompatible elements then the calc-alkaline ones. Two samples are high-Mg and low-Ti andesibasalts similar to boninites. The rocks possess moderately LREE enriched rare-earth element patterns and are characterized by negative Nb anomalies present on the multi-element spectra (Nb/Lapm = 0.14-0.47; Nb/Thpm = 0.7-1.6).The distribution of rare-earth elements (La/Smn = 0.8-2.3, Gd/Ybn = 0.7-1.9) and the results of geochemical modeling in the Nb-Yb system suggest high degrees of melting of a depleted harzburgite-bearing mantle source at spinel facies depths. Fractional crystallization of clinopyroxene, plagioclase and opaque minerals also affected the final composition of the volcanic rocks. Clinopyroxene monomineral thermometry indicates crystallization of melts at 1020-1180°C. Melt inclusion composition based numerical calculations show that primary melts were derived at 1350

  3. Stratigraphy and geochronology of the Comondú Group near Loreto, Baja California sur, Mexico (United States)

    Umhoefer, Paul J.; Dorsey, Rebecca J.; Willsey, Shawn; Mayer, Larry; Renne, Paul


    Upper Oligocene to Middle Miocene volcanic and sedimentary rocks in the Loreto region, Baja California Sur, are widely exposed and make up the Comondú Group as redefined here following McFall. The Comondú Group is part of a volcanic arc and forearc basin that formed along the northwestern margin of Mexico. Regional to detailed scale mapping, stratigraphic analysis, and geochronology in a 10-20-km-wide and 70-km-long belt from the gulf escarpment to the coast near Loreto reveal three main units in the Comondú Group and a composite thickness of ˜1.5-2 km. (1) The lower clastic unit (˜30-19 Ma) contains 200-300 m of fluvial sandstone and conglomerate with probable local eolian deposits and numerous felsic tuffs and basalt flows that accumulated in a forearc basin. (2) The middle breccia and lava flow unit (˜19-15 Ma) is up to 750 m thick and consists of massive andesite breccia that was deposited as proximal debris flows interbedded with minor andesite lava flows. (3) The upper lava flow and breccia unit (˜15-12 Ma) consists almost entirely of up to ˜600 meters of andesite lava flows a few kilometers west of Loreto that are part of a composite volcano. North and south of Loreto for up to 25 km, the unit is composed of andesite lava flows and massive andesite breccia that formed from thick debris flows near that and other volcanic centers. The three units of the Comondú Group in the Loreto area correlated with the Salto, Pelones, and Ricasón formations of the Bahı´a Concepción area. The lower clastic unit of this study is time equivalent to the marine San Gregorio, El Cien, and Isidro formations on the western and southern Baja California peninsula. The middle and upper units of the Loreto area are the proximal equivalent to the type section of the Comondú Group near the village of Comondú. During deposition of the lower part of the Comondú Group, the arc lay to the east on mainland Mexico in the Sierra Madre Occidental, and then migrated to the

  4. Petrography, geochemistry and tectonic setting of Salmabad Tertiary volcanic rocks, southeast of Sarbisheh, eastern Iran

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    Masoumeh Goodarzi


    Full Text Available Introduction The area reviewed and studied in this paper is located 5 km southeast of Sarbisheh city at eastern border of the Lut block (Jung et al., 1983; Karimpour et al., 2011; Richards et al., 2012 in eastern Iran between 59° 47′ and 59° 53′ E longitude and 32°30′ and 32°34′ N latitude. The magmatic activity in the Lut block began in middle Jurassic (165-162 Ma and reached its peak in Tertiary (Jung et al., 1983. Volcanic and subvolcanic rocks of Tertiary age cover over half of Lut block with up to 2000 m thickness and formed due to subduction prior to the collision of the Arabian and Asian plates (Camp and Griffis, 1982; Tirrul et al., 1983; Berberianet et al., 1982. Most of magmatic activity in the Lut block formed in middle Eocene (Karimpour et al., 2011 The andesitic volcanics were erupted together with the dacites and rhyodacites during a time interval of some 50 Ma from early Cretaceous to early Neogene. It can be assumed that the intensity of the volcanic activity was varying significantly during this time span (Jung et al., 1983.Tertiary volcanic rocks (Eocene-Oligocene to Pliocene with intermediate composition associated with pyroclastic rocks cropped out in eastern parts of Salmabad village, southeast of Sarbisheh. The main purpose of this paper is better understand the tectono-magmatic setting of the Tertiary volcanic rocks in southeast of Sarbisheh, eastern Iran based on geochemical characteristics. Materials and methods Eleven samples were analyzed for major elements by inductively coupled plasma (ICP technologies and trace elements were analyzed using inductively coupled plasma mass spectrometry (ICP-MS, following a lithium metaborate/tetraborate fusion and nitric acid total digestion, at the SGS Laboratories, Toronto, Canada. Results In the Salmabad area, Tertiary volcanic rocks with mainly intermediate (andesitic composition are exposed associated with pyroclastic deposits such as tuff, breccia and agglomerate

  5. Petrology of Volcán Tequila, Jalisco, Mexico: disequilibrium phenocryst assemblages and evolution of the subvolcanic magma system (United States)

    Wallace, Paul J.; Carmichael, Ian S. E.


    Volcán Tequila is an extinct stratovolcano in the western Mexican Volcanic Belt that has erupted lavas ranging from andesite to rhyolite during the last 0.9 Ma. Following an early period of rhyolitic volcanism, the main edifice of the volcano was constructed by central vent eruptions that produced ˜ 25 km3 of pyroxene-andesite. At about 0.2 Ma central activity ceased and numerous flows of hornblende-bearing andesite, dacite, and rhyodacite erupted from vents located around the flanks of the volcano. Bimodal plagioclase phenocryst rim compositions in lavas from both the main edifice and the flanks indicate that magma mixing commonly occurred shortly prior to or during eruption. Compositions of endmember magmas involved in mixing, as constrained by whole-rock major and trace element abundances, phenocryst compositions, and mineral-melt exchange equilibria, are similar to those of some lavas erupted from the central vent and on the flanks of the volcano. Estimated pre-eruptive temperatures for hornblende-bearing lavas (970° 830°C) are systematically lower than for lavas that lack hornblende (1045° 970°C), whereas magmatic H2O contents are systematically higher for hornblende-bearing lavas. In addition to stabilizing hornblende, high magmatic water contents promoted crystallization of calcic plagioclase (An70 82). Frequent injections of magma into the base of the subvolcanic plumbing system followed by eruption of mixed magma probably prevented formation of large volumes of silicic magma, which have caused paroxysmal, caldera-forming eruptions at other stratovolcanoes in western Mexico. The later stages of volcanic activity, represented by the flank lavas, indicate a change from a large magma storage reservoir to numerous small ones that developed along a NW-trending zone parallel to regional fault trends. Sr and Nd isotopic data for lavas from the Tequila region and other volcanoes in western Mexico demonstrate that differentiated calc-alkaline magmas are formed

  6. The timing of compositionally-zoned magma reservoirs and mafic 'priming' weeks before the 1912 Novarupta-Katmai rhyolite eruption (United States)

    Singer, Brad S.; Costa, Fidel; Herrin, Jason S.; Hildreth, Wes; Fierstein, Judy


    The June, 6, 1912 eruption of more than 13 km3 of dense rock equivalent (DRE) magma at Novarupta vent, Alaska was the largest of the 20th century. It ejected >7 km3 of rhyolite, ∼1.3 km3 of andesite and ∼4.6 km3 of dacite. Early ideas about the origin of pyroclastic flows and magmatic differentiation (e.g., compositional zonation of reservoirs) were shaped by this eruption. Despite being well studied, the timing of events that led to the chemically and mineralogically zoned magma reservoir remain poorly known. Here we provide new insights using the textures and chemical compositions of plagioclase and orthopyroxene crystals and by reevaluating previous U-Th isotope data. Compositional zoning of the magma reservoir likely developed a few thousand years before the eruption by several additions of mafic magma below an extant silicic reservoir. Melt compositions calculated from Sr contents in plagioclase fill the compositional gap between 68 and 76% SiO2 in whole pumice clasts, consistent with uninterrupted crystal growth from a continuum of liquids. Thus, our findings support a general model in which large volumes of crystal-poor rhyolite are related to intermediate magmas through gradual separation of melt from crystal-rich mush. The rhyolite is incubated by, but not mixed with, episodic recharge pulses of mafic magma that interact thermochemically with the mush and intermediate magmas. Hot, Mg-, Ca-, and Al-rich mafic magma intruded into, and mixed with, deeper parts of the reservoir (andesite and dacite) multiple times. Modeling the relaxation of the Fe-Mg concentrations in orthopyroxene and Mg in plagioclase rims indicates that the final recharge event occurred just weeks prior to the eruption. Rapid addition of mass, volatiles, and heat from the recharge magma, perhaps aided by partial melting of cumulate mush below the andesite and dacite, pressurized the reservoir and likely propelled a ∼10 km lateral dike that allowed the overlying rhyolite to reach the

  7. Bimodal volcanism in a tectonic transfer zone: Evidence for tectonically controlled magmatism in the southern Central Andes, NW Argentina (United States)

    Petrinovic, I. A.; Riller, U.; Brod, J. A.; Alvarado, G.; Arnosio, M.


    This field-based and analytical laboratory study focuses on the genetic relationship between bimodal volcanic centres and fault types of an important tectonic transfer zone in the southern Central Andes, the NW-SE striking Calama-Olacapato-Toro (COT) volcanic belt. More specifically, tectono-magmatic relationships are examined for the 0.55 Ma Tocomar, the 0.78 Ma San Jerónimo and the 0.45 Ma Negro de Chorrillos volcanic centres in the Tocomar area (66°30 W-24°15 S). Structures of the COT volcanic belt, notably NW-SE striking strike-slip faults and NE-SW trending normal faults, accommodated differential shortening between major N-S striking thrust faults on the Puna Plateau. We present evidence that bimodal volcanism was contemporaneous with activity of these fault types in the COT volcanic belt, whereby eruption and composition of the volcanic rocks in the Tocomar and San Jerónimo-Negro de Chorrillos areas appear to have been controlled by the kinematics of individual faults. More specifically, rhyolitic centres such as the Tocomar are associated with normal faults, whereas shoshonitic-andesitic monogenetic volcanoes, e.g., the San Jerónimo and Negro de Chorrillos centres, formed at strike-slip dominated faults. Thus, the eruption of higher viscous rhyolite magmas appears to have been facilitated in tectonic settings characterized by horizontal dilation whereas ascent and effusive volcanic activity of less viscous and hot basaltic andesites to shoshonites were controlled by subvertical strike-slip faults. While the Tocomar rhyolites are interpreted to be derived from an anatectic crustal source, geochemical characteristics of the San Jerónimo and Negro de Chorrillos shoshonitic andesites are in agreement with a deeper source. This suggests that the composition of erupted volcanic rocks as well as their spatial distribution in the Tocomar area is controlled by the activity of specific fault types. Such volcano-tectonic relationships are also evident from older

  8. Vulnerability of Karangkates dams area by means of zero crossing analysis of data magnetic

    International Nuclear Information System (INIS)

    Study with entitled Vulnerability Karangkates Dam Area By Means of Zero Crossing Analysis of Data Magnetic has been done. The study was aimed to obtain information on the vulnerability of two parts area of Karangkates dams, i.e. Lahor dam which was inaugurated in 1977 and Sutami dam inaugurated in 1981. Three important things reasons for this study are: 1). The dam age was 36 years old for Lahor dam and 32 years old for Sutami dam, 2). Geologically, the location of the dams are closed together to the Pohgajih local shear fault, Selorejo local fault, and Selorejo limestone-andesite rocks contact plane, and 3). Karangkates dams is one of the important Hydro Power Plant PLTA with the generating power of about 400 million KWH per year from a total of about 29.373MW installed in Indonesia. Geographically, the magnetic data acquisition was conducted at coordinates (112.4149oE;-8.2028oS) to (112.4839oE;-8.0989oS) by using Proton Precession Magnetometer G-856. Magnetic Data acquisition was conducted in the radial direction from the dams with diameter of about 10 km and the distance between the measurements about 500m. The magnetic data acquisition obtained the distribution of total magnetic field value in the range of 45800 nT to 44450 nT. Residual anomalies obtained by doing some corrections, including diurnal correction, International Geomagnetic Reference Field (IGRF) correction, and reductions so carried out the distribution of the total magnetic field value in the range of -650 nT to 700 nT. Based on the residual anomalies, indicate the presence of 2 zones of closed closures dipole pairs at located in the west of the Sutami dam and the northwest of the Lahor dam from 5 total zones. Overlapping on the local geological map indicated the lineament of zero crossing patterns in the contour of residual anomaly contour with the Pohgajih shear fault where located at about 4 km to the west of the Sutami dam approximately and andesite-limestone rocks contact where located

  9. Early Cretaceous arc volcanic suite in Cebu Island, Central Philippines and its implications on paleo-Pacific plate subduction: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes (United States)

    Deng, Jianghong; Yang, Xiaoyong; Zhang, Zhao-Feng; Santosh, M.


    The Philippine island arc system is a collage of amalgamated terranes of oceanic, continental and island arc affinities. Here we investigate a volcanic suite in Cebu Island of central Philippines, including basalt, diabase dike, basaltic pyroclastic rock and porphyritic andesite. LA-ICP-MS U-Pb geochronology of zircon grains from the porphyritic andesite and pyroclastic rock yielded ages of 126 ± 3 Ma and 119 ± 2 Ma, respectively, indicating an Early Cretaceous age. The age distribution of the detrital zircons from river sand in the area displays a peak at ca. 118 Ma, close to the age of the pyroclastic rock. The early Cretaceous volcanic rocks in the central Philippines were previously regarded as parts of ophiolite complexes by most investigators, whereas the Cebu volcanics are distinct from these, and display calc-alkaline affinity and island arc setting, characterized by high LREE/HREE ratios and low HFSE contents. These features are similar to the Early Cretaceous arc basalts in the Amami Plateau and east Halmahera in the northernmost and southernmost West Philippine Basin respectively. Zircon Hf isotopes of the pyroclastic rocks show depleted nature similar to those of the Amami Plateau basalts, implying the subducted Pacific-type MORB as probable source. Zircon Hf isotopes of the porphyritic andesite show slight enrichment relative to that of the pyroclastic rocks and MORB, indicating subducted sediments as a minor end-member in the source. The Hf isotopic compositions of the volcanic rocks are also reflected in the detrital zircons from the river sands. We propose that the volcanic rocks of Cebu Island were derived from partial melting of sub-arc mantle wedge which was metasomatized by dehydration of subducted oceanic crust together with minor pelagic sediments. Within the tectonic environment of Southeast Asia during Early Cretaceous, the volcanic rocks in Cebu Island can be correlated to the subduction of paleo-Pacific plate. The Early Cretaceous

  10. Vulnerability of Karangkates dams area by means of zero crossing analysis of data magnetic

    Energy Technology Data Exchange (ETDEWEB)

    Sunaryo,, E-mail:, E-mail:; Susilo, Adi [Geophysics Program Study, Physics Dept., Sciences Faculty, University of Brawijaya, Malang (Indonesia)


    Study with entitled Vulnerability Karangkates Dam Area By Means of Zero Crossing Analysis of Data Magnetic has been done. The study was aimed to obtain information on the vulnerability of two parts area of Karangkates dams, i.e. Lahor dam which was inaugurated in 1977 and Sutami dam inaugurated in 1981. Three important things reasons for this study are: 1). The dam age was 36 years old for Lahor dam and 32 years old for Sutami dam, 2). Geologically, the location of the dams are closed together to the Pohgajih local shear fault, Selorejo local fault, and Selorejo limestone-andesite rocks contact plane, and 3). Karangkates dams is one of the important Hydro Power Plant PLTA with the generating power of about 400 million KWH per year from a total of about 29.373MW installed in Indonesia. Geographically, the magnetic data acquisition was conducted at coordinates (112.4149oE;-8.2028oS) to (112.4839oE;-8.0989oS) by using Proton Precession Magnetometer G-856. Magnetic Data acquisition was conducted in the radial direction from the dams with diameter of about 10 km and the distance between the measurements about 500m. The magnetic data acquisition obtained the distribution of total magnetic field value in the range of 45800 nT to 44450 nT. Residual anomalies obtained by doing some corrections, including diurnal correction, International Geomagnetic Reference Field (IGRF) correction, and reductions so carried out the distribution of the total magnetic field value in the range of -650 nT to 700 nT. Based on the residual anomalies, indicate the presence of 2 zones of closed closures dipole pairs at located in the west of the Sutami dam and the northwest of the Lahor dam from 5 total zones. Overlapping on the local geological map indicated the lineament of zero crossing patterns in the contour of residual anomaly contour with the Pohgajih shear fault where located at about 4 km to the west of the Sutami dam approximately and andesite-limestone rocks contact where located

  11. Probing permeability and microstructure: Unravelling the role of a low-permeability dome on the explosivity of Merapi (Indonesia) (United States)

    Kushnir, Alexandra R. L.; Martel, Caroline; Bourdier, Jean-Louis; Heap, Michael J.; Reuschlé, Thierry; Erdmann, Saskia; Komorowski, Jean-Christophe; Cholik, Noer


    Low permeability dome rocks may contribute to conduit overpressure development in volcanic systems, indirectly abetting explosive activity. The permeability of dome-forming rocks is primarily controlled by the volume, type (vesicles and/or microcracks), and connectivity of the void space present. Here we investigate the permeability-porosity relationship of dome-forming rocks and pumice clasts from Merapi's 1888 to 2013 eruptions and assess their possible role in eruptive processes, with particular emphasis on the 2010 paroxysmal eruption. Rocks are divided into three simple field classifications common to all eruptions: Type 1 samples have low bulk density and are pumiceous in texture; Type 2 samples, ubiquitous to the 2010 eruption, are dark grey to black in hand sample and vary greatly in vesicularity; and Type 3 samples are weakly vesicular, light grey in hand sample, and are the only samples that contain cristobalite. Type 2 and Type 3 rocks are present in all eruptions and their permeability and porosity data define similar power law relationships, whereas data for Type 1 samples are clearly discontinuous from these trends. A compilation of permeability and porosity data for andesites and basaltic andesites with published values highlights two microstructural transitions that exert control on permeability, confirmed by modified Bayesian Information Criterion (BIC) analysis. Permeability is microcrack- and diktytaxitic-controlled at connected porosities, φc, 31 vol.%. Type 3 basaltic andesites, the least permeable of the measured samples and therefore the most likely to have originated in the uppermost low-permeability dome, are identified as relicts of terminal domes (the last dome extruded prior to quiescence). Cristobalite commonly found in the voids of Type 3 blocks may not contribute significantly to the reduction of the permeability of these samples, mainly because it is associated with an extensive microporous, diktytaxitic texture. Indeed, the low

  12. Formation and evolution stages of gold rich Barika massive sulfide deposit, east of Sardasht, northern Sanandaj-Sirjan zone: based on structural, textural and fluid inclusion studies

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    Hossein Ali Tajeddin


    Full Text Available Barika gold (and silver rich massive sulfide deposit is located 18 km east of Sardasht, north western part of Sanandaj-Sirjan metamorphic zone. Rock units outcropped in this area are Cretaceous metamorphosed volcano-sedimentary rocks in green schist facies, and include association of meta-andesite, meta-tuffite, phyllite and slate rocks, where the meta-andesitic unit (Kmv1 is host rock to the deposit. Barika deposit is composed of stratiform ore and stringer zone. Stratiform part contains massive and banded sulfide and barite associated with subordinary silica bands underlain by stringer silicic zone. The massive and banded ore is surrounded by an extensive zone of silicic stringer veins and disseminated mineralization within strongly altered and deformed andesitic volcanic rocks. Ore mineral assemblages in stratiform part of the deposit are quite variable and consist of pyrite, sphalerite, galena, stibnite, a variety of sulfosalt minerals and gold (electrum. Ore mineral assemblages in silicic veins in the stringer zone are simpler and consist of pyrite, galena, sphalerite, tetrahedrrite and trace chalcopyrite. Average gold and silver grades in stratiform ore are 8.3 and 420 g/t respectively and in silicic stringer veins are 0.7 and 30 g/t. Base metal content in both parts of the deposit are less than 1%. Based on our research, Barika is an immature Kuroko type massive sulfide deposit, which contains only black ore. The Barika deposit underwent low-grade metamorphism and high grade deformation after the ore deposition event. Geologic processes appear to control the mode of occurrence of gold in the deposit. In synvolcanism stage, deposition of a gold–bearing low temperature (140-200°C and low salinity (1-9.6 wt% NaCl hydrothermal fluid formed a Kuroko black ore type deposit. In the stage of mineralization, invisible gold was concentrated in framboidal pyrite and other sulfide minerals. The main effect of progressive metamorphism (D1 on gold

  13. Geochemistry and petrogenesis of early Cretaceous sub-alkaline mafic dykes from Swangkre-Rongmil, East Garo Hills, Shillong plateau, northeast India

    Indian Academy of Sciences (India)

    Rajesh K Srivastava; Anup K Sinha


    Numerous early Cretaceous mafic and alkaline dykes, mostly trending in N-S direction, are emplaced in the Archaean gneissic complex of the Shillong plateau, northeastern India. These dykes are spatially associated with the N-S trending deep-seated Nongchram fault and well exposed around the Swangkre-Rongmil region. The petrological and geochemical characteristics of mafic dykes from this area are presented. These mafic dykes show very sharp contact with the host rocks and do not show any signature of assimilation with them. Petrographically these mafic dykes vary from fine-grained basalt (samples from the dyke margin) to medium-grained dolerite (samples from the middle of the dyke) having very similar chemical compositions, which may be classified as basaltic-andesite/andesite. The geochemical characteristics of these mafic dykes suggest that these are genetically related to each other and probably derived from the same parental magma. Although, the high-field strength element (+rare-earth elements) compositions disallow the possibility of any crustal involvement in the genesis of these rocks, but Nb/La, La/Ta, and Ba/Ta ratios, and similarities of geochemical characteristics of present samples with the Elan Bank basalts and Rajmahal (Group II) mafic dyke samples, suggest minor contamination by assimilation with a small amount of upper crustal material. Chemistry, particularly REE, hints at an alkaline basaltic nature of melt. Trace element modelling suggests that the melt responsible for these mafic dykes had undergone extreme differentiation (∼50%) before its emplacement. The basaltic-andesite nature of these rocks may be attributed to this differentiation. Chemistry of these rocks also indicates ∼10–15% melting of the mantle source. The mafic dyke samples of the present investigation show very close geochemical similarities with the mafic rocks derived from the Kerguelen mantle plume. Perhaps the Swangkre-Rongmil mafic dykes are also derived

  14. Petrogenesis of Late Cretaceous lava flows from a Ceno-Tethyan island arc: The Raskoh arc, Balochistan, Pakistan (United States)

    Siddiqui, Rehanul Haq; Qasim Jan, M.; Asif Khan, M.


    The Raskoh arc is about 250 km long, 40 km wide and trends in an ENE direction. The oldest rock unit in the Raskoh arc is an accretionary complex (Early to Late Jurassic), which is followed in age by Kuchakki Volcanic Group, the most wide spread unit of the Raskoh arc. The Volcanic Group is mainly composed of basaltic to andesitic lava flows and volcaniclastics, including agglomerate, volcanic conglomerate, breccia and tuff, with subordinate shale, sandstone, limestone and chert. The flows generally form 3-15 m thick lenticular bodies but rarely reach up to 300 m. They are mainly basaltic-andesites with minor basalts and andesites. The main textures exhibited by these rocks are hypocrystalline porphyritic, subcumulophyric and intergranular. The phenocrysts comprise mainly plagioclase (An30-54 in Nok Chah and An56-64 in Bunap). They are embedded in a micro-cryptocrystalline groundmass having the same minerals. Apatite, magnetite, titanomagnetite and hematite occur as accessory minerals. Major, trace and rare earth elements suggest that the volcanics are oceanic island arc tholeiites. Their low Mg # (42-56) and higher FeO (total)/MgO (1.24-2.67) ratios indicate that the parent magma of these rocks was not directly derived from a mantle source but fractionated in an upper level magma chamber. The trace element patterns show enrichment in LILE and depletion in HFSE relative to N-MORB. Their primordial mantle-normalized trace element patterns show marked negative Nb anomalies with positive spikes on K, Ba and Sr which confirm their island arc signatures. Slightly depleted LREE to flat chondrite normalized REE patterns further support this interpretation. The Zr versus Zr/Y and Cr versus Y studies show that their parent magma was generated by 20-30% melting of a depleted mantle source. The trace elements ratios including Zr/Y (1.73-3.10), Ti/Zr (81.59-101.83), Ti/V (12.39-30.34), La/YbN (0.74-2.69), Ta/Yb (0.02-0.05) and Th/Yb (0.11-0.75) of the volcanics are more

  15. Viscosity controlled magma-carbonate interaction: a comparison of Mt. Vesuvius (Italy) and Mt. Merapi (Indonesia). (United States)

    Blythe, L. S.; Misiti, V.; Masotta, M.; Taddeucci, J.; Freda, C.; Troll, V. R.; Deegan, F. M.; Jolis, E. M.


    Magma-carbonate interaction is increasingly seen as a viable and extremely important cause of magma contamination, and the generation of a crustally sourced CO2 phase (Goff et al., 2001; Freda et al., 2010). Even though the process is well recognized at certain volcanoes e.g. Popocatépetl, (Mexico); Merapi, (Indonesia); and Colli Albani, (Italy) (Goff et al., 2001; Deegan et al., 2010; Freda et al., 2010), neither the kinetics of carbonate assimilation nor its consequences for controlling the explosivity of eruptions have been constrained. Here we show the results of magma-carbonate interaction experiments conducted at 1200 °C and 0.5 GPa for varying durations (0 s, 60 s, 90 s and 300 s) for the Mt. Merapi (Indonesia) and Mt. Vesuvius (Italy) volcanic systems. We performed experiments using glassy starting materials specific to each volcano (shoshonite for Mt. Vesuvius, basaltic-andesite for Mt. Merapi) with different degrees of hydration (anhydrous vs hydration with ~ 2 wt % water) and using carbonate fragments of local origin; see Deegan et al., (2010) and Jolis et al., (2011). Experimental products include a gas phase (CO2-rich) and two melt phases, one pristine (Ca-normal) and one contaminated (Ca-rich) separated by a 'contamination front' which propagates outwards from the carbonate clast. Vesicles appear to nucleate in the contaminated glass and then migrate into the pristine one. Both contamination front propagation and bubble migration away from the carbonate are slower in anhydrous basaltic-andesite (Merapi anhydrous series) than in hydrated basaltic-andesite and shoshonite (Merapi and Vesuvius hydrated series), suggesting that assimilation speed is strongly controlled by the degree of hydration and the SiO2 content, both of which influence melt viscosity and hence diffusivity. As the carbonate dissolution proceeds in our experiments, initially dissolved and eventually exsolved CO2 builds up in the contaminated Ca-rich melt phase. Once melt volatile

  16. Diverse lavas from closely spaced volcanoes drawing from a common parent: Emmons Lake Volcanic Center, Eastern Aleutian Arc (United States)

    Mangan, M.; Miller, T.; Waythomas, C.; Trusdell, F.; Calvert, A.; Layer, P.


    Emmons Lake Volcanic Center (ELVC) on the lower Alaskan Peninsula is one of the largest and most diverse volcanic centers in the Aleutian Arc. Since the Middle Pleistocene, eruption of ~ 350 km3 of basalt through rhyolite has produced a 30 km, arc front chain of nested calderas and overlapping stratovolcanoes. ELVC has experienced as many as five major caldera-forming eruptions, the most recent, at ~ 27 ka, produced ~ 50 km3 of rhyolitic ignimbrite and ash fall. These violent silicic events were interspersed with less energetic, but prodigious, outpourings of basalt through dacite. Holocene eruptions are mostly basaltic andesite to andesite and historically recorded activity includes over 40 eruptions within the last 200 yr, all from Pavlof volcano, the most active site in the Aleutian Arc. Geochemical and geophysical observations suggest that although all ELVC eruptions derive from a common clinopyroxene + spinel + plagioclase fractionating high-aluminum basalt parent in the lower crust, magma follows one of two closely spaced, but distinct paths to the surface. Under the eastern end of the chain, magma moves rapidly and cleanly through a relatively young (~ 28 ka), hydraulically connected dike plexus. Steady supply, short magma residence times, and limited interaction with crustal rocks preserve the geochemistry of deep crustal processes. Below the western part of the chain, magma moves haltingly through a long-lived (~ 500 ka) and complex intrusive column in which many generations of basaltic to andesitic melts have mingled and fractionated. Buoyant, silicic melts periodically separate from the lower parts of the column to feed voluminous eruptions of dacite and rhyolite. Mafic lavas record a complicated passage through cumulate zones and hydrous silicic residues as manifested by disequilibrium phenocryst textures, incompatible element enrichments, and decoupling of REEs and HFSEs ratios. Such features are absent in mafic lavas from the younger part of the chain

  17. Precaldera lavas of the southeast San Juan Volcanic Field: Parent magmas and crustal interactions (United States)

    Colucci, M. T.; Dungan, M. A.; Ferguson, K. M.; Lipman, P. W.; Moorbath, S.


    Early intermediate composition volcanic rocks of the Oligocene (circa 34-29 Ma) southeast San Juan volcanic field, southern Colorado, comprise the Conejos Formation. Conejos lavas include both high-K calc-alkaline and alkaline magma series (54-69% SiO2) ranging in composition from basaltic andesite (basaltic trachyandesite) to dacite (trachydacite). The subsequent Platoro caldera complex (29-27 Ma) was superimposed on a cluster of broadly precursory Conejos stratocones. Precaldera volcanism occurred in three pulses corresponding to three time-stratigraphic members: (1) the Horseshoe Mountain member, (2) the Rock Creek member, and (3) the Willow Mountain member. Each member exhibits distinctive phenocryst modes and incompatible trace element contents. Horseshoe Mountain lavas (hornblende-phyric) have relatively low alkali and incompatible element abundances, Rock Creek lavas (anhydrous phenocrysts) and ash-flow tuffs have the highest abundances, and Willow Mountain lavas (diverse mineralogy) are intermediate. All Conejos lavas exhibit low ratios of lead (206Pb/204Pb = 17.5 to 18.2) and neodymium (ɛNd = -8 to -4) isotopes and high 87Sr/86Sr (0.7045 to 0.7056) compared to depleted asthenospheric mantle. These values lie between those of likely mantle compositions and the isotopic composition of Proterozoic crust of the southern Rocky Mountains. Mafic lavas of the Horseshoe Mountain member have the lowest Pb and Nd isotope ratios among Conejos members but trend toward higher isotopic values with increasing degrees of differentiation. Compositions within the Rock Creek series trend toward higher Pb and lower Nd isotope ratios with increasing SiO2. Willow mountain volcanic sequences define diverse chemical-isotopic correlations. We interpret the chemical and isotopic differences observed between mafic lavas of each member to reflect derivation from compositionally distinct mantle derived parent magmas that have experienced extensive deep level crustal contamination

  18. The graben caldera of Guanajuato, Mexico (United States)

    Aguirre-Diaz, G. J.; Tristán-González, M.; Labarthe-Hernández, G.; Marti, J.


    Guanajuato has been an important gold and silver mineral district of Mexico since the 16th century until Present. Famous mines such as Rayas, La Valenciana and El Cubo, are part of this important mining development. Stratigraphy and structures are well known, and major faults and vein systems are precisely mapped. The series include a Mesozoic metamorphosed volcano-sedimentary sequence interpreted as a tectonically accreted terrane during Early Cretaceous subduction; a >1000 m thick red beds sequence, apparently Eocene and interpreted originally as molasses posterior to K/T Laramide orogeny, but more probably fanglomerates filling a graben formed during mid-Tertiary extension; an Eocene-Miocene volcanic sequence that accumulated in this tectonic basin and the surrounding area, including andesitic lavas, silicic ignimbrites and surge deposits, and rhyolitic domes. Pyroclastic rocks have not been studied with a volcanological approach, with the purpose of understanding the physical volcanic processes that formed them. Randall (1994) suggested a caldera source for some of them. Our purpose is to describe the volcanic processes involved in the mid-Tertiary units of Guanajuato. There are dacitic and andesitic lavas that were apparently contemporaneous with deposition of the Red Conglomerate of Guanajuato. The ignimbrites correspond to the Sierra Madre Occidental volcanic province. These units were originated as two main pyroclastic densety currents sequences that formed the Loseros-Bufa and the Calderones formations. The former is rhyolitic and the later andesitic-dacitic. Loseros is composed of a series of thin-bedded to laminated pyroclastic surge deposits in continuous and concordant contact with overlying Bufa massive ignimbrite. Bufa ignimbrite is partly welded, with columnar jointing, completely devitrified, and highly silicified by post-deposition hydrothermalism and/or vapor phase alteration. Co-ignimbrite lithic lag breccias are observed at several sites in

  19. Chronology and Geochemistry of Mesozoic Volcanic Rocks in the Linjiang Area, Jilin Province and their Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    YU Yang; XU Wenliang; PEI Fuping; YANG Debin; ZHAO Quanguo


    Zircon U-Pb ages and geochemical analytical results are presented for the volcanic rocks of the Naozhigou, Ergulazi, and Sidaogou Formations in the Linjiang area, southeastern Jilin Province to constrain the nature of magma source and their tectonic settings. The Naozhigou Formation is composed mainly of andesite and rhyolite and its weighted mean 206Pb/238U age for 13 zircon grains is 2224±1 Ma. The Ergulazi Formation consists of basaltic andesite, basaltic trachyandesite, and andesite, and six grains give a weighted mean 206Pb/238U age of 131±4 Ma. The Sidaogou Formation consists mainly of trachyandesite and rhyolite, and six zircon grains yield a weighted mean 206Pb/238U age of113±4 Ma. The volcanic rocks have SiO2=60.24%-77.46%, MgO=0.36%-1.29% (Mg#=0.32-0.40) for the Naozhigou Formation, SiO2=51.60%-59.32 %, MgO=3.70 %-5.54% (Mg#=0.50-0.60) for the Ergulazi Formation, and SiO2=58.28%-76.32%, MgO=0.07%-1.20% (Mg#=0.14-0.46) for the Sidaogou Formation. The trace element analytical results indicate that these volcanic rocks are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relative depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, Nb, Ta, and Ti), and negative Eu anomalies. Compared with the primitive mantle, the Mesozoic volcanic rocks in the Linjiang area have relatively high initial 87Sr/86Sr ratios (0.7053-0.7083) and low eNd(t) values (-8.38 to -2.43), and display an EMII trend. The late Triassic magma for the Naozhigou Formation could be derived from partial melting of a newly accretional crust with the minor involvement of the North China Craton basement and formed under an extensional environment after the collision of the Yangtze Craton and the North China Craton. The Early Cretaceous volcanic rocks for the Ergulazi and Sidaogou Formations could be formed under the tectonic setting of an active continental margin related to the westward snbduction of

  20. Flank Collapse Assessment At Kick-'em-Jenny Submarine Volcano (Lesser Antilles): A Combined Approach Using Modelling and Experiments (United States)

    Dondin, Frédéric; Heap, Michael; Robert, Richard E. A.; Dorville, Jean-Francois M.; Carey, Steven


    Volcanic landslides - the result of volcanic flank failure - are highly hazardous mass movements due to their high mobility, the wide area they can impact, and their potential to generate tsunamis. In the Lesser Antilles at least 53 episodes of flank collapse have been identified, with many of them associated with voluminous (Vdeposit exceeding 1 km3) submarine volcanic landslide deposits. The existence of such voluminous deposits highlights the hazard of potentially devastating tsunami waves to the populated islands of the Lesser Antilles. To help understand and mitigate such hazards, we applied a relative stability assessment method to the only active submarine volcano of the Lesser Antilles island arc: Kick-'em-Jenny (KeJ). KeJ - located 8 km north of the island of Grenada - is the southernmost edifice in the arc with recognized associated volcanic landslide deposits. From the three identified landslide prehistoric episodes, one is associated with a collapse volume of about 4.4 km3. Numerical simulations considering a single pulse collapse revealed that this episode would have produced a regional tsunami. A volume estimate of the present day edifice is about 1.5 km3. We aim to quantify potential initial volumes of collapsed material using relative instability analysis (RIA). The RIA evaluates the critical potential failure surface associated with factor of safety (Fs) inferior to 1 and compares them to areas of deficit/surplus of mass/volume obtained from the comparison of an high resolution digital elevation model of the edifice with an ideal 3D surface named Volcanoid. To do so we use freeware programs VolcanoFit 2.0 and SSAP 4.5. We report, for the first time, results of a Limit Equilibrium Method (Janbu's rigorous method) as a slope stability computation analysis performed using geomechanical parameters retrieved from rock mechanics tests performed on two rock basaltic-andesite rock samples collected from within the crater of the volcano during the 1

  1. Waduk Parangjoho dan Songputri: Alternatif Sumber Erupsi Formasi Semilir di daerah Eromoko, Kabupaten Wonogiri, Jawa Tengah

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    Sutikno Bronto


    Full Text Available Semilir Formation was typically originated from products of a very explosive volcanic activity, i.e. breccias, lapillistones, and tuffs containing abundant pumice. It has a light grey to white colour and high silica andesite to dacite in composition, mainly rich in volcanic glass and quartz. Sedimentary structures of these volcanic rocks are massive, grading, planar bedding, and cross-bedding to antidunes, with grain size varies from ash (≤ 2 mm to lapilli (2 – 64 mm to bomb and block (> 64 mm. The formation is widely distributed from the west side (Pleret and Piyungan areas, Bantul Regency, Special Province of Yogyakarta until Eromoko area in the east (Wonogiri Regency, Jawa Tengah Province. Stratigraphically, the Semilir Formation underlies the Nglanggeran Formation, and overlies the Mandalika Formation in the eastern part and Kebo-Butak Formation in the western part. Geomorphological- and lithological analyses of the Semilir Formation in areas of Parangjoho and Song- putri Dams, Eromoko Sub-regency, Wonogiri Regency indicate that the two depressions were alternatively volcanic sources of the Semilir Formation in the Eromoko area. This is proved by the presence of co-ignimbrite breccias(co-ignimbrite lag fall deposits, that descriptively they are polymict breccias. This rock is characterized by a mixing of pumice and various hard rock fragments that primarily are juvenile materials (volcanic blocks, bombs, accessory-, and accidental rock fragments set in pumice-rich volcanic ash and lapilli sizes. The accessory materials came from older volcanic rocks, whereas the accidental ones were originated from basement rocks. During a caldera forming event or a destruction period of an older composite volcanic cone(s, all older rocks resting above the magma chamber were ejected to the surface by a very high magmatic pressure. Since they were heavier than the juvenile material, most accessory and

  2. A New System of Marginal Arc in the North of the South China Sea of Today (United States)

    Fang, N.; Dong, H.; Zhao, H.; Liu, H.; Shen, P.; Liang, X.


    The South China Sea (SCS) of today results from rupturing of the marginal continent of South China. Both its north and west margins are of typical passivity. Some records mirroring a Cretaceous active margin were reported in the study area. Generally they were attributed to westward subduction from the fossil Pacific plate. With respect of the problem, however, whether the subduction may induce response of an area far from the Pacific margin is an open question. The present approach has been primitively undertaken with the comparison of magmatic formation between the proto-SCS and the Pacific. The adakitic granite and Mg-rich andesite collected from the southern Hainan Island have their own petrologic and chemical characters as distinct from those igneous rocks from Zhejiang-Fujian province just bordering the western Pacific. Interestingly, the characters displayed in the Hainan are repeated in the Nha Trang-Tuy hoa area, South Vietnam. According to Tapponier's model (1986), Indo-China block was SE-ward slid 500-700km along the Red River Fault since the late Eocene. If restoring it, the Nha Trang-Tuy hoa area should be on the line extended westward from the Hainan Island. The above two sites constitute a latitudinal zone representing the active margin of the proto-SCS differing from the Pacific system. Actually some elements can be concentrated as follows to illustrate the framework in the northern margin of the SCS (fig. 1): (1) the late Jurassic to late Cretaceous volcano-sedimentary sequence drilled from the Chaoshan depression 150 mile off the Pearl River Delta, accumulating in the fore-arc environment, (2) the arc-related granite, diorite and monzodiorite (118-72Ma) drilled from the northern continental shelf, the SCS, (3) the Cretaceous andesite, andesitic basalt, granite, and pyroclastic sediments, afore-said, outcropping both in Hainan and South Vietnam, (4) granite-gneiss (75Ma) drilled in the Xisha foundation of reef platform, which might be the output of

  3. Rock property measurements guide interpretation of electromagnetic, magnetic and gravity models at Mts. Adams, Baker, Rainier and St. Helens (Invited) (United States)

    Finn, C.; Bedrosian, P. A.; Horton, R.; Polster, S.


    Hydrothermally altered rocks, particularly if water saturated, can weaken volcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows. Such alteration significantly reduces the electrical resistivity, magnetization and density of volcanic rocks, resulting in a clear distinction between altered and unaltered rock in geophysical survey measurements. We measured electrical resistivity, susceptibility and density of rock samples to help constrain models of the three-dimensional distribution of water saturated, hydrothermally altered sections of several Cascade Volcanoes, Washington, critical for understanding volcanic landslide hazards. Samples ranged from fresh, massive andesite and dacite to completely altered powders composed of opal, alunite, kaolinite, and montmorillonite. The resistivity of each sample was measured over 11 frequencies ranging from 100 to 100,000 Hz for dry and wet samples. Almost all dry sample resistivities typically exceed 5000 ohm-m. Water saturation levels vary from 2 to 33 wt% in the rocks samples and surpass 50% for the powders. Fresh andesite resistivity values exceed 1500 ohm-m, even when saturated. Resistivities of saturated, moderately altered samples and an intensely altered, low-porosity (~5%) opal and alunite sample are greater than 450 ohm m. Values less than 100 ohm-m are associated with saturated (>50%), intensely altered opal + alunite powders. Magnetic susceptibilities for the fresh volcanic rocks range from 4-25 x 10-3 SI while those of altered andesites range from 0 to 0.35 x 10-3 SI. Densities for the fresh rocks range from about 2200 - 2600 kg/m3 and 1300-1900 kg/m3 for the altered rocks. The combination of the rock property measurements, geophysical data and geological mapping, indicates the presence of appreciable thicknesses (>500 m) of altered rock west of the modern summit of Mt. Rainier in the Sunset Amphitheater region and in the central core of

  4. Complex variations during a caldera-forming Plinian eruption, including precursor deposits, thick pumice fallout, co-ignimbrite breccias and climactic lag breccias: The 184 ka Lower Pumice 1 eruption sequence, Santorini, Greece (United States)

    Simmons, J. M.; Cas, R. A. F.; Druitt, T. H.; Folkes, C. B.


    The 184 ka Lower Pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases: (1) a minor precursor (LP1-Pc) and (2) a major Plinian phase (LP1-A, B, C). The precursor phase produced 13 small-volume pyroclastic fallout, surge and flow deposits, which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style, and exhibit a normal (dacite to andesitic-dacite) to reverse (andesitic-dacite to dacite) compositional zonation of juvenile pyroclasts in the stratigraphy. Incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main Plinian eruption phase. The Plinian magmatic eruption phase is defined by three major stratigraphic divisions, including a basal pumice fallout deposit (LP1-A), an overlying valley-confined ignimbrite (LP1-B) and a compositionally zoned (rhyodacite to basaltic andesite) lithic-rich lag breccia (LP1-C), which caps the sequence. This sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late-stage caldera collapse events. Similarities in pyroclast properties (i.e., chemistry, density), between the Plinian fallout (LP1-A) and pyroclastic flow (LP1-B) deposits, indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the LP1 eruption. Conversely, lithic breccias at the base of the LP1-B ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and/or the initiation of caldera collapse, leading to vent widening, an increase in magma discharge rate and the increased incorporation of lithics into the eruption column, causing mass overload. Lithic-rich lag breccia deposits (LP1-C), which cap the eruption sequence, record incremental, high

  5. The Geology and Petrography of Yücebelen and Surrounding Area, Torul-Gümüşhane (United States)

    Doǧacan, Özcan; Özpınar, Yahya


    The study area is located in the tectono-stratigraphic zone named "Eastern Pontide Zone" from the northeastern part of Turkey. Eastern Pontides were formed by the subduction of Tethys Ocean under the Eurasian plate, during the Early Cretaceous - Late Eocene. Eastern Pontide orogenic zone can be divided in two tectono-stratigraphic subgroups as the northern and southern zones. The study area is located very close to border of these two subgroups but located in northern zone. In this project, the first geological map of the study area at the scale 1:5000 was made. Subsequently, detailed geological maps at the scale 1:2000 were made for the areas rich in ores. In the study area, Upper Cretaceous volcanic rocks consisting of basalts and basaltic andesites take place at the bottom of the rock sequence. Basalts and basaltic andesites with hyaloophitic, vitrophiric and microporphyric texture comprise plagioclase +pyroxene +chlorite +calcite ±epidote ±chalcedony ±opaque minerals. They are overlain by concordant pyroclastic and dacitic-rhyodacitic rocks. Quarts + K-feldispar ±plagioclase? ±biotite ±chlorite ±calcite ±chalcedony minerals are determined as a result of microscope investigation on samples taken from these rocks. These rocks are overlain by sedimentary rocks intercalated with pyroclastic rocks. All those units mentioned above, were intruded by granitoids of supposed Upper Cretaceous-Eocene age. Granitoids that crop out in the area were classified in terms of Q-ANOR parameters as granodiorites (Adile Hamlet occurrence - investigated in detail), diorites (Tuzlak Hill occurrence- eastern-part of study area) and quartz monzodiorites (İstavroma Hill occurrence- northern part of study area). Adile Hamlet granodiorites comprise plagioclase +pyroxene +chlorite +calcite ±quarts ±epidote +opaque minerals. A sequence of quarts +orthoclase +plagioclase ±chlorite ±epidote ±calcite ±opaque minerals have been determined after investigation of the rock samples

  6. New Insights Into Volcanic Hazards in Western Mexico: Multiple Cone-Building Episodes at Arc Stratovolcanoes Revealed by 40Ar/39Ar Geochronology (United States)

    Frey, H. M.; Lewis-Kenedi, K.; Lange, R. A.; Hall, C. M.; Delgado-Granados, H.


    The detailed eruptive histories of two andesitic stratocones, Volcáns Ceboruco and Tequila, in the western Mexican arc have been documented using 40Ar/39Ar geochronology. The volumes of these volcanoes were obtained with mapping, airphotos, and digital elevation models. The age and volume data constrain the rate and duration of major cone-building events, which bears on the longevity of the underlying upper-crustal magma chambers that fed the eruptions. The results indicate that at each stratovolcano there were two discrete cone-building events, separated by a hiatus. At V. Tequila, six samples from the edifice yielded dates (196 +/- 8, 196 +/- 19, 178 +/- 8, 191 +/- 13, 216 +/- 11, and 198 +/- 11 ka; errors are 1 sigma) with a mean eruption age of 196 +/- 12 ka. Thus the bulk of the main edifice ( ˜31 km3) erupted within 24 kyrs (at the 2 sigma level), leading to a cone-building rate of > 1.3 km3/kyr. After a hiatus of ˜110 kyrs, ˜14 km3 of andesite erupted along the NW and SE flanks of V. Tequila at 90 +/- 19 ka. The last activity at V. Tequila produced a ˜2 km3 parasitic cone at ˜60 ka. Since an eruption has not occurred in the last 60 kyrs, V. Tequila is often considered an extinct volcano. This may be the view held by the > 75,000 inhabitants of the town of Tequila located on the northern flanks. A similar history of two discrete cone-building events is found at V. Ceboruco, ˜75 km to the NW. Seven samples taken from various parts of the edifice, including the inner caldera wall, indicate an initial cone-building event at ˜45 ka in which ˜37 km3 of andesite erupted. After a hiatus of nearly 44 kyrs, a second eruptive period began ˜1000 years ago. The first eruption to occur after the hiatus was Plinian and released 3-4 km3 of dacite. In the last 1 kyr, 9.5 km3 of andesite and dacite erupted effusively, culminating in the historic 1870 flow. The sobering conclusion, in terms of volcanic hazards assessment, is that the only Plinian eruption to occur

  7. Nd—Sr Isotope Geological Study on the Age of Armantai Ophiolite,Xinjiang,China

    Institute of Scientific and Technical Information of China (English)

    黄萱; 金成伟; 等


    Sm-Nd and Rb-Sr whole-rock isochron dating of the samples of cumulated gabbro,diabase and andesitic porphyrite from the Armantai ophiolite,Xinjiang,yielded the ages of 561±41(Ma(εNd(t)=6.1)and 392±17Ma(87Sr/86Sr)i=0.7041],which stand for the ages of creation and later metamorphism of the ophiolites,respectively,The creation environment of the Armantai ophiolites seems to a back-arc basin caused by the southward subduction of the the Armantai ophiloites seems to a back-arc basin caused by the southward subduction of the palaeo-Asia Ocean.

  8. Micromorphological Characterization of Some Volcanic Soil In West Java

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    Mahfud Arifin


    Full Text Available characterization has been studied on six pedons of soils developing in volcanic materials in West Java. The pedons represent deposits of different volcanoes (Mount Tangkuban Perahu, Mount Patuha and Mount Papandayan with different ages (Pleistocene, Holocene within two types of volcanisms (andesitic, basaltic, and three agroclimatic zones (A, B1, B2. Undisturbed soil samples were taken from each identifiable horizon for thin section preparations. Observations were carried out by means of a magnifying lens, binocular stereomicroscope, polarization microscope, and scanning electron microscope (SEM. The result demonstrates that micromorphological characteristics of volcanic soils developing from different ages, types of parent material, and climate were different through their c/f related distribution 2µ patterns, c/f ratios, sorting, infillings and coatings of voids, and microstructure.  

  9. Petrographic and geochemical characterization of the Triassic and Jurassic magmatic and volcanic rocks of southeastern Ecuador (United States)

    Villares, Fabián; Eguez, Arturo; Yanez, Ernesto


    Formely, the subandean zone in the southeastern Ecuador involved large volcanic and magmatic rocks included in the Misahualli Formation and Zamora batholith, both as expression of the Jurassic cal-alcaline volcanic arc. The aim of the project carried out by the INIGEMM (Instituto Nacional de Investigación Geológico Minero Metalúrgico) was discriminate the volcanic products including a continuous set going from basalts to ryolithes and volcanoclastic rocks. Geochemical characterization was done using representative 16 whole - rock chemical analysis. The oldest rocks of the investigated area called Pachicutza Unit, include greenish to black, massive basalts and basaltic andesites, locally showing pillows structures. The texture is aphanitic to microporphyritic with slight crystal growth of plagioclase and pyroxenes. The Unit include also local pyroclastic breccias and tuffs showing variable skarnification related to the intrusion of the jurassic Zamora Batholith. Two samples of basalts show tholeiitic affinity, corresponding to an N- MORB, probably representing an early stage in opening of a regional Triassic rift reported since Colombia to Peru in the Andes. These geochemical characteristics are similar to the amphibolites of Monte Olivo Unit in the Real Cordillera. The Jurassic large volcanic assembly of the Misahualli Formation was also differenciated. Basal volcanics include green, subporphyritic andesites and volcanic breccias possibly generated at an early stage of the volcanic arc, caused by a change of extensive to compressive regime. Continental volcano sedimentary and sedimentary rock were discriminate as Nueva Esperanza and Suarez Units, respectively. The volcanosedimentary sequence include massive to laminate tuffs and tuffites of intermediate composition. The sediments of the Suarez Unit include dominant conglomerats and sandstones of fluvial domain. The regional volcanic sequence is completed by the Las Peñas Unit that includes aphanitic to

  10. A Late Proterozoic Early Paleozoic magmatic cycle in Sierra de la Ventana, Argentina (United States)

    Gregori, D. A.; López, V. L.; Grecco, L. E.


    Late Proterozoic-Early Paleozoic intrusive and volcanic rocks of Sierra de la Ventana can be grouped into two magmatic assemblages: the Meyer and Cochenleufú suites. The older (700-570 Ma) is composed of S-type quartz-monzodiorites, synogranites, and monzogranites associated with andesites and rhyolites and related to volcanic-arc and postcollisional settings. The younger (540-470 Ma) corresponds to highly fractionated homogeneous A-type monzogranites, linked to final plutonic events during postorogenic extension in collisional belts. Strong similarities between Sierra de la Ventana magmatic rocks and the S- and A-type granites of the Cape granite suite in South Africa allow positive correlation. In both areas, primitive volcanic arcs or collisional orogens are recognized. Continuous transpressional shearing between the Swartland and Tygerberg terranes in the Saldania belt may have triggered the generation and emplacement of both suites.

  11. Field Geothermal Volcano Azufral (CO)

    International Nuclear Information System (INIS)

    The field geothermal Volcano Azufral is located to 60 km of Pasto City. It discharges waters chlorine-bicarbonates, diluted and of neuter pH. The riolitics of low k20, andesites, dacites as well as lava flows, hydro volcanic deposits due to events volcanic past and the influence of calcium like main component in the layer stamp are the main ones characteristic geologic of the volcanic area of Azufral. The layer stamp heats waters of the underground and it reacts until producing bicarbonates waters, more common type in the region. Glasses of sulfur toward the crater of the volcano are presented close to a sour lagoon. Thermal activity has been detected toward the southwest of the volcano with an area of covering of 1.47 there are, approximately. Changes in the last 14 years were determined by comparison of last chemical analysis with those obtained by INEA in 1996

  12. Petrography and geochemistry of metamafic rocks intercalated in gneisses from Goiás Magmatic Arc, region of Indiara (GO

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    Guillermo Rafael Beltran Navarro


    Full Text Available In Indiara region (GO, dozens of metamafic rocks lenses of various dimensions (metric to kilometric occur, intercalated in gneisses of the Goiás Magmatic Arc and oriented according to the direction of the main foliation (Sn. These lenses consist of amphibolite (amphibole schists and amphibolites, have chemical compositions of sub-alkaline basalts to andesitic basalts and sub-alkaline tholeiitic affinity. The distribution of major and trace elements, as well as rare earth elements (REE, suggests that these rocks are derived from a source with similar geochemical signature. The analyzed rocks are enriched in large ion litophile elements (Cs, Rb, Ba, K, Th and U in relation to elements of high field strength (Nb, Ta, Zr, Hf and Y and in relation to REE, Sr, P and Ti, showing weak to medium negative anomalies of Nb, Ta and P and suggesting that these rocks were generated in a magmatic arc environment.

  13. A dynamical analysis of the seismic activity of Villarrica volcano (Chile) during September-October 2000

    Energy Technology Data Exchange (ETDEWEB)

    Tarraga, Marta [Departamento de Volcanologia. Museo Nacional de Ciencias Naturales, CSIC, Madrid (Spain)], E-mail:; Carniel, Roberto [Dipartimento di Georisorse e Territorio, Universita di Udine, Via Cotonificio 114, 33100 Udine (Italy)], E-mail:; Ortiz, Ramon; Garcia, Alicia [Departamento de Volcanologia. Museo Nacional de Ciencias Naturales, CSIC, Madrid (Spain); Moreno, Hugo [Observatorio Volcanologico de los Andes del Sur (OVDAS), Servicio Nacional de Geologia y Mineria de Chile (SERNAGEOMIN), Temuco, IX Region (Chile)


    Although Villarrica volcano in Chile is one of the most active in the southern Andes, the literature studying its seismic activity is relatively scarce. An interesting problem recently tackled is the possibility for a regional tectonic event to trigger a change in the volcanic activity of this basaltic to basaltic-andesitic volcano, which is in turn reflected in the time evolution of the properly volcanic seismicity, especially in the form of a continuous volcanic tremor. In this work, we conduct a spectral, dynamical and statistical analysis of the tremor recorded during September and October 2000, in order to characterize the anomalous behaviour of the volcano following a tectonic event recorded on 20th September 2000. The observed dynamical transitions are compared with remote sensing and visual observations describing the changes in the eruptive style of the volcano.

  14. Paleocene volcano-clastic sequences in the Tuz Golu Basin, central Anatolia, Turkey: an evolution of petroleum reservoir rock properties using logs

    Energy Technology Data Exchange (ETDEWEB)

    Ayyildiz, T.


    The Paleocene unit of the Karapinar-1/1A and-2/2A wells was studied by subsurface data in the Tuz Golu Basin. The Karapinar-1/1A well mainly consists of acidic, andesite, and dasite tuff levels, which was determined according to an M-N plot chart. In the Karapinar-2/2A well, dasite tuff is characteristic and some levels have rhyolite, glassy rhyolite tuff, and zeolite tuff properties. In the Karapinar field, formation water salinity is very high (150,000-200,000 ppm), causing low resistivity and porosity values. Petrophysical properties show that tuff sequence total porosity is between 9 and 20%, and the fracture structure indicates that tuff level should be a prospect for hydrocarbon exploration in the Tuz Golu Basin. (author)

  15. Análisis e interpretación de los materiales volcánicos del Cerro de los Frailes (Cabo de Gata. Almería

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    Fernández Soler, J. M.


    Full Text Available The formation of Los Frailes volcano had two stages, which produced amphibole andesites (Frailes-I and two-pyroxene andesites (Frailes-II respectively, Iying on the extension of the dacites and andesites of the southernmost Cabo de Gata volcanoes (Revancha-Sabinal. The FRAILES-I stage is discontinuous, and has mainly produced domes and autoclastic breccias, in addition to an intermediate level of pumice-and-ash flow; this unit has some intercalated sedimentary levels. To the NE it is covered by a formation of sedimentary and hydroclastic rocks. The Frailes-II stage is continuous, and has formed some lava flows, the two summit domes, and sorne pyroclastic rocks of scarcely explosive origin. Other volcanic features are some domes and dikes of biotite-amphibole dacites, which affect to the Frailes-I-group; these are the southern continuation of the dacitic volcanic group of Rodalquilar-Rellana-Garbanzal. The generally accepted idea of a succesion in Cabo de Gata of cycles which started very explosively and ended with subvolcanic extrussions (domes does not seem to be very realistic at least in the building of Los Frailes. A review of geochronological data, and the field disposition of the described materials does not discard the hypothesis that the pyroxene andesites of FrailesI-I might have been formed simultaneously or even than later the ignimbritic dacites of the Rodalquilar group.La formación del volcán de Los Frailes se produjo en dos ciclos, de composiciones andesítica anfibólica (Frailes-I y andesitica de dos piroxenos (Frailes-II, apoyadas sobre la prolongación hacia el este de las andesitas y dacitas del extremo sur de Cabo de Gata (edificio de Revancha-Sabinal-Cabo de Gata. El ciclo Frailes-I es discontínuo y ha formado domos y brechas autoclásticas principalmente, mas un nivel intermedio de colada piroclástica pumítica; este ciclo contiene niveles sedimentarios intercalados. Al NE es cubierto por una formación de rocas

  16. The Laramide Mesa formation and the Ojo de Agua caldera, southeast of the Cananea copper mining district, Sonora, Mexico (United States)

    Cox, Dennis P.; Miller, Robert J.; Woodbourne, Keith L.


    The Mesa Formation extends from Cananea, Mexico, southeast to the Sonora River and is the main host rock of Laramide porphyry copper deposits in the Cananea District and at the Alacran porphyry prospect to the east. The Mesa consists of two members-a lower andesite and an upper dacite. The lowest part of the dacite member is a crystal tuff about 100 m thick. This tuff is the outfall of a caldera centered near the village of Ojo de Agua, dated by 40Ar/39Ar at 65.8 Ma ?0.4. The Ojo de Agua Caldera is about 9 km in diameter and is filled by a light gray biotite dacite tuff with abundant flattened pumice fragments. The volume of the caldera is estimated to be 24 km3.

  17. Characteristics of paleoproterozoic Subduction System in Western Margin of Yangtze Plate

    Institute of Scientific and Technical Information of China (English)


    Paleoproterozoic subduction strongly occurred in the western margin of Yangtze plate. The basaltic-andesite volcanics of Ailaosban Group and Dibadu Formation had been formel during paleo-Qinghai-Tibet oceanic plate subduction under the paleo-Yangtze plate. Their trace element geochemistry suggests that their forming environments are continental-margin-arc and back-arcbasin respectively. Consequently , the Paleoproterozoic subduction system in the western margin of Yangtze plate was established. Ailaohan Group and Dibadu For mation came from an enriched mantle source that was contaminated by crustal sediments carrled by subducted slab, and formed the Paleoroterozoic metamorphic basement of western margin of Yangtze plate. Ailaoshan Group is actually western boundary of Yangtze plate.

  18. Zircon U-Pb and molybdenite Re-Os geochronology and Sr-Nd-Pb-Hf isotopic constraints on the genesis of the Xuejiping porphyry copper deposit in Zhongdian, Northwest Yunnan, China (United States)

    Leng, Cheng-Biao; Zhang, Xing-Chun; Hu, Rui-Zhong; Wang, Shou-Xu; Zhong, Hong; Wang, Wai-Quan; Bi, Xian-Wu


    The Xuejiping porphyry copper deposit is located in northwestern Yunnan Province, China. Tectonically, it lies in the southern part of the Triassic Yidun island arc. The copper mineralization is mainly hosted in quartz-dioritic and quartz-monzonitic porphyries which intruded into clastic-volcanic rocks of the Late Triassic Tumugou Formation. There are several alteration zones including potassic, strong silicific and phyllic, argillic, and propylitic alteration zones from inner to outer of the mineralized porphyry bodies. The ages of ore-bearing quartz-monzonitic porphyry and its host andesite are obtained by using the zircon SIMS U-Pb dating method, with results of 218.3 ± 1.6 Ma (MSWD = 0.31, N = 15) and 218.5 ± 1.6 Ma (MSWD = 0.91, N = 16), respectively. Meanwhile, the molybdenite Re-Os dating yields a Re-Os isochronal age of 221.4 ± 2.3 Ma (MSWD = 0.54, N = 5) and a weighted mean age of 219.9 ± 0.7 Ma (MSWD = 0.88). They are quite in accordance with the zircon U-Pb ages within errors. Furthermore, all of them are contemporary with the timing of the Garzê-Litang oceanic crust subduction in the Yidun arc. Therefore, the Xuejiping deposit could be formed in a continental margin setting. There are negative ɛNd(t) values ranging from -3.8 to -2.1 and relatively high initial 87Sr/86Sr ratios from 0.7051 to 0.7059 for the Xuejiping porphyries and host andesites. The (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t values of the Xuejiping porphyries and host andesites vary from 17.899 to 18.654, from 15.529 to 15.626, and from 37.864 to 38.52, respectively, indicative of high radiogenic Pb isotopic features. In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS exhibit that there are quite uniform and slightly positive ɛHf(t) values ranging from -0.2 to +3.2 (mostly between 0 and +2), corresponding to relatively young single-stage Hf model ages from 735 Ma to 871 Ma. These isotopic features suggest that the primary magmas of the Xuejiping porphyries and

  19. Continental Collision Zones are Primary Sites of net Continental Crustal Growth: Evidence From the Linzizong Volcanic Succession in Southern Tibet (United States)

    Niu, Y.; Mo, X.; Dong, G.; Zhao, Z.; Hou, Z.; Zhou, S.; Ke, S.


    The Linzizong volcanics (ca. 65-45Ma) and the coeval batholiths (ca. 60-40Ma) of andesitic-to-rhyolitic composition are magmatic response to the India-Asia continental collision that began at ca. 70-65Ma and ended at ca. 45-40Ma with convergence continuing to present [1,2]. These syncollisional magmatic rocks are widely distributed along much of the >1500km long Gangdese Belt immediately north of the India-Asia suture (Yarlung-Zangbo) in southern Tibet [2-6]. Our study of the Linzizong volcanics from the Linzhou Basin (near Lhasa) encourages the proposal that syncollisional granitoid magmatism may in fact account for much of the net contribution to continental crust growth. The Linzizong volcanics in the Linzhou Basin show a first-order temporal change from the lower andesitic formation (64.4-60.6Ma), to the middle dacitic formation (ca. 54Ma), and to the upper rhyolitic formation (48.7-43.9Ma). The three formations show no systematic but overlapping Nd-Sr isotope variations. The isotopically depleted samples with ɛNd(t)>0 (up to + 8) indicate that their primary sources are of mantle origin. The best source candidate in the broad context of Tethyan ocean closing and India- Asia collision is the remaining part of the Tethyan ocean crust [6]. This ocean crust melts when reaching its hydrous solidus during and soon after the collision in the amphibolite facies, producing andesitic melts parental to the Linzizong volcanics (also the coeval batholiths) with inherited mantle isotopic signatures [6]. Ilmenite is abundant in amphibolite [7], and partial melting of amphibolite with ilmenite as a residual phase accounts for the depletion of Nb, Ta and Ti in the melt. The effect of ocean crust alteration plus involvement of mature crustal materials (e.g., recycled terrigeneous sediments) enhances the elevated abundances of Ba, Rb, Th, U, K and Pb in the melt [8,9]. These give the syncolissional Linzizong volcanics characteristic "arc-like" geochemical signature. Residual

  20. Sulfate Saturated Hydrous Magmas Associated with Hydrothermal Gold Ores (United States)

    Chambefort, I.; Dilles, J. H.; Kent, A. J.


    Hydrothermal ore deposits associated with arc magmatism represent important sulfur anomalies. During degassing of magmatic systems the volatile may transport metals and sulfur and produce deposits. The ultimate origin of the magma-derived sulfur is still uncertain. The Yanacocha high-sulfidation epithermal Au deposit, Peru, is hosted by a Miocene volcanic succession (ca. 16 to 8 Ma). Magmatic rocks are highly oxidized >NNO+2 and show a range of composition from andesite to dacite. Two populations of amphibole occur in the Yanacocha dacitic ignimbrite deposits (~7 and 12 wt% Al2O3). Low Al amphiboles crystallized at ~ 1.5-2 kbar and 800°C (Plag-Hb thermobarometry) in equilibrium with plagioclase and pyroxene. High Al amphiboles only contain inclusions of anhydrite associated with apatite (up to 1.2 wt% SO3), and have a higher Cr2O3 content (up to 1000 ppm). We estimate these amphiboles form near the magma's liquidus at P(H2O)> 3kbar and 950 to 1000°C of a basaltic, basaltic andesite ascending magma. Low Al amphibole presents an REE pattern with negative anomalies in Sr, Ti and Eu, characteristic of plagioclase and titanite fractionation in the magma. High Al amphiboles are less enriched in REE and have no Sr, Ti, or Eu anomaly. Rare crystals of high Al amphibole display a low Al rim marked by higher REE contents compared to the core and a negative Eu anomaly. Magmatic sulfate occurrences have been discovered through the 8 m.y. volcanic sequence. Rounded anhydrite crystals are found included within clinopyroxene and both high and low Al amphibole. The rare high Al amphiboles (from the sample RC6) contain up to ~10 vol.%, ~5-80 micrometer-long anhydrite as irregularly shaped (amoeboid) blebs that do not show crystallographic forms and do not follow host cleavages. Extremely rare sulfide inclusions are found in plagioclase (Brennecka, 2006). The major and trace element contents of Yanacocha magmatic anhydrite have been analyzed by electron microprobe and LA

  1. Wastewater treatment with multilayer media of waste and natural indigenous materials. (United States)

    Rahman, Mohammad Arifur; Ahsan, Shamim; Kaneco, Satoshi; Katsumata, Hideyuki; Suzuki, Tohru; Ohta, Kiohisa


    Wastewater treatment using waste materials (refuse concrete, waste paper and charcoal) and natural indigenous rocks (andesite, limestone, granite and nitrolite) in the form of multilayer media was investigated. The removal of suspended solids (SS), phosphate ion, nitrate ion, ammonium ion, toxic metals and chemical oxygen demand (COD) were evaluated for the multilayer wastewater treatment system. Effective removal of heavy metals such as cadmium, chromium, mercury and lead was demonstrated. SS and phosphate ion were removed with relatively high efficiency and the COD after treatment was lessened using certain combinations of media. The present wastewater treatment system is simple, convenient and low cost. Therefore, this method can be applied in small scale plants for wastewater treatment in local and nonexclusive areas. PMID:15627464

  2. Triassic rift-related sedimentary basins in northern Chile (24° 29°S) (United States)

    Suarez, M.; Bell, C. M.


    Triassic rocks in northern Chile (latitude 24°-29°S) include marine and continental rift-related sedimentary deposits, associated with basaltic, andesitic, and silicic volcanic rocks. Five main successions include the deposits of two marine basins (Profeta and San Félix) separated by three continental basins (Cifuncho, La Ternera, and La Coipa). The marine strata include turbidites and debris flow deposits interpreted as coarse-grained fan-delta sediments. The continental sediments include lacustrine fan delta, open lake, braided river, alluvial fan, and sabkha deposits. The widespread fan-delta systems (both marine and lacustrine), together with abrupt lateral and vertical facies discontinuities and large-scale depositional cycles, are indicative of rift-controlled sedimentation. The associated magmatic activity indicates that this rifting was the product of subduction-related extension or strike-slip movement on the active plate margin. Triassic rifting was followed in Late Triassic to Early Jurassic times by widespread thermotectonic subsidence.

  3. Petrology and petrogenesis of the Eocene Volcanic rocks in Yildizeli area (Sivas), Central Anatolia, Turkey (United States)

    Doğa Topbay, C.; Karacık, Zekiye; Genç, S. Can; Göçmengil, Gönenç


    Yıldızeli region to the south of İzmir Ankara Erzincan suture zone is situated on the large Sivas Tertiary sedimentary basin. After the northern branch of the Neotethyan Ocean was northerly consumed beneath the Sakarya Continent, a continent - continent collision occurred between the Anatolide- Tauride platform and Pontides and followed a severe intermediate magmatism during the Late Cretaceous- Tertiary period. This created an east-west trending volcanic belt along the whole Pontide range. In the previous studies different models are suggested for the Eocene volcanic succession such as post-collisional, delamination and slab-breakoff models as well as the arc model for its westernmost parts. We will present our field and geochemical data obtained from the Yıldızeli and its surroundings for its petrogenesis, and will discuss the tectonic model(s) on the basis of their geochemical/petrological aspects. Cenozoic volcanic sequences of Yıldızeli region which is the main subject of this study, overlie Pre-Mesozoic crustal meta-sedimentary group of Kırşehir Massif, Ophiolitic mélange and Cretaceous- Paleocene? flysch-like sequences. In the northern part of Yıldızeli region, north vergent thrust fault trending E-W seperates the ophiolitic mélange complex from the Upper Cretaceous-Paleocene and Tertiary formations. Volcano-sedimentary units, Eocene in age, of the Yıldızeli (Sivas-Turkey) which are intercalated with sedimentary deposits related to the collision of Anatolide-Tauride and a simultaneous volcanic activity (i.e. the Yıldızeli volcanics), exposed throughout a wide zone along E-W orientation. Yıldızeli volcanics consist of basalts, basaltic-andesites and andesitic lavas intercalated flow breccias and epiclastic, pyroclastic deposits. Basaltic andesite lavas contain Ca-rich plagioclase + clinopyroxene ± olivine with minor amounts of opaque minerals in a matrix comprised of microlites and glass; andesitic lavas are generally contain Ca

  4. An Early Cretaceous volcanic arc/marginal basin transition zone, Peninsula hardy, southernmost Chile (United States)

    Miller, Christopher A.; Barton, Michael; Hanson, Richard E.; Fleming, Thomas H.


    The Hardy Formation represents a latest Jurassic-Early Cretaceous volcanic arc that was located along the Pacific margin of southern South America. It was separated from the continent by a marginal basin floored by portions of an ophiolite sequence (the Rocas Verdes ophiolites). The transition between the arc and marginal basin occurs on Peninsula Hardy, southernmost Chile, where there is a lateral facies transition from arc deposits of the Hardy Formation into proximal marginal basin fill of the Yahgan Formation. Interfingering of arc and marginal basin sequences demonstrates that subduction-related arc magmatism was concurrent with marginal basin formation. The lateral facies transition is reflected in the geochemistry of volcanic rocks from the Hardy and Yahgan formations. Basalts, andesites and dacites of the arc sequence follow a calc-alkaline differentiation trend whereas basalts from the marginal basin follow a tholeiitic differentiation trend. Estimates of temperature and oxygen fugacity for crystallization of the arc andesites are similar to values reported for other calc-alkaline andesites. It is suggested that water activity influenced the early or late crystallization of Ti-magnetite and this controlled the style of differentiation of the magmas erupted on Peninsula Hardy. Magmas with high water contents evolved along the calc-alkaline differentiation trend whereas those with low water contents evolved along the tholeiitic differentiation trend. Some rhyolites are differentiated from the calc-alkaline andesites and dacites, but most appear to be the products of crustal anatexis on the basis of trace-element evidence. The arc basalts and some marginal basin basalts show relative enrichment in LILE, relative depletion in HFSE, and enrichment in LREE. Other marginal basin basalts are LREE depleted and show small relative depletions in HFSE. Basalts with both calc-alkaline and tholeiitic affinities can also be recognized in the Rocas Verdes ophiolites

  5. Constraints on Mineral-Phase Abundances and Compositions in the Low-Albedo Northern Plains of Mars using MGS-TES, OMEGA, and Laboratory Spectral Data. (United States)

    Wyatt, M. B.; Mustard, J. F.


    The abundances and compositions of mineral-phases in the low-albedo northern plains of Mars have been a focus of considerable study and debate in recent years. Large expanses of Acidalia Planitia surface materials are characterized by the MGS-TES Surface Type 2 (ST2) spectral endmember [1]. The ST2 spectrum is distinguished by a rounded, slightly V-shaped 800 to 1200 wavenumber region of absorption and uniform absorption at low wavenumbers. The same areas are also characterized by an OMEGA spectral signature that is relatively featureless, but with a strong blue slope (decreasing reflectance as a function of wavelength) from 0.9 to 2.6 microns [2]. A central question with both observations is whether they represent the spectral signature of a high-silica primary volcanic lithology (andesite) or the effects of chemical alteration on basaltic surface materials. Ambiguity in classifying the ST2 lithology arises because a spectral component of this unit (20-30 vol %) can be interpreted as volcanic siliceous glass [1, 3] (an abundant phase in andesite) or a combination of secondary phases found in altered basalt (amorphous silica-rich coatings, palagonite, smectite, and zeolite) [4-8]. Similarly, the OMEGA spectrum lacks evidence of distinct mafic mineral bands (found in andesite) as well as molecular vibration absorptions due to H2O and/or OH-, which might indicate the presence of well- crystalline alteration products and phyllosilicates [2]. Constraining these compositions is significant for understanding the petrogenesis of the Martian crust and its subsequent alteration. Identification of widespread andesite may imply an early episode of plate tectonics on Mars while altered basalt would indicate extensive surface-volatile interactions. The objective of this study is to combine TES and OMEGA observations of the low-albedo northern plains for comparison to laboratory thermal infrared and visible/near-infrared measurements of primary volcanic lithologies (basalt to

  6. Melting features along the Ryukyu slab tear, beneath the southwestern Okinawa Trough (United States)

    Lin, Jing-Yi; Hsu, Shu-Kun; Sibuet, Jean-Claude


    The present-day active volcanic front associated with the Ryukyu subduction zone extends from Japan to the Ilan plain (northern Taiwan) and is located within the Okinawa Trough, 80-100 km above the Ryukyu slab. An abnormal amount of arc volcanism, which consists of basalt, andesite and rhyolite occurs within the southwestern Okinawa Trough, above a slab tear of the Ryukyu subduction zone (CBVT). The power spectrum analysis of magnetic data shows the occurrence of a thin crust above the slab tear and a thick crust beneath this volcanic area. We suggest that an excess of H2O-rich fluid might occur at the slab tear and might increase the melt flux. Both are conveyed obliquely to the uppermost mantle and lower crust CBVT magmas. After interactions, basaltic magmas would rise up, accounting for the contrast of magnetization between this volcanic body and the adjacent OT crust.

  7. An oxygen isotope and geochemical study of meteoric-hydrothermal systems at Pilot Mountain and selected other localities, Carolina slate belt (United States)

    Klein, T.L.; Criss, R.E.


    Several epigenetic mineral deposits in the Carolina slate belt are intimately related to meteoric-hydrothermal systems of late Precambrian and early Paleozoic age. At Pilot Mountain, low 18O rocks correlate well with zones of strong silicic alteration and alkali leaching accompanied by high alumina minerals (sericite, pyrophyllite, andalusite ?? topaz) and anomalous concentrations of Cu, Mo, Sn, B, and Au. A magmatic source for much of the sulfur and metal is likely, and a subordinate magmatic water component in the fluid of the central zone is possible. This central zone is surrounded by a >30 km2 peripheral zone of low 18O sericite schists, chlorite-sericite schists, and andesitic volcanic rocks. Reconnaissance studies of other alteration zones in the Carolina slate belt have so far disclosed the involvement of meteoric-hydrothermal fluids at the Snow Camp pyrophyllite deposit, at the Hoover Hill and Sawyer Au mines, and probably at the Haile and Brewer Au mines. -from Authors

  8. K-Ar Geochronology and isotopic composition of the late oligocene- early miocene Ancud volcanic complex, Chiloe

    International Nuclear Information System (INIS)

    The Ancud Volcanic Complex (Gally and Sanchez , 1960) forms a portion of the Mid-Tertiary Coastal Magmatic Belt which outcrops in the area of northern Chiloe island. Main exposures occur at Ancud, Punta Polocue, Punihuil, Pumillahue, Tetas de Teguaco and Bahia Cocotue. The Ancud Volcanic Complex consists of basaltic to basaltic andesites lava flows and volcanic necks and rhyolitic pyroclastic flows and vitric domes. Previous studies indicate a Late Oligocene-Early Miocene age (Garcia et al., 1988; Stern and Vergara, 1992; Munoz et al., 2000). The Ancud Volcanic Complex covers and intrudes Palaeozoic-Triassic metamorphic rocks and is partially covered by an early to middle Miocene marine sedimentary sequence known as Lacui Formation (Valenzuela, 1982) and by Pleistocene glacial deposits (Heusser, 1990). At Punihuil locality, lava flows are interbedded with the lower part of the marine sedimentary sequence, which includes significant amounts of redeposited pyroclastic components. Locally, the presence of hyaloclastic breccias suggests interaction of magma with marine water (au)

  9. Achieving Mixtures of Ultra-High Performance Concrete

    Directory of Open Access Journals (Sweden)

    Mircea POPA


    Full Text Available Ultra-High Performance Concrete (UHPC is a relatively new concrete. According to [11] UHPC is that concrete which features compressive strength over C100/115 class. Up to this point standards for this type of concrete were not adopted, although its characteristic strength exceeds those specified in [33]. Its main property is high compressive strength. This provides the possibility of reducing the section of elements (beams or columns made of this type of concrete, while the load capacity remains high. The study consists in blending mixtures of UHPC made of varying proportions of materials. The authors have obtained strengths of up to 160 MPa. The materials used are: Portland cement, silica fume, quartz powder, steel fibers, superplasticiser, sand and crushed aggregate for concrete - andesite.

  10. Isotope geochemistry of lavas of central Java, Indonesia and Heard Island, Indian ocean - evidence for sedimentary and mantle plume source components

    International Nuclear Information System (INIS)

    Trace element and Sr-Nd-Pb isotopic data for Slamet basalt-andesites indicate that their parental magmas are affected by small degrees of crustal contamination. The geochemistry of their mantle sources, rich in LILE and LREE has been influenced by a sedimentary component of the underlying subducted lithosphere. This contribution presents some of the elemental and isotopic data (including new Pb- isotope data) upon which this interpretation is based, and compares the isotopic compositions of the Slamet lavas of north-central Java, Indonesia, with estimates of Heard Island (an oceanic island volcano, in the southern Indian Ocean ) low 87Sr/86Sr end-members and also lavas of Muriah and Ringgit-Beser, Java

  11. Resumen cronoestratigráfico de las rocas ígneas de Costa Rica basado en dataciones radiométricas (United States)

    Alvarado, G. E.; Kussmaul, S.; Chiesa, S.; Gillot, P.-Y.; Appel, H.; Wörner, G.; Rundle, C.


    Based on a recompilation of about 160 K-Ar and U-Th analyses of igneous rocks and their stratigraphic relationships, a synthesis of the magmatic evolution of Costa Rica is presented. The igneous rocks of Jurassic to Oligocene age belong principally to the tholeiitic series. Widespread calc-alkaline volcanism started in the late Miocene and culminated during the Pleistocene in the northern and central part of Costa Rica with the eruption of large volumes of andesitic to rhyolitic ignimbrites and the development of the stratovolcanoes of the Cordillera de Guanacaste and Cordillera Central; some of these volcanoes are still active. Alkaline rocks are subordinate and concentrated on the Caribbean side of Costa Rica. Plutonic intrusions, mainly of late Miocene age, are frequent in the southern part of Costa Rica. The histogram of the available data indicates some periods of more intensive volcanic activity.


    Institute of Scientific and Technical Information of China (English)


    <正>20091749 Cai Hou’an(College of Energy Geology,China University of Geosciences,Beijing 100083,China);Xu Debin SHRIMP U-Pb Isotope Age of Volcanic Rocks Distributed in the Badaohao Area,Liaoning Province and Its Significance(Coal Geology & Exploration,ISSN1001-1986,CN61-1155/P,36(4),2008,p.17-20,2 illus.,1 table,16 refs.)Key words:coal measures,volcanic rocks,U-Pb dating,LiaoningA set of andesite volcanic rocks distributes in the Badaohao area in Heishan County,Liaoning Province.It’s geological age and stratigraphy sequence relationship between the Lower Cretaceous Badaohao Formation and the volcanic rocks can not make sure till now and is influencing the further prospect for coals.Zircon

  13. Facies-controlled volcanic reservoirs of northern Songliao Basin, NE China

    Institute of Scientific and Technical Information of China (English)


    Volcanic rocks of the late Mesozoic are very important reservoirs for the commercial natural gases including hydrocarbon, carbon dioxide and rare gases in the northern Songliao Basin. The reservoir volcanic rocks include rhyolite,andesite, trachyte, basalt and tuff. Facies of the volcanic rocks can be classified into 5 categories and 15 special types.Porosity and permeability of the volcanic reservoirs are facies-controlled. Commercial reservoirs were commonly found among the following volcanic subfacies: volcanic neck (Ⅰ1), underground-explosive breccia (Ⅰ3), pyroclastic-bearing lava flow (Ⅱ3), upper effusive (Ⅲ3) and inner extrusive ones (Ⅳ1). The best volcanic reservoirs are generally evolved in the interbedded explosive and effusive volcanics. Rhyolites show in general better reservoir features than other types of rocks do.

  14. Paleomagnetic contributions to the Klamath Mountains terrane puzzle-a new piece from the Ironside Mountain batholith, northern California (United States)

    Mankinen, Edward A.; Gromme, C. Sherman; Irwin, W. Porter


    We obtained paleomagnetic samples from six sites within the Middle Jurassic Ironside Mountain batholith (~170 Ma), which constitutes the structurally lowest part of the Western Hayfork terrane, in the Klamath Mountains province of northern California and southern Oregon. Structural attitudes measured in the coeval Hayfork Bally Meta-andesite were used to correct paleomagnetic data from the batholith. Comparing the corrected paleomagnetic pole with a 170-Ma reference pole for North America indicates 73.5° ± 10.6° of clockwise rotation relative to the craton. Nearly one-half of this rotation may have occurred before the terrane accreted to the composite Klamath province at ~168 Ma. No latitudinal displacement of the batholith was detected.

  15. Petrogenesis of Volcanic Rocks in the Khabr-Marvast Tectonized Ophiolite: Evidence for Subduction Processes in the South-Western Margin of Central Iranian Microcontinent

    Institute of Scientific and Technical Information of China (English)



    The Late Cretaceous Khabr-Marvast tectonized ophiolite is located in the middle part of the Nain-Baft ophiolite belt, at the south-western edge of the central Iranian microcontinent. Although all the volcanic rocks in the study area indicate subduction-related magmatism (e.g. high LILE (large ion lithophile elements)/ HFSE (high field strenght elements) ratios and negative anomalies in Nb and Ta), geological and geochemical data clearly distinguish two distinct groups of volcanic rocks in the tectonized association: (1) group 1 is comprised of hyaloclustic breccias, basaltic pillow iavas, and andesite sheet flows. These rocks represent the Nain-Baft oceanic crust; and (2) group 2 is alkaline iavas from the top section of the ophiolite suite. These lavas show shoshonite affinity, but do not support the propensity of ophiolite.

  16. An experimental study of the kinetics of lherzolite reactive dissolution: Implications for contrasting styles of melt transport in the mantle. (United States)

    Liang, Y.; Morgan, Z. T.


    It has been suggested that dunite dikes or veins found in harzburgite and lherzolite hosts in the mantle sections of ophiolites are high porosity channels through which basaltic magmas were extracted from their source regions. The formation of such channels may involve pervasive melt flow and reactive dissolution. In order to better understand the kinetics of reactive dissolution we conducted two series of lherzolite dissolution experiments: one in an alkali basalt and the other in a basaltic andesite. Dissolution experiments were run at 1300° C and 1 GPa using lherzolite-melt reaction couple method. The lherzolite dissolution experiments produce a reactive boundary layer (RBL) that consists of distinct lithological units separated by sharp mineralogical interfaces. The details of the RBL depend on the relative stabilities of the lherzolite minerals with respect to the reacting melt. Dissolution of lherzolite in the basaltic andesite resulted in 2 distinct regions: harzburgite (45% ol, 45% opx, 10% melt) and lherzolite (45% ol, 35% opx, 12% cpx, 8% melt). In contrast, dissolution of lherzolite in the alkali basalt resulted in 3 distinct rock units: dunite (75% ol, 25% melt), harzburgite (60% ol, 30% opx, and 10% melt), and lherzolite (50% ol, 30% opx, 10% cpx, 10% melt). The average grain size of the dunite is greater than the average grain size of unreacted lherzolite, whereas the average grain size of the harzburgite in the two sets of dissolution experiments are nearly the same as the average grain size of the lherzolite. This implies that the permeability of the dunite is larger than either the newly created harzburgite or the unreacted lherzolite, and that the permeabilities of the harzburgite and lherzolite are about the same within the DHL sequence. Hence dunite dikes in the mantle are capable of serving as melt channels, whereas harzburgites may not. Systematic compositional variations in the interstitial melt, olivine, and to a lesser extent, pyroxenes in

  17. Origin of phenocrysts and compositional diversity in pre-Mazama rhyodacite lavas, Crater Lake, Oregon (United States)

    Nakada, S.; Bacon, C.R.; Gartner, A.E.


    Phenocrysts in porphyritic volcanic rocks may originate in a variety of ways in addition to nucleation and growth in the matrix in which they are found. Porphyritic rhyodacite lavas that underlie the eastern half of Mount Mazama, the High Cascade andesite/dacite volcano that contains Crater Lake caldera, contain evidence that bears on the general problem of phenocryst origin. Phenocrysts in these lavas apparently formed by crystallization near the margins of a magma chamber and were admixed into convecting magma before eruption. About 20 km3 of pre-Mazama rhyodacite magma erupted during a relatively short period between ~400 and 500 ka; exposed pre-Mazama dacites are older and less voluminous. The rhyodacites formed as many as 40 lava domes and flows that can be assigned to three eruptive groups on the basis of composition and phenocryst content. -from Authors

  18. Experimental Evidence for Polybaric Intracrustal Differentiation of Primitive Arc Basalt beneath St. Vincent, Lesser Antilles (United States)

    Blundy, Jon; Melekhova, Lena; Robertson, Richard


    We present experimental phase equilibria for a primitive, high-Mg basalt from St. Vincent, Lesser Antilles. Experimental details were presented in Melekhova et al (Nature Geosci, 2013); the objective here is to compare experimental phase compositions to those of erupted lavas and cumulates from St. Vincent. Starting material with 4.5 wt% H2O is multiply-saturated with a lherzolite assemblage at 1.3 GPa and 1180 ° C, consistent with mantle wedge derivation. Experimental glasses from our study, in addition to those of Pichavant et al (GCA, 2002) and Pichavant & Macdonald (CMP 2007) on a similar high-Mg basalt, encompass a compositional range from high-magnesian basalt to dacite, with a systematic dependence on H2O content, temperature and pressure. We are able to match the glasses from individual experiments to different lava types, so as to constrain the differentiation depths at which these magmas could be generated from a high-Mg parent, as follows: Composition wt% H2OP (GPa) T (° C) High-Mg basalt 3.9-4.8 1.45-1.751180-1200 Low-Mg basalt 2.3-4.5 1.0-1.3 1065-1150 High alumina basalt 3.0-4.5 0.4 1050-1080 Basaltic andesite 0.6-4.5 0.7-1.0 1050-1130 Andesite 0.6 1.0 1060-1080 The fact that St. Vincent andesites (and some basaltic andesites) appear to derive from a low-H2O (0.6 wt%) parent suggest that they are products of partial melting of older, high-Mg gabbroic rocks, as 0.6 wt% H2O is approximately the amount that can be stored in amphibole-bearing gabbros. The higher H2O contents of parents for the other lava compositions is consistent with derivation by crystallization of basalts with H2O contents that accord with those of olivine-hosted melt inclusions from St. Vincent (Bouvier et al, J Petrol, 2008). The generation of evolved melts both by basalt crystallization and gabbro melting is consistent with the hot zone concept of Annen et al (J Petrol, 2006) wherein repeated intrusion of mantle-derived basalt simultaneously crystallize by cooling and melt

  19. The Montesbelos mass-flow (southern Amazonian craton, Brazil): a Paleoproterozoic volcanic debris avalanche deposit? (United States)

    Roverato, M.


    The present contribution documents the extremely well-preserved Paleoproterozoic architecture of the Montesbelos breccia (named here for the first time), which is interpreted as a rare example of a subaerial paleoproterozoic (>1.85 Ga) granular-dominated mass-flow deposit, few of which are recorded in the literature. Montesbelos deposit is part of the andesitic Sobreiro Formation located in the São Felix do Xingu region, southern Amazonian craton, northern Brazil. The large volume, high variability of textural features, presence of broken clasts, angular low sphericity fragments, mono- to heterolithic character, and the size of the outcrops point to a volcanic debris avalanche flow. Fluviatile sandy material and debris flows are associated with the deposit as a result of post-depositional reworking processes.

  20. Mermer Ve Yapıtaşı Olarak Kullanılan Farklı Jeolojik Kökenli Kayaçların Porozite, P-Dalga Hızı Ve Basınç Dayanımı İlişkisinin İncelenmesi

    Directory of Open Access Journals (Sweden)

    Mustafa KUŞCU


    Full Text Available In this study, the relationships between the apparent porosity, porosity and uniaxial compressive strength and P-wave velocity of geologically different origins some natural stones that used as marble and building stone were investigated. For this purposes, 58 samples of diabase, andesite, trachyandesite, limestone and travertine were collected from the marble-quarries and potential industrial usable fields. According to results of the evaluation of the data while the porosity values in the igneous and sedimentary rocks decreases, which results increases in the P-wave velocity values and the highest value is observed in the hard, fossiliferous, calcite veined Balkırı Beige Limestone. The relation between uniaxial compressive strength and P-wave velocity was reveals that this relation not only depends on the porosity of the rocks, but also depends on the mineralogical, textural, alteration and structural characteristics of the rock types

  1. Different sources involved in generation of continental arc volcanism: The Carboniferous-Permian volcanic rocks in the northern margin of the North China block (United States)

    Zhang, Shuan-Hong; Zhao, Yue; Liu, Jian-Min; Hu, Zhao-Chu


    New zircon U-Pb dating results on the Carboniferous-Permian volcanic rocks in the northern margin of the North China block (NCB) indicate their eruption during the Early Carboniferous to Late Permian from 347 ± 3 Ma to 258 ± 1 Ma and a slight decrease of the upper limits of the volcanic sequences from west to east. They have a main rock association of basalt, basaltic andesite, andesite, dacite, rhyolite, tuff, and tufaceous sandstone. Most of them have calc-alkaline compositions and exhibit variable SiO2 contents from 48.2 wt.% to 77.1 wt.%. There is no significant gap between the mafic and felsic volcanic rocks in major and trace element classification diagrams, indicating that they are not bimodal in composition. The Carboniferous-Permian volcanic rocks exhibit subduction-related geochemical features such as negative Nb and Ta anomalies of mafic to intermediate rocks on primitive mantle-normalized diagrams, indicating they were formed in an Andean-type continental arc during southward subduction of the Paleo-Asian oceanic plate beneath the northern NCB. However, their wide range of whole-rock Sr-Nd and zircon Hf isotopic compositions indicate that their source areas are very complex and different sources were involved in generation of these volcanic rocks. Geochemical and Sr-Nd-Hf isotopic results show that the basalt and some andesite were produced by fractional crystallization of mafic magma derived from partial melting of mantle wedge and subducted oceanic crust; however, most of the intermediate to felsic volcanic rocks were derived from partial melting of lower continental crust. There is an increasing input of crustal materials from the Carboniferous to Permian as indicated by increasing volumes of felsic volcanic rocks in the volcanic sequences. The results show that origin of the continental arc volcanism is very complex and both materials from the subducted oceanic crust and sediments, mantle wedge and arc continental crust could be involved in their

  2. Ultramafic rocks in the Namurian C series in the Zebrzydowice area (Rybnik coal region)

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    Jochemczyk, L.


    The chemical and physical properties as well as origin of ultramafic rock samples from the Zebrzydowice area in the Rybnik coal region are evaluated. The ultramafic rocks detected by drilling were situated at depths of 1035 m in the top of dacite-andesite system and thermally alterated claystones. Chemical analyses and X-ray examination show that the ultramafic rock consists of secondarily alterated peridotite. The peridotite consists of chlorite-serpentite, phlogopite, bastite, nepheline and opaque minerals. Its chemical composition is characterized by reduced content of silica and a high content of ferric oxide. The ultramafic rock in the Zebrzydowice area differs from mineral and chemical composition of igneous rocks which occur in Carboniferous strata in the west and the southwest of the Upper Silesia basin. Rock of this type has been recorded in the Upper Silesia basin for the first time. 12 references.

  3. Naturally occurring radionuclides and rare earth elements in weathered Japanese soil samples (United States)

    Sahoo, Sarata; Hosoda, Masahiro; Prasad, Ganesh; Takahashi, Hiroyuki; Sorimachi, Atsuyuki; Ishikawa, Tetsuo; Tokonami, Shinji; Uchida, Shigeo


    The activity concentrations of 226Ra and 228Ac in weathered Japanese soils from two selected prefectures have been measured using a γ-ray spectroscopy system with high purity germanium detector. The uranium, thorium, and rare earth elements (REEs) concentrations were determined from the same soil samples using inductively coupled plasma mass spectrometry (ICP-MS). For example, granitic rocks contain higher amounts of U, Th, and light REEs compared to other igneous rocks such as basalt and andesites. Therefore, it is necessary to understand the interaction between REEs and nature of soils since soils are complex heterogeneous mixture of organic and inorganic solids, water, and gases. In this paper, we will discuss about distribution pattern of 238U and 232Th along with REEs in soil samples of weathered acid rock (granite) collected from two prefectures of Japan: Hiroshima and Miyagi.


    Schaber, Gerald C.; Kozak, R.C.; Burns, Barbara A.; Bartels, K.I.


    The objective of this poster paper is to present a site-specific atlas showing a wide variety of remote sensing data sets collected for the area of S. P. Mountain and lava flow (basaltic-andesite) in north-central Arizona. The data set to be displayed includes a number of radar images, representing three wavelength regions (1-, 3- and 25-cm), multiple incidence angles, look directions, and polarization combinations, in addition to thermal infrared scanner imagery, multispectral scanner imagery, aerial and ground photography, micro- and macro topography, and four-frequency, multipolarization radar scatterometer spectra. The expression of different surface units on the S. P. lava flow are effectively displayed on the ERIM four-channel images by the registration and combination of the four bands. Multi-color imagery of band combinations demonstrate the information content of multi-channel SAR imagery as well as the suitability of extending data manipulation methods developed for Landsat data to SAR data.

  5. Chemical and Mineralogical Features of Smectite from the Morron de Mateo Bentonite Deposit (Cabo de Gata, Almeria) in Relation to the Parent Rocks and the Alteration Processes Occurred After the Bentonite Formation: Analogies and Implications for the Engineered Clayey Barrier of a Deep Geological Rad waste Repository; Naturaleza de las Esmectitas del Yacimiento de Morron de Mateo (Cabo de Gata, Almeria) en Relacion con la Roca Madre y con los Procesos Posteriores a la Bentonitizacion: Implicaciones Analogicas para la Barrera de Ingenieria de un Almacenamiento Geologico de Residuos Radiactivos

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    Pelayo, M.; Labajo, M. A.; Garcia Romero, L.; Perez del Villar, L.


    The Morron de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on the clayey barrier of a Deep Geological Rad waste Repository (DGRR) after its closure, in relation to the radioactive decay of the fission products and the container corrosion. This bentonite deposit and their host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the bioclastic calcarenite beds close to the dome. Bentonite from the NE sector of the deposit have been chemically and mineralogically characterized. Pyroclastic rocks (white tuffs), epyclastic rocks (mass flow) and andesitic breccia all of them hydrothermally altered, have been studied at the site. Samples are composed of feldspars, quartz and amphybols, as inherited minerals, and phyllosilicates, zeolites, crystoballite and calcite, as new formed minerals. White tuffs have the highest phyllosilicate contents, mainly dioctahedral smectite of montmorillonite type. Epyclastic rocks and andesitic breccia have a highest proportion of inherited minerals, the new formed phillosilicates being di octahedral smectite of beidellite type and an ordered interlayer chlorite/smectite mineral, of corrensite type. Smectite from the epyclastic rocks have higher Fe and Mg contents and chemical variability, as a consequence of nature of their parent rocks. The presence of corrensite in the epyclastic rocks suggests that in the Morron de Mateo area a propilitic alteration process occurred after bentonite formation, which transformed Fe-Mg-rich smectite into corrensite. This transformation was probably favoured by the sub volcanic intrusion, which also produced a temperature increase in the geological media and a supply of Fe-Mg-rich solutions, which also were the responsible for the metasomatic transformations observed in the calcarenite beds. (Author) 57 refs.

  6. Mid-crustal fluid related to the Matsushiro earthquake swarm (1965-1967) in northern Central Japan: Geochemical reproduction (United States)

    Okuyama, Yasuko; Funatsu, Takahiro; Fujii, Takashi; Takamoto, Naohiko; Tosha, Toshiyuki


    The Matsushiro district in the northern part of Ngano Prefecture, Central Japan, experienced a severe earthquake swarm associated with ground uplift and groundwater outflow during a period from 1965 to 1967. Geochemistry and isotope geochemistry of surface water and groundwater in the swarm area have been investigated. Water samples for the analyses were obtained from saline springs and streams, fresh water from streams and a shallow well, and, from seven wells of up to 600 m deep drilled in the Matsushiro fault zone. The results of analyses of water from the deep wells in the fault zone indicate a linear increase in dissolved Na, K, Al, Cl, Br, B and SiO4, and isotopic ratios of δD, δ18O and δ13C. The hydrogen and oxygen isotopic ratios of the well water indicate a mixing between the surface water and isotopically heavy water exemplified by the "andesitic water" of Giggenbach (1992). Assuming that the isotopically heavy water has δD similar to the "andesitic water", the geochemistry of deep-seated brine is reproduced from the analytical data of well water. The reproduced composition of deep-seated brine is enriched in Na, Ca, Cl and HCO3 and has total dissolved solids comparable to seawater. The water of the reproduced composition is estimated to occupy a deep part (> 3 km below surface) of the fault zone. Available data show that the geochemical regime in the Matsushiro fault zone has remained unchanged since the swarm event. The reproduced composition of water is concluded to be similar to the brine triggering the swarm of earthquakes. The composition of the reproduced water is not as saline as the deep-seated fluid derived from dehydration of a subducting oceanic plate which results in water having a Cl content about twice that of the seawater. The relatively low-salinity nature comparable to seawater is one of the characteristics of mid-crustal fluid in volcanic fields.

  7. Late Pleistocene flank collapse of Zempoala volcano (Central Mexico) and the role of fault reactivation (United States)

    Arce, José Luis; Macías, Rodolfo; García Palomo, Armando; Capra, Lucia; Macías, José Luis; Layer, Paul; Rueda, Hernando


    Zempoala is an extinct Pleistocene (˜ 0.7-0.8 Ma) stratovolcano that together with La Corona volcano (˜ 0.9 Ma) forms the southern end of the Sierra de las Cruces volcanic range, Central Mexico. The volcano consists of andesitic and dacitic lava flows and domes, as well as pyroclastic and epiclastic sequences, and has had a complex history with several flank collapses. One of these collapses occurred during the late Pleistocene on the S-SE flank of the volcano and produced the Zempoala debris avalanche deposit. This collapse could have been triggered by the reactivation of two normal fault systems (E-W and NE-SW), although magmatic activity cannot be absolutely excluded. The debris avalanche traveled 60 km to the south, covers an area of 600 km 2 and has a total volume of 6 km 3, with a calculated Heim coefficient (H/L) of 0.03. Based on the textural characteristics of the deposit we recognized three zones: proximal, axial, and lateral distal zone. The proximal zone consists of debris avalanche blocks that develop a hummocky topography; the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix, which transformed to a debris flow in the lateral distal portion. The deposit is heterolithologic in composition, with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase. Several cities (Cuernavaca, Jojutla de Juárez, Alpuyeca) with associated industrial, agricultural, and tourism activities have been built on the deposit, which pose in evidence the possible impact in case of a new event with such characteristics, since the area is still tectonically active.

  8. The intra-oceanic Cretaceous (~ 108 Ma) Kata-Rash arc fragment in the Kurdistan segment of Iraqi Zagros suture zone: Implications for Neotethys evolution and closure (United States)

    Ali, Sarmad A.; Ismail, Sabah A.; Nutman, Allen P.; Bennett, Vickie C.; Jones, Brian G.; Buckman, Solomon


    The Kata-Rash arc fragment is an allochthonous thrust-bound body situated near Penjween, 100 km northeast of Sulymannia city, Kurdistan Region, within the Iraqi portion of the Zagros suture zone. It forms part of the suprasubduction zone 'Upper Allochthon' terranes (designated as the Gimo-Qandil Group), which is dominated by calc-alkaline andesite and basaltic-andesite, rhyodacite to rhyolite, crosscut by granitic, granodioritic, and dioritic dykes. Previously, rocks of the Kata-Rash arc fragment were interpreted as a part of the Eocene Walash volcanic group. However, SHRIMP zircon U-Pb dates on them of 108.1 ± 2.9 Ma (Harbar volcanic rocks) and 107.7 ± 1.9 Ma (Aulan intrusion) indicate an Albian-Cenomanian age, which is interpreted as the time of igneous crystallisation. The Aulan intrusion zircons have initial εHf values of + 8.6 ± 0.2. On a Nb/Yb-Th/Yb diagram, all Kata-Rash samples fall within the compositional field of arc-related rocks, i.e. above the mid-ocean-ridge basalt (MORB)-ocean island basalt (OIB) mantle array. Primitive-mantle-normalised trace-element patterns for the Kata-Rash samples show enrichment in the large ion lithophile elements and depletion in the high-field-strength elements supporting their subduction-related character. Low Ba/La coupled with low La/Yb and Hf/Hf* 3000 km continuity of Cretaceous arc activity (Oman to Cyprus), that consumed Neotethyian oceanic crust between Eurasia and the Gondwanan fragment Arabia.

  9. Volcanic stratigraphy of intermediate to acidic rocks in southern Paraná Magmatic Province, Brazil

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    Liza Angélica Polo


    Full Text Available This article presents the first map in detail scale for an area covered by Palmas type volcanic rocks in the south border of the eocretaceous Paraná Magmatic Province, south Brazil. The study of the structural features coupled with petrography and geochemistry made it possible to separate these rocks into three main volcanic sequences and recognize their stratigraphy. The older Caxias do Sul sequence rests directly over the first low-Ti basalt flows (Gramado type, and corresponds to the stacking of lobated lava flows, laminar flows and lava domes, mostly emitted as continuous eruptions; only the latest eruptions are intercalated with thin sandstone deposits. These rocks have dacitic composition (~ 68 wt% SiO2 with microphenocrysts of plagioclase and subordinate pyroxenes and Ti-magnetite immersed in glassy or devitrified matrix. A second volcanic sequence, named Barros Cassal, is composed of several lava flows of basaltic andesite, andesitic and dacitic composition (~ 54; ~ 57 and ~ 63 wt% SiO2 , respectively, with microphenocrysts of plagioclase, pyroxenes and Ti-magnetite. The frequent intercalation of sandstone between the flows attests to the intermittent behaviour of this event. The upper sequence, Santa Maria, is made up of more silica-rich (~ 70 wt% SiO2 rocks occurring as laminar flows, lobated flows and lava-domes. These rocks have rhyolitic composition with microphenocrysts of plagioclase and Ti-magnetite set in a glassy or devitrified matrix with microlites. The structures and textures of all three silicic sequences favor the interpretation that they had a predominantly effusive character, which is thought to be a reflection of the remarkably high temperatures of the lavas (~ 1,000 ºC.

  10. Geology and petrology of Tertiary volcanic rocks of Sarbisheh perlite mine area (eastern Iran and industrial applications

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    Seayad Sayid Mohammadi


    Full Text Available The study area is located at northwest of Sarbisheh in South Khorasan province and eastern border of Lut block. In this area, Tertiary (Eocene-Oligocene to Pliocene volcanic rocks consisting of basaltic andesite, dacite, rhyodacite, vitreous rhyolite (perlitic in some parts, tuff and ignimbrite are exposed. In the Daghar Mountain, A, B and C perlite layers with thicknesses of 102, 7 and 58 meters respectively, occur alternatively with volcanic-pyroclastic rocks. Zoning, sieve texture and embayment of plagioclase and roundness of minerals in the lavas indicate disequilibrium conditions during magma crystallization. Chemically, these are meta-aluminous, medium to high-K calc-alkaline, enriched in LILE and negative anomaly for Nb and Ti. Chondrite-normalized Rare Earth Elements (REE plots indicate enrichment of light REE in comparison with heavy REE, (La/YbN of 9.14-12.64, low negative anomaly for Eu in basaltic andesite (Eu/Eu*=0.91 and dacite (Eu/Eu*=0.78-0.87 and strong negative anomaly for Eu in the rhyolites (Eu/Eu*=0.18-0.35. Negative anomaly for Eu indicates calc-alkaline nature for these rocks. On the basis of chemical characteristics and magnetic susceptibility, these are I-type. Tectonically, the rocks belong to subduction zone and active continental margin and their parental magma originated from partial melting of enriched mantle and then crustal contamination during differentiation process. Dacites have an initial 87Sr/86Sr between 0.7048 and 0.7050 (average 0.7049 that confirm mantle source for the magma. Volcanic glasses of rhyolitic composition altered by hydration (likely meteoric water and formed perlite. Physical tests and chemical analyses show that perlite of Sarbisheh is suitable as raw material for production of expanded perlite.

  11. Variations in eruption style during the 1931A.D. eruption of Aniakchak volcano, Alaska (United States)

    Nicholson, R.S.; Gardner, J.E.; Neal, C.A.


    The 1931A.D. eruption of Aniakchak volcano, Alaska, progressed from subplinian to effusive eruptive style and from trachydacite to basaltic andesite composition from multiple vent locations. Eyewitness accounts and new studies of deposit stratigraphy provide a combined narrative of eruptive events. Additional field, compositional, grain size, componentry, density, and grain morphology data document the influences on changing eruptive style as the eruption progressed. The eruption began on 1 May 1931A.D. when a large subplinian eruption column produced vesicular juvenile-rich tephra. Subsequent activity was more intermittent, as magma interacted with groundwater and phreatomagmatic ash and lithic-rich tephra was dispersed up to 600km downwind. Final erupted products were more mafic in composition and the eruption became more strombolian in style. Stratigraphic evidence suggests that two trachydacitic lava flows were erupted from separate but adjacent vents before the phreatomagmatic phase concluded and that basaltic andesite lava from a third vent began to effuse near the end of explosive activity. The estimated total bulk volume of the eruption is 0.9km3, which corresponds to approximately 0.3km3 of magma. Eruption style changes are interpreted as follows: (1) a decrease in magma supply rate caused the change from subplinian to phreatomagmatic eruption; (2) a subsequent change in magma composition caused the transition from phreatomagmatic to strombolian eruption style. Additionally, the explosion and effusion of a similar magma composition from three separate vents indicates how the pre-existing caldera structure controlled the pathway of shallow magma ascent, thus influencing eruption style. ?? 2011 Elsevier B.V..

  12. Karakteristik mineralisasi epitermal di Daerah Taran, Hulu Kahayan, Kalimantan Tengah berdasarkan studi mikroskopis, X-Ray Diffraction (XRD, dan inklusi fluida

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    Danny Zulkifli Herman


    Full Text Available area is occupied predominantly by piroclastic rocks and locally intercalations of lenticular claystones and sandstones. The pyroclastic rocks are intruded by diorite, dacite and andesite, leading alteration and mineralization within the host rocks. Mineralization occurs as a vein type and is associated with a number of pervasive alteration types named respectively: quartz-illite- montmorillonite-kaolinite ± pyrite, quartz-illite ± pyrite, quartz-illite-chlorite ± pyrite and quartz- kaolinite-illite ± pyrite. On the other hand, a propylitic alteration also occurs within the andesite intrusion composed of calcite-epidote-chlorite-sericite-quartz ± pyrite. The mineralization is characterized by several zones of quartz stockwork containing gold and associated ore minerals of chalcopyrite, sphalerite, galena, pyrite and argentite. The quartz veins occurs as fi llings of structural openings in the form of milky quartz and amethyst with textures of sugary, comb, and dogteeth. Evaluation work on results of microscopic (petrography and mineragraphy, X-Ray Diffraction (XRD, and fl uid inclusion studies, and chemical analysis of entirely altered rock/quartz vein samples shows that the alteration and mineralization process were closely related to a change of hydrothermal fl uids, from near neutral into acid conditions at a temperature range of >290o – 100oC. The appearances of quartz variation indicate a relationship with repeated episodes of boiling in an epithermal system, as ground water mixed with hot vapor originated from a remained post-magmatic solution. Corresponding to a salinity of average 1,388 equiv.wt.% NaCl, it indicates that the ore minerals bearing quartz veins were deposited at a depth range of 640 – 1020 m beneath paleosurface.  

  13. Crystal origins and magmatic system beneath Ngauruhoe volcano (New Zealand) revealed by plagioclase textures and compositions (United States)

    Coote, Alisha C.; Shane, Phil


    The textural variation and compositional zoning of plagioclase in pre-historic and historic basaltic andesite lava flows from Ngauruhoe volcano reveals extensive crystal recycling from a multi-level magma system. Most phenocrysts have a calcic (~ An80-90) resorbed core with diffuse or no zonation that is depleted in Fe and Mg. Some cores display patchy zonation from replacement by high An crystallization prior to resorption. The cores are mantled by oscillatory-zoned rims of lower An content (originated from deep cumulates or intrusions, and were subsequently entrained in ascending magmas. Patchy-textured cores were produced during decompression in a water under-saturated magma and staged ascent. The diversity in crystal cores reflect different conduits and ascent histories. The crystal rims grew in a more differentiated magma reservoir, and are in equilibrium with the erupted melt. Most of the zoning patterns in the rim zone require water pressure and/or temperature changes. These changes could have been caused by convective self-mixing in a closed system and/or the intrusion of hydrous melts of similar bulk composition. Other crystals display rimward elemental enrichments consistent with mafic recharge. Previously reported rimward enrichment in 87Sr-86Sr compositions can be explained by the re-cycled origin of the crystal cores and progressive crustal assimilation at shallower depths in the magma system where subsequent crystal growth occurred. A steady-state balance of intrusion and crystallization in the deep crust, and remobilization and entrainment of co-magmatic crystals in newly formed and ascending magmas has produced relatively monotonous batches of basaltic andesite throughout the volcano's life. Trace element zonation (Fe and Mg) in the plagioclase mostly reflects variable diffusive loss through the crystal history, and the patterns in different crystals are highly variable. This, along with uncertainties in estimating trace element partitioning

  14. New perspectives on the eruption of 1912 in the valley of ten thousand smokes, Katmai National Park, Alaska (United States)

    Hildreth, Wes


    New data extend our understanding of the 1912 eruption, its backfilled vent complex at Novarupta, and magma-storage systems beneath adjacent stratovolcanoes. Initial Plinian rhyolite fallout is confined to a narrow downwind sector, and its maximum thickness may occur as far as 13 km from source. In contrast, the partly contemporaneous rhyolite-rich ash flows underwent relatively low-energy emplacement, their generation evidently being decoupled from the high column. Flow veneers 1 13 m thick on near-vent ridge crests exhibit a general rhyolite-to-andesite sequence like that of the much thicker valley-confined ignimbrite into which they merge downslope. Lithics in both the initial Plinian and the ignimbrite are predominantly fragments of the Jurassic Naknek Formation, which extends from the surface to a depth of ca. 1500 m. Absence of lithics from the underlying sedimentary section limits to 100 m thick near source and 10 m thick 3 km away, which dip back into an inner vent welded tuff reejected during later phases of the 3-day eruption. Adjacent to the inner vent, a 225-m-high asymmetrical accumulation of coarse near-vent ejecta is stratigraphically continuous with the regional dacite fallout. Distensional faulting of its crest may reflect spreading related to compaction and welding. Nearby andesite-dacite stratovolcanoes, i.e., Martin, Mageik, Trident, and Katmai, display at least 12 vents that define a linear volcanic front trending N65°E. The 1912 vent and adjacent dacite domes are disposed parallel to the front and ca. 4 km behind it. Mount Griggs, 10 km behind the front, is more potassic than other centers, taps isotopically more depleted source materials, and reflects a wholly independent magmatic plumbing system. Geochemical differences among the stratovolcanoes, characteristically small eruptive volumes ( gaps between them must have been intrinsic to the reservoir, not merely effects of withdrawal dynamics.

  15. Behaviour of major, minor and trace elements (including REEs during kaolinization processes at Zonouz deposit, northeast of Marand, East Azarbaidjan province

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    Vahideh Alipour


    Full Text Available The Zonouz kaolin deposit is located ~15 km northeast of Marand, East-Azarbaidjan province. Based on physical features in field investigations, such as color, five distinct kaolin types including (1 white, (2 lemon, (3 gray, (4 brown, and (5 yellow are distinguished in the deposit. Field evidence and petrographic studies indicate that the deposit is genetically close to trachy-andesite rocks. According to mineralogical data, the deposit contains quartz, kaolinite, montmorillonite, calcite, pyrophyllite, chlorite, muscovite-illite, dolomite, hematite, and anatase minerals. Geochemical data indicate that function of alteration processes on trachy-andesite rocks during development of Zonouz ore deposit was accompanied by leaching of elements such as Al, Na, K, Rb, Ba, V, Hf, Cu, Zr, Tm, Yb, and Lu, enrichment of elements such as U, Nb, and Ta, and leaching-fixation of elements such as Si, Fe, Ca, Mg, Ti, Mn, P, Cs, Sr, Th, Co, Cr, Ni, Y, Ga, LREE, Tb, Dy, Ho, and Er. Incorporation of obtained results from mineralogical and geochemical studies show that physico-chemical conditions of alteration environment, the relative stability of primary minerals, surface adsorption, preferential sorption by metallic oxides, existing of organic matters, scavenging and concentration processes, and fixation in neomorphic mineralogical phases played important role in distribution of elements in the deposit. Geochemical studies show that development of the deposit is relative to two types of processes, (1 hypogene and (2 supergene. The distribution pattern of REEs indicates that differentiation degree of LREEs from HREEs in supergene kaolins is more than hypogene kaolins. Geochemical studies indicate that minerals such as Mn-oxides, zircon, anatase, hematite, cerianite, and secondary phosphates (monazite, rhabdophane, churchite, and zenotime are the potential hosts for rare earth elements in this deposit.

  16. Petrogenesis of Rinjani Post-1257-Caldera-Forming-Eruption Lava Flows

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    Heryadi Rachmat


    Full Text Available After the catastrophic 1257 caldera-forming eruption, a new chapter of Old Rinjani volcanic activity beganwith the appearance of Rombongan and Barujari Volcanoes within the caldera. However, no published petrogeneticstudy focuses mainly on these products. The Rombongan eruption in 1944 and Barujari eruptions in pre-1944, 1966,1994, 2004, and 2009 produced basaltic andesite pyroclastic materials and lava flows. A total of thirty-one sampleswere analyzed, including six samples for each period of eruption except from 2004 (only one sample. The sampleswere used for petrography, whole-rock geochemistry, and trace and rare earth element analyses. The Rombonganand Barujari lavas are composed of calc-alkaline and high K calc-alkaline porphyritic basaltic andesite. The magmashows narrow variation of SiO2 content that implies small changes during its generation. The magma that formedRombongan and Barujari lavas is island-arc alkaline basalt. Generally, data show that the rocks are enriched in LargeIon Lithophile Elements (LILE: K, Rb, Ba, Sr, and Ba and depleted in High Field Strength Elements (HFSE: Y, Ti,and Nb which are typically a suite from a subduction zone. The pattern shows a medium enrichment in Light REEand relatively depleted in Heavy REE. The processes are dominantly controlled by fractional crystallization andmagma mixing. All of the Barujari and Rombongan lavas would have been produced by the same source of magmawith little variation in composition caused by host rock filter process. New flux of magma would likely have occurredfrom pre-1944 until 2009 period that indicates slightly decrease and increase of SiO2 content. The Rombongan andBarujari lava generations show an arc magma differentiation trend.

  17. Paleoproterozoic felsic volcanism of Iricoumé group, Erepecuru-Trombetas domain, Amazonian central province: Field and petrographic characterization and Pb-Pb zircon geochronology

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    Lúcia Travassos da Rosa Costa


    Full Text Available The Iricoumé group consists of very well preserved pyroclastic and effusive volcanic rocks as a part of an extensive volcano-plutonic event, which marked the central part of the Amazonian craton during the Orosirian. Such rocks occur in the southern part of the southwestern of Erepecuru-Trombetas Domain (NW of the Pará state, south of the Guyana Shield. Petrographic study allows distinction of two volcanic types. A dominant explosive volcanism is characterized by pyroclastic rocks (ignimbrites, rheoignimbrites, lapilli-tuff related to surge deposit, and co-ignimbrite fall tuff while a subordinated effusive volcanism is represented by coherent lavas flows and hypabissal rocks (andesites, lamprophyres and latites. Most of the pyroclastic rocks exhibit features of deposition under high temperature suggesting formation in a caldera-related environment. Pb-Pb zircon ages of 1888 +-2.5 and 1889 +-2 Ma have been obtained for the formation of trachydacitic ignimbrites and confirm that the dominant volcanism is part of the Iricoumé group. The Pb-Pb zircon age of 1992 +-3 Ma yielded by an andesite points to the occurrence in the area of an older Orosirian magmatic episode, which has been previously recognized locally southward in the Tapajós domain. These new results constitute a further evidence of the wide extent of the Iricoum group and correlated volcanic rocks in the central part of the Amazonian craton, and reinforce the assumption that this volcanic episode and correlated magmatism may be considered as a silicic large igneous province (SLIP, as previously proposed by some authors.

  18. Magmatic and tectonic evolution of the Ladakh Block from field studies (United States)

    Raz, U.; Honegger, K.


    The Ladakh Block is in an intermediate position between the Indian plate in the south and the Karakorum-Tibetan plate in the north. To the west it is separated from the Kohistan Arc by the Nanga Parbat Syntaxis, to the east it is cut off from the Lhasa Block by the Gartok-Nubra Fault. Present data, together with previously published results, show, that the Ladakh Block consists of an island arc in the south and a calc-alkaline batholith in the north with remnants of a continental crust. Migmatitic gneisses and metasedimentary sequences, such as quartzites and metapelites, interbedded with basaltic volcanics and overlain by thick platform carbonates were found as evidence of a continental crust. Remnants of megafossils ( Megalodon and Lithiotis) within the high-grade metamorphic marbles indicate a probable age of Late Triassic to Early Jurassic. These sediments were intruded by a faintly layered hornblende-gabbro, which preceded the calc-alkaline magmatic episode. Gabbro and gabbronorites are found as roof pendants and large inclusions within diorites and granodiorites. The major part of the batholith consists of granodiorite and biotite-granite plutons, ranging from Late Cretaceous to Tertiary. Associated with the intrusives are volcanic rocks with trachyandesite to alkalibasalt and basalt-andesite to rhyolite compositions. Garnet-bearing leucogranites succeeded the emplacement of the major plutons. The magmatic stage ended, finally, by intense fracturing and injections of NE-SW striking andesitic dykes. The southernmost unit of the Ladakh Block is formed by oceanic crust with serpentinized peridotite and hornblende-gabbro and is covered by volcanics of an island-arc type (Dras volcanics). These units are intruded by gabbronorite, as well as Middle and Upper Cretaceous granodiorite and coarse-grained biotite-granite. In a plate tectonic view the Ladakh Block represents a transitional sector between the pure island arc of Kohistan in the west and the Andean type

  19. Petrogenesis of Middle-Late Triassic volcanic rocks from the Gangdese belt, southern Lhasa terrane: Implications for early subduction of Neo-Tethyan oceanic lithosphere (United States)

    Wang, Chao; Ding, Lin; Zhang, Li-Yun; Kapp, Paul; Pullen, Alex; Yue, Ya-Hui


    The Gangdese belt is dominantly composed of igneous rocks that formed during the northward subduction of Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane and has played a crucial role in understanding the pre-collisional evolution of southern Tibet. This paper presents new geochronological and geochemical (whole-rock major and trace element and Sr-Nd and zircon Hf isotope) data for recently identified volcanic rocks exposed in Changguo area, southernmost part of the Lhasa terrane. Zircon U-Pb dating from six samples yields consistent ages of 237.1 ± 1.1 Ma to 211.7 ± 1.5 Ma for magma emplacement through volcanic eruption, showing the Middle-Late Triassic magmatic activity in the southernmost Gangdese Belt. The Changguo volcanic rocks are mainly composed of basaltic and andesitic rocks and exhibit LILE enrichment and HFSE depletion. They also exhibit relatively uniform Nd-Hf isotopic compositions (εNd(t) = + 5.20 to + 7.74 and εHf(t)zircon = + 10.2 to + 15.9). The basaltic magmas were likely sourced from partial melting of sub-arc mantle wedge that was metasomatized by not only the aqueous fluid derived from subducting altered oceanic crust but also hydrous melt derived from subducting seafloor sediments, and subsequently experienced fractional crystallization and juvenile crustal contamination during ascent. The andesitic magmas were generated by partial melting of mafic-ultramafic metasomes through melt/fluid-peridotite reaction at slab-mantle interface. Taking into account the temporal and spatial distribution of the Early Mesozoic magmatic rocks and regional detrital zircon data, we further propose that the northward subduction of Neo-Tethyan oceanic lithosphere beneath the Lhasa terrane commenced by Middle Triassic.

  20. Mineral chemistry of paleoproterozoic volcano-plutonism from the São Félix do Xingu (PA region, Amazonian Craton

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    Raquel Souza da Cruz


    Full Text Available The Sobreiro and Santa Rosa formations are result of large paleoproterozoic volcanic activities in the São Félix do Xingu (PA region, SE of Amazonian Craton. The Sobreiro Formation is composed of andesitic lava flow facies, with subordinate dacite and rhyodacite, and autoclastic volcaniclastic facies characterized by tuff, lapilli-tuff, and massive polymictic breccia. These rocks exhibit clinopyroxene, amphibole, and plagioclase phenocrysts in a microlytic or trachytic groundmass. The clinopyroxene is augite with subordinate diopside, and reveals chemical variations typical of minerals generated by arc-related magmatism. The amphibole is magnesiohastingsite, has oscillatory oxidizing conditions, and reveals breakdown rim textures linked to degassing during magma ascent. The Santa Rosa Formation has polyphase evolution controlled by large NE-SW crustal fissures, materialized by rhyolitic and dacitic lava flow facies. Volcaniclastic facies of ignimbrites, lapilli-tuffs, felsic crystal tuffs, and massive polymict breccias represents an explosive cycle in this unit. Metric dikes and stocks of granitic porphyries and equigranular granitoids complete this suite. K-feldspar, plagioclase, and quartz phenocrysts surrounded by quartz and K-feldspar integrowth occur in these rocks. Electron microprobe pressure and temperature estimates in clinopyroxene phenocrysts reveal formation depth between 58 and 17.5 km (17.5 – 4.5 kbar at temperatures between 1,249 and 1,082 ºC; and between 28 and 15 km (7.8 – 4.1 kbar for amphibole grains of the Sobreiro Formation, suggesting polybaric evolution. A model with generation of hydrated basaltic magma from partial melting of mantle wedge and accumulation in a hot zone of the lower crust, from which the andesitic and dacitic magmas are formed by the assimilation of continental crust and following fractional crystallization is proposed.

  1. Contributions to the petrography, geochemistry and geochronology (U-Pb and Sm-Nd) of the Paleoproterozoic effusive rocks from Iricoume Group, Amazonian Craton, Brazil

    International Nuclear Information System (INIS)

    The southernmost region of the Guyana shield, Amazonian craton, hosts large record of Paleoproterozoic effusive rocks of the Iricoume Group. They present remarkably well-preserved igneous textures and structures. The SiO2 contents reveal a bimodal association marked by a compositional gap between acid (SiO2 > 67 wt%) and intermediate (SiO2 2, alkali, Rb, Zr, Nb + Ta, La + Ce and 104 Ga/Al content and low Fe2O3tot, TiO2, CaO, Sr and Co content. They exhibit subalkaline, metaluminous-to-peraluminous compositions, and geochemically compatible to A-type magmatism emplaced in post-collisional to within-plate tectonic settings. The intermediate rocks are andesitic/basalt to andesite relatively high contents of TiO2, Al2O3, Fe2O3total, MgO, CaO, Sr and Co; low SiO2, K2O, Rb, Zr, Nb + Ta, La + Ce. They have subalkaline and metaluminous geochemical composition and plot on within-plate basalt field. The acid rocks crystallized at 1882 ± 11 Ma in U-Pb analyses for LA-MC-ICPMS zircon data. The Sm-Nd isotopic data on all rocks reveal a Nd TDM model ages between 2.59 and 2.16 Ga and εNd(t) values between -5.78 and 0.03, indicate that the magmatic evolution was related to the reworking of older Paleoproterozoic at the Rhyacian-Siderian period, continental crust (Transamazonian crust-forming event) with some mixing with a limited amount mantle-derived magmas or with contamination by Archean crust. The petrographic, geochemical and geochronological data presented in this paper suggest a within-plate to post-collisional tectonic setting for the Iricoume volcanism, involving lower crust uplift and generation of basalt magma in an extensional regime. (author)

  2. Seismogenic frictional melting in the magmatic column as the driving force of stick-slip motion (United States)

    Kendrick, J. E.; Lavallee, Y.; Hirose, T.; Di Toro, G.; Hornby, A.; De Angelis, S.; Henton De Angelis, S.; Ferk, A.; Hess, K.; Leonhardt, R.; Dingwell, D. B.


    Lava dome eruptions subjected to high extrusion rates commonly evolve from endogenous to exogenous growth and limits to their structural stability hold catastrophic potential as explosive eruption triggers. In the conduit strain localisation in magma, accompanied by seismogenic failure, marks the onset of brittle magma ascent dynamics. The rock record of exogenous dome structures preserves vestiges of cataclastic processes and of thermal anomalies, key to unravelling subsurface processes. A combined structural, thermal and magnetic investigation of shear bands from Mount St. Helens (MSH) and Soufrière Hills volcano (SHV) reveal evidence of faulting and frictional melting within the magmatic column. High velocity rotary shear (HVR) experiments demonstrate the propensity for melting of andesitic and dacitic material (from SHV and MSH respectively) at upper conduit stress conditions. Such melting events may be linked to the step-wise extrusion of magma accompanied by repetitive long-period (LP) seismicity. Using a source duration calculated from the waveforms at seismic stations around SHV, and slip distance per drumbeat calculated from extrusion rate, frictional melting of SHV andesite in a high velocity rotary shear apparatus can be achieved at small slip distances (Variable-rate HVR experiments which mimic rapid velocity fluctuations in stick-slip behavior demonstrate velocity-weakening behavior of melt, with a tendency for unstable slip. We postulate that pseudotachylyte generation could be the underlying cause of stick-slip motion and associated seismic 'drumbeats', which are so commonly observed at dome-building volcanoes, allowing for a fixed spatial locus and the occurrence of 'families' of similar seismic events. We conclude that, given the ease with which melting is achieved in volcanic rocks, and considering the high ambient temperatures in volcanic conduits, frictional melting is a highly probable consequence of viscous magma ascent.

  3. Geochemical and isotopic composition of volcanic rocks of the heterogeneous Miocene (~ 23-19 Ma) Tepoztlán Formation, early Transmexican Volcanic Belt, Mexico (United States)

    Torres-Alvarado, Ignacio S.; Lenhardt, Nils; Arce, José Luis; Hinderer, Matthias


    We present the first geochemical data (major and trace elements, as well as Sr, Nd, and Pb isotopes) on volcanic rocks from the Tepoztlán Formation in the central Transmexican Volcanic Belt. The Tepoztlán Formation is up to 800 m thick and comprises a wide range of primary volcanic rocks (lavas, pyroclastic density current deposits, pyroclastic fall deposits), and their secondary reworked products due to mass flow (lahars) and fluvial processes. Magnetostratigraphy combined with K/Ar and Ar/Ar geochronology suggests an age of Early Miocene (23-19 Ma) for this Formation. Lava flows, pyroclastic rocks, dykes and volcanic clasts range from basaltic andesite to rhyolite, with a clear dominance of andesites and dacites. All samples are subalkaline and hy-normative. These rocks show homogeneous REE patterns with LREE enrichment and higher LILE concentrations with respect to HFSE, notably the typical negative anomaly of Nb, Ta, and Ti, suggesting a subduction-related magma genesis. Major and trace element concentrations show that either assimilation of heterogeneous continental crust or crustal recycling by subduction erosion and fractional crystallization are important processes in the evolution of the Tepoztlán Formation magmas. Isotopic compositions of the Tepoztlán Formation samples range from (87Sr/86Sr)t = 0.703693 to 0.704355 and (143Nd/144Nd)t = 0.512751 to 0.512882, falling within the mantle array. All geochemical characteristics indicate that these rocks originated from a heterogeneous mantle, modified and evolved through assimilation of country rock and fractional crystallization in the upper crust.

  4. Chemical and Mineralogical Features of Smectite from the Morron de Mateo Bentonite Deposit (Cabo de Gata, Almeria) in Relation to the Parent Rocks and the Alteration Processes Occurred After the Bentonite Formation: Analogies and Implications for the Engineered Clayey Barrier of a Deep Geological Rad waste Repository

    International Nuclear Information System (INIS)

    The Morron de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on the clayey barrier of a Deep Geological Rad waste Repository (DGRR) after its closure, in relation to the radioactive decay of the fission products and the container corrosion. This bentonite deposit and their host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the bioclastic calcarenite beds close to the dome. Bentonite from the NE sector of the deposit have been chemically and mineralogically characterized. Pyroclastic rocks (white tuffs), epyclastic rocks (mass flow) and andesitic breccia all of them hydrothermally altered, have been studied at the site. Samples are composed of feldspars, quartz and amphybols, as inherited minerals, and phyllosilicates, zeolites, crystoballite and calcite, as new formed minerals. White tuffs have the highest phyllosilicate contents, mainly dioctahedral smectite of montmorillonite type. Epyclastic rocks and andesitic breccia have a highest proportion of inherited minerals, the new formed phillosilicates being di octahedral smectite of beidellite type and an ordered interlayer chlorite/smectite mineral, of corrensite type. Smectite from the epyclastic rocks have higher Fe and Mg contents and chemical variability, as a consequence of nature of their parent rocks. The presence of corrensite in the epyclastic rocks suggests that in the Morron de Mateo area a propilitic alteration process occurred after bentonite formation, which transformed Fe-Mg-rich smectite into corrensite. This transformation was probably favoured by the sub volcanic intrusion, which also produced a temperature increase in the geological media and a supply of Fe-Mg-rich solutions, which also were the responsible for the metasomatic transformations observed in the calcarenite beds. (Author) 57 refs

  5. Geochronological and Geochemical evidence of amphibolite from the Hualong Group, northwest China: Implication for the early Paleozoic accretionary tectonics of the Central Qilian belt (United States)

    Wang, Tao; Wang, Zongqi; Yan, Zhen; Ma, Zhenhui; He, Shengfei; Fu, Changlei; Wang, Dongsheng


    The Hualong Group, located in the Central Qilian belt, northwest China, consists mainly of schist, amphibolite, quartzite, and marble, ranging from greenschist to amphibolite facies metamorphism. On the basis of the medium-grade metamorphism, the group has been considered to comprise Proterozoic basement rocks. In this study, geochemical, Sr-Nd isotopic, and zircon U-Pb geochronological analyses were performed on lentoid amphibolites from the Hualong Group, to characterize their age, petrogensis, and tectonic setting. Uranium-lead zircon dating of amphibolite revealed a formation age of 456 ± 2 Ma and a metamorphic age of 440 ± 1 Ma. Major, trace, and rare earth element data indicate that the amphibolites are predominantly basaltic-andesitic to andesitic rocks, with island arc affinities. The trace element patterns show enrichment in large-ion lithophile elements and depletion in high field strength elements relative to the N-MORB which confirm their island arc signatures. Obviously enriched light REEs ((La/Yb)N = 2.5-16.9) to chondrite normalized REE patterns further support this interpretation. The εNd(t) values for the amphibolites range from 4.6 to + 2.1, indicating subducted sediments as a larger endmember in the source. Geochemical data for these rocks suggest an island arc setting, and the rocks were derived from the depleted mantle that was enriched by melts of subducted sediments in an active continental margin setting at ca. 456 Ma. Together with regional evidence it suggests that the Hualong Group is an accretionary complex that was incorporated into the Central Qilian belt during the 440-400 Ma orogenic event.

  6. New Paleomagnetic Results From Late Paleozoic and Mesozoic Rocks of Tibet: Implications for the Paleogeography of the Eastern Qiangtang Terrane (United States)

    Lippert, P. C.; Zhao, X.


    We present new paleomagnetic, rock magnetic, and geochronologic data from our ongoing study of late Paleozoic and Mesozoic paleomagnetic poles from the Eastern Qiangtang Terrane in Central Tibet. This study consists of four sampling localities of the Eastern Qiangtang Terrane, from south to north: 1) the Kaixingling basalts and andesites, with underlying marls and overlying limestones of late Permian age (11 sites, 81 samples); 2) a basalt flow and overlying quartzose sandstones exposed in the southern TuoTuo He basin, also of suggested late Permian age (4 sites, 41 samples); 3) basalts and andesites from the late Triassic (Norian) Batang Group (7 sites, 55 samples); and a mid-Cretaceous (?) tonolite 15 km south of Wudaoliang (2 sites, 18 samples). These locations have previously been dated by biostratigraphic ages of overlying and underlying strata. Here we present new geochronologic data from the volcanic rocks themselves. High NRM moment values and weak-field susceptibility vs. temperature measurements suggest that magnetite is the dominant magnetic mineral. Resistance to alternating field demagnetization in many samples, in addition to data from magnetic hysteresis measurements, however, indicate a significant amount of hematite exists in these samples as well. All samples were subjected to progressive thermal demagnetization to isolate the characteristic, primary, and secondary magnetizations. Preliminary results show useful paleomagnetic poles may be forthcoming from our collections. Our data may have significant bearing on the geodynamic history of Tibet, including paleogeography of the Eastern Qiangtang Terrane, block rotations, and the nature of the Tertiary low-paleolatitude anomaly in Central Asia.

  7. Relationship between Bajo Pobre and Chon Aike formations (Deseado Massif, Patagonia, Argentina):a melt inclusions study (United States)

    Busà, T.; Bellieni, G.; Fernandez, R.; Hecheveste, H.; Piccirillo, E. M.


    The Deseado Massif covers the centre-east of the Santa Cruz Province, in the extra-Andean Patagonia. Although the Deseado Massif is mainly composed of silicic volcanic rocks (Chon Aike Formation, CA; 151.5 ±0.5 - 177.8 ±0.4 Ma), mafic and intermediate volcanites (Bajo Pobre Formation, BP; 152.7 ±0.5 and 164 ±0.3 Ma) outcrop largely in the central part of the Massif. In this paper quarz-trapped melt inclusions (rhyolitic in composition) from selected samples of the BP and the CA are analysed. On the basis of major elements content, for BP the sequence from andesite (BP whole rock) to ryholite (trapped as inclusions in quartz) can be modelled by simple fractional crystallisation of ortho- and clinopyroxene, plagioclase, quartz and apatite. As regards trace elements, a good calculated/measured ratio (around 1 ±0.2) is obtained assuming only a relatively high apatite fractionation. Since the apatite fractionation amount is not acceptable for major elements, the evolution of BP Formation cannot be modelled by a simple process of fractional crystallisation, and a contamination process probably occurred. The sequence from BP to CA cannot be modelled by fractional crystallisation. 30% batch melting of BP andesite (BP whole rock) produces a magma from which the CA ryholites (trapped as inclusions in quartz) can be obtained by Rayleigh fractional crystallisation of ortho- and clinopyroxene, plagioclase, magnetite, quartz, apatite and small amounts of zircon and minor allanite. Since the latter one was not observed in the analysed sample, a contamination process during magma evolution cannot be completely excluded. Finally, on the basis of the different trace elements concentration (Nb anomaly, different content in LILE, B/Be and B/Nb), it is possible to suppose that, at the time of the BP and CA emplacement, a changing in the tectonic setting, from subduction to a lithospheric extension, was active.

  8. Environmental effect and genetic influence: a regional cancer predisposition survey in the Zonguldak region of Northwest Turkey (United States)

    Kadir, Selahattin; Önen-Hall, A. Piril; Aydin, S. Nihal; Yakicier, Cengiz; Akarsu, Nurten; Tuncer, Murat


    The Cretaceous-Eocene volcano-sedimentary units of the Zonguldak region of the western Black Sea consist of subalkaline andesite and tuff, and sandstone dominated by smectite, kaolinite, accessory chlorite, illite, mordenite, and analcime associated with feldspar, quartz, opal-CT, amphibole, and calcite. Kaolinization, chloritization, sericitization, albitization, Fe-Ti-oxidation, and the presence of zeolite, epidote, and illite in andesitic rocks and tuffaceous materials developed as a result of the degradation of a glass shards matrix, enclosed feldspar, and clinopyroxene-type phenocrysts, due to alteration processes. The association of feldspar and glass with smectite and kaolinite, and the suborientation of feldspar-edged, subparallel kaolinite plates to fracture axes may exhibit an authigenic smectite or kaolinite. Increased alteration degree upward in which Al, Fe, and Ti are gained, and Si, Na, K, and Ca are depleted, is due to the alteration following possible diagenesis and hydrothermal activities. Micromorphologically, fibrous mordenite in the altered units and the presence of needle-type chrysotile in the residential buildings in which cancer cases lived were detected. In addition, the segregation pattern of cancer susceptibility in the region strongly suggested an environmental effect and a genetic influence on the increased cancer incidence in the region. The most likely diagnosis was Li-Fraumeni syndrome, which is one of the hereditary cancer predisposition syndromes; however, no mutations were observed in the p53 gene, which is the major cause of Li-Fraumeni syndrome. The micromorphology observed in the altered units in which cancer cases were detected may have a role in the expression of an unidentified gene, but does not explain alone the occurrence of cancer as a primary cause in the region.

  9. The Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean: Further evidence from the Barleik subduction-related metamorphic complex in the West Junggar region, NW China (United States)

    Liu, Bo; Han, Bao-Fu; Xu, Zhao; Ren, Rong; Zhang, Jin-Rui; Zhou, Jing; Su, Li; Li, Qiu-Li


    In this study, we present new evidence from the Barleik subduction-related metamorphic complex in the southern West Junggar region, northwestern China, for the Cambrian initiation of intra-oceanic subduction in the southern Paleo-Asian Ocean. The Barleik metamorphic complex is mainly composed of blueschist and amphibolite blocks within an ophiolitic mélange and their protoliths are calc-alkaline andesite and alkali and tholeiitic basalts. The calc-alkaline andesite has a zircon U-Pb age of 502 ± 2 Ma, obtained from magmatic cores of zircon grains, and shares geochemical features similar to the 515-485 Ma intra-oceanic arc magmatic rocks in the West Junggar region. By contrast, the alkali and tholeiitic basalts have trace element features similar to ocean island and enriched mid-ocean ridge basalts, respectively. Rutile and sodic-calcic amphibole from the amphibolite have a U-Pb age of 502 ± 25 Ma and a 40Ar/39Ar age of ∼504 Ma, respectively, which are in good agreement within errors with a 40Ar/39Ar age of 492 ± 4 Ma for phengite from the blueschist. These metamorphic ages of ∼500 Ma are interpreted to represent the timing of Pacific-type subduction-related metamorphism and are also compatible with ages of the oldest supra-subduction zone ophiolites (531-512 Ma) and intra-oceanic arc plutons (515-485 Ma) in the southern West Junggar region. Being one of the oldest subduction-related metamorphic complexes (509-490 Ma) in the southern Central Asian Orogenic Belt, the Barleik metamorphic complex, together with the oldest arc plutons, definitely indicate the initial intra-oceanic subduction in the southern Paleo-Asian Ocean at least in the Early Cambrian.

  10. Origin, Age, and Geochemistry of the Tuff of Saguache Creek, Southwestern Colorado (United States)

    Turner, K. J.; Young, M. D.; Wendlandt, R. F.


    A crystal-poor, rhyolitic, ash-flow tuff in the Eastern San Juan Volcanic Field currently known as the tuff of Saguache Creek (TSC) was reinterpreted by Simon and Wendlandt (1999) as not being distal Sapinero Mesa Tuff. Currently there is no source caldera established for this tuff thereby leaving uncertainties in the volcanic history. Regional mapping of the TSC has subsequently been completed to constrain a possible source caldera. Petrographic studies, and EPMA and LA-ICPMS analyses of the mineral assemblage have been performed to characterize further the tuff, enable correlation of mapped TSC, and constrain petrogenetic models. Petrographic and chemical identification of the TSC builds on characteristics set forth by Simon (2000). These characteristics include abundant feldspar clusters, alkali feldspar mantled plagioclase, no modal quartz, Fe-Ti oxides (often with apatites and zircons), and sparse biotite and pyroxene. Pyroxenes show curiously high MnO (avg 2.70 wt%) and Mg# (avg 79.2) and might be xenocrystic. In comparison, biotites have much lower MnO (avg 0.82 wt%). Average sanidine (Or50) and plagioclase (Ab71) compositions fall within the documented range (Simon, 2000) and show little trace element substitution including Eu Conejos age volcanic deposits. Similarly, an andesitic topographic high just west of Trickle Mtn has TSC vitrophyre on the east-facing slope suggesting strong north-south channeling of the flow unit by paleo-topographic lows. Outcrop elevations also decrease from north to south supporting a possible source caldera to the north. This source could be explained by a distinct circular gravity low on the southeastern slope of the Continental Divide. The low is bordered to the north by a circular arrangement of peaks as well as debris breccias, andesitic flow breccias, and lahars.

  11. Groundmass Crystallinities of Proximal and Distal Lavas from Cinder Cone, Lassen Volcanic Field (United States)

    Szymanski, M. E.; Teasdale, R.


    Cinder Cone is located in the northeast corner of Lassen Volcanic Center, approximately 35 km southeast of Old Station, California. The area consists of a cinder cone constructed of loose scoria, lava flows and a 13-16 km diameter ash deposit. According to radiocarbon ages from trees affected by the lava flows and paleomagnetic data, Cinder Cone erupted in about 1650 AD (1). The youngest products of the Cinder Cone eruption are two Fantastic Lava Beds flows which are basaltic andesite and andesite with olivine (1). Samples were collected along the longest flow from Cinder Cone, the Fantastic Lava Beds Flow 2 (4.5 km) at approximately 0.5 km interval. The samples contain olivine, plagioclase and clinopyroxene phenocrysts in fine grained groundmass with varying vesicularity. Quartz xenocrysts also occur. SEM-Back Scatter Electron images are used to map and quantify groundmass crystallinities along the length of the Fantastic Lava Beds flow 2 and of tephra units. The average area of groundmass plagioclase crystals increases along the length of the lava flow from 94.7 to 292.6 μm2. The number of groundmass plagioclase crystals per area (μm2) decreases from 0.0045 to 0.0018 from proximal to distal samples. Crystals also become blockier in distal samples along the lava flow. The larger number of crystals per area in near vent samples establishes a baseline from which we interpret crystal growth and nucleation to have occurred in the flow channel. Increasing crystal size and a decrease in the number of crystals per area indicates growth dominated nucleation during cooling and crystallization in the flow channel. Relative cooling rates along the length of the flow from proximal to distal samples can be inferred based on groundmass crystallinities, distance travelled and estimates of flow and crystallization rates. (1) Muffler and Clynne, 2015.

  12. Stratigraphy of Reforma Caldera, Baja California Sur, Mexico (United States)

    García Sánchez, L.; Macias, J. L.; Osorio, L. S.; Pola, A.; Avellán, D. R.; Arce, J. L.; Saucedo, R.; Sánchez, J. M.; García-Tenorio, F.; Cisneros, G.; Reyes-Agustín, G.; Cardona, S.; Jimenez, A.


    The Reforma caldera is located at ~35 km to the northwest of Santa Rosalía in the central part of the Baja California peninsula. It has 10 km in diameter and a maximum height of 1200 masl in the center and between 100 and 500 masl in its slopes. Reforma is within a tectonic zone affected by two fault systems: A NW-SE normal fault system linked to the opening of the Gulf of California, and a NNW-SSE and NW-SE strike-slip fault system associated with an active Riedel system. Reforma was built upon Cretaceous granites that outcrop at the caldera center, Miocene to Pliocene volcano-sedimentary rocks of the Comondú group, and Miocene marine sediments of the Santa Rosalía basin. On top of these rocks outcrop at least four submarine to subaerial ignimbrites interbedded with marine fossiliferous beds and the lower Pleistocene deposits associated to the Reforma caldera. These deposits are formed by a ignimbrite that shifts to different lithofacies that change gradually their welding, here dubbed basal, transitional, intermediate, and upper (all of then enriched in black fiammes), followed by a pumice-rich, white fiammes, and vitrophyre lithofacies, which are distributed around the 9 km wide caldera and have been associated to the caldera formation episode. Deposits related to post-caldera volcanism are andesite-basaltic lava flows erupted along the caldera rim through localized feeding dikes and andesitic and rhyolitic domes, and scoria cinder cones exposed inside and outside the caldera. On top of these deposits rest the middle Pleistocene Aguajito caldera deposits.

  13. Orthopyroxene-enrichment in the lherzolite-websterite xenolith suite from Paleogene alkali basalts of the Poiana Ruscă Mountains (Romania

    Directory of Open Access Journals (Sweden)

    Nédli Zsuzsanna


    Full Text Available In this paper we present the petrography and geochemistry of a recently collected lherzolite-websterite xenolith series and of clinopyroxene xenocrysts, hosted in Upper Cretaceous–Paleogene basanites of Poiana Ruscă (Romania, whose xenoliths show notable orthopyroxene-enrichment. In the series a slightly deformed porphyroclastic-equigranular textured series could represent the early mantle characteristics, and in many cases notable orthopyroxene growth and poikilitic texture formation was observed. The most abundant mantle lithology, Type A xenoliths have high Al and Na-contents but low mg# of the pyroxenes and low cr# of spinel suggesting a low degree (< 10 % of mafic melt removal. They are also generally poor in overall REE-s (rare earth elements and have flat REY (rare earth elements+ Y patterns with slight LREE-depletion. The geochemistry of the Type A xenoliths and calculated melt composition in equilibrium with the xenolith clinopyroxenes suggests that the percolating melt causing the poikilitization can be linked to a mafic, Al-Na-rich, volatile-poor melt and show similarity with the Late Cretaceous–Paleogene (66–72 Ma subduction-related andesitic magmatism of Poiana Ruscă. Type B xenoliths, with their slightly different chemistry, suggest that, after the ancient depletion, the mantle went through a slight metasomatic event. A subsequent passage of mafic melts in the mantle, with similar compositions to the older andesitic magmatism of Poiana Ruscă, is recorded in the pyroxenites (Fe-rich xenoliths, whereas the megacrysts seem to be cogenetic with the host basanite. The Poiana Ruscă xenoliths differ from the orthopyroxene-enriched mantle xenoliths described previously from the Carpathian-Pannonian Region and from the Dacia block.

  14. Geology of Volcan Las Navajas, a pleistocene trachyte/peralkaline rhyolite volcanic center in Nayarit, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Hegre, J.A.; Nelson, S.A.


    Volcan Las Navajas, located in the northwestern portion of the Mexican Volcanic Belt has produced a sequence of volcanic rocks with compositions in marked contrast to the predominantly calc-alkaline volcanoes which predominate in this part of Mexico. The oldest exposed lavas consist of trachytes with 63% SiO/sub 2/, 6% FeO*, and 500 ppm Zr along with comenditic rhyolites with 68% SiO/sub 2/, 5% FeO*, 800 ppm Zr, and an agpaitic index of 1.0. These lavas were followed by the eruption of a comenditic ash-flow tuff and the formation of a caldera 2.7 km in diameter. This caldera was subsequently filled by eruptions of pantelleritic rhyolite obsidian lava flows with 72% SiO/sub 2/, 8% FeO*, 1100 ppm Zr, and an agpaitic index of 1.5 to 1.9. A second caldera was then formed which is offset to the south of the main eruptive vents for previous eruptions. This younger caldera has a diameter of about 4.8 km and its southern walls have been covered by calc-alkaline andesitic lavas erupted from nearby Sanganguey volcano. Volcanoclastic sediments in the floor of the younger caldera have been tilted and faulted in a manner suggestive of late stage resurgence. Subsequent eruptions within the caldera, however, have been restricted to calc-alkaline andesites. Tectonically, the area in which this volcano occurs appears to have been undergoing a crustal rifting event since the Pliocene. The occurrence of these peralkaline rocks lends further support to such a hypothesis.

  15. Orthopyroxene-enrichment in the lherzolite-websterite xenolith suite from Paleogene alkali basalts of the Poiana Ruscă Mountains (Romania) (United States)

    Nédli, Zsuzsanna; Szabó, Csaba; Dégi, Júlia


    In this paper we present the petrography and geochemistry of a recently collected lherzolite-websterite xenolith series and of clinopyroxene xenocrysts, hosted in Upper Cretaceous-Paleogene basanites of Poiana Ruscă (Romania), whose xenoliths show notable orthopyroxene-enrichment. In the series a slightly deformed porphyroclastic-equigranular textured series could represent the early mantle characteristics, and in many cases notable orthopyroxene growth and poikilitic texture formation was observed. The most abundant mantle lithology, Type A xenoliths have high Al and Na-contents but low mg# of the pyroxenes and low cr# of spinel suggesting a low degree (earth elements) and have flat REY (rare earth elements+ Y) patterns with slight LREE-depletion. The geochemistry of the Type A xenoliths and calculated melt composition in equilibrium with the xenolith clinopyroxenes suggests that the percolating melt causing the poikilitization can be linked to a mafic, Al-Na-rich, volatile-poor melt and show similarity with the Late Cretaceous-Paleogene (66-72 Ma) subduction-related andesitic magmatism of Poiana Ruscă. Type B xenoliths, with their slightly different chemistry, suggest that, after the ancient depletion, the mantle went through a slight metasomatic event. A subsequent passage of mafic melts in the mantle, with similar compositions to the older andesitic magmatism of Poiana Ruscă, is recorded in the pyroxenites (Fe-rich xenoliths), whereas the megacrysts seem to be cogenetic with the host basanite. The Poiana Ruscă xenoliths differ from the orthopyroxene-enriched mantle xenoliths described previously from the Carpathian-Pannonian Region and from the Dacia block.

  16. 40Ar/39Ar geochronology and geochemistry of the Central Saurashtra mafic dyke swarm: insights into magmatic evolution, magma transport, and dyke-flow relationships in the northwestern Deccan Traps (United States)

    Cucciniello, Ciro; Demonterova, Elena I.; Sheth, Hetu; Pande, Kanchan; Vijayan, Anjali


    The Central Saurashtra mafic dyke swarm in the northwestern Deccan Traps contains a few picrites, several subalkalic basalts and basaltic andesites, and an andesite. We have obtained precise 40Ar/39Ar ages of 65.6 ± 0.2 Ma, 66.6 ± 0.3, and 62.4 ± 0.3 Ma (2σ errors) for three of the dykes, indicating the emplacement of the swarm over several million years. Mineral chemical and whole-rock major and trace element and Sr-Nd isotopic data show that fractional crystallization and crystal accumulation were important processes. Except for two dykes (with ɛNd t values of -8.2 and -12.3), the magmas were only moderately contaminated by continental crust. The late-emplaced (62.4 Ma) basalt dyke has compositional characteristics (low La/Sm and Th/Nb, high ɛNd t of +4.3) suggesting little or no crustal contamination. Most dykes are low-Ti and a few high-Ti, and these contrasting Ti types cannot be produced by fractional crystallization processes but require distinct parental magmas. Some dykes are compositionally homogeneous over tens of kilometers, whereas others are heterogeneous, partly because they were formed by multiple magma injections. The combined field and geochemical data establish the Sardhar dyke as ≥62 km long and the longest in Saurashtra, but this and the other Central Saurasthra dykes cannot have fed any of the hitherto studied lava-flow sequences in Saurashtra, given their very distinct Sr-Nd isotopic compositions. As observed previously, high-Ti lavas and dykes only outcrop east-northeast of a line joining Rajkot and Palitana, probably because of underlying enriched mantle at ~65 Ma.

  17. Early-Middle Paleozoic subduction-collision history of the south-eastern Central Asian Orogenic Belt: Evidence from igneous and metasedimentary rocks of central Jilin Province, NE China (United States)

    Pei, Fu-Ping; Zhang, Ying; Wang, Zhi-Wei; Cao, Hua-Hua; Xu, Wen-Liang; Wang, Zi-Jin; Wang, Feng; Yang, Chuan


    To constrain the Early-Middle Paleozoic tectonic evolution of the south-eastern segment of the Central Asian Orogenic Belt (CAOB), we undertook zircon U-Pb dating and analyzed major and trace elements and zircon Hf isotope compositions of Late Cambrian to Middle Devonian igneous and metasedimentary rocks in central Jilin Province, NE China. LA-ICP-MS zircon U-Pb dating indicates that the Early-Middle Paleozoic magmatism in central Jilin Province can be divided into four episodes: Late Cambrian (ca. 493 Ma), Middle Ordovician (ca. 467 Ma), Late Ordovician-Early Silurian (ca. 443 Ma), and Late Silurian-Middle Devonian (425-396 Ma). The progression from subduction initiation to maturity is recorded by Late Cambrian low-K tholeiitic meta-diabase, Middle Ordovician medium-K calc-alkaline pyroxene andesite, and Late Ordovician to Early Silurian low-K tonalite, which all have subduction-related characteristics and formed in an evolving supra-subduction zone setting. Late Silurian to Middle Devonian calc-alkaline igneous rocks, with the lithological association of granodiorite, monzogranite, rhyolite, dacite, and trachydacite, show progressively increasing K2O contents from medium K to shoshonite series. Furthermore, the Early-Middle Devonian monzogranites are characterized by high K2O, Sr/Y, and [La/Yb]N values, indicating they were generated by the melting of thickened lower crust. These results suggest a transition from subduction to post-orogenic setting during the Late Silurian-Middle Devonian. Our interpretation is supported by the maximum age of molasse deposition in the Zhangjiatun member of the Xibiehe Formation. Overall, we suggest that Late Cambrian tholeiitic meta-diabase, Middle Ordovician pyroxene andesite, and Late Ordovician-Early Silurian tonalite formed above the northward-subducting and simultaneously seaward-retreating of Paleo-Asian Ocean plate. Subsequently, the northern arc collided with the North China Craton and post-orogenic extension occurred

  18. Satellite Measurements of Lava Extrusion Rate at Volcán Reventador, Ecuador (United States)

    Arnold, D. W. D.; Biggs, J.; Ebmeier, S. K.; Vallejo Vargas, S.; Naranjo, M. F.


    The extrusion rate of lava at active volcanoes provides a principle control on the style of eruptive behavior and the extent of lava flows, while also providing information about magma supply to the volcano. Measurements of extrusion rate at active volcanoes are therefore important for assessing hazard, and improving understanding of volcanic systems. Volcán Reventador is an asymmetric stratovolcano in the Cordillera Real of Ecuador. The largest historically observed eruption at Reventador in 2002 has been followed by several periods of eruptive activity. Eruptions are characterised by effusion of andesitic to basaltic-andesitic lava flows, and Vulcanian explosions. The ongoing eruption at Reventador therefor provides an excellent target for investigating the link between effusion rate, explosivity, and lava flow behaviour. Satellite InSAR provides regular observations of the volcano, even during night or periods of cloud cover. We use a dataset of Radarsat-2 and TanDEM-X imagery, with intervals of 11 to 192 days, over the period 2011 to 2014 to measure the extent, thickness and volume of new lava flows at Reventador. We use radar amplitude and inteferometric coherence to map 25 individual lava flows, as well as pyroclastic deposits and changes in lava dome morphology. We observe 43 Mm3 of deposits over a three year period, giving an average effusion rate of 0.5 m3s-1. We do not observe any ground deformation due to magmatic sources at Reventador, therefore variations in lava effusion rate can be interpreted as changes in the magma supply to the volcano. We investigate the link between variations in effusion rate and the length, area, thickness, and aspect ratio of lava flows, and the explosive-effusive transition. We also characterise the relationship between lava flow age, thickness, and subsidence rate.

  19. Hydrothermal systems in two areas of the Jemez volcanic field: Sulphur Springs and the Cochiti mining district

    Energy Technology Data Exchange (ETDEWEB)

    WoldeGabriel, G.


    K/Ar dates and oxygen isotope data were obtained on 13 clay separates (<2 of thermally altered mafic and silicic rocks from the Cochiti mining district (SE Jemez Mountains) and Continental Scientific Drilling Project (CSDP) core hole VC-2A (Sulphur Springs, Valles caldera). Illite with K/sub 2/O contents of 6.68%--10.04% is the dominant clay in the silicic rocks, whereas interstratified illite/smectites containing 1.4%--5.74% K/sub 2/O constitute the altered andesites. Two hydrothermal alteration events are recognized at the Cochiti area (8.07 m.y., n = 1, and 6.5--5.6 m.y., n = 6). The older event correlates with the waning stages of Paliza Canyon Formation andesite volcanism (greater than or equal to13 to less than or equal to8.5 m.y.), whereas the younger event correlates with intrusions and gold- and silver-bearing quartz veins associated with the Bearhead Rhyolite (7.54--5.8 m.y.). The majority of K/Ar dates in the hydrothermally altered, caldera-fill rocks of core hole VC-2A (0.83--0.66 m.y., n = 4) indicate that hydrothermal alteration developed contemporaneously with resurgence and ring fracture Valles Rhyolite domes (0.89--0.54 m.y.). One date of 0 +- 0.10 m.y. in acid-altered landslide debris of postcaldera tuffs from the upper 13 m of the core hole probably correlates with Holocene hydrothermal activity possibly associated with the final phases of the Valles Rhyolite (0.13 m.y.).

  20. Geological study of Ujungwatu area as support for NPP planning in Muria Central Java

    International Nuclear Information System (INIS)

    In accordance with growth of life in Java, the need for electricity is also growing accordingly. Efforts to provide electricity such as planning to build nuclear power plant (NPP) has been in the debate for a while. There are many factors to be considered in this planning, such as its environmental condition. Geological factor is one of the important one to be considered. Surface geological conditions around NPP area at Ujungwatu needed include stratigraphy, geological structure, geomorphology, and environmental geology. Geology in Ujungwatu at radius 5 km is quite interesting. This area is part of Genuk volcano group which is laid at south and Ujungwatu coast at north. Genuk mountain group is divided into mountain slope, mountain back, and mountain skeleton. Coastal area is composed of coast sand. Sand up to broken rock was present along river gullies. Others were volcanic rocks which was composed of lapili tuff, trachite, pyroxene andesite, tuff breccia, tephrite-andesitic tuff breccia, and basaltic tuff breccia. Volcanic structure is well reflected by morphological feature as lineaments and half circular form in mount Genuk. This structure was predominantly in NW-SE direction, and less dominant in NE-SW direction. Ujungwatu, from environmental view, is deserved to be developed because of its underground potency. Iron sand, fluvial tuff, kaolin, mud, riverstone, volcanic rock, tuff and marble were easily found underground. Those could be benefited to the people in the area so that it could change socio-economical condition of the people which in turn electricity is becoming a necessity. Last but not least, Portuguese fort as potential touristic object is also situated at Kartini beach near Ujungwatu. (author). 15 refs, 3 tabs, 5 figs

  1. Geochemical characteristics of island-arc volcanic rocks in the Nan-Nam Pat-Phetchabun zone, northern Thailand

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; YANG Wenqiang; ZHANG Zhibin; Chongpom Chonglakmani


    Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite series coming next. The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf. The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.

  2. The Early Mesozoic volcanic arc of western North America in northeastern Mexico (United States)

    Barboza-Gudiño, José Rafael; Orozco-Esquivel, María Teresa; Gómez-Anguiano, Martín; Zavala-Monsiváis, Aurora


    Volcanic successions underlying clastic and carbonate marine rocks of the Oxfordian-Kimmeridgian Zuloaga Group in northeastern Mexico have been attributed to magmatic arcs of Permo-Triassic and Early Jurassic ages. This work provides stratigraphic, petrographic geochronological, and geochemical data to characterize pre-Oxfordian volcanic rocks outcropping in seven localities in northeastern Mexico. Field observations show that the volcanic units overlie Paleozoic metamorphic rocks (Granjeno schist) or Triassic marine strata (Zacatecas Formation) and intrude Triassic redbeds or are partly interbedded with Lower Jurassic redbeds (Huizachal Group). The volcanic rocks include rhyolitic and rhyodacitic domes and dikes, basaltic to andesitic lava flows and breccias, and andesitic to rhyolitic pyroclastic rocks, including breccias, lapilli, and ashflow tuffs that range from welded to unwelded. Lower-Middle Jurassic ages (U/Pb in zircon) have been reported from only two studied localities (Huizachal Valley, Sierra de Catorce), and other reported ages (Ar/Ar and K-Ar in whole-rock or feldspar) are often reset. This work reports a new U/Pb age in zircon that confirms a Lower Jurassic (193 Ma) age for volcanic rocks exposed in the Aramberri area. The major and trace element contents of samples from the seven localities are typical of calc-alkaline, subduction-related rocks. The new geochronological and geochemical data, coupled with the lithological features and stratigraphic positions, indicate volcanic rocks are part of a continental arc, similar to that represented by the Lower-Middle Jurassic Nazas Formation of Durango and northern Zacatecas. On that basis, the studied volcanic sequences are assigned to the Early Jurassic volcanic arc of western North America.

  3. Geology, alteration, mineralization and geochemical study in Kalateh Taimour area, NE Iran

    Directory of Open Access Journals (Sweden)

    Zahra Alaminia


    Full Text Available The area is located 20 km northwest of Kashmar and about 4 km of Kalateh Taimour in Khorasan Razavi province. The study area is part of Tertiary volcanic-plutonic belt north of Daruneh fault and its situation in tectonic inliers between two important active faults, Doruneh and Taknar. Volcanic rocks are mainly intermediate to acid pyroclastic type. They formed during early Tertiary. The volcanic rocks of the Kalateh Taimour area are predominantly andesitic basalt, andesite, latite, trachyte, dacite and rhyodacite and are observed as lava, tuff, lapilli tuff and agglomerate. Field evidences and study show several subvolcanic bodies including quartz hornblende biotite monzodiorite porphyry, quartz biotite monzodiorite porphyry, quartz diorite porphyry and microdiorite which are intruded sometime in mid-Tertiary. In this belt, new methods of image processing were used for enhancing the alteration zones to help near infra red and short wavelength infrared and bands example band ratios and principle component method. Propylitic, sericitic and argillic are the main alteration types. Minor silicification is found in some areas. Alteration is extent but mineralization is limited. Mineralization is mainly controlled by fault system. Several mineralized faults are being discovered. Open space filling features are abundant. In the study area, disseminate and stock work mineralization are abundant. The amount of sulfide minerals is very small. Ancient mining is present in the area. Stream sediment geochemical study shows a very broad and high level of gold anomaly. Rock geochemical study show very high levels of Au, Ag, Cu, Pb, Zn and Au value is correlative to Cu, Pb, Zn and Ag values. Due to alteration modeling, non uniformity in mineralization and low abundance of sulfide mineralization suggest study in low sulphidation Au-Cu deposit.

  4. Temporal Evolution of Magma Flow Conditions during Dome Growth, Insights from Numerical Modelling. (United States)

    Chevalier, L. A. C.; Collombet, M.; Pinel, V.


    Transitions from effusive to explosive regime at andesitic volcanoes are almost unpredictable at the moment. The reliability of empirical methods based on geophysical precursory patterns is still debated. A better understanding of the physical processes happening in the volcanic system before explosions and associated geophysical signals is needed. At andesitic volcanoes, dome building is often observed during the effusive phase. The weight of a forming dome is expected to have several effects: 1) It obviously induces a ground subsidence in the near field; 2) pressure increase at the top of the conduit causes magma properties and flow conditions evolution; 3) it increases pressure in the surrounding rock such decreasing rock permeability and thus gas loss through the conduit walls, possibly leading to gas pressurisation. Here we use numerical models that couple realistic magma flow conditions in the upper conduit with solid deformation, in 2D axisymmetry, to investigate all these effects. Subsiding effect due to the dome emplacement is simulated by a pressure loading of the rock surrounding the conduit. From realistic initial magma flow conditions in effusive regime (Collombet, 2009), we apply increasing pressure at the conduit top. Volatile solubility increases with pressure, then dome growth causes a decrease of magma porosity and permeability at the top of the conduit. This also causes a decrease of magma viscosity. From magma flow model, we extract pressure and shear stress conditions at the conduit wall, and apply them to the surrounding rock for ground deformation calculation . Darcy flow model is used to study the impacts of permeability decrease inside the conduit and in the surrounding rock on gas loss cinematics. Permeability decrease in the conduit and pressure increase in the surrounding rock cause gas pressurisation.

  5. Robust 24 ± 6 ka 40Ar/39Ar age of a low-potassium tholeiitic basalt in the Lassen region of NE California (United States)

    Turrin, Brent D.; Muffler, L. J. Patrick; Clynne, Michael A.; Champion, Duane E.


    40Ar/39Ar ages on the Hat Creek Basalt (HCB) and stratigraphically related lava flows show that latest Pleistocene tholeiitic basalt with very low K2O can be dated reliably. The HCB underlies ∼ 15 ka glacial gravel and overlies four andesite and basaltic andesite lava flows that yield 40Ar/39Ar ages of 38 ± 7 ka (Cinder Butte; 1.65% K2O), 46 ± 7 ka (Sugarloaf Peak; 1.85% K2O), 67 ± 4 ka (Little Potato Butte; 1.42% K2O) and 77 ± 11 ka (Potato Butte; 1.62% K2O). Given these firm age brackets, we then dated the HCB directly. One sample (0.19% K2O) clearly failed the criteria for plateau-age interpretation, but the inverse isochron age of 26 ± 6 ka is seductively appealing. A second sample (0.17% K2O) yielded concordant plateau, integrated (total fusion), and inverse isochron ages of 26 ± 18, 30 ± 20 and 24 ± 6 ka, all within the time bracket determined by stratigraphic relations; the inverse isochron age of 24 ± 6 ka is preferred. As with all isotopically determined ages, confidence in the results is significantly enhanced when additional constraints imposed by other isotopic ages within a stratigraphic context are taken into account.

  6. Reconstructing the evoluortunity to study processes related to composite volction of an eroded Miocene caldera volcano (Yamanlar volcano, İzmir, Turkey) (United States)

    Karaoğlu, Özgür; Brown, Richard J.


    The Miocene Yamanlar composite volcano is located in the central part of a shear zone in western Turkey. The volcano's deeply-eroded interior provides excellent three-dimensional exposure of a faulted caldera-floor and caldera-fill rocks as well as surrounding extracaldera ignimbrites. We present a much-revised stratigraphy and geological map of Yamanlar in order to quantify the evolutionary stages of the volcano. The Yamanlar volcanic cone was composed of > 800 m of basaltic-andesite to andesite lavas and lava domes. The volcano underwent at least one phase of caldera formation associated with an explosive eruption that deposited an ignimbrite sheet within and outside the caldera. Lithofacies architecture analysis is applied to the proximal and medial exposures of the Early-Middle Yamanlar Formation, which occurs outside of the caldera. Field evidence of the succession indicates a caldera-forming eruption. Our results indicate that the formation of the Yamanlar caldera resulted from one major catastrophic eruption that generated several sustained pyroclastic density currents (PDCs) subdivided by fall deposits with sharp contacts. The ignimbrite sheet is composed of four flow units. The presence of numerous coarse-grained lithic-rich horizons within the ignimbrite sheet is consistent with caldera subsidence. Post-caldera volcanism is indicated by intrusions and lava domes erupted along the inferred caldera-bounding faults, some of which record ~ 90 m of displacement. Widespread, coarse-grained breccias that overlie the ignimbrite sheet are interpreted as debris avalanche deposits resulting from gravitational failure of the flanks of the volcano or the caldera wall during or after caldera subsidence.

  7. Variations in eruption style during the 1931 A.D. eruption of Aniakchak volcano, Alaska (United States)

    Nicholson, Robert S.; Gardner, James E.; Neal, Christina A.


    The 1931 A.D. eruption of Aniakchak volcano, Alaska, progressed from subplinian to effusive eruptive style and from trachydacite to basaltic andesite composition from multiple vent locations. Eyewitness accounts and new studies of deposit stratigraphy provide a combined narrative of eruptive events. Additional field, compositional, grain size, componentry, density, and grain morphology data document the influences on changing eruptive style as the eruption progressed. The eruption began on 1 May 1931 A.D. when a large subplinian eruption column produced vesicular juvenile-rich tephra. Subsequent activity was more intermittent, as magma interacted with groundwater and phreatomagmatic ash and lithic-rich tephra was dispersed up to 600 km downwind. Final erupted products were more mafic in composition and the eruption became more strombolian in style. Stratigraphic evidence suggests that two trachydacitic lava flows were erupted from separate but adjacent vents before the phreatomagmatic phase concluded and that basaltic andesite lava from a third vent began to effuse near the end of explosive activity. The estimated total bulk volume of the eruption is 0.9 km3, which corresponds to approximately 0.3 km3 of magma. Eruption style changes are interpreted as follows: (1) a decrease in magma supply rate caused the change from subplinian to phreatomagmatic eruption; (2) a subsequent change in magma composition caused the transition from phreatomagmatic to strombolian eruption style. Additionally, the explosion and effusion of a similar magma composition from three separate vents indicates how the pre-existing caldera structure controlled the pathway of shallow magma ascent, thus influencing eruption style.

  8. Late Cretaceous lithospheric extension in SE China: Constraints from volcanic rocks in Hainan Island (United States)

    Zhou, Yun; Liang, Xinquan; Kröner, Alfred; Cai, Yongfeng; Shao, Tongbin; Wen, Shunv; Jiang, Ying; Fu, Jiangang; Wang, Ce; Dong, Chaoge


    Petrological, geochemical and in-situ zircon U-Pb dating and Hf-isotope analyses have been carried out on a suite of basalt-andesite-rhyolite volcanic rocks exposed in the Liuluocun area, Hainan Island, SE China. Zircon analyses show that these volcanic rocks crystallized in the Early Cretaceous (ca. 102 Ma). The basalts are characterized by low MgO contents and mg-numbers but high rare earth element, high field strength element and large ion lithophile element contents and Nb-Ta negative anomalies. They have relatively uniform Sr-Nd isotope compositions with εNd(t) values of - 4.09 to - 3.63. The andesites show enrichment of high field strength element and rare earth element with negligible Eu anomalies. They have εNd(t) values of - 2.35 to - 3.88 and εHf(t) values of - 9.73 to - 1.13. The rhyolites have high K2O and SiO2 contents. They are characterized by prominent Eu, P and Ti negative anomalies and enrichment in large ion lithophile element, and show εHf(t) values of - 7.51 to + 0.47 and εNd(t) values of - 2.49 to - 2.69. Petrogenetic analysis indicates that the Liuluocun volcanic rocks were produced by incomplete reaction of the mantle wedge peridotite with felsic melts derived from partial melting of subducted sediment. All these characteristics, combined with geological observations, suggest that their formation was related to regional lithospheric extension in the South China Craton during the Early Cretaceous, which may have been caused by subduction of the Paleo-Pacific plate beneath the continental plate of China.

  9. Rare earth elements geochemistry in springs from Taftan geothermal area SE Iran (United States)

    Shakeri, Ata; Ghoreyshinia, Sayedkazem; Mehrabi, Behzad; Delavari, Morteza


    Concentrations of rare earth elements (REEs) were determined in springs and andesitic-dacitic rocks of Taftan geothermal field. Hydrochemical results of major ions indicate that thermal springs are Na-SO4-Cl and Ca-SO4-Cl types. Concentrations of REEs are in ranges of 10- 4 to 1.2 and 49 to ~ 62 times of chondrite for springwater and rock samples, respectively. The thermal (STS and TTS) and the cold (APS) springs with low pH values exhibit a very high REE contents (0.64 to 3.15 mg/l). Saturation index indicates that Fe and Al phases can control dissolved REE concentration in FTS and PF cold springs. The speciation of REE complexes indicates dominant presence of LnSO4+ and free ion in the Taftan thermal springs. In APS cold spring with pH ~ 4, fluoride complexes are dominate over the free ion and sulfate species, while in PF and FTS cold springs with pH 6.4 and 7, respectively, carbonate complexes (LnCO3+) are predominant species. Chondrite-normalized pattern for the low-pH waters show very distinctive gull-wing patterns, characteristic feature of acid-sulfate geothermal systems, and are similar to those of the host rocks. Chemical characteristics of rare earth elements in spring and volcanic rock samples indicate that REEs are originated from the andesitic-dacitic host rocks. Whole-rock-normalized REE patterns and petrographic evidences show that rare earth elements leached mainly from marginal alteration of minerals and matrix decomposition in volcanic rocks. In chondrite-normalized REE patterns, significant negative Eu anomaly in the cold springs compare to the thermal and acidic springs indicates that alteration of plagioclase is more intense in the later, corresponding to increasing in temperature and acidic state of reactant water.

  10. Petrogenesis of subvolcanic rocks from the Khunik prospecting area, south of Birjand, Iran: Geochemical, Sr-Nd isotopic and U-Pb zircon constraints (United States)

    Samiee, Somayeh; Karimpour, Mohammad Hassan; Ghaderi, Majid; Haidarian Shahri, Mohammad Reza; Klöetzli, Urs; Santos, José Francisco


    The Khunik prospecting area is located 106 km south of Birjand in eastern Iran, and is considered as an epithermal gold prospecting area. The mineralization is related to subvolcanic rocks. There are several outcrops of subvolcanic intrusions in the area which intruded into Paleocene-Eocene volcanic rocks (andesite, trachy-andesite and pyroclastic rocks). Petrographic studies indicate that subvolcanic rocks consist mainly of diorite, monzonite, quartz-monzonite, monzodiorite and quartz-monzodiorite. Mineralogically, these rocks contain plagioclase, K-feldspar, amphibole, pyroxene, biotite and quartz. Geochemically, they have features typical of high-K calk-alkaline to shoshonitic and are metaluminous, and also belong to magnetite granitoid series (I-type). Primitive mantle normalized trace element spider diagrams display enrichment in LILE, such as Rb, Ba, and Cs, compared to HFSE. Chondrite-normalized REE plots show moderately LREE enriched patterns (7.45 diagrams also show affinities with modern convergent margin magmas, suggesting that magmas of Khunik area formed in volcanic arc setting related to subduction of the oceanic crust under the Lut Block plate. The initial 87Sr/86Sr ratios (0.704196-0.704772) and εNdi values (+1.3 to +3.3) are compatible with an origin of the parental melts in a supra-subduction mantle wedge. Zircon U-Pb dating by LA-ICP-MS indicates the age of 38 ± 1 Ma (late Eocene) for subvolcanic units that are related to mineralization. A biotite granodiorite porphyry is the testimony of the youngest magmatic activity in the area, with an age of 31 ± 1 Ma (early Oligocene). The represented dates are interpreted as magmatic crystallization ages of subvolcanic intrusions.

  11. Phase segmentation of X-ray computer tomography rock images using machine learning techniques: an accuracy and performance study (United States)

    Chauhan, Swarup; Rühaak, Wolfram; Anbergen, Hauke; Kabdenov, Alen; Freise, Marcus; Wille, Thorsten; Sass, Ingo


    Performance and accuracy of machine learning techniques to segment rock grains, matrix and pore voxels from a 3-D volume of X-ray tomographic (XCT) grayscale rock images was evaluated. The segmentation and classification capability of unsupervised (k-means, fuzzy c-means, self-organized maps), supervised (artificial neural networks, least-squares support vector machines) and ensemble classifiers (bragging and boosting) were tested using XCT images of andesite volcanic rock, Berea sandstone, Rotliegend sandstone and a synthetic sample. The averaged porosity obtained for andesite (15.8 ± 2.5 %), Berea sandstone (16.3 ± 2.6 %), Rotliegend sandstone (13.4 ± 7.4 %) and the synthetic sample (48.3 ± 13.3 %) is in very good agreement with the respective laboratory measurement data and varies by a factor of 0.2. The k-means algorithm is the fastest of all machine learning algorithms, whereas a least-squares support vector machine is the most computationally expensive. Metrics entropy, purity, mean square root error, receiver operational characteristic curve and 10 K-fold cross-validation were used to determine the accuracy of unsupervised, supervised and ensemble classifier techniques. In general, the accuracy was found to be largely affected by the feature vector selection scheme. As it is always a trade-off between performance and accuracy, it is difficult to isolate one particular machine learning algorithm which is best suited for the complex phase segmentation problem. Therefore, our investigation provides parameters that can help in selecting the appropriate machine learning techniques for phase segmentation.

  12. Permian volcanisms in eastern and southeastern margins of the Jiamusi Massif, northeastern China: zircon U-Pb chronology, geochemistry and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    MENG En; XU WenLiang; YANG DeBin; PEI FuPing; Yu Yang; Zhang XingZhou


    LA-ICP-MS zircon U-Pb dating and geochemical data for the Late Paleozoic volcanic rocks from eastern and southeastern margins of the Jiamusi Massif are presented to understand the regional tectonic evolution. Zircons from eight representative volcanic rocks are euhedral-subhedral in shape and dis-play striped absorption and fine-scale oscillatory growth zoning as well as high Th/U ratios (0.33-2.37), implying a magmatic origin. The dating results show that the Late Paleozoic volcanic rocks in the study area can be divided into two stages, I.e., the Early Permian (a weighted mean 206pb/238U age of 288 Ma) and the Middle Permian volcanisms (a weighted mean 206Pb/238U age of 268 Ma). The former is com-posed mainly of basalt, basaltic-andesite, andesite and minor dacite. They are characterized by low SiO2 contents, high Mg# (0.40-0.59), enrichment in Na (Na2O/K2O = 1.26-4.25) and light rare earth elements (LREEs), relative depletion in heavy rare earth elements (HREEs) and high field strength ele-ments (HFSEs), indicating that an active continental margin setting could exist in the eastern margin of the Jiamusi Massif in the Early Permian. The latter consists mainly of rhyolite and minor dacite with high SiO2 (77.23%-77.52%), low MgO (0.11%-0.14%), enrichment in K2O (Na2O/K2O ratios <0.80) and Rb, Th, U and depletion in Eu, Sr, P and Ti, implying a crust-derived origin. Therefore, it is proposed that the Middle Permian volcanic rocks could have formed under the collision of the Jiamusi and the Khanka Massifs.

  13. Magmatic inclusions in rhyolites, contaminated basalts, and compositional zonation beneath the Coso volcanic field, California (United States)

    Bacon, C.R.; Metz, J.


    Basaltic lava flows and high-silica rhyolite domes form the Pleistocene part of the Coso volcanic field in southeastern California. The distribution of vents maps the areal zonation inferred for the upper parts of the Coso magmatic system. Subalkalic basalts (Coso volcanic field contain sparse andesitic inclusions (55-61% SiO2). Pillow-like forms, intricate commingling and local diffusive mixing of andesite and rhyolite at contacts, concentric vesicle distribution, and crystal morphologies indicative of undercooling show that inclusions were incorporated in their rhyolitic hosts as blobs of magma. Inclusions were probably dispersed throughout small volumes of rhyolitic magma by convective (mechanical) mixing. Inclusion magma was formed by mixing (hybridization) at the interface between basaltic and rhyolitic magmas that coexisted in vertically zoned igneous systems. Relict phenocrysts and the bulk compositions of inclusions suggest that silicic endmembers were less differentiated than erupted high-silica rhyolite. Changes in inferred endmembers of magma mixtures with time suggest that the steepness of chemical gradients near the silicic/mafic interface in the zoned reservoir may have decreased as the system matured, although a high-silica rhyolitic cap persisted. The Coso example is an extreme case of large thermal and compositional contrast between inclusion and host magmas; lesser differences between intermediate composition magmas and inclusions lead to undercooling phenomena that suggest smaller ??T. Vertical compositional zonation in magma chambers has been documented through study of products of voluminous pyroclastic eruptions. Magmatic inclusions in volcanic rocks provide evidence for compositional zonation and mixing processes in igneous systems when only lava is erupted. ?? 1984 Springer-Verlag.

  14. On the time-scales of magmatism at island-arc volcanoes. (United States)

    Turner, S P


    Precise information on time-scales and rates of change is fundamental to an understanding of natural processes and the development of quantitative physical models in the Earth sciences. U-series isotope studies are revolutionizing this field by providing time information in the range 10(2)-10(4) years, which is similar to that of many modern Earth processes. I review how the application of U-series isotopes has been used to constrain the time-scales of magma formation, ascent and storage beneath island-arc volcanoes. Different elements are distilled-off the subducting plate at different times and in different places. Contributions from subducted sediments to island-arc lava sources appear to occur some 350 kyr to 4 Myr prior to eruption. Fluid release from the subducting oceanic crust into the mantle wedge may be a multi-stage process and occurs over a period ranging from a few hundred kyr to less than one kyr prior to eruption. This implies that dehydration commences prior to the initiation of partial melting within the mantle wedge, which is consistent with recent evidence that the onset of melting is controlled by an isotherm and thus the thermal structure within the wedge. U-Pa disequilibria appear to require a component of decompression melting, possibly due to the development of gravitational instabilities. The preservation of large (226)Ra disequilibria permits only a short period of time between fluid addition and eruption. This requires rapid melt segregation, magma ascent by channelled flow and minimal residence time within the lithosphere. The evolution from basalt to basaltic andesite probably occurs rapidly during ascent or in magma reservoirs inferred from some geophysical data to lie within the lithospheric mantle. The flux across the Moho is broadly andesitic, and some magmas subsequently stall in more shallow crustal-level magma chambers, where they evolve to more differentiated compositions on time-scales of a few thousand years or less.

  15. Petrography, Geochemistry and Petrogenesis of Volcanic Rocks, NW Ghonabad, Iran

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    Sedigheh Zirjanizadeh


    Full Text Available Introduction The study area is located in NW Gonabad, Razavi Khorasan Province, northern Lut block and eastern Iran north of the Lut Block. Magmatism in NW Gonabad produced plutonic and volcanic rock associations with varying geochemical compositions. These rocks are related to the Cenozoic magmatic rocks in Iran and belong to the Lut Block volcanic–plutonic belt. In this study, petrogenesis of volcanic units in northwest Gonabad was investigated. The volcanic rocks are andesites/trachyandesites, rhyolites, dacites/ rhyodacites and pyroclastics.These rocks show porphyritic, trachytic and embayed textures in phenocrysts with plagioclase, sanidine and quartz (most notably in dacite and rhyolite, hornblende and rare biotite. The most important alteration zones are propylitic, silicification and argillic.Four kaolinite- bearing clay deposits have been located in areas affectedby hydrothermal alteration of Eocene rhyolite, dacite and rhyodacite. Analytical techniques Five samples were analyzed for major elements by wavelength dispersive X-ray fluorescence (XRF and six samples were analyzed for trace elements using inductively coupled plasma-mass spectrometry (ICP-MS in the Acme Laboratories, Vancouver (Canada.Sr and Nd isotopic compositions were determined for four whole-rock samples at the Laboratório de GeologiaIsotópica da Universidade de Aveiro, Portugal. Results Petrography. The rocks in this area are consist of trachyte, andesite/ trachyandesite, dacite/ rhyodacite, principally as ignimbrites and soft tuff. The textures of phenocrysts are mainly porphyritic, glomerophyric, trachytic and embayed textures in plagioclase, hornblende and biotite. The groundmasses consist of plagioclase and fine-grainedcrystals of hornblende. Plagioclase phenocrysts and microlitesare by far the most abundant textures in andesite - trachyandesites (>25% and in size from 0.01 to 0.1mm. Euhedral to subhedral hornblende phenocrysts areabundant (3-5%and 0.1 to 0

  16. The geology of the northern tip of the Arabian-Nubian Shield (United States)

    Beyth, M.; Eyal, Y.; Garfunkel, Z.


    Recently, a detailed (1:50,000) geological map of the Elat area, southern Israel was published. Attached to this map is a stratigraphic table of the Neoproterozoic metamorphic-magmatic complex of the study area. The Neoproterozoic basement in the Elat area encapsulates the Arabian Nubian Shield (ANS) geologic evolution. Uranium-Lead and Lead-Lead zircon ages, included in previous studies and referred to in this paper, reveal that these rocks were formed during more than 300 million years of Neoproterozoic time. The major process controlling the formation of the ANS as part of the East African Orogen is the closure of the Mozambique Ocean. The first orogenic phase in the Elat area, represented by the metamorphic rocks, includes the development of an island arc, erosion of the islands and deposition, and metamorphism. This event took place between ∼950 Ma and 780-790 Ma. Elat Schist, the oldest metamorphic rock in the area, was deformed and then intruded by quartz dioritic and granitic plutons that were later deformed and metamorphosed. The amphibolite metamorphic rock facies indicate metamorphic conditions of up to 650 °C and between 4 and 5 kbar. The peak of the metamorphic event was most probably before 750 Ma. A gradual change from compressional to extensional stress regime is evidenced by emplacement andesitic magnesium-rich dykes dated to 705 Ma that were later metamorphosed to schistose dykes at a greenschist metamorphic facies. The second orogenic phase (terrane amalgamation, main shaping of crust) was associated with the emplacement of large volumes (>50% of area) of calc-alkaline intrusions in a post-collision setting. These very last stages of metamorphism and deformation are characterized by intrusion of ∼630 Ma granitoids exhibiting some foliation. Pluton emplacement continued also after the end of deformation. Exhumation and transition to an extensional regime is recorded by the intrusion of shallow alkaline granites in ∼608 Ma which were

  17. Geology and ground-water resources of the islands of Lanai and Kahoolawe, Hawaii (United States)

    Stearns, Harold T.; Macdonald, Gordon Andrew; Swartz, Joel Howard


    basal water, although potable, is fairly high in salt. Several sites are recommended for developing and conserving ground water.Kahoolawe Island is 11 miles long, 6 miles wide, 1,491 feet high, covers 45 square miles, and lies 94 miles southeast of Honolulu and 6 3/4 miles southwest of Maui. It is a shield-shaped extinct volcano composed chiefly of thin flows of primitive basalt poured in rapid succession from three rift zones and a vent at their intersection. At one stage the volcano was indented with a caldera about 3 miles across which was later completely filled. A graben led southwestward from it. The rocks are divided into Late Tertiary (?) or early Pleistocene(?) pre-caldera basalts, caldera-filling basalts and basaltic andesites, post-caldera basalts and andesites, and Recent post erosional basalts. A few thin vitric tuff beds and cinder cones were found. Marine erosion has cut cliffs as high as 800 feet along the east and south shores and exposed a cross section of the caldera. Only shallow ephemeral gulches exist. The entire summit has been eroded to a hard-pan surface by the wind as a result of the vegetation being destroyed by livestock. The island is semi-arid and well water is needed for stook: "The stook is now supplied entirely from storage of rain and flood waters. During droughts water is hauled by boat from the island of Maui. All the wells dug so far yield water that is too brackish for stock except at the fairly inaccessible south side of Kanapou Bay. The resistivity survey indicates a water table 1.5 feet or less above sea level for 2.25 miles inland. A few sites for wells are recommended in the dike complex where small supplies of water suitable for stock might be found. Petrographic studies by Gordon A. Macdonald indicate that the pre-caldera and caldera-filling lavas are largely normal olivine basalt of the type which forms the bulk of all Hawaiian volcanoes thus far investigated. It represents the undifferentiated magma of the Hawaiian

  18. Geology of the region of Guadalajara, Mexico, and its relationships with processes of subsidence (United States)

    Suarez-Plascencia, C.; Delgado-Argote, L. A.; Nuñez-Cornu, F. J.; Sanchez, J. J.


    The city of Guadalajara, Mexico, began an accelerated urban growth in early 1950. During a span of 25 years a large number of gullies were artificially filled, with the aim of incorporating new areas for urbanization, particularly in the areas north and west of the city. These gullies originally formed a complex dendritic-type system, whose evolution may be associated with faults or fracture zones whose current identification are only possible based on escarpments along the Canyon of the Rio Grande de Santiago (CRGS), north of Guadalajara. Reports of affectations documented in the 80's described subsidence in buildings and infrastructure, a process that has been continued during 2008. We present the results of work done in the CRGS, which is a tectonic erosive-depression with an average depth of 500 m and exhibits a sequence of volcanic and sedimentary deposits with rapid lateral facies changes. The stratigraphic column spans a 15 km-long section along the Matatlán-Arcediano road, and, from top to bottom contains: 1) Unconsolidated pumice and tuffs with an average thickness of 12 m; 2) basaltic lavas with average thickness of 60 m; 3) the San Gaspar ignimbrite; 4) fluvial- sedimentary deposits with a thickness of approximately 20 meters that include both sub-rounded and angular volcanic clasts, with sizes up to 0.15 m; 5) a thick sequence of ignimbrites and dacitic lavas. At a depth of 1200 m.a.s.l. in the town of Arcediano, the basal sequence is composed of dacites and andesites with interbedded pumice-rich ignimbrites with 10-20 m thickness. The Rio Grande de Santiago talweg to 1018 m.a.s.l. (apparently the base of the sequence) is formed by andesite lava. In the area of San Gaspar we identified oblique-normal left-lateral faults in lavas, with a strike 191° and a dip 89°. In the Colimilla dam, 1297 m.a.s.l., we observed normal faulting (strike 267° and dip 81°), with 20-30 m jumps with reference to a unit of tephra of 3-10 m thickness. The lavas in this

  19. Eruptive history of the youngest Mexican Shield and Mexico's most voluminous Holocene eruption: Cerro El Metate (United States)

    Oryaëlle Chevrel, Magdalena; Guilbaud, Marie-Noelle; Siebe, Claus


    Small to medium-sized shield volcanoes are an important component of many volcanic fields on Earth. The Trans-Mexican Volcanic Belt, one of the most complex and active continental arcs worldwide, displays a large number of such medium-sized volcanoes. In particular the Michoacán-Guanajuato Volcanic Field (MGVF) situated in central Mexico, is the largest monogenetic volcanic field in the world and includes more than 1000 scoria cones and about four hundred medium-sized volcanoes, also known as Mexican shields. The Mexican shields nevertheless represent nearly 70% of the total volume erupted since 1 Ma and hence played a considerable role in the formation of the MGVF. However, the source, storage, and transport as well as the physical properties (density, viscosity, volatile content, etc.) of the magmas involved in these eruptions remain poorly constrained. Here, we focus on Cerro El Metate, the youngest monogenetic andesite shield volcano of the field. New C14 dates for the eruption yield a young age (~AD 1250), which briefly precedes the initial rise of the Tarascan Empire (AD 1350-1521) in this region. This volcano has a minimum volume of ~9.2 km3 DRE, and its viscous lava flows were emplaced during a single eruption over a period of ~35 years covering an area of 103 km2. By volume, this is certainly the largest eruption during the Holocene in Mexico, and it is the largest andesitic effusive eruption known worldwide for this period. Such a large volume of lava erupted in a relatively short time had a significant impact on the environment (modification of the hydrological network, forest fires, etc.), and hence, nearby human populations probably had to migrate. Its eruptive history was reconstructed through detailed mapping, and geochemical and rheological analyses of its thick hornblende-bearing andesitic flows. Early and late flows have distinct morphologies, chemical and mineralogical compositions, and isotopic signatures which show that these lavas were fed by

  20. Geologic map of the Gila Hot Springs 7.5' quadrangle and the Cliff Dwellings National Monument, Catron and Grant Counties, New Mexico (United States)

    Ratté, James C.; Gaskill, David L.; Chappell, James R.


    part of the composite Copperas Creek volcano, or volcanic complex in the Copperas Peak quadrangle to the south. The altered rocks of the Alum Mountain eruptive center have been prospected by means of several short adits, or tunnels, for alum, a mixture of the iron and aluminum sulfate minerals: alunite and halotrichite. A fault on the west side of the Gila River, opposite the hot springs in the south-central part of the map area, just north of Alum Mountain, is tentatively interpreted as a segment of the wall of the Gila Cliff Dwellings caldera. The fault, which dips about 55 degrees northwest, has a footwall of the andesitic and dacitic lava flows and flow breccias of Gila Flat. The hanging wall consists of Bloodgood Canyon Tuff overlain by Bearwallow Mountain Andesite flows. However, these rocks are not faulted against the older rocks, but apparently abut and locally overlap the footwall. These are the major geologic features of the quadrangle, about three quarters of which is covered by Bearwallow Mountain Andesite lava flows and overlying volcaniclastic rocks of the Gila Conglomerate.

  1. LA-ICP-MS analysis of trace elements in glass spherules of the El'gygytgyn impact structure, Siberia (United States)

    Adolph, Leonie; Deutsch, Alex


    The 3.58±0.04 Ma old El'gygytgyn impact structure (Central Chukotka, NE Siberia) with a diameter of 18 km (Gurov and Gurova 1979, Layer 2000) is one of only two terrestrial craters with a volcanic target; therefore, analysis of its target and impact lithologies is of basic interest for comparative planetology. Lake El'gygytgyn is a very valuable climate archive in the Arctic as it was neither covered by glaciers (Melles et al. 2007) nor has the lake ever fallen dry. Climate and impact research were the rationale for the ICDP drilling project that finished successfully in spring 2009. Impactites like melt rocks and breccias are rarely found in outcrops yet are present in the 80 m terrace of Lake El'gygytgyn (Gurov and Gurova 1979). Numerous investigations on petrography, shock metamorphism, and geochemistry of impactites from El'gygytgyn have been published so far (e.g. Gurov et al. 2007). We report the first trace element data for seven 30- to 760-μm-sized impact glass spherules that have been collected about10 km off the crater center from a terrace deposit of the Enmyvaam River outside the crater rim. The spherules are translucent with colors ranging from amber, dark brown to nearly black; they contain a few circular bubbles, schlieren, and very rarely mineral clasts and breccia fragments. Major elements were measured with the JEOL JXA 8600 MX Superprobe, 31 trace elements were analyzed with the Finnigan Element2 LA-ICP-MS with 5 Hz, 8-9 J/cm2 at with Si as internal, and NIST612 as external standard (Institut f. Mineralogie, WWU Münster). The spot size was 60 μm. All spherules show a very homogeneous major and trace element distribution yet clear differences exist between the samples in the SiO2 content (in weight percent) 53-68: four of the glasses are dacitic, two andesitic, and one basaltic-andesitic in composition. In addition, MgO (2.1-9.2), K2O (0.6-3.3), and (in ppm) Ni (317-1096), Co (25-79), Zr (100-169), Rb (18-107), and Ba (459-1092) display wide

  2. Volcanismo calcoalcalino neopaleozoico en la Precordillera de La Rioja. Petrología y caracterización litoestratigráfica de la Formación Punta del Agua (Carbonífero Superior-Pérmico Inferior Late Palaeozoic calc-alkaline volcanism in the Precordillera of La Rioja: petrology and lithostratigraphical characterization of the Punta del Agua Formation (Late Carboniferous - Early Permian

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    M. Remesal


    Pampeanas. The unit consists of interbedded lava flows, pyroclastic flows and clastic sedimentary deposits. The lava flows have been divided according to their composition and textural characteristics; a dacitic sill is also included. Pyroclastic flows consist of block- and ash-flow deposits and reoignimbrites. Between periods of volcanicity, conglomerates, lithic sandstones and scarce mudstones were deposited in lenticular bodies that reflect the irregular morphology of the volcanic area. Twelve samples of the volcanic rocks, obtained from both flanks of the Punta del Agua syncline were geochemically analysed. The variation in chemical composition ranges from basaltic andesites to rhyolites, but andesitic compositions dominate. The calc-alkaline character of these rocks and the abundance of K in the andesites, suggest that these magmas originated by subduction with crystal fractionation and contamination processes. The age of the Punta del Agua Formation was established on the basis of its stratigraphical relations and radiometric dating. Both suggest a Late Carboniferous age, although an Early Permian age for the uppermost part of the sequence cannot be disregarded.

  3. Bimodal Silurian and Lower Devonian volcanic rock assemblages in the Machias-Eastport area, Maine (United States)

    Gates, Olcott; Moench, R.H.


    Exposed in the Machias-Eastport area of southeastern Maine is the thickest (at least 8,000 m), best exposed, best dated, and most nearly complete succession of Silurian and Lower Devonian volcanic strata in the coastal volcanic belt, remnants of which crop out along the coasts of southern New Brunswick, Canada, and southeastern New England in the United States. The volcanics were erupted through the 600-700-million-year-old Avalonian sialic basement. To test the possibility that this volcanic belt was a magmatic arc above a subduction zone prior to presumed Acadian continental collision, samples representing the entire section in the Machias-Eastport area of Maine were chemically analyzed. Three strongly bimodal assemblages of volcanic rocks and associated intrusives are recognized, herein called the Silurian, older Devonian, and younger Devonian assemblages. The Silurian assemblage contains typically nonporphyritic high-alumina tholeiitic basalts, basaltic andesites, and diabase of continental characterand calc-alkalic rhyolites, silicic dacites, and one known dike of andesite. These rocks are associated with fossiliferous, predominantly marine strata of the Quoddy, Dennys, and Edmunds Formations, and the Leighton Formation of the Pembroke Group (the stratigraphic rank of both is revised herein for the Machias-Eastport area), all of Silurian age. The shallow marine Hersey Formation (stratigraphic rank also revised herein) of the Pembroke Group, of latest Silurian age (and possibly earliest Devonian, as suggested by an ostracode fauna), contains no known volcanics; and it evidently was deposited during a volcanic hiatus that immediately preceded emergence of the coastal volcanic belt and the eruption of the older Devonian assemblage. The older Devonian assemblage, in the lagoonal to subaerial Lower Devonian Eastport Formation, contains tholeiitic basalts and basaltic andesites, typically with abundant plagioclase phenocrysts and typically richer in iron and

  4. Miocene through Holocene Arc and Post-arc Volcanism in the Northern Sierra Nevada and Western Nevada (United States)

    Cousens, B.; Henry, C. D.; Timmermans, A.; Sylvester, A.; Wise, W.; Prytulak, J.; Stoffers, A. J.; Gupta, V.


    Following the cessation of Mesozoic arc activity in the Sierra Nevada of California, the eastward “leap” of magmatism to the continental interior, and the Tertiary sweep of volcanic activity across the Great Basin, arc volcanism was re-established in the Sierra Nevada of eastern California/western Nevada during early Miocene time. Ranging from 20 to 3 Ma in age, highly eroded remnants of arc volcanic edifices consist of mono- to heterolithic volcaniclastic rocks and lava flows, as well as less common isolated mafic vents. The rocks are dominantly porphyritic andesite and basaltic andesite, non-porphyritic basalt, and less common dacite and rhyolite. In the Lake Tahoe-Reno region, arc lavas are enriched in the LIL and LREE, especially Ba, and have high 87Sr/86Sr and low 143Nd/144Nd compared to modern south Cascade lavas, consistent with an old, metasomatized mantle source. Around 3 Ma, the southern edge of the Juan de Fuca plate passed north through the Tahoe-Reno region, exposing the region to a slab window. Volcanism in the Lake Tahoe-Truckee area continued between 2.6 and 1.2 Ma, but with a different style and somewhat different chemistry. Small-volume mafic flows were emplaced on the northwest shore of Lake Tahoe, along the Truckee River north to Donner Pass and then east to the northern Carson Range. The lavas are primarily non-porphyritic alkalic basalt, basaltic trachyandesite and trachyandesite, with a single complex of subalkaline andesite to dacite, and generally have higher REE concentrations but smaller negative Nb anomalies than the earlier arc lavas. Isotopically, these post-arc lavas have a more restricted range of Sr and Nd ratios that fall within the range of the earlier arc lavas. Thus, post-arc lavas present no evidence of having tapped a dramatically different mantle source. Lastly, several latest Pliocene to Holocene volcanic centers lie in a northeast-trending corridor from Carson City to Battle Mountain, NV, including the Steamboat Hills

  5. Phanerozoic Rifting Phases And Mineral Deposits (United States)

    Hassaan, Mahmoud


    In North Africa occur Mediterranean and Red Sea metallogenic provinces. In each province distribute 47 iron- manganese- barite and lead-zinc deposits with tectonic-structural control. The author presents in this paper aspects of position of these deposits in the two provinces with Phanerozoic rifting . The Mediterranean Province belongs to two epochs, Hercynian and Alpine. The Hercynian Epoch manganese deposits in only Moroccoa- Algeria belong to Paleozoic tectonic zones and Proterozoic volcanics. The Alpine Epoch iron-manganese deposits are of post-orogenic exhalative-sedimentary origin. Manganese deposits in southern Morocco occur in Kabil-Rief quartz-chalcedony veins controlled by faults in andesitic sheets and in bedded pelitic tuffs, strata-form lenses and ore veins, in Precambrian schist and in Triassic and Cretaceous dolomites. Disseminated manganese with quartz and barite and effusive hydrothermal veins are hosted in Paleocene volcanics. Manganese deposits in Algeria are limited and unrecorded in Tunisia. Strata-form iron deposits in Atlas Heights are widespread in sub-rift zone among Jurassic sediments inter-bedding volcanic rocks. In Algeria, Group Beni-Saf iron deposits are localized along the Mediterranean coast in terrigenous and carbonate rocks of Jurassic, Cretaceous and Eocene age within faults and bedding planes. In Morocco strata-form hydrothermal lead-zinc deposits occur in contact zone of Tertiary andesite inter-bedding Cambrian shale, Lias dolomites and Eocene andesite. In both Algeria and Tunisia metasomatic Pb-Zn veins occur in Campanian - Maastrichtian carbonates, Triassic breccia, Jurassic limestone, Paleocene sandstones and limestone and Neogene conglomerates and sandstones. The Red Sea metallogenic province belongs to the Late Tertiary-Miocene times. In Wadi Araba hydrothermal iron-manganese deposits occur in Cretaceous sediments within 320°and 310 NW faults related to Tertiary basalt. Um-Bogma iron-manganese deposits are closely

  6. Compositional dependence of sulfur speciation in Terrestrial and Martian magmas (United States)

    Nash, William; Wood, Bernard; Smythe, Duane


    The capacity of magmas to transport sulfur from mantle to crust strongly influences a planet's surface chemistry. Sulfur is perhaps exceptional among the elements in the diversity of it's chemical speciation, exhibiting four redox species at geologically relevant conditions: sulfide (2-), elemental sulfur (0), sulfite (4+) and sulphate (6+). Furthermore, the solubility of sulfur in a magma (and hence the magma's capacity for delivering mantle-derived sulfur to the crust) depends critically on it's oxidation state. Our aim with this experimental study was to quantitatively determine the chemical speciation of sulfur within several common magmas, as a function of oxygen fugacity (fO2). We have performed a series of experiments on six sulfur-bearing silicate melts, which together represent a broad range of naturally occurring compositions: two putative Martian basalts, two terrestrial MORBs (one primitive, one evolved), an andesite, and a dacite. These melts were equilibrated together (at one-atmosphere pressure, 1300°C) with various CO-CO2-SO2 gas mixtures, which imposed a range of fO2s. This range spanned -2 to +1.6 log units (relative to the Quartz-Fayalite-Magnetite or QFM buffer), and the step-size was 0.25 log units. The quenched glasses were analyzed by X-ray Absorption Spectroscopy (specifically XANES) at the Diamond synchrotron (UK), and the spectra obtained were used to determine the species of sulfur present in each glass. The chemical composition of each glass (including their sulfur contents) was characterized by electron-probe microanalysis. Despite the generally low concentrations of sulfur in our glasses (never exceeding 0.24 wt%), we have clearly resolved the crossover between reduced (S2-) and oxidized (S6+) species for three of our basalts. The other three melts yielded more noisy XANES spectra, and as a result their redox crossovers are visible, but less clearly resolved. For every melt composition, the redox crossover is a continuous (though

  7. Investigation on type and origin of iron mineralization at Mesgar occurrence, south of Zanjan, using petrological, mineralogical and geochemical data

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    Mohammad Ebrahimi


    Full Text Available Introduction Mesgar iron occurrence is located in northwestern part of the Central Iran, 115 km south of Zanjan. Although there is a sequence of volcanic-pyroclastic rocks accompanied by iron mineralization, no detailed works had been conducted in the area. The present paper provides an overview of the geological framework, the mineralization characteristics, and the results of geochemical study of the Mesgar iron occurrence with an application to the ore genesis. Identification of these characteristics can be used as a model for exploration of this type of iron mineralization in the Central Iran and elsewhere. Materials and methods Detailed field work has been carried out at different scales in the Mesgar area. About 16 polished thin and thin sections from host rocks and mineralized and altered zones were studied by conventional petrographic and mineralogic methods at the Department of Geology, University of Zanjan. In addition, a total of 3 samples from least-altered volcanic host rocks and 2 samples from ore zones from the Mesgar occurrence were analyzed by ICP-MS and ICP-OES for whole-rock major and trace elements and REE compositions at the Zarazma Laboratories, Tehran, Iran. Results and Discussion Based on field observation, rock units exposed in the Mesgar area consist of Miocene sedimentary rocks and volcanic-pyroclastic units (Rādfar et al., 2005. The pyroclastic units consist of volcanic breccia and agglomerate. They lie concordantly on the Miocene sedimentary units, and are in turn concordantly overlain by andesitic basalt lavas. The lavas show porphyritic texture consisting of plagioclase (up to 3 mm in size and pyroxene phenocrysts set in a fine-grained to glassy groundmass. Seriate, cumulophyric, glomeroporphyritic and trachytic textures are also observed. Iron mineralization occurs as vein and lens-shaped bodies within and along the contacts of pyroclastic (footwall and andesitic basalt lavas (hanging wall. The veins reach up to

  8. Stratigraphy, geochemistry and tectonic significance of the Oligocene magmatic rocks of western Oaxaca, southern Mexico (United States)

    Martiny, Barbara; Martínez-Serrano, Raymundo G.; Morán-Zenteno, Dante J.; Macías-Romo, Consuelo; Ayuso, Robert A.


    In western Oaxaca, Tertiary magmatic activity is represented by extensive plutons along the continental margin and volcanic sequences in the inland region. K-Ar age determinations reported previously and in the present work indicate that these rocks correspond to a relatively broad arc in this region that was active mainly during the Oligocene (˜35 to ˜25 Ma). In the northern sector of western Oaxaca (Huajuapan-Monte Verde-Yanhuitlán), the volcanic suite comprises principally basaltic andesite to andesitic lavas, overlying minor silicic to intermediate volcaniclastic rocks (epiclastic deposits, ash fall tuffs, ignimbrites) that were deposited in a lacustrine-fluvial environment. The southern sector of the volcanic zone includes the Tlaxiaco-Laguna de Guadalupe region and consists of intermediate to silicic pyroclastic and epiclastic deposits, with silicic ash fall tuffs and ignimbrites. In both sectors, numerous andesitic to dacitic hypabyssal intrusions (stocks and dikes) are emplaced at different levels of the sequence. The granitoids of the coastal plutonic belt are generally more differentiated than the volcanic rocks that predominate in the northern sector and vary in composition from granite to granodiorite. The studied rocks show large-ion lithophile element (LILE) enrichment (K, Rb, Ba, Th) relative to high-field-strength (HFS) elements (Nb, Ti, Zr) that is characteristic of subduction-related magmatic rocks. On chondrite-normalized rare earth element diagrams, these samples display light rare earth element enrichment (LREE) and a flat pattern for the heavy rare earth elements (HREE). In spite of the contrasting degree of differentiation between the coastal plutons and inland volcanic rocks, there is a relatively small variation in the isotopic composition of these two suites. Initial 87Sr/ 86Sr ratios obtained and reported previously for Tertiary plutonic rocks of western Oaxaca range from 0.7042 to 0.7054 and ɛNd values, from -3.0 to +2.4, and for the

  9. Metallogeny of the Gold Quadrilateral: style and characteristics of epithermal - subvolcanic mineralized structures, South Apuseni Mts., Romania

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    S̡erban-Nicolae Vlad


    Full Text Available The Romanian territory contains numerous ore deposits mined since pre-Roman times. An assessment of historical gold production of the Gold Quadri-lateral (GQ yielded a total estimate of 55.7 Moz of gold throughout an area of 2400 km2. Interpreted in terms of mineralization density this is 23,208 oz of gold/ km2. The geological setting of the GQ is represented mainly by Tertiary (14.7 My to 7.4 My calc-alkaline volcano-plutonic complexes of intermediate character in sedimentary basins of molasse type. These basins are tectonically controlled by NW-SE lineation across early Alpine magmatic products, i.e. subduction related Jurassic-Lower Cretaceous igneous association (island arc ophiolites and granitoids and Upper Cretaceous igneous association (banatites. The Tertiary magmatism is associated with extensional tectonics caused by NE escape of the Pannonian region during Upper Oligocene-Lower Miocene times. As a result of tectono-magmatic and mineralization-alteration characteristics, two metallogenetical types were separated in the GQ, i.e. calc-alkaline andesitic (CAM and sub-alkaline rhyodacitic (SRM. Both develop almost entirely low-sulfidation type of Au epithermal mineralization. However, two subtypes, -rich in sulfide (2-7% and -poor in sulfide (7-20% were delineated and correlated with CAM type and SRM type respectively. Furthermore, CAM is connected at deeper levels with Cu-Au+/-Mo porphyry systems in contrast with SRM, which is a non-porphyry environment. The Brad-Săcărâmb district contains mainly CAM type andesitic structures. It is a porphyry environment with epithermal low-sulfidation-rich sulfide vein halo (Barza, Troiţa-Bolcana deposits. However, a few SRM type patterns, such as Măgura Ţebii, Băiţa-Crăciuneşti and Săcărâmb, deposits exhibit Au-Ag-Te low-sulfidation-poor sulfide epithermal vein halo. The Zlatna-Stănija district exhibits similar characteristics, with Au-Ag+/-Pb, Zn veins in Cu-Au subvolcanic

  10. Intermediate sulfidation epithermal mineralization of No. 4 anomaly of Golojeh deposit (N. Zanjan based on mineralography, alteration and ore fluid geochemistry features

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    Behzad Mehrab


    Full Text Available The base (Cu–Pb–Zn and precious metals (Ag±Au mineralization at the No. 4 anomaly of Golojeh deposit occurred in volcanic and sub–volcanic Eocene–Oligocene host rocks, in the central part of the Tarom–Hashtjin zone. Basic to intermediate volcanic, volcaniclastic and sub–volcanic rocks are dominated in the area and include andesite, basaltic andesite, trachy-andesite, dacite and tuff with affinity to sub–alkaline to high–potassic calc–alkaline series. The mineralization in the area with average grade of Au (0.15 ppm, Ag (0.24%, Cu (0.6%, Zn (4% and Pb (6% occurred in two major NW–SE trending quartz–sulfide veins (A and B with crustiform, breccia, vein–veinlet and open-space filling structure and texture. The sulfide content varies from 5 to 60% and is dominated by galena, sphalerite, chalcopyrite and pyrite. SEM studies indicated presence of Ag (0.47 to 0.66 wt.% and Cd (0.33 to 0.72 wt.% in galena and Fe (0.23 wt.% in sphalerite. Hydrothermal alteration of phyllic (quartz–sericite–pyrite, argillic (quartz–illite/muscovite and silicification are related to mineralization. Correlation coefficient of metal pairs of Cd–Zn (0.86, Cd–Pb (0.82, Pb–Ag (0.80, Au–Ag (0.75, Pb–Zn (0.70 and Cd–Bi (0.74 was recorded in the quartz–sulfide ore–bearing veins. Microthermometric studies on two phases liquid–vapor fluid inclusions in ore–bearing veins, shows homogenization temperature to liquid (Thlv→l in the range of 223 to 287°C and salinity of 6.5 to 17 wt.% NaCl eq. (quartz-hosted and homogenization temperature ranging from 175 to 244°C and salinity from 1.5 to 12 wt.% NaCl eq. (sphaerite-hosted. First ice–melting temperature (Tmf ranges of fluid inclusion in sphalerite-hosted of quartz–sulfide ore–bearing veins were recorded between −23 and −18°C in NaCl–H2O system. Vein–breccia and crustified structure and texture, presence of illite/muscovite alteration assemblage accompanied by high

  11. Pickling Peridotites in the IBM Mantle Wedge: Inferences from the Guguan Cross-Chain, Mariana Arc (United States)

    Stern, R. J.; Bloomer, S. H.; Leybourne, M.; Miller, N. R.; Hargrove, U. S.; Griffin, W. R.; Fouch, M.; Kohut, E.; Vervoort, J.; Prytulak, J.


    Variations in lava compositions observed in arc `cross-chains' reveal chemical and isotopic gradients resulting from 'pickling' of convecting asthenosphere by fluids and melts from the descending slab. This can be studied using lavas from arc cross-chains. We report geochemical and isotopic data for basalts and basaltic andesites from the Guguan cross-chain at 17° 15'N in the Mariana Arc, comprising the active volcanic island Guguan (and submarine cone N. Guguan) along the magmatic front (~125 km above the subducted slab) and two seamounts to the west, W. Guguan (~150km) and Guguan II (~230 km). Guguan lavas represent the `fluid-dominated' endmember of Mariana arc lavas, and comprise fractionated basalts, basaltic andesites, and subordinate andesites (Mg# = 35-51, Ni<30ppm). Lavas from N. Guguan seamount consists of less fractionated basalts (Mg# = 52, ~50ppm Ni). Basalts from W. Guguan (Mg# = 61, 60-80 ppm Ni) and Guguan II (Mg#= 63-75, 100-400 ppm Ni) are much less fractionated. Guguan, N. Guguan, and W. Guguan lavas straddle the Low- to Medium-K boundary on a K2O-SiO2 plot, whereas Guguan II lavas are slightly more enriched and plot in the Medium-K field. Strong enrichments in K and other LIL elements observed for the Kasuga cross-chain farther north in the Mariana arc are absent. Olivine Fo decreases and plagioclase An increases towards the magmatic front. These relations suggest that water contents increase towards the magmatic front in the Guguan cross-chain. Spider diagrams for Guguan cross-chain lavas show the characteristic elemental enrichments of arc lavas, most notably LIL elements (Rb, Ba, Th, U, K, Pb, and Sr); similar but muted enrichments are found in basalts formed by seafloor spreading in the Mariana Trough (MTSB). Trace element variations observed across the Guguan cross-chain indicate that the fluid-dominated `Subduction Component' diminishes away from the magmatic front and is replaced by a component that manifests either sediment melt or the

  12. Oxygen isotope geochemistry of the lassen volcanic center, California: Resolving crustal and mantle contributions to continental Arc magmatism (United States)

    Feeley, T.C.; Clynne, M.A.; Winer, G.S.; Grice, W.C.


    This study reports oxygen isotope ratios determined by laser fluorination of mineral separates (mainly plagioclase) from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the Lassen Volcanic Center (LVC), northern California. Plagioclase separates from nearly all rocks have ??18O values (6.1-8.4%) higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back-arc regions of the southernmost Cascades during the late Cenozoic. Most LVC magmas must therefore contain high 18O crustal material. In this regard, the ??18O values of the volcanic rocks show strong spatial patterns, particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust. Rhyodacitic magmas erupted from vents located within 3.5 km of the inferred center of the LVC have consistently lower ??18 O values (average 6.3% ?? 0.1%) at given SiO2 contents relative to rocks erupted from distal vents (>7.0 km; average 7.1% ?? 0.1%). Further, magmas erupted from vents situated at transitional distances have intermediate values and span a larger range (average 6.8% ?? 0.2%). Basaltic andesitic to andesitic composition rocks show similar spatial variations, although as a group the ??18O values of these rocks are more variable and extend to higher values than the rhyodacitic rocks. These features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas, followed by mixing or mingling with silicic magmas formed by partial melting of initially high 18O continental crust (??? 9.0%) increasingly hybridized by lower ??18O (???6.0%) mantle-derived basaltic magmas toward the center of the system. Mixing calculations using estimated endmember source ??18O values imply that LVC magmas contain on a molar oxygen basis approximately 42 to 4% isotopically heavy continental crust, with proportions declining in a broadly regular fashion toward the

  13. Structural observations from the Canavese Fault west of Valle d'Ossola (Piemonte) and some time constraints (United States)

    Pleuger, Jan; Mancktelow, Neil


    The Canavese Fault (CF) is the SW part of the most important fault system in the Alps, the Periadriatic Fault. The CF has a complex kinematic history involving an older stage of NW-side-up faulting and a younger stage of SE-side-up plus dextral faulting in the area of Valle d'Ossola (Schmid et al. 1987). There, shearing occurred under greenschist-facies conditions and the fault is a c. 1 km thick mylonite zone. Toward SW, faulting took place under progressively lower temperatures and the volume of rocks affected by S-side-up plus dextral shearing becomes larger at the expense of the N-side-up mylonites. S of Valle Sesia, brittle fault rocks dominate over mylonites. Still further SW, close to the Serra d'Ivrea, the CF splits into two branches, the Internal Canavese Fault (ICF) and the External Canavese Fault (ECF). S-side-up plus dextral faulting is localised along the ICF while the observed displacement senses at the ECF are mostly, though not always, N-side-up and sinistral. Age constraints for faulting along the CF are mostly derived from absolute ages of magmatic rocks exposed alongside or within the fault. In the section around Biella, NW-side-up faulting cannot have lasted longer than until 31±2 Ma (Scheuring et al. 1974) because this is the age of andesites overlying the basement of the Penninic Sesia Zone. However, some additional uplift of the Sesia Zone with respect to the South Alpine Ivrea Zone was accommodated by down-to-the-SE tilting of the Sesia zone around a roughly NNE-SSW-trending subhorizontal axis which is evidenced by palaeomagnetic data (Lanza 1977). As a result of that, the Early Oligocene Biella Pluton (c. 31 Ma, Romer et al. 1996) today occupies a similar altitude level as the andesites of the same age. Post-31-Ma uplift of the Ivrea Zone with respect to the andesites is evidenced by the Early Oligocene (29-33 Ma, Carraro & Ferrara 1968) Miagliano Pluton which is hosted by the Ivrea Zone rocks and exposed at the present topographic surface

  14. Viscous flow behavior of tholeiitic and alkaline Fe-rich martian basalts (United States)

    Chevrel, Magdalena Oryaëlle; Baratoux, David; Hess, Kai-Uwe; Dingwell, Donald B.


    may explain the lower range of viscosities (102-104 Pa s) inferred from lava flow morphology. Further, the differences between the rheological behaviors of tholeiitic vs. trachy-basalts are significant enough to affect their emplacement as intrusive bodies or as effusive lava flows. The upper range of viscosities (106-108 Pa s) suggested from lava flow morphology is found consistent with the occurrence of alkali basalt documented from in situ analyses and does not necessarily imply the occurrence of basaltic-andesite or andesitic rocks.

  15. Origin and accumulation mechanisms of petroleum in the Carboniferous volcanic rocks of the Kebai Fault zone, Western Junggar Basin, China (United States)

    Chen, Zhonghong; Zha, Ming; Liu, Keyu; Zhang, Yueqian; Yang, Disheng; Tang, Yong; Wu, Kongyou; Chen, Yong


    The Kebai Fault zone of the West Junggar Basin in northwestern China is a unique region to gain insights on the formation of large-scale petroleum reservoirs in volcanic rocks of the western Central Asian Orogenic Belt. Carboniferous volcanic rocks are widespread in the Kebai Fault zone and consist of basalt, basaltic andesite, andesite, tuff, volcanic breccia, sandy conglomerate and metamorphic rocks. The volcanic oil reservoirs are characterized by multiple sources and multi-stage charge and filling history, characteristic of a complex petroleum system. Geochemical analysis of the reservoir oil, hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source, the petroleum filling history, and the dominant mechanisms controlling the petroleum accumulation. Reservoir oil geochemistry indicates that the oil contained in the Carboniferous volcanic rocks of the Kebai Fault zone is a mixture. The oil is primarily derived from the source rock of the Permian Fengcheng Formation (P1f), and secondarily from the Permian Lower Wuerhe Formation (P2w). Compared with the P2w source rock, P1f exhibits lower values of C19 TT/C23 TT, C19+20TT/ΣTT, Ts/(Ts + Tm) and ααα-20R sterane C27/C28 ratios but higher values of TT C23/C21, HHI, gammacerane/αβ C30 hopane, hopane (20S) C34/C33, C29ββ/(ββ + αα), and C29 20S/(20S + 20R) ratios. Three major stages of oil charge occurred in the Carboniferous, in the Middle Triassic, Late Triassic to Early Jurassic, and in the Middle Jurassic to Late Jurassic periods, respectively. Most of the oil charged during the first stage was lost, while moderately and highly mature oils were generated and accumulated during the second and third stages. Oil migration and accumulation in the large-scale stratigraphic reservoir was primarily controlled by the top Carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity. Secondary dissolution

  16. Petrogenesis of the flood basalts from the Early Permian Panjal Traps, Kashmir, India: Geochemical evidence for shallow melting of the mantle (United States)

    Shellnutt, J. Gregory; Bhat, Ghulam M.; Wang, Kuo-Lung; Brookfield, Michael E.; Jahn, Bor-Ming; Dostal, Jaroslav


    The Early Permian Panjal Traps of northern India represent a significant eruption of volcanic rocks which occurred during the opening of the Neotethys Ocean. Basaltic, basaltic-andesites, dacitic and rhyolitic rocks collected from Guryal Ravine and Pahalgam show evidence for subaerial and subaqueous eruptions indicating that they are contemporaneous with the formation of a shallow marine basin. The major and trace element geochemistry of the basalts is consistent with a within-plate setting and there are basalts which have high-Ti (TiO2 > 2.0 wt.%) and low-Ti (TiO2 < 1.8 wt.%) compositions. The ‘high-Ti’ basalts are similar to OIB whereas the ‘low-Ti’ basalts are similar to continental tholeiites. The identification of ‘high- and low-Ti’ basalts within the Panjal Traps is analogous to other large igneous provinces (e.g. Karoo, Deccan, Parana, Emeishan). The Sr-Nd isotopic values (εNd(T) = - 5.3 to + 1.3; ISr = 0.70432 to 0.71168) of both types of basalts overlap indicating that the rocks may have originated from the same ancient subcontinental lithospheric (i.e. EMII-like) mantle source (TDM = ~ 2000 Ma). The two groups of basalts can be modeled by using a primitive mantle source and different degrees of partial melting where the high-Ti rocks are produced by ~ 1% partial melting of a spinel peridotite source whereas the low-Ti rocks are produced by ~ 8% partial melting. Trace elemental and isotope modeling indicates that some of the basalts assimilated ≤ 10% crustal material. In contrast, the basaltic-andesites are likely formed by mixing between basaltic magmas and crustal melts which produced rocks with higher SiO2 (~ 55 wt.%) content and enriched isotopic signatures (εNd(T) = - 6.1; ISr = 0.70992). The Panjal Trap volcanism was likely due to partial melting of the SCLM within a passive extensional setting related to the rifting of Cimmeria from Gondwana. Contemporaneous volcanic and plutonic granitic rocks throughout the Himalaya are probably

  17. Geochemistry and Sr, Nd isotopic composition of the Hronic Upper Paleozoic basic rocks (Western Carpathians, Slovakia

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    Vozár Jozef


    Full Text Available The paper presents new major and trace element and first Sr-Nd isotope data from selected lavas among the Permian basaltic andesite and basalts of the Hronicum Unit and the dolerite dykes cutting mainly the Pennsylvanian strata. The basic rocks are characterized by small to moderate mg# numbers (30 to 54 and high SiO2 contents (51-57 wt. %. Low values of TiO2 (1.07-1.76 wt. % span the low-Ti basalts. Ti/Y ratios in the dolerite dykes as well as the basaltic andesite and basalt of the 1st eruption phase are close to the recommended boundary 500 between high-Ti and low-Ti basalts. Ti/Y value from the 2nd eruption phase basalt is higher and inclined to the high-Ti basalts. In spite of this fact, in all studied Hronicum basic rocks Fe2O3* is lower than 12 wt. % and Nb/La ratios (0.3-0.6 are low, which is more characteristic of low-Ti basalts. The basic rocks are characterized by Nb/La ratios (0.56 to 0.33, and negative correlations between Nb/La and SiO2, which point to crustal assimilation and fraction crystallization. The intercept for Sr evolution lines of the 1st intrusive phase basalt is closest to the expected extrusions age (about 290 Ma with an initial 87Sr/86Sr ratio of about 0.7054. Small differences in calculated values ISr document a partial Sr isotopic heterogeneity source (0.70435-0.70566, or possible contamination of the original magma by crustal material. For Nd analyses of the three samples, the calculated values εCHUR (285 Ma are positive (from 1.75 to 3.97 for all samples with only subtle variation. Chemical and isotopic data permit us to assume that the parental magma for the Hronicum basic rocks was generated from an enriched heterogeneous source in the subcontinental lithospheric mantle.

  18. Geology of El Chichon volcano, Chiapas, Mexico (United States)

    Duffield, Wendell A.; Tilling, Robert I.; Canul, Rene


    The (pre-1982) 850-m-high andesitic stratovolcano El Chichón, active during Pleistocene and Holocene time, is located in rugged, densely forested terrain in northcentral Chiapas, México. The nearest neighboring Holocene volcanoes are 275 km and 200 km to the southeast and northwest, respectively. El Chichón is built on Tertiary siltstone and sandstone, underlain by Cretaceous dolomitic limestone; a 4-km-deep bore hole near the east base of the volcano penetrated this limestone and continued 770 m into a sequence of Jurassic or Cretaceous evaporitic anhydrite and halite. The basement rocks are folded into generally northwest-trending anticlines and synclines. El Chichón is built over a small dome-like structure superposed on a syncline, and this structure may reflect cumulative deformation related to growth of a crustal magma reservoir beneath the volcano. The cone of El Chichón consists almost entirely of pyroclastic rocks. The pre-1982 cone is marked by a 1200-m-diameter (explosion?) crater on the southwest flank and a 1600-m-diameter crater apparently of similar origin at the summit, a lava dome partly fills each crater. The timing of cone and dome growth is poorly known. Field evidence indicates that the flank dome is older than the summit dome, and K-Ar ages from samples high on the cone suggest that the flank dome is older than about 276,000 years. At least three pyroclastic eruptions have occurred during the past 1250 radiocarbon years. Nearly all of the pyroclastic and dome rocks are moderately to highly porphyritic andesite, with plagioclase, hornblende and clinopyroxene the most common phenocrysts. Geologists who mapped El Chichón in 1980 and 1981 warned that the volcano posed a substantial hazard to the surrounding region. This warning was proven to be prophetic by violent eruptions that occurred in March and April of 1982. These eruptions blasted away nearly all of the summit dome, blanketed the surrounding region with tephra, and sent pyroclastic

  19. Re-awakening of a Volcano: The 3. November 2002 eruption of El Reventador, NE Ecuador (United States)

    Reischmann, T.; Toulkeridis, T.; Aguillera, E.


    At 3 Nov 2002, 7.15 after a repose of 26 years "El Reventador" exploded unexpectedly forming a vulcanian type eruption with a volcanic explosivity index (VEI) of 4. Ecuador's easternmost and second most active continental volcano covered with a few million tons of ash a huge area of Ecuador, parts of Colombia, Peru and Brazil reaching even the islands of Galapagos. Reventador belongs to the few stratovolcanoes on the western edge of the Amazonian platform well east of the principal volcanic axis of the North Andean Volcanic Zone. The ca. 20.000 year old andesitic steep-sloping cone of the active volcano Reventador III is situated within the western end of an older steep-walled horse-shoe shaped caldera, which is open to the ESE. This caldera was formed by the previous volcanoes Reventador I and II, which reached an estimated height of ca. 600 m high above the actual edifice before their activities terminated in a sector collapse and lateral blast to the ESE. Lavas, pyroclastic flows, debris flows and lahars of Reventador III then filled the ca. 4 km wide caldera. In the morning of 3 Nov, unpredicted and within seconds, the volcano's WNW flank slided away in a large landslide against the western caldera wall, triggering a destructive, lateral blast of hot gas, steam, ash and rock debris that swept across the landscape. More than a third of the actual cone disappeared in Ecuador's biggest explosion of the last 120 years. Ongoing decompression of the magma caused the continuing eruption and the formation of an eruption column reaching 16 km height. A few hours later another ca. 12 km high eruption followed. Further minor eruptions generated lavas and pyroclasitic flows until the end of November while the emission of ash and gases (mainly H_2O and SO_2) continued until January. The porphyric volcanic rocks contain plag (An 40--70%), cpx, opx, occasionally amphibole and Fe-Ti oxides. Ash and rock fragments of the pyroclasitic flows have almost identical andesitic

  20. The bimodal pH distribution of volcanic lake waters (United States)

    Marini, Luigi; Vetuschi Zuccolini, Marino; Saldi, Giuseppe


    Volcanic lake waters have a bimodal pH distribution with an acidic mode at pH 0.5-1.5 and a near neutral mode at pH 6-6.5, with relatively few samples having pH 3.5-5. To investigate the reasons for this distribution, the irreversible water-rock mass exchanges during the neutralization of acid SO 4-Cl waters with andesite, under both low- and high-temperature conditions, were simulated by means of the EQ3/6 software package, version 7.2. Reaction path modeling under low temperature and atmospheric P CO 2 and f O 2, suggests that several homogeneous and/or heterogeneous pH buffers exist both in the acidic and neutral regions, but no buffer is active in the intermediate, central pH region. Again, the same titration, under high-temperature, hydrothermal-magmatic conditions, is expected to produce comparatively infrequent aqueous solutions with pH values in the 3.5-5 range, upon their cooling below 100°C. Substantially different pH values are obtained depending on the cooling paths, either through boiling or conductive heat losses. These distinct pH values are governed by either HSO 4- and HCl (aq), in poorly neutralized aqueous solutions, or the CO 2(aq)/HCO 3- couple and the P CO 2 value as well, in neutralized aqueous solutions. Finally, mixing of the acid lake water with the aqueous solutions produced through high-temperature titration and cooled below 100°C is unlikely to generate mixtures with pH values higher than 3, unless the fraction of the acidic water originally present in the lake becomes very small, which means its virtually complete substitution. Summing up, the evidence gathered through reaction path modeling of the neutralization of acid lake waters with andesite, both at low and high temperatures, explains the scarcity of volcanic lake waters with measured pH values of 3.5-5.

  1. The Punta del Cobre Formation, Punta del Cobre Candelaria area, northern Chile (United States)

    Marschik, Robert; Fontboté, Lluís.


    The Punta del Cobre Formation hosts the iron oxide-rich Cu-Au(-Zn-Ag) deposits of the Punta del Cobre belt, Chile. Hydrothermal alteration associated with mineralization and/or contact metamorphism caused by the Coastal Batholith exposed in the west resulted in new mineral assemblages and significant changes in the geochemical composition of its rocks. This paper presents a redefinition of the Punta del Cobre Formation and discusses its geologic context. The Punta del Cobre Formation is subdivided, from bottom to top, into: (1) the 'Geraldo-Negro Member', composed mainly of massive andesitic volcanic rocks (>300 m) and locally dacitic rocks (up to 200 m) that overlie the latter, and (2) the 'Algarrobos Member' (up to >800 m) comprising mainly volcaniclastic rocks, basalt andesitic and basaltic flows, and volcanic breccias. The Punta del Cobre Formation is overlain by the Chañarcillo Group, the lowest part of which is represented by alternating carbonate and volcaniclastic beds of the Abundancia Formation, which pass vertically and laterally into limestones of the Nantoco Formation. The contact between the Punta del Cobre Formation and the overlying Abundancia Formation is transitional and defined by the first continuous bed of massive limestone or its metamorphosed equivalent. A pre-upper Valanginian age for the Punta del Cobre Formation is suggested by ammonites of Berriasian age found in the upper part of the Algarrobos Member and Late Valanginian-Early Hauterivian fauna in the overlying Abundancia Formation. Despite the intense alteration, immobile element compositions of the volcanic rocks of the Punta del Cobre Formation enable the recognition of a calc-alkaline suite with a trend to more primitive, less differentiated magmas towards the top of the stratigraphic sequence, reflecting initial stages of basin development. The transgressive nature of the sedimentary part of the Punta del Cobre Formation marks the onset of increased subsidence that eventually

  2. Geochemistry characteristics of Seamounts in the Tonga arc : Influence of subduction component (United States)

    Myeong, B.; Kim, J. H.; Woo, H.; Jang, Y. D.


    Located in the southwest Pacific ocean, The seamounts, from TA07 seamount to TA26, in the Tonga arc are located from 20 °S to 25 °S. At 25 °S, the Tonga trench is intersected by the Louisville ridge, a ~4,300-km-long chain of seamounts and the Osbourn trough, a paleo-spreading center. For this reason, magma which created these seamounts may have various origin. Based on this, the seamounts which forming the Tonga arc are divided into three groups; including group 1(region that the earliest Louisville ridge subduction arised, correspond to TA07-12), group 2(region that the second Louisville ridge subduction arised, correspond to TA14-24); and group 3(region that the Louisville ridge and the Osbourn trough are subducting, correspond to TA25-26). These seamounts are mostly stratovolcanoes with caldera. Rocks recovered by dredging have been identified as pumice, dacite, andesite, basaltic andesites and basalts(most abundant). Major element concentrations are constant, trace element concentrations are enriched LILE, depleted HFSE compared with MORB. The Tonga arc is affected by subduction components divided into the shallow and deep subduction components. Related to subduction components, variables include mantle source, AOC(altered oceanic crust), PS(pelagic sediment), LSC(Louisville seamount chain) and OS(Osbourn trough). In the case of shallow subduction component, it tends to have higher contents in group 1, 3 and lower contents in group 2. Thus, comparatively speaking, it seems that group 1, 3 have been heavily influenced by the fluid. However, origin of the fluid seems to be different, since its locations are not continuous. In the case of deep subduction component, it shows similar range in the group 1, 2, and shows a significantly lower ratio in the group 3. The reason why its values are similar is that it is effected by the melt during the Louisville ridge was subducting and the reason why the ratio in the group 3 shown lower is because of the fluid effect

  3. Re-Os dating on pyrite and metal sources tracing in porphyry-type and neutral epithermal deposits: example of the Bolcana, Troita and Magura deposits, Apuseni Mountains, Romania

    International Nuclear Information System (INIS)

    Many porphyry-type (Cu-Au) and neutral epithermal (Pb-Zn and Au ± Ag) ore deposits are encountered in the region of the Apuseni Mountains, located at the foot of the Carpathian chain in the Western Romania. These deposits are related to a Neogene andesitic volcanism. In order to demonstrate possible genetic relationships between the porphyry-type and neutral epithermal deposits, the Bolcana porphyry has been investigated since it is surrounded by a number of epithermal low-sulfidation veins with a Pb-Zn ± Au mineralisation. These veins are currently mined at the Troita and Magura sites. A structural analysis and a 3D modelling pf these deposits indicate that the geometry and orientation of fractures and mineralized vein are consistent both with direction of regional extension and with a NW-SE progression of the different andesitic intrusions. In order to establish precisely the temporal relationship between the different ore deposits, a Re-Os dating method has been developed and applied on pyrite which is ubiquitous in all of the deposits. This method enabled us to assign an age of 10.9 ± 1.9 Ma for the porphyry-hosted mineralization. The ages obtained for the epithermal systems are somewhat approximative as perturbations of the Re-Os system are observed for these environments. A fractionation of rhenium responsible for a significant enrichment in this element for the apical zone of the porphyry has been demonstrated. This enrichment is most probably related to a maximum boiling event, which may also explain a similar enrichment in arsenic for the pyrite in the same zone. The sources for the metals have been characterized at the district scale by combining two isotopic systems (Re-Os and Pb-Pb) on both pyrite and galena. The osmium data indicate that the Troita deposit has composition which is similar to that of the Bolcana porphyry. In contrast the results obtained for the Magura deposits indicate the Re-OS system has in this case been perturbed due to a

  4. The eruptive chronology of the Ampato-Sabancaya volcanic complex (Southern Peru) (United States)

    Samaniego, Pablo; Rivera, Marco; Mariño, Jersy; Guillou, Hervé; Liorzou, Céline; Zerathe, Swann; Delgado, Rosmery; Valderrama, Patricio; Scao, Vincent


    We have reconstructed the eruptive chronology of the Ampato-Sabancaya volcanic complex (Southern Peru) on the basis of extensive fieldwork, and a large dataset of geochronological (40K-40Ar, 14C and 3He) and geochemical (major and trace element) data. This volcanic complex is composed of two successive edifices that have experienced discontinuous volcanic activity from Middle Pleistocene to Holocene times. The Ampato compound volcano consists of a basal edifice constructed over at least two cone-building stages dated at 450-400 ka and 230-200 ka. After a period of quiescence, the Ampato Upper edifice was constructed firstly during an effusive stage (80-70 ka), and then by the formation of three successive peaks: the Northern, Southern (40-20 ka) and Central cones (20-10 ka). The Southern peak, which is the biggest, experienced large explosive phases, resulting in deposits such as the Corinta plinian fallout. During the Holocene, eruptive activity migrated to the NE and constructed the mostly effusive Sabancaya edifice. This cone comprised many andesitic and dacitic blocky lava flows and a young terminal cone, mostly composed of pyroclastic material. Most samples from the Ampato-Sabancaya define a broad high-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagioclase, amphibole, biotite, ortho- and clino-pyroxene, and Fe-Ti oxides. A secondary trend also exists, corresponding to rare dacitic explosive eruptions (i.e. Corinta fallout and flow deposits). Both magmatic trends are derived by fractional crystallisation involving an amphibole-rich cumulate with variable amounts of upper crustal assimilation. A marked change in the overall eruptive rate has been identified between Ampato (~ 0.1 km3/ka) and Sabancaya (0.6-1.7 km3/ka). This abrupt change demonstrates that eruptive rates have not been homogeneous throughout the volcano's history. Based on tephrochronologic studies, the Late Holocene Sabancaya activity is characterised by strong

  5. High-silica Rocks from Oceans, Arcs and Ophiolites: What Can They Tell Us About Ophiolite Origins? (United States)

    Perfit, M. R.; Lundstrom, C.; Wanless, V. D.


    Although the volumes of high-silica rocks in submarine oceanic and supra-subduction zone environments are not well constrained, their common occurrence, field relations and compositions have led to various hypotheses suggesting that silicic intrusions (plagiogranites) in ophiolites formed by similar processes to high-silica volcanic rocks at mid-ocean ridge (MOR) or island arc environments. Geochemical attributes of andesite-rhyolite suites from MOR (East Pacific Rise, Juan de Fuca Ridge, Galapagos Spreading Center, Pacific-Antarctic Rise) and back-arc basins (Manus Basin, Lau Basin, East Scotia Ridge) show both similarities and differences to plagiogranitic suites (qtz. diorite-tonalite-trondhjemite) from ophiolites (Troodos and Semail). Both suites are commonly attributed to: extreme (>90%) fractional crystallization of basaltic melts; fractional crystallization coupled with assimilation of hydrated oceanic crust (AFC); or partial melting of preexisting crust. Normalized incompatible trace element patterns show either highly elevated, relatively flat patterns with negative Eu and Sr anomalies similar to high silica volcanics or have complimentary patterns with low abundance, more depleted patterns with positive Eu and Sr anomalies. None of the mechanisms, however, provide a consistent explanation for the compositional and isotopic variations that are observed among plagiogranites. In fact, ophiolitic plagiogranites can have at least two petrogenetic signatures - one indicative of a MORB parent and another that has been related to later, off-axis formation associated with supra-subduction zone magmatism. Based on thermal gradient experiments, the systematic changes in Fe and Si stable isotope ratios with differentiation observed in ophiolite and MOR high-silica suites may result from melt-mineral reactions within a temperature gradient near the boundaries of MOR magma lenses. Comparative major element, trace element and isotopic data will be presented from MOR

  6. Petrogenesis of eocene lava flows from the chagai arc, Balochistan, Pakistan and its tectonic implications

    International Nuclear Information System (INIS)

    The Eocene Lava flows occur in the northwestern part of an EW trending subduction related-magmatic belt known as Chagai arc in the Western part of Pakistan. The volcanism in this arc was initiated during the Late Cretaceous, which intermittently continued up to the Quaternary period. In the regional geotectonic context this arc belongs to the Tethyan convergence zone and was believed to have formed due to the northward subduction of Arabian oceanic plate below the southern margin of Afghan micro plate and hence considered as an Andean type arc. Although Bocene volcaniclastic rock occurs throughout the Chagai arc but the lava flows only crop out in a NW-SE elongated (1 km x 6 kIn) area in the northwestern part of the Chagai arc. These lava flows are represented by two discrete cycles of eruptions found towards the top of the lower pyroclastic sequence of Saindak Formation of Ecocene age. The older flow is about 100 m thick and extends for 2 km whereas the younger flow is 700 metre thick and extends for more than 6 km. The lava flows are mainly represented by amigdaloidal basaltic-andesites (55.50- 54.53 wt. % SiO/sub 2/) and andesites (57.40-62.79 wt. % SiO/sub 2/) with minor basalt (51.88 wt. % SiO/sub 2/) and dacite (67.81 wt. % SiO/sub 2/). The main textures exhibited by these flows are hypocrystalline, porphyritic, cummulophyric, vitrophyric and sub pilotaxitic. Large phenocrysts ( < 1 mm - 4mm) of plagioclase (An-38-58) and pyroxene are embedded in a micro to criptocrystalline groundmass having the same minerals with devitrified volcanic glass. The phenocrysts groundmass ratio is 35:65. Apatite, hematite, ilmenite and magnetite are common accessory mineral. Petrochemical studies reveal that these volcanics belong to medium to low K-calc- alkaline series. They have low Mg = (39-50), and higher FeO (total)/MgO (1.81-2.78) ratios, which suggest that parent magma of these rock suites was not directly derived from a partially melted mantle source but fractionated in

  7. Calc-alkaline rear-arc magmatism in the Fuegian Andes: Implications for the mid-cretaceous tectonomagmatic evolution of southernmost South America (United States)

    Guillot, Mauricio González; Escayola, Mónica; Acevedo, Rogelio


    The magmatic arc of the Fuegian Andes is composed mostly of Upper Mesozoic to Cenozoic calc-alkaline plutons and subordinated lavas. To the rear arc, however, isolated mid-Cretaceous monzonitic plutons and small calc-alkaline dykes and sills crop out. This calc-alkaline unit (the Ushuaia Peninsula Andesites, UPA) includes hornblende-rich, porphyritic quartz meladiorites, granodiorites, andesites, dacites and lamprophyres. Radiometric dating and cross-cutting relationships indicate that UPA is younger than the monzonitic suite. The geochemistry of UPA is medium to high K, with high LILE (Ba 500-2000 ppm, Sr 800-1400 ppm), HFSE (Th 7-23 ppm, Nb 7-13 ppm, Ta 0.5-1.1 ppm) and LREE (La 16-51 ppm) contents, along with relatively low HREE (Yb 1.7-1.3 ppm) and Y (9-19 ppm). The similar mineralogy and geochemistry of all UPA rocks suggest they evolved from a common parental magma, by low pressure crystal fractionation, without significant crustal assimilation. A pure Rayleigh fractionation model indicates that 60-65% of crystal fractionation of 60% hornblende + 34% plagioclase + 4% clinopyroxene + 1% Fe-Ti oxide, apatite and sphene (a paragenesis similar of UPA mafic rocks) can explain evolution from lamprophyres to dacites. The UPA has higher LILE, HFSE and LREE, and lower HREE and Y than the calc-alkaline plutons and lavas of the volcanic front. The HREE and Y are lower than in the potassic plutons as well. High concentrations of Th, Nb, Ta, Zr, Hf, LREE and Ce/Pb, and low U/Th, Ba/Th ratios in UPA, even in the least differentiated samples, suggest contributions from subducted sediments to the mantle source. On the other hand, relatively low HREE and Y, high LREE/HREE (La/Yb 11-38) ratios and Nb-Ta contents can be interpreted as mantle metasomatism by partial melts of either subducted garnetiferous oceanic sediment or basalt as well. Additionally, high LILE content in UPA, similar to the potassic plutons, suggests also a mantle wedge previously metasomatized by potassic

  8. Geology, lithogeochemistry and paleotectonic setting of the host sequence to the Kangasjärvi Zn-Cu deposit, central Finland: implications for volcanogenic massive sulphide exploration in the Vihanti-Pyhäsalmi district

    Directory of Open Access Journals (Sweden)

    Michael D. Roberts


    Full Text Available The Kangasjärvi Zn-Cu deposit is a highly deformed and metamorphosed Paleoproterozoic volcanogenic massive sulphide (VMS deposit located in the Vihanti-Pyhäsalmi base metal mining district of central Finland. The host sequence to the deposit, referred to as the Inner Volcanic Sequence (IVS, is comprised of a bimodal suite of metavolcanic rocks and a regionally extensive tonalite-trondhjemite gneiss (sub-volcanic intrusions?. A separate and perhaps younger sequence of mafic volcanic rocks, with irregular intervals of undifferentiated intermediate to felsic schists and metalimestones, referred to as the Outer Volcanic Sequence (OVS, are separated from the IVS sequence by intervals of metagreywacke and U-P-bearing graphitic schists. A stratigraphic scheme for rocks within the IVS is proposed based on outcrop observations, locally preserved volcanic textures, aspects of seafloor-related hydrothermal alteration and lithogeochemistry. In this scheme, rare andesites form the lowermostvolcanic stratigraphy and are overlain by typical island-arc basalts that were erupted in a subaqueous setting. Tonalite-trondhjemite subvolcanic intrusions were locally emplaced within andesites and coeval rhyolites were extruded on the basaltic substrate. The extrusion of rhyolites, including high-silica rhyolites, was coeval with regional-scale, pre-metamorphic seafloor hydrothermal alteration and local sulphide mineralization. Extensively altered rhyolites envelope massive sulphides and are underlain by altered basalts. The latter rocks are now characterized by a variety of low-variance metamorphic mineral assemblages (e.g. orthoamphibole-cordierite rocks and define a domain of intense pre-metamorphic chlorite ± sericite alteration in the stratigraphic footwall of the deposit. The altered nature of these rocks is attributed to reaction with seawater-related hydrothermal fluids within a zone of upflow at or near the seafloor. The fundamental controls on convective

  9. 准噶尔盆地春晖油田石炭系火山岩储层控制因素分析%Controlling factors of the Carboniferous volcanic reservoirs in the Chunhui Oil Field, Junggar Basin

    Institute of Scientific and Technical Information of China (English)



    春晖油田石炭系火山岩地层中,油气富集程度与储层发育程度呈正相关关系。研究认为,储层的发育与分布主要受岩相、岩性和构造运动的控制。岩相控制岩性,岩性控制储集空间组合类型,溢流相和火山沉积相围绕爆发相具有环带状分布特点,从火山角砾岩→玄武岩、安山岩→凝灰岩,储集性能逐渐变差;构造运动则控制裂缝的发育及溶蚀作用,断层周边微裂缝发育,沿着微裂缝则溶蚀作用增强,次生孔隙发育。%The Chunhui Oil Field in the Junggar Basin lies in the western part of the Halaalate Mountain tectonic zone, in which the Carboniferous volcanic strata consist dominantly of the volcanic rocks such as tuff, andesite, basalt and volcanic breccias. There is a positive correlation between the hydrocarbon enrichment and reservoir development in the Carboniferous volcanic reservoir rocks from the Chunhui Oil Field. The distribution and development of the volcanic reservoir rocks are primarily controlled by lithofacies, lithology and tectonism. On the whole, the lithofacies may exercise a major control on lithology of the volcanic reservoir rocks, which, in turn, may control the reservoir spaces types. The volcanic rocks in the Chunhui Oil Field exhibit a trend of the girdle pattern of lithofacies changes from the explosive facies through the effusive facies to the volcano-sedimentary facies. The reservoir capacity is gradually getting poor and poor from volcanic breccias to basalt and andesite and finally to tuff. The tectonism is also believed to be a major control on the fissure development and dissolution. The structural stress may give rise to the formation of the cracks or fissures in the brittle rocks, which may greatly improve the reservoir spaces of the Carboniferous volcanic reservoir rocks in the study area.

  10. Recent Two Distinct Eruptions at Sinabung and Kelud, Indonesia (United States)

    Nakada, S.; Yoshimoto, M.; Maeno, F.; Iguchi, M.; Zaenudin, A.; Hendrasto, M.


    Two distinct eruptions occurred in 2014 at Sinabung and Kelud volcanoes in Indonesia. Lava dome-forming eruption started at Sinabung volcano, N Sumatra, in the end of 2013, which was preceded by the phreatic events since 2010 and shallow inflation with high seismicity since 3 months before eruption. The 2010 eruption was the first historic eruption, and the latest eruption geologically recorded occurred in the 9 to 10th Century. The eruption had continued in a nearly constant rate of magma effusion as of the summer of 2014. The lava complex extended on the SE slope (~2.5 km long from the source), frequently generating pyroclastic flows. The volume of erupted magma reached about 0.1 km3 in the 2014 summer. The lava is porphyritic andesite (SiO2 ~57%). The existence of mafic blobs in rocks and plagioclase microlites more calcic than the phenocryst rims, and the absence of breakdown rim on hornblende phenocrysts suggest magma mixing prior to eruption and relatively fast magma ascent. On the other hand, the Plinian eruption began at Kelud volcano, W Java on the evening of February 13, 2014, which had declined almost within about 6 hours. The eruption cloud rose to 18-25 km in altitude, and tephra deposited on extensive areas. The precursory seismic activity started two weeks before eruption and the intensity increased with time. This short but explosive eruption was one of recent large eruptions (VEI 4) at Kelud, which had repeated every ~20 years. A lava dome of 0.035 km3 was accidentally (?) formed within the crater in 2007-2008. The total volume of tephra of the 2014 eruption is 0.2-0.3 km3 in DRE. The magma is crystal-rich basaltic andesite (SiO2 ~56%; phenocryst proportion of ~60%). The petrological characteristics are close to the 2007-2008 dome lava except higher crystallinity in the latter. Mobilization of crystal-rich chamber magma probably was brought by intrusion of new magma. Thus, these recent examples in Indonesia are less-explosive and explosive

  11. Crustal Magma Evolution: the View from the Chemistry of Large Central Andean Ignimbrites (United States)

    Kay, S. M.; Coira, B.


    Voluminous andesitic to rhyodacitic ignimbritic fields linked to giant calderas are distinctive features of the Neogene magmatic record of the central Andean Altiplano-Puna plateau. These magmas evolved in a thickened backarc crust of an active subduction regime at a compressional margin. Their chemistry reflects the thermo-mechanical conditions that control the generation of large crustal magma systems, and tracks changes in a crust subjected to thickening, flow and delamination. Correlations with high resolution geophysical images help to decipher magma generation and eruption processes. A compilation of some 400 published and new chemical analyses allows a view of the spatial-temporal crustal evolution of large complexes in the Puna (22° -28°S) over the last 12 Ma. Data are from the 11-10 Ma Granada and Pairique, 9 to 8 Ma Vilama, 6.8 to 6.5 Ma Coranzulí, 6.7-6.1 Ma Panizos, 5.3-4 Ma Toconao, 4.2-3.8 Ma Atana, and 1.3 Ma Purico complexes in the north, the 12-10 Ma Aguas Calientes complex in the central Puna and the 5.1-3.6 Ma Laguna Amarga/Verde and 6.4 2.2 Ma Cerro Galan complexes in the south. A notable older to younger chemical trend that is seen is for La/Yb (40 to 10) and Sm/Yb (7.5 to 2) ratios to decrease without a corresponding pattern in Eu anomalies. This trend suggests a change from garnet to amphibole as a controlling residual phase at depth followed by feldspar fractionation at higher levels, possibly in magmas chambers near 20 km imaged by seismic data. Xenocrysts in mafic andesitic lavas could be phenocrysts from magmas at this level. A correlated temporal change to lower Al/(K+Na+Ca) and ^8^7Sr/^86Sr ratios and increasing epsilon Nd in the northern Puna requires a changing source linked to an evolving crust. Other patterns are better linked to regional basement differences and variability in the mantle-derived mafic magmas that supply the heat for melting.

  12. Contributions to the petrography, geochemistry and geochronology (U-Pb and Sm-Nd) of the Paleoproterozoic effusive rocks from Iricoume Group, Amazonian Craton, Brazil

    Energy Technology Data Exchange (ETDEWEB)

    Marques, Suelen Nonata de Souza; Nascimento, Rielva Solimairy Campelo do, E-mail:, E-mail: [Universidade Federal do Amazonas (UFAM), Manaus, AM (Brazil). Inst. de Geociencias; Souza, Valmir da Silva; Dantas, Elton Luiz, E-mail:, E-mail: [Universidade de Brasilia (UnB), DF (Brazil). Inst. de Geociencias; Valerio, Cristovao da Silva, E-mail: [Universidade Federal de Roraima (UFRR), Boa Vista, RR (Brazil). Inst. de Geociencias


    The southernmost region of the Guyana shield, Amazonian craton, hosts large record of Paleoproterozoic effusive rocks of the Iricoume Group. They present remarkably well-preserved igneous textures and structures. The SiO{sub 2} contents reveal a bimodal association marked by a compositional gap between acid (SiO{sub 2} > 67 wt%) and intermediate (SiO{sub 2} < 57.7 wt%) rocks. The acid effusive rocks are rhyolites to rhyodacites with high SiO{sub 2}, alkali, Rb, Zr, Nb + Ta, La + Ce and 104 Ga/Al content and low Fe{sub 2}O{sub 3tot}, TiO{sub 2}, CaO, Sr and Co content. They exhibit subalkaline, metaluminous-to-peraluminous compositions, and geochemically compatible to A-type magmatism emplaced in post-collisional to within-plate tectonic settings. The intermediate rocks are andesitic/basalt to andesite relatively high contents of TiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3total}, MgO, CaO, Sr and Co; low SiO{sub 2}, K{sub 2}O, Rb, Zr, Nb + Ta, La + Ce. They have subalkaline and metaluminous geochemical composition and plot on within-plate basalt field. The acid rocks crystallized at 1882 ± 11 Ma in U-Pb analyses for LA-MC-ICPMS zircon data. The Sm-Nd isotopic data on all rocks reveal a Nd TDM model ages between 2.59 and 2.16 Ga and ε{sub Nd}(t) values between -5.78 and 0.03, indicate that the magmatic evolution was related to the reworking of older Paleoproterozoic at the Rhyacian-Siderian period, continental crust (Transamazonian crust-forming event) with some mixing with a limited amount mantle-derived magmas or with contamination by Archean crust. The petrographic, geochemical and geochronological data presented in this paper suggest a within-plate to post-collisional tectonic setting for the Iricoume volcanism, involving lower crust uplift and generation of basalt magma in an extensional regime. (author)

  13. Oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 Merapi eruption (Central Java, Indonesia) (United States)

    Borisova, Anastassia Y.; Gurenko, Andrey A.; Martel, Caroline; Kouzmanov, Kalin; Cathala, Annick; Bohrson, Wendy A.; Pratomo, Indyo; Sumarti, Sri


    Chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions. In this work, high-resolution multicollector secondary ion mass spectrometry data reveal strong variations of δ18O values in three plagioclase crystals (800-1700 μm) from two representative basaltic andesite samples of the 2010 Merapi eruption (Central Java, Indonesia). The δ18O values (from 4.6‰ to 7.9‰) are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth. The lowest δ18O values (4.6-6.6‰) are found in anorthite-rich cores (An82-97), whereas higher δ18O values (5.7-7.9‰) are found in anorthite-poorer zones (An33-86), typically in crystal rims. Combining these new plagioclase δ18O data with δ18O of calc-silicate crustal xenoliths erupted between 1994 and 1998, the composition of glass inclusions hosted by the anorthite-rich plagioclase (An82-92), available experimental data, and the results of thermodynamic modeling using the Magma Chamber Simulator code, we conclude that the abundant anorthite-rich cores crystallized from a mantle-derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper (200-600 MPa) magma storage zone, whereas lower anorthite zones crystallized at shallower levels (100-200 MPa). The oxygen isotope variations in the plagioclase are explained by a two-stage model of interaction of the hydrous, mafic mantle-derived magma (1) with old crustal rocks depleted in 18O due to high temperature alteration that yielded the low δ18O values in the anorthite-rich cores at deep levels (13-20 km), and later (2) with 18O-enriched carbonate material that yielded the high δ18O values in anorthite-poorer zones at shallow levels (∼4.5-9 km). Thermodynamic modeling is consistent with ∼18 wt.% assimilation of crustal calc-silicate material at 925-950 °C and 100-200 MPa by the 2010 Merapi basaltic andesite magma prior to

  14. Upper Cretaceous to Holocene magmatism and evidence for transient Miocene shallowing of the Andean subduction zone under the northern Neuquén Basin (United States)

    Kay, Suzanne M.; Burns, W. Matthew; Copeland, Peter; Mancilla, Oscar


    Evidence for a Miocene period of transient shallow subduction under the Neuquén Basin in the Andean backarc, and an intermittent Upper Cretaceous to Holocene frontal arc with a relatively stable magma source and arc-to-trench geometry comes from new 40Ar/39Ar, major- and trace-element, and Sr, Pb, and Nd isotopic data on magmatic rocks from a transect at ∼36°–38°S. Older frontal arc magmas include early Paleogene volcanic rocks erupted after a strong Upper Cretaceous contractional deformation and mid-Eocene lavas erupted from arc centers displaced slightly to the east. Following a gap of some 15 m.y., ca. 26–20 Ma mafic to acidic arc-like magmas erupted in the extensional Cura Mallín intra-arc basin, and alkali olivine basalts with intraplate signatures erupted across the backarc. A major change followed as ca. 20–15 Ma basaltic andesite–dacitic magmas with weak arc signatures and 11.7 Ma Cerro Negro andesites with stronger arc signatures erupted in the near to middle backarc. They were followed by ca. 7.2–4.8 Ma high-K basaltic to dacitic hornblende-bearing magmas with arc-like high field strength element depletion that erupted in the Sierra de Chachahuén, some 500 km east of the trench. The chemistry of these Miocene rocks along with the regional deformational pattern support a transient period of shallow subduction that began at ca. 20 Ma and climaxed near 5 Ma. The subsequent widespread eruption of Pliocene to Pleistocene alkaline magmas with an intraplate chemistry in the Payenia large igneous province signaled a thickening mantle wedge above a steepening subduction zone. A pattern of decreasingly arc-like Pliocene to Holocene backarc lavas in the Tromen region culminated with the eruption of a 0.175 ± 0.025 Ma mafic andesite. The northwest-trending Cortaderas lineament, which generally marks the southern limit of Neogene backarc magmatism, is considered to mark the southern boundary of the transient shallow subduction zone.

  15. Geochemical and Sr-Nd-Pb isotopic evidence for ancient lower continental crust beneath the Xi Ujimqin area of NE China (United States)

    Gao, Xiaofeng; Guo, Feng; Xiao, Peixi; Kang, Lei; Xi, Rengang


    The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogen on Earth. The role that Precambrian continental microblocks played in its formation, however, remains a highly controversial topic. New zircon U-Pb age data and whole-rock geochemical and Sr-Nd-Pb isotopic studies on Permian (253-251 Ma) andesites from the Xi Ujimqin area provide the first evidence for the existence of a continental lower mafic crust in the eastern segment of the CAOB. These Permian lavas generally have chemical compositions similar to experimental melts of garnet pyroxenites. Based on Sr-Nd-Pb isotopic compositional differences, they can be further subdivided into two groups. Group 1 has moderately radiogenic Sr (87Sr/86Sr(i) = 0.7060-0.7062) and nonradiogenic Nd (εNd(t) = - 9.0-8.3) and Pb (e.g., 206Pb/204Pb = 17.18-17.23) isotopic compositions similar to the ancient lower mafic crust beneath the North China Craton (NCC). Compared with Group 1, Group 2 has less radiogenic Sr (87Sr/86Sr(i) = 0.7051-0.7055), and more radiogenic Nd (εNd(t) = - 0.2-+1.4) and Pb (e.g., 206Pb/204Pb = 18.04-18.20) isotopic compositions as observed in the Phanerozoic granitoids and felsic lavas of the CAOB. The combined geochemical and isotopic data indicate that Group 1 was derived from ancient lower mafic crust of the NCC affinity, with a residual assemblage of pyroxene + plagioclase + amphibole. The source for Group 2 was a mixture of ancient lower mafic crust and a juvenile crustal component, and melting left a residue of orthopyroxene + clinopyroxene + plagioclase + garnet + amphibole. Generation of these two types of late Permian andesites favors a model whereby breakoff of a subducted slab and subsequent lithospheric extension triggered extensive asthenospheric upwelling and melting of the continental mafic lower crust of the eastern CAOB. The discovery of ancient lower continental crust of the NCC affinity in the CAOB implies that the NCC experienced continental breakup during

  16. Morphology, volcanism, and mass wasting in Crater Lake, Oregon (United States)

    Bacon, C.R.; Gardner, J.V.; Mayer, L.A.; Buktenica, M.W.; Dartnell, P.; Ramsey, D.W.; Robinson, J.E.


    Crater Lake was surveyed nearly to its shoreline by high-resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys. The bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca. 7700 calibrated yr B.P. caldera. The andesitic Wizard Island and central-plattform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents. Wizard Island eruptions ceased when the lake was ~80 m lower than at present. Lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor. The Wizard Island and central-platform volcanoes, andesitic Merriam Cone, and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse, whereas a small rhydacite dome was emplaced on the flank of Wizard Island at ca. 4800 cal. yr B.P. Bedrock outcrops on the submerged caldera walls are shown in detail and, in some cases, can be correlated with exposed geologic units of Mount Mazama. Fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer, wider ridges downslope. Hummocky topography and scattered blocks up to ~280 m long below many of the embayments in the caldera wall mark debris-avalanche deposits that probably formed in single events and commonly are affected by secondary failures. The flat-floored, deep basins contain relatively fine-grained sediment transported from the debris aprons by sheet-flow turbidity currents. Crater Lake apparently filled rapidly (ca. 400-750 yr) until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at ~1845 m elevation

  17. New geochronological constraints of the Lassen segment's regional volcanism (United States)

    Germa, A.; Connor, C.; Connor, L.; Malservisi, R.; Tavarez, S.; Charbonnier, S. J.; Clynne, M. A.; Perry, C.; Quidelleur, X.; Ricci, J.


    The Lassen region is the southernmost active volcanic field in the Cascade Range. Since ~3.5 Ma distributed mafic to intermediate calc-alkaline magmas continuously built hundreds of cinder cones, lava flows, and a few small shield volcanoes. A set of 10 new unspiked K-Ar ages obtained on groundmass separates help reveal the timing of this regional volcanism. Although most lavas show a high atmospheric contamination level and a low K content, significant ages were obtained with this technique. Shields were dated at about 2.5 Ma (Clynne and Muffler, 2010) and are commonly dissected by erosion. However, we obtained a K-Ar age of 374 ± 25 ka for the late lava flow at the summit of Crater Mountain, which is less eroded than the other shields. This indicates that this regional volcano's activity overlapped that of the Lassen Volcanic Center (LVC), and raises questions regarding the ages of other shields. The Caribou Volcanic field (CVF), at the eastern boundary of the Lassen region, was also contemporaneous with the LVC. The field's activity initiated ~425 ka ago, but does not appear to have extended into the Holocene (Clynne and Muffler, 2010). We obtained a K-Ar age of 296 ± 13 ka on the basaltic andesite of Eleanor Lake, extending further the activity of the Caribou sequence. Our K-Ar age of 59 ± 3 ka on a basaltic flow confirms that the Bidwell Spring Chain was active between 20 and 70 ka as previously shown. We dated the basaltic andesite tuya of Turnaround Lake at 4 ± 5 ka. However, this conflicts with the timing of Tuya chain (15-18 ka). Finally, to the south-west of LVC, basalts of Cold Creek Butte yield an age of 207 ± 26 ka, and we dated a basaltic flow from Inskip Hill at ~5 ka. The new ages obtained, especially the Holocene ones, are consistent with magnetotelluric soundings and gravity data that show mid-crustal anomalies in the back-arc (Tavarez, 2015). These data demonstrate that the CVF is still active and has the potential for future eruptions.

  18. El Estribo Volcanic Complex: Evolution from a shield volcano to a cinder cone, Pátzcuaro Lake, Michoacán, México (United States)

    Pola, A.; Macías, J. L.; Osorio-Ocampo, S.; Sosa-Ceballos, G.; Garduño-Monroy, V. H.; Martínez-Martínez, J.


    El Estribo Volcanic Complex (EVC) is located in the northern part of the Michoacán-Guanajuato Volcanic Field within the Trans-Mexican Volcanic Belt (TMVB). El Estribo is located at the southern edge of the E-W Pátzcuaro fault that belongs to the Pátzcuaro-Jarácuaro graben, a western extension of the E-W Morelia-Acambay fault system. Stratigraphy, geochronology, chemistry, and mineral assemblages suggest that the volcanic complex was constructed in two periods separated by a ~ 100 ka volcanic hiatus: a) emission of lava flows that constructed a shield volcano between 126 ka, and b) mixed phreatomagmatic to Strombolian activity that formed a cinder cone ~ 28 ka. The magmas that fed these monogenetic volcanoes were able to use the same feeding system. The cinder cone itself was constructed by Strombolian fallouts and remobilized scoria beds, followed by an erosion period, and by a mixed phreatomagmatic to magmatic phase (Strombolian fallouts ending with lava flows). Soft-sedimentary deformation of beds and impact sags, cross-bedding, as well as pitting and hydrothermal cracks found in particles support the phreatomagmatic phase. The erupted magmas through time ejected basaltic andesitic lava flows (56.21-58.88% SiO2) that built the shield volcano and then basaltic andesitic scoria (57.65-59.05% SiO2) that constructed the cinder cone. Although they used the same feeding system, the geochemical data and the mineral chemistry of the magmas indicate that the shield volcano and the cinder cone were fed by different magma batches erupted thousands of years apart. Therefore, the location of El Estribo Volcanic Complex along an E-W fault that has generated two sector collapses of the shield volcano to the north may be directly linked to this complex redistribution of the magmatic paths to the surface. Our findings show that magmatic feeding systems within monogenetic volcanic fields could be long lived, questioning the classic view of the monogenetic nature of their

  19. A review of the geology of the Argentinian Fuegian Andes (United States)

    Olivero, Eduardo B.; Martinioni, Daniel R.


    Seven stratigraphic units reflect the tectonic evolution of the Argentinian Fuegian Andes: Basement (Paleozoic-Jurassic); Lemaire Formation (Upper Jurassic); Yahgan-Beauvoir formations (Lower Cretaceous); Cerro Matrero Formation (Upper Cretaceous); Rı´o Claro Formation (Paleocene); La Despedida Group (Eocene); and Cabo Peña Formation (uppermost Eocene-Lower Oligocene). Basement rocks (garnet, quartz-sericite, and chlorite schists; and amphibolites) are unconformably covered by the Lemaire Formation (rhyolites; basalts; slates; and acidic volcaniclastic breccias, tuffs, conglomerates, and turbidites), formed during extensional tectonism. The post-rift Yahgan Formation (deep-marine black mudstones, andesitic volcaniclastic turbidites and tuffs) interfingers northward with the Beauvoir Formation (slope and platform black mudstones), and covers the Lemaire Formation unconformably. The Yahgan Formation represents an andesitic, volcaniclastic apron, coeval with a Pacific volcanic-arc, filling a marginal basin floored with oceanic crust. The Late Cretaceous compressional orogeny resulted in tectonic inversion, closure of the marginal basin, peak metamorphism and folding, and initial uplifting of the Fuegian Andes. By the latest Cretaceous-earliest Paleogene, the Andes were exposed to subaerial erosion, and the lowest Danian Rı´o Claro Formation bears clear evidence of an Andean clastic provenance. The Rı´o Claro Formation represents the first molasse deposits of the foreland stage of evolution of the Fuegian Andes. Earliest Paleogene north-verging thrust propagation deformed the Rı´o Claro Formation and older units, producing northward depocenter migration. La Despedida Group rests unconformably on the Rı´o Claro Formation and is involved in the thrust and fold belt. Important Eocene compression resulted in thrusting of central Andean basement schists and the Lemaire Formation over Lower Cretaceous and continental Paleogene rocks, respectively. In the

  20. Liquid Immiscibility of Boninite in Xiangcheng, Southwestern China, and Its implication to Genetic Relationship between Boninite and Komatiitic Basalt

    Institute of Scientific and Technical Information of China (English)


    Boninitic rocks and associated high-magnesian basalt and high-iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island-Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well-developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low-Ca pyroxenes and by low CaO/Al2O3 ratios (1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low-Ca modern boninites and SHMB in the Archaean and Proterozoic. As a mechanism of ocellar texture, liquid immiscibility in boninite is supported by the following lines of evidence: (a) sharp contact between ocelli and matrix, (b) constant volumetric ratios of ocelli/matrix and common coalescence of ocelli in ocellar rocks, (c) identical micro-spinifex textures and mineral assemblages with different modal mineral contents in ocelli-matrix pairs, (d) bubbles and acicular clinopyroxene crystal strand over the boundary between ocelli and matrix, and (e) chemical compositions of ocelli and matrix corresponding to high-Mg andesite and komatiitic basalt, respectively. The close association and geochemical similarities between ocellar boninites and pillow boninite/massive boninite suggest that these are comagmatic rocks. The primary features of the ocellar boninite indicated by high Mg/(Mg+Fe2+) ratio and high Cr and Ni abundance show that liquid immiscibility took place in the early evolution stage of the boninitic magma. The miscibility gap in boninite which is smaller than that in tholeiite is likely to be due to the low FeO*/MgO+FeO* ratio and high MgO content of the boninitic magma. The association of komatiite-komatiitic basalt-boninite (or SHMB) and the immiscibility phenomenon in high-Mg lavas in some Archaean greenstone belts and ophiolites is also

  1. Blue Mountain and The Gas Rocks: Rear-Arc Dome Clusters on the Alaska Peninsula (United States)

    Hildreth, Wes; Fierstein, Judy; Calvert, Andrew T.


    Behind the single-file chain of stratovolcanoes on the Alaska Peninsula, independent rear-arc vents for mafic magmas are uncommon, and for silicic magmas rarer still. We report here the characteristics, compositions, and ages of two andesite-dacite dome clusters and of several nearby basaltic units, all near Becharof Lake and 15 to 20 km behind the volcanic front. Blue Mountain consists of 13 domes (58-68 weight percent SiO2) and The Gas Rocks of three domes (62-64.5 weight percent SiO2) and a mafic cone (52 weight percent SiO2). All 16 domes are amphibole-biotite-plagioclase felsite, and nearly all are phenocryst rich and quartz bearing. Although the two dome clusters are lithologically and chemically similar and only 25 km apart, they differ strikingly in age. The main central dome of Blue Mountain yields an 40Ar/39Ar age of 632?7 ka, and two of the Gas Rocks domes ages of 25.7?1.4 and 23.3?1.2 ka. Both clusters were severely eroded by glaciation; surviving volumes of Blue Mountain domes total ~1 km3, and of the Gas Rocks domes 0.035 km3. Three basaltic vents lie close to The Gas Rocks, another lies just south of Blue Mountain, and a fifth is near the north shore of Becharof Lake. A basaltic andesite vent 6 km southeast of The Gas Rocks appears to be a flank vent of the arc-front center Mount Peulik. The basalt of Ukinrek Maars has been called transitionally alkalic, but all the other basaltic rocks are subalkaline. CO2-rich gas emissions near the eponymous Gas Rocks domes are not related to the 25-ka dacite dome cluster but, rather, to intracrustal degassing of intrusive basalt, one batch of which erupted 3 km away in 1977. The felsic and mafic vents all lie along or near the Bruin Bay Fault where it intersects a broad transverse structural zone marked by topographic, volcanologic, and geophysical discontinuities.

  2. Petrological and tectono-magmatic significance of ophiolitic basalts from the Elba Island within the Alpine Corsica-Northern Apennine system (United States)

    Saccani, Emilio; Principi, G.


    Two distinct ophiolitic units, which represent remnants of the Jurassic Ligurian-Piedmont Ocean, crop out in the Elba Island. They are the Monte Strega unit in central-eastern Elba and the Punta Polveraia-Fetovaia unit in western Elba. Ophiolitic rocks from the Monte Strega unit are commonly affected by ocean floor metamorphism, whereas those from the Punta Polveraia-Fetovaia unit are affected to various extent by thermal metamorphism associated with the Late Miocene Monte Capanne monzogranitic intrusion. Both ophiolitic units include pillow lavas and dykes with compositions ranging from basalt to basaltic andesite, Fe-basalt, and Fe-basaltic andesite. Basaltic rocks from these distinct ophiolitic units show no chemical differences, apart those due to fractional crystallization processes. They display a clear tholeiitic nature with low Nb/Y ratios and relatively high TiO2, P2O5, Zr, and Y contents. They generally display flat N-MORB normalized high field strength element patterns, which are similar to those of N-MORB. Chondrite-normalized rare earth element patterns show light REE / middle REE (LREE/MREE) depletion and marked heavy (H-) REE fractionation with respect to MREE. This HREE/MREE depletion indicates a garnet signature of their mantle sources. Accordingly, they can be classified as garnet-influenced MORB (G-MORB), based on Th, Nb, Ce, Dy, and Yb systematics. We suggest that the Elba Island ophiolitic basalts were generated at a magma starved, slow-spreading mid-ocean ridge. REE, Th, and Nb partial melting modelling shows that the compositions of the relatively primitive Elba Island ophiolitic basalts are compatible with partial melting of a depleted MORB mantle (DMM) source bearing garnet-pyroxenite relics. Hygromagmatophile element ratios suggest that basalts from both ophiolitic units were originated from chemically very similar mantle sources. A comparison with basalts and metabasalts from Alpine Corsica and northern Apennine ophiolitic units shows

  3. Petrogenesis of the Neoproterozoic Ngondo Plutonic complex (Cameroon, west central Africa): a case of late-collisional ferro-potassic magmatism (United States)

    Tagne-Kamga, Gabriel


    The Ngondo complex is a late-collisional pluton, which was emplaced around 600 Ma along a N030° E strike-slip shear zone in the southwestern part of the Neoproterozoic Fold Belt of Cameroon. It comprises three successively emplaced plutonic groups of rocks: (i) mafic to felsic intrusive rocks (MFR), (ii) fine-grained granites (FGG) and (iii) coarse-grained granites (CGG). Late aplitic and pegmatite dykes were emplaced along brittle fractures in these plutons. The complex is metaluminous to weakly peraluminous, high-K, calc-alkaline to " trans-alkaline" ferro-potassic, with mineralogical and geochemical characteristic of I-type granites. The plutonic rocks are characterised by high Ba, Sr, Rb and ∑REE concentrations and low Ni and Cr contents in the mafic members. They also display chondrite-normalised REE patterns characterised by variable LREE enrichment, moderate to minor HREE fractionation with moderate to pronounced negative Eu anomalies (Eu/Eu∗: 0.6-0.9 (MFR), 0.2-0.5 (FGG), 0.3-0.7 (CGG)). Trace element distribution patterns for the three plutonic groups are similar with a distinctive depletion in Nb, Sr and Ti relative to other trace elements and a greater enrichment in LILE compared to HFSE. These plutonic groups present distinct evolutionary trends precluding their origin from differentiation of a single parental magma. The geochemical and isotopic data indicate that they derived from partial melting of heterogeneous (meta)-igneous mafic lower crustal materials, having possibly the composition of amphibolitised high-K calc-alkaline basaltic andesites and andesitic metagreywackes. Petrographic evidences such as the presence of quartz-ocelli, xenocrysts of feldspar, fragments of country rocks (migmatitic gneisses) strongly indicate that crustal contamination may have played an important role in the genesis of the plutonic rocks. This contamination process is further supported by the variation of major and trace elements together with Sr-Nd isotopic data

  4. Blowing off steam: Tuffisite formation as a regulator for lava dome eruptions (United States)

    Kendrick, Jackie; Lavallée, Yan; Varley, Nick; Wadsworth, Fabian; Lamb, Oliver; Vasseur, Jérémie


    Tuffisites are veins of variably sintered, pyroclastic particles that form in conduits and lava domes as a result of localized fragmentation events during gas-and-ash explosions. Those observed in-situ on the active 2012 lava dome of Volcán de Colima range from voids with intra-clasts showing little movement and interpreted to be failure-nuclei, to sub-parallel lenses of sintered granular aggregate interpreted as fragmentation horizons, through to infilled fractures with evidence of viscous remobilization. All tuffisites show evidence of sintering. Further examination of the complex fracture-and-channel patterns reveals viscous backfill by surrounding magma, suggesting that lava fragmentation was followed by stress relaxation and continued viscous deformation as the tuffisites formed. The natural tuffisites are more permeable than the host andesite, and have a wide range of porosity and permeability compared to a narrower window for the host rock, and gauging from their significant distribution across the dome, we posit that the tuffisite veins may act as important outgassing pathways. To investigate tuffisite formation we crushed and sieved andesite from the lava dome and sintered it at magmatic temperatures for different times. We then assessed the healing and sealing ability by measuring porosity and permeability, showing that sintering reduces both over time. During sintering the porosity-permeability reduction occurs due to the formation of viscous necks between adjacent grains, a process described by the neck-formation model of Frenkel (1945). This process leads the granular starting material to a porosity-permeability regime anticipated for effusive lavas, and which describes the natural host lava as well as the most impervious of natural tuffisites. This suggests that tuffisite formation at Volcán de Colima constructed a permeable network that enabled gas to bleed passively from the magma. We postulate that this progressively reduced the lava dome

  5. Chemical Variation and Origin of Pleistocene Silicic Pyroclastic Flows from Central American Volcanic Arc (United States)

    Patino, L. C.; Vogel, T. A.; Alvarado, G. E.; Rose, W. I.; Viray, E. L.


    Silicic pyroclastic flows have occurred along the Central American volcanic arc during the Pleistocene. The volcanic products from these eruptions range in composition have SiO{2} mode of 70 wt.%. In the latest part of the Pleistocene (Costa Rica. Phenocryst phases of the silicic pyroclastic flows along Central America are generally very similar. Plagioclase dominates as phenocryst and in the groundmass. Sub-calcic augite, hypersthene are common in dacites. Amphibole as well as biotite are common in the rhyolites and rhyodacites in Guatemala and El Salvador, but these minerals are absent from all units in Nicaragua, and from the youngest unit in Costa Rica. In addition, Ti-oxides, apatite, quartz, are common. It is worth noting that the silicic rocks from Central America contain very little alkali feldspar. There are some chemical variations in the composition of ash-flow tuffs along the arc. The most primitive materials in ignimbrites from Guatemala and Costa Rica are basaltic andesites and andesites; but in Nicaragua and El Salvador, basaltic scorias are present. The ignimbrites from Central Costa Rica have higher alkali content, than the rest of the Pleistocene ash-flow tuffs from Central America, a pattern similar to that observed in lavas. Furthermore, some trace element and trace element ratios also vary along the arc in a pattern similar to that observed in the lavas. The ignimbrites from Nicaragua tend to have the lowest concentrations of Zr (200 ppm); Ba/Th, U/Th are highest and La/Yb is the lowest in Nicaragua.Fractional crystallization has played a role in the evolution of ash-flow sheets in the Central American volcanic arc. Some samples from Guatemala and El Salvador have Eu/Eu*Caribbean large igneous province in the south, are not possible sources for the Pleistocene silicic pyroclastic flows. Based on the similar key trace-element ratios of the ignimbrites and the arc lavas, we concluded that remelting of the calc-alkaline plutons, emplaced at depth

  6. Paleocene Turbidite Deposition in the Central American Seaway (NW Costa Rica): Geochemical Analysis and Provenance of Detrital Spinel and Clinopyroxene (United States)

    Giblin, A. C.


    The Central American Land Bridge is the crucial connection between North and South America, and the Miocene closure of the Panama seaway led to a change in global oceanic circulation patterns. Modern Costa Rica is part of the island arc that formed over the western Caribbean subduction zone, and the Santa Elena peninsula is on the northwest coast of Costa Rica next to the Sandino forearc basin. This study focuses on the origin and provenance of the Paleocene deep-water Rivas and Descartes turbidites that crop out on the northern part of the Santa Elena peninsula in northwestern Costa Rica. Understanding the sedimentary fill of the Sandino Basin that contributed to the closing of the seaway may lead to a better understanding of the Late Cretaceous-Paleogene arcs. Provenance studies of the Santa Elena Peninsula turbidite sandstone bodies constrain the history of the paleogeography and tectonics of the region. Petrographic analyses of rock thin sections constrain source areas; geochemical analysis of individual detrital heavy minerals from rock samples give indications of sediment sources and tectonic setting during deposition. This study is a provenance analysis based on (i) semi-quantitative energy-dispersive spectrometry analysis of heavy minerals, (ii) quantitative wavelength-dispersive spectrometry for major elements of detrital clinopyroxene and spinel grains, (iii) trace element analysis through laser ablation of single detrital clinopyroxene grains, and (iv) comparative analysis of the different potential source rocks to clearly identify the most likely sediment sources. The detrital spinel and clinopyroxene are possibly sourced from: mantle ophiolites, mid-ocean ridge gabbros, or volcanic arc tholeiitic basalts or calc-alkaline andesites. Spinel and clinopyroxne geochemistry suggests a possible peridotitic source, linked to mantle rocks that are now covered by Tertiary volcanics or have completely eroded. The character of the crustal minerals indicates

  7. Significance of an Active Volcanic Front in the Far Western Aleutian Arc (United States)

    Yogodzinski, G. M.; Kelemen, P. B.; Hoernle, K.


    Discovery of a volcanic front west of Buldir Volcano, the western-most emergent Aleutian volcano, demonstrates that the surface expression of Aleutian volcanism falls below sea level just west of 175.9° E longitude, but is otherwise continuous from mainland Alaska to Kamchatka. The newly discovered sites of western Aleutian seafloor volcanism are the Ingenstrem Depression, a 60 km-long structural depression just west of Buldir, and an unnamed area 300 km further west, referred to as the Western Cones. These locations fall along a volcanic front that stretches from Buldir to Piip Seamount near the Komandorsky Islands. Western Aleutian seafloor volcanic rocks include large quantities of high-silica andesite and dacite, which define a highly calc-alkaline igneous series and carry trace element signatures that are unmistakably subduction-related. This indicates that subducting oceanic lithosphere is present beneath the westernmost Aleutian arc. The rarity of earthquakes below depths of 200 km indicates that the subducting plate is unusually hot. Some seafloor volcanoes are 6-8 km wide at the base, and so are as large as many emergent Aleutian volcanoes. The seafloor volcanoes are submerged in water depths >3000 m because they sit on oceanic lithosphere of the Bering Sea. The volcanic front is thus displaced to the north of the ridge of arc crust that underlies the western Aleutian Islands. This displacement, which developed since approximately 6 Ma when volcanism was last active on the islands, must be a consequence of oblique convergence in a system where the subducting plate and large blocks of arc crust are both moving primarily in an arc-parallel sense. The result is a hot-slab system where low subduction rates probably limit advection of hot mantle to the subarc, and produce a relatively cool and perhaps stagnant mantle wedge. The oceanic setting and highly oblique subduction geometry also severely limit rates of sediment subduction, so the volcanic rocks, which

  8. Development of Waterfall Cliff Face: An Implication from Multitemporal High-definition Topographic Data (United States)

    Hayakawa, Y. S.; Obanawa, H.


    Bedrock knickpoints (waterfalls) often act as erosional front in bedrock rivers, whose geomorphological processes are various. In waterfalls with vertical cliffs, both fluvial erosion and mass movement are feasible to form the landscape. Although morphological changes of such steep cliffs are sometimes visually observed, quantitative and precise measurements of their spatiotemporal distribution have been limited due to poor accessibility to such cliffs. For the clarification of geomorphological processes in such cliffs, multi-temporal mapping of the cliff face at a high resolution can be advantaged by short-range remote sensing approaches. Here we carry out multi-temporal terrestrial laser scanning (TLS), as well as structure-from-motion multi-view stereo (SfM-MVS) photogrammetry based on unmanned aerial system (UAS) for accurate topographic mapping of cliffs around a waterfall. The study site is Kegon Falls in central Japan, having a vertical drop of surface water from top of its overhanging cliff and groundwater outflows from its lower portions. The bedrock consists of alternate layers of jointed andesite lava and conglomerates. The latest major rockfall in 1986 caused approximately 8-m recession of the waterfall lip. Three-dimensional changes of the rock surface were detected by multi-temporal measurements by TLS over years, showing the portions of small rockfalls and surface lowering in the bedrock. Erosion was frequently observed in relatively weak the conglomerates layer, whereas small rockfalls were often found in the andesite layers. Wider areas of the waterfall and cliff were also measured by UAS-based SfM-MVS photogrammetry, improving the mapping quality of the cliff morphology. Point clouds are also projected on a vertical plane to generate a digital elevation model (DEM), and cross-sectional profiles extracted from the DEM indicate the presence of a distinct, 5-10-m deep depression in the cliff face. This appears to have been formed by freeze-thaw and

  9. Dacite petrogenesis on mid-ocean ridges: Evidence for oceanic crustal melting and assimilation (United States)

    Wanless, V.D.; Perfit, M.R.; Ridley, W.I.; Klein, E.


    Whereas the majority of eruptions at oceanic spreading centers produce lavas with relatively homogeneous mid-ocean ridge basalt (MORB) compositions, the formation of tholeiitic andesites and dacites at mid-ocean ridges (MORs) is a petrological enigma. Eruptions of MOR high-silica lavas are typically associated with ridge discontinuities and have produced regionally significant volumes of lava. Andesites and dacites have been observed and sampled at several locations along the global MOR system; these include propagating ridge tips at ridge-transform intersections on the Juan de Fuca Ridge and eastern Gal??pagos spreading center, and at the 9??N overlapping spreading center on the East Pacific Rise. Despite the formation of these lavas at various ridges, MOR dacites show remarkably similar major element trends and incompatible trace element enrichments, suggesting that similar processes are controlling their chemistry. Although most geochemical variability in MOR basalts is consistent with low-pressure fractional crystallization of various mantle-derived parental melts, our geochemical data for MOR dacitic glasses suggest that contamination from a seawater-altered component is important in their petrogenesis. MOR dacites are characterized by elevated U, Th, Zr, and Hf, low Nb and Ta concentrations relative to rare earth elements (REE), and Al2O3, K2O, and Cl concentrations that are higher than expected from low-pressure fractional crystallization alone. Petrological modeling of MOR dacites suggests that partial melting and assimilation are both integral to their petrogenesis. Extensive fractional crystallization of a MORB parent combined with partial melting and assimilation of amphibole-bearing altered crust produces a magma with a geochemical signature similar to a MOR dacite. This supports the hypothesis that crustal assimilation is an important process in the formation of highly evolved MOR lavas and may be significant in the generation of evolved MORB in

  10. Geology of El Chichon volcano, Chiapas, Mexico (United States)

    Duffield, W.A.; Tilling, R.I.; Canul, R.


    The (pre-1982) 850-m-high andesitic stratovolcano El Chicho??n, active during Pleistocene and Holocene time, is located in rugged, densely forested terrain in northcentral Chiapas, Me??xico. The nearest neighboring Holocene volcanoes are 275 km and 200 km to the southeast and northwest, respectively. El Chicho??n is built on Tertiary siltstone and sandstone, underlain by Cretaceous dolomitic limestone; a 4-km-deep bore hole near the east base of the volcano penetrated this limestone and continued 770 m into a sequence of Jurassic or Cretaceous evaporitic anhydrite and halite. The basement rocks are folded into generally northwest-trending anticlines and synclines. El Chicho??n is built over a small dome-like structure superposed on a syncline, and this structure may reflect cumulative deformation related to growth of a crustal magma reservoir beneath the volcano. The cone of El Chicho??n consists almost entirely of pyroclastic rocks. The pre-1982 cone is marked by a 1200-m-diameter (explosion?) crater on the southwest flank and a 1600-m-diameter crater apparently of similar origin at the summit, a lava dome partly fills each crater. The timing of cone and dome growth is poorly known. Field evidence indicates that the flank dome is older than the summit dome, and K-Ar ages from samples high on the cone suggest that the flank dome is older than about 276,000 years. At least three pyroclastic eruptions have occurred during the past 1250 radiocarbon years. Nearly all of the pyroclastic and dome rocks are moderately to highly porphyritic andesite, with plagioclase, hornblende and clinopyroxene the most common phenocrysts. Geologists who mapped El Chicho??n in 1980 and 1981 warned that the volcano posed a substantial hazard to the surrounding region. This warning was proven to be prophetic by violent eruptions that occurred in March and April of 1982. These eruptions blasted away nearly all of the summit dome, blanketed the surrounding region with tephra, and sent

  11. Geochemical features of the mantle source beneath Irazú and Turrialba volcanoes, Costa Rica (United States)

    Rizzo, A. L.; Di Piazza, A.; Alvarado-Induni, G.; Carapezza, M. L.; de Moor, M. J.; Martinez, M.


    Irazú and Turrialba are active arc volcanoes located at the southeastern terminus of the Central American Volcanic Arc (CAVA). These volcanoes have been considered in literature as "twin volcanoes" or as a linked volcanic system. Effectively their proximity may lead to the assumption that they share a common plumbing system, but geochemical data on rocks and fluids reveal a more complicated framework. In this study, we analyzed the rock chemistry of a selected suite of eruptive products emitted in the last 50ka from Irazú volcano, including products from the 1963-1965 eruption. We also analyzed He-Ne-Ar isotopes in fluid inclusions hosted in olivines and pyroxenes hand-picked from these products, and we compared our results with those available for Irazú and the neighboring Turrialba. Rock samples from Irazú are basalts to andesites with MgO content ranging between 3 and 8 wt%, with a variability that follows typical trends of fractional crystallization. The pattern of trace elements is subduction-related with an OIB-like component, testified by an unusual enrichment (e.g., K, REE; e.g., Benjamin et al., 2007 and references therein), associated with the subduction of the Galapagos seamounts. In addition, Turrialba volcano shows the presence of andesites with adakite-like affinity (Di Piazza et al., 2015) which is not observed in rocks from Irazú . The 3He/4He ratio measured in olivine crystals from Irazú varies from 7.1 to 7.5 Ra, overlapping the measurements performed in surface gases (7.2 Ra; Fischer et al., 2002). This range is also comprised in the measurements carried out in gases and rocks from Turrialba (7.0-8.1 Ra; Di Piazza et al., 2015), which showed the presence of a MORB- and OIB-like component at the mantle source. Based on these evidences, we propose that the mantle beneath Irazú reflects an intermediate composition respect to the extreme components recognized at Turrialba. Irazú shows more typical arc-like geochemical signatures, whereas

  12. Amphibole-melt trace element partitioning of fractionating calc-alkaline magmas in the lower crust: an experimental study (United States)

    Nandedkar, Rohit H.; Hürlimann, Niklaus; Ulmer, Peter; Müntener, Othmar


    Amphibole is one of the most important hydrous minerals of the middle and lower continental crust and plays a key role in the formation of intermediate to silica-rich magmas. This study reports a consistent set of amphibole trace element partition coefficients derived from fractional crystallization experiments at 0.7 GPa in a piston cylinder apparatus. Starting materials were doped with trace elements on the 20-40 ppm level and measured using laser ablation (LA)-ICP-MS. Amphibole is stable from 1010 to 730 °C and systematically changes its composition from pargasite to magnesiohornblende to cummingtonite, while coexisting liquids vary from andesite to dacite and rhyolite. Amphibole-liquid partition coefficients increase systematically with decreasing temperature and increasing SiO2 in the liquid. Potassium displays an inverse behavior and partitioning decreases with decreasing temperature. Rare earth element (REE) partition coefficients, assumed to occupy the M4 site within the amphibole structure, increase continuously up to one order of magnitude. The calculated lattice parameters, ideal cation radius ( r 0) and Young's modulus ( E) remain nearly constant with decreasing temperature. The high-field strength elements Zr and Hf that occupy the M2 site of the amphibole structure reveal a fivefold increase in partition coefficients with decreasing temperature and constant lattice parameters r 0 and E. Partition coefficients correlate with edenite, tschermaks and cummingtonite exchange vectors indicating that the maximum partition coefficient ( D 0) for an ideal cation radius increases with decreasing edenite component, while the latter decreases linearly with temperature. Regressing Amph/L D Ca against trace elements results in fair to excellent correlations ( r 2 0.55-0.99) providing a predictive tool to implement the trace element partition coefficients in numerical geochemical modeling. Our data result in positive correlations between Amph/L D Nb/Ta and Amph/L D

  13. The origin of high-Mg magmas in Mt Shasta and Medicine Lake volcanoes, Cascade Arc (California): higher and lower than mantle oxygen isotope signatures attributed to current and past subduction (United States)

    Martin, E.; Bindeman, I.; Grove, T. L.


    We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ18O (δ18OOl) values of 5.9-6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast, HAOT lavas from Medicine Lake have δ18OOl values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived magmas. Other magma types from both volcanoes show intermediate δ18OOl values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ18OOl signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ18OOl reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ18O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting process in the mantle wedge above the modern subduction zone and require a mantle source enriched in 18O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades.

  14. The delicate balance between soil production and erosion, and its role on landscape evolution

    Energy Technology Data Exchange (ETDEWEB)

    Dosseto, A., E-mail: [GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong. Wollongong, NSW (Australia); Buss, Heather [US Geological Survey. Menlo Park, CA (United States); Suresh, P.O. [Department of Environment and Geography, Macquarie University. North Ryde, NSW (Australia)


    Highlights: > The uranium-series isotope composition of regolith material can be used to determine the soil residence time. > Soil residence times up to 30 and 90 kyr are calculated for Frogs Hollow and Bisley, respectively. > Production rates are relatively similar for granitic and shale lithologies, but much higher over volcanic parent rock. > Soil production matches erosion in soil-mantled landscapes, demonstrating quantitatively that this type of landscape results from a balance between these two processes > Soil production is up to two orders of magnitude slower than erosion in cultivated areas. - Abstract: The diversity in landscapes at the Earth's surface is the result, amongst other things, of the balance (or imbalance) between soil production and erosion. While erosion rates are well constrained, it is only recently that we have been able to quantify rates of soil production. Uranium-series isotopes have been useful to provide such estimates independently of erosion rates. In this study, new U-series isotope are presented data from weathering profiles developed over andesitic parent rock in Puerto Rico, and granitic bedrock in southeastern Australia. The site in Australia is located on a highland plateau, neighbouring a retreating escarpment where soil production rates between 10 and 50 mm/kyr have been determined. The results show that production rates are invariant in these two regions of Australia with values between 15 and 25 mm/kyr for the new site. Andesitic soils show much faster rates, about 200 mm/kyr. Overall, soil production rates determined with U-series isotopes range between 10 and 200 mm/kyr. This is comparable to erosion rates in soil-mantled landscapes, but faster than erosion in cratonic areas and slower than in alpine regions and cultivated areas. This suggests that soil-mantled landscapes maintain soil because they can: there is a balance between production and erosion. Similarly, thick weathering profiles develop in cratonic areas

  15. Sustained Water Quality Impacts in Marine Environments Due to Mechanical Milling of Volcanic Deposits (United States)

    Genareau, K. D.; Cronin, S. J.; Stewart, C.; Back, E.


    Explosive volcanic eruptions are known to be a significant geohazard, but post- or inter-eruptive processes (such as lahars, landslides, and debris avalanches) can be equally damaging to local and regional areas by remobilizing deposits. Numerous studies have found that soluble salts bound to ash grain surfaces may be quickly released into exposed waters, often lowering pH and adding trace metals with both beneficial and deleterious effects on marine flora and fauna (e.g., Fe influx initiating blooms of marine phytoplankton). Most of the cation content of pyroclastic deposits is released slowly into the environment through weathering and alteration processes. However, other pathways exist through the physical comminution of pyroclasts in fluvial and marine settings. In this case, mechanical fracturing of pyroclasts during progressive stages of disaggregation will lead to exposure of reactive particle surfaces. This study evaluates the potential, ongoing effects on water quality by experimental, mechanical milling of pyroclasts and the evaluation of released metals into exposed waters using the pyroclastic density current deposits of both the 2010 eruption of Merapi and the 2014 eruption of Kelud (Java, Indonesia), which have a bulk basaltic andesite/andesite composition (60-65 wt% SiO2). The electrical conductivity (EC) of water samples positively correlates with Ca and Sr concentrations in the case of bulk ash, whole, and crushed lapilli, but correlates with Na for the milled samples. Compared to other stages of pyroclast disaggregation, milled lapilli have the greatest effect on the concentration of alkali elements and produce a significant increase in Ca, Na, K, and Si. Mechanical milling of pyroclasts grinds down minerals and glass, resulting in an increased EC, pH, and Na concentration of exposed waters. Similar experiments are currently being conducted using basalt (50 wt% SiO2) and rhyolite (70 wt% SiO2) deposits, and these results will be presented

  16. Geochemistry and U-Pb zircon geochronology of Late-Mesozoic lavas from Xishan, Beijing

    Institute of Scientific and Technical Information of China (English)

    YUAN; Honglin; LIU; Xiaoming; LIU; Yongsheng; GAO; Shan; LING; Wenli


    Zircon U-Pb dating by both SHRIMP and LA-ICP-MS and geochemical study of the Tiaojishan Formation and the Donglintai Formation from Xishan, Beijing, reveal that ages of upper lavas of Tiaojishan Formation and Middle of Donglintai Formation are 137.1±4.5 Ma(2σ) and 130-134 Ma, respectively. The fomer is slightly older than the latter and the age difference between these two formations is less than 5 Ma. These lines of evidence prove that the two volcanoes erupted within a short time. The age of the Tiaojishan Formation from Xishan, Beijing is distinctively different from that of the Chende Basin. This indicated that the ages of Tiaojishan lavas varied in different regions. The Tiaojishan Formation consists of typical adakite (SiO2=56%, Na2O = 3.99-6.17, Na2O/K2O = 2.2-3.1, Sr = 680-1074×10-6, Y = 13.2-16.3×10-6, Yb = 1.13-1.52×10-6, Sr/Y = 43-66), high-Mg adakite and high-Mg andesite (Mg# = 54-55). Features of continental crust of adakite from the Tiaojishan Formation and its syngeneric middle silicic vocanic rocks, such as typical Nd-Ta negative abnormality and Pb possive abnormality, indicate that these lavas are originated from partial melts of continental crust. These results suggest that the adakite from the Tiaojishan Formation of Xishan, Beijing derived from thickened eclogitic lower crust and lithosphere beneath the North China craton at mesozoic that was foundered into the aesthenosphere, and subsequenctly partially melted and interacted with mantle olivine during melts upward migration. The age of lavas from the Tiaojishan Formation restrained the foundation which should last at least until 137 Ma. Lavas of the Donglintai Formation are rhyolith and andesite with normal Mg# and thus they did not interact with the mantle. These lavas represent remobilized melts of lower crust material caused by mantle aesthenosphere upwelling migration induced by foundation.

  17. Modelling of Magma Density and Viscocity Changes and Their Influences towards the Characteristic of Kelud Volcano Eruption

    Directory of Open Access Journals (Sweden)

    Hanik Humaida


    Full Text Available DOI: 10.17014/ijog.v6i4.129The effusive eruption of Kelud Volcano in 2007 was different from the previous ones, which in general were more explosive. Among others, density and viscosity are factors that determine the type of eruption. Therefore, the study on the difference of the recent eruption style based on the density and viscosity of magma was carried out. The method used in this study was based on geochemical analysis of the rock and then a modeling was established by using the above parameter. The study on the explosive eruption was emphasized on the data of 1990 eruption, whereas the effusive eruption was based on the data of 2007 eruption. The result shows that the magma viscosity of Kelud Volcano depend on the H O concentration as one of the volatile compound in magma, and temperature which gives the exponential equation. The higher the increase of H O content the smaller the value of its viscosity as well as the higher the temperature. The H O content in silica fluid can break the polymer bond of the silica fluid, because a shorter polymer will produce a lower viscosity. The density of the silica content of Kelud Volcano ranges between andesitic and basaltic types, but andesite is more likely. The fluid density of the material of 1990 eruption is different from 2007 eruption. Compared to the 2007, the 1990 eruption material gave a lower density value in its silica fluid than that of the 2007 one. The low density value of the silica fluid of the 1990 eruption material was reflecting a more acid magma. The level of density value of silica fluid depends on its temperature. At the temperature of 1073 K the density of the 1990 Kelud magma is 2810 kg/m3 and the 2007 magma is 2818 kg/m3, whereas at a temperature of 1673 K, the density is 2672 kg/m3 and 2682 kg/m3 of the 1990 and 2007 eruptions respectively. A modeling by using an ideal gas law of Henry’s Law illustrated that the ascent of Kelud’s magma to the surface may cause changes

  18. Pre-breakup magmatism on the Vøring Margin: Insight from new sub-basalt imaging and results from Ocean Drilling Program Hole 642E (United States)

    Abdelmalak, M. M.; Meyer, R.; Planke, S.; Faleide, J. I.; Gernigon, L.; Frieling, J.; Sluijs, A.; Reichart, G.-J.; Zastrozhnov, D.; Theissen-Krah, S.; Said, A.; Myklebust, R.


    Improvements in sub-basalt imaging combined with petrological and geochemical observations from the Ocean Drilling Program (ODP) Hole 642E core provide new constraints on the initial breakup processes at the Vøring Margin. New and reprocessed high-quality seismic data allow us to identify a new seismic facies unit which we define as the Lower Series Flows. This facies unit is seismically characterized by wavy to continuous subparallel reflections with an internal disrupted and hummocky shape. Drilled lithologies, which we correlate to this facies unit, have been interpreted as subaqueous flows extruding and intruding into wet sediments. Locally, the top boundary of this facies unit is defined as a negative in polarity reflection and referred as the K-Reflection. This reflection can be correlated with the spatial extent of pyroclastic deposits, emplaced during transitional shallow marine to subaerial volcanic activities during the rift to drift transition. The drilled Lower Series Flows consist of peraluminous, cordierite bearing peperitic basaltic andesitic to dacitic flows interbedded with thick volcano-sedimentary deposits and intruded sills. The peraluminous geochemistry combined with available C (from calcite which fills vesicles and fractures), Sr, Nd, and Pb isotopes data points toward upper crustal rock-mantle magma interactions with a significant contribution of organic carbon rich pelagic sedimentary material during crustal anatexis. From biostratigraphic analyses, Apectodinium augustum was found in the Lower Series Flows. This dinoflagellate cyst species is a marker for the Paleocene - Eocene Thermal Maximum (PETM). However, based on very high stable carbon isotope ratios of bulk organic matter we exclude that these strata represent the PETM. This implies that A. augustum was reworked into the early Eocene sediments of this facies unit. Crucially, this unit predates the breakup time of the Vøring Margin. Finally, a conceptual emplacement model for the

  19. New approaches to inferences for steep-sided domes on Venus (United States)

    Quick, Lynnae C.; Glaze, Lori S.; Baloga, Stephen M.; Stofan, Ellen R.


    New mathematical approaches for the relaxation and emplacement of viscous lava domes are presented and applied to steep-sided domes on Venus. A similarity solution approach is applied to the governing equation for fluid flow in a cylindrical geometry for two distinct scenarios. In the first scenario, dome relaxation is explored assuming a constant volume of fluid (i.e. lava) has been rapidly emplaced onto the surface. Cooling of lava is represented by a time-variable viscosity and singularities inherent in previous models for dome relaxation have been eliminated. At the onset of relaxation, bulk dynamic viscosities lie in the range between 1010-1016 Pa s, consistent with basaltic-andesite to rhyolitic compositions. Plausible relaxation times range from 5 to 5000 years, depending on initial lava viscosity. The first scenario, however, is only valid during the final stages of dome relaxation and does not consider the time taken for lava to be extruded onto the surface. In the second scenario, emplacement and growth of a steep-sided dome is considered when the volume of lava on the surface increases over time (i.e. time-variable volume approach). The volumetric flowrate may depend on an arbitrary power of the dome thickness, thus embracing Newtonian as well as other rheologies for describing terrestrial and planetary mass flows. The approach can be used to distinguish between basic flowrate models for fluid emplacement. The formalism results in radial expansion of a dome proportional to t1/2, consistent with the diffusive nature of the governing equation. The flow at the front is shown to thicken as the front advances for a constant rate of lava supply. Emplacement times are intimately correlated with the bulk rheology. Comparison of the theoretical profiles with the shape of a typical dome on Venus indicates that a Newtonian bulk rheology is most appropriate, consistent with prior studies. However, results here suggest a bulk dynamic viscosity of 1012-1013 Pa s and

  20. The intra-oceanic Cretaceous (~ 108 Ma) Kata-Rash arc fragment in the Kurdistan segment of Iraqi Zagros suture zone: Implications for Neotethys evolution and closure (United States)

    Ali, Sarmad A.; Ismail, Sabah A.; Nutman, Allen P.; Bennett, Vickie C.; Jones, Brian G.; Buckman, Solomon


    The Kata-Rash arc fragment is an allochthonous thrust-bound body situated near Penjween, 100 km northeast of Sulymannia city, Kurdistan Region, within the Iraqi portion of the Zagros suture zone. It forms part of the suprasubduction zone 'Upper Allochthon' terranes (designated as the Gimo-Qandil Group), which is dominated by calc-alkaline andesite and basaltic-andesite, rhyodacite to rhyolite, crosscut by granitic, granodioritic, and dioritic dykes. Previously, rocks of the Kata-Rash arc fragment were interpreted as a part of the Eocene Walash volcanic group. However, SHRIMP zircon U-Pb dates on them of 108.1 ± 2.9 Ma (Harbar volcanic rocks) and 107.7 ± 1.9 Ma (Aulan intrusion) indicate an Albian-Cenomanian age, which is interpreted as the time of igneous crystallisation. The Aulan intrusion zircons have initial εHf values of + 8.6 ± 0.2. On a Nb/Yb-Th/Yb diagram, all Kata-Rash samples fall within the compositional field of arc-related rocks, i.e. above the mid-ocean-ridge basalt (MORB)-ocean island basalt (OIB) mantle array. Primitive-mantle-normalised trace-element patterns for the Kata-Rash samples show enrichment in the large ion lithophile elements and depletion in the high-field-strength elements supporting their subduction-related character. Low Ba/La coupled with low La/Yb and Hf/Hf* temperature melt from subducted slab sediment, in an oceanic setting. This mechanism can explain the sub-DM initial εHf value, without the need to invoke melting of significantly older (continental) crust in an Andean setting. We interpret the Kata-Rash igneous rocks as a fragment of the Late Cretaceous suprasubduction zone system (named here the Kata-Rash arc) that most likely developed within the Neotethys Ocean rather than at a continental margin. Subsequently during the latest Cretaceous to Paleocene, the arc was accreted to the northern margin of the Arabian plate. The results indicate a > 3000 km continuity of Cretaceous arc activity (Oman to Cyprus), that consumed

  1. Formation conditions of the Rudny Altai metallogenic province (United States)

    Kozlov, M. S.


    The results of previous geological, petrochemical, and metallogenic surveys conducted from the 1960s to the 1990s provide the geological and tectonic basis of this study. The unique mineral deposits of the Rudny Altai metallogenic province were formed in the Middle Paleozoic (S2-C1) at the junction between different structures of the Altai-Mongolian terrane: the Alei-Charysh-Tigirek rift (in the north) with the Korgon-Markakol' island arc and Belaya Uba-Maimyr intra-arc trough (in the southwest). The Rudny Altai structural-formational zone that formed at the junction between these structures evolved as a magmatic arc and was characterized by the formation of granite-greenschist arches, volcanoplutonic magmatism and high heat and fluid flow (greenschist-facies metamorphism of Upper Silurian-Upper Devonian rocks and deposition of pyrite-bearing hydrothermal-sedimentary horizons, VMS and copper-VMS deposits and isolated base-metal ore bodies). The tectonomagmatic history of the Rudny Altai zone can be subdivided into several stages: Ludlow-Emsian, Late Emsian-Givetian, Frasnian-Early Famennian, Middle Famennian-Early Visean, and Late Visean-Serpukhovian. The island arc is represented by volcanic rocks of the andesite-dacite-rhyolite (early stage), basalt-rhyolite (Late Emsian-Eifelian), and basalt-andesite-rhyolite series (Late Visean). Volcanosedimentary strata (until the Givetian age) and turbidites up to 3-5 km thick were deposited in the interarc trough. Because of their metastable behavior, the volcanic rocks became actively involved in ion-exchange reactions with the formational waters, whereas the differences in hydraulic head between arches and troughs created favorable conditions for the transport of the metamorphic fluids, and the thermal gradient promoted thermodiffusion of divalent species of Mg, Pb, Zn, Cu, etc. toward the high-temperature zone and development of the high-Mg metamorphic-metasomatic alteration with a VMS-base-metal mineralization. As a

  2. Physical volcanology, geochemistry and basin evolution of the Ediacaran volcano-sedimentary succession in the Bas Draâ inlier (Ouarzazate Supergroup, Western Anti-Atlas, Morocco) (United States)

    Karaoui, Brahim; Breitkreuz, Christoph; Mahmoudi, Abdelkader; Youbi, Nasrrddine


    New geologic mapping, lithofacies and granulometric analysis, and geochemistry from the volcano-sedimentary successions of the central part of the Bas Draâ inlier, Western Anti-Atlas, constrain the Ediacaran Ouarzazate Supergroup evolution during the post-collisional stage of the Pan-African orogeny. Volcanosedimentary facies analysis is the key aspect of the present contribution. We distinguished sixteen terrestrial volcanosedimentary lithofacies in the Bas Draâ succession (BDS), which reaches a total thickness of 2000 m. BDS evolution can be grouped into four units (Aouinet Aït Oussa I to IV, AO I-AO IV). The earliest volcanic activity produced rhyolitic ignimbrite sheets (AO I), which had been considered as lava flows by previous workers, and which were presumably related to caldera system(s). During AO II, a complex of high-silica andesitic and rhyolitic lavas formed, punctuated by the explosive eruption of a high-temperature silica-rich magma leading to the formation of parataxitic ignimbrite. AO III consists of basalt and andesite lava fields and small explosive, in parts phreatomagmatic volcanic vents. It is dissected by fluvial systems depositing external non-volcanic and local volcanic debris. BDS evolution terminated with the formation of a large SiO2-rich lava dome complex (AO IV), accompanied by small basalt effusive event. Volcanosedimentary facies analysis infers that the BDS evolved in a continental extensional setting developing in a low topography under humid paleoclimatic conditions. Alteration textures are dominated by a piemontite-calcite-albite-quartz (+ iron oxides) assemblage. Chemical analysis of BDS volcanic and subvolcanic rocks belongs to high-k calc-alkaline and alkali-calcic to alkaline magmatic trend typical for a post-collision setting. Trace elements spidergrams show a pattern typical for subduction-related suites of orogenic belts. REE patterns show moderate enrichment in LREE relative to flat HREE, with strong negative Eu

  3. Continental collision zones are primary sites for net continental crust growth — A testable hypothesis (United States)

    Niu, Yaoling; Zhao, Zhidan; Zhu, Di-Cheng; Mo, Xuanxue


    The significance of the continental crust (CC) on which we live is self-evident. However, our knowledge remains limited on its origin, its way and rate of growth, and how it has acquired the "andesitic" composition from mantle derived magmas. Compared to rocks formed from mantle derived magmas in all geological environments, volcanic arc rocks associated with seafloor subduction share some common features with the CC; both are relatively depleted in "fluid-insoluble" elements (e.g., Nb, Ta and Ti), but enriched in "fluid-soluble" elements (e.g., U, K and Pb). These chemical characteristics are referred to as the "arc-like signature", and point to a possible link between subduction-zone magmatism and CC formation, thus leading to the "island arc" model widely accepted for the origin of the CC over the past 45 years. However, this "island-arc" model has many difficulties: e.g., (1) the bulk arc crust (AC) is basaltic whereas the bulk CC is andesitic; (2) the AC has variably large Sr excess whereas the CC is weakly Sr deficient; and (3) AC production is mass-balanced by subduction erosion and sediment recycling, thus contributing no net mass to the CC growth, at least in the Phanerozoic. Our recent and ongoing studies on granitoid rocks (both volcanic and intrusive) formed in response to the India-Asia continental collision (~ 55 ± 10 Ma) show remarkable compositional similarity to the bulk CC with the typical "arc-like signature". Also, these syncollisional granitoid rocks exhibit strong mantle isotopic signatures, meaning that they were recently derived from a mantle source. The petrology and geochemistry of these syncollisional granitoid rocks are most consistent with an origin via partial melting of the upper ocean crust (i.e., last fragments of underthrusting ocean crust upon collision) under amphibolite facies conditions, adding net mantle-derived materials to form juvenile CC mass. This leads to the logical and testable hypothesis that continental collision

  4. Silicic Arc Magmas And Silicic Slab Melts: The Melt-Rock Reaction Link (United States)

    Straub, S. M.; Gomez-Tuena, A.; Bolge, L. L.; Espinasa-Perena, R.; Bindeman, I. N.; Stuart, F. M.; Zellmer, G. F.


    While a genetic link between silicic arc magmas and silicic melts from the subducted slab has long been proposed, this hypothesis is commonly refuted because most arc magmas lack a 'garnet-signature' which such slab melts must have. A comprehensive geochemical study of high-Mg# arc magmas from the Quaternary central Mexican Volcanic Belt (MVB), however, shows that this conflict can be reconciled if melt-rock reaction processes in the mantle wedge were essential to arc magma formation. In the central MVB, monogenetic and composite volcanoes erupt high-Mg# basalts to andesites with highly variable trace element patterns. These magmas contain high-Ni olivines (olivine Ni higher than permissible for olivines in partial peridotite melts) with high 3He/4He = 7-8 Ra that provide strong evidence for silicic slab components that infiltrate the subarc mantle to produce olivine-free segregations of 'reaction pyroxenite' in the sources of individual volcanoes. Melting of silica-excess and silica-deficient reaction pyroxenites can then produce high-Mg# basaltic and dacitic primary melts that mix during ascent through mantle and crust to form high-Mg# andesites. Mass balance requires that reaction pyroxenites contain at least >15-18 wt%, and likely more, of slab component. However, because the HREE of the slab component are efficiently retained in the eclogitic slab, elements Ho to Lu in partial melts from reaction pyroxenites remain controlled by the mantle and maintain MORB-normalized Ho/Lun ˜1.15 close to unity. In contrast, the MREE to LREE and fluid mobile LILE of the arc magmas are either controlled, or strongly influenced, by slab-contributions. The origin from hybrid sources also shows in the major elements that are blends of mantle-derived elements (Mg, Ca, Mn, Fe, Ti) and elements augmented by slab contributions (Si, Na, K, P, and possibly Al). Moreover, strong correlations between bulk rock SiO2, 87Sr/86Sr and δ18O (olivines) can be interpreted as mixtures of subarc

  5. Continental Crust Growth as a Result of Continental Collision: Ocean Crust Melting and Melt Preservation (United States)

    Niu, Y.; Zhao, Z.; Zhou, S.; Zhu, D.; Dong, G.; Mo, X.; Xie, G.; Dong, X.


    The significance of the continental crust (CC) on which we live is self-evident. However, our knowledge remains limited on its origin, its way and rate of growth, and how it has acquired the “andesitic” composition from mantle derived magmas. Compared to rocks formed from mantle derived magmas in all tectonic settings, volcanic arc rocks associated with oceanic lithosphere subduction share some common features with the CC; both are relatively depleted in “fluid-insoluble” elements (e.g., Nb, Ta and Ti), but enriched in “fluid-soluble” elements (e.g., U, K and Pb). These chemical characteristics are referred to as the “arc-like signature”, and point to a genetic link between subduction-zone magmatism and CC formation, thus leading to the “island-arc” model widely accepted for the origin of the CC over the past 40 years. However, it has been recognized also that this “island-arc” model has several difficulties. These include (1) bulk arc crust (AC) is basaltic, whereas the bulk CC is andesitic [1]; (2) AC has a variably large Sr excess whereas the CC is Sr deficient [2]; and (3) AC production is mass-balanced by subduction-erosion and sediment recycling, thus contributing no new mass to CC growth, at least in the Phanerozoic [3,4]. Our data on magmatic rocks (both volcanic and intrusive) formed during the India-Asia continental collision (~65 - ~45Ma) [5] show a remarkable compositional similarity to the bulk CC with the typical “arc-like signature” [6]. Also, these syncollisional felsic rocks exhibit strong mantle isotopic signatures, implying that they were recently derived from a mantle source. The petrology and geochemistry of these syncollisional felsic rocks is most consistent with an origin via partial melting of upper oceanic crust (i.e., last fragments of underthrusting oceanic crust) under amphibolite facies conditions, adding net mantle-derived materials to form juvenile CC mass. This leads to the logical and testable hypothesis

  6. Fossil slabs attached to unsubducted fragments of the Farallon plate. (United States)

    Wang, Yun; Forsyth, Donald W; Rau, Christina J; Carriero, Nina; Schmandt, Brandon; Gaherty, James B; Savage, Brian


    As the Pacific-Farallon spreading center approached North America, the Farallon plate fragmented into a number of small plates. Some of the microplate fragments ceased subducting before the spreading center reached the trench. Most tectonic models have assumed that the subducting oceanic slab detached from these microplates close to the trench, but recent seismic tomography studies have revealed a high-velocity anomaly beneath Baja California that appears to be a fossil slab still attached to the Guadalupe and Magdalena microplates. Here, using surface wave tomography, we establish the lateral extent of this fossil slab and show that it is correlated with the distribution of high-Mg andesites thought to derive from partial melting of the subducted oceanic crust. We also reinterpret the high seismic velocity anomaly beneath the southern central valley of California as another fossil slab extending to a depth of 200 km or more that is attached to the former Monterey microplate. The existence of these fossil slabs may force a reexamination of models of the tectonic evolution of western North America over the last 30 My. PMID:23509274

  7. Magnetic prospecting in Kaibuki-yama ancient tomb; Kaibukiyama kofun ni okeru zenjiryoku sokutei

    Energy Technology Data Exchange (ETDEWEB)

    Nishitani, T. [Akita University, Akita (Japan). Mining College


    Kaibuki-yama ancient tomb located in Kumeda, Kishiwada City, Osaka has a square shape in the front and an orbicular shape in the rear, which was considered to be made in the 4th century. This ancient tomb has a total length about 135 m, a diameter of orbicular shape in the rear about 82 m, and a height about 9 m, which is a symbolical existence of the Kumeda ancient tombs. Stone chamber and stone casket made of Sanbagawa crystalline schist or rhyolitic-andesitic tuff are expected in this tomb. Magnetic prospecting in this study is accompanied with this survey. A differential type proton magnetometer was used for the measurements, which were conducted using meshes with 1 m edges. A pair of distinct positive and negative magnetic anomalies were observed in the center of orbicular shape in the rear. This coincides with a location of main body buried, which is archaeologically estimated. The magnetic anomaly might be caused by the article buried in the tomb, such as ironware, based on the measurement of magnetic intensity. From the calculated values of magnetic anomaly using a model, the buried article with magnetic anomaly was considered to have a size with length of 1 m, width of 0.1 m, and height of 0.2m. The negative magnetic anomaly could not be explained only by this. It is necessary to consider the other reasons. 8 refs., 8 figs.

  8. Reactividad potencial de las rocas andesíticas de Cabo de Gata (SE de España

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    Soriano, J.


    Full Text Available Andesitic rocks produce an alkali-silica reaction with the components of the interstitial phase of concrete. This reaction can be considered as belonging to the slow-kinetic type, since the incongruent dissolution of the rock-forming minerals leads to the late formation of siliceous calc-alkaline gel. As a conquence, the conventional mortar-bar method does not detect such reaction until 90 days later.

    Las rocas andesíticas producen una reacción álcalis-sílice con los componentes de la fase intersticial del hormigón. Esta reacción puede encuadrarse dentro de las de cinética lenta, ya que la disolución incongruente de los minerales constituyentes de las rocas, da lugar a la formación tardía de geles silicocalco-alcalinos. En consecuencia, la utilización convencional del método de ensayo de barras de mortero no detecta la reacción hasta transcurridos al menos 90 días.

  9. Field Observation of Joint Structures in Various Types of Igneous Rocks (United States)

    Kano, Shingo; Tsuchiya, Noriyoshi


    In this study, field observations of natural fracture network systems in some intrusive and extrusive rocks were undertaken, to clarify the fracturing mechanism in the rocks. Shallow intrusives, whose depth of emplacement was less than several hundred metres, include the Momo-iwa Dacite dome on Rebun Island (Hokkaido), and Jodogahama Rhyolite in Iwate prefecture. Extrusive complexes studied include the Tojinbo Andesite and Ojima Rhyodacite in Fukui prefecture. Rocks of `granitic' composition were collected from the Takidani (Japan Alps) and Hijiori (Yamagata prefecture) plutons. The joint structure in Hijiori Granite was evaluated by analysis of core samples extracted from the HDR-3 geothermal production well. Based on detailed field observation, joint structures related to thermal contraction of a rock mass could be classified according to their inferred depth of formation. Joints from a near surface setting, such as shallow intrusive rocks and extrusives, tend to form pentagonal — hexagonal columnar structures (for a variety of rock types), whilst granitic rocks (from a deeper setting) typically exhibit a parallelepiped structure. The apparent differences in joint form are inferred to be dependent on the confining pressure, which acts on joint generation and propagation. In cases of non-confining pressure, such as the near-surface (shallow intrusive/extrusive) setting, joint networks typically form a columnar structure. On the contrary, confining pressure is considerably greater for deeper rock masses, and these form a parallelepiped joint structure.

  10. Comparison of Permeability and Groutability of Ostur Dam Site Rock Mass for Grout Curtain Design (United States)

    Sadeghiyeh, S. M.; Hashemi, M.; Ajalloeian, R.


    The focus of this study is the empirical hydromechanical behaviour of the Ostur dam site rock mass. The area surrounding the dam mostly consists of diorite and andesite, with primary fractures and hydrothermal veins. The hydromechanical behaviour of the rocks was determined using 500 water pressure tests at 5-m intervals. The hydrothermal veins and 2,739 discontinuities were studied and mapped along the dam axis. As a result, it was possible to design an optimum grout curtain for the dam axis. The empirical hydromechanical behaviour of the rock was studied to determine water flow and grout pressurised flow during the field tests that were conducted on two representative A-series grouting operation boreholes (one borehole for each abutment). The secondary permeability index (SPI), Lugeon value (LU), rock quality designation (RQD) and cement take (CT) values are presented and compared in this article. It is concluded that permeability and groutability are mostly controlled by the specifications and characteristics of the veins, especially in shallow areas and lower depths. A procedure is proposed based on a comparison of the trends in the RQD-SPI and LU-CT, and it is suggested that the areas with diverging trends require no treatment and that those with converging trends require heavy treatment. Additional complementary studies that were conducted during the construction stage have validated these results.

  11. Experimental assessment of the sealing effectiveness of rock fracture grouting

    International Nuclear Information System (INIS)

    The objective of this investigation is to determine the effectiveness of cement grouts as sealants of fractures in rock. Laboratory experiments have been conducted on seven 15-cm granite cubes containing saw cuts, three 23-cm diameter andesite cores containing induced tension cracks, and one 15-cm diameter marble core containing a natural fracture. Prior to grouting, the hydraulic conductivity of the fractures is determined under a range of normal stresses, applied in loading and unloading cycles, from 0 to 14 MPa (2000 psi). Grout is injected through an axial borehole, at a pressure of 1.2 to 8.3 MPa (180 to 1200 psi), pressure selected to provide a likely groutable fracture aperture, while the fracture is stressed at a constant normal stress. The fracture permeability is measured after grouting. Flow tests on the ungrouted samples confirm the inverse relation between normal stress and fracture permeability. The equivalent aperture determined by these tests is a reliable indicator of groutability. Postgrouting permeability measurements as performed here, and frequently in practice, can be misleading, since incomplete grouting of fractures can result in major apparent reductions in permeability. The apparent permeability reduction is caused by grouting of a small area of a highly preferential flowpath directly adjacent to the hole used for grouting and for permeability testing. Experimental results confirm claims in the literature that ordinary portland cement inadequately penetrates fine fractures

  12. Characterization of mesostasis regions in lunar basalts: Understanding late-stage melt evolution and its influence on apatite formation (United States)

    Potts, Nicola J.; TartèSe, Romain; Anand, Mahesh; Westrenen, Wim; Griffiths, Alexandra A.; Barrett, Thomas J.; Franchi, Ian A.


    Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile-bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk-rock basaltic composition and that of bulk-mesostasis regions, indicating that bulk-rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late-stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO2 abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite-melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.

  13. The timing of uplift, volcanism, and rifting peripheral to the Red Sea: a case for passive rifting? (United States)

    Bohannon, R.G.; Naeser, C.W.; Schmidt, D.L.; Zimmermann, R.A.


    Prior to the formation of the Red Sea the northeastern Afro/Arabian continent had low relief and was largely below sea level from the Late Cretaceous to the early Oligocene. The events leading to the formation of the Red Sea followed the sequence (1) alkaline volcanism and rifting beginning about 30-32 Ma affecting a narrow linear zone in the continent, (2) rotational block faulting and detachment faulting, well underway by 25 Ma, (3) gabbro and diorite magmatism, andesite to rhyolite volcanism, and fine-grained nonmarine sedimentation in the rift between 20 and 25 Ma, (4) fine-grained marine sedimentation in the rift as the early shelves started to subside in the middle Miocene, and (5) uplift of the adjacent continents (about 3 km) and subsidence of the shelves (about 4 km) between 13.8 and 5 Ma. The youth of the uplift is suggested by 44 fission track dates on apatites from rocks of the Proterozoic Arabian Shield that range in age from 13.8 to 568 Ma. The youngest of these ages, coupled with the present high relief along the Arabian escarpment and published heat flow measurements, indicate that 2.5-4 km uplift has occurred in the last 13.8 m.y. -from Authors

  14. Dispersal of key subplinian-Plinian tephras from Hekla volcano, Iceland: implications for eruption source parameters (United States)

    Janebo, Maria H.; Thordarson, Thorvaldur; Houghton, Bruce F.; Bonadonna, Costanza; Larsen, Gudrun; Carey, Rebecca J.


    Hekla is the most active silicic volcano in Iceland, with 18 subplinian-Plinian eruptions since AD 1104. In the period 1970 to 2000, the frequency of such eruptions increased to once every decade. Hekla is currently inflated to above the levels observed prior to the most recent eruptions in 1991 and 2000. The next eruption could pose a hazard to air traffic between North America and Europe because explosive eruptions of Hekla, independent of size, typically start with a subplinian or Plinian phase that produces a sustained ash plume. We present an overview of five of the largest historical Hekla eruptions (taking place in 1104, 1158, 1300, 1693, and 1766). These eruptions cover a compositional range of rhyolite to andesite, previously estimated Volcanic Explosivity Index (VEI) values of 4-5 and are characterised by contrasting wind dispersal (dispersal axes NW-NE). New isopach maps show both greater deposit thicknesses in the proximal region and wider dispersal than previously inferred, resulting in different volume estimates (minimal values ranging between 0.18 and 0.91 km3). New isopleth maps were also compiled and resulted in inferred plume heights of about 13-25 km. These changes in the estimated values of volume and mass eruption rates have large implications on the forecasting and impacts of future Hekla eruptions.

  15. Geologic map of the Harvard Lakes 7.5' quadrangle, Park and Chaffee Counties, Colorado (United States)

    Kellogg, Karl S.; Lee, Keenan; Premo, Wayne R.; Cosca, Michael A.


    The Harvard Lakes 1:24,000-scale quadrangle spans the Arkansas River Valley in central Colorado, and includes the foothills of the Sawatch Range on the west and Mosquito Range on the east. The Arkansas River valley lies in the northern end of the Rio Grande rift and is structurally controlled by Oligocene and younger normal faults mostly along the west side of the valley. Five separate pediment surfaces were mapped, and distinctions were made between terraces formed by the Arkansas River and surfaces that formed from erosion and alluviation that emanated from the Sawatch Range. Three flood deposits containing boulders as long as 15 m were deposited from glacial breakouts just north of the quadrangle. Miocene and Pliocene basin-fill deposits of the Dry Union Formation are exposed beneath terrace or pediment deposits in several places. The southwestern part of the late Eocene Buffalo Peaks volcanic center, mostly andesitic breccias and flows and ash-flow tuffs, occupy the northeastern corner of the map. Dated Tertiary intrusive rocks include Late Cretaceous or early Paleocene hornblende gabbro and hornblende monzonite. Numerous rhyolite and dacite dikes of inferred early Tertiary or Late Cretaceous age also intrude the basement rocks. Basement rocks are predominantly Mesoproterozoic granites, and subordinately Paleoproterozoic biotite gneiss and granitic gneiss.

  16. Effect of sintering temperature and boron carbide content on the wear behavior of hot pressed diamond cutting segments

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    Islak S.


    Full Text Available The aim of this study was to investigate the effect of sintering temperature and boron carbide content on wear behavior of diamond cutting segments. For this purpose, the segments contained 2, 5 and 10 wt.% B4C were prepared by hot pressing process carried out under a pressure of 35 MPa, at 600, 650 and 700 °C for 3 minutes. The transverse rupture strength (TRS of the segments was assessed using a three-point bending test. Ankara andesite stone was cut to examine the wear behavior of segments with boron carbide. Microstructure, surfaces of wear and fracture of segments were determined by scanning electron microscopy (SEM-EDS, and X-ray diffraction (XRD analysis. As a result, the wear rate decreased significantly in the 0-5 wt.% B4C contents, while it increased in the 5-10 wt.% B4C contents. With increase in sintering temperature, the wear rate decreased due to the hard matrix.

  17. Unusual diagenetic alteration of volcanoclastic sediments in the Tonga fore-are: Evidence from chemical and strontium isotopic compositions of interstitial waters (United States)

    Blanc, Gérard; Vitali, Frédéric; Stille, Peter


    The depth variations in the major chemical components dissolved in interstitial waters from the Tonga margin (ODP Site 841) are much more pronounced than those usually observed in deep-sea sediments. The extensive alteration of volcanic Miocene sediments to secondary minerals such as analcime, clays, and thaumasite forms a CaCl 2-rich brine. The brine results from a high exchange of Ca to Na, K, and Mg and an increase in Cl concentrations due to removal of H 2O from the fluid during the authigenesis of hydrous minerals. The formation of thaumasite could have partly controlled the concentration of dissolved SO 4, HCO 3, and Ca in the Miocene sediments. The strontium isotopic signature of the interstitial water suggests that alteration of the volcanic Miocene sediments occurred a long time after sedimentation. A transient diffusion model indicates that molecular diffusion was not prevented by lithologic barriers and that the formation of secondary minerals in the Miocene sediment occurred over a short period of time (e.g.,≤1,000 years). The extensive diagenetic processes in the Tonga margin were mostly caused by the recent intrusion of andesite sills and dikes into the Miocene sediments.

  18. Geochemical characteristics and petrogenesis of Mesozoic basalts from the North China Craton: A case study in Fuxin, Liaoning Province

    Institute of Scientific and Technical Information of China (English)


    Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalts occur as volcanic channel phases with well-developed columnar jointings and contain few spinel lherzolite and pyroxenite xenoliths. They are poor in silica and rich in alkalis, Ti and Al, belonging to alkaline basalts. In trace element compositions, Jianguo basalts are moderately enriched in LREE and LILE, but not depleted in HFSE. They have low Sr and high Nd and Pb isotopic ratios. These geochemical characteristics suggest that Jianguo basalts originated from the depleted asthenosphere, representing an undifferentiated and uncontaminated primitive magma. Presence of these basalts indicates that the lithosphere beneath the region had thickness less than 65 km at the time of basalt eruption and was mainly composed of fertile pargasite-bearing spinel lherzolite and plagioclase pyroxenite. The voluminous basaltic-andesitic magmatism during the early Jurassic-late Cretaceous time indicates that the commencement and accomplishment of lithosphere thinning in the NNCC was much earlier than that in the southern margin, since the mafic-intermediate volcanism only occurred at the Cretaceous time in the southern margin and the basalts with an asthenosphere isotopic signature at the Tertiary. This shows that highly spatial and temporal heterogeneity existed in the Mesozoic lithosphere evolution.

  19. Hubungan Kumpulan Mineral Berat pada Sedimen Pantai dan Lepas Pantai dengan Batuan Asal Darat di Perairan Teluk Pelabuhan Ratu, Jawa Barat

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    Deny Setiady


    Full Text Available DOI: 10.17014/ijog.v5i1.93Based on the depth contour, the sea bottom morphology in southern part of the researched area is very steep, while in the northern area it is sloped slightly. It shows that sedimentation process is from south to the north and continues to the west. It is supported by the current process in studied area. Rock slope stability of hilly morphology in the Cimandiri River area is related to weathering, erosion, and transportation process in coastal and nearshore areas. The presence of mineral in the studied area caused by those processes, was accumulated in the mouth of Cimandiri River, coastal, and nearshore areas. Those minerals were deposited in Cibelendung to Karangbeureum nearshore area by the longshore current. Magnetite and pyroxene minerals are dominant along the coastal and offshore areas of Pelabuhan Ratu Bay. The presence of augite and diopside shows that the source rock is basic igneous rocks (basalt, while the presence of hornblende and biotite minerals tend to indicate that the source rock is intermediate igneous rocks (andesite.


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    V. A. Vanin


    Full Text Available Metamorphosed volcanic rocks of the Ushmukan suite were studied in the Mukodek gold-ore field located in the Baikal-Muya belt in the Northern Baikal area, Russia. The Ushmukan suite shows interleaving of orto