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Sample records for volcanic rocks occur

  1. Volcanic Rocks and Features

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Volcanoes have contributed significantly to the formation of the surface of our planet. Volcanism produced the crust we live on and most of the air we breathe. The...

  2. Fluid and rock interaction in permeable volcanic rock

    International Nuclear Information System (INIS)

    Lindley, J.I.

    1985-01-01

    Four types of interrelated changes -geochemical, mineralogic, isotopic, and physical - occur in Oligocene volcanic units of the Mogollon-Datil volcanic field, New Mexico. These changes resulted from the operation of a geothermal system that, through fluid-rock interaction, affected 5 rhyolite ash-flow tuffs and an intercalated basaltic andesite lava flow causing a potassium metasomatism type of alteration. (1) Previous studies have shown enrichment of rocks in K 2 O as much as 130% of their original values at the expense of Na 2 O and CaO with an accompanying increase in Rb and decreases in MgO and Sr. (2) X-ray diffraction results of this study show that phenocrystic plagioclase and groundmass feldspar have been replaced with pure potassium feldspar and quartz in altered rock. Phenocrystic potassium feldspar, biotite, and quartz are unaffected. Pyroxene in basaltic andesite is replaced by iron oxide. (3) delta 18 O increases for rhyolitic units from values of 8-10 permil, typical of unaltered rock, to 13-15 permil, typical of altered rock. Basaltic andesite, however, shows opposite behavior with a delta 18 of 9 permil in unaltered rock and 6 permit in altered. (4) Alteration results in a density decrease. SEM revealed that replacement of plagioclase by fine-grained quartz and potassium feldspar is not a volume for volume replacement. Secondary porosity is created in the volcanics by the chaotic arrangement of secondary crystals

  3. Cenozoic volcanic rocks of Saudi Arabia

    Science.gov (United States)

    Coleman, R.G.; Gregory, R.T.; Brown, G.F.

    2016-01-01

    The Cenozoic volcanic rocks of Saudi Arabia cover about 90,000 km2, one of the largest areas of alkali olivine basalt in the world. These volcanic rocks are in 13 separate fields near the eastern coast of the Red Sea and in the western Arabian Peninsula highlands from Syria southward to the Yemen Arab Republic.

  4. Groundwater characteristics and problems in volcanic rock terrains

    International Nuclear Information System (INIS)

    Custodio, E.

    1989-01-01

    Volcanic rock formations, each with their own particular hydrogeological characteristics, occur in circumstances that cover a multiplicity of situations. These range from permeable porous rock formations to permeable fissured formations and include all types of intermediate situation between the two. The type of volcanism, distance from the source of emission, age, alteration processes and tectonics are all factors which determine their behaviour. Volcanic formations usually constitute a single aquifer system, even though this may be very heterogeneous and may locally be separated into clearly defined subunits. At times, formations may be hundreds of metres thick and are fairly permeable almost throughout. As a rule, volcanic material does not yield directly soluble salts to the water that flows through it. Mineralization of the water is due to the concentration of rainfall and the hydrolysis of silicates as a result of CO 2 being absorbed from the atmosphere and the ground, or as a result of volcanism itself. Cationic grouping is usually closely correlated to that of the rock formation in which the chemical composition is formed. Most environmental isotope and radioisotope techniques may be used, and at times are of unquestionable value. However, the existence of evaporation in the soil with possible isotopic fractionation, the effects of marked relief, the dilution of dissolved carbon by volcanic carbon and isotopic exchange brought about by volcanic carbon, etc., should be taken into account before valid conclusions are drawn. The paper uses examples taken from existing studies, mainly those being carried out in the Canary Islands (Spain). (author). 98 refs, 18 figs, 4 tabs

  5. Tungsten abundances in some volcanic rocks

    International Nuclear Information System (INIS)

    Helsen, J.N.; Shaw, D.M.; Crocket, J.H.

    1978-01-01

    A radiochemical N.A.A. method was used to obtain new values on W distribution in some 125 volcanic rocks, mainly basalts and andesites, from different petrotectonic environments. These W data are below previously reported abundances. New median values in various types of rocks are suggested (ppm W). Basalts: ocean floor, 0.15; ocean islands subalkaline, 0.28; ocean islands alkaline, 0.60; island arc, 0.19; continental margin, 0.40; continental subalkaline, 0.30; continental alkaline, 1.35. Andesites: island arc, 0.23; continental margin, 1.05. Median values for all 91 basalts and all 20 andesites are 0.36 and 0.29 ppm respectively. (author)

  6. Compositional Differences between Felsic Volcanic rocks from the ...

    African Journals Online (AJOL)

    The elemental and Sr-Nd isotopic compositions of the volcanic rocks suggest that fractional crystallization from differing basic parents accompanied by a limited assimilation (AFC) was the dominant process controlling the genesis of the MER felsic volcanic rocks. Keywords: Ethiopia; Northern Main Ethiopian Rift; Bimodal ...

  7. Viscosity characteristics of selected volcanic rock melts

    Science.gov (United States)

    Hobiger, Manuel; Sonder, Ingo; Büttner, Ralf; Zimanowski, Bernd

    2011-02-01

    A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic rocks using wide gap viscometry. The complex composition of magmatic melts leads to complicated rheologic behavior which cannot be described with one simple model. Therefore, measurement procedures which are able to quantify non-Newtonian behavior have to be employed. Furthermore, the experimental apparatus must be able to deal with inhomogeneities of magmatic melts. We measured the viscosity of a set of materials representing a broad range of volcanic processes. For the lower viscous melts (low-silica compositions), non-Newtonian behavior is observed, whereas the high-silica melts show Newtonian behavior in the measured temperature and shear rate range (T = 1423 K - 1623 K, γ˙ = 10 - 2 s - 1 - 20 s - 1 ). The non-Newtonian materials show power-law behavior. The measured viscosities η and power-law indexes m lie in the intervals 8 Pa s ≤ η ≤ 210 3 Pa s, 0.71 ≤ m ≤ 1.0 (Grímsvötn basalt), 0.9 Pa s ≤ η ≤ 350 Pa s, 0.61 ≤ m ≤ 0.93 (Hohenstoffeln olivine-melilitite), and 8 Pa s ≤ η ≤ 1.510 4 Pa s, 0.55 ≤ m ≤ 1.0 (Sommata basalt). Measured viscosities of the Newtonian high-silica melts lie in the range 10 4 Pa s ≤ η ≤ 310 5 Pa s.

  8. An Overview of the Soutpansberg Sedimentary and Volcanic Rocks

    Directory of Open Access Journals (Sweden)

    J.W. Bristow

    1986-11-01

    Full Text Available Volcanic and sedimentary rocks occupy a faulted graben within the previously uplifted and eroded high-grade gneiss terrain of the Limpopo Mobile Belt. The rocks comprise the Soutpansberg Group and represent an important sequence of Proterozoic rocks. Their general geology and volcanology is summarised in this paper.

  9. The phosphorus status of andisols as influenced by nanoparticles of volcanic ash and rock phosphate

    Science.gov (United States)

    Devnita, Rina; Joy, Benny; Arifin, Mahfud; Setiawan, Ade; Rosniawaty, Santi; Meidina, Felia Shella

    2018-02-01

    Andisols need to be ameliorated to improve the phosphorus status. The objective of this research is to investigate the effect of nanoparticles of volcanic ash and rock phosphate as ameliorants in Andisols to P-retention, available P and potential P in Andisols. The research used a complete randomized experimental design in factorial with two factors. The first factor was nanoparticle of volcanic ash (a) and the second factor was rock phosphate (p). Both ameliorants consist of four doses on soil weight percentage (0%, 2.5%, 5.0% and 7.5%). The combined treatments were replicated three times. The soil and treatments were mixed and incubated for 4 months. Soil samples were taken after one month and four months of incubation to be analyzed the P-retention, available P and potential P. The results showed that there are interactions between the volcanic ash and rock phosphate on available P and potential P after one month of incubation. However, there were no interactions occurring between the volcanic ash and rock phosphate on P-retention after one and four months of incubation and no interactions on available P and potential P after four months. The best combined treatments in increasing available P and potential P after one month was obtained in 2.5% of volcanic ash and 5% of rock phosphate that increased available P to 405.75 ppm. The 2.5% of volcanic ash and 7.5% of rock phosphate increased potential P to 2190.26 mg/100 g. Independently, 7.5% of volcanic ash and rock phosphate decreased P-retention to 71.49% after one month and 89.74% after four months. Higher effect on the application of nanoparticle of volcanic ash and rock phosphate to the phosphorus status of Andisols recieved after one month of incubation is compared with four months of incubation.

  10. Strength and deformation properties of volcanic rocks in Iceland

    DEFF Research Database (Denmark)

    Foged, Niels Nielsen; Andreassen, Katrine Alling

    2016-01-01

    rock from Iceland has been the topic for rock mechanical studies carried out by Ice-landic guest students at the Department of Civil Engineering at the Technical University of Den-mark over a number of years in cooperation with University of Iceland, Vegagerðin (The Icelandic Road Directorate......) and Landsvirkjun (The National Power Company of Iceland). These projects involve engineering geological properties of volcanic rock in Iceland, rock mechanical testing and parameter evaluation. Upscaling to rock mass properties and modelling using Q- or GSI-methods have been studied by the students......Tunnelling work and preinvestigations for road traces require knowledge of the strength and de-formation properties of the rock material involved. This paper presents results related to tunnel-ling for Icelandic water power plants and road tunnels from a number of regions in Iceland. The volcanic...

  11. Transition of neogene arc volcanism in central-western Hokkaido, viewed from K-Ar ages, style of volcanic activity, and bulk rock chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Hirose, Wataru; Iwasaki, Miyuki; Nakagawa, Mitsuhiro [Hokkaido Univ., Sapporo (Japan)

    2000-02-01

    Spatial and temporal variations in late Cenozoic volcanism of southwestern Hokkaido at the northern end of NE-Japan arc have been clarified by 261 K-Ar and 76 FT ages including 49 newly determined K-Ar ages, volcanic stratigraphy, physical volcanology and whole-rock geochemistry. Arc volcanism characterized by rocks with low-Ti and Nb, and by across-arc increase in K{sub 2}O content in these rocks has continued at least since 12 Ma. Based on volcanic stratigraphy, physical volcanology and whole-rock geochemistry, volcanism after 12 Ma can be subdivided into 4 stages, 12-5, 5-1.7, and 1.7-0 Ma. The volcanism from 12 Ma to 5 Ma extended northward widely compared with distribution of Quaternary arc volcanism (1.7-0 Ma). This suggests that the arc trench junction between Kuril and NE-Japan arc's trenches was located about 100 km northward from the present position. Since around 5 Ma until 1.7 Ma, different type of volcanism under local extension field, characterized by a group of monogenetic volcanoes of alkali basalt and shield volcanoes of calc-alkaline andesite, had occurred at northern end of the volcanic region (Takikawa-Mashike region). During and after this volcanism, the northern edge of arc volcanism in the area has migrated southward. This suggests that the trench junction has migrated about 100 km southward since {approx}5 Ma. The quaternary arc volcanism (1.7-0 Ma) has been restricted at the southern part of the region. The volcanism since 12 Ma might be influenced by oblique subduction of Pacific plate beneath Kuril arc, resulting in the formation of local back arc basin at the junction and to southward migration of the trench junction. (author)

  12. Assessment and Evaluation of Volcanic Rocks Used as Construction ...

    African Journals Online (AJOL)

    Assessment and Evaluation of Volcanic Rocks Used as Construction Materials in the City of Addis Ababa. ... So, field observation and sample collection for laboratory investigations were conducted on six selected target areas of the city periphery. In doing so, the compressive strength, open porosity, water absorption and ...

  13. Permeability of volcanic rocks to gas and water

    Science.gov (United States)

    Heap, M. J.; Reuschlé, T.; Farquharson, J. I.; Baud, P.

    2018-04-01

    The phase (gas or liquid) of the fluids within a porous volcanic system varies in both time and space. Laboratory experiments have shown that gas and water permeabilities can differ for the same rock sample, but experiments are biased towards rocks that contain minerals that are expected react with the pore fluid (such as the reaction between liquid water and clay). We present here the first study that systematically compares the gas and water permeability of volcanic rocks. Our data show that permeabilities to argon gas and deionised water can differ by a factor between two and five in two volcanic rocks (basalt and andesite) over a confining pressure range from 2 to 50 MPa. We suggest here that the microstructural elements that offer the shortest route through the sample-estimated to have an average radius 0.1-0.5 μm using the Klinkenberg slip factor-are accessible to gas, but restricted or inaccessible to water. We speculate that water adsorption on the surface of these thin microstructural elements, assumed here to be tortuous/rough microcracks, reduces their effective radius and/or prevents access. These data have important implications for fluid flow and therefore the distribution and build-up of pore pressure within volcanic systems.

  14. Unzen volcanic rocks as heat source of geothermal activity

    Energy Technology Data Exchange (ETDEWEB)

    Hayashi, Masao; Sugiyama, Hiromi

    1987-03-25

    Only a few radiometric ages have been reported so far for the Unzen volcanic rocks. In this connection, in order to clarify the relation between volcanism and geothermal activity, fission track ages of zircon seperated from the Unzen volcanic rocks in western Kyushu have been dated. Since all the rocks are thought to be young, the external surface re-etch method was adopted. The results are that the age and standard error of the basal volcaniclastic rocks of the Tatsuishi formation are 0.28 +- 0.05 Ma and 0.25 +- 0.05 Ma. The next oldest Takadake lavas range from 0.26 to 0.20 Ma. The Kusenbudake lavas fall in a narrow range from 0.19 to 0.17 Ma. The latest Fugendake lavas are younger than 0.07 Ma.In conclusion, the most promising site for geothermal power generation is the Unzen hot spring field because of its very high temperature. After that, comes the Obama hot spring field because of the considerable high temperature chemically estimated. In addition, the northwestern area of the Unzen volcanic region will be promising for electric power generation in spite of no geothermal manifestations, since its volcanos are younger than 0.2 Ma. (14 figs, 14 tabs, 22 refs)

  15. Geology and zircon fission track ages of volcanic rocks in the western part of Hoshino gold area, Fukuoka Prefecture, Japan

    Energy Technology Data Exchange (ETDEWEB)

    Belhadi, Ahmed; Himeno, Osamu; Watanabe, Koichiro; Izawa, Eiji [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering

    1999-12-01

    The Hoshino gold area is located in the western part of the Hohi volcanic zone, northern Kyushu. Volcanic rocks in this area vary from andesitic rocks in the north to dacite and rhyolite in the South. The basement is constituted by metamorphic rocks of pre-Cretaceous age. The volcanic rocks of Pliocene age were subdivided into eight volcanic units. Seven fission track ages of zircons from five volcanic units have been determined, using the external detector method. The age data obtained, combined with some previously reported ages, show that two main volcanic activities have occurred in the area. The first volcanic activity took place around 4.3 Ma, and resulted into the deposition of the Hoshino Andesite and the Ikenoyama Conglomerate. The second main volcanism started around 3.5 Ma, and was characterized by the eruption of the Shakadake Andesite and the Reiganji Andesite at the early stage, then, by more acidic rocks of the Takeyama Andesite, the Hyugami Dacite and the Kuroki Rhyolite at the later stage. The main volcanism in the area ceased around 2.6 Ma. (author)

  16. Fluorine geochemistry in volcanic rock series

    DEFF Research Database (Denmark)

    Stecher, Ole

    1998-01-01

    A new analytical procedure has been established in order to determine low fluorine concentrations (30–100 ppm F) in igneous rocks, and the method has also proven successful for higher concentrations (100–4000 ppm F). Fluorine has been measured in a series of olivine tholeiites from the Reykjanes ...

  17. Geochemical characterization of Parana Basin volcanic rocks: petrogenetic implications

    International Nuclear Information System (INIS)

    Marques, L.S.

    1988-01-01

    A detailed study of the geochemical characteristics of Parana Basin volcanic rocks is presented. The results are based on the analyses of major and trace elements of 158 samples. Ninety three of these volcanic samples belong to 8 flow sequences from Rio Grande do Sul and Santa Catarina States. The remaining sixty five samples are distributed over the entire basin. In order to study the influence of crustal contamination processes in changing chemical characteristics of the volcanic rocks, 47 samples representative of the crystalline basement of the southern and southeastern Parana Basin were also analysed. Several petrogenetic models were tested to explain the compocional variability of the volcanic rocks, in particular those of southern region. The results obtained sugest an assimilation-fractional crystallization process as viable to explain the differences of both the chemical characteristics and Sr isotope initial ratios observed in basic and intermediate rocks. A model involving melting processes of basic material, trapped at the base of the crust, with composition similar to low and high TiO 2 basalts appears to be a possibility to originate the Palmas and Chapeco acid melts, respectively. The study of ''uncontaminated'' or poorly contaminated low TiO 2 basic rocks from the southern, central and northern regions shows the existence of significant differences in the geochemical charactetistics according to their geographical occurrence. A similar geochemical diversity is also observed in high TiO 2 basalts and Chapeco volcanics. Differences in incompatible element ratios between low and high TiO 2 ''uncontaminated'' or poorly contaminated basalts suggest that they could have been produced by different degrees of melting in a garnet peridotite source. Geochemical and isotopic (Sr and Nd) data also support the view that basalts from northern and southern regions of Parana Basin originated from mantle source with different composition. (author) [pt

  18. 40Ar/39Ar ages of the post-collision volcanic rocks and their geological significance in Yangyingxiang area, south Tibet

    International Nuclear Information System (INIS)

    Zhou Su; Mo Xuanxue; Zhao Zhidan; Zhang Shuangquan; Guo Tieying; Qiu Ruizhao

    2003-01-01

    Ten new 40 Ar/ 39 Ar age determination of mineral separates have been carried out to date volcanic rocks of Yangyingxiang in the eastern part of the Gangdese, Tibet. The age range of Sanidine and biotite in the five volcanic rock samples from the Yangyingxiang is 10.68 ± 0.05 - 11.42 ± 0.09 Ma. These results, combining with the previously published data, confirmed that Neogene post-collision volcanic rocks in the Gangdese widely occurred and their ages were getting younger eastwards. These volcanic rocks are different from those in Pana Formation of Linzizhong group (52.9 ± 2 Ma) outside Yangyingxiang geothermal field. (authors)

  19. Ejection age of volcano rocks and trend of volcanic activity

    Energy Technology Data Exchange (ETDEWEB)

    Sakaguchi, Keiichi

    1987-10-01

    This report is II-7 of an interim report on research and development of the Sunshine Project for 1986. This report considers on the trend of volcanic activities in the South of Kyushu area. K-Ar age measurement was newly made and reported. Age values obtained were 1.09 plus minus 0.21 Ma for Nagaoyama andesite, 1.33 plus minus 0.18 Ma for Nozato andesite, and 0.3 plus minus 0.1 Ma for Imuta volcanos. Including these age values, from the age values and their distribution of the volcanic rocks in the South Kyushu district, the following three districts were selected to represent the volcanic activities since the Pliocene Epoch. As these districts are mutually overwrapped, verification at these overwrapped districts are necessary. (4 figs, 1 tab, 12 refs)

  20. A preliminary evaluation of volcanic rock powder for application in agriculture as soil a remineralizer

    Energy Technology Data Exchange (ETDEWEB)

    Ramos, Claudete G., E-mail: claudeterms@brturbo.com.br [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil); Querol, Xavier [Institute of Environmental Assessment and Water Research (IDÆA-CSIC), C/Luis Solé y Sabarís s/n, 08028 Barcelona (Spain); Oliveira, Marcos L.S. [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil); Pires, Karen [Departamento Nacional de Produção Mineral (DNPM), Washington Luiz, 815, Centro, 90010-460 Porto Alegre, RS (Brazil); Kautzmann, Rubens M. [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil); Oliveira, Luis F.S., E-mail: felipeqma@hotmail.com [Laboratory of Environmental Researches and Nanotechnology Development, Centro Universitário La Salle, Mestrado em Avaliação de Impactos Ambientais, Victor Barreto, 2288 Centro, 92010-000 Canoas, RS (Brazil)

    2015-04-15

    Mineralogical and geochemical characteristics of volcanic rock residue, from a crushing plant in the Nova Prata Mining District, State of Rio Grande do Sul (RS), Brazil, in this work named rock powder, were investigated in view of its potential application as soil ammendment in agriculture. Abaut 52,400 m{sup 3} of mining waste is generated annually in the city of Nova Prata without a proper disposal. The nutrients potentially available to plants were evaluated through leaching laboratory tests. Nutrient leaching tests were performed in Milli-Q water; citric acid solution 1% and 2% (AC); and oxalic acid solution 1% and 5% (AO). The bulk and leachable contents of 57 elements were determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Mining waste were made up by CaO, K{sub 2}O, SiO{sub 2}, Al{sub 2}O{sub 3}, Fe{sub 2}O{sub 3}, and P{sub 2}O{sub 5}. The analysis by X-ray diffraction (XRD) showed the major occurence of quartz, anorthite, cristobalite, sanidine, and augite. The water leachable concentrations of all elements studied were lower than 1.0 mg/kg, indicating their low solubility. Leaching tests in acidic media yield larger leachable fractions for all elements being studied are in the leachate of the AO 1%. These date usefulness of volcanic rock powder as potential natural fertilizer in agriculture in the mining district in Nova Prata, Rio Grande do Sul, Brazil to reduce the use of chemical fertilizers. - Highlights: • Volcanic rock powder as fertilizer in agriculture • Volcanic rock powder as a source of nutrients to plants • This technology may favor the use of volcanic rock in agriculture.

  1. A preliminary evaluation of volcanic rock powder for application in agriculture as soil a remineralizer

    International Nuclear Information System (INIS)

    Ramos, Claudete G.; Querol, Xavier; Oliveira, Marcos L.S.; Pires, Karen; Kautzmann, Rubens M.; Oliveira, Luis F.S.

    2015-01-01

    Mineralogical and geochemical characteristics of volcanic rock residue, from a crushing plant in the Nova Prata Mining District, State of Rio Grande do Sul (RS), Brazil, in this work named rock powder, were investigated in view of its potential application as soil ammendment in agriculture. Abaut 52,400 m 3 of mining waste is generated annually in the city of Nova Prata without a proper disposal. The nutrients potentially available to plants were evaluated through leaching laboratory tests. Nutrient leaching tests were performed in Milli-Q water; citric acid solution 1% and 2% (AC); and oxalic acid solution 1% and 5% (AO). The bulk and leachable contents of 57 elements were determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Mining waste were made up by CaO, K 2 O, SiO 2 , Al 2 O 3 , Fe 2 O 3 , and P 2 O 5 . The analysis by X-ray diffraction (XRD) showed the major occurence of quartz, anorthite, cristobalite, sanidine, and augite. The water leachable concentrations of all elements studied were lower than 1.0 mg/kg, indicating their low solubility. Leaching tests in acidic media yield larger leachable fractions for all elements being studied are in the leachate of the AO 1%. These date usefulness of volcanic rock powder as potential natural fertilizer in agriculture in the mining district in Nova Prata, Rio Grande do Sul, Brazil to reduce the use of chemical fertilizers. - Highlights: • Volcanic rock powder as fertilizer in agriculture • Volcanic rock powder as a source of nutrients to plants • This technology may favor the use of volcanic rock in agriculture

  2. Uranium sorption on tezontle volcanic rock

    International Nuclear Information System (INIS)

    Lopez M, B. E.; Duran B, J. M.; Iturbe G, J. L.; Olguin G, M. T.

    2009-01-01

    It is described a study that demonstrates that hexavalent uranium ions were sorbed by the naturally occurring mineral using a batch technique. This mineral is found in abundant quantities in Mexico. Our study focused on the separation of U Vi from synthetic aqueous systems of both H 2 O-UO 2 (NO 3 ) 2 .6H 2 O (acid) and H 2 O-Na 4 [UO 2 (CO 3 ) 3 ] (basic). The chemical speciation was performed by using high voltage electrophoresis, and the uranium content was determined by UV-Vis spectroscopy. The quantified U(Vi) sorption by tezontle from acidic and basic systems was 2.72 and 1.68 μmol/g, respectively, and the sorption behavior is discussed considering the surface charge of the tezontle at different ph values based on the point of zero charge characteristic of this material. (Author)

  3. Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada

    Science.gov (United States)

    du Bray, Edward A.; John, David A.; Box, Stephen E.; Vikre, Peter G.; Fleck, Robert J.; Cousens, Brian L.

    2013-04-23

    Petrographic and geochemical data for Cenozoic volcanic rocks of the Bodie Hills, California and Nevada // // This report presents petrographic and geochemical data for samples collected during investigations of Tertiary volcanism in the Bodie Hills of California and Nevada. Igneous rocks in the area are principally 15–6 Ma subduction-related volcanic rocks of the Bodie Hills volcanic field but also include 3.9–0.1 Ma rocks of the bimodal, post-subduction Aurora volcanic field. Limited petrographic results for local basement rocks, including Mesozoic granitoid rocks and their metamorphic host rocks, are also included in the compilation. The petrographic data include visual estimates of phenocryst abundances as well as other diagnostic petrographic criteria. The geochemical data include whole-rock major oxide and trace element data, as well as limited whole-rock isotopic data.

  4. Stratigraphical sequence and geochronology of the volcanic rock series in caifang basin, south jiangxi

    International Nuclear Information System (INIS)

    Xu Xunsheng; Wu Jianhua

    2010-01-01

    The late Mesozoic volcanic rocks in Jiangxi constitute two volcanic belts: the northern is Xiajiang-Guangfeng volcanic belt, the volcanic rocks series belong to one volcano cycle and named Wuyi group which is subdivided into three formations (Shuangfengling formation, Ehuling formation and Shixi formation); the southern is Sannan-Xunwu volcanic belt, the volcanic rocks series in Caifang basin which locates on Sannan-Xunwu volcanic belt also belong to only one volcano cycle. It can be subdivided into two lithology and lithofacies units (upper and lower): the lower unit consists of sedimentary rocks and associated with a subordinate amount of volcanic rocks, it belongs to erupt-deposit facies which is the product of early volcanic stage; the upper unit is mostly composed of volcanic rocks, it belongs to erupt facies that is the volcanic eruption product. SHRIMP zircon U-Pb age of rhyolite? which locates at the top of the upper unit is 130.79 ± 0.73) Ma. According to the new International Stratigraphic Chart, the boundary of Jurassic and Cretaceous is (145.4 ± 4.0) Ma, so the age shows that the geologic period of Caifang volcanic rocks series is early Early Cretaceous epoch. On the basis of lithological correlation, lithofacies and stratigraphic horizon analysis, the volcanic rock series in Caifang basin fall under Wuyi group, and the lower unit could be incorporated into Shuangfengling formation, the upper unit could be incorporated into Ehuling formation. The subdivision of sequence and the determination of geochronology of the volcanic rock series in Caifang basin provide some references for the study of the late Mesozoic volcanic rocks series of the Sannan-Xunwu volcanic belt. (authors)

  5. Alteration of submarine volcanic rocks in oxygenated Archean oceans

    Science.gov (United States)

    Ohmoto, H.; Bevacqua, D.; Watanabe, Y.

    2009-12-01

    Most submarine volcanic rocks, including basalts in diverging plate boundaries and andesites/dacites in converging plate boundaries, have been altered by low-temperature seawater and/or hydrothermal fluids (up to ~400°C) under deep oceans; the hydrothermal fluids evolved from shallow/deep circulations of seawater through the underlying hot igneous rocks. Volcanogenic massive sulfide deposits (VMSDs) and banded iron formations (BIFs) were formed by mixing of submarine hydrothermal fluids with local seawater. Therefore, the behaviors of various elements, especially of redox-sensitive elements, in altered submarine volcanic rocks, VMSDs and BIFs can be used to decipher the chemical evolution of the oceans and atmosphere. We have investigated the mineralogy and geochemistry of >500 samples of basalts from a 260m-long drill core section of Hole #1 of the Archean Biosphere Drilling Project (ABDP #1) in the Pilbara Craton, Western Australia. The core section is comprised of ~160 m thick Marble Bar Chert/Jasper Unit (3.46 Ga) and underlying, inter-bedded, and overlying submarine basalts. Losses/gains of 65 elements were quantitatively evaluated on the basis of their concentration ratios against the least mobile elements (Ti, Zr and Nb). We have recognized that mineralogical and geochemical characteristics of many of these samples are essentially the same as those of hydrothermally-altered modern submarine basalts and also those of altered volcanic rocks that underlie Phanerozoic VMSDs. The similarities include, but are not restricted to: (1) the alteration mineralogy (chlorite ± sericite ± pyrophyllite ± carbonates ± hematite ± pyrite ± rutile); (2) the characteristics of whole-rock δ18O and δ34S values; (3) the ranges of depletion and enrichment of Si, Al, Mg, Ca, K, Na, Fe, Mn, and P; (4) the enrichment of Ba (as sulfate); (5) the increases in Fe3+/Fe2+ ratios; (6) the enrichment of U; (7) the depletion of Cr; and (8) the negative Ce anomalies. Literature data

  6. Uranium sorption on tezontle volcanic rock

    Energy Technology Data Exchange (ETDEWEB)

    Lopez M, B. E.; Duran B, J. M.; Iturbe G, J. L.; Olguin G, M. T., E-mail: beatriz.lopez@inin.gob.m [ININ, Departamento de Quimica, Carretera Mexico-Toluca s/n, 52750 Ocoyoacac, Estado de Mexico (Mexico)

    2009-07-01

    It is described a study that demonstrates that hexavalent uranium ions were sorbed by the naturally occurring mineral using a batch technique. This mineral is found in abundant quantities in Mexico. Our study focused on the separation of U Vi from synthetic aqueous systems of both H{sub 2}O-UO{sub 2}(NO{sub 3}){sub 2}.6H{sub 2}O (acid) and H{sub 2}O-Na{sub 4}[UO{sub 2}(CO{sub 3}){sub 3}] (basic). The chemical speciation was performed by using high voltage electrophoresis, and the uranium content was determined by UV-Vis spectroscopy. The quantified U(Vi) sorption by tezontle from acidic and basic systems was 2.72 and 1.68 mumol/g, respectively, and the sorption behavior is discussed considering the surface charge of the tezontle at different ph values based on the point of zero charge characteristic of this material. (Author)

  7. Strontium isotopic ratios of Tertiary volcanic rocks of northeastern Honshu, Japan: implication for the spreading of the Japan Sea

    International Nuclear Information System (INIS)

    Kurasawa, Hajime; Konda, Tadashi.

    1986-01-01

    Strontium isotopic ratios of sixty-seven Tertiary volcanic rocks from the northeastern Honshu, Japan, were determined for the purpose of examining the genesis among the volcanic rocks. Two distince suites of volcanic rocks occur in the northeastern Honshu; the rocks older than 16 Ma (Monzen-Daijima Stege) of predominantly intermediate composition and the rocks younger than 16 Ma (Nishikurosawa-Funakawa Stege) with bimodal suite of mafic and felsic composition. Initial values of 87 Sr/ 86 Sr in the Teriary volcanic rocks from the northeastern Honshu, lie in the range from 0.7033 to 0.7068. High ( 87 Sr/ 86 Sr) I ratios are observed for the rocks older than 16 Ma from the Japan Sea side (H zone). It is noteworthy that the rocks younger than 16 Ma show significantly lower ( 87 Sr/ 86 Sr) I ratios in the Dewa Hill, Japan Sea coast and North Akita areas in the northeastern Honshu (L zone). The rocks younger than 16 Ma from the L zone can also be interpreted as having been originated as a mantle-diapir associated with the spreading of the Japan Sea basin. If the basaltic magma was formed from the diapir, the 87 Sr/ 86 Sr ratio would be close to the range from 0.7033 to 0.7037 as the low-Sr isotopic ratio zone (L zone) in the northeastern Honshu, Japan. (author)

  8. Petrography, Geochemistry and Petrogenesis of Volcanic Rocks, NW Ghonabad, Iran

    Directory of Open Access Journals (Sweden)

    Sedigheh Zirjanizadeh

    2016-07-01

    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

  9. Is there a geochemical link between volcanic and plutonic rocks in the Organ Mountains caldera?

    Science.gov (United States)

    Memeti, V.; Davidson, J.

    2013-12-01

    determine within-crystal geochemical variations. Our current conclusions and working hypotheses are: 1) All igneous rocks from the Organ Mountains are crustal-mantle melt mixtures indicating two component mixing; 2) the caldera-forming ignimbrites are likely derived from a fractionating Organ Needle pluton; 3) pre- and post-caldera lavas are isotopically similar to the post-caldera Sugarloaf Peak quartz-monzonite; 4) K-feldspar cumulate textures in the structurally top 0.5-1 km of the Organ Needle pluton indicate that interstitial melt was lost from the magma mush, which likely fed the ignimbrite eruptions. 5) Plutonic feldspar textures are complex compared to rather simple zoned volcanic feldspars including K-feldspar rimmed plagioclase, plagioclase rimmed K-feldspar and unrimmed feldspars occurring over a range of grain sizes at thin section scale. Some volcanic feldspar phenocrysts have any previous zonation erased due to late stage albitization. Although the single mineral studies are still work in progress and details need resolving, our data so far suggest a geochemical link between volcanic and plutonic rocks of the Organ Mountains caldera, albeit a complex one; and greater complexity in plutonic versus volcanic minerals. [1] Seager (1980), NM Bureau of Mines and Min. Res. Memoir 36, 97 p. [2] Zimmerer & McIntosh (2013) Journal of Geophysical Research, v. 93, p. 4421-4433

  10. Hydrological and geochemical investigation on the volcanic rock and gneissic rock area

    Energy Technology Data Exchange (ETDEWEB)

    Koh, Yong Kwon; Jeong, Chan Ho; Ryu, Kun Seok; Kim, Byoung Yeop; Park, Hyung Kun; Yu, Sang Woo; Jang, Hyu Kun; Lee, Suk Chi; Choi, Ki Young; Jeon, Hyu Woong; Kim, Do Hyoung [Daejong University, Daejeon (Korea, Republic of)

    2010-01-15

    The purpose of this study is to supply the basic data and optimum study site among volcanic rock area and gneissic rock area for high-level radioactive waste disposal. For this purpose, geological, hydrogeological and geochemical data from previously published literatures were collected and analyzed. In this study, we selected 36 volcanic rock sites and 26 gneissic sites as the candidate sites for high level radwaste disposal. Finally, for four sites(M-1, M-13, V-1 and V-13 sites) were selected as the study sites. The geochemical characteristics of groundwaters of each study site were statistically analyzed. The nitrate contamination and the sea water mixing will be important factors on the assessment of behaviour of radionuclides under groundwater environment. From the deep geothermal study, alkaline and sodium-bicarbonate chemical environment, and sea water mixing should be considered as the key factors for the deep disposal of high-level radioactive waste

  11. Geomechanical characterization of volcanic rocks using empirical systems and data mining techniques

    OpenAIRE

    T. Miranda; L.R. Sousa; A.T. Gomes; J. Tinoco; C. Ferreira

    2018-01-01

    This paper tries to characterize volcanic rocks through the development and application of an empirical geomechanical system. Geotechnical information was collected from the samples from several Atlantic Ocean islands including Madeira, Azores and Canarias archipelagos. An empirical rock classification system termed as the volcanic rock system (VRS) is developed and presented in detail. Results using the VRS are compared with those obtained using the traditional rock mass rating (RMR) system....

  12. Geochemical and geochronological constrains on the Chiang Khong volcanic rocks (northwestern Thailand) and its tectonic implications

    Science.gov (United States)

    Qian, Xin; Feng, Qinglai; Chonglakmani, Chongpan; Monjai, Denchok

    2013-12-01

    Volcanic rocks in northwestern Thailand exposed dominantly in the Chiang Khong area, are commonly considered to be genetically linked to the tectonic evolution of the Paleo-Tethyan Ocean. The volcanic rocks consist mainly of andesitic to rhyolitic rocks and are traditionally mapped as Permian-Triassic sequences. Our zircon U-Pb geochronological results show that two andesitic samples (TL-1-B and TL-31-B), are representative of the Doi Yao volcanic zone, and give a mean weighted age of 241.2±4.6 Ma and 241.7±2.9 Ma, respectively. The rhyolitic sample (TL-32-B1) from the Doi Khun Ta Khuan volcanic zone erupted at 238.3±3.8 Ma. Such ages indicate that Chiang Khong volcanic rocks erputed during the early Middle Triassic period. Seven samples from the Doi Yao and Doi Khun Ta Khuan zones exhibit an affinity to arc volcanics. Three rhyolitic samples from the Chiang Khong area have a geochemical affinity to both arc and syn-collisional volcanic rocks. The Chiang Khong arc volcanic rocks can be geochemically compared with those in the Lampang area in northern Thailand, also consistent with those in Jinghong area of southwestern Yunnan. This indicates that the Chiang Rai arc-volcanic zone might northwardly link to the Lancangjiang volcanic zone in southwestern China.

  13. Rare earth element mobility in arc-type volcanic rocks

    International Nuclear Information System (INIS)

    Kuschel, E.; Smith, I.E.M.

    1990-01-01

    Some samples from arc-type volcanic suites collected in northern New Zealand and southeastern Papua New Guinea show rare earth element (REE) and Y abundances which are enriched relative to the those typical of their respective associations. This enrichment appears to be the result of an alteration process which selectively mobilises the REE and re-precipitates them as REE-bearing minerals in veins and interstitial patches. The alteration is on a micron scale and is not detected in routine petrographic examination. It is emphasised that the pattern of REE mobility in young, fresh rocks is important to igneous geochemists who use REE abundances to constrain petrogenetic models and may also be important because it indicates the operation of a natural REE enrichment process which could operate in the formation of economic REE deposits. 3 refs., 5 figs

  14. Platinum, palladium, and rhodium in volcanic and plutonic rocks from the Gravina-Nutzotin belt, Alaska

    Science.gov (United States)

    Page, Norman J; Berg, Henry C.; Haffty, Joseph

    1977-01-01

    The Gravina-Nutzotin belt of Middle (?) Jurassic to middle Cretaceous sedimentary and volcanic rocks in south and southeastern Alaska includes concentrically zoned ultramafic complexes known to contain platinum-group metals. Previous isotopic, petrologic, and geologic studies suggested a close relation in time and space between the volcanic rocks and the ultramafic complexes. Interpretation of 40 analyses for platinum, palladium, and rhodium in volcanic and plutonic rocks of the belt indicates a strong geochemical correlation between the two groups of rocks and is in support of their being cogenetic either from directly connected magma chambers and flows or indirectly by selective concentration processes from similar mantle material.

  15. The volcanic rocks construction of the late paleozoic era and uranium mineralization in Beishan area of Gansu province

    International Nuclear Information System (INIS)

    An Zhengchang; Luo Xiaoqiang

    2010-01-01

    Late Paleozoic volcanic rocks in Beishan area are the favorable constructions of hydrothermal type and volcanic type deposit. From the distribution of volcanic rocks, the volcanic compositions, the volcanic facies, volcanic eruption method and rhythm, chemical and trace elements compositions, and so on, it discusses the characteristics of the Late Devonian volcanic construction in this area and its relationship with uranium mineralization, analyzes the role of volcanic ore-control mechanism, and summarizes uranium ore forming regularity of volcanic construction in Late Paleozoic. (authors)

  16. K-Ar age of the Tertiary volcanic rocks in the Tohoku area, Japan

    International Nuclear Information System (INIS)

    Konda, Tadashi; Ueda, Yoshio.

    1980-01-01

    The absolute age of the Tertiary volcanic rocks in Tohoku area has been estimated by K-Ar method. The results are: (1) in case of the volcanic rocks of Monzen-Aikawa stage, 32.8 - 38.5 m.y.B.P., (2) in case of the volcanic rocks of Nozaki-Daijima stage, 22.0 - 25.1 m.y.B.P., (3) in case of the volcanic rocks of Nishikurosawa stage, 15.5 - 16.5 m.y.B.P., (4) in case of the volcanic rocks of Onnagawa stage, 12.6 - 14.8 m.y.B.P., (5) in case of the volcanic rocks of Funakawa stage, 9.6 - 11.3 m.y.B.P., and (6) in case of the volcanic rocks of Kitaura stage, 6.9 - 9.0 m.y.B.P. The samples used are such as biotite and whole rocks. The eruption periods in Tertiary volcanic activities presumed by K-Ar method are geologically significant. In the measurements made on the same system of samples under same conditions, there was difference in the K-Ar ages between the Monzen-Aikawa and the Nozaki-Daijima stages, and it was significantly noteworthy. It is indicated that the volcanic rock activities in the former stage had took place before those in the latter stage. In the Tohoku arc of northern Japan, the simultaneity in initial volcanic activities is not seen in the direction across the arc. (J.P.N.)

  17. Uranium mineralization in tertiary volcanic rocks of the Los Frailes formation (Bolivia)

    International Nuclear Information System (INIS)

    Aparicio, A.

    1981-01-01

    The Los Frailes Formation, a 9000 km 2 area of Miocene-Pliocene age, contains uranium mineralization in acid tuffs, ignimbrites and lavas. Uranium also occurs in sedimentary rocks of various types and ages which outcrop in adjacent areas. So far the most extensive mineralization seems to be confined in volcanic pyroclastic rocks. Although the surface mineralization varies in grade from 0.01% to more than 2.5%, the average grade in the only deposit being mined (Cotaje) is 0.05% of U 3 O 8 . On the basis of the available data it is believed that certain leaching processes, during the last erosion cycle (Pliocene-Pleistocene) and under very humid conditions, brought about the mobilization of the uranium from the volcanic rocks in aqueous alkaline and calco-alkaline solutions circulating on the surface and underground. Uranium minerals were deposited, generally by chemical reduction, in tectonic zones and/or zones of high porosity. The common metallogenetic model in the western area, defined as the 'Sevaruyo uraniferous district', is exogenic and is characterized by epigenetic uranium occurrences and deposits formed by supergene enrichment. On the basis of their mechanism of formation, control of mineralization and mineral associations, these deposits are classified according to: those with strictly tectonic control, those with sedimentary control and those of mixed genetics. Recent discoveries in the eastern area of the volcanic complex give evidence of epigenetic mineralization, apparently linked with hypogene hydrothermal processes, in addition to exogenic mineralizations contained in rocks stratigraphically subjacent to the Los Frailes Formation. There is no intention of making an evaluation of the recently discovered resources since the studies and exploration are still at too early a stage to warrant prediction of their real potential. (author)

  18. Research on petrologic, geochemical characteristics and genesis of volcanic rocks in Dachangsha basin

    International Nuclear Information System (INIS)

    Wei Sanyuan

    1999-01-01

    On the basis of research on petrologic, geochemical characteristics and isotope composition of volcanic rocks in Dachangsha basin, the author concludes that the volcanic rocks formed from magma of different genesis and depth are double-cycle effusive. It is proposed that the magma forming the intermediate-basic volcanics of the first cycle comes from the mixing of the partial melting of the deep crust and mantle, and the intermediate-acidic volcanics of the secondary cycle are derived from the remelting of the upper crust

  19. Reservoir Space Evolution of Volcanic Rocks in Deep Songliao Basin, China

    Science.gov (United States)

    Zheng, M.; Wu, X.; Zheng, M.; HU, J.; Wang, S.

    2015-12-01

    Recent years, large amount of natural gas has been discovered in volcanic rock of Lower Crataceous of Songliao basin. Volcanic reservoirs have become one of the important target reservoir types of eastern basin of China. In order to study the volcanic reservoirs, we need to know the main factors controlling the reservoir space. By careful obsercation on volcanic drilling core, casting thin sections and statistical analysis of petrophysical properties of volcanic reservoir in Songliao basin, it can be suggested that the igneous rock reservoir in Yingcheng formation of Lower Crataceous is composed of different rock types, such ad rohylite, rohylitic crystal tuff, autoclastic brecciation lava and so on. There are different reservoirs storage space in in various lithological igneous rocks, but they are mainly composed of primary stoma, secondary solution pores and fractures.The evolution of storage space can be divided into 3 stage: the pramary reservoir space,exogenic leaching process and burial diagenesis.During the evolution process, the reservoir space is effected by secondary minerals, tectonic movement and volcanic hydrothermal solution. The pore of volcanic reservoirs can be partially filled by secondary minerals, but also may be dissoluted by other chemical volcanic hydrothermal solution. Therefore, the favorable places for better-quality volcanic reservoirs are the near-crater facies of vocanic apparatus and dissolution zones on the high position of paleo-structures.

  20. Geomechanical characterization of volcanic rocks using empirical systems and data mining techniques

    Directory of Open Access Journals (Sweden)

    T. Miranda

    2018-02-01

    Full Text Available This paper tries to characterize volcanic rocks through the development and application of an empirical geomechanical system. Geotechnical information was collected from the samples from several Atlantic Ocean islands including Madeira, Azores and Canarias archipelagos. An empirical rock classification system termed as the volcanic rock system (VRS is developed and presented in detail. Results using the VRS are compared with those obtained using the traditional rock mass rating (RMR system. Data mining (DM techniques are applied to a database of volcanic rock geomechanical information from the islands. Different algorithms were developed and consequently approaches were followed for predicting rock mass classes using the VRS and RMR classification systems. Finally, some conclusions are drawn with emphasis on the fact that a better performance was achieved using attributes from VRS.

  1. Influence of mesostasis in volcanic rocks on the alkali-aggregate reaction

    KAUST Repository

    Tiecher, Francieli

    2012-11-01

    Mesostasis material present in the interstices of volcanic rocks is the main cause of the alkali-aggregate reaction (AAR) in concretes made with these rock aggregates. Mesostasis often is referred to as volcanic glass, because it has amorphous features when analyzed by optical microscopy. However, this study demonstrates that mesostasis in the interstitials of volcanic rocks most often consists of micro to cryptocrystalline mineral phases of quartz, feldspars, and clays. Mesostasis has been identified as having different characteristics, and, thus, this new characterization calls for a re-evaluation of their influence on the reactivity of the volcanic rocks. The main purpose of this study is to correlate the characteristics of mesostasis with the AAR in mortar bars containing basalts and rhyolites. © 2012 Elsevier Ltd. All rights reserved.

  2. Some evidence of uranium in volcanic feldspar rocks in the state of Sonora

    Energy Technology Data Exchange (ETDEWEB)

    Marquina M, O. E. [Uranio Mexicano, Mexico City

    1983-05-15

    Description is given of four projects of exploration and survey for uranium associated with tertiary volcanic feldspar rocks importantly dispersed in the State of Sonora and being carried out by Uranium Mexicano.

  3. Influence of mesostasis in volcanic rocks on the alkali-aggregate reaction

    KAUST Repository

    Tiecher, Francieli; Dal Molin, Denise Carpena Coitinho; Gomes, Má rcia Elisa Boscato; Hasparyk, Nicole Pagan; Monteiro, Paulo José Meleragno

    2012-01-01

    Mesostasis material present in the interstices of volcanic rocks is the main cause of the alkali-aggregate reaction (AAR) in concretes made with these rock aggregates. Mesostasis often is referred to as volcanic glass, because it has amorphous features when analyzed by optical microscopy. However, this study demonstrates that mesostasis in the interstitials of volcanic rocks most often consists of micro to cryptocrystalline mineral phases of quartz, feldspars, and clays. Mesostasis has been identified as having different characteristics, and, thus, this new characterization calls for a re-evaluation of their influence on the reactivity of the volcanic rocks. The main purpose of this study is to correlate the characteristics of mesostasis with the AAR in mortar bars containing basalts and rhyolites. © 2012 Elsevier Ltd. All rights reserved.

  4. Evaluation of early Archean volcaniclastic and volcanic flow rocks as possible sites for carbonaceous fossil microbes.

    Science.gov (United States)

    Walsh, Maud M

    2004-01-01

    Sedimentary rocks have traditionally been the focus of the search for Archean microfossils; the Earth's oldest fossil bacteria are associated with carbonaceous matter in sedimentary cherts in greenstone belts in the eastern Pilbara block of Western Australia and Barberton greenstone belt of South Africa. Reports of possible fossils in a martian meteorite composed of igneous rock and the discovery of modern bacteria associated with basalts have stimulated a new look at Archean volcanic rocks as possible sites for fossil microbes. This study examines silicified volcaniclastic rocks, near-surface altered volcanic flow rocks, and associated stromatolite- like structures from the Archean Barberton greenstone belt to evaluate their potential for the preservation of carbonaceous fossils. Detrital carbonaceous particles are widely admixed with current-deposited debris. Carbonaceous matter is also present in altered volcanic flow rocks as sparse particles in silica veins that appear to be fed by overlying carbonaceous chert layers. Neither microfossils nor mat-like material was identified in the altered volcanic rocks or adjacent stromatolite-like structures. Ancient volcanic flow and volcaniclastic rocks are not promising sites for carbonaceous fossil preservation.

  5. Stratigraphy and structure of volcanic rocks in drill hole USW-G1, Yucca Mountain, Nye County, Nevada

    International Nuclear Information System (INIS)

    Spengler, R.W.; Byers, F.M. Jr.; Warner, J.B.

    1981-01-01

    Detailed subsurface studies in connection with the Nevada Nuclear Waste Storage Investigations program are being conducted to investigate the stratigraphic and structural features of volcanic rocks underlying Yucca Mountain, a volcanic highland situated along the western boundary of the Nevada Test Site in southern Nevada. As part of this continuing effort, drill hole USW-G1 was cored from 292 ft to a depth of 6000 ft from March to August 1980. The stratigraphic section is composed of thick sequences of ash-flow tuff and volcanic breccia interbedded with subordinate amounts of fine- to coarse-grained volcaniclastic rocks. All rocks are of Tertiary age and vary in composition from rhyolite to dacite. The 3005-ft level in the drill hole represents a significant demarcation between unaltered and altered volcanic rocks. For the most part, tuff units above 3005 ft appear devitrified and show little secondary alteration except within tuffaceous beds of Calico Hills, where the rock contains 60 to 80% zeolites. Below 3005 ft, most rocks show intermittent to pervasive alteration to clay minerals and zeolites. Examination of core for structural features revealed the presence of 61 shear fractures, 528 joints, and 4 conspicuous fault zones. Shear fractures mainly occurred in the Topopah Spring Member of the Paintbrush Tuff, flow breccia, and near fault zones. Nearly 88% of shear and joint surfaces show evidence of coatings. Approximately 40% of the fractures were categorized as completely healed. Rock quality characteristics as defined by the core index indicate that greater amounts of broken and lost core are commonly associated with (1) the densely welded zone of the Topopah Spring, (2) highly silicified zones, and (3) fault zones

  6. Petrology, Geochemistry and Tectonomagmatic Setting of Farmahin Volcanic Rocks (North of Arak

    Directory of Open Access Journals (Sweden)

    Reza Zarei Sahamieh

    2018-04-01

    -J diagram located in the Mg-Fe-Ca (Quad field and in the 2Ti+Cr+AlVI vs. Na+AlIV diagram (Morimoto et al., 1988 located above on the Fe3+=0 line that indicate high oxygen fugacity during crystallization. Microscopic study on these rocks such as oscillatory zoning, resorption rims in plagioclase and the presence of basic inclusions suggest the occurrence of magmatic contamination on the parent magma. The presence of oxidized amfibool rims (in hornbelende as oxy hornbelende indicate the high temperature of the magma at the time of eruption. According to the classification diagrams such as total alkaline vs. SiO2 (Irvine and Baragar, 1971 TAS (Le Bas et al., 1986 and tectonic discrimination diagrams (Pearce et al., 1984 samples are plotted in sub-alkaline, basaltic-andesite, andesite, dacite and rhyodacite, subduction and volcanic arc fields, respectively. The geochemical diagrams such as AFM are used for the identification of magma series and show that the studied rocks are calc-alkaline and A/NK vs. The A/CNK diagram shows the metaluminous to peraluminous nature. Incompatible and LIL elements such as Ba, K and Rb enrichment show that the contamination of magma with continental crust has occurred. The similarity between the REE patterns in all of the collected samples in Alam Baghi, Vashaghan, Sarban and Ghermez Cheshmeh areas suggest the same source for all of the volcanic rocks. Discussion The tectonic setting diagrams show that these rocks belong to the continental margin which has been involved in a subduction zone. The position of the samples on the major elements vs. SiO2 diagrams indicate that magma differentiation has occurred. Spider diagrams show a positive anomalous in Rb and a negative anomalous in Nb and Ti This phenomenon shows a contamination between the magma and the crustal rocks (Rollinson, 1993. Also, MORB-normalized incompatible element patterns of the Farmahin area show that the parent magma has been contaminated. It appears that assimilation and

  7. K-Ar ages of the Neogene volcanic rocks from the Oshamambe district, southwestern Hokkaido

    International Nuclear Information System (INIS)

    Kubo, Kazuya; Shibata, Ken; Ishida, Masao

    1988-01-01

    Oshamanbe district is on the northern extension of the so-called green tuff district in northeastern Japan, and the sedimentary rocks in a sea area and volcanic rocks from Miocene to Pleistocene widely distribute. The authors carried out the geological survey of this district, and published the results as the geological features in Oshamanbe district. The volcanic rocks distributing in this district range from andesite to dacite and rhyolite. Their lithofacies are mostly volcanic breccia and tuff breccia, accompanied by lava and dikes. This time, the measurement of the age of these volcanic rocks was carried out, and the stratigraphical table made by the authors was investigated. It is considered that those age values offer important information for determining the age of the Setana formation. The outline of the geological features, the samples for the measurement, the method of measurement of Ar isotopic ratio and K, and the results of measurement are reported. As the results, 4.38 - 4.47 Ma were obtained for Garogawa volcanic rocks, and 2.59 Ma for Shamanbesan volcanic rocks. The period of sedimentation of the Setana formation was from the latter period of Pliocene to pleistocene. (Kako, I.)

  8. Uranium mineralization in fluorine-enriched volcanic rocks

    Energy Technology Data Exchange (ETDEWEB)

    Burt, D.M.; Sheridan, M.F.; Bikun, J.; Christiansen, E.; Correa, B.; Murphy, B.; Self, S.

    1980-09-01

    Several uranium and other lithophile element deposits are located within or adjacent to small middle to late Cenozoic, fluorine-rich rhyolitic dome complexes. Examples studied include Spor Mountain, Utah (Be-U-F), the Honeycomb Hills, Utah (Be-U), the Wah Wah Mountains, Utah (U-F), and the Black Range-Sierra Cuchillo, New Mexico (Sn-Be-W-F). The formation of these and similar deposits begins with the emplacement of a rhyolitic magma, enriched in lithophile metals and complexing fluorine, that rises to a shallow crustal level, where its roof zone may become further enriched in volatiles and the ore elements. During initial explosive volcanic activity, aprons of lithicrich tuffs are erupted around the vents. These early pyroclastic deposits commonly host the mineralization, due to their initial enrichment in the lithophile elements, their permeability, and the reactivity of their foreign lithic inclusions (particularly carbonate rocks). The pyroclastics are capped and preserved by thick topaz rhyolite domes and flows that can serve as a source of heat and of additional quantities of ore elements. Devitrification, vapor-phase crystallization, or fumarolic alteration may free the ore elements from the glassy matrix and place them in a form readily leached by percolating meteoric waters. Heat from the rhyolitic sheets drives such waters through the system, generally into and up the vents and out through the early tuffs. Secondary alteration zones (K-feldspar, sericite, silica, clays, fluorite, carbonate, and zeolites) and economic mineral concentrations may form in response to this low temperature (less than 200 C) circulation. After cooling, meteoric water continues to migrate through the system, modifying the distribution and concentration of the ore elements (especially uranium).

  9. Uranium mineralization in fluorine-enriched volcanic rocks

    International Nuclear Information System (INIS)

    Burt, D.M.; Sheridan, M.F.; Bikun, J.; Christiansen, E.; Correa, B.; Murphy, B.; Self, S.

    1980-09-01

    Several uranium and other lithophile element deposits are located within or adjacent to small middle to late Cenozoic, fluorine-rich rhyolitic dome complexes. Examples studied include Spor Mountain, Utah (Be-U-F), the Honeycomb Hills, Utah (Be-U), the Wah Wah Mountains, Utah (U-F), and the Black Range-Sierra Cuchillo, New Mexico (Sn-Be-W-F). The formation of these and similar deposits begins with the emplacement of a rhyolitic magma, enriched in lithophile metals and complexing fluorine, that rises to a shallow crustal level, where its roof zone may become further enriched in volatiles and the ore elements. During initial explosive volcanic activity, aprons of lithicrich tuffs are erupted around the vents. These early pyroclastic deposits commonly host the mineralization, due to their initial enrichment in the lithophile elements, their permeability, and the reactivity of their foreign lithic inclusions (particularly carbonate rocks). The pyroclastics are capped and preserved by thick topaz rhyolite domes and flows that can serve as a source of heat and of additional quantities of ore elements. Devitrification, vapor-phase crystallization, or fumarolic alteration may free the ore elements from the glassy matrix and place them in a form readily leached by percolating meteoric waters. Heat from the rhyolitic sheets drives such waters through the system, generally into and up the vents and out through the early tuffs. Secondary alteration zones (K-feldspar, sericite, silica, clays, fluorite, carbonate, and zeolites) and economic mineral concentrations may form in response to this low temperature (less than 200 C) circulation. After cooling, meteoric water continues to migrate through the system, modifying the distribution and concentration of the ore elements

  10. Tectonic implications of the contrasting geochemistry of Damaran mafic volcanic rocks, South West Africa

    International Nuclear Information System (INIS)

    Miller, R.McG.

    1983-01-01

    Ortho-amphibolites occur in the southern and central parts of the north-east-trending branch of the Damara Orogen. The Matchless Member amphibolites are interbedded with quartzose mica schist. Mobility of Si, ΣFe, Mn, Mg, Ca, Na, K, P, CO 2 , H 2 O, Rb, Ba, Sr and possibly LREE and immobility of Co, V, Sc, Ga, Zr, Nb, Y and HREE are indicated during metamorphism and reaction with country rock. Central Zone amphibolites are alkaline. The stratigraphically lower amphibolites have a within-plate chemistry; their distribution and associated rock types indicate a continental origin. The Matchless amphibolites have an ocean-floor chemistry. The Damaran sedimentary and orogenic cycle was initiated by continental rifting in three parallel zones in which alkaline acid volcanics occur locally. Widespread subsidence of the rift zones and the intervening areas followed and led to deposition of carbonate and clastic rocks under shallow marine conditions. During renewed rifting, submarine, alkaline basic lavas were extruded. The Southern Margin Zone amphibolites are interbedded with continental slope mixtites and continental rise deep-water fans. Spreading led to continental breakup and the formation of oceanic crust

  11. Suprasubduction volcanic rocks of the Char ophiolite belt, East Kazakhstan: new geochemical and first geochronological data

    Science.gov (United States)

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

    2016-04-01

    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

  12. Isotopic feature and uranium dating of the volcanic rocks in the Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Volcanic rocks from the northern and middle Okinawa Trough were dated by uranium-series dating method. Differential fractions using magnetic procedure were designed to separate samples. New report on the ages and isotopic data of rocks in the northern trough (especially black pumice) was discussed. Based on the uranium dates and Sr-Nd isotopic ratio, magmatic evolution process of the Okinawa Trough was noted. Firstly, there have been wide silicic volcanic activities in the Okinawa Trough from late Pleistocene to present, and the volcanic rocks can be divided into three subgroups. Secondly, magma generally came from PREMA source area under the Okinawa Trough. Magmatic evolution in the northern trough was similar to the middle, but different to the south. Finally, volcanic activities indicated that opening of the southern Okinawa Trough did not happen due to the collision between Luson Arc and Eurasian Plate until the early Pleistocene.

  13. New Data on the Composition of Cretaceous Volcanic Rocks of the Alazeya Plateau, Northeastern Yakutia

    Science.gov (United States)

    Tsukanov, N. V.; Skolotnev, S. G.

    2018-02-01

    This work presents new data on the composition of volcanics, developed within the Alazeya Plateau of the Kolyma-Indigirka fold area (Northeast Russia), which indicate essential differences in their composition and, accordingly, different geodynamic settings of the formation of rocks. The studied igneous rocks are subdivided into two groups. Volcanics of the first group of the Late Cretaceous age, which are represented by differentiated volcanic rock series (from andesitobasalts to dacites and rhyolites), were formed under island arc conditions in the continent-ocean transition zone. Volcanics of the second group are ascribed to the tholeiitic series and were formed under the other geodynamic setting, which is associated with the regime of extension and riftogenesis, manifested in the studied area probably at the later stage.

  14. Cenozoic alkaline volcanic rocks with carbonatite affinity in the Bohemian Massif: Their sources and magma generation

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Štěpánková-Svobodová, Jana

    2014-01-01

    Roč. 46, 1/2 (2014), s. 45-58 ISSN 0369-2086 R&D Projects: GA AV ČR(CZ) IAA300130902 Institutional support: RVO:67985831 Keywords : alkaline volcanic rocks * melilitic rocks * carbonatites * magma generation * metasomatism * Cenozoic * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy

  15. Sr–Nd isotopic compositions of Paleoproterozoic metavolcanic rocks from the southern Ashanti volcanic belt, Ghana

    OpenAIRE

    Dampare, Samuel; Shibata, Tsugio; Asiedu, Daniel; Okano, Osamu; Manu, Johnson; Sakyi, Patrick

    2009-01-01

    Neodymium (Nd) and strontium (Sr) isotopic data are presented for Paleoproterozoic metavolcanic rocks in the southern part of the Ashanti volcanic belt of Ghana. The metavolcanic rocks are predominantly basalts/basaltic andesites and andesites with minor dacites. Two types of basalts/basaltic andesites (B/A), Type I and Type II, have been identified. The Type I B/A are stratigraphically overlain by the Type II B/A, followed by the andesites and the dacites. The analyzed volcanic rocks commonl...

  16. Geochemical of trace elements in volcanics rocks Peninsula Fildes, Fildes Bay Rey Jorge island, south Shetland

    International Nuclear Information System (INIS)

    Masquelin, H.; Vaz Chavez, N.

    1987-01-01

    The authors present some geochemical data derived from the multielement analysis of three different types of volcanic rocks collected around Fildes Bay on King George Island, South Shetland. Volcanic rocks from Fildes Peninsula Group may be distinguished from those Marian Cove by their hydrothermal alteration. Apparently the correlation between NI ands Cr allows for the observation of the stratigraphic separation of samples of the same kind. Consequently, the correlation between Cu and As show a distinction between Marian Cove propylitised tuffites and both Brecciated Andesites and pyroclastic rock from Fildes Peninsula Group.

  17. Correlations between silicic volcanic rocks of the St Mary's Islands (southwestern India) and eastern Madagascar

    DEFF Research Database (Denmark)

    Melluso, Leone; Sheth, Hetu C.; Mahoney, John J.

    2009-01-01

    The St Mary's, Islands (southwestern India) expose silicic volcanic and sub-volcanic rocks (rhyolites and granophyric dacites) emplaced contemporaneously with the Cretaceous igneous province of Madagascar, roughly 88-90 Ma ago. I he St Mary's Islands rocks have phenocrysts of plagioclase...... and isotopic Compositions very close to those of rhyolites exposed between Vatomandry Ilaka and Mananjary in eastern Madagascar, and are distinctly different from rhyolites front other sectors of the Madagascan province. We therefore postulate that the St Mary's and the Vatomandry-Ilaka Mananjary silicic rock...

  18. Sr-Nd isotope systematics of xenoliths in Cenozoic volcanic rocks from SW Japan

    International Nuclear Information System (INIS)

    Kagami, Hiroo; Iwata, Masatoshi; Iizumi, Shigeru; Nureki, Terukazu.

    1993-01-01

    Based on new and previously published Sr and Nd isotope data, we examined the petrogenetic relationship between deep crust- and upper mantle-derived xenoliths contained in Cenozoic volcanic rocks and Cretaceous-Paleogene granitoid rocks in SW Japan. The deep crust- and upper mantle-derived mafic to ultramafic xenoliths contained in Cenozoic volcanic rocks from SW Japan have comparable initial Sr and Nd isotope ratios to the Cretaceous-Paleogene granitoid rocks in their respective districts. This may suggest that these xenoliths were genetically related to the Cretaceous-Paleogene granitoid rocks in SW Japan, and that regional variations in Sr and Nd isotope ratios observed in the granitoid rocks are attributed to differences in the geochemistry of the magma sources. (author)

  19. Precursors predicted by artificial neural networks for mass balance calculations: Quantifying hydrothermal alteration in volcanic rocks

    Science.gov (United States)

    Trépanier, Sylvain; Mathieu, Lucie; Daigneault, Réal; Faure, Stéphane

    2016-04-01

    This study proposes an artificial neural networks-based method for predicting the unaltered (precursor) chemical compositions of hydrothermally altered volcanic rock. The method aims at predicting precursor's major components contents (SiO2, FeOT, MgO, CaO, Na2O, and K2O). The prediction is based on ratios of elements generally immobile during alteration processes; i.e. Zr, TiO2, Al2O3, Y, Nb, Th, and Cr, which are provided as inputs to the neural networks. Multi-layer perceptron neural networks were trained on a large dataset of least-altered volcanic rock samples that document a wide range of volcanic rock types, tectonic settings and ages. The precursors thus predicted are then used to perform mass balance calculations. Various statistics were calculated to validate the predictions of precursors' major components, which indicate that, overall, the predictions are precise and accurate. For example, rank-based correlation coefficients were calculated to compare predicted and analysed values from a least-altered test dataset that had not been used to train the networks. Coefficients over 0.87 were obtained for all components, except for Na2O (0.77), indicating that predictions for alkali might be less performant. Also, predictions are performant for most volcanic rock compositions, except for ultra-K rocks. The proposed method provides an easy and rapid solution to the often difficult task of determining appropriate volcanic precursor compositions to rocks modified by hydrothermal alteration. It is intended for large volcanic rock databases and is most useful, for example, to mineral exploration performed in complex or poorly known volcanic settings. The method is implemented as a simple C++ console program.

  20. Tertiary volcanic rocks and uranium in the Thomas Range and northern Drum Mountains, Juab County, Utah

    Science.gov (United States)

    Lindsey, David A.

    1982-01-01

    (?) Formation was erupted 30-31 m.y. ago from an unknown source. Mineralization probably did not occur during the rhyolitic stage of volcanism. The last stage of volcanism was contemporaneous with basin-and-range faulting and was characterized by explosive eruption of ash and pumice, forming stratified tuff, and by quiet eruption of alkali rhyolite as viscous flows and domes. The first episode of alkali rhyolite volcanism deposited the beryllium tuff and porphyritic rhyolite members of the Spor Mountain Formation 21 m.y. ago. After a period of block faulting, the stratified tuff and alkali rhyolite of the Topaz Mountain Rhyolite were erupted 6-7 m.y. ago along faults and fault intersections. Erosion of Spor Mountain, as well as explosive eruptions through dolomite, provided abundant dolomite detritus to the beryllium tuff member. The alkali rhyolite of both formations is fluorine rich, as is evident from abundant topaz, and contains anomalous amounts of lithophile metals. Alkali rhyolite volcanism was accompanied by lithophile metal mineralization which deposited fluorite, beryllium, and uranium. The structure of the area is dominated by the Thomas caldera and the younger Dugway Valley cauldron, which is nested within the Thomas caldera; the Thomas caldera is surrounded by a rim of Paleozoic rocks at Spor Mountain and Paleozoic to Precambrian rocks in the Drum Mountains. The Joy fault and Dell fault system mark the ring-fracture zone of the Thomas caldera. These structural features began to form about 39 m.y. ago during eruption of the Mt. Laird Tuff and caldera subsidence. The Dugway Valley cauldron sank along a series of steplike normal faults southeast of Topaz Mountain in response to collapse of the magma chamber of the Joy Tuff. Caldera structure was modified by block faulting between 21 and 7 m.y. ago, the time of widespread extensional faulting in the Basin and Range Province. Vents erupted alkali rhyolite 6-7 m.y. ago along basin-and-range faults.

  1. Search for Magnetic Monopoles in Polar Volcanic Rocks

    DEFF Research Database (Denmark)

    Bendtz, K.; Milstead, D.; Hächler, H. -P.

    2013-01-01

    following the passage of igneous rock samples through a SQUID-based magnetometer. A total of 24.6 kg of rocks from various selected sites, among which 23.4 kg are mantle-derived rocks from the Arctic and Antarctic areas, was analyzed. No monopoles were found, and a 90% confidence level upper limit of 9.8 x...

  2. Compositional Differences between Felsic Volcanic Rocks from the ...

    African Journals Online (AJOL)

    Bheema

    characteristics of the volcanic units, we describe the compositional differences ...... Geology and mineral resources of Somalia and surrounding regions. ... zone (Ethiopia) Journal of Volcanological and Geothermal Research, 80: 267-280.

  3. Origin of metaluminous and alkaline volcanic rocks of the Latir volcanic field, northern Rio Grande rift, New Mexico

    Science.gov (United States)

    Johnson, C.M.; Lipman, P.W.

    1988-01-01

    Volcanic rocks of the Latir volcanic field evolved in an open system by crystal fractionation, magma mixing, and crustal assimilation. Early high-SiO2 rhyolites (28.5 Ma) fractionated from intermediate compositionmagmas that did not reach the surface. Most precaldera lavas have intermediate-compositions, from olivine basaltic-andesite (53% SiO2) to quartz latite (67% SiO2). The precaldera intermediate-composition lavas have anomalously high Ni and MgO contents and reversely zoned hornblende and augite phenocrysts, indicating mixing between primitive basalts and fractionated magmas. Isotopic data indicate that all of the intermediate-composition rocks studied contain large crustal components, although xenocrysts are found only in one unit. Inception of alkaline magmatism (alkalic dacite to high-SiO2 peralkaline rhyolite) correlates with, initiation of regional extension approximately 26 Ma ago. The Questa caldera formed 26.5 Ma ago upon eruption of the >500 km3 high-SiO2 peralkaline Amalia Tuff. Phenocryst compositions preserved in the cogenetic peralkaline granite suggest that the Amalia Tuff magma initially formed from a trace element-enriched, high-alkali metaluminous magma; isotopic data suggest that the parental magmas contain a large crustal component. Degassing of water- and halogen-rich alkali basalts may have provided sufficient volatile transport of alkalis and other elements into the overlying silicic magma chamber to drive the Amalia Tuff magma to peralkaline compositions. Trace element variations within the Amalia Tuff itself may be explained solely by 75% crystal fractionation of the observed phenocrysts. Crystal settling, however, is inconsistent with mineralogical variations in the tuff, and crystallization is thought to have occurred at a level below that tapped by the eruption. Spatially associated Miocene (15-11 Ma) lavas did not assimilate large amounts of crust or mix with primitive basaltic magmas. Both mixing and crustal assimilation processes

  4. Acidic volcanic rock and its potential as an objective for uranium prospecting

    International Nuclear Information System (INIS)

    Rodriguez Torres, R.; Yza Dominguez, R.; Chavez Aguirre, R.; Constantino, H.E.S.E.

    1976-01-01

    The geographical distribution of recent Mexican volcanic rocks is continuous; the older formations are dispersed in isolated outcrops. Continental volcanic events, acidic and basal, took place in the Caenozoic, Mesozoic and Palaeozoic; basic submarine volcanism predominated in the Mesozoic, Palaeozoic and late Precambrian. Access to the Sierra Madre Occidental, a circum-Pacific mountain range covered by rhyolitic rocks, is limited, which restricts the sections studied. Calderas, sources of volcanic emission and preliminary litho-stratigraphic sections have been delimited on the eastern edge of the range. Subduction by the ocean magmatized the continent from the Permian onwards, extravasating and depositing cyclically various magmata through inverted and normal cortical throws. The Sierra Pena Blanca (Chihuahua) section consists of epiclastic and pyroclastic rocks. A calcareous conglomerate is overburdened by alternate basal tuffs and imbricates, forming five units. In the uraniferous district of the Sierra Pena Blanca the hydrothermal alteration argillitized both components of the ''Nopal'' formation. Primary minerals (pitchblende) are found together with silicification. Leaching favours secondary mineralization (uranium silicates) associated with opals. After extrapolation of the features, the following are considered worth-while objectives: the faces, offsets and prolongations of the Sierra Madre Occidental and the southern volcanic mesetas south of the Mexican Transcontinental Rift. Similar objectives of Mesozoic or Palaeozoic age exist in central and southern Mexico. Possible objectives for uranium are: the acidic volcanic rock of the southern and south-western United States of America, the circum-Pacific acidic volcanic rocks of North America and the acidic volcanic mesetas of Central America and in the Andes. (author)

  5. Economic potential of the Rooiberg Group: volcanic rocks in the floor and roof of the Bushveld Complex

    Science.gov (United States)

    Schweitzer, J. K.; Hatton, C. J.; de Waal, S. A.

    1995-04-01

    Volcanic rocks of the Rooiberg Group are preserved in the floor and roof of the mafic Rustenburg Layered Suite of the Bushveld Complex. Field and geochemical characteristics of these volcanic rocks imply that they are genetically related to the Rustenburg Layered Suite. Four major ore-forming events are identified in the Rooiberg Group. The first phase was accompanied by volcanic hosted, fault controlled, hydrothermal copper mineralisation, which is found in the lowermost portion of the Rooiberg Group, underlying the Rustenburg Layered Suite. This type of mineralisation is tentatively linked to initial Rustenburg Layered Suite intrusions. Stratabound arsenic mineralisation that possibly formed in response to contact metamorphism, characterises the second phase, and occurred after extrusion of the Damwal Formation, possibly due to shallow granophyric intrusion. The third mineralising event occurred in response to contact metamorphism during the final stages of the Rustenburg Layered Suite, where especially Pb and Zn were introduced into the felsite roof rocks. This type of mineralisation affected the majority of the Rooiberg Group, but is most pronounced towards the contact with the Rustenburg Layered Suite. The fourth phase is restricted to the Rooiberg Group in the Nylstroom area and is linked to the granite intrusions of the Lebowa Granite Suite, from which Sn and F were introduced into the uppermost felsite succession. Mineralisation in the Rooiberg Group appears to be controlled by the character and intrusion level of the associated Bushveld magmas. Different styles of mineralisation in Rooiberg Group volcanic rocks are encountered at various stratigraphic levels. Major primary volcanogenic ore deposits appear to be absent.

  6. Multi-elemental characterization of volcanic and vulcano-sedimentary rocks from Pina petroleum ore, central Cuba

    International Nuclear Information System (INIS)

    Montero-Cabrera, M.E.; Herrera-Peraza, E.; Betancourt-Tanda, L.; Campa-Menendez, R.; Diaz-Rizo, O.; Rodriguez-Martinez, N.; Segura-Soto, R.; Hernandez-Lopez, B.; Valdes-Lopez, S.

    1994-01-01

    Concentrations of 32 elements in 22 clay, limestone, tuff and volcanic rock samples from the Pina ore have been obtained by neutron activation and X-ray fluorescence analyses. Several LILE (large ion lithofile elements) and REE (rare earth element) concentration diagrams showed the calc-alkaline character of the volcanic rocks corresponding to the Greater Antilles Island, Arc. The basaltic andesite behavior of the rocks studied was confirmed by comparing the average concentrations obtained from tuffs and volcanic rocks with proper mean values of rock elemental compositions of the earth's crust. (Author)

  7. Multi-elemental characterization of volcanic and vulcano-sedimentary rocks from Pina petroleum ore, central Cuba

    Energy Technology Data Exchange (ETDEWEB)

    Montero-Cabrera, M.E.; Herrera-Peraza, E.; Betancourt-Tanda, L.; Campa-Menendez, R.; Diaz-Rizo, O. (Instituto Superior de Ciencia y Tecnologia Nuclear (ISCTN), La Habana (Cuba)); Rodriguez-Martinez, N.; Segura-Soto, R.; Hernandez-Lopez, B.; Valdes-Lopez, S. (Centro de Investigaciones y Desarrollo del Petroleo, La Habana (Cuba))

    1994-08-01

    Concentrations of 32 elements in 22 clay, limestone, tuff and volcanic rock samples from the Pina ore have been obtained by neutron activation and X-ray fluorescence analyses. Several LILE (large ion lithofile elements) and REE (rare earth element) concentration diagrams showed the calc-alkaline character of the volcanic rocks corresponding to the Greater Antilles Island, Arc. The basaltic andesite behavior of the rocks studied was confirmed by comparing the average concentrations obtained from tuffs and volcanic rocks with proper mean values of rock elemental compositions of the earth's crust. (Author).

  8. Petrography of the Paleogene Volcanic Rocks of the Sierra Maestra, Southeastern Cuba

    Science.gov (United States)

    Bemis, V. L.

    2006-12-01

    This study is a petrographic analysis of over 200 specimens of the Paleogene volcanic rocks of the Sierra Maestra (Southerneastern Cuba), a key structure in the framework of the northern Caribbean plate boundary evolution. The purpose of this study is to understand the eruptive processes and the depositional environments. The volcanic sequence in the lower part of the Sierra Maestra begins with highly porphyritic pillow lavas, topped by massive tuffs and autoclastic flows. The presence of broken phenocrystals, palagonitic glass and hyaloclastites in this section of the sequence suggests that the prevalent mode of eruption was explosive. The absence of welding in the tuffs suggests that the rocks were emplaced in a deep submarine environment. Coherent flows, much less common than the massive tuffs, show evidence of autoclastic fracturing, also indicating low temperature-submarine environments. These observations support the hypothesis that the Sierra Maestra sequence may be neither part of the Great Antilles Arc of the Mesozoic nor any other fully developed volcanic arc, rather a 250 km long, submarine eruptive system of dikes, flows and sills, most likely a back-arc structure. The volcanic rocks of the upper sequence are all very fine grained, reworked volcaniclastic materials, often with the structures of distal turbidities, in mode and texture similar to those drilled on the Cayman Rise. This study suggests that the Sierra Maestra most likely records volcanism of diverse sources: a local older submarine source, and one or more distal younger sources, identifiable with the pan-Caribbean volcanic events of the Tertiary.

  9. A simple source preparation method for alpha-ray spectrometry of volcanic rock sample

    International Nuclear Information System (INIS)

    Takahashi, Masaomi; Kurihara, Yuichi; Sato, Jun

    2006-01-01

    A simple source preparation method was developed for the alpha-ray spectrometry to determine U and Th in volcanic rockes. Isolation of U and Th from volcanic rocks was made by use of UTEVA-Spec. resin, extraction chromatograph material. U and Th were extracted by TTA-benzene solution and organic phase was evaporated drop by drop on a hot stainless steel planchet to dryness. This method was found to be effective for the preparation of sources for alpha-ray spectrometry. (author)

  10. Petrology and geochronology of metamorphosed volcanic rocks and a middle Cretaceous volcanic neck in the east-central Sierra Nevada, California.

    Science.gov (United States)

    Kistler, R.W.; Swanson, S.E.

    1981-01-01

    Metamorphosed Mesozoic volcanic rocks from the E-central Sierra Nevada range in composition from basalt to rhyolite and have ages, based on whole rock Rb-Sr and U-Pb zircon dating, of about 237- 224, 185, 163, 134, and 100Ma. The major plutons of the batholith in this area are of Triassic (215-200Ma) and Cretaceous (94-80Ma) ages. Initial 87Sr/86Sr values for the metamorphosed volcanic rocks of the area are in the range from 0.7042 to 0.7058 and are generally different from the values for the surrounding batholithic rocks (0.7056-0.7066). A circular, zoned granitic pluton, with an outcrop area of 2.5km2, similar in appearance to a ring dike complex, was apparently a conduit for some or possibly all of the middle-Cretaceous metamorphosed volcanic rocks exposed about 5km to the S in the western part of the Ritter Range. Samples from the metamorphosed volcanic rocks and the pluton yield a Rb/Sr whole rock isochron age of 99.9+ or -2.2Ma with an intitial 87Sr/86Sr of 0.7048+ or -0.00001. Major element variation diagrams of the pluton and volcanic rocks define coincident compositional trends. The ages of volcanic events relative to the ages of the major intrusive epochs and the major element and isotopic compositions of the volcanic rocks relative to the major plutons indicate that the volcanic rocks are not simply or directly related to the major plutons in the Sierra Nevada. -from Authors

  11. Assessment and Evaluation of Volcanic Rocks Used as Construction ...

    African Journals Online (AJOL)

    Tesfaye

    as engineering material throughout the world as aggregates in cement concrete, ... properties directly affect the mechanical behavior of the rock in question. ... As the physical and mechanical tests determined the usability of the geological.

  12. The Ediacaran volcanic rocks and associated mafic dykes of the Ouarzazate Group (Anti-Atlas, Morocco): Clinopyroxene composition, whole-rock geochemistry and Sr-Nd isotopes constraints from the Ouzellarh-Siroua salient (Tifnoute valley)

    Science.gov (United States)

    Belkacim, Said; Gasquet, Dominique; Liégeois, Jean-Paul; Arai, Shoji; Gahlan, Hisham A.; Ahmed, Hassan; Ishida, Yoshito; Ikenne, Moha

    2017-03-01

    Belonging to the huge Ouarzazate volcanic Group that covered the whole Anti-Atlas during the late Ediacaran (580-545 Ma), the Tifnoute valley volcanic formations are mainly pyroclastic and show a large composition, from trachybasalt to rhyolite and are crosscut by dolerite dykes. The Tifnoute valley volcanic rocks are located within a rigid salient of the Anti-Atlas that gives them special extreme characteristics. Due to the heavy greenschist alteration that affects this volcanic group, we focused the more immobile elements, but as REE can also be affected, we used the composition of unaltered clinopyroxene crystals to determine the nature of these volcanic rocks. The clinopyroxene is an augite diopside in the basalt, an augite in the andesite and an augite-salite in the dolerite. Petrography of the Tifnoute mafic volcanic rocks and clinopyroxene compositions indicate the presence of two magmatic series: (i) older high-K calc-alkaline (alkali-calcic) andesite and basalt characterized by the early crystallization of Fe-Ti oxides and of the late fractionation of plagioclase, the modal proportion of the latter increasing from the basalt to the andesite and (ii) younger alkalic dolerite dykes. With clinopyroxene trace element compositions obtained using laser ablation ICP-MS, we calculated the composition of the melts in equilibrium with the pyroxenes. The volcanic rocks of the Tifnoute Valley have positive εNd570 (+1.7 to +5.0), low Sri (volcanic rocks emplaced in a Pan-African transtensive post-collisional environment that evolved towards the major rifting event that will give rise to the Rheic ocean, in a similar way to what occurred just after the Variscan orogeny during the Triassic period that evolved to the Tethys ocean opening.

  13. Deriving spatial patterns from a novel database of volcanic rock geochemistry in the Virunga Volcanic Province, East African Rift

    Science.gov (United States)

    Poppe, Sam; Barette, Florian; Smets, Benoît; Benbakkar, Mhammed; Kervyn, Matthieu

    2016-04-01

    The Virunga Volcanic Province (VVP) is situated within the western branch of the East-African Rift. The geochemistry and petrology of its' volcanic products has been studied extensively in a fragmented manner. They represent a unique collection of silica-undersaturated, ultra-alkaline and ultra-potassic compositions, displaying marked geochemical variations over the area occupied by the VVP. We present a novel spatially-explicit database of existing whole-rock geochemical analyses of the VVP volcanics, compiled from international publications, (post-)colonial scientific reports and PhD theses. In the database, a total of 703 geochemical analyses of whole-rock samples collected from the 1950s until recently have been characterised with a geographical location, eruption source location, analytical results and uncertainty estimates for each of these categories. Comparative box plots and Kruskal-Wallis H tests on subsets of analyses with contrasting ages or analytical methods suggest that the overall database accuracy is consistent. We demonstrate how statistical techniques such as Principal Component Analysis (PCA) and subsequent cluster analysis allow the identification of clusters of samples with similar major-element compositions. The spatial patterns represented by the contrasting clusters show that both the historically active volcanoes represent compositional clusters which can be identified based on their contrasted silica and alkali contents. Furthermore, two sample clusters are interpreted to represent the most primitive, deep magma source within the VVP, different from the shallow magma reservoirs that feed the eight dominant large volcanoes. The samples from these two clusters systematically originate from locations which 1. are distal compared to the eight large volcanoes and 2. mostly coincide with the surface expressions of rift faults or NE-SW-oriented inherited Precambrian structures which were reactivated during rifting. The lava from the Mugogo

  14. The effects of naturally occurring impurities in rock salt

    Indian Academy of Sciences (India)

    In this paper we investigate the effect that naturally occurring impurities in salt mines have both on effective permittivity of the medium and on radio wave propagation at ∼200 MHz. The effective permittivity is determined based on the dielectric properties of salt and the characteristics of the main impurities. We conclude that ...

  15. Late Paleozoic volcanic rocks of the Intra-Sudetic Basin, Bohemian Massif: Petrological and geochemical characteristics

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Fediuk, F.; Lang, Miloš; Martinec, Petr

    2004-01-01

    Roč. 64, č. 2 (2004), s. 127-153 ISSN 0009-2819 R&D Projects: GA AV ČR(CZ) IAA3013903 Keywords : Late Paleozoic * volcanic rocks * Bohemian Massif Subject RIV: DB - Geology ; Mineralogy Impact factor: 0.643, year: 2004

  16. Upper Cretaceous to Pleistocene melilitic volcanic rocks of the Bohemian Massif: Petrology and mineral chemistry

    Czech Academy of Sciences Publication Activity Database

    Skála, Roman; Ulrych, Jaromír; Krmíček, Lukáš; Fediuk, F.; Balogh, K.; Hegner, E.

    2015-01-01

    Roč. 66, č. 3 (2015), s. 197-216 ISSN 1335-0552 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Cenozoic volcanism * isotope geochemistry * melilitic rock * mineralogy * petrology Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.523, year: 2015

  17. Uranium occurrences in the volcanic rocks of Upper Mahakam, east Kalimantan

    International Nuclear Information System (INIS)

    Djokolelono, S.; Agoes, E.

    1988-01-01

    The Kawat area, which is about 35 km 2 in size, is located in the Upper Mahakam region and is one of the areas being prospected in Kalimantan. It has already been covered by general, detailed and systematic prospection. The Kawat area formed a tectonical depression and was intercepted by the volcanic products of various episodes. The regional stratigraphy of this area, from the bottom upwards, is as follows: Unit 1: quartzite and ophiolitic green rock; Unit 2: black shale, sometimes with boulders of quartzite and radiolarite; Unit 3: massive conglomeratic sandstone, alternating with claystone and sandstone sequences; Unit 4: sandstone, siltstone and claystone, with an intercalation of volcanic rocks. Uraniferous occurrences are reflected by anomalous zones located in the volcanic facies of Unit 4, usually in aphanitic rhyolite. Mineralization consists of pitchblende associated with molybdenite and pyrite. Although the Kawat area is very remote, future development is of great interest. (author). 4 figs

  18. Nature and origin of secondary mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain, and Kane Springs Wash volcanic centers, southern, Nevada

    Science.gov (United States)

    Taranik, James V.; Hsu, Liang C.; Spatz, David M.; Chenevey, Michael J.

    1989-01-01

    The following subject areas are covered: (1) genetic, spectral, and LANDSAT Thematic Mapper imagery relationship between desert varnish and tertiary volcanic host rocks, southern Nevada; (2) reconnaissance geologic mapping of the Kane Springs Wash Volcanic Center, Lincoln County, Nevada, using multispectral thermal infrared imagery; (3) interregional comparisons of desert varnish; and (4) airborne scanner (GERIS) imagery of the Kane Springs Wash Volcanic Center, Lincoln County, Nevada.

  19. Stratigraphy and eruption age of the volcanic rocks in the west of Miyanoharu area, Kumamoto Prefecture

    International Nuclear Information System (INIS)

    Kamata, Hiroki

    1985-01-01

    The detailed stratigraphic survey, K-Ar age determinations and NRM measurements of the volcanic rocks in the west of Miyanoharu area revealed the volcanic history as follows: Hornblende andesite lava with plagioclase megacryst (Yoshinomoto lava) erupted during 2.8 - 2.5 Ma (Gauss normal epoch), accompanied by small amount of pyroclastic materials. After this eruption, Kamitarumizu hypersthene-augite andesite lava (1.7 - 1.3 Ma; reversed), Yabakei pyroclastic flow (0.99 Ma; Jaramillo normal event), Yamakogawa biotite rhyolite lava (0.9 Ma; reversed) and Daikanbo hypersthene-augite andesite lava (0.8 Ma; normal) erupted successively prior to the Aso-1 pyroclastic flow (0.3 - 0.4 Ma). Both the K-Ar ages and NRM data are consistent with the stratigraphic sequence (Fig. 2), which suggests that the activity of andesite and rhyolite is intercalated with each other during Pleistocene in the studied area. The compiled radiometric age data in the central-north Kyushu show that the age of volcanic activity that has previously been inferred as middle Miocene is of Pliocene, and its distribution is limited within the quadrilateral (60 km x 40 km) where the pre-Tertiary basement rocks are absent. The distribution of volcanic rocks is historically zonated such that the rocks of older age up to 5 Ma develop toward the outer rim of the quadrilateral, which coincides with the 0 mgal contour bordering the large low Bouguer anomaly. These facts suggest that the volcanic activity is remarkably relevant to the subsidence of this area, where the volcano-tectonic depression has been formed after 5 Ma to the present, and filled with lavas and pyroclastic materials with scarce sedimentary rocks in the tension stress field during Plio-Pleistocene age. (Kubozono, M.)

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

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    Oktay KILIÇ

    2009-02-01

    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.

  1. /sup 40/Ar//sup 39/Ar and K-Ar dating of altered glassy volcanic rocks: the Dabi Volcanics, P. N. G

    Energy Technology Data Exchange (ETDEWEB)

    Walker, D.A. (Australian National Univ., Canberra. Dept. of Geology); McDougall, I. (Australian National Univ., Canberra. Research School of Earth Sciences)

    1982-11-01

    K-Ar and /sup 40/Ar//sup 39/Ar ages have been determined for altered submarine tholeiitic and boninite (high-Mg andesite) lavas from the Dabi Volcanics, Cape Vogel Peninsula, Papua New Guinea. /sup 40/Ar//sup 39/Ar whole rock total fusion and plateau ages identify a Late Paleocene age for the tholeiitic lavas (58.9 +- 1.1 Ma), and also for the boninitic lavas (58.8 +- 0.8 Ma). Apparent K-Ar ages for the same samples range from 27.2 +- 0.7 to 63.9 +- 4.5 Ma, and young K-Ar ages for glassy boninites are probably due to variable radiogenic /sup 40/Ar(/sup 40/Ar*) loss. These new ages effectively reconcile previously ambiguous age data for the Dabi Volcanics, and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast PNG during the Late Paleocene. Smectites, developed as alteration products after glass in oceanic lavas commonly do not retain /sup 39/Ar during or subsequent to irradiation, but in some cases may contain /sup 40/Ar*. The results are discussed.

  2. 40Ar/39Ar and K-Ar dating of altered glassy volcanic rocks: the Dabi Volcanics, P.N.G

    International Nuclear Information System (INIS)

    Walker, D.A.; McDougall, I.

    1982-01-01

    K-Ar and 40 Ar/ 39 Ar ages have been determined for altered submarine tholeiitic and boninite (high-Mg andesite) lavas from the Dabi Volcanics, Cape Vogel Peninsula, Papua New Guinea. 40 Ar/ 39 Ar whole rock total fusion and plateau ages identify a Late Paleocene age for the tholeiitic lavas (58.9 +- 1.1 Ma), and also for the boninitic lavas (58.8 +- 0.8 Ma). Apparent K-Ar ages for the same samples range from 27.2 +- 0.7 to 63.9 +- 4.5 Ma, and young K-Ar ages for glassy boninites are probably due to variable radiogenic 40 Ar( 40 Ar*) loss. These new ages effectively reconcile previously ambiguous age data for the Dabi Volcanics, and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast PNG during the Late Paleocene. Smectites, developed as alteration products after glass in oceanic lavas commonly do not retain 39 Ar during or subsequent to irradiation, but in some cases may contain 40 Ar*. The results are discussed. (author)

  3. Petrography and petrology of Quaternary volcanic rocks from Ghezel Ghaleh, northwest Qorveh

    Directory of Open Access Journals (Sweden)

    Alireza Bajelan

    2014-10-01

    Full Text Available Introduction In the east and northeast of Sanandaj in the Qorveh-Bijar-Takab axis, there are series of basaltic composition volcanoes with Quaternary age. The study area is part of the Sanandaj-Sirjan zone and is located between 47°52' and 47°57' E longitudes and 35°26 and '35°30' N latitudes. Due to the location of the volcanic cone on Pliocene clastic sediments and Quaternary travertine, the age of these volcanoes is considered to be Quaternary. The cones mostly consist of low scoria, ash, volcanic bombs, lapilli deposits and basaltic lava (Moein Vaziri and Aminsobhani, 1985. Petrological and geochemical studies have been carried out to evaluate Quaternary magmatism in the area and to determine the nature of the lithological characteristics, such as the evaluation of source rocks and magma type, degree of partial melting and the tectonic setting of Ghezel Ghaleh rocks (Moein Vaziri, 1997. Simplified geological map of the study area is characterized by ER-Mapper software. Materials and methods In the course of field studies in the region, 40 samples were taken, 30 thin sections were prepared and polished. XRD analyses were performed on some whole rock samples. All major, minor and trace elements were assessed by ICP-MS at Lab Weft Laboratory in Australia. Results Based on the classification of structural zones, the area is located in the Sanandaj-Sirjan zone, hundred kilometers away from the main Zagros thrust along the NW-SE direction. After early Cimmerian orogeny, andesitic volcanic activity took place (Moein Vaziri and Aminsobhani, 1985. A major secondary mineral in these rocks is iddingsite, formed by hydration and oxidation of the olivine (Shelley, 1993. According to SiO2 against Na2O + K2O (TAS diagram (Irvine and Baragar , 1971 and cationic R1 and R2 diagram (De La Roche et el., 1980, volcanic rocks of the area indicate alkaline series. Discussion To obtain more information on the tectonic setting of these rocks, the Zr/Y-Zr diagram

  4. Petrogenesis and tectonic implication of the Late Triassic post-collisional volcanic rocks in Chiang Khong, NW Thailand

    Science.gov (United States)

    Qian, Xin; Wang, Yuejun; Feng, Qinglai; Zi, Jian-Wei; Zhang, Yuzhi; Chonglakmani, Chongpan

    2016-04-01

    The volcanic rocks exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand provide important constraints on the tectonic evolution of the eastern Paleotethys ocean. An andesite sample from the Chiang Khong area yields a zircon U-Pb age of 229 ± 4 Ma, significantly younger than the continental-arc and syn-collisional volcanic rocks (ca. 238-241 Ma). The Chiang Khong volcanic rocks are characterized by low MgO (1.71-6.72 wt.%) and high Al2O3 (15.03-17.76 wt.%). They are enriched in LILEs and LREEs and depleted in HFSEs, and have 87Sr/86Sr (i) ratios of 0.7050-0.7065, εNd (t) of - 0.32 to - 1.92, zircon εHf (t) and δ18O values of 3.5 to - 11.7 and 4.30-9.80 ‰, respectively. The geochemical data for the volcanic rocks are consistent with an origin from the enriched lithospheric mantle that had been modified by slab-derived fluid and recycled sediments. Based on available geochronological and geochemical evidences, we propose that the Late Triassic Chiang Khong volcanic rocks are equivalent to the contemporaneous volcanic rocks in the Lancangjiang igneous zone in SW China. The formation of these volcanic rocks was possibly related to the upwelling of the asthenospheric mantle during the Late Triassic, shortly after slab detachment, which induced the melting of the metasomatized mantle wedge.

  5. Change with time in extrusion and chemical composition of volcanic rock in geothermal areas in central Kyushu

    Energy Technology Data Exchange (ETDEWEB)

    Kamata, Hiroki

    1986-10-01

    Changes with time in extrusion and chemical composition of volcanic rocks in central Kyushu are studied to provide basic data required for evaluation of geothermal resources. Distribution of volcanic rocks in successive 1Ma (10/sup 6/ year) periods and the average thickness of volcanic rock layers in each period are determined, from which the volume of volcanic rocks in each 1Ma period is calculated. Results indicate that volcanos in central Kyushu extruded about 3,000 km/sup 3//Ma of volcanic rocks during the early periods (about 5Ma), followed by a series of declining periods up to the present. Comparison of volcanic extrusive rocks of each 1Ma period shows that lava of hornblende andesite and pyroxenic andesite has been extruded in great quantities in every period. Chemical composition is studied based on diagrams showing changes in SiO/sub 2/ content. The K/sub 2/O content is relatively high in most volcanos younger than 1.6Ma, compared to those older than 1.6Ma. the K/sub 2/O content in extruded rocks has been high during the latest 0.4Ma in the Aso volcanic area, unlike other island arc conjunction areas. (4 figs, 5 tabs, 28 refs)

  6. Development of a mixed seawater-hydrothermal fluid geochemical signature during alteration of volcanic rocks in the Archean (∼2.7 Ga) Abitibi Greenstone Belt, Canada

    Science.gov (United States)

    Brengman, Latisha A.; Fedo, Christopher M.

    2018-04-01

    We investigated a group of silicified volcanic rocks from the ∼2.72 Ga Hunter Mine Group (HMG), Abitibi Greenstone Belt, Canada, in order to document progressive compositional change associated with alteration in a subaqueous caldera system. Rocks of the HMG divide into three groups based on mineralogy and texture for petrographic and geochemical analyses. Volcanic features (phenocrysts, pseudomorphs after primary glass shards, lapilli, volcanic clasts) are preserved in all groups, despite changing mineralogy from primarily quartz, feldspar, chlorite (Groups 1 and 2), to quartz, hematite and carbonate (Groups 2 and 3). Compositionally, Group 1 rocks resemble volcanic rocks in the region, while Group 2 and 3 rocks show a change in mineralogy to iron, silica, and carbonate minerals, which is associated with depletion of many major and trace elements associated with volcanic rocks (Al2O3, Na2O, K2O, Zr). In addition, rare earth elements display a clear progression from volcanic signatures in Group 1 (PrSN/YbSN = 1.7-2.96, EuSN/EuSN∗ = 0.84-1.72, Y/Ho = 25.20-27.41, LaSN/LaSN∗ = 0.97-1.29, and Zr/Hf = 38.38-42.09) to transitional mixed volcanic, hydrothermal, and seawater signatures in Group 2 (PrSN/YbSN 1.33-2.89, EuSN/EuSN∗ 1.33-2.5, Y/Ho = 23.94-30, LaSN/LaSN∗ 0.93-1.34, and Zr/Hf = 40-70), to mixed hydrothermal and seawater signatures in Group 3 (PrSN/YbSN 0.62-2.88, EuSN/EuSN∗ 1.30-7.15, LaSN/LaSN∗ 1.02-1.86, Y/Ho = 25.56-55, and Zr/Hf = 35-50). We interpret that silicification of volcanic rocks (Group 1) produced transitional altered volcanic rocks (Group 2), and siliceous and jaspilitic rocks (Group 3), based on preservation of delicate volcanic features. Building on this explanation, we interpret that major, trace- and rare-earth element mobility occurred during the process of silicification, during which siliceous and jaspilitic rocks (Group 3) acquired aspects of the rare-earth element geochemical signatures of marine chemical precipitates. We

  7. Petrogenesis of volcanic rocks that host the world-class Agsbnd Pb Navidad District, North Patagonian Massif: Comparison with the Jurassic Chon Aike Volcanic Province of Patagonia, Argentina

    Science.gov (United States)

    Bouhier, Verónica E.; Franchini, Marta B.; Caffe, Pablo J.; Maydagán, Laura; Rapela, Carlos W.; Paolini, Marcelo

    2017-05-01

    We present the first study of the volcanic rocks of the Cañadón Asfalto Formation that host the Navidad world-class Ag + Pb epithermal district located in the North Patagonian Massif, Patagonia, Argentina. These volcanic and sedimentary rocks were deposited in a lacustrine environment during an extensional tectonic regime associated with the breakup of Gondwana and represent the mafic to intermediate counterparts of the mainly silicic Jurassic Chon Aike Volcanic Province. Lava flows surrounded by autobrecciated carapace were extruded in subaerial conditions, whereas hyaloclastite and peperite facies suggest contemporaneous subaqueous volcanism and sedimentation. LA-ICPMS Usbnd Pb ages of zircon crystals from the volcanic units yielded Middle Jurassic ages of 173.9 ± 1.9 Ma and 170.8 ± 3 Ma. In the Navidad district, volcanic rocks of the Cañadón Asfalto Formation show arc-like signatures including high-K basaltic-andesite to high-K dacite compositions, Rb, Ba and Th enrichment relative to the less mobile HFS elements (Nb, Ta), enrichment in light rare earth elements (LREE), Ysbnd Ti depletion, and high Zr contents. These characteristics could be explained by assimilation of crustal rocks in the Jurassic magmas, which is also supported by the presence of zircon xenocrysts with Permian and Middle-Upper Triassic ages (281.3 Ma, 246.5, 218.1, and 201.3 Ma) and quartz xenocrysts recognized in these volcanic units. Furthermore, Sr and Nd isotope compositions suggest a contribution of crustal components in these Middle Jurassic magmas. High-K basaltic andesite has initial 87Sr/86Sr ratios of 0.70416-0.70658 and ξNd(t) values of -5.3 and -4. High-K dacite and andesite have initial 87Sr/86Sr compositions of 0.70584-0.70601 and ξNd(t) values of -4,1 and -3,2. The range of Pb isotope values (206Pb/204Pb = 18.28-18.37, 207Pb/204Pb = 15.61-15.62, and 208Pb/204Pb = 38.26-38.43) of Navidad volcanic rocks and ore minerals suggest mixing Pb sources with contributions of

  8. Volcanic instability: the effects of internal pressurisation and consideration of rock mass properties

    Science.gov (United States)

    Thomas, M.; Petford, N.; Bromhead, E. N.

    2003-04-01

    Since the events at mount St Helens during May 1980, there has been considerable attention focused on the mechanisms and consequences of volcanic edifice collapse. As a result catastrophic edifice failure is now recognised as perhaps the most socially devastating natural disaster associated with volcanic activity. The tendency of volcanic edifices to fail appears ubiquitous behaviour, and a number of failure precursors and more importantly triggers have been suggested, of which magmagenic (e.g. thermal and mechanical pore pressure increases) and seismogenic (e.g. tectonic or volcanic earthquakes) are common. Despite the increased interest in this field, large-scale, deep seated catastrophic edifice failure has still only be successfully modelled in the most extreme of cases, which does not account for the volume of field evidence of edifice collapse. One possible reason for this is the way that pore pressures are considered. For pore fluids that are entering the system from the surface (e.g. rain water) there is a set volume and therefore a set pressure that the system can accommodate, as once the edifice becomes saturated, any new fluids to fall on the surface of the edifice simply run off. If we consider internal pore fluid pressurisation from magmatic gasses, then the pressurising fluid is already in the system and the only limit to how much pressure can be accommodated is the strength of the edifice itself. The failure to fully consider the strength and deformability of a rock mass compared to an intact laboratory sample of a volcanic rock may result in a misleading assessment of edifice strength. An intact laboratory sample of basalt may yield a strength of 100--350 MPa (from uniaxial compression tests), a volcanic edifice however is not an intact rock, and is cut through by many discontinuities, including; faults, fractures and layering from discrete lava flows. A better approximation of the true strength can be determined from the rock mass rating (RMR

  9. The systematics of lithium abundances in young volcanic rocks

    International Nuclear Information System (INIS)

    Ryan, J.G.; Langmuir, C.H.

    1987-01-01

    Lithium is a moderately incompatible trace element in magmatic systems. High precision analyses for lithium conducted on well characterized suites of MORB and ocean island basalts suggest a bulk distribution coefficient of 0.25-0.35 and behavior which is similar to Yb during low pressure fractionation and V during melting, as long as garnet is not an important residual phase. Data for peridotites and basalts suggest a mantle lithium content of about 1.9 ppm and show that significant concentrations of lithium reside in olivine and orthopyroxene, resulting in unusual inter-mineral partitioning of Li and complex relationships between lithium and other incompatible trace elements. The lithium abundances of arc basalts are similar to those of MORB, but their Li/Yb ratios are considerably higher. The high Li/Yb suggests the addition of a Li-rich component to arc sources; relatively low Yb abundances are consistent with the derivation of some arc magmas by larger extents of melting or from a more depleted source than MORB. Although Li is enriched at arcs, K is enriched more, leading to elevated K/Li ratios in arc volcanics. The high K/Li and relatively low La/Yb of primitive arc basalts requires either incorporation of altered ocean crust into arc magma sources, or selective removal of K and Li from subducted sediments. Bulk incorporation of sediments alone does not explain the Li systematics. Data from primitive MORB indicate a relatively low (3-4 ppm) Li content for new oceanic crust. Thus, the Li flux from the ocean crust is probably 11 g/yr, and the oceanic crust may not be an important net source in the oceanic budget of lithium. (author)

  10. The relationship between carbonate facies, volcanic rocks and plant remains in a late Palaeozoic lacustrine system (San Ignacio Fm, Frontal Cordillera, San Juan province, Argentina)

    Science.gov (United States)

    Busquets, P.; Méndez-Bedia, I.; Gallastegui, G.; Colombo, F.; Cardó, R.; Limarino, O.; Heredia, N.; Césari, S. N.

    2013-07-01

    The San Ignacio Fm, a late Palaeozoic foreland basin succession that crops out in the Frontal Cordillera (Argentinean Andes), contains lacustrine microbial carbonates and volcanic rocks. Modification by extensive pedogenic processes contributed to the massive aspect of the calcareous beds. Most of the volcanic deposits in the San Ignacio Fm consist of pyroclastic rocks and resedimented volcaniclastic deposits. Less frequent lava flows produced during effusive eruptions led to the generation of tabular layers of fine-grained, greenish or grey andesites, trachytes and dacites. Pyroclastic flow deposits correspond mainly to welded ignimbrites made up of former glassy pyroclasts devitrified to microcrystalline groundmass, scarce crystals of euhedral plagioclase, quartz and K-feldspar, opaque minerals, aggregates of fine-grained phyllosilicates and fiammes defining a bedding-parallel foliation generated by welding or diagenetic compaction. Widespread silicified and silica-permineralized plant remains and carbonate mud clasts are found, usually embedded within the ignimbrites. The carbonate sequences are underlain and overlain by volcanic rocks. The carbonate sequence bottoms are mostly gradational, while their tops are usually sharp. The lower part of the carbonate sequences is made up of mud which appear progressively, filling interstices in the top of the underlying volcanic rocks. They gradually become more abundant until they form the whole of the rock fabric. Carbonate on volcanic sandstones and pyroclastic deposits occur, with the nucleation of micritic carbonate and associated production of pyrite. Cyanobacteria, which formed the locus of mineral precipitation, were related with this nucleation. The growth of some of the algal mounds was halted by the progressive accumulation of volcanic ash particles, but in most cases the upper boundary is sharp and suddenly truncated by pyroclastic flows or volcanic avalanches. These pyroclastic flows partially destroyed the

  11. Petrogenesis of Pliocene Alkaline Volcanic Rocks from Southeastern Styrian Basin, Austria

    Science.gov (United States)

    Ali, Sh.; Ntaflos, Th.

    2009-04-01

    Petrogenesis of Pliocene Alkaline Volcanic Rocks from Southeastern Styrian Basin, Austria Sh. Ali and Th. Ntaflos Dept. of Lithospheric Research, University of Vienna, Austria Neogene volcanism in the Alpine Pannonian Transition Zone occurred in a complex geodynamic setting. It can be subdivided into a syn-extentional phase that comprises Middle Miocene dominantly potassic, intermediate to acidic volcanism and a post-extensional phase, which is characterized by eruption of alkaline basaltic magmas during the Pliocene to Quartenary in the Styrian Basin. These alkaline basaltic magmas occur as small eruptive centers dominating the geomorphology of the southeastern part of the Styrian Basin. The eruptive centers along the SE Styrian Basin from North to South are: Oberpullendorf, Pauliberg, Steinberg, Strandenerkogel, Waltrafelsen and Klöch. The suite collected volcanic rocks comprise alkali basalts, basanites and nephelinites. Pauliberg: consists of alkali basalts that exhibit a narrow range of SiO2 (44.66-47.70 wt %) and wide range of MgO (8.52-13.19-wt %), are enriched in TiO2 (3.74-4.18 wt %). They are enriched in incompatible trace elements such as Zr (317-483 ppm), Nb (72.4-138 ppm) and Y (30.7-42 ppm). They have Nb/La ratio of 1.89 (average) and Cen/Ybn=15.22-23.11. Oberpullendorf: it also consists of alkali basalts with higher SiO2 (50.39 wt %) and lower TiO2 (2.80 wt %) if compared with the Pauliberg suite. Incompatible trace elements are lower than in Pauliberg; Zr =217 ppm, Nb=49.8 ppm, Y=23.6 ppm and Nb/La=1.93. The Oberpullendorf alkalibasalts are relative to Pauliberg lavas more depleted in LREE (Cen/Ybn=12.78). Steinberg: it consists of basanites with SiO2=44.49-46.85 wt %, MgO=6.30-9.13-wt %, and TiO2 =2.09-2.26 wt %. They are enriched in incompatible trace elements such as Zr (250-333 ppm), Nb (94-130 ppm), Y (24.7-31.9 ppm) and Nb/La=1.59 (average). The Cen/Ybn ratio varies between 18.17 and 22.83 indicating relative steep REE chondrite normalized

  12. Complex conductivity of volcanic rocks and the geophysical mapping of alteration in volcanoes

    Science.gov (United States)

    Ghorbani, A.; Revil, A.; Coperey, A.; Soueid Ahmed, A.; Roque, S.; Heap, M. J.; Grandis, H.; Viveiros, F.

    2018-05-01

    Induced polarization measurements can be used to image alteration at the scale of volcanic edifices to a depth of few kilometers. Such a goal cannot be achieved with electrical conductivity alone, because too many textural and environmental parameters influence the electrical conductivity of volcanic rocks. We investigate the spectral induced polarization measurements (complex conductivity) in the frequency band 10 mHz-45 kHz of 85 core samples from five volcanoes: Merapi and Papandayan in Indonesia (32 samples), Furnas in Portugal (5 samples), Yellowstone in the USA (26 samples), and Whakaari (White Island) in New Zealand (22 samples). This collection of samples covers not only different rock compositions (basaltic andesite, andesite, trachyte and rhyolite), but also various degrees of alteration. The specific surface area is found to be correlated to the cation exchange capacity (CEC) of the samples measured by the cobalthexamine method, both serving as rough proxies of the hydrothermal alteration experienced by these materials. The in-phase (real) conductivity of the samples is the sum of a bulk contribution associated with conduction in the pore network and a surface conductivity that increases with alteration. The quadrature conductivity and the normalized chargeability are two parameters related to the polarization of the electrical double layer coating the minerals of the volcanic rocks. Both parameters increase with the degree of alteration. The surface conductivity, the quadrature conductivity, and the normalized chargeability (defined as the difference between the in-phase conductivity at high and low frequencies) are linearly correlated to the CEC normalized by the bulk tortuosity of the pore space. The effects of temperature and pyrite-content are also investigated and can be understood in terms of a physics-based model. Finally, we performed a numerical study of the use of induced polarization to image the normalized chargeability of a volcanic edifice

  13. Magmatic evolution of Panama Canal volcanic rocks: A record of arc processes and tectonic change.

    Directory of Open Access Journals (Sweden)

    David W Farris

    Full Text Available Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21-25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm. exhibit reduced Nb-Ta anomalies, flattened REE curves, depleted fluid mobile elements, a THI of 1.45, a H2Ocalc of <1 wt. %, and plot in mid-ocean ridge/back-arc basin fields. Geochemical modeling of Miocene rocks indicates 0.5-0.1 kbar crystallization depths of hot (1100-1190°C magmas in which most compositional diversity can be explained by fractional crystallization (F = 0.5. However, the most silicic lavas (Las Cascadas Fm. require an additional mechanism, and assimilation-fractional-crystallization can reproduce observed compositions at reasonable melt fractions. The Canal volcanic rocks, therefore, change from hydrous basaltic pyroclastic deposits typical of mantle-wedge-derived magmas, to hot, dry bi-modal magmatism at the Oligocene-Miocene boundary. We suggest the primary reason for the change is onset of arc perpendicular extension localized to central Panama. High-resolution mapping along the Panama Canal has revealed a sequence of inward dipping maar-diatreme pyroclastic pipes, large basaltic sills, and bedded silicic ignimbrites and tuff deposits. These volcanic bodies intrude into the sedimentary Canal Basin and are cut by normal and subsequently strike-slip faults. Such pyroclastic pipes and basaltic sills are most common in extensional arc and large igneous province environments. Overall, the change in volcanic edifice form and geochemistry are related to onset of arc perpendicular extension, and are consistent with the

  14. Magmatic evolution of Panama Canal volcanic rocks: A record of arc processes and tectonic change

    Science.gov (United States)

    Cardona, Agustin; Montes, Camilo; Foster, David; Jaramillo, Carlos

    2017-01-01

    Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21–25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm. exhibit reduced Nb-Ta anomalies, flattened REE curves, depleted fluid mobile elements, a THI of 1.45, a H2Ocalc of arc basin fields. Geochemical modeling of Miocene rocks indicates 0.5–0.1 kbar crystallization depths of hot (1100–1190°C) magmas in which most compositional diversity can be explained by fractional crystallization (F = 0.5). However, the most silicic lavas (Las Cascadas Fm.) require an additional mechanism, and assimilation-fractional-crystallization can reproduce observed compositions at reasonable melt fractions. The Canal volcanic rocks, therefore, change from hydrous basaltic pyroclastic deposits typical of mantle-wedge-derived magmas, to hot, dry bi-modal magmatism at the Oligocene-Miocene boundary. We suggest the primary reason for the change is onset of arc perpendicular extension localized to central Panama. High-resolution mapping along the Panama Canal has revealed a sequence of inward dipping maar-diatreme pyroclastic pipes, large basaltic sills, and bedded silicic ignimbrites and tuff deposits. These volcanic bodies intrude into the sedimentary Canal Basin and are cut by normal and subsequently strike-slip faults. Such pyroclastic pipes and basaltic sills are most common in extensional arc and large igneous province environments. Overall, the change in volcanic edifice form and geochemistry are related to onset of arc perpendicular extension, and are consistent with the idea that Panama arc crust fractured during collision

  15. Measurement of hydrogeologic parameters of Indian volcanic rocks by sub-surface hydronuclear techniques

    International Nuclear Information System (INIS)

    Bardhan, M.

    1977-01-01

    Sub-surface hydronuclear techniques namely neutron-neutron, gamma-gamma and tracer dilution logging and single and double well tracer methods were adopted to investigate the hitherto inadequately studied hydrophysical properties of the Deccan lava flows which constitute the principal Indian volcanic suit of rocks. The hydrogeologic parameters measured in the field pertain to hydrostratigraphy, hydrostorage properties and geohydraulic characteristics of these layered hard formations. Results of the studies are presented and discussed briefly. (author)

  16. Problems in the K-Ar dating of Quaternary volcanic rocks younger than 1 Ma

    International Nuclear Information System (INIS)

    Takaoka, Nobuo

    1989-01-01

    The assumption that the 40 Ar/ 36 Ar ratio of Ar trapped in volcanic rocks at eruption is atmospheric often gives a large systematic error in the K-Ar dating of Quaternary volcanic rocks younger than 1 Ma. There are two possible sources of error, the existence of excess Ar and mass-fractionated, initial Ar. The major source of excess Ar is supposed to be magma. The 40 Ar/ 36 Ar ratio for magmatic Ar in the North-East Japan arc is tentatively estimated to be 340±10 from measurements of Ar in large phenocrysts separated from Quaternary volcanic rocks. Separation of phenocrysts is the most effective to decrease the systematic error caused by excess Ar. The mass-fractionation of initial Ar should give the 38 Ar/ 36 Ar ratio which was changed from the atmospheric ratio. This can be checked by determining the 38 Ar/ 36 Ar ratio in samples. Since the systematic error caused by the mass-fractionated, initial Ar increases greatly with the increasing atmospheric Ar correction, it is important to correct the result for the mass-fractionation. Correction formulae are given. The error sources other than those mentioned above are uncertainty in the blank correction and instabilities in the sensitivity of spectrometer and the Ar isotopic ratio measurement. In order to increase accuracy of the K-Ar age obtained, to check the systematic errors by measuring samples together with standard samples is of great importance in the K-Ar dating of very young volcanic rocks. (author)

  17. The effect of offset on fracture permeability of rocks from the Southern Andes Volcanic Zone, Chile

    Science.gov (United States)

    Pérez-Flores, P.; Wang, G.; Mitchell, T. M.; Meredith, P. G.; Nara, Y.; Sarkar, V.; Cembrano, J.

    2017-11-01

    The Southern Andes Volcanic Zone (SVZ) represents one of the largest undeveloped geothermal provinces in the world. Development of the geothermal potential requires a detailed understanding of fluid transport properties of its main lithologies. The permeability of SVZ rocks is altered by the presence of fracture damage zones produced by the Liquiñe-Ofqui Fault System (LOFS) and the Andean Transverse Faults (ATF). We have therefore measured the permeability of four representative lithologies from the volcanic basement in this area: crystalline tuff, andesitic dike, altered andesite and granodiorite. For comparative purposes, we have also measured the permeability of samples of Seljadalur basalt, an Icelandic rock with widely studied and reported hydraulic properties. Specifically, we present the results of a systematic study of the effect of fractures and fracture offsets on permeability as a function of increasing effective pressure. Baseline measurements on intact samples of SVZ rocks show that the granodiorite has a permeability (10-18 m2), two orders of magnitude higher than that of the volcanic rocks (10-20 m2). The presence of throughgoing mated macro-fractures increases permeability by between four and six orders of magnitude, with the highest permeability recorded for the crystalline tuff. Increasing fracture offset to produce unmated fractures results in large increases in permeability up to some characteristic value of offset, beyond which permeability changes only marginally. The increase in permeability with offset appears to depend on fracture roughness and aperture, and these are different for each lithology. Overall, fractured SVZ rocks with finite offsets record permeability values consistent with those commonly found in geothermal reservoirs (>10-16 m2), which potentially allow convective/advective flow to develop. Hence, our results demonstrate that the fracture damage zones developed within the SVZ produce permeable regions, especially within the

  18. Subaqueous early eruptive phase of the late Aptian Rajmahal volcanism, India: Evidence from volcaniclastic rocks, bentonite, black shales, and oolite

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    Naresh C. Ghose

    2017-07-01

    Full Text Available The late Aptian (118–115 Ma continental flood basalts of the Rajmahal Volcanic Province (RVP are part of the Kerguelen Large Igneous Province, and constitute the uppermost part of the Gondwana Supergroup on the eastern Indian shield margin. The lower one-third of the Rajmahal volcanic succession contains thin layers of plant fossil-rich inter-trappean sedimentary rocks with pyroclasts, bentonite, grey and black shale/mudstone and oolite, whereas the upper two-thirds consist of sub-aerial fine-grained aphyric basalts with no inter-trappean material. At the eastern margin and the north-central sector of the RVP, the volcanics in the lower part include rhyolites and dacites overlain by enstatite-bearing basalts and enstatite-andesites. The pyroclastic rocks are largely felsic in composition, and comprise ignimbrite as well as coarse-grained tuff with lithic clasts, and tuff breccia with bombs, lapilli and ash that indicate explosive eruption of viscous rhyolitic magma. The rhyolites/dacites (>68 wt.% are separated from the andesites (<60 wt.% by a gap in silica content indicating their formation through upper crustal anatexis with only heat supplied by the basaltic magma. On the other hand, partially melted siltstone xenoliths in enstatite-bearing basalts suggest that the enstatite-andesites originated through mixing of the upper crust with basaltic magma, crystallizing orthopyroxene at a pressure-temperature of ∼3 kb/1150 °C. In contrast, the northwestern sector of the RVP is devoid of felsic-intermediate rocks, and the volcaniclastic rocks are predominantly mafic (basaltic in composition. Here, the presence of fine-grained tuffs, tuff breccia containing sideromelane shards and quenched texture, welded tuff breccia, peperite, shale/mudstone and oolite substantiates a subaqueous environment. Based on these observations, we conclude that the early phase of Rajmahal volcanism occurred under predominantly subaqueous conditions. The presence

  19. Mineral chemistry and petrogenesis of the Gurgur Mount volcanic rocks (Northeast Takab

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    Dariush Esmaeily

    2016-12-01

    Full Text Available Andesitic and andesitic-basaltic lavas are widespread over most of the ground surface of the Gurgur area altered mostly by the hydrothermal solutions. The main rock forming minerals in these rocks are plagioclase, pyroxene and olivine affected by the hydrothermal solutions. The altered rocks do contain minerals including calcite, sericite and chlorite. Given the results obtained and the mineral chemistry studies, the clinopyroxenes formed in the area are, chemically, calkalkaline and of diopside-augite type formed in subvolcanic to near surface levels contemporaneous with magma ascending. Plagioclase minerals show zoning textures and lie within the two andesine and albite-oligoclase fields. These units, in terms of total rock chemistry, are classified as the calk-alkaline volcanic rocks formed in the continental arcs. On the other hand, on the trace elements chondrite-normalized diagrams and enriched mantle-normalized multi- element diagrams, the LREE enrichment relative to the HREE is observed. The LILE (i.e. Rb, K and Th and the LREE (e.g. La, Ce and Nd show an enrichment in comparison to the HFSE (Zr, Hf, Nb, Yb, Y and Sm. Given the Nd/Th (1.42-1.15, Zr/Nb (12.27-21.22, Ba/La (18.64-29.77 as well as LILE enrichment associated with depletion in Nb, Ta and Ti, an environment related to the subduction zones can be proposed for the area under study. Moreover, the similarity between the REE distribution pattern and the incompatible elements point to the genetic relationship between these rocks. Finally, on the base of the obtained data, it can be concluded that the volcanic rocks in the Gurgur Mountain were likely formed during the extended magmatism of the Urumieh-Dokhtar in the Cenozoic.

  20. 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

    2014-10-01

    the presence of labradorite, bytownite, anorthite as the plagioclases in volcanic rocks, as well as augite, pigeonite and clinoenstatite among the pyroxenes are abundant. Microscopic study of these lavas and pyroclastic rocks show evidences of magmatic contamination in the form of oscillatory zoning, resorption rims in plagioclase and presence of basic inclusions. The presence of oxidized amphibole rims (in hornblende indicates the high temperature of the magma at the time of eruption. Based on geochemistry especially the ratio of Eu/Eu* is variable between liquid and solid phases. The calculated of this ratio in studied rocks show negative anomaly (Eu According to classification diagrams is used of different diagrams for example TAS/SiO2, R1-R2 and Zr/TiO2-Nb/Y. TAS/SiO2 diagram show that the rocks are of basaltic-andesite, andesite and dacite. R1-R2 diagram show these rocks are andesite, andesi-basalt, dacite and rhyodacite. Finally, based on Zr/TiO2-Nb/Y the rocks in area under study are andesite, basalt, dacite and rhyodacite type. The geochemical diagrams (such as AFM for identify of mama series show that the rocks studied are calc-alkaline and A/NK-A/CNK show magma is peraluminous to metaluminous in nature. Enrichment of incompatible and LILE elements such as Ba, K and Rb show that contamination of magma with continental crust have been occurred in this area. Similarity between REE patterns in all samples is related to common source for all volcanic rocks in the studied area. Discussion The tectonic setting diagrams show that these rocks belong to the continental margin which have been involved in a subduction zone and belong to the orogenic andesite belt. The position of the samples on the major elements-SiO2 diagrams indicate that magma differentiation has been occurred. Spider diagrams show depletion and enrichment that the type of rocks in studied area have positive anomalous of Rb and negative anomalous of Nb and Ti, this phenomenon shows contamination

  1. Influence of hydrothermal processes on changes of volcanic rocks (data of physical modelling)

    Science.gov (United States)

    Shanina, V. V.; Bychkov, A. Y.

    2009-04-01

    Due to active development of geothermal energy, in middle of the last century have begun papers devoted to experiments, directed on study of transformations of minerals [4] and rocks [1, 2, 5] under action of geothermal processes. But any researcher did not estimate thus change of their physical and physico-mechanical properties. The purpose of job - to study character and dynamics changes of volcanic rocks (to simulate conditions of geothermal transformations). Tasks: creation of the whole series of experiments in autoclavs at various temperatures, pressure and composition of solutions, preparation of samples, study of chemical and mineral composition, structure and properties of rocks and solutions before and after experiments. In 2006 the first similar experiments were begun [3]. Researched rocks basalts, hyaloclasites and obsidian, selected from Iceland and tuffs Payzhetka Geothermal Field, Southern Kamchatka, Russia. Were used autoclavs, consisting from titanic of an alloy ВТ-8, volume 116-119 мл, in each of which was located from 2 up to 4 samples of rocks of the investigated structure and properties. The heating was made in OVEN ТРМ-10 with accuracy + 1 °С, the constancy of temperature was supervised by thermocouples. 15 experiences (temperature 200, 300 and 450 °С; pressure 16, 86 and 1000 bars accordingly now are carried out; 4 solutions (1 alkaline and 3 acid); duration 14, 15, 30 and 60 days). All four groups of the investigated rocks appreciablly react under geothermal influence. The changes are observed in colour of samples (brighten in acid solutions), their microstructure, that for basalts is visible only in raster electronic microscope, and in education of new mineral phases, is especially active in a acid solution, the X-Ray analysis (has executed by Dr. Krupskaya V.V., apparatuses - DRON- UM1) has shown, that 94,2 % is smectite, 3,5 % - kaolinite, 1,2 % - crisrobalite, 1,1 % - diopside (?), in others pores fills chlorite, and in an

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

    Directory of Open Access Journals (Sweden)

    Masoumeh Goodarzi

    2014-10-01

    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

  3. Division of volcanic activity cycles in the late mesozoic in South Jiangxi and North Guangdong

    International Nuclear Information System (INIS)

    Li Qinglong; Wu Jianhua

    1999-01-01

    Based on stratigraphical unconformity, rock association, fossil assemblage, isotope age and tectonic features, the volcanic activity in late Mesozoic in south Jiangxi and north Guandong can be divided into four cycles: Yutian volcanic activity cycle, Lianhuazhai volcanic activity cycle. Banshi volcanic activity cycle and Nanxiong volcanic activity cycle. Yutian volcanic cycle which occurs in middle Jurassic epoch is the bimodal rock association composed of rhyolite and basalt. Lianhuazhai volcanic cycle which occurs in late Jurassic epoch is unimodal rock association composed of rhyolite. Banshi volcanic cycle occurs from the late stage of early Cretaceous to the early stage of late Cretaceous epoch. There are two types of rock associations related to this cycle: unimodal rock association composed of rhyolite or basalt and bimodal rock association composed of rhyolite and basalt. Nanxiong volcanic activity cycle which occurred in late stage of late Cretaceous epoch is the unimodal rock association composed of basalt which is the interlayer of the red sedimentary series

  4. Fracturing Fluid Leak-off for Deep Volcanic Rock in Zhungeer Basin: Mechanism and Control Method

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    Huang Bo

    2017-01-01

    Full Text Available The deep volcanic reservoir in Zhungeer Basin is buried in over 4000m depth, which is characterized by complex lithology (breccia, andesite, basalt, etc., high elastic modulus and massive natural fractures. During hydraulic fracturing, hydraulic fracture will propagate and natural fractures will be triggered by the increasing net pressure. However, the extension of fractures, especially natural fractures, would aggravate the leak-off effect of fracturing fluid, and consequently decrease the fracturing success rate. 4 out of 12 fracturing wells in the field have failed to add enough proppants due to fluid loss. In order to increase the success rate and efficiency of hydraulic fracturing for deep volcanic reservoir, based on theoretical and experimental method, the mechanism of fracturing fluid leak-off is deeply studied. We propose a dualistic proppant scheme and employ the fluid loss reducer to control the fluid leak-off in macro-fractures and micro-fractures respectively. The proposed technique remarkably improved the success rate in deep volcanic rock fracturing. It bears important theoretical value and practical significance to improve the hydraulic fracturing design for deep volcanic reservoir.

  5. Neogene seismites and seismic volcanic rocks in the Linqu area, Shandong Province, E China

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    Tian H.S.

    2014-07-01

    Full Text Available The Yishu Fault Zone runs through the centre of Shandong Province (E China; it is a deep-seated large fault system that still is active. Two volcanic faulted basins (the Shanwang and Linqu Basins in the Linqu area, west of the fault zone, are exposed to rifting, which process is accompanied by a series of tectonic and volcanic earthquakes with a magnitude of 5-8. Lacustrine sediments in the basins were affected by these earthquakes so that seismites with a variety of soft-sediment deformation structures originated. The seismites form part of the Shanwang Formation of the Linqu Group. Semi-consolidated fluvial conglomerates became deformed in a brittle way; these seismites are present at the base of the Yaoshan Formation. Intense earthquakes triggered by volcanic activity left their traces in the form of seismic volcanic rocks associated with liquefied-sand veins in the basalt/sand intercalations at the base of the Yaoshan Formation. These palaeo-earthquake records are dated around 14-10 Ma; they are responses to the intense tectonic extension and the basin rifting in this area and even the activity of the Yishu Fault Zone in the Himalayan tectonic cycle.

  6. Petrography and geochemistry of the volcanic rocks of the Rodeio Velho Member, Ordovician of the Camaqua basin (RS-Brazil): preliminary results

    International Nuclear Information System (INIS)

    Almeida, Delia del Pilar M. de; Lopes, Ricardo da C.; Gomes, Cristiane H.; Lima, Larissa de.

    2000-01-01

    A geochemical study based in REE, minor elements and petrographic analyses from the volcanic rocks pertaining to the Rodeio Velho Member, comprising lava flows and epizonal intrusive bodies, both corresponding to andesites, subalkaline and alkaline basalts and trachyandesites; and stratified pyroclastic deposits, showed that fractional crystallization of deep source magma is the fundamental mechanism controlling the relationships among these rocks. This igneous event occurred in an alkaline intraplate environment, associated to a widespread extension tectonics, probably corresponding to a final stage of the Pan African - Brasiliano Orogeny during the Middle Ordovician. (author)

  7. A study on the characteristics of site-scale fracture system in granite and volcanic rock

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Kyung Su; Kim, Chun Soo; Bae, Dae Seok; Park, Byoung Yoon; Koh, Young Kown [Korea Atomic Energy Research Institute, Taejeon (Korea)

    2000-03-01

    The safety of waste disposal can be achieved by a complete isolation of radioactive wastes from biosphere or by a retardation of nuclide migration to reach an acceptable dose level. For the deep geological disposal of high-level radioactive waste, the potential pathways of nuclide primarily depend on the spatial distribution characteristics of conductive fractures. Major key issues in the quantification of fracture system for a disposal site are involved in classification criteria, hydraulic parameters, geometry, field investigation methods etc. This research aims to characterize the spatial distribution characteristics of conductive fractures in granite and volcanic rock mass. 10 refs., 32 figs., 13 tabs. (Author)

  8. Clinopyroxene application in petrogenesis identification of volcanic rocks associated with salt domes from Shurab (Southeast Qom

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    Somayeh Falahaty

    2016-07-01

    Full Text Available Introduction The study area is located in the Shurab area that is about 50 Km Southeast of Qom. Volcanic rocks of the Shurab area have basaltic composition that is associated with salt and marl units. Igneous rocks of the Shurab area have not been comprehensively studied thus far. Clinopyroxene composition of volcanic rocks, and especially the phenocrysts show Magma chemistry and can help to identify magma series (Lebas, 1962; Verhooge, 1962; Kushiro, 1960, Leterrier et al., 1982, tectonic setting (Leterrier et al., 1982; Nisbet and Pearce, 1977 as well as temperature formation and pressure of rock formation. Some geologists have estimated temperature of clinopyroxene formation by clinopyroxene composition (Adams and Bishop, 1986 and clinopyroxene-olivine couple. So, clinopyroxene is used in this study in order to identify magma series, tectonic setting, plus the temperature and pressure of volcanic rocks of the Shurab. Material and method Clinopyroxene analyses were conducted by wavelength-dispersive EPMA (JEOL JXA-8800R at the Cooperative Centre of Kanazawa University (Japan. The analyses were performed under an accelerating voltage of 15 kV and a beam current of 20 nA. The ZAF program was used for data corrections. Natural and synthetic minerals of known composition were used as standards. The Fe3+ content in minerals was estimated by Droop method (Droop, 1987. Discussion In the Shurab area, the volcanic rocks area with basaltic composition are located 50 km Southeast of Qom. Their age is the early Oligocene and they are associated with the salty marl units of the Lower Red Formation (LRF. The hand specimens of the studied rocks look green. These rocks are intergranular, microlitic, porphyric, vitrophyric and amygdaloidal and they consist of olivine, pyroxene and plagioclase. Accessory minerals contain sphene, apatite and opaque. According to Wo-En-Fs diagram (Morimoto, 1988, clinopyroxenes indicate diopside composition. Clinopyroxenes are

  9. Nd and Sr isotopes and K-Ar ages of the Ulreungdo alkali volcanic rocks in the East Sea, South Korea

    International Nuclear Information System (INIS)

    Kim Kyuhan; Jang Sunkyung; Tanaka, Tsuyoshi; Nagao, Keisuke

    1999-01-01

    Temporal geochemical and isotopical variations in the Ulreundgo alkali volcanic rocks provide important constraints on the origin and evolution of the volcanic rocks in relation to backarc basin tectonism. We determined the K-Ar ages, major and trace element contents, and Nd and Sr isotopic rations of the alkali volcanic rocks. The activities of Ulreungdo volcanoes can be divided, on the basis of radiometric ages and field occurrences, into five stages, though their activities range from 1.4 Ma to 0.01 Ma with short volcanic hiatus (ca. 0.05-0.3 Ma). The Nd-Sr isotopic data for Ulreungdo volcanic rocks enable us to conclude that: (1) the source materials of Ulreungdo volcanics are isotopically heterogeneous in composition, which is explained by the mixing of mantle derived magma and continental crustal source rocks. There is no systematic isotopic variations with eruption stages. Particularly, some volcanic rocks of stage 2 and 3 have extremely wide initial 87 Sr/ 86 Sr isotopic variations ranging from 0.7038 to 0.7092, which are influenced by seawater alterations; (2) the Ulreungdo volcanic rocks show EMI characteristic, while volcanic rocks from the Jejudo, Yeong-il and Jeon-gok areas have slightly depleted mantle source characteristics; (3) the trachyandesite of the latest eruption stage was originated from the mantle source materials which differ from other stages. A schematic isotopic evolution model for alkali basaltic magma is presented in the Ulreungdo volcanic island of the backarc basin of Japanese island arc system. (author)

  10. Origin of the ca. 50 Ma Linzizong shoshonitic volcanic rocks in the eastern Gangdese arc, southern Tibet

    Science.gov (United States)

    Liu, An-Lin; Wang, Qing; Zhu, Di-Cheng; Zhao, Zhi-Dan; Liu, Sheng-Ao; Wang, Rui; Dai, Jin-Gen; Zheng, Yuan-Chuan; Zhang, Liang-Liang

    2018-04-01

    The origin of the Eocene shoshonitic rocks within the upper part of the extensive Linzizong volcanic succession (i.e., the Pana Formation) in the Gangdese arc, southern Tibet remains unclear, inhibiting the detailed investigations on the crust-mantle interaction and mantle dynamics that operate the generation of the coeval magmatic flare-up in the arc. We report mineral composition, zircon U-Pb age and zircon Hf isotope, whole-rock element and Sr-Nd-Hf isotope data for the Pana Formation volcanic rocks from Pangduo, eastern Gangdese arc in southern Tibet. The Pana volcanic rocks from Pangduo include basalts, basaltic andesites, and dacites. SIMS and LA-ICPMS zircon U-Pb dating indicates that the Pangduo dacites were erupted at 50 ± 1 Ma, representing the volcanic equivalent of the coeval Gangdese Batholith that define a magmatic flare-up at 51 ± 1 Ma. The Pangduo volcanic rocks are exclusively shoshonitic, differing from typical subduction-related calc-alkaline volcanic rocks. The basalts have positive whole-rock ƐNd(t) (+1.7) and ƐHf(t) (+3.8) with high Zr abundances (121-169 ppm) and Zr/Y ratios (4.3-5.2), most likely derived from the partial melting of an enriched garnet-bearing lithospheric mantle that was metasomatized by subduction-related components with input from asthenosphere. Compared to the basalts, similar trace elemental patterns and decreased whole-rock ƐNd(t) (-3.5 to -3.3) and ƐHf(t) (-2.5 to -1.6) of the basaltic andesites can be attributed to the input of the ancient basement-derived material of the central Lhasa subterrane into the basaltic magmas. The coherent whole-rock Sr-Nd-Hf isotopic compositions ((87Sr/86Sr)i = 0.7064-0.7069, ƐNd(t) = -6.0 to -5.2, ƐHf(t) = -5.6 to -5.0) and varying zircon ƐHf(t) (-6.0 to +4.1) of the dacites can be interpreted by the partial melting of a hybrid lower crust source (juvenile and ancient lower crust) with incorporation of basement-derived components. Calculations of zircon-Ti temperature and whole-rock

  11. Pyroclastic rocks: another manifestation of ultramafic volcanism on Gorgona Island, Colombia

    Science.gov (United States)

    Echeverría, Lina M.; Aitken, Bruce G.

    1986-04-01

    Tertiary ultramafic volcanism on Gorgona Island, Colombia, is manifested not only by komatiite flows, but also by a more voluminous sequence of tuff breccias, which is cut by comagmatic picrite dikes. The ultramafic pyroclastic rocks are chaotic to stratified mixtures of angular to subrounded glassy picritic blocks and a fine grained volcaniclastic matrix that consists primarily of plastically-deformed, glassy globules. The entire deposit is interpreted to have formed by an explosive submarine eruption of phenocryst-laden picritic magma. MgO contents of tuff breccias and picrite dikes range from 21 to 27 wt%. Relative to nearby komatiite flows, these rocks are MgO-rich, and FeO-, TiO2- and Ni-poor. HREE concentrations are very low (rock geochemistry preclude such a connection, either due to olivine fractionation/accumulation or to different degrees of partial melting. These ultramafic rock types crystallized from magmas which most likely were extracted from distinct mantle source regions.

  12. A Comprehensive Study on Dielectric Properties of Volcanic Rock/PANI Composites

    Science.gov (United States)

    Kiliç, M.; Karabul, Y.; Okutan, M.; İçelli, O.

    2016-05-01

    Basalt is a very well-known volcanic rock that is dark colored and relatively rich in iron and magnesium, almost located each country in the world. These rocks have been used in the refused rock industry, to produce building tiles, construction industrial, highway engineering. Powders and fibers of basalt rocks are widely used of radiation shielding, thermal stability, heat and sound insulation. This study examined three different basalt samples (coded CM-1, KYZ-13 and KYZ-24) collected from different regions of Van province in Turkey. Polyaniline (PANI) is one of the representative conductive polymers due to its fine environmental stability, huge electrical conductivity, as well as a comparatively low cost. Also, the electrical and thermal properties of polymer composites containing PANI have been widely studied. The dielectric properties of Basalt/Polyaniline composites in different concentrations (10, 25, 50 wt.% PANI) have been investigated by dielectric spectroscopy method at the room temperature. The dielectric parameters (dielectric constants, loss and strength) were measured in the frequency range of 102 Hz-106 Hz at room temperature. The electrical mechanism change with PANI dopant. A detailed dielectrically analysis of these composites will be presented.

  13. GIS database and discussion for the distribution, composition, and age of Cenozoic volcanic rocks of the Pacific Northwest Volcanic Aquifer System study area

    Science.gov (United States)

    Sherrod, David R.; Keith, Mackenzie K.

    2018-03-30

    A substantial part of the U.S. Pacific Northwest is underlain by Cenozoic volcanic and continental sedimentary rocks and, where widespread, these strata form important aquifers. The legacy geologic mapping presented with this report contains new thematic categorization added to state digital compilations published by the U.S. Geological Survey for Oregon, California, Idaho, Nevada, Utah, and Washington (Ludington and others, 2005). Our additional coding is designed to allow rapid characterization, mainly for hydrogeologic purposes, of similar rocks and deposits within a boundary expanded slightly beyond that of the Pacific Northwest Volcanic Aquifer System study area. To be useful for hydrogeologic analysis and to be more statistically manageable, statewide compilations from Ludington and others (2005) were mosaicked into a regional map and then reinterpreted into four main categories on the basis of (1) age, (2) composition, (3) hydrogeologic grouping, and (4) lithologic pattern. The coding scheme emphasizes Cenozoic volcanic or volcanic-related rocks and deposits, and of primary interest are the codings for composition and age.

  14. Carboniferous volcanic rocks associated with back-arc extension in the western Chinese Tianshan, NW China: Insight from temporal-spatial character, petrogenesis and tectonic significance

    Science.gov (United States)

    Su, Wenbo; Cai, Keda; Sun, Min; Wan, Bo; Wang, Xiangsong; Bao, Zihe; Xiao, Wenjiao

    2018-06-01

    The Yili-Central Tianshan Block, as a Late Paleozoic major continental silver of the Central Asian Orogenic Belt, holds a massive volume of Carboniferous volcanic rocks, occurring as subparallel magmatic belts. However, the petrogenesis and tectonic implications of these volcanic rocks remain enigmatic. This study compiled isotopic age data for mapping their temporal-spatial character, and conducted petrogenetic study of these magmatic belts, aiming to understand their tectonic implications. Our compiled dataset reveals four magmatic belts in the Yili-Central Tianshan Block, including the Keguqinshan-Tulasu belt and the Awulale belt in the north, and the Wusun Mountain belt and the Haerk-Nalati belt in the south. In addition, our new zircon U-Pb dating results define two significant Early Carboniferous eruptive events (ca. 355-350 Ma and 325 Ma) in the Wusun Mountain belt. Volcanic rocks of the early significant eruptive event (ca. 355-350 Ma) in the Wusun Mountain comprise basalt, trachy-andesite, andesite, dacite and rhyolite, which are similar to the typical rock assemblage of a continental arc. Their positive εNd(t) values (+0.3 to +1.5) and relatively high Th/Yb and Nb/Yb ratios suggest the derivation from a mantle source with additions of slab-derived components. The gabbroic dykes and rhyolites of the late volcanic event (ca. 325 Ma) form a bimodal rock association, and they show alkaline features, with relatively low Th/Yb and Th/Nb ratios, and higher positive εNd(t) values (εNd(t) = +3.3-+5.0). It is interpreted that the gabbroic dykes and rhyolites may have been derived from mantle and juvenile crustal sources, respectively. The isotopic and trace elemental variations with time elapse of the Wusun Mountain magmatic belt show an important clue for strengthening depletion of the magma sources. Considering the distinctive temporal-spatial character of the Carboniferous volcanic rocks, two separate subduction systems in the southern and northern margins of

  15. Petrology, Magnetic susceptibility, Tectonic setting and mineralization associated with Plutonic and Volcanic Rocks, Eastern Bajestan and Taherabad, Iran

    Directory of Open Access Journals (Sweden)

    Malihe Ghoorchi

    2009-09-01

    Full Text Available Study area is located in district of Bajestan and Ferdows cities, NE of Iran. Structurally, this area is part of Lut block. The oldest exposed rocks, to the north of intrusive rocks and in Eastern Bajestan, are meta-chert, slate, quartzite, thin-bedded crystalline limestone and meta-argillite. The sedimentary units are: Sardar Formation (Carboniferous, Jamal Formation (Permian, Sorkh Shale and Shotori Formations (Triassic, carbonateous rocks (Cretaceous and lithostratigraphically equivalent to Kerman conglomerate (Cretaceous-Paleocene are exposed in this area. Based on relative age, magmatism in eastern Bajestan and Taherabad started after Late Cretaceous and it has been active and repeated during Tertiary time. At least, three episodes of volcanic activities are recognized in this area. The first stage was mainly volcanic flow with mafic composition and minor intermediate. The second episode was mainly intermediate in composition. The third stage was changed to acid-intermediate in composition. Since the plutonic rocks intruded the volcanic rocks, therefore they may be Oligo-Miocene age. Bajestan intrusive rocks are granite-granodiorite-quartz monzonite. Taherabad intrusive rocks are diorite-quartz diorite- monzonite-latite. Bajestan intrusive rocks are reduced type (ilmenite series and Taherabad intrusive rocks are oxidized type (magnetite series.Based on geochemical analysis including trace elements, REE and isotopic data, Bajestan intrusive rocks formed in continental collision zone and the magma has crustal origin. Taherabad intrusive rocks were formed in subduction zone and magma originated from oceanic crust. Taherabad intrusive rock has exploration potential for Cu-Au and pb.

  16. Evaluation of bedrock mainly composed of volcanic aggregate rocks at the Higashidori Nuclear Power Station

    International Nuclear Information System (INIS)

    Hashimoto, Shuichi; Miwa, Tadashi; Nishidachi, Masayuki

    2000-01-01

    When carrying out engineering evaluation on foundation bedrock for important constructions such as nuclear power station, dam, and so forth, it is required as a premise on carrying out various surveys, tests, and analyses to select adequate geological elements, to classify them to some groups capable of regarding as a common engineering property, and to rate them. On a hard bedrock, there is a classification method with relatively higher versatility adding condition of crack and weathering to performances at each site as an index, but on a soft one, most of its classification are carried out individually for its site in response to an index caused by the bedrock itself. Here were shown the results carried out some bedrock classifications on a base of grouping for rock sorts and rock phases, according to some concepts on a draft of the standard on the soft bedrock classification due to the nuclear engineering committee of the Japan Society of Civil Engineers, a reference draft on the soft bedrock classification of the 'Technical indications on seismic resistance design of the nuclear power station' of the Japan Electric Association, (JEAG4601-1987), and so forth. As a result applied the reference draft on the soft bedrock, and so forth to the bedrock at the Higashidori Nuclear Power Station composed of volcanic aggregate rocks of the Miocene epoch of the new Tertiary system, an adequate engineering evaluation was made possible by making grouping of rock sorts and rock phases to a foundation. And, on property evaluation of the quality changed vein, as a result of various tests, appropriate properties could be obtained. (G.K.)

  17. Tectonic setting of the Tertiary volcanic rocks of the Olympic Peninsula, Washington

    Science.gov (United States)

    Cady, Wallace M.

    1975-01-01

    Lower and middle Eocene abyssal and Hawaiian type tholeiitic basalts form two accumulations that apparently were once far out on the east flank of the Juan de Fuca Ridge, within the Juan de Fuca plate. One of these (more than 15 km thick) is near the eastern and southeastern periphery of the Olympic Peninsula, and the other (about 5 km thick) is on the north. The tholeiites stratigraphically overlie and interfinger with Paleocene(?) and lower and middle Eocene marine turbidites and shales; one flow includes boulders that, like clasts in the sediments, were derived from the North American continental plate immediately to the east. The basalts are overlain stratigraphically by middle Eocene to middle Miocene clastic marine sedimentary rocks, which are in turn overlapped unconformably on the south and west by upper Miocene (?) and Pliocene, chiefly shallow-marine clastic rocks. These various peripheral rocks flank a middle or late Miocene structurally complex dome, or orocline convex to the east, in which originally east dipping and low angle late Eocene to late Miocene underthrusts are flexed. The outermost underthrust of the complex separates the chiefly volcanic peripheral rocks to the north, east, and south from stratigraphically correlative and comparable, though predominantly sedimentary, core rocks arranged in northwest trending arcuate belts or packets bounded by fault zones. Before underthrusting, and perhaps oroclinal folding connected with doming, the pre-middle Miocene section was possibly 150 to 200 km wide compared with the present Olympic Peninsula which is 120 km wide. The section accumulated on the ocean floor near the western margin of the continent, before and during subduction of the oceanic crust.

  18. A new method for determining the uranium and thorium distribution in volcanic rock samples using solid state nuclear track detectors

    International Nuclear Information System (INIS)

    Misdaq, M.A.; Bakhchi, A.; Ktata, A.; Koutit, A.; Lamine, J.; Ait nouh, F.; Oufni, L.

    2000-01-01

    A method based on using solid state nuclear track detectors (SSNTD) CR- 39 and LR-115 type II and calculating the probabilities for the alpha particles emitted by the uranium and thorium series to reach and be registered on these films was utilized for uranium and thorium contents determination in various geological samples. The distribution of uranium and thorium in different volcanic rocks has been investigated using the track fission method. In this work, the uranium and thorium contents have been determined in different volcanic rock samples by using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTD). The mean critical angles of etching of the solid state nuclear track detectors utilized have been calculated. A petrographical study of the volcanic rock thin layers studied has been conducted. The uranium and thorium distribution inside different rock thin layers has been studied. The mechanism of inclusion of the uranium and thorium nuclei inside the volcanic rock samples studied has been investigated. (author)

  19. In situ Laser Induced Breakdown Spectroscopy as a tool to discriminate volcanic rocks and magmatic series, Iceland

    Energy Technology Data Exchange (ETDEWEB)

    Roux, C.P.M., E-mail: clement.roux@u-bourgogne.fr [Laboratoire interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne, BP 47 870, F-21078 Dijon Cedex (France); Rakovský, J.; Musset, O. [Laboratoire interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne, BP 47 870, F-21078 Dijon Cedex (France); Monna, F. [Laboratoire ARTéHIS, UMR 6298 CNRS-Université de Bourgogne, 6 Boulevard Gabriel, F-21000 Dijon (France); Buoncristiani, J.-F.; Pellenard, P.; Thomazo, C. [Laboratoire Biogéosciences, UMR 6282 CNRS-Université de Bourgogne, 6 Boulevard Gabriel, F-21000 Dijon (France)

    2015-01-01

    This study evaluates the potentialities of a lab-made pLIBS (portable Laser-Induced Breakdown Spectroscopy) to sort volcanic rocks belonging to various magmatic series. An in-situ chemical analysis of 19 atomic lines, including Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Na, Si, Sr and Ti, from 21 sampled rocks was performed during a field exploration in Iceland. Iceland was chosen both for the various typologies of volcanic rocks and the rugged conditions in the field in order to test the sturdiness of the pLIPS. Elemental compositions were also measured using laboratory ICP-AES measurements on the same samples. Based on these latter results, which can be used to identify three different groups of volcanic rocks, a classification model was built in order to sort pLIBS data and to categorize unknown samples. Using a reliable statistical scheme applied to LIBS compositional data, the classification capability of the pLIBS system is clearly demonstrated (90–100% success rate). Although this prototype does not provide quantitative measurements, its use should be of particular interest for future geological field investigations. - Highlights: • Portable LIBS applied to field geology • Fast semi-quantitative geochemical analysis of volcanic rocks and magmatic series • Discriminant analysis and statistical treatments for LIBS compositional data.

  20. Volcanic sequence in Late Triassic – Jurassic siliciclastic and evaporitic rocks from Galeana, NE Mexico

    International Nuclear Information System (INIS)

    Cruz-Gómez, E.M.; Velasco-Tapia, F.; Ramírez-Fernández, J.A.; Jenchen, U.; Rodríguez-Saavedra, P.; Rodríguez-Díaz, A.A.; Iriondo, A.

    2017-01-01

    In northeastern Mexico, volcanic rocks interbedded with Late Triassic–Jurassic siliciclastic and evaporitic strata have been linked to magmatic arcs developed in the Pangea western margin during its initial phase of fragmentation. This work provides new petrographic and geochemical data for volcanism included in the El Alamar and Minas Viejas formations outcropping in the Galeana region. Andesitic dykes and sills (n= 10) in the El Alamar redbeds show SiO2= 47.5–59.1% and MgO= 1.2–4.2%, as well as a geochemical affinity to island arc magmas. This work represents the first report of this tectonic setting in the region. Geological and petrographic evidence suggest that this arc system likely developed after ~220 and before ~193Ma. Trachy-andesitic and rhyodacitic domes (n= 20) associated with the Minas Viejas gypsum-carbonates sequence show SiO2= 61.8–82.7% and MgO= 0.1–4.0% with a tectonic affinity to continental arc. A rhyodacite sample from this region has been dated by U-Pb in zircon, yielding an age of 149.4 ± 1.2Ma (n= 21), being the youngest age related to this arc. Finally, we propose a threestep model to explain the tectonic evolution from Late Triassic island arc to Jurassic continental arc system in the northeastern Mexico.

  1. Volcanic sequence in Late Triassic – Jurassic siliciclastic and evaporitic rocks from Galeana, NE Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Cruz-Gómez, E.M.; Velasco-Tapia, F.; Ramírez-Fernández, J.A.; Jenchen, U.; Rodríguez-Saavedra, P.; Rodríguez-Díaz, A.A.; Iriondo, A.

    2017-11-01

    In northeastern Mexico, volcanic rocks interbedded with Late Triassic–Jurassic siliciclastic and evaporitic strata have been linked to magmatic arcs developed in the Pangea western margin during its initial phase of fragmentation. This work provides new petrographic and geochemical data for volcanism included in the El Alamar and Minas Viejas formations outcropping in the Galeana region. Andesitic dykes and sills (n= 10) in the El Alamar redbeds show SiO2= 47.5–59.1% and MgO= 1.2–4.2%, as well as a geochemical affinity to island arc magmas. This work represents the first report of this tectonic setting in the region. Geological and petrographic evidence suggest that this arc system likely developed after ~220 and before ~193Ma. Trachy-andesitic and rhyodacitic domes (n= 20) associated with the Minas Viejas gypsum-carbonates sequence show SiO2= 61.8–82.7% and MgO= 0.1–4.0% with a tectonic affinity to continental arc. A rhyodacite sample from this region has been dated by U-Pb in zircon, yielding an age of 149.4 ± 1.2Ma (n= 21), being the youngest age related to this arc. Finally, we propose a threestep model to explain the tectonic evolution from Late Triassic island arc to Jurassic continental arc system in the northeastern Mexico.

  2. Link between the granitic and volcanic rocks of the Bushveld Complex, South Africa

    Science.gov (United States)

    Schweitzer, J. K.; Hatton, C. J.; De Waal, S. A.

    1997-02-01

    Until recently, it was proposed that the Bushveld Complex, consisting of the extrusive Rooiberg Group and the intrusive Rashoop Granophyre, Rustenburg Layered and Lebowa Granite Suites, evolved over a long period of time, possibly exceeding 100 Ma. Most workers therefore considered that the various intrusive and extrusive episodes were unrelated. Recent findings suggest that the intrusive, mafic Rustenburg Layered Suite, siliceous Rashoop Granophyre Suite and the volcanic Rooiberg Group were synchronous, implying that the Bushveld igneous event was short-lived. Accepting the short-lived nature of the complex, the hypothesis that the granites are genetically unrelated to the other events of the Bushveld Complex can be reconsidered. Re-examination of the potential Rooiberg Group/Lebowa Granite Suite relationship suggests that the granites form part of the Bushveld event. Rhyolite lava, granite and granophyre melts originated from a source similar in composition to upper crustal rocks. This source is interpreted to have been melted by a thermal input associated with a mantle plume. Granite intruded after extrusion of the last Rooiberg rhyolite, or possibly overlapped in time with the formation of the youngest volcanic flows.

  3. K-Ar geochronology and palaeomagnetism of volcanic rocks in the lesser Antilles island arc

    International Nuclear Information System (INIS)

    Briden, J.C.; Rex, D.C.; Faller, A.M.; Tomblin, J.F.

    1979-01-01

    K-Ar age determinations on rocks and minerals from 95 locations in the Lesser Antilles. An age range of 38 - 10 million years was found for the outer arc (Limestone Caribbees) but less than 7.7 million years in the inner arc (Volcanic Caribbees). From Martinique southwards the two arcs are superimposed. These age ranges fit between discontinuities in sea floor spreading in the North Atlantic at about 38 and 9 million years and a causal connection between spreading change and relocation of arc volcanicity is suggested. Paleomagnetic directions at 108 localities in 10 islands fall into normal and reversed groups with 6 sites intermediate and 5 indeterminate. The mean dipole axis is within 2% of the present rotation axis. The data generally agrees with the established geomagnetic polarity time scale but there is some suggestion of a normal polarity event at about 1.18 million years. The paleomagnetic data suggest that in the past 10 million years the Lesser Antilles have not changed their latitude or geographical orientation and the geomagnetic field has averaged that of a central axial dipole. (author)

  4. Compilation of modal analyses of volcanic rocks from the Nevada Test Site area, Nye County, Nevada

    International Nuclear Information System (INIS)

    Page, W.R.

    1990-01-01

    Volcanic rock samples collected from the Nevada Test Site, Nye County, Nevada, between 1960 and 1985 were analyzed by thin section to obtain petrographic mode data. In order to provide rapid accessibility to the entire database, all data from the cards were entered into a computerized database. This computer format will enable workers involved in stratigraphic studies in the Nevada Test Site area and other locations in southern Nevada to perform independent analyses of the data. The data were compiled from the mode cards into two separate computer files. The first file consists of data collected from core samples taken from drill holes in the Yucca Mountain area. The second group of samples were collected from measured sections and surface mapping traverses in the Nevada Test Site area. Each data file is composed of computer printouts of tables with mode data from thin section point counts, comments on additional data, and location data. Tremendous care was taken in transferring the data from the cards to computer, in order to preserve the original information and interpretations provided by the analyzer. In addition to the data files above, a file is included that consists of Nevada Test Site petrographic data published in other US Geological Survey and Los Alamos National Laboratory reports. These data are presented to supply the user with an essentially complete modal database of samples from the volcanic stratigraphic section in the Nevada Test Site area. 18 refs., 4 figs

  5. Sr, Nd isotope geochemistry of volcanic rock series and its geological significance in the middle Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    There exists extensive basic-acidic volcanic rock series in the middle section of the Okinawa Trough. Different types of these volcanic rocks have their own average strontium ratios of 0.704 749, 0.705 062, 0.708 771, 0.704 840 and 0.720 301 with average 143Nd/144Nd ratios of 0.512 820, 0.512 673, 0.512 413, 0.512 729 and 0.512 034. These ratios of Sr and Nd isotopes all fall on a theoretic hyperbolic curve of mixing between two end-members of MORB and rhyolitic magma. So we infer that these different kinds of volcanic rocks in the middle Okinawa Trough are the erupted product in different stages of formation and evolution of the trough crust. MORB magma, which had suffered assimilation, mixed with the early-formed crust-derived rhyolitic partial melt mass at different ratios; then, these mixed magma erupted and formed volcanic rock types of the trough. This study indicates that the Okinawa Trough is coming into a stage of submarine spreading from the stage of continental rift.

  6. Sr, Nd isotope geochemistry of volcanic rock series and its geological significance in the middle Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    孟宪伟; 陈志华; 杜德文; 吴金龙

    2000-01-01

    There exists extensive basic-acidic volcanic rock series in the middle section of the Okinawa Trough. Different types of these volcanic rocks have their own average strontium ratios of 0.704749, 0.705062, 0.708771, 0.704840 and 0.720301 with average 143Nd/144Nd ratios of 0.512 820, 0.512 673, 0.512 413, 0.512 729 and 0.512 034. These ratios of Sr and Nd isotopes all fall on a theoretic hyperbolic curve of mixing between two end-members of MORE and rhyolitic magma. So we infer that these different kinds of volcanic rocks in the middle Okinawa Trough are the erupted product in different stages of formation and evolution of the trough crust. MORE magma, which had suffered assimilation, mixed with the early-formed crust-derived rhyolitic partial melt mass at different ratios; then, these mixed magma erupted and formed volcanic rock types of the trough. This study indicates that the Okinawa Trough is coming into a stage of submarine spreading from the stage of continental rift.

  7. Short-Wavelength Infrared (SWIR) spectroscopy of low-grade metamorphic volcanic rocks of the Pilbara Craton

    NARCIS (Netherlands)

    Abweny, Mohammad S.; van Ruitenbeek, Frank J A; de Smeth, Boudewijn; Woldai, Tsehaie; van der Meer, Freek D.; Cudahy, Thomas; Zegers, Tanja; Blom, Jan Kees; Thuss, Barbara

    This paper shows the results of Short-Wavelength Infrared (SWIR) spectroscopy investigations of volcanic rocks sampled from low-grade metamorphic greenstone belts of the Archean Pilbara Craton in Western Australia. From the reflectance spectra a range of spectrally active minerals were identified,

  8. ∼1400 Ma alkali metasomatic event in the sericite deposits and basal Aravalli volcanic rocks of Udaipur region, Rajasthan

    International Nuclear Information System (INIS)

    Padmakumari, V.M.; Sreenivas, B.; Srinivasan, R.; Gopalan, K.; Roy, A.B.

    1996-01-01

    Paleosols are residual soil profiles of the geological past. They throw light on the climatic conditions prevalent during their formation. Constraining their age is of importance for deciphering the paleoclimatic history of a region. A suite of K-rich spilitic volcanic rocks immediately overlying the paleosol near Nagaria have been analysed

  9. The questa magmatic system: Petrologic, chemical and isotopic variations in cogenetic volcanic and plutonic rocks of the latir volcanic field and associated intrusives, northern New Mexico

    International Nuclear Information System (INIS)

    Johnson, C.M.

    1986-01-01

    Field, chemical and isotopic data demonstrate that nearly all igneous rocks at Questa resulted from interactions between mantle-derived parental magmas and the crust. Strontium, neodymium and lead isotope ratios of early andesites to rhyolites (28 to 26 Ma) indicate that these magmas assimilated > 25% lower crust. Injection of basaltic magmas extensively modified the strontium and neodymium but not the lead isotope compositions of the lower crust. Eruption of comendite magmas and the peralkaline Amalia Tuff 26 Ma is correlated with inception of regional extension. Lead isotope ratios identify different sources for the metaluminous granites and the peralkaline rocks. 26 Ma metaluminous granite to granodiorite intrusions have chemical and isotopic compositions to those of the precaldera intermediate-composition rocks, and are interpreted as representing the solidified equivalents of the precaldera magmatic episode. However, both conventional and ion-microprobe isotopic data prohibit significant assimilation of crustal rocks at the level of exposure, suggesting that the plutons were emplaced a relatively crystal-rich mushes which did not have sufficient heat to assimilate country rocks. This suggest that in some cases plutonic rocks are better than volcanic rocks in representing the isotopic compositions of their source regions, because the assimilation potential of crystal-rich magmas is significantly less than that of largely liquid magmas

  10. Acceleration to failure in geophysical signals prior to laboratory rock failure and volcanic eruptions (Invited)

    Science.gov (United States)

    Main, I. G.; Bell, A. F.; Greenhough, J.; Heap, M. J.; Meredith, P. G.

    2010-12-01

    The nucleation processes that ultimately lead to earthquakes, volcanic eruptions, rock bursts in mines, and landslides from cliff slopes are likely to be controlled at some scale by brittle failure of the Earth’s crust. In laboratory brittle deformation experiments geophysical signals commonly exhibit an accelerating trend prior to dynamic failure. Similar signals have been observed prior to volcanic eruptions, including volcano-tectonic earthquake event and moment release rates. Despite a large amount of effort in the search, no such statistically robust systematic trend is found prior to natural earthquakes. Here we describe the results of a suite of laboratory tests on Mount Etna Basalt and other rocks to examine the nature of the non-linear scaling from laboratory to field conditions, notably using laboratory ‘creep’ tests to reduce the boundary strain rate to conditions more similar to those in the field. Seismic event rate, seismic moment release rate and rate of porosity change show a classic ‘bathtub’ graph that can be derived from a simple damage model based on separate transient and accelerating sub-critical crack growth mechanisms, resulting from separate processes of negative and positive feedback in the population dynamics. The signals exhibit clear precursors based on formal statistical model tests using maximum likelihood techniques with Poisson errors. After correcting for the finite loading time of the signal, the results show a transient creep rate that decays as a classic Omori law for earthquake aftershocks, and remarkably with an exponent near unity, as commonly observed for natural earthquake sequences. The accelerating trend follows an inverse power law when fitted in retrospect, i.e. with prior knowledge of the failure time. In contrast the strain measured on the sample boundary shows a less obvious but still accelerating signal that is often absent altogether in natural strain data prior to volcanic eruptions. To test the

  11. Geochemistry and Mineral Chemistry of Zeolites Bearing Basic Volcanic Rocks from the Boumehen-Roudehen Area, East of Tehran

    Directory of Open Access Journals (Sweden)

    Amir Ali Tabbakh Shabani

    2017-11-01

    Full Text Available Introduction The Upper Eocene basic volcanic rocks that have cropped out in Karaj formation in the Boumehen and Roudehen area in the east of Tehran are characterized by fibrous zeolites filling their vesicles, cavities and fractures creating amygdale texture. The study area is located structurally in the Central Alborz orogenic belt. The presence of large volumes of shoshonitic magma during the Middle to Late Eocene in southern–central Alborz implies that partial melting to produce shoshsonitic melts was not a local petrological event. Thus, their ages, formation processes, and interpretations are of regional tectonic significance. In this study, we present a detailed petrography, mineral chemistry, and whole-rock geochemistry of high-K (shoshonitic basic rocks to understand the petrogenesis and source region and to deduce the nature of the tectonomagmatic regime of the Alborz. Materials and methods In this study, we present new major and trace element data for a selection of 4 of the least altered samples by a combination of X-ray fluorescence (XRF and ICP-OES techniques at the Zarazma Mineral Studies Company. Mineral analyses were obtained by wavelength dispersive X-ray spectrometry on polished thin sections prepared from each rock sample described above for 12 elements using a Cameca SX-50 electron microprobe at the Istituto di Geologia e Geoingegneria Ambientale, C.N.R., University La Sapienza of Rome, Italy. Typical beam operating conditions were 15 kV and probe current of 15 nA. The accuracy of the analyses is 1% for major and 10% for minor elements. A total of 24 point analyses were collected. Results and Discussion The extent of alteration in the study rocks varies from slight to severe and shows porphyritic to glomeroporphyritic textures. Pyroxenes are generally subhedral to euhedral and occur as discrete crystals as well as aggregates. Olivine may occur only as relics filled with iddingsite, chlorite and calcite. Plagioclase is

  12. Geochronology and correlation of Tertiary volcanic and intrusive rocks in part of the southern Toquima Range, Nye County, Nevada

    Science.gov (United States)

    Shawe, Daniel R.; Snee, Lawrence W.; Byers, Frank M.; du Bray, Edward A.

    2014-01-01

    Extensive volcanic and intrusive igneous activity, partly localized along regional structural zones, characterized the southern Toquima Range, Nevada, in the late Eocene, Oligocene, and Miocene. The general chronology of igneous activity has been defined previously. This major episode of Tertiary magmatism began with emplacement of a variety of intrusive rocks, followed by formation of nine major calderas and associated with voluminous extrusive and additional intrusive activity. Emplacement of volcanic eruptive and collapse megabreccias accompanied formation of some calderas. Penecontemporaneous volcanism in central Nevada resulted in deposition of distally derived outflow facies ash-flow tuff units that are interleaved in the Toquima Range with proximally derived ash-flow tuffs. Eruption of the Northumberland Tuff in the north part of the southern Toquima Range and collapse of the Northumberland caldera occurred about 32.3 million years ago. The poorly defined Corcoran Canyon caldera farther to the southeast formed following eruption of the tuff of Corcoran Canyon about 27.2 million years ago. The Big Ten Peak caldera in the south part of the southern Toquima Range Tertiary volcanic complex formed about 27 million years ago during eruption of the tuff of Big Ten Peak and associated air-fall tuffs. The inferred Ryecroft Canyon caldera formed in the south end of the Monitor Valley adjacent to the southern Toquima Range and just north of the Big Ten Peak caldera in response to eruption of the tuff of Ryecroft Canyon about 27 million years ago, and the Moores Creek caldera just south of the Northumberland caldera developed at about the same time. Eruption of the tuff of Mount Jefferson about 26.8 million years ago was accompanied by collapse of the Mount Jefferson caldera in the central part of the southern Toquima Range. An inferred caldera, mostly buried beneath alluvium of Big Smoky Valley southwest of the Mount Jefferson caldera, formed about 26.5 million years

  13. Crystallisation condition of the Quaternary basanites of volcanic centre Black Rock, monogenetic field Lunar Crater

    Science.gov (United States)

    Turova, Mariia; Plechov, Pavel; Scherbakov, Vasily; Larin, Nikolay

    2017-04-01

    The Lunar Crater volcanic field is located in a tension zone Basin and Range Province (USA). This tension is connected with dives oceanic plate under the continental plate [1]. Lunar Crater consists of flows basalt, basanite, trachybasalt has a different age [2]. In this work we investigate the youngest rock - basanite. The basanite is highly crystalline consisting of about megacrysts (3-10 cm) 30-60 wt% phenocrysts ( 800-1500 µm) and microphenocrysts (100-800 µm) and 40-60% microlites (Mathematical, Physical and Engineering Sciences. - 1981. - T. 300. - №. 1454. - C. 407-434. 2. Wood, X., and Keinle, Y., 1990, Volcanoes of North America: Cambridge,United Kingdom, Cambridge University Press, 354 p. 3. Nimis P. Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems //Contributions to Mineralogy and Petrology. - 1999. - T. 135. - №. 1. - C. 62-74. 4. Ballhaus C., Berry R. F., Green D. H. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle //Contributions to Mineralogy and Petrology. - 1991. - T. 107. - №. 1. - C. 27-40.

  14. High-resolution 40Ar/39Ar geochronology of volcanic rocks from the Siebengebirge (Central Germany)—Implications for eruption timescales and petrogenetic evolution of intraplate volcanic fields

    Science.gov (United States)

    Przybyla, Thomas; Pfänder, Jörg A.; Münker, Carsten; Kolb, Melanie; Becker, Maike; Hamacher, Uli

    2017-11-01

    A key parameter in understanding mantle dynamics beneath continents is the temporal evolution of intraplate volcanism in response to lithospheric thinning and asthenospheric uplift. To contribute to a better understanding of how intraplate volcanic fields evolve through time, we present a high precision 40Ar/39Ar age dataset for volcanic rocks from the Siebengebirge volcanic field (SVF) from central Germany, one of the best studied and compositionally most diverse intraplate volcanic fields of the Cenozoic Central European Volcanic Province (CEVP). Petrological and geochemical investigations suggest that the formation of the different rock types that occur in the SVF can be explained by a combination of assimilation and fractional crystallisation processes, starting from at least two different parental magmas with different levels of silica saturation (alkali basaltic and basanitic), and originating from different mantle sources. These evolved along two differentiation trends to latites and trachytes, and to tephrites and tephriphonolites, respectively. In contrast to their petrogenesis, the temporal evolution of the different SVF suites is poorly constrained. Previous K/Ar ages suggested a time of formation between about 28 and 19 Ma for the mafic rocks, and of about 27 to 24 Ma for the differentiated rocks. Our results confirm at high precision that the differentiated lithologies of both alkaline suites (40Ar/39Ar ages from 25.3 ± 0.2 Ma to 25.9 ± 0.3 Ma) erupted contemporaneously within a very short time period of 0.6 Ma, whereas the eruption of mafic rocks (basanites) lasted at least 8 Ma (40Ar/39Ar ages from 22.2 ± 0.2 Ma to 29.5 ± 0.3 Ma). This implies that felsic magmatism in the central SVF was likely a single event, possibly triggered by an intense phase of rifting, and that ongoing melting and eruption of mostly undifferentiated mafic lavas dominate the > 8 Ma long magmatic history of this region. Among the mafic lavas, most basanites and tephrites

  15. Mechanical and physical properties of hydrothermally altered rocks, Taupo Volcanic Zone, New Zealand

    Science.gov (United States)

    Wyering, L. D.; Villeneuve, M. C.; Wallis, I. C.; Siratovich, P. A.; Kennedy, B. M.; Gravley, D. M.; Cant, J. L.

    2014-11-01

    Mechanical characterization of hydrothermally altered rocks from geothermal reservoirs will lead to an improved understanding of rock mechanics in a geothermal environment. To characterize rock properties of the selected formations, we prepared samples from intact core for non-destructive (porosity, density and ultrasonic wave velocities) and destructive laboratory testing (uniaxial compressive strength). We characterised the hydrothermal alteration assemblage using optical mineralogy and existing petrography reports and showed that lithologies had a spread of secondary mineralisation that occurred across the smectite, argillic and propylitic alteration zones. The results from the three geothermal fields show a wide variety of physical rock properties. The testing results for the non-destructive testing shows that samples that originated from the shallow and low temperature section of the geothermal field had higher porosity (15 - 56%), lower density (1222 - 2114 kg/m3) and slower ultrasonic waves (1925 - 3512 m/s (vp) and 818 - 1980 m/s (vs)), than the samples from a deeper and higher temperature section of the field (1.5 - 20%, 2072 - 2837 kg/m3, 2639 - 4593 m/s (vp) and 1476 - 2752 m/s (vs), respectively). The shallow lithologies had uniaxial compressive strengths of 2 - 75 MPa, and the deep lithologies had strengths of 16 - 211 MPa. Typically samples of the same lithologies that originate from multiple wells across a field have variable rock properties because of the different alteration zones from which each sample originates. However, in addition to the alteration zones, the primary rock properties and burial depth of the samples also have an impact on the physical and mechanical properties of the rock. Where this data spread exists, we have been able to derive trends for this specific dataset and subsequently have gained an improved understanding of how hydrothermal alteration affects physical and mechanical properties.

  16. Spectral characterization of volcanic rocks in the VIS-NIR for martian exploration

    Science.gov (United States)

    De Angelis, Simone; Carli, Cristian; Manzari, Paola; De Sanctis, Maria Cristina; Capaccioni, Fabrizio

    2016-10-01

    Igneous effusive rocks cover much of the surface of Mars [1,2,3]. Initially only two types of lithologies were thought to constitute the Martian crust, i.e. a basaltic one and a more andesitic one [1,2], while more evolved lithologies were ruled out.Nevertheless a more complex situation is appearing in the last years. Recently several observations have highlighted the presence of evolved, acidic rocks. High-silica dacite units were identified in Syrtis Major caldera by thermal IR data [4]. Outcrops in Noachis Terra were interpreted as constituted of felsic (i.e. feldspar-rich) rocks essentially by the observation of a 1.3-µm spectral feature in CRISM data, attributed to Fe2+ in feldspars [5]. However different interpretations exist, invoking plagioclase-enriched basalts [6] rather than felsic products.The increasing of high-resolution and in-situ rover-based observations datasets and the changing of the initial paradigm justify a new systematic spectral study of igneous effusive rocks. In this work we focus on the spectral characterization of volcanic effusive rocks in the 0.35-2.5-µm range. We are carrying out measurements and spectral analyses on a wide ensemble of effusive samples, from mafic to sialic, with variable alkali contents, following the classification in the Total-Alkali-Silica diagram, and discussing the influence on spectral characteristics of different mineral assemblages and/or texture ([7], [8]). [1] Bandfield J.L., et al., Science, 287, 1626, 2000; [2] Christensen P.R., et al., J. Geophys. Res., 105, N.E4, 9609-9621, 2000; [3] Ehlmann B.L. & Edwards C.S., Annu. Rev. Earth Planet. Sci., 42, 291-315, 2014; [4] Christensen P.R., et al., Nature, 436, 504-509, 2005; [5] Wray J.J., et al., 44th LPSC, abs. n.3065, 2013; [6] Rogers A.D. & Nekvasil H., Geophys. Res. Lett., 42, 2619-2626, 2015; [7] Carli C. and Sgavetti M.,Icarus, 211, 1034-1048, 2011; [7] Carli C. et al., SGL, doi 10.1144/SP401.19, 2015.

  17. Agronomic behavior of phosphoric rock from Bahia Inglesa using isotopic techniques. 2. Greenhouse experiment in three volcanic ash soils

    International Nuclear Information System (INIS)

    Pino N, I.; Casas G, L.

    1989-01-01

    With the aim to evaluate the behaviour of phosphoric rock in regard to the sorption capacity from three volcanic ash soils, a greenhouse trial was carried out. The isotopic dilution method with triple superphosphate labeled P32 (TSP-32) was used. Total dry matter, P total was determined by colorimetry and the liquid scintillation method for P32 was used. The evaluation of the rock was measured through different isotopical parameters such as A value and P derived from the rock. The behaviour of this material was affected by the different properties of the soils mainly on account of the diverse sorption capacity of them giving an inverse relation among sorption and effectiveness of the rock. The results showed a higher efficiency of TSP for the three soils compared with the phosphoric rock either concentrated or not. (author)

  18. SHRIMP zircon U-Pb age and its significances of volcanic rocks from banshi basin in south jiangxi province

    International Nuclear Information System (INIS)

    Wang Baofeng; Wu Jianhua

    2011-01-01

    SHRIMP zircon U-Pb dating is applied to geochronological study for tuff of original Jilongzhang formation and rhyolite of original Banshi formation in Banshi basin, located in the Sannan (Longnan, Dingnan, Quannan) -Xunwu volcanic rocks belts in the south of Jiangxi. The result shows that zircon SHRIMP U-Pb age of the tuff is (142.5 ± 1.3) Ma and the age of the rhyolite is (131.4 ± 1.3) Ma. According to the latest international stratigraphic chart, the boundary between Jurassic and Cretaceous is (145.4 ± 4.0) Ma. So original Jilongzhang Formation and original Banshi Formation in Banshi basin were formed during early Early Cretaceous. The volcanic series in Banshi basin belongs to only one volcanic cycle. The features of the rock associations consistent with Wuyi group on the Xiajiang-Guangfeng volcanic rocks belts in the north of Jiangxi, so original Jilongzhang formation falls under E'huling formation and original Banshi formation falls under Shixi formation. (authors)

  19. Role of crustal assimilation and basement compositions in the petrogenesis of differentiated intraplate volcanic rocks: a case study from the Siebengebirge Volcanic Field, Germany

    Science.gov (United States)

    Schneider, K. P.; Kirchenbaur, M.; Fonseca, R. O. C.; Kasper, H. U.; Münker, C.; Froitzheim, N.

    2016-06-01

    The Siebengebirge Volcanic Field (SVF) in western Germany is part of the Cenozoic Central European Volcanic Province. Amongst these volcanic fields, the relatively small SVF comprises the entire range from silica-undersaturated mafic lavas to both silica-undersaturated and silica-saturated differentiated lavas. Owing to this circumstance, the SVF represents a valuable study area representative of intraplate volcanism in Europe. Compositions of the felsic lavas can shed some new light on differentiation of intraplate magmas and on the extent and composition of potential crustal assimilation processes. In this study, we provide detailed petrographic and geochemical data for various differentiated SVF lavas, including major and trace element concentrations as well as Sr-Nd-Hf-Pb isotope compositions. Samples include tephriphonolites, latites, and trachytes with SiO2 contents ranging between 53 and 66 wt%. If compared to previously published compositions of mafic SVF lavas, relatively unradiogenic 143Nd/144Nd and 176Hf/177Hf coupled with radiogenic 87Sr/86Sr and 207Pb/204Pb lead to the interpretation that the differentiated volcanic rocks have assimilated significant amounts of lower crustal mafic granulites like the ones found as xenoliths in the nearby Eifel volcanic field. These crustal contaminants should possess unradiogenic 143Nd/144Nd and 176Hf/177Hf, radiogenic 87Sr/86Sr, and highly radiogenic 207Pb/204Pb compositions requiring the presence of ancient components in the central European lower crust that are not sampled on the surface. Using energy-constrained assimilation-fractional crystallisation (EC-AFC) model calculations, differentiation of the SVF lithologies can be modelled by approximately 39-47 % fractional crystallisation and 6-15 % crustal assimilation. Notably, the transition from silica-undersaturated to silica-saturated compositions of many felsic lavas in the SVF that is difficult to account for in closed-system models is also well explained by

  20. Assessment of radiological significance of naturally occurring radionuclides in soil and rock matrices around Kakrapar environment

    International Nuclear Information System (INIS)

    Patra, A.K.; Jaison, T.J.; Baburajan, A.; Hegde, A.G.

    2008-01-01

    The activity and gamma-absorbed dose rate due to the naturally occurring radionuclides in the terrestrial environment such as 238 U, 232 Th and 40 K were determined in soil and rock samples collected around Kakrapar Atomic Power Plant site, using gamma-ray spectrometry. The mean concentration levels measured in Kakrapar soil from naturally occurring radioisotopes such as 238 U, 232 Th and 40 K are lower than the corresponding global average values obtained in worldwide soil. The external hazard index (Hex) and absorbed gamma dose rate in air outdoors is observed to be 0.04-0.18 and 3.1-14.1 nGy h -1 , respectively. (authors)

  1. Nd and Sr isotopes and K-Ar ages of the Ulreungdo alkali volcanic rocks in the East Sea, South Korea

    Energy Technology Data Exchange (ETDEWEB)

    Kim Kyuhan; Jang Sunkyung [Ewha Womans Univ., Seoul (Korea); Tanaka, Tsuyoshi; Nagao, Keisuke

    1999-07-01

    Temporal geochemical and isotopical variations in the Ulreundgo alkali volcanic rocks provide important constraints on the origin and evolution of the volcanic rocks in relation to backarc basin tectonism. We determined the K-Ar ages, major and trace element contents, and Nd and Sr isotopic rations of the alkali volcanic rocks. The activities of Ulreungdo volcanoes can be divided, on the basis of radiometric ages and field occurrences, into five stages, though their activities range from 1.4 Ma to 0.01 Ma with short volcanic hiatus (ca. 0.05-0.3 Ma). The Nd-Sr isotopic data for Ulreungdo volcanic rocks enable us to conclude that: (1) the source materials of Ulreungdo volcanics are isotopically heterogeneous in composition, which is explained by the mixing of mantle derived magma and continental crustal source rocks. There is no systematic isotopic variations with eruption stages. Particularly, some volcanic rocks of stage 2 and 3 have extremely wide initial {sup 87}Sr/{sup 86}Sr isotopic variations ranging from 0.7038 to 0.7092, which are influenced by seawater alterations; (2) the Ulreungdo volcanic rocks show EMI characteristic, while volcanic rocks from the Jejudo, Yeong-il and Jeon-gok areas have slightly depleted mantle source characteristics; (3) the trachyandesite of the latest eruption stage was originated from the mantle source materials which differ from other stages. A schematic isotopic evolution model for alkali basaltic magma is presented in the Ulreungdo volcanic island of the backarc basin of Japanese island arc system. (author)

  2. Unravelling the magmatic system beneath a monogenetic volcanic complex (Jagged Rocks Complex, Hopi Buttes, AZ, USA)

    Science.gov (United States)

    Re, G.; Palin, J. M.; White, J. D. L.; Parolari, M.

    2017-12-01

    The Jagged Rocks complex is the eroded remnant of the plumbing systems of closely spaced monogenetic alkaline volcanic centres in the southern Hopi Buttes Volcanic Field (AZ, USA). It contains different clinopyroxene populations with distinctive textures and geochemical patterns. In the Northwestern part of the complex, which exposes the best developed system of conduits, most of the clinopyroxenes consist of large- to medium-sized resorbed cores overgrown by euhedral rims (type 1), small moderately resorbed greenish cores with the same overgrown rims (type 2), and phlogopite as an accessory phase. By contrast, in the Southern part of the complex the majority of clinopyroxenes are euhedral with oscillatory zonation (type 3) and are accompanied by minor euhedral olivine. The differences between these mineral assemblages indicate a composite history of crystallization and magmatic evolution for the two parts of the complex, governed by different mechanisms and ascent patterns from a single source at 50 km depth (16 kbar). The Northwest system preserves a high-pressure assemblage that cooled rapidly from near-liquidus conditions, suggesting direct ascent from the source to the surface at high-to-moderate transport rates (average 1.25 m/s). By contrast, the Southern system represents magma that advanced upward at much lower overall ascent rates, stalling at times to form small-volume mid-crustal storage zones (e.g., sills or a network of sheeted intrusions); this allowed the re-equilibration of the magma at lower pressure ( 30 km; 8 kbar), and led to nucleation and growth of euhedral clinopyroxene and olivine phenocrysts.

  3. Mapping local singularities using magnetic data to investigate the volcanic rocks of the Qikou depression, Dagang oilfield, eastern China

    Directory of Open Access Journals (Sweden)

    G. Chen

    2013-07-01

    Full Text Available The spatial structural characteristics of geological anomaly, including singularity and self-similarity, can be analysed using fractal or multifractal modelling. Here we apply the multifractal methods to potential fields to demonstrate that singularities can characterise geological bodies, including rock density and magnetic susceptibility. In addition to enhancing weak gravity and magnetic anomalies with respect to either strong or weak background levels, the local singularity index (α ≈ 2 can be used to delineate the edges of geological bodies. Two models were established to evaluate the effectiveness of mapping singularities for extracting weak anomalies and delineating edges of buried geological bodies. The Qikou depression of the Dagang oilfield in eastern China has been chosen as a study area for demonstrating the extraction of weak anomalies of volcanic rocks, using the singularity mapping technique to analyse complex magnetic anomalies caused by complex geological background. The results have shown that the singularities of magnetic data mapped in the paper are associated with buried volcanic rocks, which have been verified by both drilling and seismic survey, and the S–N and E–W faults in the region. The targets delineated for deeply seated faults and volcanic rocks in the Qikou depression should be further investigated for the potential application in undiscovered oil and gas reservoirs exploration.

  4. Magnesium Isotopic Evidence for Ancient Subducted Oceanic Crust in LOMU-Like Potassium-Rich Volcanic Rocks

    Science.gov (United States)

    Sun, Yang; Teng, Fang-Zhen; Ying, Ji-Feng; Su, Ben-Xun; Hu, Yan; Fan, Qi-Cheng; Zhou, Xin-Hua

    2017-10-01

    To evaluate the role of subducted oceanic crust in the genesis of potassium-rich magmas, we report high-precision Mg isotopic data for a set of Cenozoic volcanic rocks from Northeast China. These rocks overall are lighter in Mg isotopic composition than the normal mantle and display considerable Mg isotopic variations, with δ26Mg ranging from -0.61 to -0.23. The covariation of δ26Mg with TiO2 in these rocks suggests that their light Mg isotopic compositions were derived from recycled oceanic crust in the form of carbonated eclogite in the source region. The strong correlations between δ26Mg and (Gd/Yb)N ratio as well as Sr-Pb isotopes further indicate a multicomponent and multistage origin of these rocks. Magnesium isotopes may thus be used as a novel tracer of recycled oceanic crust in the source region of mantle-derived magmas.

  5. Measurement of cosmogenic 36Cl/Cl in young volcanic rocks: An application of accelerator mass spectrometry in geochronology

    International Nuclear Information System (INIS)

    Leavy, B.D.; Phillips, F.M.; Elmore, D.; Kubik, P.W.

    1987-01-01

    We have measured 36 Cl/Cl ratios in a number of young volcanic rocks in order to test the feasibility of using 36 Cl buildup as a geochronometer for materials less than about 700,000 years old. All of the analyzed rocks have been dated independently using K-Ar or other radiometric dating methods and have exposure histories that are known or can be reasonably assumed. Measured 36 Cl/Cl ratios in these rocks are in good agreement with the calculated in-situ 36 Cl buildup curve. These analyses indicate that AMS measurement of 36 Cl buildup in young rocks is a potentially powerful new method for dating materials that had previously been undatable, and as such will have broad applications in volcanology, tectonics, geophysics, and Quaternary research

  6. Determination of naturally occurring radionuclides in selected rocks from Hetaunda area, Central Nepal

    International Nuclear Information System (INIS)

    Wallova, G.

    2010-01-01

    The specific activities of the naturally occurring radionuclides 238 U, 232 Th, and 40 K were measured in rock samples from the Hetaunda area, central Nepal, by using gamma spectrometry. The specific activities were found to be in the range of 17 - 95 Bq.kg -1 for 238 U, 24 - 260 Bq.kg -1 for 232 Th and 32 - 541 Bq.kg -1 for 40 K. From these data absorbed dose rates in air and annual effective doses were calculated and compared with respective data from the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) compilation. The results from our study open the door to the safe applicability of most of the investigated materials as a cheep building material. (author)

  7. Zircon U-Pb chronology, geochemistry and Sr-Nd-Pb isotopic compositions of the Volcanic Rocks in the Elashan area, NW China: petrogenesis and tectonic implications

    Science.gov (United States)

    Zhou, H.; Wei, J.; Shi, W.; Li, P.; Chen, M.; Zhao, X.

    2017-12-01

    Elashan area is located in the intersection of the East Kunlun Orogenic Belt (EKOB) and the West Qinling Orogenic (WQOB). We present petrology, zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Pb isotopic compositions from the andesite and felsic volcanic rocks (rhyolite and rhyolitic tuffs) in Elashan group volcanic rock. The LA-ICP-MS zircon U-Pb age data indicate that the volcanic rocks are emplaced at 250 247 Ma. The volcanic rocks have high -K and aluminum - peraluminous characteristics, A/CNK = 1.07 1.82, δ ranges from 1.56 2.95, the main body is calc-alkaline rock. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in some high field strength elements (HFSEs, e.g., Nb, Ta, P and Ti), while having a flat heavy REE (HREEs) pattern. The ∑REE values of 178.68 to 298.11 ppm, average 230.50 ppm. The LREE/HREE values of 4.39 to 11.78 ppm, average 6.77 ppm. REE fractionation is obvious, REE distribution curve was right smooth, and have slightly negative Eu anomalies (Eu/Eu*=0.44-0.80, average 0.60), which as similar to the island arc volcanic rocks. The volcanic rocks have initial 87Sr/86Sr ratios of 0.71028-0.71232, ɛNd(t) values of -6.7 to -7.6, with T2DM-Nd ranging from 1561 to 1640 Ma. Pb isotopic composition (206 Pb / 204 Pb)t = 18.055 18.330, (207 Pb / 204 Pb)t = 15.586 15.618, (208 Pb / 204 Pb)t = 37.677 38.332. Geochemical and Sr-Nd-Pb isotopes indicates that Elashan group volcanic magma derived mainly from the lower crust. Elashan group volcanic rocks is the productive East Kunlun block and West Qinling block collision, which makes the thicken crust caused partial melting in the study area. The source rocks is probably from metamorphic sandstone of Bayankala. But with Y-Nb and Rb-(Y+Nb), R1-R2 and Rb/10-Hf-Ta*3 diagrams showing that intermediate-acid rocks mainly formed in volcanic arc-collision environment, probably the collision event is short , therefore rocks retain the original island

  8. Subaqueous volcanism in the Etnean area: evidence for hydromagmatic activity and regional uplift inferred from the Castle Rock of Acicastello

    Science.gov (United States)

    Corsaro, R. A.; Cristofolini, R.

    2000-01-01

    The subalkaline rocks outcropping at the Acicastello Castle Rock, Catania, Sicily, and on its abrasion platforms, are related to the oldest Etnean volcanism (500-300 ka; [Gillot, P.Y., Kieffer, G., Romano, R., 1994. The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanol. 5, 81-87.]). Here, submarine lavas with pillows closely packed onto each other are associated with heterogeneous and poorly sorted volcaniclastic breccia levels with sub-vertical sharp boundaries. The present-day attitude was previously interpreted as due to a local tilt [Di Re, M., 1963. Hyaloclastites and pillow-lavas of Acicastello (Mt. Etna). Bull. Volcanol. 25, 281-284.; Kieffer, G., 1985. Evolution structurale et dynamique d'un grand volcan polygenique: stades d'edification et activitè actuelle de l'Etna (Sicile). Clermont Ferrand IIDoctorat Etat Tesi, Clermont Ferrand II.], or to the seaward sliding of the entire eastern Etnean flank [Borgia, A., Ferrari, L., Pasquarè, G., 1992. Importance of gravitational spreading in the tectonic and volcanic evolution of Mount Etna. Nature 357, 231-235.], on the assumption of originally horizontal boundaries. On the contrary, our observations do not match the hypothesis of a significantly tilted succession and lead us to conclude that, apart from the strong regional uplift, the present Castle Rock exposure did not suffer any substantial change of its attitude.

  9. Formation of a spatter-rich pyroclastic density current deposit in a Neogene sequence of trachytic-mafic igneous rocks at Mason Spur, Erebus volcanic province, Antarctica

    Science.gov (United States)

    Martin, A. P.; Smellie, J. L.; Cooper, A. F.; Townsend, D. B.

    2018-01-01

    Erosion has revealed a remarkable section through the heart of a volcanic island, Mason Spur, in the southwestern Ross Sea, Antarctica, including an unusually well-exposed section of caldera fill. The near-continuous exposure, 10 km laterally and > 1 km vertically, cuts through Cenozoic alkalic volcanic rocks of the Erebus volcanic province (McMurdo Volcanic Group) and permits the study of an ancient volcanic succession that is rarely available due to subsequent burial or erosion. The caldera filling sequence includes an unusual trachytic spatter-rich lapilli tuff (ignimbrite) facies that is particularly striking because of the presence of abundant black fluidal, dense juvenile spatter clasts of trachytic obsidian up to 2 m long supported in a pale cream-coloured pumiceous lapilli tuff matrix. Field mapping indicates that the deposit is an ignimbrite and, together with petrological considerations, it is suggested that mixing of dense spatter and pumiceous lapilli tuff in the investigated deposit occurred during emplacement, not necessarily in the same vent, with the mixed fragmental material emplaced as a pyroclastic density current. Liquid water was not initially present but a steam phase was probably generated during transport and may represent water ingested during passage of the current as it passed over either wet ground, stream, shallow lake or (possibly) snow. Well-exposed caldera interiors are uncommon and that at Mason Spur is helping understand eruption dynamics associated with a complex large island volcano. The results of our study should help to elucidate interpretations of other, less well exposed, pyroclastic density current deposits elsewhere in Antarctica and globally.

  10. The alkaline volcanic rocks of Craters of the Moon National Monument, Idaho and the Columbia Hills of Gusev Crater, Mars

    Science.gov (United States)

    Neakrase, L. D.; Lim, D. S. S.; Haberle, C. W.; Hughes, S. S.; Kobs-Nawotniak, S. E.; Christensen, P. R.

    2016-12-01

    Idaho's Eastern Snake River Plain (ESRP) is host to extensive expressions of basaltic volcanism dominated by non evolved olivine tholeiites (NEOT) with localized occurrences of evolved lavas. Craters of the Moon National Monument (COTM) is a polygenetic lava field comprised of more than 60 lava flows emplaced during 8 eruptive periods spanning the last 15 kyrs. The most recent eruptive period (period A; 2500-2000 yr B.P.) produced flows with total alkali vs. silica classifications spanning basalt to trachyte. Coeval with the emplacement of the COTM period A volcanic pile was the emplacement of the Wapi and King's Bowl NEOT 70 km SSE of COTM along the Great Rift. Previous investigations have determined a genetic link between these two compositionally distinct volcanic centers where COTM compositions can be generated from NEOT melts through complex ascent paths and variable degrees of fractionation and assimilation of lower-middle crustal materials. The Mars Exploration Rover, Spirit, conducted a robotic investigation of Gusev crater from 2004-2010. Spirit was equipped with the Athena science payload enabling the determination of mineralogy (mini-Thermal Emission Spectrometer, Pancam multispectral camera, and Mössbauer spectrometer), bulk chemistry (Alpha Particle X-ray Spectrometer) and context (Pancam and Microscopic Imager). During sol 32 Spirit investigated an olivine basalt named Adirondack, the type specimen for a class of rock that composes much of the plains material within Gusev Crater and embays the Columbia Hills. Following the characterization of the plains material, Spirit departed the plains targeting the Columbia Hills and ascending at Husband Hill. During Spirit's ascent of Husband Hill three additional classes of volcanic rock were identified as distinct by their mini-TES spectra; Wishstone, Backstay and Irvine. These rocks are classified as tephrite, trachy-basalt and basalt, respectively, and are the first alkaline rocks observed on Mars. These

  11. K-Ar ages for the Yahazudake volcanic rocks from southwest Kyushu, Japan; Kyushu nanseibu yahazudake kazanganrui no K-Ar nendai

    Energy Technology Data Exchange (ETDEWEB)

    Yokose, H.; Kikuchi, W. [Kumamoto Univ. (Japan)] Nagao, K. [Okayama Univ. (Japan)264000] Kodama, K. [Kochi Univ. (Japan)

    1998-05-05

    Many volcanic rocks, seemed to be erupted during the period from the Pliocene epoch to the Pleistocene epoch, are distributed abounding in Kyushu, Japan. In this study, K-Ar ages determination about the 4 samples which represents the Hisatsu volcanic rocks distributed around Yahazudake and rhyolite distributed in Gesujima placed in the southernmost extremity of Amakusa Shimojima, was conducted. And consideration of time/space distribution of the Hisatsu volcanic rocks upon collecting the data which were reported until now and the data obtained by the present K-Ar age determination, was done. In the result of the present measurement, the absolute age of the Hisatsu volcanic rocks distributed around Minamata-shi became clear. I was clarified that Yahazudake volcanic rocks consisted of andesite, which is comparatively lacking in potassium, were formed during about 100 thousand years from 1.98 to 2.08 Ma, and Ontake volcanic rocks which exists for the bottom erupted at about 2.15 Ma. And, the age value of 2.89 Ma was obtained from Ushibuka rhyolite distributed in Gesujima. 35 refs., 4 figs., 3 tabs.

  12. Petrogenesis of siliceous high-Mg series rocks as exemplified by the Early Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched mantle versus crustal contamination

    Science.gov (United States)

    Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii

    2015-04-01

    The Early Paleoproterozoic stage in the Earth's evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of mantle melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted mantle melts, and by generation from a mantle source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the

  13. Lead isotopic compositions of South Sandwich Island volcanic rocks and their bearing on magmagenesis in intra-oceanic island arcs

    International Nuclear Information System (INIS)

    Barreiro, B.

    1983-01-01

    Pb isotope ratios have been measured in 12 volcanic rocks from the South Sandwich Islands. The results are reported. In 207 Pb/ 204 Pb- 206 Pb/ 204 Pb and 208 Pb/ 204 Pb- 206 Pb/ 204 Pb correlation diagrams, the South Sandwich data plot distinctly above the fields for ocean ridge basalts, and yield trends showing apparent mixing with a sedimentary end member similar to South Atlantic pelagic sediments as reported by Chow and Patterson (1962) and this study. Armstrong and Cooper (1971) have likewise shown that volcanics from the Lesser Antilles show mixing trends with North Atlantic sediments in Pb isotope correlation diagrams. The North Atlantic sediments have distinctly higher 206 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios compared to the South Atlantic sediments. The parallel relationships between sediments and volcanic island arc rocks of the North and South Atlantic provide strong evidence for a component of Pb from subducted sediments in the lavas of the west Atlantic basin. In contrast to these data, lavas from the Mariana Arc in the western Pacific show little or no component of Pb from pelagic sediments. The reason for the different behaviors in the two settings is speculative. (author)

  14. The origin of volcanic rock fragments in Upper Pliocene Grad Member of the Mura Formation, North-Eastern Slovenia

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    Polona Kralj

    2006-12-01

    Full Text Available Fresh-water, coarse-grained and detritus-dominated Mura Formation in North Eastern Slovenia includes pyroclastic and volcaniclastic deposits originating from Upper Pliocene volcanic activity of basaltic geochemical character. Although localized in occurrence at the hamlet Grad, these pyroclastic and volcaniclastic sediments forma distinctive depositional unit, for which the term “Grad Member” is proposed and introduced in this paper.In the Grad area no lavas or cinder cones are preserved, and the origin of volcaniclastic fragments still uncertain. For this reason, chemical composition of basaltic rock fragments from the Grad Member volcaniclastics has been studied and compared with basaltic rocks from the neighboring locations at Klöch, Kindsberg, Dölling and Neuhaus. The Grad Member pyroclastic and volcaniclastic deposits seem to be fed from the same source which is different from the occurrences in Austria. That supports the idea about the existence of a local volcanic centre in the present Grad area. The old volcanic edificeswerepossiblydestroyed by the late-stage hydrovolcanic eruptions, and pyroclastic and volcaniclastic deposits subjected to constant reworking by fluvial currents in a dynamic sedimentary environment of alluvial fan and braided river systems.

  15. Geochemical, petrographic and physical characterizations and associated alterations of the volcanic rocks of the Romanesque San Nicola Church (Ottana, central Sardinia, Italy)

    Science.gov (United States)

    Columbu, Stefano; Palomba, Marcella; Sitzia, Fabio

    2015-04-01

    In this research, the volcanic rocks belonging to the Sardinia Oligo-Miocene volcanic cycle (32 - 11 Ma) and building up the structure of the San Nicola church, one of the most representative churches of the Romanesque architecture, were studied. These stones were widely used in medieval architecture for the excellent workability, but they present some disadvantages, since they are greatly affected by alteration phenomena. The main objectives of this research are i) to focus the mineral, chemical and petrographic compositions of the San Nicola stones, ii) the chemical and physical alteration processes affecting these materials, and iii) to establish the exactly provenance of the volcanic rocks. Furthermore, a comparative study between the rocks from the ancient quarries and those forming the structure of the church was performed. In the ancient quarries, where presumably a more advanced alteration occurs due to the vertical alteration gradient, different facies of the same volcanic lithology, characterized by macroscopical evidences of chemical-physical degradation degree, were sampled. Petrographic, geochemical (both major elements that the traces) and physical-mechanical features of the collected samples were determined to highlight the compositional differences (density, porosity, water-absorption kinetics, mechanical resistance) as a function of the different alteration degree. Moreover, chemical-mineralogical analysis of the sample surfaces from the church, was performed, to highlight possible presence and nature of secondary newly-formed phases (e.g., salt efflorescence). Several methodologies were applied to carry out physical-chemical and petrographic analysis: X-Ray fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS), X-Ray Diffractometry (XRD) for chemical and mineral composition; Optical and Scanning Electron Microscopy (SEM) for textures, mineral assemblages and microstructures studies; He-picnometry, water-absorption and mechanical

  16. Petrography, mineral chemistry and geochemistry of post-ophiolitic volcanic rocks in the Ratouk area (south of Gazik, east of Iran

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    Zahra Vahedi Tabas

    2017-11-01

    Full Text Available Introduction Basaltic volcanoes are one of the volcanisms that have occurred in different parts of the world. The study of these lavas is important for petrologists, because they are seen in different tectonic settings and therefore diverse mechanisms affect their formation (Chen et al., 2007. Young volcanic rocks such as Quaternary basalts are one of latest products of magmatism in Iran that are related to deep fractures and active faults in Quaternary (Emami, 2000. The study area is located at 140km east of Birjand at Gazik 1:100000 geological map (Guillou et al., 1981 and have 60̊ 11' to 60̊ 15 '27" eastward longitude and 32̊ 33' 24" to 32̊ 39' 10" northward latitude. On the basis of structural subdivisions of Iran, this area is located in the northern part of the Sistan suture zone (Tirrul et al., 1983. Because of the importance of basaltic rocks in Sistan suture, this research is done with the aim of investigating the petrography and mineralogy of basaltic lavas, the nature of basaltic and intermediate magmatism and finally determination of tectonomagmatic regime. Materials and methods After field studies and sampling, 85 thin sections were prepared and carefully studied. Then ten samples with the lowest alteration 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 Acme laboratories, Vancouver, Canada. Electron probe micro analyses of clinopyroxene and olivine were done at the Iranian mineral processing research center (IMPRC by Cameca SX100 machine. X-ray diffraction analysis of minerals was done at the X-ray laboratory of the University of Birjand. Results In 60km south of GaziK at the east of the southern Khorasan province and the northern part of the Sistan suture zone, volcanic rocks with intermediate (Oligomiocene and

  17. Dating and source determination of volcanic rocks from Khunik area (South of Birjand, South Khorasan using Rb-Sr and Sm-Nd isotopes

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    Somayeh Samiee

    2016-12-01

    Full Text Available The Khunik area is located in the south of Birjand, Khorasan province, in the eastern margin of Lut block. Tertiary volcanic rocks have andesite to trachy-andesite composition. Dating analyzing by Rb-Sr method on plagioclase and hornblende as well as whole-rock isochron method was performed on pyroxene-hornblende andesite rock unit. On this basis the emplacement age is Upper Paleocene (58±11 Ma. These rocks have initial 87Sr/86Sr and εNd 0.7046-0.7049 and 2.16-3.12, respectively. According to isotopic data, volcanic rocks originated from depleted mantle and have the least crust contamination while it was fractionated. Geochemically, Khunik volcanic rocks have features typical of calk-alkaline to shoshonite and are metaluminous. Enrichment in LILEs and typical negative anomalies of Nb and Ti are evidences that the volcanic rocks formed in a subduction zone and active continental margin. Modeling suggests that these rocks were derived dominantly from 1–5% partial melting of a mainly spinel garnet lherzolite mantle source that is metasomatized by slab-derived fluid.

  18. Paleointensity Variation of The Earth's Magnetic Field Obtained from Neogene and Quaternary Volcanic Rocks in Central Anatolian Plateau

    Science.gov (United States)

    Kaya, Nurcan; Makaroǧlu, Özlem; Hisarlı, Z. Mümtaz

    2017-04-01

    We present the variation of the earth magnetic field intensity obtained from Neogene and Quaternary volcanic rocks located in the Central Anatolian plateau. Total of four hundred and fifty volcanic rocks were sub-sampled in eighteen different sites around the study region. A modified Thellier method including the Leonhardt protocol was used to determine paleointensity values. Paleointensity results from ten sites were accepted according to the confidence criteria . According to first results the average total paleointensity field values, indicated by F, are 51.797±5.044 μT for site NK8,NK17,NK18,NK15 with age of 4.4-10.7 my, 51.91±4.651 for site NK4, NK3, NK12, NK6, NK11, NK14 with age of 0.1-2.6 m.y. The average VDMs (Virtual Dipol Moments) correspond to 8.39x1022 , 8.92x1022 Am2 for the four Neogene and six Quaternary rocks sites respectively. Our data were correlated with IAGA database that were obtained from the surrounding area. The correlation showed that the paleointensity data from the Central Anatolia plateau considerably agree with the IAGA data.

  19. Paleointensities of the Auckland Excursion from Volcanic Rocks in New Zealand

    Science.gov (United States)

    Mochizuki, N.; Tsunakawa, H.; Shibuya, H.; Cassidy, J.; Smith, I. E.

    2001-12-01

    Shibuya et al. (1992) reported the Auckland excursion from several basaltic lava flows of monogenetic volcanic centers (Auckland Volcanic Field, New Zealand. The Auckland excursion was recorded in five centers in three intermediate direction groups of north-down, west and south. We carried out paleointensity and rock-magnetic studies in order to obtain the absolute paleointensities associated with three intermediate geomagnetic fields. Thermomagnetic analyses indicated typical Curie temperatures of 150-200, 450-500 and/or 550-580 oC. The Day plot (Day et al., 1977) showed a linear trend in the pseudo-single-domain range of magnetic carriers. Those results, combined with the reflection microscope observations, identified the magnetic carriers as titanomagnetites with wide variation in titanium content and grain size. First, the Coe's version of the Thellier method (Coe, 1967) was applied to the samples. Several samples seemed to give paleointensities ranging from 3.2 to 6.4 μ T (Shibuya and Cassidy, 1995 AGU fall meeting), but they were often affected by thermal alteration in the furnace even from fairly low temperature steps like 200oC. We were forced to introduce correction for thermal alterations in laboratory heating, using low temperature part of the Arai plot. We, therefore, applied the double heating technique (DHT) of Shaw method (Tsunakawa and Shaw, 1994), which was capable of detecting inappropriate results by the ARM correction, to the samples. The low temperature demagnetization (LTD) was combined with DHT (Yamamoto et al., submitted) before AF demagnetization and samples were heated in a vacuum of 10-100 Pa. Sixty-one samples from the five lava flows were subjected to the LTD-DHT Shaw method. Twenty-three of these samples yielded successful results passing the selection criteria. Five out of six paleointensities from the Crater Hill lava were consistent with each other. A mean paleointensity was given to be 10.9+/- 1.9 μ T (N=5) for the Crater Hill

  20. Regional stratigraphy, sedimentology, and tectonic significance of Oligocene-Miocene sedimentary and volcanic rocks, northern Baja California, Mexico

    Science.gov (United States)

    Dorsey, Rebecca J.; Burns, Beverly

    1994-01-01

    Upper Oligocene (?) to middle Miocene sedimentary and volcanic rocks in northern Baja California were deposited along the western margin of North America during subduction of the Guadalupe plate and southward migration of the Rivera Triple Junction. Regional mapping and compilation of stratigraphic data reveal a sequence of three regionally traceable stratigraphic units. (1) Oligocene (?) to lower Miocene Mesa Formation: basal quartz-rich fluvial sandstone, grus, conglomerate, and accessory facies, whose detrital compositions reflect the composition of local pre-Tertiary basement rock. (2) Lower to middle Miocene Comondú Formation: laterally variable sequence of volcaniclastic conglomerate, breccia, sandstone, tuff and minor volcanic flow units. (3) Widespread mesa-capping rhyolite tuff, typically welded and crystal-rich, probably upper Miocene in age. The Mesa Formation overlies a highly irregular and deeply dissected erosional surface developed on pre-Tertiary basement rock. The shift from pre-Mesa erosion to widespread (though localized) deposition and valley-filling records the final phase of late Cretaceous to middle Tertiary regional subsidence and eastward transgression that resulted from slow cooling and thermal contraction of Cretaceous arc crust during a temporal gap in magmatic activity along the western Cordilleran margin. Nonmarine sediments of the Mesa Formation were deposited in small, steep-walled paleovalleys and basins that gradually filled and evolved to form through-going, low-energy ephemeral stream systems. The gradational upward transition from the Mesa to Comondú Formation records the early to middle Miocene onset of subduction-related arc magmatism in eastern Baja California and related westward progradation of alluvial volcaniclastic aprons shed from high-standing eruptive volcanic centers. Pre-existing streams were choked with the new influx of volcanic detritus, causing the onset of rapid sediment deposition by stream flows and dilute

  1. Research on evolutionary laws of Sr, Nd, Pb isotopes of uranium metallization and volcanic rocks in south china

    International Nuclear Information System (INIS)

    Ying Junlong

    1998-01-01

    According to research on evolutionary tracer of Sr, Nd, Pb isotopes, the author proposes that isotopic evolution of Mesozoic volcanics in south China is controlled by regionally metamorphic rocks of ancient land basement, early reformed derivates and recycled continental crust. Isotopic composition of uranium metallization shows the characteristics of crust sources, and Yanshanian accretion of continental margin caused the crust movement such as magmatic activity in lower crust within continent, extension-down-faulting, etc., promoting the migration, enrichment and ore formation of uranium

  2. Preliminary study of the uranium favorability of Mesozoic intrusive and Tertiary volcanic and sedimentary rocks of the Central Mojave Desert, Kern and San Bernardino counties, California

    International Nuclear Information System (INIS)

    Leedom, S.H.; Kiloh, K.D.

    1978-02-01

    Numerous, small, low-grade, supergene uranium deposits are found in Tertiary volcanic and sedimentary rocks in the central Mojave Desert of southern California. Large thorium-to-uranium ratios in samples of Mesozoic intrusive rocks exposed in the area indicate that these rocks have been extensively weathered, eroded, and subsequently leached by ground waters, and that they may have been the primary source of uranium for the deposits. The uranium content of samples of volcanic intrusive and extrusive rocks is average for intermediate to silicic rocks, but samples of basalt flows in the area contain six times the average uranium content of mafic igneous rocks. Devitrified tuffs and tuffaceous sedimentary rocks, interbedded with calcareous units, are additional sources of uranium for supergene uranium deposits found in calcareous units. Uranium is also found in accessory minerals in a few Mesozoic quartz-rich pegmatite dikes. Uranium deposits in the central Mojave Desert have been formed by enrichment during diagenetic replacement of Tertiary carbonate rocks; by supergene enrichment along fractures, joints, and bedding planes in Tertiary volcanic and sedimentary rocks; during formation of Holocene caliche; and by deposition within hydrothermally altered shear zones. Within the area, the diagenetic replacement type of deposit has the greatest potential for large, low-grade uranium occurrences. The other type of uranium deposits are small, erratically distributed, and extensively covered by alluvium

  3. Quantitative Determination of Noa (Naturally Occurring Asbestos) in Rocks : Comparison Between Pcom and SEM Analysis

    Science.gov (United States)

    Baietto, Oliviero; Amodeo, Francesco; Giorgis, Ilaria; Vitaliti, Martina

    2017-04-01

    The quantification of NOA (Naturally Occurring Asbestos) in a rock or soil matrix is complex and subject to numerous errors. The purpose of this study is to compare two fundamental methodologies used for the analysis: the first one uses Phase Contrast Optical Microscope (PCOM) while the second one uses Scanning Electron Microscope (SEM). The two methods, although they provide the same result, which is the asbestos mass to total mass ratio, have completely different characteristics and both present pros and cons. The current legislation in Italy involves the use of SEM, DRX, FTIR, PCOM (DM 6/9/94) for the quantification of asbestos in bulk materials and soils and the threshold beyond which the material is considered as hazardous waste is a concentration of asbestos fiber of 1000 mg/kg.(DM 161/2012). The most used technology is the SEM which is the one among these with the better analytical sensitivity.(120mg/Kg DM 6 /9/94) The fundamental differences among the analyses are mainly: - Amount of analyzed sample portion - Representativeness of the sample - Resolution - Analytical precision - Uncertainty of the methodology - Operator errors Due to the problem of quantification of DRX and FTIR (1% DM 6/9/94) our Asbestos Laboratory (DIATI POLITO) since more than twenty years apply the PCOM methodology and in the last years the SEM methodology for quantification of asbestos content. The aim of our research is to compare the results obtained from a PCOM analysis with the results provided by SEM analysis on the base of more than 100 natural samples both from cores (tunnel-boring or explorative-drilling) and from tunnelling excavation . The results obtained show, in most cases, a good correlation between the two techniques. Of particular relevance is the fact that both techniques are reliable for very low quantities of asbestos, even lower than the analytical sensitivity. This work highlights the comparison between the two techniques emphasizing strengths and weaknesses of

  4. The behavior of biogenic silica-rich rocks and volcanic tuffs as pozzolanic additives in cement

    Science.gov (United States)

    Fragoulis, Dimitris; Stamatakis, Michael; Anastasatou, Marianthi

    2015-04-01

    Cements currently produced, include a variety of pozzolanic materials, aiming for lower clinker addition and utilization of vast deposits of certain raw materials and/or mining wastes and byproducts. The major naturally occurring pozzolanic materials include glassy tuffs, zeolitic tuffs, diatomites and volcanic lavas rich in glassy phase, such as perlites. Therefore, based on the available raw materials in different locations, the cement composition might vary according to the accessibility of efficient pozzolanic materials. In the present investigation, the behavior of pozzolanic cements produced with representative samples of the aforementioned materials was studied, following the characterization of the implemented pozzolanas with respect to their chemical and mineralogical characteristics. Laboratory cements were produced by co-grinding 75% clinker, 5% gypsum and 20% pozzolana, for the same period of time (45 min). Regarding pozzolanic materials, four different types of pozzolanas were utilized namely, diatomite, perlite, zeolite tuff and glassy tuff. More specifically, two diatomite samples originated from Australia and Greece, with high and low reactive silica content respectively, two perlite samples originated from Turkey and from Milos Island, Greece, with different reactive silica contents, a zeolite tuff sample originated from Turkey and a glassy tuff sample originated from Milos Island, Greece. The above pozzolana samples, which were ground in the laboratory ball mill for cement production performed differently during grinding and that was reflected upon the specific surface area (cm2/gr) values. The perlites and the glassy tuff were the hardest to grind, whereas, the zeolite tuff and the Australian diatomite were the easiest ones. However, the exceedingly high specific surface area of the Australian diatomite renders cement difficult to transport and tricky to use for concrete manufacturing, due to the high water demand of the cement mixture. Regarding

  5. The SHRIMP zircon U-Pb dating of felsic volcanic rocks and its geological significance from yutian group in southern jiangxi

    International Nuclear Information System (INIS)

    Ji Chunyu; Wu Jianhua

    2010-01-01

    Past researches have showed that the Rb-Sr isochron ages of felsic end member for r hyolite-basalt b imodal volcanic rocks of Yutian Group in the Changpu and Longnan Basin in Southern Jiangxi Province are 175 ∼ 148 Ma, not only does its amplitude change more significantly, but it does not match with the Rb-Sr isochron ages (179 ∼ 173 Ma) of basic end member. As a result, I choose a method of zircon U-Pb dating with a higher accuracy, to obtain the rhyolite in the bottom of bimodal volcanic rocks in the Changpu Basin and the dacite in the top of of bimodal volcanic rocks in the Longnan Basin, whose zircon SHIRMP U-Pb age are respectively (195.2 ± 2.8) Ma and (191 ± 1.7) Ma. What's more, they are both almost the same in the error limit. It shows that the bimodal volcanic rocks in these both two basins are the product of the same session of magma movement. Simultaneously, it explains they form in a flash during the eruption intervals. According to the the newest International Stratigraphic Chart (Gradsrein et al. , 2004), in terms of geological age, the bimodal volcanic rocks in Changpu Basin and Longnan Basin, belonging to the early Early Jurassic. The zircon SHIRMP U-Pb age are distinctly older than the whole-rock Rb-Sr isochron age, it is probably because of the deviation of the dating method for the wholerock Rb-Sr isochron age. The zircon SHIRMP U-Pb age of bimodal volcanic rocks are 191 ∼ 195 Ma in Southern Jiangxi Province, which indicates that there had been an extensional environment. And after the bimodal volcanic activity, The zircon SHIRMP U-Pb age of felsic volcanic rocks are 145 ∼ 130 Ma. Both of the ages shows a as long as 45 Ma quiet period between 190 Ma and 145 Ma. It is unreasonable possible to interpreted by the single pattern of pacific plate subducting to eurasian plate. (authors)

  6. The structure environment, rock-magma system, mineral-forming series and pattern of volcanic mineral-forming of uranium deposit in southeast of China

    International Nuclear Information System (INIS)

    Yu Dagan

    1992-01-01

    The Volcanic uranium deposit of rock-magma belt-the Mid-Cz Volcano in the Southeast of China mainly formed around 120 ∼ 130 Ma and 90 ∼ 100 Ma Which is in harmony with the two rock magma activities of k within the region. The rock-magma system of this period formed around the turning period from pressure to tension in the continent margin of southeast China, which is mainly characterized by the appearance of A-type granite and alkaline, sub-alkaline rocks (trachyte, trachyandensite, trachybasalt, basic rock alkaline basalt). The uranium deposit is controlled by the base rift of dissection to the mantle, the volcanic basin is of the double characteristics of transversal rift valley basin (early period) ad tension rift valley basin (laster period). The leading role of the deep source is stressed in terms of internal-forming series of volcanic uranium deposits is considered to exist; and also in terms of internal-forming series of volcanic uranium deposits is considered to exist; and also in terms of mineral-forming patterns, the multi-pattern led by the deep-source is stressed, including the mineral-forming pattern of uranium deposit of continental thermos, repeated periphery mineral-forming pattern of uranium deposit and the mineral-forming pattern of uranium deposit of rising pole-like thermos. Ten suggestions are put forward to the next mineral-search according to the above thoughts

  7. Paleomagnetism of volcanic rocks from the Northeast of Brazil and the time of the opening of the South Atlantic

    International Nuclear Information System (INIS)

    Guerreiro, S.D.C.

    1983-01-01

    In the first part of this paper palaeomagnetic and rock magnetism investigations were developed in volcanic samples from the Northeast of Brazil. The age of the samples spans the Jurassic and Cretaceous periods. To accomplish this task four areas were studied and a total of 495 samples from 58 sites were analysed. A portable drilling machine with 2.5 em core diameter was used to collect the samples. The orientation of the samples were obtained by means of a magnetic compass, and a clinometer. The analysis of the magnetic minerals of these samples was done by thermomagnetic curves and by X-ray diffraction. In most cases the magnetic phase in the rocks is mainly titanomagnetite with poor titanium content. Maghemite and sometimes hematite, usually a product of weathering, did not obscure the initial thermoremanent magnetization of these rocks. The second part of this paper deals with the determination of the time of the opening of the South Atlantic ocean by means of palaeomagnetic data. In this paper, however, instead of using the polar wandering paths of the continents (the usual method) statistical tests were applied that give the probability that a certain configuration for the two continents be consistent or not with the palaeomagnetic data for a chosen period. (author)

  8. Geochronology of the Swift Current granite and host volcanic rocks of the Love Cove group, southwestern Avalon zone, Newfoundland

    International Nuclear Information System (INIS)

    Dallmeyer, R.D.; O'Driscoll, C.F.; Hussey, E.M.

    1981-01-01

    Zircon fractions from the variably deformed and metamorphosed Swift Current granite and host volcanic rocks of the Love Cove Group record individually discordant U-Pb ages with well-defined upper concordia intercept ages of 580 +- 20 and 590 +- 30 Ma, respectively. These are interpreted to be crystallization dates and indicate a late Proterozoic cogmagmatic relationship. Primary hornblende from the pluton record disturbed 40 Ar/ 39 Ar age spectra that suggest postcrystallization argon loss, probably during Acadian (Devonian) regional metamorphism. 40 Ar/ 39 Ar plateau ages of 560-566 Ma are well defined for the hornblende and are interpreted to date times of postmagmatic cooling. The similarity between zircon and hornblende dates suggests relatively rapid postmagmatic cooling. A six-point, Rb-Sr whole-rock isochron age of 548 +- 11 Ma is defined for the pluton. The slight discordancy of this date in comparison with the zircon and hornblende ages may reflect a minor disturbance of whole-rock isotopic systems during Acadian regional metamorphism. (author)

  9. Mineral chemistry of clinopyroxene: guidance on geo- thermobarometry and tectonomagmatic setting of Nabar volcanic rocks, South of Kashan

    Directory of Open Access Journals (Sweden)

    Rezvan Mehvari

    2017-02-01

    Full Text Available Introduction The Nabar area that is a part of the Urumieh- Dokhtar volcano- plutonic belt is located in the south of Kashan. Research works such as Emami (Emami, 1993 and Abbasi (Abbasi, 2012 have been done about the geology of this area. Rock units in the study area contain middle- upper Eocene intermediate to acidic lavas and pyroclastic rocks, green marl, shale and sandy marls of Oligo- Miocene, limestones of Qom formation, intrusive granitoids with Oligo- Miocene age and quaternary travertine and recent alluvium (Emami, 1993. The volcanic and sub volcanic rocks of this area are composed of andesite, trachyandesite, dacite, rhyolite and porphyric pyroxene diorite along with pyroclastic rocks. Materials and methods In order to achieve the aims of this work, at first field surveying and sampling were done. Then, thin and polished thin sections were prepared. Some of the samples were selected for microprobe analysis and clinopyroxene minerals were analyzed by using JEOL- JXA-8800 analyzer with a voltage of 20 Kv and a current of 12 nA in the Kanazava University of Japan and Cameca-Sx100 analyzer with a voltage of 15 Kv and a current of 15 nA in the Iranian mineral processing research center, Karaj. Discussion On the basis of petrographic investigations, porphyritic, porphyroid, fluidal, amygdaloidal and porphyry with microlitic groundmass are common textures of these rocks. Also plagioclase, clinopyroxene, amphibole, biotite, sanidine and quartz are essential minerals, opaque, zircon and apatite as accessory minerals are observed in the studied rocks. Clinopyroxenes are observed with corona texture that resulted during the uralitization process. On the basis of minerals’ chemistry, pyroxenes are Fe- Mg- Ca type in composition (Morimoto et al., 1988. These clinopyroxenes are augite. Investigations indicate that mineral composition of clinopyroxene can be effectively used to evaluation the P-T conditions during crystallization. Previous research

  10. Geochemistry and tectonomagatic setting of Tertiary volcanic rocks of the Kangan area, northeast of Sarbisheh, southern Khorasan

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    Mahshid Malekian Dastjerdi

    2017-02-01

    Full Text Available Introduction The study area is located 12km away from the north east of Sarbisheh at the eastern border of the Lut block (Karimpour et al., 2011; Richards et al., 2012. The magmatic activity in the Lut blockhas begun in the middle Jurassic (165-162 Ma and reached its peak in the Tertiary age (Jung et al., 1983; Karimpour et al., 2011. Volcanic and subvolcanic rocks in the Tertiary age cover over half of the Lut block with up to 2000 m thickness and they were formed due to subduction prior to the collision of the Arabian and Asian plates (Jung et al., 1983; Karimpour et al., 2011. In the Kangan area, the basaltic lavas cropped out beyond the above intermediate to acid volcanic rocks. In this area, bentonite and perlite deposits have an economic importance. The main purpose of this paper is to present a better understanding of the tectono-magmatic settings of volcanic rocks in the northeast of Sarbisheh, east of Iran based on their geochemical characteristics. Materials and methods Fifteen samples were analyzed for major elements by inductively coupled plasma (ICP technologies and trace elements by using inductively coupled plasma mass spectrometry (ICP-MS, following a lithium metaborate/tetraborate fusion and nitric acid total digestion, at the Acme laboratories, Vancouver, Canada. Results The Kangan area is located at the northeast of Sarbishe, Southern Khorasan and the eastern border of the Lut block. In this area, basaltic lavas have cropped out above intermediate to acid lavas such as andesite, dacite, rhyolite (sometimes perlitic .The main minerals in the basalt are plagioclase, olivine and pyroxene, in andesite contain plagioclase, pyroxene, biotite and amphibole and in acid rocks include plagioclase, quartz, sanidine, biotite and amphibole. Intermediate to acid rocks have medium to high-K calc-alkaline nature and basalt is alkaline. Enrichment in LREE relative to HREE (Ce/Yb= 21.14-28.7, high ratio of Zr/Y(4.79- 10.81, enrichment in LILE

  11. Fracturing Fluid Leak-off for Deep Volcanic Rock in Zhungeer Basin: Mechanism and Control Method

    OpenAIRE

    Huang Bo; Cheng Hao; He Yidong; Fu Yanming

    2017-01-01

    The deep volcanic reservoir in Zhungeer Basin is buried in over 4000m depth, which is characterized by complex lithology (breccia, andesite, basalt, etc.), high elastic modulus and massive natural fractures. During hydraulic fracturing, hydraulic fracture will propagate and natural fractures will be triggered by the increasing net pressure. However, the extension of fractures, especially natural fractures, would aggravate the leak-off effect of fracturing fluid, and consequently decrease the ...

  12. Across and along arc geochemical variations in altered volcanic rocks: Evidence from mineral chemistry of Jurassic lavas in northern Chile, and tectonic implications

    Science.gov (United States)

    Rossel, Pablo; Oliveros, Verónica; Ducea, Mihai N.; Hernandez, Laura

    2015-12-01

    Postmagmatic processes mask the original whole-rock chemistry of most Mesozoic igneous rocks from the Andean arc and back-arc units preserved in Chile. Mineral assemblages corresponding to subgreenschist metamorphic facies and/or propylitic hydrothermal alteration are ubiquitous in volcanic and plutonic rocks, suggesting element mobility at macroscopic and microscopic scale. However, fresh primary phenocrysts of clinopyroxene and plagioclase do occur in some of the altered rocks. We use major and trace element chemistry of such mineral phases to infer the geochemical variations of four Jurassic arc and four back-arc units from northern Chile. Clinopyroxene belonging to rocks of the main arc and two units of the bark-arc are augites with low contents of HFSE and REE; they originated from melting of an asthenospheric mantle source. Clinopyroxenes from a third back-arc unit show typical OIB affinities, with high Ti and trace element contents and low Si. Trace elemental variations in clinopyroxenes from these arc and back-arc units suggest that olivine and clinopyroxene were the main fractionating phases during early stages of magma evolution. The last back-arc unit shows a broad spectrum of clinopyroxene compositions that includes depleted arc-like augite, high Al and high Sr-Ca diopside (adakite-like signature). The origin of these lavas is the result of melting of a mixture of depleted mantle plus Sr-rich sediments and subsequent high pressure fractionation of garnet. Thermobarometric calculations suggest that the Jurassic arc and back-arc magmatism had at least one crustal stagnation level where crystallization and fractionation took place, located at ca. ~ 8-15 km. The depth of this stagnation level is consistent with lower-middle crust boundary in extensional settings. Crystallization conditions calculated for high Al diopsides suggest a deeper stagnation level that is not consistent with a thinned back-arc continental crust. Thus minor garnet fractionation

  13. Glass inclusions in volcanic rocks in the Okinawa Trough back-arc basin: constraints on magma genesis and evolution

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The major elemnt compositions of glass inclusions in plagioclase and pyroxene phenocrysts of basalt and pumice in the Okinawa Trough back-arc basin are determined by electron microprobe. The results indicate that basalt and pumice are cognate and respectively represent the proluots at early stages of mgmtism and at late stage of crystal fractionation. The initial magrma in the trough is rich in H2O. The variation of H2O content in magma may play an important role in the magma evolution. Plagioclase is the mineral crystallized throughout the whole magrmatic process and accumulates in the zoned magma chamber. From these features it can he inferred that the initial magma in the Okinawa Trough, whose opening began in recent years, is serious ly affected by fluid or other materials carried by subducting slab and the geocbemical feature of volcanic rocks is in some degree similar to that of lavas in island-arc environments.

  14. Stable isotope compositions and water contents of boninite series volcanic rocks from Chichi-jima, Bonin Islands, Japan

    Science.gov (United States)

    Dobson, P.F.; O'Neil, J.R.

    1987-01-01

    Measurements of stable isotope compositions and water contents of boninite series volcanic rocks from the island of Chichi-jima, Bonin Islands, Japan, confirm that a large amount (1.6-2.4 wt.%) of primary water was present in these unusual magmas. An enrichment of 0.6??? in 18O during differentiation is explained by crystallization of 18O-depleted mafic phases. Silicic glasses have elevated ??18O values and relatively low ??D values indicating that they were modified by low-temperature alteration and hydration processes. Mafic glasses, on the other hand, have for the most part retained their primary isotopic signatures since Eocene time. Primary ??D values of -53 for boninite glasses are higher than those of MORB and suggest that the water was derived from subducted oceanic lithosphere. ?? 1987.

  15. Variable slab and subarc mantle signatures within dying arc setting-clues from the volcanology and geochemistry of Quaternary volcanic rocks from Armenia.

    Science.gov (United States)

    Savov, I. P.; Luhr, J.; D'Antonio, M.; Connor, C.; Karakhanian, A.; Ghukasyan, Y.; Djrbashian, R.

    2007-05-01

    Armenian volcanoes occur within the active continental collision zone involving the Arabian and Eurasian plates. The volcanism is hosted by a chain of pull-apart basins, cumulatively forming an arc across Armenia and extending into Turkey and Iran. We collected fresh volcanic rocks from >100 volcanoes in proximity to the large calc-alkaline strato-volcano Mt.Ararat (Turkey) and the sub-alkaline shield-volcano Mt.Aragats (Armenia).The samples are trachybasalt-andesites o dacites (Aragats Volcanic Plateau) and trachybasalts to rhyolites (Arteni Volcanic Complex, Gegham Plateau and Lake Sevan regions).The major and trace element systematics of the Armenian volcanics reveal mixed arc-like and OIB-like signatures may accompany the transition from subduction to collision (Miocene-recent). Relative to N-MORB our samples show enrichments of fluid mobile elements,Th,U,LILE and LREE,and depletions of HREE and Hf, Nb, Ta and Zr.The lower 87Sr/86Sr ratios (0.7041 to 0.7051) compared to any known crustal material in the region, the regional mantle 144Nd/143Nd isotope ratios [0.5128-0.5129] and the absence of crustal xenoliths cause us to conclude that crustal assimilation did not play a significant role in the magmagenesis.We will report large mineral chemistry dataset and detailed textural observations revealing no significant mineral zoning.Based on mineral rim and groundmass chemistries and using variety of hygrothermometers, we calculated melt H2O contents ranging from 1.9 to 4.5 wt% and also elevated eruption temperatures [range= 1030- 1060°C].This calculations are in agreement with the generally anhydrous nature of the mineral assemblages [Pl+Opx+Cpx+Ol+TiMt] and with the ionprobe study of volatile contents in olivine hosted melt inclusions [H2O = 0.5-2.8 wt%; CO2 = 10-371 ppm; F= 1865-2905 ppm, S= 225-5122 ppm;Cl= 650-1013 ppm]. Although other mechanisms such as delamination and localized extension related to strike slip faulting might also contribute to magma

  16. Geochemical behaviour of rare earth elements on metasomatic alteration of volcanic rocks

    International Nuclear Information System (INIS)

    Jordanov, J.A.; Kunov, A.J.

    1987-01-01

    Investigations are carried out on metasomatically altered Paleogene latites in order to follow up the rare earth elements (REE) geochemical behavour. Representative samples of the initial rocks (latites), from propylitized latites and quartz-sericite rocks, as well as from dickite, alumite, diaspore and monoquartzites, are analysed. The results show that REE have a behaviour of moderately mobile elements. They undergo redistribution both in quantity and in the composition of the group. The different concentrations and changes in the ΣREE compared to the initial rocks are observed and direct relationships to the degree of endogenic leaching are made. The REE mobility and redistribution during the metasomatic alterations in the region investigated are controlled by the physical-chemical conditions which play a significant role both in determining the composition of the mineral paragenese and in the fixing of REE. The distribution patterns indicate that REE redistribution in the case of metasomatic alterations is almost isochemical without any supply from hydrothermal solutions

  17. Development of micro-scale joints in volcanic rocks under thermal ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging Solutions)

    Petrographic studies of samples of the Rajmahal basalt reveal a variety of microscopic joints ... To study the micro-scale joints in rock systems, ..... fiber-like crystal habit of the material chosen for ... stress, Y is the numerical modification factor to.

  18. Petrogenesis and tectonic implications of Late Devonian arc volcanic rocks in southern Beishan orogen, NW China: Geochemical and Nd-Sr-Hf isotopic constraints

    Science.gov (United States)

    Guo, Qian-Qian; Chung, Sun-Lin; Xiao, Wen-Jiao; Hou, Quan-Lin; Li, Shan

    2017-05-01

    Late Devonian (ca. 370 Ma) volcanic rocks provide important information about the nature of magmatism during the tectonic transition between the Early and Late Paleozoic in the Beishan orogen, southern Central Asian Orogenic Belt. They are predominantly an andesitic-dacitic-rhyolitic assemblage, characterized by alkali contents ranging from slightly calcic to slightly alkaline. The rhyolitic rocks are generally ferroan, whereas the andesitic rocks are magnesian. These volcanic rocks exhibit similar trace element characteristics to those of continental arcs. Strongly negative εNd(t) values (- 2.8 to - 3.6) and high Sr isotopic compositions (initial 87Sr/86Sr = 0.7036-0.7108) suggest that they are mainly derived from an ancient crust. However, the positive zircon εHf(t) values (+ 1.4 to + 16.4) support the role of juvenile components in their genesis, indicating the significant input of new mantle-derived magmas. These characteristics imply a hybrid derivation, from an ancient crustal source with the addition of juvenile materials during magma genesis, or perhaps heterogeneous contamination or hybridization during magma emplacement. Combined with the regional geology, our results indicate that the Late Devonian magmatism resulted from a southward retreat of the subduction zone, which records significant continental crustal growth in a transitional arc or an accretionary arc setting. The distinct geochemical compositions, especially the Nd-Hf isotope decoupling of the Dundunshan volcanic rocks, imply a significant change in the geodynamic setting in the Late Paleozoic.

  19. Comparison of thermally induced and naturally occurring water-borne leakages from hard rock depositories for radioactive waste

    International Nuclear Information System (INIS)

    Bourke, P.J.; Robinson, P.C.

    1981-01-01

    The relative importance of thermally induced and naturally occurring flows of water as causes of leakage from hard rock depositories for radioactive wastes is assessed. Separate analyses are presented for involatile, high level waste from reprocessing of fuel and for plutonium contaminated waste from fabrication of fuel. The effects of varying the quantities of wastes, pre-burial storage and the shapes and depths of depositories are considered. It is concluded that for representative values of these variables, thermal flow will remain the major cause of leakage for long times after the burial of both types of waste. (Auth.)

  20. New records of rare lichenicolous and lichen-forming fungi from volcanic rocks in SW Poland

    Directory of Open Access Journals (Sweden)

    Katarzyna Szczepańska

    2015-08-01

    Full Text Available Records of two lichenicolous and nine lichen-forming fungi found in the southwestern part of Poland are presented. All of the reported species are very rare and they have only a few scattered localities in the country. One of them, Lecanora pannonica, is reported for the second time from Poland. Additionally, the new, contemporary records of Cercidospora macrospora, Rhizocarpon disporum, R. viridiatrum and Stereocaulon pileatum in Lower Silesia were noted. These species were known only from historical collections in the study area. Furthermore, Lecidea fuscoatra has been found a new host for Sagediopsis barbara. All of the localities of recorded species were found on natural outcrops of basalt rocks.

  1. Petrology, geochemistry, and tectonic setting of Tertiary volcanic and intrusive rocks in the north of Shahr-e-Firouzeh (northeast of Iran)

    International Nuclear Information System (INIS)

    Malekzadeh Shafaroudi, A.; Karimpour, M. H.; Zarei, A.

    2016-01-01

    The study area is located in 15 km of the north of Shahr-e-Firouzeh in Khorasan Razavi province. The area is situated in the southeast of Quchan-Sabzevar arc magmatic. Lithology of the district includes dacitic lavas, which are intruded by Oligocene porphyritic hornblende granodioritic stock and granodioritic dike as subvolcanic and plutonic rocks. Igneous rocks were overlapped by younger sedimentary rocks. The texture of dacitic unit is porphyric to glomeroporphic with flow groundmass. Quartz, plagioclase, K-feldspar, and hornblende are the main minerals. The texture of hornblende granodiorite porphyry is porphyric to glomeroporphic and plagioclase, K-feldspar, hornblende, and quartz are the common minerals, whereas granodiorite unit is granular and hornblende is not present. Based on geochemical studies, the acidic volcanic and intrusive rocks show metaluminous and medium-K nature. These rocks belong to the I-type granitoid. Enrichment of LREE versus HREE and enrichment of LILE and depletion in HFSE indicate magma formed in subduction zone. The melt originated from partial melting of amphibolite with 10 to 25% garnet. Based on the average amount of major oxides, enrichment of LREE, mostly positive Eu anomaly, high Sr (up to 499 ppm), and low Y (<13 ppm) and Yb (<1.4 ppm) contents, the magma show silica-rich adakitic nature. The intrusive and volcanic rocks of the northern Shahr-e-Firouzeh were generated by partial melting of Sabzevar Neotethyan young and hot subducted oceanic crust and mantle wedge in the continental margin of the Turan plate.

  2. Determining magmatic series and oxygen fugacity of volcanic rocks in the east of Kamu, north of Isfahan, based on biotite chemistry

    Directory of Open Access Journals (Sweden)

    Mohammad Sayari

    2014-04-01

    Full Text Available Volcanic rocks of interest are situated in the middle part of the Urumieh-Dokhtar Magmatic Arc (UDMA. They are parts of a vast magmatic province located in the north of Bitlis-Zagros suture zone. Having a prevailing porphyritic texture, these rocks include phenocrysts of plagioclase, amphibole and biotite in a matrix composed of feldspar, quartz, opaque, glass and microlite and mineralogically show composition of dacite to andesite. Minerals are mostly fresh. Effects of alteration are limited to weak chloritization and saussuritization in some amphiboles and rim of plagioclases, respectively. All of the analyzed biotites in the Miocene-Pliocene volcanic rocks in the east of Kamu are of Mg-biotite. According to a widespread classification of micas to 6 general end-members, biotites of interest are averagely composed of 55.45% phlogopite, 15.90% talc, 12.72% Ti-phlogopite, 11.44% eastonite, 3.71% ferri-eastonite and 0.78% muscovite. Chemical composition of biotites indicates a calk-alkaline magmatic series for the magma from which biotites are crystallized. Estimation of the oxygen fugacity of magma, based on chemical composition and Fe3+ content of biotite, shows that the oxygen fugacity was limited to FMQ buffer in quality and was about 10-15 bar in quantity. This value accords the oxygen fugacity for intermediate-acidic volcanic rocks.

  3. Geochemical and isotopic characteristics of volcanic rocks from the northern East China Sea shelf margin and the Okinawa Trough

    Institute of Scientific and Technical Information of China (English)

    ZENG Zhigang; YU Shaoxiong; WANG Xiaoyuan; FU Yongtao; YIN Xuebo; ZHANG Guoliang; WANG Xiaomei; CHEN Shuai

    2010-01-01

    Volcanic rocks both from the northern East China Sea (NECS) shelf margin and the northern Okinawa Trough are subalkaline less aluminous,and lower in High Field Strength Elements (HFSE).These rocks are higher in Large Ion Lithophile Elements (LILE),thorium and uranium contents,positive lead anomalies,negative Nb-Ta anomalies,and enrichment in Light Rare Earth Elements (LREE).Basalts from the NECS shelf margin are akin to Indian Ocean Mid-Ocean Ridge Basalt (MORB),and rhyolites from the northern Okinawa Trough have the highest 207Pb/204Pb and 208Pb/204Pb ratios.The NECS shelf margin basalts have lower 87Sr/86Sr ratios,εNd and σ18O than the northern Okinawa Trough silicic rocks.According to 40K-40Ar isotopic ages of basalts from the NECS shelf margin,rifting of the Okinawa Trough may have been active since at least 3.65-3.86 Ma.The origin of the NECS shelf margin basalt can be explained by the interaction of melt derived from Indian Ocean MORB-like mantle with enriched subcontinental lithosphere.The basalts from both sides of the Okinawa Trough may have a similar origin during the initial rifting of the Okinawa Trough,and the formation of basaltic magmas closely relates to the thinning of continental crust.The source of the formation of the northern Okinawa Trough silicic rocks was different from that of the middle Okinawa Trough,which could have been generated by the interaction of basaltic melt with an enriched crustal component.From the Ryukyu island arc to East China,the Cenozoic basalts have apparently increasing trends of MgO contents and ratios of LREE to Heavy Rare Earth Elements (HREE),suggesting that the trace element variabilities of basalts may have been influenced by the subduction of the Philippine Sea plate,and that the effects of subduction of the Philippine Sea plate on the chemical composition of basaltic melts have had a decreasing effect from the Ryukyu island arc to East China.

  4. Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane

    Science.gov (United States)

    Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan

    2017-05-01

    Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

  5. Petrochemical Results for Volcanic Rocks recovered from SHINKAI 6500 diving on the Bonin Ridge (27°15'N-28°25'N): submarine extension of Ogasawara forearc volcanism

    Science.gov (United States)

    Bloomer, S. H.; Kimura, J.; Stern, R. J.; Ohara, Y.; Ishii, T.; Ishizuka, O.; Haraguchi, S.; Machida, S.; Reagan, M.; Kelley, K.; Hargrove, U.; Wortel, M.; Li, Y. B.

    2004-12-01

    Four SHINKAI 6500 submersible dives (dive #823 to #826) were performed along the Bonin Ridge escarpment west of Ogasawara (Bonin) Islands in the West Pacific during May 2004, in the hopes of finding exposures of lower crust of the IBM forearc. The Ogasawara Islands are located on the Bonin ridge, exposing 48-40 Ma boninites on Chichi-jima and depleted arc tholeiite lavas of the same age on Haha-jima. These extremely depleted lavas are believed to have been generated when subduction began beneath the Izu-Bonin-Mariana oceanic arc system. Subsequent rifting (35-30 Ma) formed the Bonin Trough and a 350 km long N-S trending eastern escarpment (Bonin Ridge), where we concentrated our dives. We observed lavas and volcaniclastic sequences by the four SHINKAI dives along the escarpment, and 16 fresh basaltic to andesitic lava samples have been recovered. The first three dives appear to have sampled volcanic constructs, of presumed Oligocene age, along the escarpment, whereas the last dive sampled exposures similar to Eocene rocks of the Bonin islands, including nummulitic limestone. The lava samples were analyzed by ICP-MS at Shimane University for 30 incompatible trace elements. All samples show arc-like chemical signatures, including elevated concentrations of LIL elements, depletions in Ta and Nb, and spikes in Pb, Sr, and Li. All samples show modest enrichments in LREE. A lava sample from the northernmost dive #824 is identical with the depleted tholeiite from Haha-jima Islands at the southernmost end of the Bonin Ridge in terms of trace element characteristics. Other lava samples from northern three dives (#823, #824, #825) have tholeiitic affinities with more elevated highly incompatible elements. This suggests derivation of the series of lavas by different degree of partial melting of a similar source mantle. Samples from southernmost dive site #826, immediately northwest of Chichi-jima Islands, are boninites with U-shaped REE patterns and relatively enriched Zr and

  6. A "La Niña-like" state occurring in the second year after large tropical volcanic eruptions during the past 1500 years

    Science.gov (United States)

    Sun, Weiyi; Liu, Jian; Wang, Bin; Chen, Deliang; Liu, Fei; Wang, Zhiyuan; Ning, Liang; Chen, Mingcheng

    2018-04-01

    Using an ensemble of nine El Niño/Southern Oscillation (ENSO) reconstructed proxies and volcano eruption proxies for the past 1500 years, this study shows that a significant La Niña state emerges in the second year (year (2) hereafter) after large tropical volcanic eruptions. The reasons for the development of La Niña are investigated using the Community Earth System Model (CESM). In the volcanic eruption experiment (Vol), a robust La Niña signal occurs in year (2), resembling the proxy records. The eastward positioning of the western North Pacific anomalous anticyclone (WNPAC) in Vol plays a critical role in the advanced decay of year (2) warming and the strong intensification of cooling in the equatorial eastern Pacific. The enhanced easterlies located on the southern edge of the WNPAC can stimulate consecutive oceanic upwelling Kelvin waves, shallowing the thermocline in the eastern Pacific, thereby resulting in a greater cooling rate by the enhanced thermocline feedback and cold zonal advection. Over the equatorial eastern Pacific, the reduced shortwave radiation contributes to the advanced decay of warming, while the upward latent heat flux augments the strong intensification of the cooling. Essentially, the eastward positioning of the WNPAC is a result of the volcanic forcing. The volcanic effect cools the maritime continent more than its adjacent oceans, thus pushing convective anomalies eastward during year (1). This induces vertical thermal advection and upward surface latent heat flux, thereby suppressing the development of warm Sea Surface Temperature over the central-western Pacific and causing the eastward positioning of the WNPAC in Vol.

  7. Geochemistry, geochronology, and tectonic setting of Early Cretaceous volcanic rocks in the northern segment of the Tan-Lu Fault region, northeast China

    Science.gov (United States)

    Ling, Yi-Yun; Zhang, Jin-Jiang; Liu, Kai; Ge, Mao-Hui; Wang, Meng; Wang, Jia-Min

    2017-08-01

    We present new geochemical and geochronological data for volcanic and related rocks in the regions of the Jia-Yi and Dun-Mi faults, in order to constrain the late Mesozoic tectonic evolution of the northern segment of the Tan-Lu Fault. Zircon U-Pb dating shows that rhyolite and intermediate-mafic rocks along the southern part of the Jia-Yi Fault formed at 124 and 113 Ma, respectively, whereas the volcanic rocks along the northern parts of the Jia-Yi and Dun-Mi faults formed at 100 Ma. The rhyolite has an A-type granitoid affinity, with high alkalis, low MgO, Ti, and P contents, high rare earth element (REE) contents and Ga/Al ratios, enrichments in large-ion lithophile (LILEs; e.g., Rb, Th, and U) and high-field-strength element (HFSEs; e.g., Nb, Ta, Zr, and Y), and marked negative Eu anomalies. These features indicate that the rhyolites were derived from partial melting of crustal material in an extensional environment. The basaltic rocks are enriched in light REEs and LILEs (e.g., Rb, K, Th, and U), and depleted in heavy REEs, HFSEs (e.g., Nb, Ta, Ti, and P), and Sr. These geochemical characteristics indicate that these rocks are calc-alkaline basalts that formed in an intraplate extensional tectonic setting. The dacite is a medium- to high-K, calc-alkaline, I-type granite that was derived from a mixed source involving both crustal and mantle components in a magmatic arc. Therefore, the volcanic rocks along the Jia-Yi and Dun-Mi faults were formed in an extensional regime at 124-100 Ma (Early Cretaceous), and these faults were extensional strike-slip faults at this time.

  8. Decolorization of textile dye RB19 using volcanic rock matrix immobilized Bacillus thuringiensis cells with surface displayed laccase.

    Science.gov (United States)

    Wan, Juan; Sun, Xiaowen; Liu, Cheng; Tang, Mengjun; Li, Lin; Ni, Hong

    2017-06-01

    A triplicate volcanic rock matrix-Bacillus thuringiensis-laccase WlacD (VRMs-Bt-WlacD) dye decolorization system was developed. WlacD was displayed on the B. thuringiensis MB174 cell surface to prepare a whole-cell laccase biocatalyst by using two repeat N-terminal domains of autolysin Mbg (Mbgn) 2 as the anchoring motif. Immunofluorescence microscopic assays confirmed that the fusion protein (Mbgn) 2 -WlacD was anchored on the surface of the recombinant B. thuringiensis MB174. After optimization by a single factor test, L 9 (3 4 )-orthogonal test, Plackett-Burman test, steepest ascent method, and Box-Behnken response surface methodology, the whole-cell specific laccase activity of B. thuringiensis MB174 was improved to 555.2 U L -1 , which was 2.25 times than that of the primary culture condition. Optimized B. thuringiensis MB174 cells were further adsorbed by VRMs to prepare VRMs-Bt-WlacD, an immobilized whole-cell laccase biocatalyst. Decolorization capacity of as-prepared VRMs-Bt-WlacD toward an initial concentration of 500 mg L -1 of an textile dye reactive blue 19 (RB19) aqueous solution reached 72.36% at a solid-to-liquid ratio of 10 g-100 mL. Repeated decolorization-activation operations showed the high decolorization capacity of VRMs-Bt-WlacD and have the potential for large-scale or continuous operations.

  9. REE behavior during weathering of basaltic rocks from the Lisbon Volcanic Complex (Portugal)

    International Nuclear Information System (INIS)

    Prudencio, M.I.; Cabral, J.M.P.; Sequeira Braga, M.A.

    1991-01-01

    Two weathering profiles developed in alkali basalts from the Lisbon Volcanic Complex were chosen for a REE behavior study. Profile 1 consists of a lava flow with porphyritic texture. Olivine and clinopyroxene are set in a groundmass which mainly comprises plagioclase, clinopyroxene, olivine, biotite, glass and Fe-Ti oxides. X-ray diffraction analysis of the 0 < 2μm fraction revealed: 45-95% smectites and 5-40% halloysite (7.3 angstrom), and Fe and/or Ti oxides. Profile 2 consists of a lava flow with an intergranular texture, where olivine, clinopyroxene and spinel grains are surrounded by large feldspars laths. The 0 < 2μ fraction consists of 80-100% halloysite (7.3 angstrom), < 20% micas and < 10% palygorskite and Fe and/or Ti oxides. The REE were determined by instrumental neutron activation analysis. The clay-sized fractions of the more weathered samples were separated and analyzed too. For the whole samples it was observed that: (1) when halloysites are the dominant clay-minerals (profile 2), REE are more retained in the profile and (2) in general the light REE are less concentrated in the profiles than the intermediate or even the heavy REE. In most weathered samples of profile 1 a significant loss of Ce was found. The REE in the 0 < 2μm fractions are in general enriched relative to the whole samples. In profile 1, where smectites dominate, a significant negative Ce anomaly is also present except for one sample collected at an intermediate level. Among the REE analyzed, Nd is the most enriched compared to the whole samples. In profile 2, where halloysites dominate and micas are present mainly at the bottom of the profile, it was observed that: (a) REE are less fractionated than in profile 1, (b) Ce is depleted at the bottom of the profile but increases upwards, so that at the top the 0 < 2μm fraction reveals a small positive anomaly relative to whole sample

  10. Analysis of the rock mechanics properties of volcanic tuff units from Yucca Mountain, Nevada Test Site

    International Nuclear Information System (INIS)

    Price, R.H.

    1983-08-01

    Over two hundred fifty mechanical experiments have been run on samples of tuff from Yucca Mountain, Nevada Test Site. Cores from the Topopah Spring, Calico Hills, Bullfrog and Tram tuff units were deformed to collect data for an initial evaluation of mechanical (elastic and strength) properties of the potential horizons for emplacement of commercial nuclear wastes. The experimental conditions ranged in sample saturation from room dry to fully saturated, confining pressure from 0.1 to 20 MPa, pore pressure from 0.1 to 5 MPa, temperature from 23 to 200 0 C, and strain rate from 10 -7 to 10 -2 s -1 . These test data have been analyzed for variations in elastic and strength properties with changes in test conditions, and to study the effects of bulk-rock characteristics on mechanical properties. In addition to the site-specific data on Yucca Mountain tuff, mechanical test results on silicic tuff from Rainier Mesa, Nevada Test Site, are also discussed. These data both overlap and augment the Yucca Mountain tuff data, allowing more definitive conclusions to be reached, as well as providing data at some test conditions not covered by the site-specific tests

  11. Ancient xenocrystic zircon in young volcanic rocks of the southern Lesser Antilles island arc

    Science.gov (United States)

    Rojas-Agramonte, Yamirka; Williams, Ian S.; Arculus, Richard; Kröner, Alfred; García-Casco, Antonio; Lázaro, Concepción; Buhre, Stephan; Wong, Jean; Geng, Helen; Echeverría, Carlos Morales; Jeffries, Teresa; Xie, Hangqian; Mertz-Kraus, Regina

    2017-10-01

    The Lesser Antilles arc is one of the best global examples in which to examine the effects of the involvement of subducted sediment and crustal assimilation in the generation of arc crust. Most of the zircon recovered in our study of igneous and volcaniclastic rocks from Grenada and Carriacou (part of the Grenadines chain) is younger than 2 Ma. Within some late Paleogene to Neogene ( 34-0.2 Ma) lavas and volcaniclastic sediments however, there are Paleozoic to Paleoarchean ( 250-3469 Ma) xenocrysts, and Late Jurassic to Precambrian zircon ( 158-2667 Ma) are found in beach and river sands. The trace element characteristics of zircon clearly differentiate between different types of magmas generated in the southern Lesser Antilles through time. The zircon population from the younger arc (Miocene, 22-19 Ma, to Present) has minor negative Eu anomalies, well-defined positive Ce anomalies, and a marked enrichment in heavy rare earth elements (HREE), consistent with crystallization from very oxidized magmas in which Eu2 + was in low abundance. In contrast, zircon from the older arc (Eocene to mid-Oligocene, 30-28 Ma) has two different REE patterns: 1) slight enrichment in the light (L)REE, small to absent Ce anomalies, and negative Eu anomalies and 2) enriched High (H)REE, positive Ce anomalies and negative Eu anomalies (a similar pattern is observed in the xenocrystic zircon population). The combination of positive Ce and negative Eu anomalies in the zircon population of the older arc indicates crystallization from magmas that were variably, but considerably less oxidized than those of the younger arc. All the igneous zircon has positive εHf(t), reflecting derivation from a predominantly juvenile mantle source. However, the εHf(t) values vary significantly within samples, reflecting considerable Hf isotopic heterogeneity in the source. The presence of xenocrystic zircon in the southern Lesser Antilles is evidence for the assimilation of intra-arc crustal sediments and

  12. K-U-Th systematics of terrestrial igneous rocks for planetological comparisons: volcanic rocks of the Earth oceanic island arc and Venus surface material

    International Nuclear Information System (INIS)

    Nikolaeva, O.V.

    1997-01-01

    Principles of the formation o data base for 339 samples of oceanic island arc (OIA) igneous rocks of the Earth available in literature are described as well as of the formation of fresh rock sample, characteristics of this sample, and K-U-Th-systematics of the fresh igneous rocks of Earth OIA. Results of comparison of the Venus measured rocks and Earth OIA rocks by K, U, Th

  13. Frictional processes during flank motion at Mount Etna (Italy): experimental characterisation of slip on similar and dissimilar volcanic and sedimentary rocks.

    Science.gov (United States)

    Rozanski, Wojciech; Lavallee, Yan; Kendrick, Jackie; Castagna, Angela; Mitchell, Thomas; Heap, Michael; Vinciguerra, Sergio; Hirose, Takehiro; Dingwell, Donald

    2015-04-01

    The edifice of Mount Etna (Italy) is structurally unstable, exhibiting a near continuous ESE seaward sliding along a set of faults due to interplay between regional tectonics, gravity instability and magma intrusion. Continuous seismic and ground deformation monitoring reveals the resulting large-scale flank motion at variable rates. The mechanisms controlling this faulting kinetic remains, however, poorly constrained. Examination of the fault zones reveals a range of rock types along the different fault segments: fresh and altered basalt, clay and limestone. As lithological contrasts can jeopardise the structural stability of an edifice, we experimentally investigate the frictional properties of these rocks using low- to high-velocity-rotary shear tests on similar and dissimilar rocks to better understand episodes of slow flank motion as well as rapid and catastrophic sector collapse events. The first set of experiments was performed at velocities up to 1.2 m/s and at normal stresses of 1.5 MPa, commensurate with depths of the contacts seen in the Etna edifice. Friction experiments on clay gouge shows the strong rate-weakening dependence of slip in this material as well as the release of carbon dioxide. Friction experiments on solid rocks show a wider range of mechanical behaviour. At high velocity (>0.6 m/s) volcanic rocks tend to melt whereas the clay and limestone do not; rather they decarbonate, which prevents the rock from achieving the temperature required for melting. Experiments on dissimilar rocks clearly show that composition of host rocks affects the composition and viscosity of the resultant frictional melt, which can have a dramatic effect on shear stress leading to fault weakening or strengthening depending on the combination of host rock samples. A series of low- to moderate-slip velocity experiments is now being conducted to complement our dataset and provide a more complete rock friction model applicable to Mount Etna.

  14. Geochemistry of the late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems

    Science.gov (United States)

    Portnyagin, Maxim; Duggen, Svend; Hauff, Folkmar; Mironov, Nikita; Bindeman, Ilya; Thirlwall, Matthew; Hoernle, Kaj

    2015-12-01

    We present new major and trace element, high-precision Sr-Nd-Pb (double spike), and O-isotope data for the whole range of rocks from the Holocene Tolbachik volcanic field in the Central Kamchatka Depression (CKD). The Tolbachik rocks range from high-Mg basalts to low-Mg basaltic trachyandesites. The rocks considered in this paper represent mostly Late Holocene eruptions (using tephrochronological dating), including historic ones in 1941, 1975-1976 and 2012-2013. Major compositional features of the Tolbachik volcanic rocks include the prolonged predominance of one erupted magma type, close association of middle-K primitive and high-K evolved rocks, large variations in incompatible element abundances and ratios but narrow range in isotopic composition. We quantify the conditions of the Tolbachik magma origin and evolution and revise previously proposed models. We conclude that all Tolbachik rocks are genetically related by crystal fractionation of medium-K primary magmas with only a small range in trace element and isotope composition. The primary Tolbachik magmas contain 14 wt.% of MgO and 4% wt.% of H2O and originated by partial melting ( 6%) of moderately depleted mantle peridotite with Indian-MORB-type isotopic composition at temperature of 1250 °C and pressure of 2 GPa. The melting of the mantle wedge was triggered by slab-derived hydrous melts formed at 2.8 GPa and 725 °C from a mixture of sediments and MORB- and Meiji-type altered oceanic crust. The primary magmas experienced a complex open-system evolution termed Recharge-Evacuation-Fractional Crystallization (REFC). First the original primary magmas underwent open-system crystal fractionation combined with periodic recharge of the magma chamber with more primitive magma, followed by mixing of both magma types, further fractionation and finally eruption. Evolved high-K basalts, which predominate in the Tolbachik field, and basaltic trachyandesites erupted in 2012-2013 approach steady-state REFC liquid

  15. Mid–Late Neoproterozoic rift-related volcanic rocks in China: Geological records of rifting and break-up of Rodinia

    Directory of Open Access Journals (Sweden)

    Linqi Xia

    2012-07-01

    Full Text Available Early Cambrian and Mid–Late Neoproterozoic volcanic rocks in China are widespread on several Precambrian continental blocks, which had aggregated to form part of the Rodinia supercontinent by ca. 900 Ma. On the basis of petrogeochemical data, the basic lavas can be classified into two major magma types: HT (Ti/Y > 500 and LT (Ti/Y  0.85 and HT2 (Nb/La ≤ 0.85, and LT1 (Nb/La > 0.85 and LT2 (Nb/La ≤ 0.85 subtypes, respectively. The geochemical variation of the HT2 and LT2 lavas can be accounted for by lithospheric contamination of asthenosphere- (or plume- derived magmas, whereas the parental magmas of the HT1 and LT1 lavas did not undergo, during their ascent, pronounced lithospheric contamination. These volcanics exhibit at least three characteristics: (1 most have a compositional bimodality; (2 they were formed in an intracontinental rift setting; and (3 they are genetically linked with mantle plumes or a mantle surperplume. This rift-related volcanism at end of the Mid–Neoproterozoic and Early Cambrian coincided temporally with the separation between Australia–East Antarctica, South China and Laurentia and between Australia and Tarim, respectively. The Mid–Late Neoproterozoic volcanism in China is the geologic record of the rifting and break-up of the supercontinent Rodinia.

  16. Assessing hydraulic connections across a complex sequence of volcanic rocks - Analysis of U-20 WW multiple-well aquifer test, Pahute Mesa, Nevada National Security Site, Nevada

    Science.gov (United States)

    Garcia, C. Amanda; Fenelon, Joseph M.; Halford, Keith J.; Reiner, Steven R.; Laczniak, Randell J.

    2011-01-01

    Groundwater beneath Pahute Mesa flows through a complexly layered sequence of volcanic rock aquifers and confining units that have been faulted into distinct structural blocks. Hydraulic property estimates of rocks and structures in this flow system are necessary to assess radionuclide migration near underground nuclear testing areas. The U.S. Geological Survey (USGS) used a 12 month (October 1, 2008— October 1, 2009) intermittent pumping schedule of well U-20 WW and continuously monitored water levels in observation wells ER-20-6 #3, UE-20bh 1, and U-20bg as a multi-well aquifer test to evaluate hydraulic connections across structural blocks, bulk hydraulic properties of volcanic rocks, and the hydraulic significance of a major fault. Measured water levels were approximated using synthetic water levels generated from an analytical model. Synthetic water levels are a summation of environmental water-level fluctuations and a Theis (1935) transform of the pumping signal from flow rate to water-level change. Drawdown was estimated by summing residual differences between measured and synthetic water levels and the Theis-transformed pumping signal from April to September 2009. Drawdown estimates were used in a three‑dimensional numerical model to estimate hydraulic properties of distinct aquifers, confining units, and a major fault.

  17. A new genetic interpretation for the Caotaobei uranium deposit associated with the shoshonitic volcanic rocks in the Hecaokeng ore field, southern Jiangxi, China

    Directory of Open Access Journals (Sweden)

    Dong-Sheng Yang

    2017-03-01

    Full Text Available Combined with in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS zircon UPb geochronology, published and unpublished literature on the Caotaobei uranium deposit in southern Jiangxi province, China, is re-examined to provide an improved understanding of the origin of the main ore (103 Ma. The Caotaobei deposit lies in the Hecaokeng ore field and is currently one of China's largest, volcanic-related uranium producers. Unlike commonly known volcanogenic uranium deposits throughout the world, it is spatially associated with intermediate lavas with a shoshonitic composition. Uranium mineralization (pitchblende occurs predominantly as veinlets, disseminations, and massive ores, hosted by the cryptoexplosive breccias rimming the Caotaobei crater. Zircons from one latite define four distinct 206Pb/238U age groups at 220–235 Ma (Triassic, 188 Ma (Early Jurassic, 131–137 Ma (Early Cretaceous, and 97–103 Ma (Early-Late Cretaceous transition, hereafter termed mid-Cretaceous. The integrated age (134 ± 2 Ma of Early Cretaceous zircons (group III is interpreted as representing the time of lava emplacement. The age data, together with the re-examination of literature, does not definitively support a volcanogenic origin for the generation of the deposit, which was proposed by the previous workers based mainly on the close spatial relationship and the age similarity between the main ore and volcanic lavas. Drill core and grade-control data reveal that rich concentrations of primary uranium ore are common around the granite porphyry dikes cutting the lavas, and that the cryptoexplosive breccias away from the dikes are barren or unmineralized. These observations indicate that the emplacement of the granite porphyries exerts a fundamental control on ore distribution and thus a genetic link exists between main-stage uranium mineralization and the intrusions of the dikes. Zircon overgrowths of mid-Cretaceous age (99.6

  18. Isotope dates and strontium isotopic ratios for plutonic and volcanic rocks in the Quesnel Trough and Nicola Belt, south central British Columbia

    International Nuclear Information System (INIS)

    Preto, V.A.; McMillan, W.J.; Armstrong, R.L.

    1979-01-01

    Four distinct events of the southern Intermontane Belt are represented in new K-Ar and Rb-Sr dates. The first and regionally most important event is sharply defined by new K-Ar dates between 200 and 209 Ma for the Thuya, Wildhorse, Iron Mask, and Allison batholiths and a 205 +- 10 Ma Rb-Sr isochron for the Guichon Creek batholith. All these plutons were emplaced approximately at the change from Triassic to Jurassic time. The related and slightly older Nicola volcanic rocks are altered by addition of more radiogenic sedimentary Sr (Carnian Nicola limestone having 87 Sr/ 86 Sr=0.7075+- 1) and do not give an isochron date. The Coldwater stock is anomalously old (K-Ar dates range from 215-267 Ma). The Mid- to late Jurassic igneous event is indicated by a 141 Ma K-Ar date for the Mount Martley batholith. Mid-Cretaceous volcanic rocks of the Kingsvale Group give a Rb-Sr isochron date of 112 +- 10 Ma and are postdated by the crosscutting and slightly younger Summers Creek stock (100 Ma by K-Ar). The final event straddles the Cretaceous-Tertiary boundary with the Nicola batholith emplaced about 60 Ma ago (K-Ar) and the Rey Lake stock perhaps slightly earlier (69 Ma by K-Ar). Initial 87 Sr/ 86 Sr ratios range from 0.7025-0.7046 with a mean and mode near 0.7037 which is within the range of modern circum-Pacific volcanoes. Initial ratios of 0.7034 +- 1 for the Guichon Creek batholith, 0.7035 +- 1 for the Iron Mask batholith 70435 +-10 for the Thuya batholith, and 0.70379 +- 4 for the Kingsvale volcanic rocks are the most precisely determined. The Coldwater stock is anomalously low at 0.7025. For the other plutonic bodies only scattered or single analyses are available. The Nicola volcanic rocks appear to have once been similar in initial ratio the the Guichon Creek batholith but their calculated initial ratios now scatter from 0.7034-0.7073. (auth)

  19. A REMAINING OPEN PALEOGEOGRAPHY OF PALEO-ASIAN OCEAN BY EARLY PERMIAN: PALEOMAGNETIC CONSTRAINTS FROM THE PERMIAN VOLCANIC ROCKS IN MIDDLE-EAST INNER MONGOLIA, NE CHINA

    Directory of Open Access Journals (Sweden)

    Donghai Zhang

    2017-01-01

    Full Text Available We report a paleomagnetic investigation on Permian volcanic rocks in the middle-east Inner Mongolia, NE China, aiming to puzzle out the timing and position of the final closure of the eastern Paleo-Asian ocean (PAO and further to better understand tectonic evolution of the Central Asian Orogenic Belt (CAOB. Two pre-folding characteristic components are isolated from the Sanmianjing and Elitu formations (~283–266 Ma in the northern margin of the North China block (NMNCB and the Dashizhai Formation (~280 Ma in the Songliao-Xilinhot block (SXB, respectively.

  20. Carboniferous-Permian volcanic evolution in Central Europe-U/Pb ages of volcanic rocks in Saxony (Germany) and northern Bohemia (Czech Republic)

    Czech Academy of Sciences Publication Activity Database

    Hoffmann, U.; Breitkreuz, Ch.; Breiter, Karel; Sergeev, S.; Stanek, K.; Tichomirowa, M.

    2013-01-01

    Roč. 102, č. 1 (2013), s. 73-99 ISSN 1437-3254 Institutional support: RVO:67985831 Keywords : pyroclastic rocks * dykes * stratigraphy * SHRIMP U/Pb ages * Pb/Pb single zircon age * Variscides Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.084, year: 2013

  1. Can a primary remanence be retrieved from partially remagnetized Eocence volcanic rocks in the Nanmulin Basin (southern Tibet) to date the India-Asia collision?

    Science.gov (United States)

    Huang, Wentao; Dupont-Nivet, Guillaume; Lippert, Peter C.; van Hinsbergen, Douwe J. J.; Dekkers, Mark J.; Guo, Zhaojie; Waldrip, Ross; Li, Xiaochun; Zhang, Xiaoran; Liu, Dongdong; Kapp, Paul

    2015-01-01

    Paleomagnetic dating of the India-Asia collision hinges on determining the Paleogene latitude of the Lhasa terrane (southern Tibet). Reported latitudes range from 5°N to 30°N, however, leading to contrasting paleogeographic interpretations. Here we report new data from the Eocene Linzizong volcanic rocks in the Nanmulin Basin, which previously yielded data suggesting a low paleolatitude ( 10°N). New zircon U-Pb dates indicate an age of 52 Ma. Negative fold tests, however, demonstrate that the isolated characteristic remanent magnetizations, with notably varying inclinations, are not primary. Rock magnetic analyses, end-member modeling of isothermal remanent magnetization acquisition curves, and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low-temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously. Previously reported paleomagnetic data from the Nanmulin Basin implying low paleolatitude should thus not be used to estimate the time and latitude of the India-Asia collision. We show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization. We tentatively propose a new method to recover a primary remanence with inclination of 38.1° (35.7°, 40.5°) (95% significance) and a secondary remanence with inclination of 42.9° (41.5°,44.4°) (95% significance). The paleolatitude defined by the modeled primary remanence—21°N (19.8°N, 23.1°N)—is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper Linzizong Group corrected for inclination shallowing. The start of the Tibetan Himalaya-Asia collision was situated at 20°N and took place by 50 Ma.

  2. Mineral chemistry, thermobarometry and tectonomagmatic setting of Late-Cretaceous volcanic rocks from the Kojid area (south of Lahijan, northern Alborz

    Directory of Open Access Journals (Sweden)

    morteza delavari

    2018-03-01

    Full Text Available The volcanic rocks of Kojid area (south of Lahijan crop out in northern Alborz. They show mainly pillow structure with numerous cross-cutting dykes. Based on lithostratigraphic relationships and interpillow pelagic limestones, the volcanics are Late Cretaceous in age. The volcanics of Kojid area are predominantly basic in composition (olivine basalt and basalt and minor more evolved suites such as trachyandesite and dacite. Olivine phenocrysts display forsterite (Fo content of 63 to 83%. The phenocrystic and interstitial clinopyroxene crystals are augite to diopside in composition, with Na2O, Al2O3 and TiO2 contents of 0.24- 0.68, 2.3-6.53 and 1-5.1 wt.%, respectively. Furthermore, plagioclase is labradorite (An%= 51-68. The results of various geothermobarometric methods of clinopyroxene, plagioclase and olivine indicate good correlation with each other. Different thermometric calculations yielded temperatures in the range of 1100 to 1250 °C which are compatible with temperatures of basic melts. Moreover, clinopyroxene and plagioclase barometry of the phenocrysts (4 to 8 Kb and interstitial phases (

  3. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    Science.gov (United States)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    Mantle xenoliths in alkali basaltic rocks from the Catalan Volcanic Zone, associated with the Neogene-Quaternary rift system in NE Spain, are formed of anhydrous spinel lherzolites and harzburgites with minor olivine websterites. Both peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism, especially the harzburgites. These and the websterites display protogranular microstructures, whereas lherzolites show continuous variation between protogranular, porphyroclastic and equigranular forms. Thermometric data of new xenoliths indicate that protogranular harzburgites, lherzolites and websterites were equilibrated at higher temperatures than porphyroclastic and equigranular lherzolites. Mineral chemistry also indicates lower equilibrium pressure for porphyroclastic and equigranular lherzolites than for the protogranular ones. Crystal preferred orientations (CPOs) of olivine and pyroxenes from these new xenoliths were determined with the EBSD-SEM technique to identify the deformation stages affecting the lithospheric mantle in this zone and to assess the relationships between the deformation fabrics, processes and microstructures. Olivine CPOs in protogranular harzburgites, lherzolites and a pyroxenite display [010]-fiber patterns characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane. Olivine CPO symmetry in porphyroclastic and equigranular lherzolites varies continuously from [010]-fiber to orthorhombic and [100]-fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The rare [100]-fiber patterns display strong point concentration of [100] axis, with normal girdle distribution of the other two axes, which are aligned with each other. The patterns of pyroxene CPOs are more dispersed than those of olivine, especially for clinopyroxene, but

  4. Late Triassic Porphyritic Intrusions And Associated Volcanic Rocks From The Shangri-La Region, Yidun Terrane, Eastern Tibetan Plateau: Implications For Adakitic Magmatism And Porphyry Copper Mineralization

    Science.gov (United States)

    Wang, B.; Zhou, M.; Li, J.; Yan, D.

    2011-12-01

    The Yidun terrane, located on the eastern margin of the Tibetan plateau, has been commonly considered to be a Triassic volcanic arc produced by subduction of the Ganzi-Litang oceanic lithosphere. The Yidun terrane is characterized by numerous arc-affinity granitic intrusions located along a 500-km-long, north-south-trending belt. Among these granitic bodies, several small porphyritic intrusions in the southern segment of the terrane (Shangri-La region) are associated with large porphyry copper deposits. These porphyritc intrusions are composed of diorite and quartz diorite, and spatially associated with andesites and dacites. LA-ICP-MS zircon U-Pb ages of the intrusions range from 230 to 215 Ma. The andesites and dacites are intercalated with slates and sandstones and have ages of around 220 Ma. The intrusive and volcanic rocks have SiO2 contents from 56.6 to 67.1 wt.%, Al2O3 from 14.2 to 17.4 wt.% and MgO from 1.9 to 4.2 wt.%. They show significant negative Nb-Ta anomalies on primitive mantle-normalized spidergrams. They have high La/Yb (13-49) ratios with no prominent Eu anomalies. All the rocks have high Sr (258-1980 ppm), and low Y (13-21 ppm) with high Sr/Y ratios (29-102). The geochemical features indicate that both the volcanic rocks and porphyritic intrusions were derived from adakitic magmas. They have similar initial 87Sr/86Sr ratios (0.7058 to 0.7077) and ɛNd (-1.88 to -4.93) values, but can be further divided into two groups: high silica (HSA) and low silica adakitic rocks (LSA). The HSA, representing an early stage of magmatism (230 to 215 Ma), were derived from oceanic slab melts with limited interaction with the overlying mantle wedge. At 215 Ma, more extensive interaction resulted in the formation of LSA. We propose that HSA were produced by flat subduction leading to melting of oceanic slab, whereas subsequent slab break-off caused the significant interaction between slab melts and the mantle wedge and thus the generation of the LSA. Compared with

  5. Self-similar rupture implied by scaling properties of volcanic earthquakes occurring during the 2004-2008 eruption of Mount St. Helens, Washington

    Science.gov (United States)

    Harrington, Rebecca M.; Kwiatek, Grzegorz; Moran, Seth C.

    2015-01-01

    We analyze a group of 6073 low-frequency earthquakes recorded during a week-long temporary deployment of broadband seismometers at distances of less than 3 km from the crater at Mount St. Helens in September of 2006. We estimate the seismic moment (M0) and spectral corner frequency (f0) using a spectral ratio approach for events with a high signal-to-noise (SNR) ratio that have a cross-correlation coefficient of 0.8 or greater with at least five other events. A cluster analysis of cross-correlation values indicates that the group of 421 events meeting the SNR and cross-correlation criteria forms eight event families that exhibit largely self-similar scaling. We estimate the M0 and f0 values of the 421 events and calculate their static stress drop and scaled energy (ER/M0) values. The estimated values suggest self-similar scaling within families, as well as between five of eight families (i.e.,  and  constant). We speculate that differences in scaled energy values for the two families with variable scaling may result from a lack of resolution in the velocity model. The observation of self-similar scaling is the first of its kind for such a large group of low-frequency volcanic tectonic events occurring during a single active dome extrusion eruption.

  6. 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)

    Pelayo, M.; Labajo, M. A.; Garcia Romero, L.; Perez del Villar, L.

    2009-01-01

    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

  7. The Ignimbritic tertiary volcanism of the Andes (Peru, Bolivia, Argentina): its characteristics and uraniferous potentiality

    International Nuclear Information System (INIS)

    Leroy, J.L.; George-Aniel, B.

    1988-01-01

    The petrographic and geochemical characteristics of the volcanism and the primary U distribution at the magmatic stage: alkali-rich volcanic rocks (Peru) appear to be fertile source-rocks, whereas sub alkaline and calc-alkaline rocks (Bolivia and Argentina) are less favorable. Uranium can only be leached from the matrix, due to the stability of the accessory minerals during all the following events. The fertility of a volcanic rock is thus directly controlled by the volume proportion of the matrix and the U fractionation between glass and accessory minerals. The preconcentration and concentration stages: the existence of mineralizations in relation with a fertile rock will depend on other events which must occur successively at the same place: the cooling type and rate of the volcanic pile (pre-concentration stage), the intensity and the duration of the hydrothermal circulations, the presence of reducing agents and trapps. (author)

  8. The volcanic and geochemical development of São Nicolau, Cape Verde Islands

    DEFF Research Database (Denmark)

    Duprat, Helene Inga; Holm, Paul Martin; Sherson, Jacob Friis

    2007-01-01

    We present 34 new age results from 40 Ar/39 Ar incremental heating analyses of groundmass separates from volcanic rocks from São Nicolau, Cape Verde. Combining the age results with field observations, we show that the volcanic activity that formed the island occurred in four separate stages: 1: >6...

  9. What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou basin, Tibet)

    Science.gov (United States)

    Huang, Wentao; Dupont-Nivet, Guillaume; Lippert, Peter C.; van Hinsbergen, Douwe J. J.; Dekkers, Mark J.; Waldrip, Ross; Ganerød, Morgan; Li, Xiaochun; Guo, Zhaojie; Kapp, Paul

    2015-03-01

    The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus, here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou basin. The lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes. We report consistent 40Ar/39Ar and U-Pb zircon dates of 52 Ma for the upper Linzizong, and 40Ar/39Ar dates ( 51 Ma) from the lower Linzizong are significantly younger than U-Pb zircon dates (64-63 Ma), suggesting that the lower Linzizong was thermally and/or chemically reset. Paleomagnetic results from 24 sites in lower Linzizong confirm a low apparent paleolatitude of 5°N, compared to the upper part ( 20°N) and to underlying Cretaceous strata ( 20°N). Detailed rock magnetic analyses, end-member modeling of magnetic components, and petrography from the lower and upper Linzizong indicate widespread secondary hematite in the lower Linzizong, whereas hematite is rare in upper Linzizong. Volcanic rocks of the lower Linzizong have been hydrothermally chemically remagnetized, whereas the upper Linzizong retains a primary remanence. We suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower Linzizong. We estimate that the Paleogene latitude of Lhasa terrane was 20 ± 4°N, consistent with previous results suggesting that India-Asia collision likely took place by 52 Ma at 20°N.

  10. Petrogenesis of Miocene alkaline volcanic suites from western Bohemia. Whole rock geochemistry and Sr-Nd-Pb isotopic signatures.

    Czech Academy of Sciences Publication Activity Database

    Ulrych, Jaromír; Krmíček, Lukáš; Tomek, Č.; Lloyd, F. E.; Ladenberger, A.; Ackerman, Lukáš; Balogh, K.

    2016-01-01

    Roč. 76, č. 1 (2016), s. 77-93 ISSN 0009-2819 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Cenozoic alkaline volcanism * Geochemistry * K-Ar ages * Sr-Nd-Pb isotopes Subject RIV: DD - Geochemistry Impact factor: 1.380, year: 2016

  11. Application of Clinopyroxene Chemistry to Interpret the Physical Conditions of Ascending Magma, a Case Study of Eocene Volcanic Rocks in the Ghohrud Area (North of Isfahan

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    Mohammad Sayari

    2016-07-01

    Full Text Available Introduction Volcanic rocks with a porphyritic texture have experienced two crystallization stages. The first is slow, resulting in phenocrysts, and the second, which took place at, or near the surface, or during intrusion into a cooler body of rock, result in a groundmass of glass, or fine crystals. The pressure and temperature history of a magma during crystallization is recorded in the chemical composition of the phenocrysts during both stages. These phenocrysts provide valuable data about the physicochemical conditions of the parent magma during the process of crystallization. The composition of clinopyroxene (cpx reflects not only the chemical condition and therefore the magmatic series, but also the physical conditions, i.e., temperature and pressure of a magma at the time when clinopyroxene crystallized. The Ghohrud area lies in the middle part of the Urumieh-Dokhtar Magmatic Arc , which is part of a much larger magmatic province extending in a vast region of convergence between Arabia and Eurasia north of the Zagros-Bitlis suture zone (Dilek et al., 2010. In the Ghohrud area, north of Isfahan, exposed Eocene volcanic rocks belong to the first pulse of Cenozoic volcanism of Iran (Sayari, 2015, ranging in composition from andesitic basalt to basalt. The basaltic rocks of the Ghohrud area are composed mainly of plagioclase phenocrysts surrounded by smaller crystals of clinopyroxene in a groundmass of microlites, glass and opaques. In this study, the clinopyroxene and plagioclase of these rocks were analyzed in order to estimate the physicochemical conditions of the parent magmas. Results Clinopyroxene and plagioclase phenocrysts of nineteen samples were analyzed with the electron microprobe. The chemical compositions of the clinopyroxenes were used to estimate both the chemical evolution and temperature and pressure conditions of the magmas during crystallization, using SCG, a specialized software for clinopyroxene thermobarometry (Sayari

  12. The Quaternary calc-alkaline volcanism of the Patagonian Andes close to the Chile triple junction: geochemistry and petrogenesis of volcanic rocks from the Cay and Maca volcanoes (˜45°S, Chile)

    Science.gov (United States)

    D'Orazio, M.; Innocenti, F.; Manetti, P.; Tamponi, M.; Tonarini, S.; González-Ferrán, O.; Lahsen, A.; Omarini, R.

    2003-08-01

    Major- and trace-element, Sr-Nd isotopes, and mineral chemistry data were obtained for a collection of volcanic rock samples erupted by the Cay and Maca Quaternary volcanoes, Patagonian Andes (˜45°S, Chile). Cay and Maca are two large, adjacent stratovolcanoes that rise from the Chiloe block at the southern end of the southern volcanic zone (SVZ) of the Andes. Samples from the two volcanoes are typical medium-K, calc-alkaline rocks that form two roughly continuous, largely overlapping series from subalkaline basalt to dacite. The overall geochemistry of the samples studied is very similar to that observed for most volcanoes from the southern SVZ. The narrow range of Sr-Nd isotope compositions ( 87Sr/ 86Sr=0.70389-0.70431 and 143Nd/ 144Nd=0.51277-0.51284) and the major- and trace-element distributions indicate that the Cay and Maca magmas differentiated by crystal fractionation without significant contribution by crustal contamination. This is in accordance with the thin (Maca magmas is investigated by means of the relative concentration of fluid mobile (e.g. Ba) and fluid immobile (e.g. Nb, Ta, Zr, Y) elements and other relevant trace-element ratios (e.g. Sr/Y). The results indicate that small amounts (Maca volcanoes and that, despite the very young age (Maca magma sources to the northern edge of the slab window generated by the subduction of the Chile ridge under the South American plate, we did not find any geochemical evidence for a contribution of a subslab asthenospheric mantle. However, this mantle has been used to explain the peculiar geochemical features (e.g. the mild alkalinity and relatively low ratios between large ion lithophile and high field strength elements) of the Hudson volcano, which is located even closer to the slab window than the Cay and Maca volcanoes are.

  13. Petrology and geochemistry of volcanic rocks of Cheshmeh Khuri and Shekasteh Sabz areas, Khur, northwest of Birjand

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    Maryam Javidi Moghaddam

    2016-09-01

    Full Text Available Khur area is located in east of Iran and northwest of Birjand. The area comprises outcrops of Eocene to Oligocene volcanics with basaltic andesite to rhyolite composition, which were intruded by subvolcanic and intrusive bodies of granodiorite to gabbro. In the present work, petrogenesis of volcanic units in Cheshmeh Khuri and Shekasteh Sabz areas was studied, which are located in Khur area and these volcanics have most widespread in them. Rhyolite, dacite, andesite, trachyandesite and basaltic andesite units in Cheshmeh Khuri and trachyandesite unit in Shekasteh Sabz were identified. The main textures of these units are porphyritic, hialoporphyritic and microlitic and plagioclase, pyroxene, K-feldspar, hornblende, biotite and quartz are the main minerals. Volcanic units of Cheshmeh Khuri have characteristic of high-K Calc-alkaline. Enrichment of LREE relative to HREE and LILE to HFSE are important evidences that magma was formed in a magmatic belt of a subduction zone. Based on the initial 87Sr/86Sr of andesite and dacite, their magma has originated from partial melting of an enriched mantle and contaminated with the crust through its differentiation. Trachyandesites of Shekaste Sabz have characteristic of shoshonitic nature. These units are characterized by high FeOt/FeOt+MgO, K2O/Na2O and Zr>360 ppm, Y>39 ppm, and Ce> 100 ppm. Also, they are enrichment in REE particularly in LREE, depletion of Eu, strong enrichment in HFSE, and depletion in Ba and Sr. Therefore, trachyandesites of Shekaste Sabz belong to post collision volcanics.

  14. Mineral chemistry of clinopyroxene: guidance on geo- thermobarometry and tectonomagmatic setting of Nabar volcanic rocks, South of Kashan

    OpenAIRE

    Rezvan Mehvari; Moussa Noghreyan; Mortaza Sharifi; Mohammad Ali Mackizadeh; Seyed Hassan Tabatabaei; Ghodrat Torabi

    2017-01-01

    Introduction The Nabar area that is a part of the Urumieh- Dokhtar volcano- plutonic belt is located in the south of Kashan. Research works such as Emami (Emami, 1993) and Abbasi (Abbasi, 2012) have been done about the geology of this area. Rock units in the study area contain middle- upper Eocene intermediate to acidic lavas and pyroclastic rocks, green marl, shale and sandy marls of Oligo- Miocene, limestones of Qom formation, intrusive granitoids with Oligo- Miocene age and quaternar...

  15. Friction in volcanic environments

    Science.gov (United States)

    Kendrick, Jackie E.; Lavallée, Yan

    2016-04-01

    Volcanic landscapes are amongst the most dynamic on Earth and, as such, are particularly susceptible to failure and frictional processes. In rocks, damage accumulation is frequently accompanied by the release of seismic energy, which has been shown to accelerate in the approach to failure on both a field and laboratory scale. The point at which failure occurs is highly dependent upon strain-rate, which also dictates the slip-zone properties that pertain beyond failure, in scenarios such as sector collapse and pyroclastic flows as well as the ascent of viscous magma. High-velocity rotary shear (HVR) experiments have provided new opportunities to overcome the grand challenge of understanding faulting processes during volcanic phenomena. Work on granular ash material demonstrates that at ambient temperatures, ash gouge behaves according to Byerlee's rule at low slip velocities, but is slip-weakening, becoming increasingly lubricating as slip ensues. In absence of ash along a slip plane, rock-rock friction induces cataclasis and heating which, if sufficient, may induce melting (producing pseudotachylyte) and importantly, vesiculation. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The shear-thinning behaviour and viscoelasticity of frictional melts yield a tendency for extremely unstable slip, and occurrence of frictional melt fragmentation. This velocity-dependence acts as an important feedback mechanism on the slip plane, in addition to the bulk composition, mineralogy and glass content of the magma, that all influence frictional behaviour. During sector collapse events and in pyroclastic density currents it is the frictional properties of the rocks and ash that, in-part, control the run-out distance and associated risk. In addition, friction plays an important role in the eruption of viscous magmas: In the conduit, the rheology of magma is integral

  16. A Sr-isotopic comparison between thermal waters, rocks, and hydrothermal calcites, Long Valley caldera, California

    Science.gov (United States)

    Goff, F.; Wollenberg, H.A.; Brookins, D.C.; Kistler, R.W.

    1991-01-01

    The 87Sr/86Sr values of thermal waters and hydrothermal calcites of the Long Valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks. Five thermal waters display 87Sr/86Sr of 0.7081-0.7078 but show systematically lighter values from west to east in the direction of lateral flow. We believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression. All types of pre-, syn-, and post-caldera volcanic rocks in the west and central caldera have (87Sr/86Sr)m between about 0.7060 and 0.7072 and values for Sierra Nevada granodiorites adjacent to the caldera are similar. Sierran pre-intrusive metavolcanic and metasedimentary rocks can have considerably higher Sr-isotope ratios (0.7061-0.7246 and 0.7090-0.7250, respectively). Hydrothermally altered volcanic rocks inside the caldera have (87Sr/86Sr)m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites (0.7068-0.7105) occupy a midrange of values between the volcanic/plutonic rocks and the Sierran metamorphic rocks. These data indicate that the Long Valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks. Reequilibration of Sr-isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill. ?? 1991.

  17. Late Triassic porphyritic intrusions and associated volcanic rocks from the Shangri-La region, Yidun terrane, Eastern Tibetan Plateau: Adakitic magmatism and porphyry copper mineralization

    Science.gov (United States)

    Wang, Bai-Qiu; Zhou, Mei-Fu; Li, Jian-Wei; Yan, Dan-Ping

    2011-11-01

    Early Mesozoic porphyritic intrusions in the Shangri-La region, southern Yidun terrane, SW China, are spatially associated with andesites and dacites. These intrusions are composed of diorite and quartz diorite, and are closely related to copper mineralization. LA-ICP-MS zircon U-Pb ages of the intrusions range from 230 to 215 Ma. The associated andesites and dacites are interlayered with slates and sandstones and have ages of around 220 Ma. All of the intrusive and extrusive rocks have similar, highly fractionated REE patterns and high La/Yb (13-49) ratios with no prominent Eu anomalies. They display pronounced negative Nb-Ta and Ti anomalies on primitive mantle-normalized spidergrams. Their SiO2 contents range from 56.6 to 67.1 wt.%, Al2O3 from 14.2 to 17.4 wt.% and MgO from1.9 to 4.2 wt.%. All the rocks have high Sr (258-1980 ppm), and low Y (13-21 ppm) with high Sr/Y ratios (29-102). These features suggest that both the volcanic rocks and porphyritic intrusions were derived from adakitic magmas. They have similar initial 87Sr/86Sr ratios (0.7058 to 0.7077) and εNd (- 1.88 to - 4.93) values, but belong to high silica (HSA) and low silica adakitic rocks (LSA). The HSA represent an early stage of magmatism (230 to 215 Ma) and were derived from oceanic slab melts with limited interaction with the overlying mantle wedge during ascent. At 215 Ma, more extensive interaction produced the LSA. We propose that the early adakitic magmas (HSA) formed by flat subduction leading to melting of oceanic slab, whereas subsequent slab break-off caused the significant interaction between slab melts and the mantle wedge and thus the generation of the later adakitic magmas (LSA).

  18. Research on supplying potential of uranium source from rocks in western provenance area of Hailaer basin

    International Nuclear Information System (INIS)

    Xia Yuliang; Liu Hanbin; Chinese Academy of Geological Sciences, Beijing

    2006-01-01

    Using U-Pb isotope composition evolution, this paper expounds the initial uranium content in volcanic rocks of provenance area of Xihulitu basin and in granites of provenance area of Kelulun sag, western Hailaer basin. The initial uranium content (U 0 ) in volcanic rocks of provenance area is higher, the average initial uranium content of volcanic rocks is 10.061 x 10 -6 , the average uranium variation coefficient (ΔU) is -49.57%; the average initial uranium content of granites is 18.381 x 10 -6 , the average uranium variation coefficient (ΔU) is -80%. The results indicate that rocks in provenance area could provide the pre-enrichment of uranium in deposited sandstone. U-Ra equilibrium coefficients of rocks indicate that there is obvious U-Ra disequilibrium phenomenon in volcanic rocks, and the time when granites provided uranium source occurred 16000 a ago. (authors)

  19. New K-Ar ages of volcanic rocks and associated mineralization in Canada Honda district, San Luis, Argentina

    International Nuclear Information System (INIS)

    Urbina, N.E.; Oggier, F.P

    2001-01-01

    New K-Ar ages in the Late Tertiary gold-bearing volcanic belt of the Sierras Pampeanas of San Luis, Argentina are presented. At Canada Honda district, an age of 8.49±0.2 Ma yielded by Cerro del Valle andesite indicates that the dome emplacement postdates the Diente Verde eruptive event. An even younger age of 7.3±0.2 Ma was obtained for illite from hydrothermal alteration at La Reynela mineralization which is hosted by Cerro del Valle andesite (au)

  20. Database for the geologic map of upper Eocene to Holocene volcanic and related rocks in the Cascade Range, Washington

    Science.gov (United States)

    Barron, Andrew D.; Ramsey, David W.; Smith, James G.

    2014-01-01

    This geospatial database for a geologic map of the Cascades Range in Washington state is one of a series of maps that shows Cascade Range geology by fitting published and unpublished mapping into a province-wide scheme of lithostratigraphic units. Geologic maps of the Eocene to Holocene Cascade Range in California and Oregon complete the series, providing a comprehensive geologic map of the entire Cascade Range that incorporates modern field studies and that has a unified and internally consistent explanantion. The complete series will be useful for regional studies of volcanic hazards, volcanology, and tectonics.

  1. [Combination of phosphorus solubilizing and mobilizing fungi with phosphate rocks and volcanic materials to promote plant growth of lettuce (Lactuca sativa L.)].

    Science.gov (United States)

    Velázquez, María S; Cabello, Marta N; Elíades, Lorena A; Russo, María L; Allegrucci, Natalia; Schalamuk, Santiago

    Arbuscular mycorrhizal fungi (AMF) increase the uptake of soluble phosphates, while phosphorus solubilizing fungi (S) promote solubilization of insoluble phosphates complexes, favoring plant nutrition. Another alternative to maintaining crop productivity is to combine minerals and rocks that provide nutrients and other desirable properties. The aim of this work was to combine AMF and S with pyroclastic materials (ashes and pumices) from Puyehue volcano and phosphate rocks (PR) from Rio Chico Group (Chubut) - to formulate a substrate for the production of potted Lactuca sativa. A mixture of Terrafertil®:ashes was used as substrate. Penicillium thomii was the solubilizing fungus and Rhizophagus intraradices spores (AMF) was the P mobilizer (AEGIS® Irriga). The treatments were: 1) Substrate; 2) Substrate+AMF; 3) Substrate+S; 4) Substrate+AMF+S; 5) Substrate: PR; 6) Substrate: PR+AMF; 7) Substrate: PR+S and 8) Substrate: PR+AMF+S. Three replicates were performed per treatment. All parameters evaluated (total and assimilable P content in substrate, P in plant tissue and plant dry biomass) were significantly higher in plants grown in substrate containing PR and inoculas with S and AMF. This work confirms that the combination of S/AMF with Puyehue volcanic ashes, PR from the Río Chico Group and a commercial substrate promote the growth of L. sativa, thus increasing the added value of national geomaterials. Copyright © 2017 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.

  2. Indication Of Hydrothermal Alteration Activities Based On Petrography Of Volcanic Rocks In Abang Komba Submarine Volcano, East Flores Sea

    OpenAIRE

    Sarmili, Lili; Hutabarat, Johanes

    2014-01-01

    The presence of mineral alteration or secondary processes to rocks on submarine volcano of Abang Komba was caused by an introduction of hydrothermal solutions. Those are indicated by the presence of a resembly of minerals alteration seen in their petrographic analyses. They are characterized by replacement partially surrounding of plagioclase phenocrysts, partially replacing plagioclase by sericite, carbonate and clay minerals. The replacement of pyroxene partly by chlorite, and the presence ...

  3. Attempts of whole-rock K/Ar dating of mesozoic volcanic and hypabissal igneous rocks from the Central Subbetic (Southern Spain: A case of differential Argon loss related to very low-grade metamorphism

    Directory of Open Access Journals (Sweden)

    Sanz de Galdeano, C.

    1988-04-01

    Full Text Available 12 samples of basic intrusives within Triassic rocks «ophites» and 11 samples of volcanic and associated intrusives within Jurassic to Early Cretaceous sequences of the Subbetic Zone were subjected to whole-rock K/Ar dating in combination with chemical/petrological analysis. Satisfactory results were obtained only from a number of samples of volcanic rocks, however, analytical ages commonly agree, within about 10 relative percent, with those deduced from stratigraphic location. «Ophite» samples, on the other hand, may reveal considerably lower analytic ages than the volcanics and show much stronger scattering, even among samples collected within a small area. It is argued that the inferred loss of Ar results from very-low-grade alpine metamorphic alteration, which affected the «ophites» more intensely than the higher volcanic rocks. Other post-emplacement chemical changes, such as the degree of secondary oxidation of Fe, are also distintive among the two groups of samples, and are to some extent consistent with the above view in that the alteration environment of the ophites should have produced conditions for more penetrative fluid-rock interactions and homogeneous recrystallization. Overall, the magmatic activity from which the ophitic rocks originated might have started in the Late Triassic and continued in the Lower Jurassic. 80th, the «ophites» and the volcanics are though to be the result of magmatic events Collowing tensional to transtensive crustal movements affecting the external basins of the Betic Cordilleras Crom Late Triassic to Early Cretaceous times.Doce muestras de cuerpos básicos intrusivos en rocas triásicas («ofitas» y 11 muestras de volcanitas y rocas intrusivas asociadas en secuencias jurásico-cretáceas de la zona Subbética han sido objeto de datación radiométrica K/Ar (roca total en combinación con análisis químico-petrográfico. Las edades analíticas obtenidas son 's

  4. Characteristics and genesis of porphyroclastic lava rock in Xiangshan

    International Nuclear Information System (INIS)

    Zhou Xiaohua; Wang Zhuning

    2012-01-01

    Due to the transitional characteristics of porphyroclastic lava rock in Xiangshan of Jiangxi province, there are a variety of views on its genesis, petrographic attribution. This is because the marginal facies of the porphyroclastic lava is with ignimbrite and tuff characteristics, its transition phase has the characteristics of lava, and its intermediate phase has the feature of sub-volcanic rocks, further more, different texture of the rocks bears transition relationship. By the study of mineral composition, REE pattern, trace elements, isotopes, we put forward that the porphyroclastic lava is formed by the remelting of basement metamorphic rocks. The rocks was believed to be formed in the environment similar to volcanics and subvolcanics, and quite different to plutonic rocks due to the features of low-structure of potassium feldspar phenocrysts and solution mechanism, because the porphyroclastic lava phenocrysts occurs as fragments and maybe related to cryptoexplosion. Therefore the rocks was believed to belong to the volcano extrusive facies. (authors)

  5. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing

    Science.gov (United States)

    Chang, J.M.; Feeley, T.C.; Deraps, M.R.

    2009-01-01

    The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

  6. Experimental and natural constraints on the generation of calc-alkaline volcanic rocks in the Western Aleutian arc

    Science.gov (United States)

    Cottrell, E.; Kelley, K. A.; Grant, E.; Coombs, M. L.; Pistone, M.

    2016-12-01

    A new experimental technique with unique geometry is presented investigating deformation of simulated boreholes using standard axisymmetric triaxial deformation equipment. The Sandia WEllbore SImulation, SWESI, geometry, uses right cylinders of rock 50mm in diameter and 75mm in length. A 11.3mm hole is drilled perpendicular to the axis of the cylinder in the center of the sample to simulate a borehole. The hole is covered with a solid metal cover, and sealed with polyurethane. The metal cover can be machined with a high-pressure port to introduce different fluid chemistries into the borehole at controlled pressures. Samples are deformed in a standard load frame under confinement, allowing for a broad range of possible stresses, load paths, and temperatures. Experiments in this study are loaded to the desired confining pressure, then deformed at a constant axial strain rate or 10-5 sec-1. Two different suites of experiments are conducted in this study on sedimentary and crystalline rock types. The first series of experiments are conducted on Mancos Shale, a finely laminated transversely isotropic rock. Samples are cored at three different orientations to the laminations. A second series of experiments is conducted on Sierra White granite with different fluid chemistries inside the borehole. Numerical modelling and experimental observations including CT-microtomography demonstrate that stresses are concentrated around the simulated wellbore and recreate wellbore deformation mechanisms. Borehole strength and damage development is dependent on anisotropy orientation and fluid chemistry. Observed failure geometries, particularly for Mancos shale, can be highly asymmetric. These results demonstrate uncertainties in in situ stresses measurements using commonly-applied borehole breakout techniques in complicated borehole physico-chemical environments. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering

  7. The Origin of Widespread Long-lived Volcanism Across the Galapagos Volcanic Province

    Science.gov (United States)

    O'Connor, J. M.; Stoffers, P.; Wijbrans, J. R.; Worthington, T. J.

    2005-12-01

    40Ar/39Ar ages for rocks dredged (SO144 PAGANINI expedition) and drilled (DSDP) from the Galapagos Volcanic Province (Cocos, Carnegie, Coiba and Malpelo aseismic ridges and associated seamounts) show evidence of 1) increasing age with distance from the Galapagos Archipelago, 2) long-lived episodic volcanism at many locations, and 3) broad overlapping regions of coeval volcanism. The widespread nature of synchronous volcanism across the Galapagos Volcanic Province (GVP) suggests a correspondingly large Galapagos hotspot melting anomaly (O'Connor et al., 2004). Development of the GVP via Cocos and Nazca plate migration and divergence over this broad melting anomaly would explain continued multiple phases of volcanism over millions of years following the initial onset of hotspot volcanism. The question arising from these observations is whether long-lived GVP episodic volcanism is equivalent to `rejuvenescent' or a `post-erosional' phase of volcanism that occurs hundreds of thousands or million years after the main shield-building phase documented on many mid-plate seamount chains, most notably along the Hawaiian-Emperor Seamount Chain? Thus, investigating the process responsible for long-lived episodic GVP volcanism provides the opportunity to evaluate this little understood process of rejuvenation in a physical setting very different to the Hawaiian-Emperor Chain (i.e. on/near spreading axis versus mid-plate). We consider here timing and geochemical information to test the various geodynamic models proposed to explain the origin of GVP hotspot volcanism, especially the possibility of rejuvenated phases that erupt long after initial shield-building.

  8. Basic rocks in Finland

    International Nuclear Information System (INIS)

    Piirainen, T.; Gehoer, S.; Iljina, M.; Kaerki, A.; Paakkola, J.; Vuollo, J.

    1992-10-01

    Basic igneous rocks, containing less than 52% SiO 2 , constitute an important part of the Finnish Archaean and Proterozoic crust. In the Archaean crust exist two units which contain the majority of the basic rocks. The Arcaean basic rocks are metavolcanics and situated in the Greenstone Belts of Eastern Finland. They are divided into two units. The greenstones of the lower one are tholeiites, komatiites and basaltic komatiites. The upper consists of bimodal series of volcanics and the basic rocks of which are Fe-tholeiites, basaltic komatiites and komatiites. Proterozoic basic rocks are divided into seven groups according to their ages. The Proterozoic igneous activity started by the volominous basic magmatism 2.44 Ga ago. During this stage formed the layered intrusions and related dykes in the Northern Finland. 2.2 Ga old basic rocks are situated at the margins of Karelian formations. 2.1 Ga aged Fe-tholeiitic magmatic activity is widespread in Eastern and Northern Finland. The basic rocks of 1.97 Ga age group are met within the Karelian Schist Belts as obducted ophiolite complexes but they occur also as tholeiitic diabase dykes cutting the Karelian schists and Archean basement. The intrusions and the volcanics of the 1.9 Ga old basic igneous activity are mostly encountered around the Granitoid Complex of Central Finland. Subjotnian, 1.6 Ga aged tholeiitic diabases are situated around the Rapakivi massifs of Southern Finland, and postjotnian, 1.2 Ga diabases in Western Finland where they form dykes cutting Svecofennian rocks

  9. Hydraulic characterization of volcanic rocks in Pahute Mesa using an integrated analysis of 16 multiple-well aquifer tests, Nevada National Security Site, 2009–14

    Science.gov (United States)

    Garcia, C. Amanda; Jackson, Tracie R.; Halford, Keith J.; Sweetkind, Donald S.; Damar, Nancy A.; Fenelon, Joseph M.; Reiner, Steven R.

    2017-01-20

    An improved understanding of groundwater flow and radionuclide migration downgradient from underground nuclear-testing areas at Pahute Mesa, Nevada National Security Site, requires accurate subsurface hydraulic characterization. To improve conceptual models of flow and transport in the complex hydrogeologic system beneath Pahute Mesa, the U.S. Geological Survey characterized bulk hydraulic properties of volcanic rocks using an integrated analysis of 16 multiple-well aquifer tests. Single-well aquifer-test analyses provided transmissivity estimates at pumped wells. Transmissivity estimates ranged from less than 1 to about 100,000 square feet per day in Pahute Mesa and the vicinity. Drawdown from multiple-well aquifer testing was estimated and distinguished from natural fluctuations in more than 200 pumping and observation wells using analytical water-level models. Drawdown was detected at distances greater than 3 miles from pumping wells and propagated across hydrostratigraphic units and major structures, indicating that neither faults nor structural blocks noticeably impede or divert groundwater flow in the study area.Consistent hydraulic properties were estimated by simultaneously interpreting drawdown from the 16 multiple-well aquifer tests with an integrated groundwater-flow model composed of 11 well-site models—1 for each aquifer test site. Hydraulic properties were distributed across volcanic rocks with the Phase II Pahute Mesa-Oasis Valley Hydrostratigraphic Framework Model. Estimated hydraulic-conductivity distributions spanned more than two orders of magnitude in hydrostratigraphic units. Overlapping hydraulic conductivity ranges among units indicated that most Phase II Hydrostratigraphic Framework Model units were not hydraulically distinct. Simulated total transmissivity ranged from 1,600 to 68,000 square feet per day for all pumping wells analyzed. High-transmissivity zones exceeding 10,000 square feet per day exist near caldera margins and extend

  10. Zircon Hf-O isotopic constraints on the origin of Late Mesozoic felsic volcanic rocks from the Great Xing'an Range, NE China

    Science.gov (United States)

    Gong, Mingyue; Tian, Wei; Fu, Bin; Wang, Shuangyue; Dong, Jinlong

    2018-05-01

    The voluminous Late Mesozoic magmatism was related to extensive re-melting of juvenile materials that were added to the Central East Asia continent in Phanerozoic time. The most favoured magma generation mechanism of Late Mesozoic magmas is partial melting of underplated lower crust that had radiogenic Hf-Nd isotopic characteristics, but this mechanism faces difficulties when interpreting other isotopic data. The tectonic environment controlling the generation of the Late Mesozoic felsic magmas is also in dispute. In this study, we obtained new U-Pb ages, and geochemical and isotopic data of representative Jurassic (154.4 ± 1.5 Ma) and Cretaceous (140.2 ± 1.5 Ma) felsic volcanic samples. The Jurassic sample has inherited zircon cores of Permian age, with depleted mantle-like εHf(t) of +7.4 - +8.5, which is in contrast with those of the magmatic zircons (εHf(t) = +2.4 ± 0.7). Whereas the inherited cores and the magmatic zircons have identical mantle-like δ18O composition ranges (4.25-5.29‰ and 4.69-5.54‰, respectively). These Hf-O isotopic characteristics suggest a mixed source of enriched mantle materials rather than ancient crustal components and a depleted mantle source represented by the inherited Permian zircon core. This mechanism is manifested by the eruption of Jurassic alkaline basalts originated from an enriched mantle source. The Cretaceous sample has high εHf(t) of +7.0 - +10.5, suggesting re-melting of a mafic magma derived from a depleted mantle-source. However, the sub-mantle zircon δ18O values (3.70-4.58‰) suggest the depleted mantle-derived mafic source rocks had experienced high temperature hydrothermal alteration at upper crustal level. Therefore, the Cretaceous felsic magma, if not all, could be generated by re-melting of down-dropped supracrustal volcanic rocks that experienced high temperature oxygen isotope alteration. The two processes, enriched mantle-contribution and supracrustal juvenile material re-melting, are new

  11. Explosive volcanism, shock metamorphism and the K-T boundary

    International Nuclear Information System (INIS)

    Desilva, S.L.; Sharpton, V.L.

    1988-01-01

    The issue of whether shocked quartz can be produced by explosive volcanic events is important in understanding the origin of the K-T boundary constituents. Proponents of a volcanic origin for the shocked quartz at the K-T boundary cite the suggestion of Rice, that peak overpressures of 1000 kbars can be generated during explosive volcanic eruptions, and may have occurred during the May, 1980 eruption of Mt. St. Helens. Attention was previously drawn to the fact that peak overpressures during explosive eruptions are limited by the strength of the rock confining the magma chamber to less than 8 kbars even under ideal conditions. The proposed volcanic mechanisms for generating pressures sufficient to shock quartz are further examined. Theoretical arguments, field evidence and petrographic data are presented showing that explosive volcanic eruptions cannot generate shock metamorphic features of the kind seen in minerals at the K-T boundary

  12. Sources of Quaternary volcanism in the Itasy and Ankaratra volcanic fields, Madagascar

    Science.gov (United States)

    Rasoazanamparany, C.; Widom, E.; Kuentz, D. C.; Raharimahefa, T.; Rakotondrazafy, F. M. A.; Rakotondravelo, K. M.

    2017-12-01

    We present new major and trace element and Sr, Nd, Pb and Os isotope data for Quaternary basaltic lavas and tephra from the Itasy and Ankaratra volcanic fields, representing the most recent volcanism in Madagascar. Mafic magmas from Itasy and Ankaratra exhibit significant inter- and intra-volcanic field geochemical heterogeneity. The Itasy eruptive products range in composition from foidite to phonotephrite whereas Ankaratra lavas range from basanite to trachybasalts. Trace element signatures of samples from both volcanic fields are very similar to those of ocean island basalts (OIB), with significant enrichment in Nb and Ta, depletion in Rb, Cs, and K, and relatively high Nb/U and Ce/Pb. However, the Itasy volcanic rocks show enrichment relative to those of Ankaratra in most incompatible elements, indicative of a more enriched source and/or lower degrees of partial melting. Significant inter- and intra-volcanic field heterogeneity is also observed in Sr, Nd, Pb and Os isotope signatures. The Itasy volcanic rocks generally have less radiogenic Sr and Nd isotopic ratios but more radiogenic Pb isotopic signatures than the Ankaratra volcanic field. Together, the Itasy and Ankaratra volcanic rocks form a well-defined negative correlation in Sr vs. Pb isotopes that could be attributed to lithospheric contamination or variable degrees of mixing between distinct mantle sources. However, the lack of correlation between isotopes and indices of crustal contamination (e.g. MgO and Nb/U) are inconsistent with shallow lithospheric contamination, and instead suggest mixing between compositionally distinct mantle sources. Furthermore, although Sr-Pb isotope systematics are apparently consistent with mixing between two different sources, distinct trends in Sr vs. Nd isotopes displayed by samples from Itasy and Ankaratra, respectively, argue for more complex source mixing involving three or more sources. The current data demonstrate that although the Itasy and Ankaratra volcanic

  13. Source mechanism of volcanic tremor

    Energy Technology Data Exchange (ETDEWEB)

    Ferrick, M.G.; Qamar, A.; St. Lawrence, W.F.

    1982-10-10

    Low-frequency (<10 Hz) volcanic earthquakes originate at a wide range of depths and occur before, during, and after magmatic eruptions. The characteristics of these earthquakes suggest that they are not typical tectonic events. Physically analogous processes occur in hydraulic fracturing of rock formations, low-frequency icequakes in temperate glaciers, and autoresonance in hydroelectric power stations. We propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low-frequency volcanic earthquakes (tremor). The fluid dynamic source mechanism explains low-frequency earthquakes of arbitrary duration, magnitude, and depth of origin, as unsteady flow is independent of physical properties of the fluid and conduit. Fluid transients occur in both low-viscosity gases and high-viscosity liquids. A fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid, material properties, geometry and roughness of the conduit, and boundary conditions. To demonstrate the analytical potential of the fluid dynamic theory, we consider a single-phase fluid, a melt of Mount Hood andesite at 1250/sup 0/C, in which significant pressure and velocity variations occur only in the longitudinal direction. Further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations.

  14. Upper Paleozoic mafic and intermediate volcanic rocks of the Mount Pleasant caldera associated with the Sn-W deposit in southwestern New Brunswick (Canada): Petrogenesis and metallogenic implications

    Science.gov (United States)

    Dostal, Jaroslav; Jutras, Pierre

    2016-10-01

    Upper Paleozoic ( 365 Ma) mafic and intermediate volcanic rocks of the Piskahegan Group constitute a subordinate part of the Mount Pleasant caldera, which is associated with a significant polymetallic deposit (tungsten-molybdenum-bismuth zones 33 Mt ore with 0.21% W, 0.1% Mo and 0.08% Bi and tin-indium zones 4.8 Mt with 0.82% Sn and 129 g/t In) in southwestern New Brunswick (Canada). The epicontinental caldera complex formed during the opening of the late Paleozoic Maritimes Basin in the northern Appalachians. The mafic and intermediate rocks make up two compositionally distinct associations. The first association includes evolved rift-related continental tholeiitic basalts, and the second association comprises calc-alkaline andesites, although both associations were emplaced penecontemporaneously. The basalts have low Mg# 0.34-0.40, smooth chondrite-normalized REE patterns with (La/Yb)n 5-6, primitive mantle-normalized trace element patterns without noticeable negative Nb-Ta anomalies, and their ɛNd(T) ranges from + 2.5 to + 2.2. The basalts were generated by partial melting of a transition zone between spinel and garnet mantle peridotite at a depth of 70-90 km. The calc-alkaline andesites of the second association have chondrite-normalized REE patterns that are more fractionated, with (La/Yb)n 7-8.5, but without significant negative Eu anomalies. Compared to the basaltic rocks, they have lower ɛNd(T) values, ranging from + 0.5 to + 1.9, and their mantle-normalized trace element plots show negative Nb-Ta anomalies. The ɛNd(T) values display negative correlations with indicators of crustal contamination, such as Th/La, Th/Nb and SiO2. The andesitic rocks are interpreted to have formed by assimilation-fractional crystallization processes, which resulted in the contamination of a precursor basaltic magma with crustal material. The parent basaltic magma for both suites underwent a different evolution. The tholeiitic basalts experienced shallow-seated fractional

  15. Massive Rock Detachments from the Continental slope of the Balsas River Submarine Delta that occur due to Instability of Sediments which Produce Turbidity Currents and Tsunamis

    Science.gov (United States)

    Sandoval-Ochoa, J.; Aguayo-Camargo, J.

    2007-05-01

    During the NOAA oceanographic delivery cruise of the US R/V "Roger Revelle" to the Scripps Institution of Oceanography at the University of California in San Diego, California USA, in July 1996; a well calibrated bathymetric equipment, the SeaBeam* 2012, was tested. Good resolutions in data allowed bathymetric mapping to visualize the sea floor relief. Detailed colorful chartographic images showed a portion of the continental slope between the Balsas River Delta and the Middle America Trench and between the Balsas Canyon and La Necesidad Canyon. The surveyed area covered more than 3 000 square kilometers. After the delivery cruise, one of the goals was to measure and analyze the Morphobathymetry of the uneven lower portion of the Balsas River Submarine Delta. So far some of the findings with the morphometric analyses consist of several isolated slump scars that each comprise more than 12 cubic kilometers in volume and a multiple slump scar with an evident steep hollow about 200 cubic kilometers absent of rock. These volumes of rock apparently underwent a remobilization from the slope during the Late Quaternary. The rock detachments occured in relatively small portions but in instantaneous massive displacements because of their instability as well as other identified factors in the region. Over time more and more authors have accepted that coastal cuts or submarine slump scars have been left by sudden movements of rock and fluids. The phenomena that occur in the region in general, are accompanied on one side by potential and kinetic energies like falling bodies, flows and gravity waves, and on the other side, by mass transfer of rock and fluid mobilization like turbidity currents, accumulations, sea wave surges or tsunamis. In some cases the phenomena is produced by another natural triggering forces or by an earthquake. We propose that events like these, i.e. massive detachments and their products such as accumulations, turbidity currents and depositional debrites

  16. K-Ar ages of basalts from the Higashi-Matsuura district, northwestern Kyushu, Japan and regional geochronology of the Cenozoic alkaline volcanic rocks in eastern Asia

    International Nuclear Information System (INIS)

    Nakamura, Eizo; Campbell, I.H.; McDougall, I.

    1986-01-01

    Seven new K-Ar age determinations are presented on whole rock samples from alkaline and tholeiitic basalts of the Higashi-Matsuura district, northwestern Kyushu, Japan. Ages obtained range from 2.92 ± 0.03 Ma to 3.01 ± 0.04 Ma; these ages are essentially identical within analytical errors and yield an average age of 2.98 ± 0.03 Ma (Late Pliocene). When combined on an isochron type diagram the six Higashi-Matsuura samples give an age of 3.00 ± 0.03 Ma with the composition of nonradiogenic 40 Ar/ 36 Ar = 294.2 ± 2.0. The excellent age agreement of samples with different K contents and petrographic characteristics provides strong evidence that the tholeiitic and alkaline basalts were erupted for an extremely short period in the Higashi-Matsuura district. A basalt from Ogawashima Island yields a K-Ar age of 3.58 ± 0.04 Ma. This study and previously reported data support the hypothesis that alkaline volcanic activity in southwestern Japan commenced some 10 Ma ago and continued intermittently until recent times. Systematic variations of age and distribution of Cenozoic alkaline basalts are recognized in northeastern China, Korea and southwestern Japan. It is suggested that these variations are related to the initiation of 'mantle plumes' resulting from convection in the mantle wedge caused or controlled by subduction of the Kula and Pacific plates. (author)

  17. Water - rock interaction in different rock environments

    International Nuclear Information System (INIS)

    Lamminen, S.

    1995-01-01

    The study assesses the groundwater geochemistry and geological environment of 44 study sites for radioactive waste disposal. Initially, the study sites were divided by rock type into 5 groups: (1) acid - intermediate rocks, (2) mafic - ultramafic rocks, (3) gabbros, amphibolites and gneisses that contain calc-silicate (skarn) rocks, (4) carbonates and (5) sandstones. Separate assessments are made of acid - intermediate plutonic rocks and of a subgroup that comprises migmatites, granite and mica gneiss. These all belong to the group of acid - intermediate rocks. Within the mafic -ultramafic rock group, a subgroup that comprises mafic - ultramafic plutonic rocks, serpentinites, mafic - ultramafic volcanic rocks and volcanic - sedimentary schists is also evaluated separately. Bedrock groundwaters are classified by their concentration of total dissolved solids as fresh, brackish, saline, strongly saline and brine-class groundwaters. (75 refs., 24 figs., 3 tabs.)

  18. Characterization of calculation of in-situ retardation factors of contaminant transport using naturally-radionuclides and rock/water interaction occurring U-Series disequilibria timescales. 1997 annual progress report

    International Nuclear Information System (INIS)

    Goldstein, S.; Ku, T.L.; Luo, S.; Murrel, M.; Roback, R.

    1997-01-01

    'The research is directed toward a quantitative assessment of contaminant transport rates in fracture-rock systems using uranium-series radionuclides. Naturally occurring uranium-and thorium-series radioactive disequilibria will provide information on the rates of adsorption-desorption and transport of radioactive contaminants as well as on fluid transport and rock dissolution in a natural setting. This study will also provide an improved characterization of preferential flow and contaminant transport at the Idaho Environmental and Engineering Lab. (INEEL) site. To a lesser extent, the study will include rocks in the unsaturated zone. The authors will produce a realistic model of radionuclide migration under unsaturated and saturated field conditions at the INEEL site, taking into account the retardation processes involved in the rock/water interaction. The major tasks are to (1) determine the natural distribution of U, Th, Pa and Ra isotopes in rock minerals. sorbed phases on the rocks, and in fluids from both saturated and unsaturated zones at the site, and (2) study rock/water interaction processes using U/Th series disequilibrium and a statistical analysis-based model for the Geologic heterogeneity plays an important role in transporting contaminants in fractured rocks. Preferential flow paths in the fractured rocks act as a major pathway for transport of radioactive contaminants in groundwaters. The weathering/dissolution of rock by groundwater also influences contaminant mobility. Thus, it is important to understand the hydrogeologic features of the site and their impact on the migration of radioactive contaminants. In this regard, quantification of the rock weathering/dissolution rate and fluid residence time from the observed decay-series disequilibria will be valuable. By mapping the spatial distribution of the residence time of groundwater in fractured rocks, the subsurface preferential flow paths (with high rock permeability and short fluid residence

  19. Elemental and Sr-Nd isotopic geochemistry of Cretaceous to Early Paleogene granites and volcanic rocks in the Sikhote-Alin Orogenic Belt (Russian Far East): implications for the regional tectonic evolution

    Science.gov (United States)

    Zhao, Pan; Jahn, Bor-ming; Xu, Bei

    2017-09-01

    The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80-57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87Sr/86Sr ratios range from 0.7048 to 0.7114, and εNd(t) values vary from +1.7 to -3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The

  20. Re — Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

    Science.gov (United States)

    Walker, R. J.; Echeverria, L. M.; Shirey, S. B.; Horan, M. F.

    1991-04-01

    The Re — Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155±43 Ma. Subsequent episodes of volcanism produced basalts at 88.1±3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (ɛNd+9±1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (γOs) ranged from 0 to +22, and model-initial μ values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re — Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions.

  1. Re - Os isotopic constraints on the origin of volcanic rocks, Gorgona Island, Colombia: Os isotopic evidence for ancient heterogeneities in the mantle

    Science.gov (United States)

    Walker, R.J.; Echeverria, L.M.; Shirey, S.B.; Horan, M.F.

    1991-01-01

    The Re - Os isotopic systematics of komatiites and spatially associated basalts from Gorgona Island, Colombia, indicate that they were produced at 155??43 Ma. Subsequent episodes of volcanism produced basalts at 88.1??3.8 Ma and picritic and basaltic lavas at ca. 58 Ma. The age for the ultramafic rocks is important because it coincides with the late-Jurassic, early-Cretaceous disassembly of Pangea, when the North- and South-American plates began to pull apart. Deep-seated mantle upwelling possibly precipitated the break-up of these continental plates and caused a tear in the subducting slab west of Gorgona, providing a rare, late-Phanerozoic conduit for the komatiitic melts. Mantle sources for the komatiites were heterogeneous with respect to Os and Pb isotopic compositions, but had homogeneous Nd isotopic compositions (??Nd+9??1). Initial 187Os/186Os normalized to carbonaceous chondrites at 155 Ma (??Os) ranged from 0 to +22, and model-initial ?? values ranged from 8.17 to 8.39. The excess radiogenic Os, compared with an assumed bulk-mantle evolution similar to carbonaceous chondrites, was likely produced in portions of the mantle with long-term elevated Re concentrations. The Os, Pb and Nd isotopic compositions, together with major-element constraints, suggest that the sources of the komatiites were enriched more than 1 Ga ago by low (<20%) and variable amounts of a basalt or komatiite component. This component was added as either subducted oceanic crust or melt derived from greater depths in the mantle. These results suggest that the Re - Os isotope system may be a highly sensitive indicator of the presence of ancient subducted oceanic crust in mantle-source regions. ?? 1991 Springer-Verlag.

  2. Reassessment of petrogenesis of Carboniferous–Early Permian rift-related volcanic rocks in the Chinese Tianshan and its neighboring areas

    Directory of Open Access Journals (Sweden)

    Linqi Xia

    2012-07-01

    Full Text Available The Carboniferous−Early Permian rift-related volcanic successions, covering large areas in the Chinese Tianshan and its adjacent areas, make up a newly recognized important Phanerozoic large igneous province in the world, which can be further divided into two sub-provinces: Tianshan and Tarim. The regional unconformity of Lower Carboniferous upon basement or pre-Carboniferous rocks, the ages (360–351 Ma of the youngest ophiolite and the peak of subduction metamorphism of high pressure–low temperature metamorphic belt and the occurrence of Ni-Cu-bearing mafic-ultramafic intrusion with age of ∼352 Ma and A-type granite with age of ∼358 Ma reveal that the final closure of the Paleo-Asian Ocean might take place in the Early Mississippian. Our summation shows that at least four criteria, being normally used to identify ancient asthenosphere upwelling (or mantle plumes, are met for this large igneous province: (1 surface uplift prior to magmatism; (2 being associated with continental rifting and breakup events; (3 chemical characteristics of asthenosphere (or plume derived basalts; (4 close links to large-scale mineralization and the uncontaminated basalts, being analogous to those of many “ore-bearing” large igneous provinces, display Sr-Nd isotopic variations between plume and EM1 geochemical signatures. These suggest that a Carboniferous asthenosphere upwelling and an Early Permian plume played the central role in the generation of the Tianshan–Tarim (central Asia large igneous province.

  3. A rock- and palaeomagnetic study of recent lavas and 1995 volcanic glass on Fogo (Cape Verde Islands)

    DEFF Research Database (Denmark)

    Knudsen, M.F.; Abrahamsen, N.; Riisager, P.

    2005-01-01

    Fogo is the only island in the Cape Verde archipelago with accounts of historical volcanic activity.Here we present palaeomagnetic data from seven geologically recent lava flows on Fogo, including one glassy, volcanic flow from the eruption in 1995. Almost all samples behaved well during alternat......Fogo is the only island in the Cape Verde archipelago with accounts of historical volcanic activity.Here we present palaeomagnetic data from seven geologically recent lava flows on Fogo, including one glassy, volcanic flow from the eruption in 1995. Almost all samples behaved well during...

  4. The Volcanism Ontology (VO): a model of the volcanic system

    Science.gov (United States)

    Myer, J.; Babaie, H. A.

    2017-12-01

    We have modeled a part of the complex material and process entities and properties of the volcanic system in the Volcanism Ontology (VO) applying several top-level ontologies such as Basic Formal Ontology (BFO), SWEET, and Ontology of Physics for Biology (OPB) within a single framework. The continuant concepts in BFO describe features with instances that persist as wholes through time and have qualities (attributes) that may change (e.g., state, composition, and location). In VO, the continuants include lava, volcanic rock, and volcano. The occurrent concepts in BFO include processes, their temporal boundaries, and the spatio-temporal regions within which they occur. In VO, these include eruption (process), the onset of pyroclastic flow (temporal boundary), and the space and time span of the crystallization of lava in a lava tube (spatio-temporal region). These processes can be of physical (e.g., debris flow, crystallization, injection), atmospheric (e.g., vapor emission, ash particles blocking solar radiation), hydrological (e.g., diffusion of water vapor, hot spring), thermal (e.g., cooling of lava) and other types. The properties (predicates) relate continuants to other continuants, occurrents to continuants, and occurrents to occurrents. The ontology also models other concepts such as laboratory and field procedures by volcanologists, sampling by sensors, and the type of instruments applied in monitoring volcanic activity. When deployed on the web, VO will be used to explicitly and formally annotate data and information collected by volcanologists based on domain knowledge. This will enable the integration of global volcanic data and improve the interoperability of software that deal with such data.

  5. Magnetic properties of frictional volcanic materials

    Science.gov (United States)

    Kendrick, Jackie E.; Lavallée, Yan; Biggin, Andrew; Ferk, Annika; Leonhardt, Roman

    2015-04-01

    During dome-building volcanic eruptions, highly viscous magma extends through the upper conduit in a solid-like state. The outer margins of the magma column accommodate the majority of the strain, while the bulk of the magma is able to extrude, largely undeformed, to produce magma spines. Spine extrusion is often characterised by the emission of repetitive seismicity, produced in the upper <1 km by magma failure and slip at the conduit margins. The rheology of the magma controls the depth at which fracture can occur, while the frictional properties of the magma are important in controlling subsequent marginal slip processes. Upon extrusion, spines are coated by a carapace of volcanic fault rocks which provide insights into the deeper conduit processes. Frictional samples from magma spines at Mount St. Helens (USA), Soufriere Hills (Montserrat) and Mount Unzen (Japan) have been examined using structural, thermal and magnetic analyses to reveal a history of comminution, frictional heating, melting and cooling to form volcanic pseudotachylyte. Pseudotachylyte has rarely been noted in volcanic materials, and the recent observation of its syn-eruptive formation in dome-building volcanoes was unprecedented. The uniquely high thermal conditions of volcanic environments means that frictional melt remains at elevated temperatures for longer than usual, causing slow crystallisation, preventing the development of some signature "quench" characteristics. As such, rock-magnetic tests have proven to be some of the most useful tools in distinguishing pseudotachylytes from their andesite/ dacite hosts. In volcanic pseudotachylyte the mass normalised natural remanent magnetisation (NRM) when further normalised with the concentration dependent saturation remanence (Mrs) was found to be higher than the host rock. Remanence carriers are defined as low coercive materials across all samples, and while the remanence of the host rock displays similarities to an anhysteretic remanent

  6. Geochronology, stratigraphy and geochemistry of Cambro-Ordovician, Silurian and Devonian volcanic rocks of the Saxothuringian Zone in NE Bavaria (Germany)—new constraints for Gondwana break up and ocean-island magmatism

    Science.gov (United States)

    Höhn, Stefan; Koglin, Nikola; Klopf, Lisa; Schüssler, Ulrich; Tragelehn, Harald; Frimmel, Hartwig E.; Zeh, Armin; Brätz, Helene

    2018-01-01

    Stratigraphically well-defined volcanic rocks in Palaeozoic volcano-sedimentary units of the Frankenwald area (Saxothuringian Zone, Variscan Orogen) were sampled for geochemical characterisation and U-Pb zircon dating. The oldest rock suite comprises quartz keratophyre, brecciated keratophyre, quartz keratophyre tuff and basalt, formed in Upper Cambrian to Tremadocian time (c. 497-478 Ma). Basaltic volcanism continued until the Silurian. Quartz keratophyre shows post-collisional calc-alkaline signature, the Ordovician-Silurian basalt has alkaline signature typical of continental rift environments. The combined datasets provide evidence of Cambro-Ordovician bimodal volcanism and successive rifting until the Silurian. This evolution very likely resulted from break-up of the northern Gondwana margin, as recorded in many terranes throughout Europe. The position at the northern Gondwana margin is supported by detrital zircon grains in some tuffs, with typical Gondwana-derived age spectra mostly recording ages of 550-750 Ma and minor age populations of 950-1100 and 1700-2700 Ma. The absence of N-MORB basalt in the Frankenwald area points to a retarded break-off of the Saxothuringian terrane along a continental rift system from Uppermost Cambrian to Middle Silurian time. Geochemical data for a second suite of Upper Devonian basalt provide evidence of emplacement in a hot spot-related ocean-island setting south of the Rheic Ocean. Our results also require partial revision of the lithostratigraphy of the Frankenwald area. The basal volcanic unit of the Randschiefer Formation yielded a Tremadocian age and, therefore, should be attributed to the Vogtendorf Formation. Keratophyre of the Vogtendorf Formation, previously assigned to the Tremadoc, is most likely of Upper Devonian age.

  7. What, When, Where, and Why of Secondary Hawaiian Hotspot Volcanism

    Science.gov (United States)

    Garcia, M. O.; Ito, G.; Applegate, B.; Weis, D.; Swinnard, L.; Flinders, A.; Hanano, D.; Nobre-Silva, I.; Bianco, T.; Naumann, T.; Geist, D.; Blay, C.; Sciaroni, L.; Maerschalk, C.; Harpp, K.; Christensen, B.

    2007-12-01

    Secondary hotspot volcanism occurs on most oceanic island groups (Hawaii, Canary, Society) but its origins remain enigmatic. A 28-day marine expedition used multibeam bathymetry and acoustic imagery to map the extent of submarine volcanic fields around the northern Hawaiian Islands (Kauai, Niihau and Kaula), and the JASON2 ROV to sample many volcanoes to characterize the petrology, geochemistry (major and trace elements, and isotopes) and ages of the lavas from these volcanoes. Our integrated geological, geochemical and geophysical study attempts to examine the what (compositions and source), where (distribution and volumes), when (ages), and why (mechanisms) of secondary volcanism on and around the northern Hawaiian Islands. A first-order objective was to establish how the submarine volcanism relates in space, time, volume, and composition to the nearby shield volcanoes and their associated onshore secondary volcanism. Our surveying and sampling revealed major fields of submarine volcanoes extending from the shallow slopes of these islands to more than 100 km offshore. These discoveries dramatically expand the volumetric importance, distribution and geodynamic framework for Hawaiian secondary volcanism. New maps and rock petrology on the samples collected will be used to evaluate currently proposed mechanisms for secondary volcanism and to consider new models such as small-scale mantle convection driven by thermal and melt-induced buoyancy to produce the huge volume of newly discovered lava. Our results seem to indicate substantial revisions are needed to our current perceptions of hotspot dynamics for Hawaii and possibly elsewhere.

  8. Synthesis of morphotectonics and volcanics of the Central Indian Ocean Basin

    Digital Repository Service at National Institute of Oceanography (India)

    Mukherjee, A.D.; Iyer, S.D.

    to the hydrothermal effect on the pre-existing subalkaline basalts. Besides these rocks, there is a wide occurrence of pumice of probably in situ origin. A distinct relation occurs between the morpho-tectonic forms and the volcanics. For example, in and around...

  9. Sr-Nd-Pb isotope systematics of the Permian volcanic rocks in the northern margin of the Alxa Block (the Shalazhashan Belt) and comparisons with the nearby regions: Implications for a Permian rift setting?

    Science.gov (United States)

    Shi, Guanzhong; Wang, Hua; Liu, Entao; Huang, Chuanyan; Zhao, Jianxin; Song, Guangzeng; Liang, Chao

    2018-04-01

    The petrogenesis of the Permian magmatic rocks in the Shalazhashan Belt is helpful for us to understand the tectonic evolution of the Central Asian Orogenic Belt (CAOB) in the northern margin of the Alxa Block. The Permian volcanic rocks in the Shalazhashan Belt include basalts, trachyandesites and trachydacites. Our study shows that two basalt samples have negative εNd(t) values (-5.4 to -1.5) and higher radiogenic Pb values, which are relevant to the ancient subcontinental lithospheric mantle. One basalt sample has positive εNd(t) value (+10) representing mafic juvenile crust and is derived from depleted asthenosphere. The trachyandesites are dated at 284 ± 3 Ma with εNd(t) = +2.7 to +8.0; ISr = 0.7052 to 0.7057, and they are generated by different degrees of mixing between mafic magmas and crustal melts. The trachydacites have high εNd(t) values and slightly higher ISr contents, suggesting the derivation from juvenile sources with crustal contamination. The isotopic comparisons of the Permian magmatic rocks of the Shalazhashan Belt, the Nuru-Langshan Belt (representing the northern margin of the Alxa Block), the Solonker Belt (Mandula area) and the northern margin of the North China Craton (Bayan Obo area) indicate that the radiogenic isotopic compositions have an increasingly evolved trend from the south (the northern margins of the Alxa Block and the North China Craton) to the north (the Shalazhashan Belt and the Solonker Belt). Three end-member components are involved to generate the Permian magmatic rocks: the ancient subcontinental lithospheric mantle, the mafic juvenile crust or newly underplated mafic rocks that were originated from depleted asthenosphere, and the ancient crust. The rocks correlative with the mafic juvenile crust or newly underplated mafic rocks are predominantly distributed along the Shalazhashan Belt and the Solonker Belt, and the rocks derived from ancient, enriched subcontinental lithospheric mantle are mainly distributed along

  10. Constraints of texture and composition of clinopyroxene phenocrysts of Holocene volcanic rocks on a magmatic plumbing system beneath Tengchong, SW China

    Science.gov (United States)

    Hu, Jun-Hao; Song, Xie-Yan; He, Hai-Long; Zheng, Wen-Qin; Yu, Song-Yue; Chen, Lie-Meng; Lai, Chun-Kit

    2018-04-01

    Understanding processes of magma replenishment in a magma plumbing system is essential to predict eruption potential of a dormant volcano. In this study, we present new petrologic and thermobarometric data for youngest lava flows from the Holocene Heikongshan volcano in the Tengchong area, SW China. Clinopyroxene phenocrysts from the trachytic lava flows display various textural/compositional zoning styles (i.e., normal, reverse and oscillatory). Such zoning patterns are indicative of an open magmatic plumbing system with multiphase magma replenishment and mixing, which were likely a key drive of the volcanic eruptions. Thermobarometric calculations of these zoned clinopyroxene phenocrysts yield crystallization pressures of 3.8-7.1 kbar (peak at 4.5-7.0 kbar), corresponding to a magma chamber at depths of 14-21 km. The calculated depths are consistent with the large low-resistivity body at 12-30 km beneath the Heikongshan volcano, implying that the magmatic plumbing system may still be active. Recent earthquakes in the Tengchong area suggest that the regional strike-slip faulting are still active, and may trigger future volcanic eruptions if the magma chamber(s) beneath the Tengchong volcanic field is disturbed, in spite of the volcanic quiescence since 1609 CE.

  11. 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

    Energy Technology Data Exchange (ETDEWEB)

    Pelayo, M; Labajo, M A; Garcia Romero, L; Perez del Villar, L

    2009-10-12

    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.

  12. Assessment of the uranium potential of the Jurassic volcanism (Bahía Laura and El Quemado Complexes), Province of Santa Cruz, using ground-borne gamma-ray spectrometry and rock geochemistry

    International Nuclear Information System (INIS)

    Kleinman, L.E.; Maloberti, A.L.; Gayone, M.R.; Kaufmann, C.; Sruoga, P.

    2013-01-01

    Radiometric surveys are a rapid tool to measure uranium (U), thorium (Th) and potassium (K) concentrations in rocks and are very useful in the exploration for radioactive minerals. The distribution of uranium in Jurassic volcanic rocks of the province of Santa Cruz is evaluated in this work using ground gamma-ray spectrometry and rock geochemistry in order to assess its potential to form uranium deposits. Five areas were selected, which had some previous data of high radiometric values and detailed geological information. Measurements were carried out with a portable gamma-ray spectrometer (Exploranium-GR 320®) in andesites, ignimbrites, rhyolites, silicified areas, ash-fall tuffs and lacustrine sediments corresponding to the Bahía Laura and to El Quemado complexes. The results were similar in the five surveyed areas: radiometric concentrations show good positive correlations with chemical composition of the studied rocks for both K and Th, and a relatively poorer correlation for U. Different processes such as magmatic differentiation, vapor phase crystallization, hydrothermal alteration and supergene alteration are reflected in the distribution of these elements. U concentrations increase in the more glassy rocks, in areas with hydrothermal silicification, and in fracture zones, features that should be considered in future surveys. The calkalkaline composition and arc-signatures of the Jurassic magmatism are not the most favorable for uranium enrichment and for concentration of significant mineralizations. However, the extensional tectonic setting; the occurrence of calderas with facies slightly enriched in U and Th, in addition to hydrothermal activity are positive factors for U exploration. (authors) [es

  13. Lahar—River of volcanic mud and debris

    Science.gov (United States)

    Major, Jon J.; Pierson, Thomas C.; Vallance, James W.

    2018-05-09

    Lahar, an Indonesian word for volcanic mudflow, is a mixture of water, mud, and volcanic rock flowing swiftly along a channel draining a volcano. Lahars can form during or after eruptions, or even during periods of inactivity. They are among the greatest threats volcanoes pose to people and property. Lahars can occur with little to no warning, and may travel great distances at high speeds, destroying or burying everything in their paths.Lahars form in many ways. They commonly occur when eruptions melt snow and ice on snow-clad volcanoes; when rains fall on steep slopes covered with fresh volcanic ash; when crater lakes, volcano glaciers or lakes dammed by volcanic debris suddenly release water; and when volcanic landslides evolve into flowing debris. Lahars are especially likely to occur at erupting or recently active volcanoes.Because lahars are so hazardous, U.S. Geological Survey scientists pay them close attention. They study lahar deposits and limits of inundation, model flow behavior, develop lahar-hazard maps, and work with community leaders and governmental authorities to help them understand and minimize the risks of devastating lahars.

  14. Geochemical and Sr-Nd-Pb-Li isotopic characteristics of volcanic rocks from the Okinawa Trough: Implications for the influence of subduction components and the contamination of crustal materials

    Science.gov (United States)

    Guo, Kun; Zhai, Shikui; Yu, Zenghui; Wang, Shujie; Zhang, Xia; Wang, Xiaoyuan

    2018-04-01

    The Okinawa Trough is an infant back-arc basin developed along the Ryukyu arc. This paper provides new major and trace element and Sr-Nd-Pb-Li isotope data of volcanic rocks in the Okinawa Trough and combines the published geochemical data to discuss the composition of magma source, the influence of subduction component, and the contamination of crustal materials, and calculate the contribution between subduction sediment and altered oceanic crust in the subduction component. The results showed that there are 97% DM and 3% EMI component in the mantle source in middle trough (MS), which have been influenced by subduction sediment. The Li-Nd isotopes indicate that the contribution of subduction sediment and altered oceanic crust in subduction component are 4 and 96%, respectively. The intermediate-acidic rocks suffer from contamination of continental crust material in shallow magma chamber during fractional crystallization. The acidic rocks in south trough have experienced more contamination of crustal material than those from the middle and north trough segments.

  15. U-Th-Pb zircon geochronology on igneous rocks in the Toija and Salittu Formations, Orijärvi area, southwestern Finland: constraints on the age of volcanism and metamorphism

    Directory of Open Access Journals (Sweden)

    Christopher L. Kirkland

    2008-01-01

    Full Text Available Zircons from a felsic volcanic rock in the Toija Formation and a synvolcanic gabbro intrusion in the Salittu Formation within the Orijärvi area were dated by U-Th-Pb SIMS in order to provide depositional constraints on these formations. Zircon crystals from the felsic rock preserve a two-stage crystallisation history with zoned core domains and homogeneous rim domains. Inner domains yield a 1878±4 Ma concordia age, interpreted to determine the crystallisation of this rock. Rims yield a 1815±3 Ma concordia age interpretedto determine the regional metamorphism. Small rounded zircon grains from the Salittu gabbro, located within the Jyly shear zone, yield a concordia age of 1792±5 Ma. We interpret the grain textures to suggest that they recrystallised from inherited zircon seeds during the heat and fluid flow into the shear zone. Although no direct ages for the Salittu Formation have been recovered, field relationships imply that it was deposited between 1878−1875 Ma.

  16. A 3D model of crustal magnetization at the Pinacate Volcanic Field, NW Sonora, Mexico

    Science.gov (United States)

    García-Abdeslem, Juan; Calmus, Thierry

    2015-08-01

    The Pinacate Volcanic Field (PVF) is located near the western border of the southern Basin and Range province, in the State of Sonora NW Mexico, and within the Gulf of California Extensional Province. This volcanic field contains the shield volcano Santa Clara, which mainly consists of basaltic to trachytic volcanic rocks, and reaches an altitude of 1200 m. The PVF disrupts a series of discontinuous ranges of low topographic relief aligned in a NW direction, which consist mainly of Proterozoic metamorphic rocks and Proterozoic through Paleogene granitoids. The PVF covers an area of approximately 60 by 55 km, and includes more than 400 well-preserved cinder cones and vents and eight maar craters. It was active from about 1.7 Ma until about 13 ka. We have used the ages and magnetic polarities of the volcanic rocks, along with mapped magnetic anomalies and their inverse modeling to determine that the Pinacate Volcanic Field was formed during two volcanic episodes. The oldest one built the Santa Clara shield volcano of basaltic and trachytic composition, and occurred during the geomagnetic Matuyama Chron of reverse polarity, which also includes the normal polarity Jaramillo and Olduvai Subchrons, thus imprinting both normal and reverse magnetization in the volcanic products. The younger Pinacate series of basaltic composition represents monogenetic volcanic activity that extends all around the PVF and occurred during the subsequent geomagnetic Brunhes Chron of normal polarity. Magnetic anomalies toward the north of the Santa Clara volcano are the most intense in the PVF, and their inverse modeling indicates the presence of a large subsurface body magnetized in the present direction of the geomagnetic field. This suggests that the magma chambers at depth cooled below the Curie temperature during the Brunhes Chron.

  17. Rb-Sr and Ar-Ar systematics of Malani volcanic rocks of southwest Rajasthan: evidence for a younger post-crystallization thermal event

    International Nuclear Information System (INIS)

    Rathore, S.S.; Srivastava, R.K.

    1996-01-01

    A new Rb-Sr age of 779 ± 10 Ma has been obtained for a suite of andesite-dacite-rhyolite from the Malani igneous province of southwestern Rajasthan, dated earlier at 745 ± 10 Ma by Crawford and Compston (1970). The associated basalts may be slightly younger than the felsic volcanics and have a mantle source. The felsic volcanics on the other hand were most probably derived by fractional crystallization of a crustal magma. 40 Ar- 39 Ar systematics of three samples viz., a basalt, a dacite and a rhyolite show disturbed age spectra indicating a thermal event around 500-550 Ma ago. This secondary thermal event is quite wide-spread and possibly related to the Pan-African thermo-tectonic episode observed in the Himalayas and south India. (author). 38 refs., 5 figs., 2 tabs

  18. Rock- and Paleomagnetic Properties and Modeling of a Deep Crustal Volcanic System, the Reinfjord Ultramafic Complex, Seiland Igneous Province, Northern Norway

    Science.gov (United States)

    ter Maat, G. W.; Pastore, Z.; Michels, A.; Church, N. S.; McEnroe, S. A.; Larsen, R. B.

    2017-12-01

    The Reinfjord Ultramafic Complex is part of the 5000 km2 Seiland Igneous Province (SIP) in Northern Norway. The SIP is argued to be the deep-seated conduit system of a Large Igneous Province and was emplaced at 25-35 km depth in less than 10 Ma (570-560 Ma). The Reinfjord Ultramafic Complex was emplaced during three major successive events at 22-28km depth at pressures of 6-8kb, with associated temperatures 1450-1500°C (Roberts, 2006). The rocks are divided into three formations: the central series (CS) consisting of mainly dunites, upper layered series (ULS) consisting of dunites and wehrlites, a lower layered series (LLS) containing most pyroxene-rich rocks and a marginal zone (MZ) which formed where the ultramafic melts intruded the gabbro-norite and metasedimentary gneisses. Deep exposures such as the Reinfjord Ultramafic Complex are rare, therefore this study gives a unique insight in the rock magnetic properties of a deep ultramafic system. Localised serpentinised zones provide an opportunity to observe the effect of this alteration process on the magnetic properties of deep-seated rocks. Here, we present the results from the rock magnetic properties, a paleomagnetic study and combined potential-fields modeling. The study of the rock magnetic properties provides insight in primary processes associated with the intrusion, and later serpentinization. The paleomagnetic data yields two distinct directions. One direction corresponds to a Laurentia pole at ≈ 532 Ma while the other, though younger, is not yet fully understood. Rock magnetic properties were measured on > 700 specimens and used to constrain the modelling of gravity, high-resolution helicopter, and ground magnetic data. The intrusion is modelled as a cylindrically shaped complex with a dunite core surrounded by wehrlite and gabbro. The ultramafic part of the complex dips to the NE and its maximum vertical extent is modelled to 1400m. Furthermore, modelling allows estimation of relative volumes of

  19. Fluids in volcanic and geothermal systems

    Science.gov (United States)

    Sigvaldason, Gudmundur E.

    Mineral buffers control the composition of most volatile components of magmas and dissolved species in geothermal fluids. The only element which occurs in significant quantities in volcanic and geothermal fluids and is not controlled by mineral buffers is chlorine. It is argued that in absence of marine influence, geothermal fluids reflect the chlorine content of associated magmatic fluids. The chlorine content of oceanic volcanic rocks has a positive correlation with elements, which are believed to indicate a heterogenous source region. Since the source is generally believed to be the Earth's mantle, the implication is that the mantle is heterogenous with regard to chlorine and other volatiles. Such heterogeneities would have important consequences for genesis and distribution of ore. All major magma types of the oceanic environment occur in Iceland. Their spatial distribution is closely related to a volcanotectonic pattern, suggesting crustal control. A geophysical model of crustal accretion in a rift zone is used in conjunction with classical petrology to predict geochemical processes in a rift zone crust. The model has two kinematic parameters-drift rate and subsidence rate-which combined describe trajectories of mass particles deposited on the surface. When considering in conjunction with thermal gradients of the rift zone a series of metamorphic reactions and chemical fractionation processes are bound to occur, eventually resulting in a layering of the oceanic crust. The physical parameters result in a derived variable, rift zone residence time, which depends on the width of a rift zone. Long residence times in a wide rift zone lead to multistage recycling of material. Other properties of the model, based on geometric arrangement of productive fissure swarms within a rift zone, explain off-rift volcanism as directly related to rift zone processes, either as plate trapped magmatic domains or a transgressive thermal anomaly into an older crust. Off

  20. Natural factors and mining activity bearings on the water quality of the Choapa basin, North Central Chile: insights on the role of mafic volcanic rocks in the buffering of the acid drainage process.

    Science.gov (United States)

    Parra, Amparo; Oyarzún, Jorge; Maturana, Hugo; Kretschmer, Nicole; Meza, Francisco; Oyarzún, Ricardo

    2011-10-01

    This contribution analyzes water chemical data for the Choapa basin, North Central Chile, for the period 1980-2004. The parameters considered are As, Cu Fe, pH, EC, SO₄⁻², Cl⁻¹, and HCO[Formula: see text], from samples taken in nine monitoring stations throughout the basin. Results show rather moderate contents of As, Cu, and Fe, with the exception of the Cuncumén River and the Aucó creek, explained by the influence of the huge porphyry copper deposit of Los Pelambres and by the presence of mining operations, respectively. When compared against results obtained in previous researches at the neighboring Elqui river basin, which host the El Indio Au-Cu-As district, a much reduced grade of pollution is recognized for the Choapa basin. Considering the effect of acid rock drainage (ARD)-related Cu contents on the fine fraction of the sediments of both river basins, the differences recorded are even more striking. Although the Los Pelambres porphyry copper deposit, on the headwaters of the Choapa river basin, is between one and two orders of magnitude bigger than El Indio, stream water and sediments of the former exhibit significantly lower copper contents than those of the latter. A main factor which may explain these results is the smaller degree of H( + )-metasomatism on the host rocks of the Los Pelambres deposit, where mafic andesitic volcanic rocks presenting propylitic hydrothermal alteration are dominant. This fact contrast with the highly altered host rocks of El Indio district, where most of them have lost their potential to neutralize ARD.

  1. Stratigraphy, sedimentology and petrology of neogene rocks in the Deschutes Basin, Central Oregon: a record of continental-margin volcanism and its influence on fluvial sedimentation in an arc-adjacent basin

    International Nuclear Information System (INIS)

    Smith, G.A.

    1986-07-01

    Neogene rocks of the Deschutes basin include the middle Miocene Columbia River Basalt Group and Simtustus Formation, and late Miocene to early Pliocene Deschutes Formation. Assignment of Prineville chemical-type flows to the Grande Ronde Basalt of the Columbia River Basalt Group is based on correlation of these lavas from their type area through the Deschutes basin and onto the Columbia Plateau, where they have been previously mapped as Grande Ronde Basalt. Simtustus Formation is a newly defined unit intercalated with and conformable upon these basalts, and is unconformably overlain by Deschutes Formation. Burial of mature topography by middle Miocene basalts raised local base levels and initiated aggradation by low-gradient streams within the basin represented by the tuffaceous sandstones and mudstones of the Simtustus Formation. These sediments are enriched in pyroclastic constituents relative to contemporaneous Western Cascades volcanics, reflecting preferential incorporation of easily eroded and more widespread pyroclastic debris in distal sedimentary sequences compared to epiclastic contributions from lavas. The abundance of basalts, combined with the paucity of hydrous minerals and FeO and TiO 2 enrichment in intermediate lavas, characterizes early High Cascade volcanics as atypical for convergent-margin arcs. These petrologic characteristics are consistent with high-level fractionation in an extensional regime. Extension culminated in the development of an intra-arc graben, which ended Deschutes Formation deposition by structurally isolating the basin from the High Cascade source area

  2. Search for underground openings for in situ test facilities in crystalline rock

    Energy Technology Data Exchange (ETDEWEB)

    Wollenberg, H.A.; Strisower, B.; Corrigan, D.J.; Graf, A.N.; O' Brien, M.T.; Pratt, H.; Board, M.; Hustrulid, W.

    1980-01-01

    With a few exceptions, crystalline rocks in this study were limited to plutonic rocks and medium to high-grade metamorphic rocks. Nearly 1700 underground mines, possibly occurring in crystalline rock, were initially identified. Application of criteria resulted in the identification of 60 potential sites. Within this number, 26 mines and 4 civil works were identified as having potential in that they fulfilled the criteria. Thirty other mines may have similar potential. Most of the mines identified are near the contact between a pluton and older sedimentary, volcanic and metamorphic rocks. However, some mines and the civil works are well within plutonic or metamorphic rock masses. Civil works, notably underground galleries associated with pumped storage hydroelectric facilities, are generally located in tectonically stable regions, in relatively homogeneous crystalline rock bodies. A program is recommended which would identify one or more sites where a concordance exists between geologic setting, company amenability, accessibility and facilities to conduct in situ tests in crystalline rock.

  3. Search for underground openings for in situ test facilities in crystalline rock

    International Nuclear Information System (INIS)

    Wollenberg, H.A.; Strisower, B.; Corrigan, D.J.; Graf, A.N.; O'Brien, M.T.; Pratt, H.; Board, M.; Hustrulid, W.

    1980-01-01

    With a few exceptions, crystalline rocks in this study were limited to plutonic rocks and medium to high-grade metamorphic rocks. Nearly 1700 underground mines, possibly occurring in crystalline rock, were initially identified. Application of criteria resulted in the identification of 60 potential sites. Within this number, 26 mines and 4 civil works were identified as having potential in that they fulfilled the criteria. Thirty other mines may have similar potential. Most of the mines identified are near the contact between a pluton and older sedimentary, volcanic and metamorphic rocks. However, some mines and the civil works are well within plutonic or metamorphic rock masses. Civil works, notably underground galleries associated with pumped storage hydroelectric facilities, are generally located in tectonically stable regions, in relatively homogeneous crystalline rock bodies. A program is recommended which would identify one or more sites where a concordance exists between geologic setting, company amenability, accessibility and facilities to conduct in situ tests in crystalline rock

  4. Paraná flood basalt volcanism primarily limited to 1 Myr beginning at 135 Ma: New 40Ar/39Ar ages for rocks from Rio Grande do Sul, and critical evaluation of published radiometric data

    Science.gov (United States)

    Baksi, Ajoy K.

    2018-04-01

    40Ar/39Ar step heating analyses were carried out on seven rocks (five basalts, an andesite and a rhyolite) from the southern Paraná Province ( 28°S-30°S); they yield plateau/isochron ages of 135-134 Ma, in good agreement with published step heating data on rocks from the same area. Critical review of laser spot isochron ages for rocks from the Province, ranging from 140 to 130 Ma, are shown to be unreliable estimates of crystallization ages, as the rocks were substantially altered; step heating results on three of these rocks thought to yield good plateau ages, are shown to be incorrect, as a result of a technicality in dating procedures followed. U-Pb ages on zircon and baddeleyite separated from a variety of rock types ( 30°S-23°S) fall in the range 135 to 134 Ma. All reliable 40Ar/39Ar and U-Pb ages indicate volcanism was sharply focused, initiated at 135 Ma, and 1 Myr in duration; no variation of age with either latitude or longitude is noted, Scrutiny of published 40Ar/39Ar ages on the Florianopolis dykes shows they cannot be used as reliable crystallization ages. U-Pb work shows that this dyke swarm was formed coevally with the main part of the Parana province. Most of the published 40Ar/39Ar ages on the Ponta Grossa dyke swarm are unreliable; a few ages appear reliable and suggest the magmatic event in this area, may have postdated the main Paraná pulse by 1-2 Myr. A single 40Ar/39Ar age from a high-Nb basalt in the southernmost part ( 34°S) of the Paraná at 135 Ma, highlights the need for further radiometric work on other areas of this flood basalt province. The Paraná Province postdates the time of the Jurassic-Cretaceous bound­ary by 10 Myr.

  5. Geochemistry of Volcanic Rocks from International Ocean Discovery Program (IODP) Site 1438, Amami Sankaku Basin: Implications for Izu-Bonin-Mariana (IBM) Arc Initiation

    Science.gov (United States)

    Hickey-Vargas, R.; Ishizuka, O.; Yogodzinski, G. M.; Bizimis, M.; Savov, I. P.; McCarthy, A. J.; Arculus, R. J.; Bogus, K.

    2015-12-01

    IODP Expedition 351 drilled 150 m of volcanic basement overlain by 1461 m of sedimentary material at Site 1438 in the Amami Sankaku basin, just west of the Kyushu Palau Ridge, the locus of IBM arc initiation. Age interpretations based on biostratigraphy (Arculus et al., Nat. Geosci., in-press) determined that the age of the basement section is between 64 and 51 Ma, encompassing the age of the earliest volcanic products of the IBM arc. The Site 1438 volcanic basement consists of multiple flows of aphyric microcrystalline to finely crystalline basalts containing plagioclase and clinopyroxene with rare olivine pseudomorphs. New XRF major and ICPMS trace element data confirm findings of shipboard analysis that the basalts are moderately differentiated (6-14 % MgO; Mg# = 51-83; 73-490 ppm Cr and 58-350 ppm Ni) with downcore variations related to flow units. Ti/V and Ti/Sc ratios are 16-27 and 75-152, respectively, with lowest values at the base of the core. One prominent characteristic of the basalts is their depletion of immobile highly incompatible elements compared with MORB. Basalts have MORB-normalized La/Nd of 0.5 to 0.9, and most have Th/La 3 and primitive mantle normalized La/Yb > 1. Our results suggest that mantle melting at the onset of subduction involved exceptionally depleted sources. Enrichment over time may be related to increasing subduction inputs and/or other processes, such as entrainment of fertile asthenosphere during extension of the overriding plate.

  6. Toll-Like Receptor 9-Dependent AMPKα Activation Occurs via TAK1 and Contributes to RhoA/ROCK Signaling and Actin Polymerization in Vascular Smooth Muscle Cells.

    Science.gov (United States)

    McCarthy, Cameron G; Wenceslau, Camilla F; Ogbi, Safia; Szasz, Theodora; Webb, R Clinton

    2018-04-01

    Traditionally, Toll-like receptor 9 (TLR9) signals through an MyD88-dependent cascade that results in proinflammatory gene transcription. Recently, it was reported that TLR9 also participates in a stress tolerance signaling cascade in nonimmune cells. In this noncanonical pathway, TLR9 binds to and inhibits sarcoplasmic/endoplasmic reticulum Ca 2+ -ATPase 2 (SERCA2), modulating intracellular calcium handling, and subsequently resulting in the activation of 5'-AMP-activated protein kinase α (AMPK α ). We have previously reported that TLR9 causes increased contraction in isolated arteries; however, the mechanisms underlying this vascular dysfunction need to be further clarified. Therefore, we hypothesized that noncanonical TLR9 signaling was also present in vascular smooth muscle cells (VSMCs) and that it mediates enhanced contractile responses through SERCA2 inhibition. To test these hypotheses, aortic microsomes, aortic VSMCs, and isolated arteries from male Sprague-Dawley rats were incubated with vehicle or TLR9 agonist (ODN2395). Despite clear AMPK α activation after treatment with ODN2395, SERCA2 activity was unaffected. Alternatively, ODN2395 caused the phosphorylation of AMPK α via transforming growth factor β -activated kinase 1 (TAK1), a kinase involved in TLR9 inflammatory signaling. Downstream, we hypothesized that that TLR9 activation of AMPK α may be important in mediating actin cytoskeleton reorganization. ODN2395 significantly increased the filamentous-to-globular actin ratio, as well as indices of RhoA/Rho-associated protein kinase (ROCK) activation, with the latter being prevented by AMPK α inhibition. In conclusion, AMPK α phosphorylation after TLR9 activation in VSMCs appears to be an extension of traditional inflammatory signaling via TAK1, as opposed to SERCA2 inhibition and the noncanonical pathway. Nonetheless, TLR9-AMPK α signaling can mediate VSMC function via RhoA/ROCK activation and actin polymerization. Copyright © 2018 by The

  7. Stability and predictability in younger crystalline rock system: Japanese Islands case

    International Nuclear Information System (INIS)

    Yoshida, S.

    2009-01-01

    The Japanese Islands consist of igneous, sedimentary, and metamorphic rocks ranging in age from Paleozoic to Cenozoic. Among these, Carboniferous to Paleogene rocks occupy about 60% of the total area of the Japanese Islands. It should be noted that Quaternary volcanic rocks occupy only about 9% of the total area, although Quaternary volcanoes occur throughout the Japanese Islands. Long-term stability and predictability in the rock system are discussed in terms of volcanic activity, active faulting, and plate motion. Volcanic activity in the Japanese Islands is intimately related to subduction of the Pacific Plate and the Philippine Sea Plate. The volcanic front related to the Pacific and the Philippine Sea plates has been essentially fixed since about 6 Ma. The main active faults, which are distributed sporadically throughout the Japanese Islands, number about 150 and have been extensively investigated. The modes of the Pacific Plate and the Philippine Sea Plate have been essentially invariable since 10 Ma and 6 Ma, respectively. These lines of evidence imply that volcanism and tectonism in the Japanese Islands will scarcely change for hundreds of thousands of years into the future. It is clear that many places suitable for geological disposal will be present in this rock system. (author)

  8. Isotopic clues to magmatic source regions for neogene Andean volcanic rocks in the El Teniente area near 38oS latitude

    International Nuclear Information System (INIS)

    Kay, Suzanne Mahlburg; Kurtz, A.C

    2001-01-01

    The origin of isotopic variations in Central Andean arc lavas is a long-standing problem that involves identifying mantle and crustal source regions. Advances have come from analyzing temporal and spatial variations in constrained tectonic settings. The purpose here is to highlight the similarities of temporal variations in an east-west transect of Neogene magmatic units near 34 O S latitude with those from a south-north transect along the modern Southern Volcanic Zone (SVZ, e.g. Hildreth and Moorbath 1988, Tormey et al. 1991). The comparison shows the importance of crustal thickening processes associated with compressional shortening and of lithospheric scale adjustments associated with eastward migration of the arc front on magma sources. Sr, Nd and Pb isotopic analyses of 27 Neogene volcanic and plutonic samples from the El Teniente area are presented in Table 1 and plotted along with some analyses from Skewes and Stern (1994) and Stern and Skewes (1995) in Figure 2. The data show a clear progression from older samples with more 'depleted' isotopic signatures (lower 87 Sr/ 86 Sr and Pb isotopic ratios, higher εNd) to younger samples with more 'enriched' signatures (higher 87 Sr/ 86 Sr and Pb isotopic ratios, lower εNd). In detail, four temporal and spatial groups marked by discontinuities in isotopic trends can be defined. Within each group, εNd tends to decrease and 87 Sr/ 86 Sr ratios to increase with SiO2 concentration (au)

  9. Analysis of volcano rock from Canary islands

    International Nuclear Information System (INIS)

    Sitek, J.; Sedlackova, K.; Dekan, J.

    2013-01-01

    In this work we have analyzed the basalt rock from Lanzarote, which is the easternmost island of the Canary Islands lying in the Atlantic Ocean and has a volcanic origin. It was born through fiery eruptions and has solidified lava streams as well as extravagant rock formations. We compared our results with composition of basalt rocks from some other places on the Earth. Different iron oxides created on the volcanic rocks during their weathering on the Earth surface has been also analyzed. (authors)

  10. High-pressure mechanical instability in rocks.

    Science.gov (United States)

    Byerlee, J D; Brace, W F

    1969-05-09

    At a confining pressure of a few kilobars, deformation of many sedimentary rocks, altered mafic rocks, porous volcanic rocks, and sand is ductile, in that instabilities leading to audible elastic shocks are absent. At pressures of 7 to 10 kilobars, however, unstable faulting and stick-slip in certain of these rocks was observed. This high pressure-low temperature instability might be responsible for earthquakes in deeply buried sedimentary or volcanic sequences.

  11. Neogene felsic volcanic rocks in the Hoggar province: Volcanology, geochemistry and age of the Azrou trachyte-phonolite association (Algerian Sahara)

    Science.gov (United States)

    Ben El Khaznadji, Riad; Azzouni-Sekkal, Abla; Benhallou, Amel; Liégeois, Jean-Paul; Bonin, Bernard

    2017-03-01

    The Azrou volcanic district, located to the south-east to the Atakor district in the Hoggar, has a landscape is governed by a number of felsic volcanic highs and dissected mafic plateau lavas. Our new Rb-Sr age (i.e. 23.1 ± 1.6 Ma) indicates that the Azrou felsic lavas are contemporaneous with the Achkal ring complexes (Anahef region). The Azrou felsic lavas (mainly trachyte and phonolite) show remarkably homogeneous compositions both in major elements (57.5 ≤ SiO2≤ 63.1 wt%; 10.8 ≤(Na2O + K2O)≤12.4 wt%), trace elements (33.2 ≤ Th ≤ 107 ppm; 170 ≤ La≤472 ppm; 8.7<(La/Yb)N < 27.3) and radiogenic isotopes (0.703359 < 87Sr/86Sr < 0.706539; 0.512727 <143Nd/144Nd < 0.512925; 2<εNd <5.84. These data indicate that the lavas have been only very weakly contaminated by the Precambrian basement. Geodynamically, this genesis coupled with the low volume of both trachytic and phonolitic trends implies the reworking of pre-existing shear-zones allowing the rapid ascent of these small batches of magmas. This is in agreement with the general model of linear delamination along these shear zones due to the Africa-Europe convergence developed by Liégeois et al. (2005) and recently imaged by the magneto-telluric investigation of Bouzid et al. (2015).

  12. Alteration of rhyolitic (volcanic) glasses in natural Bolivian salt lakes. - Natural analogue for the behavior of radioactive waste glasses in rock salt repositories

    International Nuclear Information System (INIS)

    Abdelouas, A.

    1996-06-01

    Alteration experiments with the R7T7 glass in three salt brines, saturated respectively in MgCl 2 , MgCl 2 -CaCl 2 and NaCl, showed that the solubilities of most radionuclides are controlled by the secondary phases. Nd, La, and Pr are trapped in powellite, Ce in cerianite, U in coffinite, and Sr is partially immobilized in barite. There is a good similarity between the secondary phases formed experimentally on volcanic glasses and the R7T7 glass altered in MgCl 2 CaCl 2 -saturated brine (formation of hydrotalcite and chlorite-serpentine at short-term and saponite at long-term). These results support the use of volcanic glasses alteration patterns in Mg-rich solutions (seawater, brines) to understand the long-term behavior of nuclear waste glasses and to evaluate the stability of the secondary phases. The study of the sediments of Uyuni (Bolivia) showed that the corrosion rate of the rhyolitic glass in brines at 10 C is 12 to 30 time lower than those of rhyolitic glasses altered in high dilute conditions. The neoformed phases in the sediments are: Smectite, alunite, pyrite, barite, celestite and cerianite. The low alteration rate of rhyolitic glasses in brines and the formation of secondary phases such as smectite, barite and cerianite (also formed during the experimental alteration of the R7T7 glass), permit us to expect the low alteration of nuclear waste glasses at long-term in brines and the trapping of certain radionuclides in secondary phases. (orig.) [de

  13. Stratigraphy, structure, and some petrographic features of Tertiary volcanic rocks at the USW G-2 drill hole, Yucca Mountain, Nye County, Nevada

    International Nuclear Information System (INIS)

    Maldonado, F.; Koether, S.L.

    1983-01-01

    A continuously cored drill hole penetrated 1830.6 m of Tertiary volcanic strata comprised of the following in descending order: Paintbrush Tuff, tuffaceous beds of Calico Hills, Crater Flat Tuff, lava and flow breccia (rhyodacitic), tuff of Lithic Ridge, bedded and ash-flow tuff, lava and flow breccia bedded tuff, conglomerate and ash-flow tuff, and older tuffs of USW G-2. Comparison of unit thicknesses at USW G-2 to unit thicknesses at previously drilled holes at Yucca Mountain indicate: (1) thickening of the Paintbrush Tuff members and tuffaceous beds of Calico Hills toward the northern part of Yucca Mountain; (2) thickening of the Prow Pass Member but thinning of the Bullfrog Member and Tram unit; (3) thinning of the tuff of Lithic Ridge; (4) presence of about 280 m of lava and flow breccia not previously penetrated by any drill hole; and (5) presence of an ash-flow tuff unit at the bottom of the drill hole not previously intersected, apparently the oldest unit penetrated at Yucca Mountain to date. Petrographic features of some of the units include: (1) decrease in quartz and K-feldspar and increases in biotite and plagioclase with depth in the tuffaceous beds of Calico Hills; (2) an increase in quartz phenocrysts from the top to the bottom members of the Crater Flat Tuff; (3) a low quartz content in the tuff of Lithic Ridge, suggesting tapping of the magma chamber at quartz-poor levels; (4) a change in zeolitic alteration from heulandite to clinoptilolite to mordenite with increasing depth; (5) lavas characterized by a rhyolitic top and dacitic base, suggesting reverse compositional zoning; and (6) presence of hydrothermal mineralization in the lavas that could be related to an itrusive under Yucca Mountain or to volcanism associated with the Timber Mountain-Claim Canyon caldera complex. A fracture analysis of the core resulted in tabulation of 7848 fractures, predominately open and high angle

  14. The Chinese North Tianshan Orogen was a rear-arc (or back-arc) environment in the Late Carboniferous: constraint from the volcanic rocks in the Bogda Mountains

    Science.gov (United States)

    Xie, W.

    2017-12-01

    The Tianshan Orogen is a key area for understanding the Paleozoic tectonics and long-lasting evolution of the Central Asian Orogenic Belt (CAOB). However, considerable debate persists as to its tectonic setting during the late Paleozoic, with active subduction system and intraplate large igneous provinces as two dominant schools (Ma et al., 1997; Gu et al., 2000; Xiao et al., 2004; Han et al., 2010; Shu et al., 2011; Chen et al., 2011; Xia et al., 2012). With aims of providing constraints on this issue, petrology, mineralogy, geochronological and geochemistry for the Late Carboniferous volcanics from the Bogda Mountains have been carried out. We find two suits of high-Al basalt (HAB, 315-319 Ma) and a suit of submarine pillow basalt ( 311 Ma) in this region. Both of the two basalts belong to the tholeiitic magma (the tholeiitic index THI > 1) and contain low pre-eruptive magmatic H2O (coexisted with the Bogda HABs is I-type intermediate ignimbrites and rhyolite lavas. The rhyolites are formed by partial melting of a hydrated and juvenile arc crust and the ignimbrites are affected by magma mingling and feldspar fractionation (Xie et al., 2016c). The two basalts both have the MORB-like Sr-Nd-Hf-Pb isotopes and arc-like trace element compositions. We discuss that they may have been generated from a dry and depleted mantle source metasomatized by coexisted felsic volcanics were likely formed in a rear-arc or back-arc environment, probably related to southward subduction of the Paleo-Tianshan Ocean (Xie et al., 2016a, b, c).

  15. Volcanic systems of Iceland and their magma source

    Science.gov (United States)

    Sigmarsson, Olgeir

    2017-04-01

    Several active hot-spot volcanoes produce magma from mantle sources which composition varies on decadal time scale. This is probably best demonstrated by the recent work of Pietruszka and collaborators on Kilauea, Hawaii. In marked contrast, basalt lavas from volcanic system in Iceland located above the presumed centre of the Iceland mantle plume have uniform isotope composition over the last 10 thousand years. Volcanic systems are composed of a central volcano and a fissure swarm, or a combination of both and they represent a fundamental component of the neovolcanic zones in Iceland. Four such systems, those of Askja, Bárðarbunga, Kverkfjöll and Grímsvötn in central Iceland were chosen for investigation. The last three have central volcanoes covered by the Vatnajökull ice-sheet whereas part of their fissure swarms is ice-free. Tephra produced during subglacial eruptions together with lavas from the fissure swarms of Holocene age have been collected and analysed for Sr, Nd and Th isotope ratios. Those volcanic formations that can be univocally correlated to a given volcanic system display uniform isotope ratio but different from one volcanic system to another. An exception to this regularity is that Askja products have isotope ratios indistinguishable from those of Gímsvötn, but since these volcanic systems lies far apart their lava fields do not overlap. A practical aspect of these findings was demonstrated during the rifting event of Bárðarbunga and fissure eruption forming the Holuhraun lava field. Relatively low, O isotope ratios in these basalts and heterogeneous macrocrystal composition have been ascribed to important metabasaltic crustal contamination with or without crystal mush recycling. In that case a surprisingly efficient magma mixing and melt homogenization must have occurred in the past beneath the volcanic systems. One possibility is that during the rapid deglaciation much mantle melting occurred and melts accumulated at the mantle

  16. Scientific results from the deepened Lopra-1 borehole, Faroe Islands: Hydrocarbon gases in Palaeogene volcanic rocks from the Lopra-1/1A well, Faroe Islands

    Directory of Open Access Journals (Sweden)

    Laier, Troels

    2006-07-01

    Full Text Available Hydrocarbon gases were monitored in the drilling fluid during deepening of the Lopra-1 well from 2178–3565 m, in which thermogenic, methane-rich gases had been found previously. The mud gas concentration, up to 105 ppm of methane, was generally higher in the hyaloclastite sequence, 2470 m – terminal depth (TD, than in the overlying lavas of the lower basalt formation. The highest concentrations of mud gas in the lower basalt formation were associated with the more porous tuffaceous zones, whereas no simple relationship could be established between measured mud gas concentrations and porosity of the hyaloclastic rocks, which showed less marked porosity variations than the lavas.Chemical (C2+ 104 ppm. No particularly gas-rich zones were indicated, however, by the mud gas, nor was any significant change in lithology noted for this interval. It is possible that the technique of turbo-drilling, that had been attempted over a short interval, 2657–2675 m prior to collection of the high-level methane samples, may have caused enhanced degassingdue to the very fine cuttings produced. Chemical and isotopic composition of headspace gas and mud gas indicated the same type of gas throughout the well, although headspace methane tended to bemore enriched with respect to the 13C isotope.The origin of the Lopra-1 gas is discussed in the light of recent information obtained from source rock studies of central East Greenland and the Faroe–Shetland Basin.

  17. The origin of an oceanic plateau: Isotope geochemistry (Sr, Nd, Pb and Hf) of volcanic rocks from IODP Site U1347 and ODP Site 1213 (Hf data) on the Shatsky Rise (Northwest Pacific)

    Science.gov (United States)

    Heydolph, K.; Geldmacher, J.; Hoernle, K.

    2011-12-01

    K.HEYDOLPH1*, J.GELDMACHER2, 1 ,K.HOERNLE1 1IFM-GEOMAR, Wischhofstr. 1-3. D-24148 Kiel, Germany, (*correspondence: kheydolph@ifm-geomar.de) 2 Integrated Ocean Drilling Program, Texas A&M University, 1000 Discovery Drive, College Station, Texas 77845-9547 (geldmacher@iodp.tamu.edu) The submarine Shatsky Rise plateau, a unique large igneous province (LIP) in the northwest Pacific Ocean ca. 1500 km east of Japan, is the only large intraoceanic plateau, which formed during the Late Jurassic to Early Cretaceous at a time period with numerous reversals of the Earth's magnetic field. These magnetic reversals combined with bathymetric data allow a detailed reconstruction of the tectonic history. Accordingly the three main volcanic edifices Tamu, Ori and Shirshov massifs formed by massive volcanism during a short time span along a southwest - northeast trending, rapidly spreading triple junction. Therefore, the magnetic and bathymetric data suggest that the Shatsky Rise formed through the interaction of a mantle plume head with a ridge [1, 2]. We present new Sr, Nd and Pb (double spike) and for the first time Hf isotope data from volcanic rocks of relatively fresh basaltic lava flows from recent IODP Exp. 324 Site U1347 and ODP Leg 198 Site 1213 (Hf data) both located on Tamu massif the southernmost (oldest) volcanic edifice of Shtasky Rise. Initial 176Hf/177Hf and 143Nd/144Nd isotopic compositions are fairly uniform throughout the entire holes ranging between 0.283076 to 0.283100 and 0.512903 to 0.512981 respectively, showing neither distinct MORB nor intraplate (plume) affinity. Relatively unradiogenic 87Sr/86Sr data ranging from 0.70276 to 0.70296 mostly overlaps with Pacific MORB like values. In a Nd vs Hf isotope plot they form a tight cluster at the edge of the Pacific MORB field below the present-day Hf-Nd mantle array. Although initial Pb double spike 206Pb/204Pb and 208Pb/204Pb isotopic compositions for Site U1347 range from 18.13 to 18.46 and 37.71 to 37

  18. Litho stratigraphy of precambrian rocks in middle Xingu river basin -Altamira, Para state, Brazil

    International Nuclear Information System (INIS)

    Santos, M.V. dos; Sousa Filho, E.E. dos; Tassinari, C.C.G.

    1988-01-01

    The basement rocks from the Xingu river is divided into five litho stratigraphic units. They are broadly characterized by domains of ortho and para gneisses, volcano-sedimentary sequences, migmatites and by syntectonic and latetectonic granitoids. In addition acid to intermediate volcanics (Iriri formation) and several sub-volcanic granitic plutons (Maloquinha suite) also occur within the investigated area, as well as basic intrusions and minor arenous sediments covers, slightly metamorphosed. Geochronological studies carried out on the basement rocks and on the volcanics demonstrates an geologic evolution restricted to the trans Amazonian cycle (2.1 - 1.9 Ga). Sr isotopic evolution (high initial 87 Sr/ 86 Sr ratios) suggest that strong reworking of crustal material occurred at this time, in association with the tectonic evolution of the Maroni-Itacaiunas mobile belt related to the lower proterozoic, which borders the northern and northerneast part of the Archean central Amazonian province. (author)

  19. Evidence of volcanic activity in the base of the Pendencia Formation, onshore Potiguar Basin; Evidencia de atividade vulcanica na base da Formacao Pendencia, Bacia Potiguar emersa

    Energy Technology Data Exchange (ETDEWEB)

    Anjos, S.M.C.; Souza, R.S. de; Sombra, C.L. [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas; Silva Scuta, M. da [PETROBRAS, Rio de Janeiro, RJ (Brazil)

    1990-10-01

    The occurrence of volcanic rocks on the Pendencia Formation on the onshore part of Potiguar Basin, the porosity and permeability characteristics, are presented. The studies suggest that the evidence of the volcanic activity occurred associated with the rift process, all the wells drilling in the basin presents profiles characteristics at those volcanos-sedimentary sequences found in other sedimentary basins, and the lithic sandstones permit the conclusion that the occurrence of under water volcanic activity is contemporary of sedimentation in the Pendencia Lake. 4 figs., 8 refs.

  20. Application of Clinopyroxene Chemistry to Interpret the Physical Conditions of Ascending Magma, a Case Study of Eocene Volcanic Rocks in the Ghohrud Area (North of Isfahan)

    International Nuclear Information System (INIS)

    Sayari, M.; Sharifi, M.

    2016-01-01

    Clinopyroxene and plagioclase phenocrysts of nineteen samples were analyzed with the electron microprobe. The chemical compositions of the clinopyroxenes were used to estimate both the chemical evolution and temperature and pressure conditions of the magmas during crystallization, using SCG, a specialized software for clinopyroxene thermo barometry (Sayari and Sharifi, 2014). Microprobe analyses show that plagioclases in the Eocene basaltic rocks are labradorite-bytownite (An85-58Ab15-41) and clinopyroxenes are augite (En41-49Di29-38Fs17-26). The compositions of the clinopyroxenes indicate a tholeiitic affinity for the magma. After plotting the cpx thermobarometry results on a P-T diagram, and applying a linear regression, an equation of P-T describing the physical conditions of the ascending magma was obtained.

  1. Deciphering shallow paleomagnetic inclinations: 1. Implications from correlation of Albian volcanic rocks along the Insular/Intermontane Superterrane boundary in the southern Canadian Cordillera

    Science.gov (United States)

    Haskin, M. L.; Enkin, R. J.; Mahoney, J. B.; Mustard, P. S.; Baker, J.

    2003-04-01

    Geologic and paleomagnetic data lead to two contradictory hypotheses regarding the paleoposition of the Insular and Intermontane Superterranes that presently constitute the western Canadian Cordillera. Paleomagnetic data from the Insular and Intermontane superterranes suggest a southerly origin coinciding with the latitude of Mexico and the northwest United States, respectively, during the mid-Cretaceous. Geologic evidence points to a northerly origin for these same tectonic entities during this period; both models cannot be correct. Geologic and paleomagnetic data from the Empire Valley-Churn Creek area in south central British Columbia (51.5°N, 122.5°W) are critical to resolving these contradictory hypotheses. Late Cretaceous rocks correlated to the Insular Superterrane with large paleomagnetic displacements unconformably overlie mid-Cretaceous rocks correlative to the Spences Bridge Group of the Intermontane Superterrane. We provide paleomagnetic evidence of this correlation based on similar magnetic properties, opaque mineral assemblages, demagnetization behavior, fold test results, mean inclinations, clockwise vertical axes rotations, and statistically indistinguishable paleomagnetic poles and displacement estimates. This correlation and the observed geologic relationships in the Empire Valley-Churn Creek area indicate that the Insular and Intermontane Superterranes were linked by the mid-Cretaceous. Sites from the two previous Spences Bridge Group studies are combined with their correlatives in the Empire Valley-Churn Creek area to give 81 sites that yield a paleomagnetic pole of 60.5°N, 304.5°E, dp = 3.7°, dm = 5.5° which corresponds to 1050 ± 450 km of displacement from the south. This new displacement estimate suggests that the Spences Bridge arc formed at the latitude of southern Oregon during the mid-Cretaceous.

  2. Candidate constructional volcanic edifices on Mercury

    OpenAIRE

    Wright, J.; Rothery, D. A.; Balme, M. R.; Conway, S. J.

    2018-01-01

    [Introduction] Studies using MESSENGER data suggest that Mercury’s crust is predominantly a product of effusive volcanism that occurred in the first billion years following the planet’s formation. Despite this planet-wide effusive volcanism, no constructional volcanic edifices, characterized by a topographic rise, have hitherto been robustly identified on Mercury, whereas constructional volcanoes are common on other planetary bodies in the solar system with volcanic histories. Here, we descri...

  3. Volcanic Characteristics of Kueishantao in Northeast Taiwan and Their Implications

    Directory of Open Access Journals (Sweden)

    Ching-Lung Chiu

    2010-01-01

    Full Text Available Kueishantao (KST is a small offshore volcanic island located at the southernmost part of the Okinawa Trough. In this study, we conducted a detailed mapping incorporating the new high resolution LiDAR DTM laser scanning device to accurately construct a volcanic sequence. A new 1/5000 geological map was established. One primary volcanic cone, composed of layers of both lava flows and pyroclastic rocks constituted the major edifice of KST. The other minor volcanic cone, which consists of volcanic lapillis and blocks, is seated to the east of the main cone. The escarped and nearly straight coast in the southern part of the KST indicates that the volcano suffered a large post-volcanic edifice collapse erasing nearly one half of the volume of both volcanic cones. The increase in the abundance of the xenoliths of sedimentary rocks from the lower to the upper part of the volcanic sequence indicates that the formation of volcanic rocks of the KST involved an intensification of crustal contamination. The possibility of volcanic eruption can not be excluded in the future based on the present thermolu¬minescene age data of 7 ka. The associated eruptive ash fall and tsunami induced by the further collapse of the KST volcanic edifice might have great influence to the adjacent inland. Thus, long-term monitoring of volcanic activities around KST should be required for future hazard assessments.

  4. Geophysical expression of caldera related volcanism, structures and mineralization in the McDermitt volcanic field

    Science.gov (United States)

    Rytuba, J. J.; Blakely, R. J.; Moring, B.; Miller, R.

    2013-12-01

    The High Rock, Lake Owyhee, and McDermitt volcanic fields, consisting of regionally extensive ash flow tuffs and associated calderas, developed in NW Nevada and SE Oregon following eruption of the ca. 16.7 Ma Steens flood basalt. The first ash flow, the Tuff of Oregon Canyon, erupted from the McDermitt volcanic field at 16.5Ma. It is chemically zoned from peralkaline rhyolite to dacite with trace element ratios that distinguish it from other ash flow tuffs. The source caldera, based on tuff distribution, thickness, and size of lithic fragments, is in the area in which the McDermitt caldera (16.3 Ma) subsequently formed. Gravity and magnetic anomalies are associated with some but not all of the calderas. The White Horse caldera (15.6 Ma), the youngest caldera in the McDermitt volcanic field has the best geophysical expression, with both aeromagnetic and gravity lows coinciding with the caldera. Detailed aeromagnetic and gravity surveys of the McDermitt caldera, combined with geology and radiometric surveys, provides insight into the complexities of caldera collapse, resurgence, post collapse volcanism, and hydrothermal mineralization. The McDermitt caldera is among the most mineralized calderas in the world, whereas other calderas in these three Mid Miocene volcanic fields do not contain important hydrothermal ore deposits, despite having similar age and chemistry. The McDermitt caldera is host to Hg, U, and Li deposits and potentially significant resources of Ga, Sb, and REE. The geophysical data indicate that post-caldera collapse intrusions were important in formation of the hydrothermal systems. An aeromagnetic low along the E caldera margin reflects an intrusion at a depth of 2 km associated with the near-surface McDermitt-hot-spring-type Hg-Sb deposit, and the deeper level, high-sulfidation Ga-REE occurrence. The Li deposits on the W side of the caldera are associated with a series of low amplitude, small diameter aeromagnetic anomalies that form a continuous

  5. Geochemical Signatures of Potassic to Sodic Adang Volcanics, Western Sulawesi: Implications for Their Tectonic Setting and Origin

    Directory of Open Access Journals (Sweden)

    Godang Shaban

    2016-11-01

    Full Text Available DOI:10.17014/ijog.3.3.195-214The Adang Volcanics represent a series of (ultra potassic to sodic lavas and tuffaceous rocks of predominantly trachytic composition, which forms the part of a sequence of Late Cenozoic high-K volcanic and associated intrusive rocks occurring extensively throughout Western Sulawesi. The tectonic setting and origin of these high-K rocks have been the subject of considerable debates. The Adang Volcanics have mafic to mafitic-intermediate characteristics (SiO2: 46 - 56 wt% and a wide range of high alkaline contents (K2O: 0.80 - 9.08 %; Na2O: 0.90 - 7.21 % with the Total Alkali of 6.67 - 12.60 %. Al2O3 values are relatively low (10.63 - 13.21 % and TiO2 values relatively high (1.27 - 1.91 %. Zr and REE concentrations are also relatively high (Zr: 1154 - 2340 ppm; Total REE (TREY = TRE: 899.20 - 1256.50 ppm; TRExOy: 1079.76 - 1507.97 ppm, with an average Zr/TRE ratio of ~ 1.39. The major rock forming minerals are leucite/pseudoleucite, diopside/aegirine, and high temperature phlogopite. Geochemical plots (major oxides and trace elements using various diagrams suggest the Adang Volcanics formed in a postsubduction, within-plate continental extension/initial rift tectonic setting. It is further suggested magma was generated by minor (< 0.1 % partial melting of depleted MORB mantle material (garnet-lherzolite with the silicate melt having undergone strong metasomatism. Melt enrichment is reflected in the alkaline nature of the rocks and geochemical signatures such as Nb/Zr > 0.0627 and (Hf/SmPM > 1.23. A comparison with the Vulsini ultrapotassic volcanics from the Roman Province in Italy shows both similarities (spidergram pattern indicating affinity with Group III ultrapotassics volcanics and differences (nature of mantle metasomatism.

  6. The Impact of Space Flight on Survival and Interaction of Cupriavidus metallidurans CH34 with Basalt, a Volcanic Moon Analog Rock

    Directory of Open Access Journals (Sweden)

    Natalie Leys

    2017-04-01

    Full Text Available Microbe-mineral interactions have become of interest for space exploration as microorganisms could be used to biomine from extra-terrestrial material and extract elements useful as micronutrients in life support systems. This research aimed to identify the impact of space flight on the long-term survival of Cupriavidus metallidurans CH34 in mineral water and the interaction with basalt, a lunar-type rock in preparation for the ESA spaceflight experiment, BIOROCK. Therefore, C. metallidurans CH34 cells were suspended in mineral water supplemented with or without crushed basalt and send for 3 months on board the Russian FOTON-M4 capsule. Long-term storage had a significant impact on cell physiology and energy status (by flow cytometry analysis, plate count and intracellular ATP measurements as 60% of cells stored on ground lost their cell membrane potential, only 17% were still active, average ATP levels per cell were significantly lower and cultivability dropped to 1%. The cells stored in the presence of basalt and exposed to space flight conditions during storage however showed less dramatic changes in physiology, with only 16% of the cells lost their cell membrane potential and 24% were still active, leading to a higher cultivability (50% and indicating a general positive effect of basalt and space flight on survival. Microbe-mineral interactions and biofilm formation was altered by spaceflight as less biofilm was formed on the basalt during flight conditions. Leaching from basalt also changed (measured with ICP-OES, showing that cells release more copper from basalt and the presence of cells also impacted iron and magnesium concentration irrespective of the presence of basalt. The flight conditions thus could counteract some of the detrimental effects observed after the 3 month storage conditions.

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

    International Nuclear Information System (INIS)

    Munoz B, Jorge; Duhart O, Paul; Farmer, G. Lang; Stern, Charles R

    2001-01-01

    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)

  8. High-Temperature, Perhaps Silicic, Volcanism on Mars Evidenced by Tridymite Detection in High-SiO2 Sedimentary Rock at Gale Crater, Mars

    Science.gov (United States)

    Morris, R. V.; Vaniman, D. T.; Blake, D. F.; Gellert, R.; Chipera, S. J.; Rampe, E. B.; Ming, D. W.; Morrison, S. M.; Downs, R. T.; Treiman, A. H.; hide

    2016-01-01

    The Mars Science Laboratory (MSL) rover, Curiosity, has been exploring sedimentary rocks within Gale crater since landing in August, 2012. On the lower slopes of Aeolis Mons (a.k.a. Mount Sharp), drill powder was collected from a high-silica (74 wt% SiO2) outcrop named Buckskin (BK). It was a surprise to find that the Buckskin sample contained significant amounts of the relatively rare silica polymorph tridymite. We describe the setting of the Buckskin sample, the detection of tridymite by the MSL Chemistry and Mineralogy (CheMin) X-ray diffraction instrument, and detection implications. Geologic setting: The Buckskin outcrop is part of the Murray formation exposed in the Marias Pass area. The formation was previously studied by CheMin in the Pahrump Hills member [1] where three samples of drill fines were analyzed (Confidence Hills (CH), Mojave2 (MJ) and Telegraph Peak (TP) [2]). Assuming approximately horizontal bedding, the Buckskin outcrop is approx.15 m stratigraphically above the bottom of the Pahrump Hills member. Mudstone, generally characterized by fine lamination, is the dominant depositional facies [1]. Buckskin Mineralogical and Chemical Composition: The CheMin instrument and XRD pattern analysis procedures have been previously discussed [3-6]. The diffraction pattern used for quantitative XRD analysis (Fig. 1) is the sum of the first 4 of 45 diffraction images. The remaining images are all characterized by both on-ring and off-ring diffraction spots that we attributed to poor grain motion and particle clumping. Coincident with particle clumping was a significant decrease in the intensity of the tridymite diffraction peaks (Fig. 2a). The derived mineralogical composition of the crystalline component (derived from the first 4 diffraction images) is given in Table 1. The tridymite is well-crystalline and its pattern is refined as monoclinic tridymite (Fig 1). Mineral chemical compositions were derived from XRD unit cell parameters or obtained from

  9. White Rock

    Science.gov (United States)

    2002-01-01

    (Released 19 April 2002) The Science 'White Rock' is the unofficial name for this unusual landform which was first observed during the Mariner 9 mission in the early 1970's. As later analysis of additional data sets would show, White Rock is neither white nor dense rock. Its apparent brightness arises from the fact that the material surrounding it is so dark. Images from the Mars Global Surveyor MOC camera revealed dark sand dunes surrounding White Rock and on the floor of the troughs within it. Some of these dunes are just apparent in the THEMIS image. Although there was speculation that the material composing White Rock could be salts from an ancient dry lakebed, spectral data from the MGS TES instrument did not support this claim. Instead, the White Rock deposit may be the erosional remnant of a previously more continuous occurrence of air fall sediments, either volcanic ash or windblown dust. The THEMIS image offers new evidence for the idea that the original deposit covered a larger area. Approximately 10 kilometers to the southeast of the main deposit are some tiny knobs of similarly bright material preserved on the floor of a small crater. Given that the eolian erosion of the main White Rock deposit has produced isolated knobs at its edges, it is reasonable to suspect that the more distant outliers are the remnants of a once continuous deposit that stretched at least to this location. The fact that so little remains of the larger deposit suggests that the material is very easily eroded and simply blows away. The Story Fingers of hard, white rock seem to jut out like icy daggers across a moody Martian surface, but appearances can be deceiving. These bright, jagged features are neither white, nor icy, nor even hard and rocky! So what are they, and why are they so different from the surrounding terrain? Scientists know that you can't always trust what your eyes see alone. You have to use other kinds of science instruments to measure things that our eyes can

  10. Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey

    Science.gov (United States)

    Deligne, Natalia I.; Mckay, Daniele; Conrey, Richard M.; Grant, Gordon E.; Johnson, Emily R.; O'Connor, Jim; Sweeney, Kristin

    2017-08-16

    The Cascade Range in central Oregon has been shaped by tectonics, volcanism, and hydrology, as well as geomorphic forces that include glaciations. As a result of the rich interplay between these forces, mafic volcanism here can have surprising manifestations, which include relatively large tephra footprints and extensive lava flows, as well as water shortages, transportation and agricultural disruption, and forest fires. Although the focus of this multidisciplinary field trip will be on mafic volcanism, we will also look at the hydrology, geomorphology, and ecology of the area, and we will examine how these elements both influence and are influenced by mafic volcanism. We will see mafic volcanic rocks at the Sand Mountain volcanic field and in the Santiam Pass area, at McKenzie Pass, and in the southern Bend region. In addition, this field trip will occur during a total solar eclipse, the first one visible in the United States in more than 25 years (and the first seen in the conterminous United States in more than 37 years).The Cascade Range is the result of subduction of the Juan de Fuca plate underneath the North American plate. This north-south-trending volcanic mountain range is immediately downwind of the Pacific Ocean, a huge source of moisture. As moisture is blown eastward from the Pacific on prevailing winds, it encounters the Cascade Range in Oregon, and the resulting orographic lift and corresponding rain shadow is one of the strongest precipitation gradients in the conterminous United States. We will see how the products of the volcanoes in the central Oregon Cascades have had a profound influence on groundwater flow and, thus, on the distribution of Pacific moisture. We will also see the influence that mafic volcanism has had on landscape evolution, vegetation development, and general hydrology.

  11. Timing of the volcanism of the southern Kivu province: Implications for the evolution of the western branch of the East African rift system

    International Nuclear Information System (INIS)

    Pasteels, P.

    1989-01-01

    New K-Ar datings of a large rock sampling from the South Kivu volcanic province (Zaire, Rwanda, Burundi) are reported. No ages older than 10 Ma have been obtained. This result contrasts with older assumptions and puts severe constraints on the relations between volcanism and rift evolution. From 10 to 7.5 Ma tholeiitic volcanism predominates corresponding to an episode of fissural eruptions; from 7.5 to 5 Ma alkali basalts and their differentiates are mainly erupted in localized rifts. A culmination of activity occurs between 6.0 and 5.5 Ma ago. Pleistocene alkalic volcanism is restricted to localized areas. The transition from tholeiites to alkali-basaltic volcanism dated around 7.5 Ma would correspond to a major rifting phase which corresponds with the initiation of Lake Kivu Basin formation. The distribution of tholeiitic rocks in the central part of the rift, and predominantly alkalic rocks along the western active border fault, strengthens the idea that the former are associated with tension, the latter with vertical, possibly also strike-slip movements. Volcanism in the Western Rift is restricted to areas where tension occurs in a zone which is located between two zones of strike-slip. In the South Kivu area normal faults intersect strike-slip faults and this seems to have determined the location of volcanic activity. Magma formation is considered to be related with shear heating combined with adiabatic decompression in ascending diapirs. This implies heating at the lithosphere-asthenosphere boundary as a result of extension. Generation of tholeiitic or alkalic magmas is connected with the variable ascent velocity of mantle diapirs or with variable shear heating along the shear zone. Changes in both magma composition and intensity of volcanic activity with time are considered to be related to major phases of rift evolution. (orig.)

  12. Miocene magmatism in the Bodie Hills volcanic field, California and Nevada: A long-lived eruptive center in the southern segment of the ancestral Cascades arc

    Science.gov (United States)

    John, David A.; du Bray, Edward A.; Blakely, Richard J.; Fleck, Robert J.; Vikre, Peter; Box, Stephen E.; Moring, Barry C.

    2012-01-01

    The Middle to Late Miocene Bodie Hills volcanic field is a >700 km2, long-lived (∼9 Ma) but episodic eruptive center in the southern segment of the ancestral Cascades arc north of Mono Lake (California, U.S.). It consists of ∼20 major eruptive units, including 4 trachyandesite stratovolcanoes emplaced along the margins of the field, and numerous, more centrally located silicic trachyandesite to rhyolite flow dome complexes. Bodie Hills volcanism was episodic with two peak periods of eruptive activity: an early period ca. 14.7–12.9 Ma that mostly formed trachyandesite stratovolcanoes and a later period between ca. 9.2 and 8.0 Ma dominated by large trachyandesite-dacite dome fields. A final period of small silicic dome emplacement occurred ca. 6 Ma. Aeromagnetic and gravity data suggest that many of the Miocene volcanoes have shallow plutonic roots that extend to depths ≥1–2 km below the surface, and much of the Bodie Hills may be underlain by low-density plutons presumably related to Miocene volcanism.Compositions of Bodie Hills volcanic rocks vary from ∼50 to 78 wt% SiO2, although rocks with Bodie Hills rocks are porphyritic, commonly containing 15–35 vol% phenocrysts of plagioclase, pyroxene, and hornblende ± biotite. The oldest eruptive units have the most mafic compositions, but volcanic rocks oscillated between mafic and intermediate to felsic compositions through time. Following a 2 Ma hiatus in volcanism, postsubduction rocks of the ca. 3.6–0.1 Ma, bimodal, high-K Aurora volcanic field erupted unconformably onto rocks of the Miocene Bodie Hills volcanic field.At the latitude of the Bodie Hills, subduction of the Farallon plate is inferred to have ended ca. 10 Ma, evolving to a transform plate margin. However, volcanism in the region continued until 8 Ma without an apparent change in rock composition or style of eruption. Equidimensional, polygenetic volcanoes and the absence of dike swarms suggest a low differential horizontal stress regime

  13. Grinding into Soft, Powdery Rock

    Science.gov (United States)

    2004-01-01

    This hole in a rock dubbed 'Clovis' is the deepest hole drilled so far in any rock on Mars. NASA's Mars Exploration Rover Spirit captured this view with its microscopic imager on martian sol 217 (Aug. 12, 2004) after drilling 8.9 millimeters (0.35 inch) into the rock with its rock abrasion tool. The view is a mosaic of four frames taken by the microscopic imager. The hole is 4.5 centimeters (1.8 inches) in diameter. Clovis is key to a developing story about environmental change on Mars, not only because it is among the softest rocks encountered so far in Gusev Crater, but also because it contains mineral alterations that extend relatively deep beneath its surface. In fact, as evidenced by its fairly crumbly texture, it is possibly the most highly altered volcanic rock ever studied on Mars. Scientific analysis shows that the rock contains higher levels of the elements sulfur, chlorine, and bromine than are normally encountered in basaltic rocks, such as a rock dubbed 'Humphrey' that Spirit encountered two months after arriving on Mars. Humphrey showed elevated levels of sulfur, chlorine, and bromine only in the outermost 2 millimeters (less than 0.1 inch) of its surface. Clovis shows elevated levels of the same elements along with the associated softness of the rock within a borehole that is 4 times as deep. Scientists hope to compare Clovis to other, less-altered rocks in the vicinity to assess what sort of water-based processes altered the rock. Hypotheses include transport of sulfur, chlorine, and bromine in water vapor in volcanic gases; hydrothermal circulation (flow of volcanically heated water through rock); or saturation in a briny soup containing the same elements. In this image, very fine-grained material from the rock has clumped together by electrostatic attraction and fallen into the borehole. NASA/JPL/Cornell/USGS

  14. Drought occurence

    Science.gov (United States)

    John W. Coulston

    2007-01-01

    Why Is Drought Important? Drought is an important forest disturbance that occurs regularly in the Western United States and irregularly in the Eastern United States (Dale and others 2001). Moderate drought stress tends to slow plant growth while severedrought stress can also reduce photosynthesis (Kareiva and others 1993). Drought can also interact with...

  15. Chemical, multispectral, and textural constraints on the composition and origin of rocks at the Mars Pathfinder landing site

    Science.gov (United States)

    McSween, H.Y.; Murchie, S.L.; Crisp, J.A.; Bridges, N.T.; Anderson, R.C.; Bell, J.F.; Britt, D.T.; Brückner, J.; Dreibus, G.; Economou, T.; Ghosh, A.; Golombek, M.P.; Greenwood, J.P.; Johnson, J. R.; Moore, H.J.; Morris, R.V.; Parker, T.J.; Rieder, R.; Singer, R.; Wänke, H.

    1999-01-01

    Rocks at the Mars Pathfinder site are probably locally derived. Textures on rock surfaces may indicate volcanic, sedimentary, or impact-generated rocks, but aeolian abration and dust coatings prevent unambiguous interpretation. Multispectral imaging has resolved four spectral classes of rocks: gray and red, which occur on different surfaces of the same rocks; pink, which is probably soil crusts; and maroon, which occurs as large boulders, mostly in the far field. Rocks are assigned to two spectral trends based on the position of peak reflectance: the primary spectral trend contains gray, red, and pink rocks; maroon rocks constitute the secondary spectral trend. The spatial pattern of spectral variations observed is oriented along the prevailing wind direction. The primary spectral trend arises from thin ferric coatings of aeolian dust on darker rocks. The secondary spectral trend is apparently due to coating by a different mineral, probably maghemite or ferrihydrite. A chronology based on rock spectra suggests that rounded maroon boulders constitute the oldest petrologic unit (a flood deposit), succeeded by smaller cobbles possibly deposited by impact, and followed by aeolian erosion and deposition. Nearly linear chemical trends in alpha proton X-ray spectrometer rock compositions are interpreted as mixing lines between rock and adhering dust, a conclusion supported by a correlation between sulfur abundance and red/blue spectral ratio. Extrapolations of regression lines to zero sulfur give the composition of a presumed igneous rock. The chemistry and normative mineralogy of the sulfur-free rock resemble common terrestrial volcanic rocks, and its classification corresponds to andesite. Igneous rocks of this composition may occur with clastic sedimentary rocks or impact melts and breccias. However, the spectral mottling expected on conglomerates or breccias is not observed in any APXS-analyzed rocks. Interpretation of the rocks as andesites is complicated by absence

  16. Shield Through Rejuvenated Stage Volcanism On Kauai and Niihau, Hawaii

    Science.gov (United States)

    Cousens, B.; Clague, D. A.

    2013-12-01

    Kauai and Niihau are the northwesternmost large islands in the Hawaiian chain and consist of shield, rare postshield, and abundant rejuvenated stage lavas. We present new geochronological, geochemical and isotopic data for all phases of volcanic activity on the adjacent islands. K-Ar ages show Niihau shield volcanism occurred from 6.3-4.4 Ma, and K-Ar and new Ar-Ar ages for postshield volcanism range from 5.4-4.7 Ma. Kauai shield volcanism (K-Ar) overlaps with shield volcanism on Niihau. A new Ar-Ar age for a Kauai postshield dike is 4.4 Ma, older than previously-dated postshield lavas (3.95-3.58 Ma). New Ar-Ar ages show that Kauai rejuvenated stage volcanism began prior to 3.42 Ma (Izuka & Sherrod, 2011), compared to ~2.3 Ma on Niihau. Tholeiitic shield lavas from Kauai vary only slightly in trace element chemistry but have variable isotopic compositions. Subtle trends in some trace element and isotopic ratios between Napali Member shield lavas from the east and west side of Kauai support the two-shield hypothesis of Holcomb et al. (1997). Shield lavas from Niihau are chemically similar to those on Kauai, although Niihau tholeiites extend to higher 143Nd/144Nd ratios. Onland and submarine postshield rocks from Niihau are slightly more alkaline and LREE-enriched compared to shield lavas, but postshield rocks from Kauai are more chemically evolved, more LREE-enriched, and have more depleted Sr and Nd isotopic signatures than Kauai tholeiites. Postshield rocks on Kauai overlap in apparent age with lavas that are chemically like later rejuvenated stage lavas, suggesting either interfingering of the chemically distinct lavas or problems with the K-Ar ages. Rejuvenated stage lavas from the two islands differ dramatically; Kauai lavas are alkaline, LREE-enriched, and have even more depleted Sr and Nd isotopic compositions than postshield lavas, whereas Niihau lavas are only mildly alkaline, have lower REE abundances than postshield basalts, but isotopically are like

  17. Petrogenesis of the Cenozoic alkaline volcanic rock series of the České Středohoří Complex (Bohemian Massif), Czech Republic: A case for two lineages

    Czech Academy of Sciences Publication Activity Database

    Dostal, J.; Schellnutt, J. G.; Ulrych, Jaromír

    2017-01-01

    Roč. 317, June (2017), s. 677-706 ISSN 0002-9599 Institutional support: RVO:67985831 Keywords : Bohemian Massif * Central European volcanic province * continental alcaline volcanism * fractional crystallization * magmatic fluids Subject RIV: DB - Geology ; Mineralogy OBOR OECD: Geology Impact factor: 4.099, year: 2016

  18. Biogeochemistry and nitrogen cycling in an Arctic, volcanic ecosystem

    Science.gov (United States)

    Fogel, M. L.; Benning, L.; Conrad, P. G.; Eigenbrode, J.; Starke, V.

    2007-12-01

    As part of a study on Mars Analogue environments, the biogeochemistry of Sverrefjellet Volcano, Bocfjorden, Svalbard, was conducted and compared to surrounding glacial, thermal spring, and sedimentary environments. An understanding of how nitrogen might be distributed in a landscape that had extinct or very cold adapted, slow- growing extant organisms should be useful for detecting unknown life forms. From high elevations (900 m) to the base of the volcano (sea level), soil and rock ammonium concentrations were uniformly low, typically less than 1- 3 micrograms per gm of rock or soil. In weathered volcanic soils, reduced nitrogen concentrations were higher, and oxidized nitrogen concentrations lower. The opposite was found in a weathered Devonian sedimentary soil. Plants and lichens growing on volcanic soils have an unusually wide range in N isotopic compositions from -5 to +12‰, a range rarely measured in temperate ecosystems. Nitrogen contents and isotopic compositions of volcanic soils and rocks were strongly influenced by the presence or absence of terrestrial herbivores or marine avifauna with higher concentrations of N and elevated N isotopic compositions occurring as patches in areas immediately influenced by reindeer, Arctic fox ( Alopex lagopus), and marine birds. Because of the extreme conditions in this area, ephemeral deposition of herbivore feces results in a direct and immediate N pulses into the ecosystem. The lateral extent and distribution of marine- derived nitrogen was measured on a landscape scale surrounding an active fox den. Nitrogen was tracked from the bones of marine birds to soil to vegetation. Because of extreme cold, slow biological rates and nitrogen cycling, a mosaic of N patterns develops on the landscape scale.

  19. Volcanic risk

    International Nuclear Information System (INIS)

    Rancon, J.P.; Baubron, J.C.

    1995-01-01

    This project follows the previous multi-disciplinary studies carried out by the French Bureau de Recherches Geologiques et Minieres (BRGM) on the two active volcanoes of the French lesser Antilles: Mt Pelee (Martinique) and Soufriere (Guadeloupe) for which geological maps and volcanic risk studies have been achieved. The research program comprises 5 parts: the study of pyroclastic deposits from recent eruptions of the two volcanoes for a better characterization of their eruptive phenomenology and a better definition of crisis scenarios; the study of deposits and structures of active volcanoes from Central America and the study of eruptive dynamics of andesite volcanoes for a transposition to Antilles' volcanoes; the starting of a methodological multi-disciplinary research (volcanology, geography, sociology...) on the volcanic risk analysis and on the management of a future crisis; and finally, the development of geochemical survey techniques (radon, CO 2 , H 2 O) on active volcanoes of Costa-Rica and Europe (Fournaise, Furnas, Etna) and their application to the Soufriere. (J.S.). 9 refs., 3 figs

  20. Spatial distribution of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah: A mechanical analog for faulting in pyroclastic deposits on Mars

    Science.gov (United States)

    Okubo, Chris H.

    2012-01-01

    Volcanic ash is thought to comprise a large fraction of the Martian equatorial layered deposits and much new insight into the process of faulting and related fluid flow in these deposits can be gained through the study of analogous terrestrial tuffs. This study identifies a set of fault-related processes that are pertinent to understanding the evolution of fault systems in fine-grained, poorly indurated volcanic ash by investigating exposures of faults in the Miocene-aged Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah. The porosity and granularity of the host rock are found to control the style of localized strain that occurs prior to and contemporaneous with faulting. Deformation bands occur in tuff that was porous and granular at the time of deformation, while fractures formed where the tuff lost its porous and granular nature due to silicic alteration. Non-localized deformation of the host rock is also prominent and occurs through compaction of void space, including crushing of pumice clasts. Significant off-fault damage of the host rock, resembling fault pulverization, is recognized adjacent to one analog fault and may reflect the strain rate dependence of the resulting fault zone architecture. These findings provide important new guidelines for future structural analyses and numerical modeling of faulting and subsurface fluid flow through volcanic ash deposits on Mars.

  1. Volcanism at 1.45 Ma within the Yellowstone Volcanic Field, United States

    Science.gov (United States)

    Rivera, Tiffany A.; Furlong, Ryan; Vincent, Jaime; Gardiner, Stephanie; Jicha, Brian R.; Schmitz, Mark D.; Lippert, Peter C.

    2018-05-01

    Rhyolitic volcanism in the Yellowstone Volcanic Field has spanned over two million years and consisted of both explosive caldera-forming eruptions and smaller effusive flows and domes. Effusive eruptions have been documented preceding and following caldera-forming eruptions, however the temporal and petrogenetic relationships of these magmas to the caldera-forming eruptions are relatively unknown. Here we present new 40Ar/39Ar dates for four small-volume eruptions located on the western rim of the second-cycle caldera, the source of the 1.300 ± 0.001 Ma Mesa Falls Tuff. We supplement our new eruption ages with whole rock major and trace element chemistry, Pb isotopic ratios of feldspar, and paleomagnetic and rock magnetic analyses. Eruption ages for the effusive Green Canyon Flow (1.299 ± 0.002 Ma) and Moonshine Mountain Dome (1.302 ± 0.003 Ma) are in close temporal proximity to the eruption age of the Mesa Falls Tuff. In contrast, our results indicate a period of volcanism at ca 1.45 Ma within the Yellowstone Volcanic Field, including the eruption of the Bishop Mountain Flow (1.458 ± 0.002 Ma) and Tuff of Lyle Spring (1.450 ± 0.003 Ma). These high-silica rhyolites are chemically and isotopically distinct from the Mesa Falls Tuff and related 1.3 Ma effusive eruptions. The 40Ar/39Ar data from the Tuff of Lyle Spring demonstrate significant antecrystic inheritance, prevalent within the upper welded ash-flow tuff matrix, and minimal within individual pumice. Antecrysts are up to 20 kyr older than the eruption, with subpopulations of grains occurring every few thousand years. We interpret these results as an indicator for the timing of magmatic pulses into a growing magmatic system that would ultimately erupt the Tuff of Lyle Spring, and which we more broadly interpret as the tempo of crustal accumulation associated with bimodal magmatism. We propose a system whereby chemically, isotopically, and temporally distinct, isolated small-volume magma batches are

  2. U-Pb zircon geochronology of Late Devonian to Early Carboniferous extension-related silicic volcanism in the northern New England Fold Belt

    International Nuclear Information System (INIS)

    Bryan, S.E.; Holcombe, R.J.; Fielding, C.R.; Allen, C.M.

    2004-01-01

    Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of zircons confirm a Late Devonian to Early Carboniferous age (ca 360-350 Ma) for silicic volcanic rocks of the Campwyn Volcanics and Yarrol terrane of the northern New England Fold Belt (Queensland). These rocks are coeval with silicic volcanism recorded elsewhere in the fold belt at this time (Connors Arch, Drummond Basin). The new U-Pb zircon ages, in combination with those from previous studies, show that silicic magmatism was both widespread across the northern New England Fold Belt (>250 000 km 2 and >500 km inboard of plate margin) and protracted, occurring over a period of -15 million years. Zircon inheritance is commonplace in the Late Devonian - Early Carboniferous volcanics, reflecting anatectic melting and considerable reworking of continental crust. Inherited zircon components range from ca 370 to ca 2050 Ma, with Middle Devonian (385-370 Ma) zircons being common to almost all dated units. Precambrian zircon components record either Precambrian crystalline crust or sedimentary accumulations that were present above or within the zone of magma formation This contrasts with a lack of significant zircon inheritance in younger Permo-Carboniferous igneous rocks intruded through,and emplaced on top of, the Devonian-Carboniferous successions. The inheritance data and location of these volcanic rocks at the eastern margins of the northern New England Fold Belt, coupled with Sr-Nd, Pb isotopic data and depleted mantle model ages for Late Palaeozoic and Mesozoic magmatism, imply that Precambrian mafic and felsic crustal materials (potentially as old as 2050 Ma), or at the very least Lower Palaeozoic rocks derived from the reworking of Precambrian rocks, comprise basement to the eastern parts of the fold belt. This crustal basement architecture may be a relict from the Late Proterozoic breakup of the Rodinian supercontinent. Copyright (2004) Geological Society of Australia

  3. Model to Assess the Quality of Magmatic Rocks for Reliable and Sustainable Constructions

    Directory of Open Access Journals (Sweden)

    Mihaela Toderaş

    2017-10-01

    Full Text Available Geomechanical assessment of rocks requires knowledge of phenomena that occur under the influence of internal and external factors at a macroscopic or microscopic scale, when rocks are submitted to different actions. To elucidate the quantitative and qualitative geomechanical behavior of rocks, knowing their geological and physical–mechanical characteristics becomes an imperative. Mineralogical, petrographical and chemical analyses provided an opportunity to identify 15 types of igneous rocks (gabbro, diabases, granites, diorites, rhyolites, andesites, and basalts, divided into plutonic and volcanic rocks. In turn, these have been grouped into acidic, neutral (intermediate and basic magmatites. A new ranking method is proposed, based on considering the rock characteristics as indicators of quantitative assessment, and the grading system, by given points, allowing the rocks framing in admissibility classes. The paper is structured into two parts, experimental and interpretation of experimental data, showing the methodology to assess the quality of igneous rocks analyzed, and the results of theoretical and experimental research carried out on the analyzed rock types. The proposed method constitutes an appropriate instrument for assessment and verification of the requirements regarding the quality of rocks used for sustainable construction.

  4. Sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone terrane, western Dharwar Craton: Implications on pyroclastic volcanism and sedimentation in an active continental margin

    Science.gov (United States)

    Manikyamba, C.; Saha, Abhishek; Ganguly, Sohini; Santosh, M.; Lingadevaru, M.; Rajanikanta Singh, M.; Subba Rao, D. V.

    2014-12-01

    We report sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone belt of western Dharwar Craton which is associated with rhyolites, chlorite schists and pyroclastic rocks. The pyroclastic rocks of Yalavadahalli area of Shimoga greenstone belt host volcanogenic Pb-Cu-Zn mineralization. The sediment-infill volcanic breccia is clast-supported and comprises angular to sub-angular felsic volcanic clasts embedded in a dolomitic matrix that infilled the spaces in between the framework of volcanic clasts. The volcanic clasts are essentially composed of alkali feldspar and quartz with accessory biotite and opaques. These clasts have geochemical characteristics consistent with that of the associated potassic rhyolites from Daginkatte Formation. The rare earth elements (REE) and high field strength element (HFSE) compositions of the sediment-infill volcanic breccia and associated mafic and felsic volcanic rocks suggest an active continental margin setting for their generation. Origin, transport and deposition of these rhyolitic clasts and their aggregation with infiltrated carbonate sediments may be attributed to pyroclastic volcanism, short distance transportation of felsic volcanic clasts and their deposition in a shallow marine shelf in an active continental margin tectonic setting where the rhyolitic clasts were cemented by carbonate material. This unique rock type, marked by close association of pyroclastic volcanic rocks and shallow marine shelf sediments, suggest shorter distance between the ridge and shelf in the Neoarchean plate tectonic scenario.

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

    Directory of Open Access Journals (Sweden)

    Marinel Kovacs

    2003-04-01

    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.

  6. Payenia volcanic province, southern Mendoza, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina; Holm, Paul Martin; Llambias, Eduardo Jorge

    2013-01-01

    The Pleistocene to Holocene Payenia volcanic province is a backarc region of 60,000 km2 in Mendoza, Argentina, which is dominated by transitional to alkaline basalts and trachybasalts. We present major and trace element compositions of 139 rocks from this area of which the majority are basaltic...

  7. Volcanic features of Io

    International Nuclear Information System (INIS)

    Carr, M.H.; Masursky, H.; Strom, R.G.; Terrile, R.J.

    1979-01-01

    The volcanic features of Io as detected during the Voyager mission are discussed. The volcanic activity is apparently higher than on any other body in the Solar System. Its volcanic landforms are compared with features on Earth to indicate the type of volcanism present on Io. (U.K.)

  8. Can rain cause volcanic eruptions?

    Science.gov (United States)

    Mastin, Larry G.

    1993-01-01

    Volcanic eruptions are renowned for their violence and destructive power. This power comes ultimately from the heat and pressure of molten rock and its contained gases. Therefore we rarely consider the possibility that meteoric phenomena, like rainfall, could promote or inhibit their occurrence. Yet from time to time observers have suggested that weather may affect volcanic activity. In the late 1800's, for example, one of the first geologists to visit the island of Hawaii, J.D. Dana, speculated that rainfall influenced the occurrence of eruptions there. In the early 1900's, volcanologists suggested that some eruptions from Mount Lassen, Calif., were caused by the infiltration of snowmelt into the volcano's hot summit. Most such associations have not been provable because of lack of information; others have been dismissed after careful evaluation of the evidence.

  9. Volcanism and associated hazards: the Andean perspective

    Science.gov (United States)

    Tilling, R. I.

    2009-12-01

    Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (Colombia) killed about 25 000 people - the worst volcanic disaster in the Andean region as well as the second worst in the world in the 20th century. The Ruiz tragedy has been attributed largely to ineffective communications of hazards information and indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant

  10. Basaltic volcanic episodes of the Yucca Mountain region

    International Nuclear Information System (INIS)

    Crowe, B.M.

    1990-01-01

    The purpose of this paper is to summarize briefly the distribution and geologic characteristics of basaltic volcanism in the Yucca Mountain region during the last 10--12 Ma. This interval largely postdates the major period of silicic volcanism and coincides with and postdates the timing of major extensional faulting in the region. Field and geochronologic data for the basaltic rocks define two distinct episodes. The patterns in the volume and spatial distribution of these basaltic volcanic episodes in the central and southern part of the SNVF are used as a basis for forecasting potential future volcanic activity in vicinity of Yucca Mountain. 33 refs., 2 figs

  11. Geology and porphyry copper-type alteration-mineralization of igneous rocks at the Christmas Mine, Gila County, Arizona

    Science.gov (United States)

    Koski, Randolph A.

    1979-01-01

    The Christmas copper deposit, located in southern Gila County, Arizona, is part of the major porphyry copper province of southwestern North America. Although Christmas is known for skarn deposits in Paleozoic carbonate rocks, ore-grade porphyry-type copper mineralization also occurs in a composite granodioritic intrusive complex and adjacent mafic volcanic country rocks. This study considers the nature, distribution, and genesis of alteration-mineralization in the igneous rock environment at Christmas. At the southeast end of the Dripping Spring Mountains, the Pennsylvanian Naco Limestone is unconformably overlain by the Cretaceous Williamson Canyon Volcanics, a westward-thinning sequence of basaltic volcanic breccia and lava flows, and subordinate clastic sedimentary rocks. Paleozoic and Mesozoic strata are intruded by Laramide-age dikes, sills, and small stocks of hornblende andesite porphyry and hornblende rhyodacite porphyry, and the mineralized Christmas intrusive complex. Rocks of the elongate Christmas stock, intruded along an east-northeast-trending fracture zone, are grouped into early, veined quartz diorite (Dark Phase), biotite granodiorite porphyry (Light Phase), and granodiorite; and late, unveined dacite porphyry and granodiorite porphyry. Biotite rhyodacite porphyry dikes extending east and west from the vicinity of the stock are probably coeval with biotite granodiorite porphyry. Accumulated normal displacement of approximately 1 km along the northwest-trending Christmas-Joker fault system has juxtaposed contrasting levels (lower, intrusive-carbonate rock environment and upper, intrusive-volcanic rock environment) within the porphyry copper system. K-Ar age determinations and whole-rock chemical analyses of the major intrusive rock types indicate that Laramide calc-alkaline magmatism and ore deposition at Christmas evolved over an extended period from within the Late Cretaceous (~75-80 m.y. ago) to early Paleocene (~63-61 m.y. ago). The sequence of

  12. Results of isotopic geochemical and mineralogical investigations of crystalline rocks of the Carpathian Massif in 1973-1975

    International Nuclear Information System (INIS)

    Shcherbak, N.P.; Bartnitskij, E.N.; Eliseeva, G.D.

    1979-01-01

    The most frequent accesory mineral in crystalline rocks in the Czechoslovak and Ukrainian Carpathians is zircon, the least frequent is monazite. The differences are described in the mineralogical properties of zircon of different origin. For dating volcanism, the content and the isotope composition was determined of U and Pb in zircon and of U, Pb and Th in monazite. The earliest volcanic processes occurred in the Eastern Carpathians approximately 600 to 640 million years ago, in the Western Carpathians approximately 400 million years ago. (Ha)

  13. Mercury and Iodine systematics of volcanic arc fluids

    Science.gov (United States)

    Varekamp, J. C.; Kading, T.; Fehn, U.; Lu, Z.

    2008-12-01

    The mantle has low Mercury and Iodine concentrations, but these elements occur in volcanic gases and hydrothermal fluids at ppb (Hg) and ppm (Iodine) levels. Possibly, the Hg and Iodine concentrations in volcanic fluids reflect subducted sediment sources in arc magmas. Iodine is a biophilic element, and I129/I values indicate that subducted sediment (especially organic matter) is an important Iodine source for arc magmas. It is uncertain if this is true for Hg as well, although in the surface environment Hg is commonly associated with organic matter. We present 60 new analyses of Hg and I in fluids from volcanoes in Central America, New Zealand, Japan, and the Cascades. A first assessment suggests that Iodine is released to some degree in the early stage of subduction in the forearc, whereas Hg may be released largely below the main volcanic arc. Isotope and trace element signatures of volcanic rocks of the investigated volcanoes show no simple correlation with Hg or Iodine abundances. The acid hot spring fluids of Copahue volcano (Argentina) carried ~ 200 ppt Hg in January 1999, ~80 ppt Hg in March 2008, and 90 ppt Hg in the crater lake in March 1997. The dissolved Hg fluxes from the Copahue hydrothermal system are ~300 gr Hg/year in 1999 and ~130 gr Hg/year in 2008. The bulk hydrothermal Hg flux (particle bound+dissolved) in 2008 was ~ 350 gr Hg/year. The potential Mercury evasion from these hydrothermal spring fluids into the air has not yet been incorporated in these estimates.

  14. Geochemical characteristics and petrogenesis of phonolites and trachytic rocks from the České Středohoří Volcanic Complex, the Ohře Rift, Bohemian Massif

    Czech Academy of Sciences Publication Activity Database

    Ackerman, Lukáš; Ulrych, Jaromír; Řanda, Zdeněk; Erban, V.; Hegner, E.; Magna, T.; Balogh, K.; Frána, Jaroslav; Lang, Miloš; Novák, Jiří Karel

    224/225, May (2015), s. 256-271 ISSN 0024-4937 R&D Projects: GA AV ČR IAA3048201 Institutional support: RVO:67985831 ; RVO:61389005 Keywords : phonolite * trachyte * Sr–Nd–Li isotopes * Cenozoic alkaline volcanism * Ohře (Eger) Rift * Bohemian Massif Subject RIV: DD - Geochemistry Impact factor: 3.723, year: 2015

  15. Depositional environment of the Onverwacht sedimentary rocks Barberton greenstone belt, South Africa

    Science.gov (United States)

    Paris, I. A.

    The Onverwacht Group is the basal part of the ca 3.5 Ga succession forming the Barberton greenstone belt. It comprises a volcanic pile overlain by a thin layer of volcaniclastic sediments which, due to silicification, are extremely well preserved. There has been a controversy as to how and in what environment these sediments were formed, different sets of data being presented to reach opposite conclusions. The Onverwacht Group has been extensively repeated tectonically and here for the first time, sediments from different structural levels are studied together. Three separate facies have been recognised, a distal and proximal turbidite facies and a subaerial facies. Deposition of Onverwacht Group sedimentary rocks occurred in an oceanic basin characterised by the presence of emergent volcanic islands. After eruption, material was deposited both subaerially and in a shallow submarine environment on the volcanic slopes and, as a result of pyroclastic flow, in the deeper parts of the basin.

  16. Volcanic glasses, their origins and alteration processes

    Science.gov (United States)

    Friedman, I.; Long, W.

    1984-01-01

    Natural glass can be formed by volcanic processes, lightning (fulgarites) burning coal, and by meteorite impact. By far the most common process is volcanic - basically the glass is rapidly chilled molten rock. All natural glasses are thermodynamically unstable and tend to alter chemically or to crystallize. The rate of these processes is determined by the chemical composition of the magma. The hot and fluid basaltic melts have a structure that allows for rapid crystal growth, and seldom forms glass selvages greater than a few centimeters thick, even when the melt is rapidly cooled by extrusion in the deep sea. In contrast the cooler and very viscous rhyolitic magmas can yield bodies of glass that are tens of meters thick. These highly polymerized magmas have a high silica content - often 71-77% SiO2. Their high viscosity inhibits diffusive crystal growth. Basalt glass in sea water forms an alteration zone called palagonite whose thickness increases linearly with time. The rate of diffusion of water into rhyolitic glass, which follows the relationship - thickness = k (time) 1 2, has been determined as a function of the glass composition and temperature. Increased SiO2 increases the rate, whereas increased CaO, MgO and H2O decrease the rate. The activation energy of water diffusion varies from about 19 to 22 kcal/mol. for the glasses studied. The diffusion of alkali out of rhyolite glass occurs simultaneously with water diffusion into the glass. The rate of devitrification of rhyolitic glass is a function of the glass viscosity, which in turn is a function of water content and temperature. Although all of the aforementioned processes tend to destroy natural glasses, the slow rates of these processes, particularly for rhyolitic glass, has allowed samples of glass to persist for 60 million years. ?? 1984.

  17. Soft Rock Yields Clues to Mars' Past

    Science.gov (United States)

    2004-01-01

    [figure removed for brevity, see original site] Figure 1 This image taken by the Mars Exploration Rover Spirit shows the rock outcrop dubbed 'Clovis.' The rock was discovered to be softer than other rocks studied so far at Gusev Crater after the rover easily ground a hole into it with its rock abrasion tool. Spirit's solar panels can be seen in the foreground. This image was taken by the rover's navigation camera on sol 205 (July 31, 2004). Elemental Trio Found in 'Clovis' Figure 1 above shows that the interior of the rock dubbed 'Clovis' contains higher concentrations of sulfur, bromine and chlorine than basaltic, or volcanic, rocks studied so far at Gusev Crater. The data were taken by the Mars Exploration Rover Spirit's alpha particle X-ray spectrometer after the rover dug into Clovis with its rock abrasion tool. The findings might indicate that this rock was chemically altered, and that fluids once flowed through the rock depositing these elements.

  18. Supervolcanoes within an ancient volcanic province in Arabia Terra, Mars.

    Science.gov (United States)

    Michalski, Joseph R; Bleacher, Jacob E

    2013-10-03

    Several irregularly shaped craters located within Arabia Terra, Mars, represent a new type of highland volcanic construct and together constitute a previously unrecognized Martian igneous province. Similar to terrestrial supervolcanoes, these low-relief paterae possess a range of geomorphic features related to structural collapse, effusive volcanism and explosive eruptions. Extruded lavas contributed to the formation of enigmatic highland ridged plains in Arabia Terra. Outgassed sulphur and erupted fine-grained pyroclastics from these calderas probably fed the formation of altered, layered sedimentary rocks and fretted terrain found throughout the equatorial region. The discovery of a new type of volcanic construct in the Arabia volcanic province fundamentally changes the picture of ancient volcanism and climate evolution on Mars. Other eroded topographic basins in the ancient Martian highlands that have been dismissed as degraded impact craters should be reconsidered as possible volcanic constructs formed in an early phase of widespread, disseminated magmatism on Mars.

  19. Volcanic signals in oceans

    KAUST Repository

    Stenchikov, Georgiy L.; Delworth, Thomas L.; Ramaswamy, V.; Stouffer, Ronald J.; Wittenberg, Andrew; Zeng, Fanrong

    2009-01-01

    Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean

  20. Reservoir characteristics and control factors of Carboniferous volcanic gas reservoirs in the Dixi area of Junggar Basin, China

    Directory of Open Access Journals (Sweden)

    Ji'an Shi

    2017-02-01

    Full Text Available Field outcrop observation, drilling core description, thin-section analysis, SEM analysis, and geochemistry, indicate that Dixi area of Carboniferous volcanic rock gas reservoir belongs to the volcanic rock oil reservoir of the authigenic gas reservoir. The source rocks make contact with volcanic rock reservoir directly or by fault, and having the characteristics of near source accumulation. The volcanic rock reservoir rocks mainly consist of acidic rhyolite and dacite, intermediate andesite, basic basalt and volcanic breccia: (1 Acidic rhyolite and dacite reservoirs are developed in the middle-lower part of the structure, have suffered strong denudation effect, and the secondary pores have formed in the weathering and tectonic burial stages, but primary pores are not developed within the early diagenesis stage. Average porosity is only at 8%, and the maximum porosity is at 13.5%, with oil and gas accumulation showing poor performance. (2 Intermediate andesite and basic basalt reservoirs are mainly distributed near the crater, which resembles the size of and suggests a volcanic eruption. Primary pores are formed in the early diagenetic stage, secondary pores developed in weathering and erosion transformation stage, and secondary fractures formed in the tectonic burial stage. The average porosity is at 9.2%, and the maximum porosity is at 21.9%: it is of the high-quality reservoir types in Dixi area. (3 The volcanic breccia reservoir has the same diagenetic features with sedimentary rocks, but also has the same mineral composition with volcanic rock; rigid components can keep the primary porosity without being affected by compaction during the burial process. At the same time, the brittleness of volcanic breccia reservoir makes it easily fracture under the stress; internal fracture was developmental. Volcanic breccia developed in the structural high part and suffered a long-term leaching effect. The original pore-fracture combination also made

  1. Sr, Nd and Pb isotope and geochemical data from the Quaternary Nevado de Toluca volcano, a source of recent adakitic magmatism, and the Tenango Volcanic Field, Mexico

    Science.gov (United States)

    Martínez-Serrano, Raymundo G.; Schaaf, Peter; Solís-Pichardo, Gabriela; Hernández-Bernal, Ma. del Sol; Hernández-Treviño, Teodoro; Julio Morales-Contreras, Juan; Macías, José Luis

    2004-11-01

    Volcanic activity at Nevado de Toluca (NT) volcano began 2.6 Ma ago with the emission of andesitic lavas, but over the past 40 ka, eruptions have produced mainly lava flows and pyroclastic deposits of predominantly orthopyroxene-hornblende dacitic composition. In the nearby Tenango Volcanic Field (TVF) pyroclastic products and lava flows ranging in composition from basaltic andesite to andesite were erupted at most of 40 monogenetic volcanic centers and were coeval with the last stages of NT. All volcanic rocks in the study area are characterized by a calc-alkaline affinity that is consistent with a subduction setting. Relatively high concentrations of Sr (>460 ppm) coupled with low Y (45 km) that underlies the volcanoes of the study area, the geochemical and isotopic patterns of these rocks indicate low interaction with this crust. NT volcano was constructed at the intersection of three fault systems, and it seems that the Plio-Quaternary E-W system played an important role in the ascent and storage of magmas during the recent volcanic activity in the two regions. Chemical and textural features of orthopyroxene, amphibole and Fe-Ti oxides from NT suggest that crystallization of magmas occurred at polybaric conditions, confirming the rapid upwelling of magmas.

  2. Radioisotope distribution characteristics of the groundwater system in volcanic-type U deposits and isotope-dating estimation of the system

    International Nuclear Information System (INIS)

    Zhou Bingguan

    1988-01-01

    On the basis of groundwater sample measurements collected from the uranogenic belt of Mesozoic volcanic rocks in East China, the distribution characteristics of radioisotopes, including the total U content (CΣu), the activity of nuclides (Aui) or their activity ratio (ARu) and the relationship among the three ((Aui,ARu)=f(CΣu)), have been studied. Also, it is performed for radioactive water halos in the area to be divided into four various mineralization tendencies: (1) the convergent tendency of negative correlation, which has the genetic relationship with the primary U accumulation in volcanic rocks; (2) the scattered tendency of positive correlation, which is intimately related to epigenetic U mineralization in the supergene zone of volcanic rocks or in the sandstones; (3) the both positive and negative multiple-correlative tendency, which indicates that the primary volcanic-type U deposit has been leached and destroyed, and the secondary U enrichment has occurred within the supergene zone; (4) non-correlative tendency, which mainly results from increasing dispersion U. For the above recognitions, an evolution model for radioactive water halos related to this type of U deposit has been derived, and an attempt to estimate the radioisotopic age of the groundwater system also has been made. (author). 14 refs, 9 figs, 2 tabs

  3. A 150-ka-long record for the volcano-tectonic deformation of Central Anatolian Volcanic Province

    Science.gov (United States)

    Karabacak, Volkan; Tonguç Uysal, I.; Ünal-İmer, Ezgi; Mutlu, Halim; Zhao, Jian-xin

    2017-04-01

    The Anatolian Block represents one of the most outstanding examples of intra-plate deformation related to continental collision. Deformation related to the convergence of the Afro-Arabian continent toward north gives rise to widespread and intense arc volcanism in the Central Anatolia. All the usual studies on dating the volcano-tectonic deformation of the region are performed entirely on volcanic events of the geological record resulted in eruptions. However, without volcanic eruption, magma migration and related fluid pressurization also generate crustal deformation. In the current study has been funded by the Scientific and Technological Research Council of Turkey with the project no. 115Y497, we focused on fracture systems and their carbonate veins around the Ihlara Valley (Cappadocia) surrounded by well-known volcanic centers with latest activities of the southern Central Anatolian Volcanic Province. We dated 37 samples using the Uranium-series technique and analyzed their isotope systematics from fissure veins, which are thought to be controlled by the young volcanism in the region. Our detailed fracture analyses in the field show that there is a regional dilatation as a result of a NW-SE striking extension which is consistent with the results of recent GPS studies. The Uranium-series results indicate that fracture development and associated carbonate vein deposition occurred in the last 150 ka. Carbon and oxygen isotope systematics have almost remained unchanged in the studied time interval. Although veins in the region were precipitated from fluids primarily of meteoric origin, fluids originating from water-rock interaction also contribute for the deposition of carbonate veins. The age distribution indicates that the crustal deformation intensified during 7 different period at about 4.7, 34, 44, 52, 83, 91, 149 ka BP. Four of these periods (4.7, 34, 91, 149 ka BP) correspond to the volcanic activities suggested in the previous studies. The three crustal

  4. Mineral and rock chemistry of Mata da Corda Kamafugitic Rocks (Minas Gerais State, Brazil)

    International Nuclear Information System (INIS)

    Albuquerque Sgarbi, Patricia B. de; Valenca, Joel G.

    1995-01-01

    The volcanic rocks of the Mata da Corda Formation (Upper Cretaceous) in Minas Gerais, Brazil, are mafic potassic to ultra potassic rocks of kamafugitic affinity containing essentially clinopyroxenes, perovskite, magnetite and occasionally olivine, phlogopite, melilite pseudomorphs and apatite. The felsic phases are kalsilite and/or leucite pseudomorphs. The rocks are classified as mafitites, leucitites and kalsilitites. The analysis of the available data of the rocks studied, based on the relevant aspects of the main proposals for the classification of alkaline mafic to ultramafic potassic rocks leads to the conclusion that Sahama's (1974) proposal to divide potassium rich alkaline rocks in two large families is the one to which the Mata da Corda rocks adapt best. According to this and the data in the literature on the mineralogy and mineral and rock chemistries of the other similar occurrences, these rocks may be interpreted as alkaline potassic to ultra potassic rocks of hamafugitic affinity. 11 figs., 5 tabs

  5. The unzipping of Africa and South America; New insights from the Etendeka and younger volcanic events along the Angola/Namibia margin.

    Science.gov (United States)

    Jerram, D. A.

    2015-12-01

    The volcanic margin along Angola is relatively poorly constrained. This study uses new petrographic, geochronological and geochemical observations on a new sample set collected along the margin to help understand the various types and relative timings of volcanic events along the margin. This new study has identified 3 main volcanic events that occur at ~100Ma (Sumbe event 1), 90-92Ma (Serra de Neve (SDN)-Elefantes event 2) and 80-81Ma (Namibe event 3), with the oldest event in the north of the margin and younging southwards. This is contrasting with the main Etendeka pulse in Namibia at around 130 Ma. There is a marked variety of igneous rocks along the margin with a grouping of evolved alkaline rocks in the central SDN-Elefantes section, basic submarine volcanics in the north, and basanite eruptions in the southern section. There is some overlap with geochemical types along the margin. The Sumbe event contains predominantly submarine volcanics and shallow Intrusions. SDN-Elefantes rocks have a mixed type but with a distinctive feldspar rich evolved alkali suite of rocks (nepheline syenites and variations around this composition) which occur as lava flows and shallow intrusions as well as making up the core of the SDN complex. The SDN complex itself is analogous in size to the main volcanic centres in Namibia (such as Messum, Brandberg etc.) and suggests that large volcanic feeding centres are still active along the margin as young as 90ma. These in turn will form large volcano-topographic features. In the south the Ponta Negra and Canico sites mainly contain basanites in the form of lava flows, invasive flows and shallow intrusions. At Canico one intrusive plug was sampled with a similar composition to the evolved SDN-Elefantes suite. In all three events it is clear that the volcanic systems have interacted with the sedimentary systems, in some cases dynamically, in others with regional implications for volcano-tectonic uplift. Specific thanks is given for

  6. Rock strength under explosive loading

    International Nuclear Information System (INIS)

    Rimer, N.; Proffer, W.

    1993-01-01

    This presentation emphasizes the importance of a detailed description of the nonlinear deviatoric (strength) response of the surrounding rock in the numerical simulation of underground nuclear explosion phenomenology to the late times needed for test ban monitoring applications. We will show how numerical simulations which match ground motion measurements in volcanic tuffs and in granite use the strength values obtained from laboratory measurements on small core samples of these rocks but also require much lower strength values after the ground motion has interacted with the rock. The underlying physical mechanisms for the implied strength reduction are not yet well understood, and in fact may depend on the particular rock type. However, constitutive models for shock damage and/or effective stress have been used successfully at S-Cubed in both the Geophysics Program (primarily for DARPA) and the Containment Support Program (for DNA) to simulate late time ground motions measured at NTS in many different rock types

  7. Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling

    Science.gov (United States)

    Chiaradia, Massimo; Müntener, Othmar; Beate, Bernardo; Fontignie, Denis

    2009-11-01

    In the Northern Andes of Ecuador, a broad Quaternary volcanic arc with significant across-arc geochemical changes sits upon continental crust consisting of accreted oceanic and continental terranes. Quaternary volcanic centers occur, from west to east, along the Western Cordillera (frontal arc), in the Inter-Andean Depression and along the Eastern Cordillera (main arc), and in the Sub-Andean Zone (back-arc). The adakite-like signatures of the frontal and main arc volcanoes have been interpreted either as the result of slab melting plus subsequent slab melt-mantle interactions or of lower crustal melting, fractional crystallization, and assimilation processes. In this paper, we present petrographic, geochemical, and isotopic (Sr, Nd, Pb) data on dominantly andesitic to dacitic volcanic rocks as well as crustal xenolith and cumulate samples from five volcanic centers (Pululagua, Pichincha, Ilalo, Chacana, Sumaco) forming a NW-SE transect at about 0° latitude and encompassing the frontal (Pululagua, Pichincha), main (Ilalo, Chacana), and back-arc (Sumaco) chains. All rocks display typical subduction-related geochemical signatures, such as Nb and Ta negative anomalies and LILE enrichment. They show a relative depletion of fluid-mobile elements and a general increase in incompatible elements from the front to the back-arc suggesting derivation from progressively lower degrees of partial melting of the mantle wedge induced by decreasing amounts of fluids released from the slab. We observe widespread petrographic evidence of interaction of primary melts with mafic xenoliths as well as with clinopyroxene- and/or amphibole-bearing cumulates and of magma mixing at all frontal and main arc volcanic centers. Within each volcanic center, rocks display correlations between evolution indices and radiogenic isotopes, although absolute variations of radiogenic isotopes are small and their values are overall rather primitive (e.g., ɛNd = +1.5 to +6, 87Sr/86Sr = 0

  8. Carbonatite ring-complexes explained by caldera-style volcanism.

    Science.gov (United States)

    Andersson, Magnus; Malehmir, Alireza; Troll, Valentin R; Dehghannejad, Mahdieh; Juhlin, Christopher; Ask, Maria

    2013-01-01

    Carbonatites are rare, carbonate-rich magmatic rocks that make up a minute portion of the crust only, yet they are of great relevance for our understanding of crustal and mantle processes. Although they occur in all continents and from Archaean to present, the deeper plumbing system of carbonatite ring-complexes is usually poorly constrained. Here, we show that carbonatite ring-complexes can be explained by caldera-style volcanism. Our geophysical investigation of the Alnö carbonatite ring-complex in central Sweden identifies a solidified saucer-shaped magma chamber at ~3 km depth that links to surface exposures through a ring fault system. Caldera subsidence during final stages of activity caused carbonatite eruptions north of the main complex, providing the crucial element to connect plutonic and eruptive features of carbonatite magmatism. The way carbonatite magmas are stored, transported and erupt at the surface is thus comparable to known emplacement styles from silicic calderas.

  9. Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

    Science.gov (United States)

    Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

    1995-01-01

    Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

  10. Rock fragmentation

    Energy Technology Data Exchange (ETDEWEB)

    Brown, W.S.; Green, S.J.; Hakala, W.W.; Hustrulid, W.A.; Maurer, W.C. (eds.)

    1976-01-01

    Experts in rock mechanics, mining, excavation, drilling, tunneling and use of underground space met to discuss the relative merits of a wide variety of rock fragmentation schemes. Information is presented on novel rock fracturing techniques; tunneling using electron beams, thermocorer, electric spark drills, water jets, and diamond drills; and rock fracturing research needs for mining and underground construction. (LCL)

  11. Moessbauer Study of Sedimentary Rocks from King George Island, Antarctica

    International Nuclear Information System (INIS)

    Kuzmann, E.; Souza, P. A. de; Schuch, L. A.; Oliveira, A. C. de; Garg, R.; Garg, V. K.

    2002-01-01

    The separation of continents at the periphery of Antarctica occurred about 180 ma ago due to volcanic activity. Geological faults can be very important in the study of geological occurrences. Such geological faults occur across the Admiralty Bay, King George Island, and have been studied in detail previously. Controversial statements were given in earlier works, based on conventional geological investigations, as to whether altered 'Jurassic' and unaltered Tertiary rocks were separated by a major fault which goes across the Admiralty Bay, or whether there is no difference in the alteration of the rocks located at either side of the fault. The aim of our work is to investigate rock samples from the Admiralty Bay of King George Island, Antarctica, from different locations on both sides of the geological fault. For these investigations 57 Fe Moessbauer spectroscopy and X-ray diffractometry were used. We have found that the phase composition, and the iron distribution among the crystallographic sites of iron-bearing minerals, are characteristic of the location of the rock samples from the Admiralty Bay of King George Island. There is a much higher amount of iron oxides in the rocks from the south part of the geological fault than in the north part. The differences in the mineral composition and iron distribution showed that the rocks in the southern part of the geological fault of King George Island are significantly altered compared to the rocks in the northern part. Our present results support and complement well the results obtained earlier on soils from King George Island.

  12. Hydrothermal Alteration Products as Key to Formation of Duricrust and Rock Coatings on Mars

    Science.gov (United States)

    Bishop, J. L.

    1999-03-01

    A model is presented for the formation of duricrust and rock coatings on Mars. Hydrothermal alteration of volcanic tephra may produce a corrosive agent that attacks rock surfaces and binds dust particles to form duricrust.

  13. Uranium occurrence in major rock types by fission-track mapping

    International Nuclear Information System (INIS)

    Ledger, E.G.; Bomber, B.J.; Schaftenaar, W.E.; Tieh, T.T.

    1984-01-01

    Microscopic occurrence of uranium has been determined in about 50 igneous rocks from various location, and in a genetically unrelated sandstone from south Texas. Precambrian granites from the Llano uplift of central Texas contain from a few ppm uranium (considered normal) to over 100 ppm on a whole-rock basis. In granite, uranium is concentrated in: (1) accessory minerals including zircon, biotite, allanite, Fe-Ti oxides, and altered sphene, (2) along grain boundaries and in microfractures by precipitation from deuteric fluids, and (3) as point sources (small inclusions) in quartz and feldspars. Tertiary volcanic rocks from the Davis Mountains of west Texas include diverse rock types from basalt to rhyolite. Average uranium contents increase from 1 ppm in basalts to 7 ppm in rhyolites. Concentration occurs: (1) in iron-titanium-oxides, zircon, and rutile, (2) in the fine-grained groundmass as uniform and point-source concentrations, and (3) as late uranium in cavities associated with banded, silica-rich material. Uranium in ore-grade sandstone is concentrated to more than 3%. Specific occurrences include (1) leucoxene and/or anatase, (2) opaline and calcite cements, (3) mud clasts and altered volcanic rock fragments, and (4) in a few samples, as silt-size uranium- and molybdenum-rich spheres. Uranium content is quite low in pyrite, marcasite, and zeolites

  14. New Approach for Monitoring Seismic and Volcanic Activities Using Microwave Radiometer Data

    Science.gov (United States)

    Maeda, Takashi; Takano, Tadashi

    Interferograms formed from the data of satellite-borne synthetic aperture radar (SAR) enable us to detect slight land-surface deformations related to volcanic eruptions and earthquakes. Currently, however, we cannot determine when land-surface deformations occurred with high time resolution since the time lag between two scenes of SAR used to form interferograms is longer than the recurrent period of the satellite carrying it (several tens of days). In order to solve this problem, we are investigating new approach to monitor seismic and vol-canic activities with higher time resolution from satellite-borne sensor data, and now focusing on a satellite-borne microwave radiometer. It is less subject to clouds and rainfalls over the ground than an infrared spectrometer, so more suitable to observe an emission from land sur-faces. With this advantage, we can expect that thermal microwave energy by increasing land surface temperatures is detected before a volcanic eruption. Additionally, laboratory experi-ments recently confirmed that rocks emit microwave energy when fractured. This microwave energy may result from micro discharges in the destruction of materials, or fragment motions with charged surfaces of materials. We first extrapolated the microwave signal power gener-ated by rock failures in an earthquake from the experimental results and concluded that the microwave signals generated by rock failures near the land surface are strong enough to be detected by a satellite-borne radiometer. Accordingly, microwave energy generated by rock failures associated with a seismic activity is likely to be detected as well. However, a satellite-borne microwave radiometer has a serious problem that its spatial res-olution is too coarse compared to SAR or an infrared spectrometer. In order to raise the possibility of detection, a new methodology to compensate the coarse spatial resolution is es-sential. Therefore, we investigated and developed an analysis method to detect local

  15. Volcanic Aggregates from Azores and Madeira Archipelagos (Portugal): An Overview Regarding the Alkali Silica Reactions

    Science.gov (United States)

    Medeiros, Sara; Ramos, Violeta; Fernandes, Isabel; Nunes, João Carlos; Fournier, Benoit; Santos Silva, António; Soares, Dora

    2017-12-01

    Alkali-silica reaction (ASR) is a type of deterioration that has been causing serious expansion, cracking and durability/operational issues in concrete structures worldwide. The presence of sufficient moisture, high alkali content in the cement paste and reactive forms of silica in the aggregates are the required conditions for this reaction to occur. Reactive aggregates of volcanic nature have been reported in different countries such as Japan, Iceland and Turkey, among others. The presence of silica minerals and SiO2-rich volcanic glass is regarded as the main cause for the reactivity of volcanic rocks. In Portugal, volcanic aggregates are mainly present in Azores and Madeira Archipelagos and, for several years, there was no information regarding the potential alkali-reactivity of these rocks. Since the beginning of this decade some data was obtained by the work of Medeiros (2011) and Ramos (2013) and by the national research projects ReAVA, (Characterization of potential reactivity of the volcanic aggregates from the Azores Archipelago: implications on the durability of concrete structures) and IMPROVE (Improvement of performance of aggregates in the inhibition of alkali-aggregate reactions in concrete), respectively. In order to investigate the potential alkali-reactivity of aggregates from both archipelagos, a total of sixteen aggregates were examined under the optical microscope and, some of them, also under the Scanning Electron Microscope with Energy Dispersive X-ray Spectroscopy. A set of geochemical analyses and laboratory expansion tests were also performed on those volcanic aggregates. The main results showed that the presence of volcanic glass is rare in both archipelagos and that the samples of Madeira Archipelago contain clay minerals (mainly from scoria/tuff formations inter-layered with the lava flows), which can play a role in concrete expansion. The results of the laboratory tests showed that one of the samples performed as potentially reactive

  16. Volcanic stratigraphy: A review

    Science.gov (United States)

    Martí, Joan; Groppelli, Gianluca; Brum da Silveira, Antonio

    2018-05-01

    Volcanic stratigraphy is a fundamental component of geological mapping in volcanic areas as it yields the basic criteria and essential data for identifying the spatial and temporal relationships between volcanic products and intra/inter-eruptive processes (earth-surface, tectonic and climatic), which in turn provides greater understanding of the geological evolution of a region. Establishing precise stratigraphic relationships in volcanic successions is not only essential for understanding the past behaviour of volcanoes and for predicting how they might behave in the future, but is also critical for establishing guidelines for exploring economic and energy resources associated with volcanic systems or for reconstructing the evolution of sedimentary basins in which volcanism has played a significant role. Like classical stratigraphy, volcanic stratigraphy should also be defined using a systematic methodology that can provide an organised and comprehensive description of the temporal and spatial evolution of volcanic terrain. This review explores different methods employed in studies of volcanic stratigraphy, examines four case studies that use differing stratigraphic approaches, and recommends methods for using systematic volcanic stratigraphy based on the application of the concepts of traditional stratigraphy but adapted to the needs of volcanological environment.

  17. Feasibility study on volcanic power generation system

    Energy Technology Data Exchange (ETDEWEB)

    None

    1977-07-01

    Investigations were carried out to determine the feasibility of volcanic power generation on Satsuma Io Island. Earthquakes were studied, as were the eruptions of subaerial and submarine hot springs. Hydrothermal rock alteration was studied and electrical surveys were made. General geophysical surveying was performed with thermocameras and radiation monitoring equipment. In particular, the Toyoba mine was studied, both with respect to its hot spring and its subsurface temperatures.

  18. Origin and Development of El Bajío Basin in the Central Sector of Trans-Mexican Volcanic Belt

    Science.gov (United States)

    Botero, P. A.; Alaniz Álvarez, S. A.; Nieto Samaniego, Á. F.; Lopez-Martinez, M.; Levresse, G.; Xu, S.; Ortega Obregón, C.

    2015-12-01

    Volcanism of the Trans-Mexican Volcanic Belt has been placed on pre-existing tectonic basins; one of them is El Bajío Basin. We present the origin and evolution of this basin through the study of its deformation events occurring mainly on the El Bajío fault, at the boundary between the Trans-Mexican Volcanic Belt and the Mesa Central. Detailed stratigraphy, and structural analysis suggest 4 deformation events in the northwest of the Sierra de Guanajuato. The first event (D1) with E-W shortening is characterized by the development of axial plane foliation (S1) with N-S direction, this event occurred between the Tithonian and Aptian age. In the second event (D2), occurred between the Albian and the early Eocene, foliations NW-SE (S2) were generated with a NE-SW shortening trend dated between the Albian and early Eocene, this deformation is related to the Laramide Orogeny. The Granito Comanja was emplaced during the third event (D3) and generated foliation (S3) in sediments of the complejo vulcanosedimentario Sierra de Guanajuato that circumscribes the Granito Comanja in response to its intrusion. After its emplacement, NW-SE normal faults were generated along the S-SE contact of the Granito Comanja, at that time El Bajío fault began. The fourth event (D4) has three phases that affected the sedimentary and volcanic Cenozoic rocks. D4F1 is marked by continental conglomerates deposition with variable thickness along of the main trace of the El Bajío fault. D4F2 affected the Oligocene volcanic rocks showing an important fault activity at that time, as evidenced the tilting above 45o in the Oligocene rocks, temporarily coincides with the triaxial extension to the Mesa Central. The direction of elongation of D4F3 is ESE-WNW, El Bajío fault had little movement. Since the Miocene the deformation was concentrated along the southern central sector of the Trans-mexican Volcanic Belt and there were few deformation in the Mesa central. During the three phases of deformation

  19. Holocene volcanic geology, volcanic hazard, and risk on Taveuni, Fiji

    International Nuclear Information System (INIS)

    Cronin, S.J.; Neall, V.E.

    2001-01-01

    The Holocene volcanic geology of Taveuni has been mapped in order to produce a volcanic hazard and risk assessment for the island. Taveuni is the third-largest island of the Fiji group and home to 14,500 people. At least cubic km 2.7 of olivine-alkali-basalt magma was erupted from over 100 events throughout the Holocene. Vents are concentrated along a northeast-striking rift zone that is parallel to other regional structural trends. There is an overall trend of younging southward along the rift. Holocene lavas and tephras are grouped within six newly defined eruptive periods, established on a basis of radiocarbon dating. Within these periods, 14 tephra layers, useful as local marker horizons, are recognised. At least 58% of Holocene eruptions produced lava flows, while almost all produced some tephra. Individual eruption event volumes ranged between 0.001 and cubic km 0.20 (dense rock equivalent). Many eruptions involved at least some phases of phreatic and/or phreato-magmatic activity, although dominant hydrovolcanic activity was limited to only a few events. A volcanic hazard map is presented, based on the Holocene geology map and statistical analyses of eruption recurrence. The highest levels of ground-based and near-vent hazards are concentrated along the southern portion of the island's rift axis, with the paths of initial lava flows predicted from present topography. Tephra fall hazards are based on eruption parameters interpreted from mapped Holocene tephra layers. Hawaiian explosive-style eruptions appear to be a dominant eruptive process, with prevailing low-level (<3 km) southeasterly winds dispersing most tephra to the northwestern quadrant. Vulnerable elements (population centres, infrastructure, and economy) on Taveuni have been considered in deriving a volcanic risk assessment for the island. A number of infrastructural and subdivision developments are either under way or planned for the island, driven by its highly fertile soils and availability of

  20. Excess europium content in Precambrian sedimentary rocks and continental evolution

    Science.gov (United States)

    Jakes, P.; Taylor, S. R.

    1974-01-01

    It is proposed that the europium excess in Precambrian sedimentary rocks, relative to those of younger age, is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances, and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a granodioritic upper crust by partial melting in the lower crust, which selectively retains europium.

  1. Relationship between water quality of deep-groundwater and geology in non-volcanic areas in Japan

    International Nuclear Information System (INIS)

    Oyama, Yoichi; Takahashi, Masaaki; Tsukamoto, Hitoshi; Kazahaya, Kohei; Yasuhara, Masaya; Takahashi, Hiroshi; Morikawa, Noritoshi; Ohwada, Michiko; Shibahara, Akihiko; Inamura, Akihiko

    2011-01-01

    Geochemical characteristics in groundwater such as groundwater chemistry and physicochemical parameters are affected by their source and the interaction with rocks and minerals. We observed the relationships between groundwater chemistry of the deep-groundwater and the geology in non-volcanic areas in Japan using about 9300 of deep-groundwater data. A Geographical Information System (GIS) was used to extract data in non-volcanic areas and numbers of water data are about 5200. The data were further classified into four types of geology (sedimentary rock, accretionary complex, volcanic rock and plutonic rock). The pH, temperature and major ion concentrations among deep-groundwaters in each geology have been statistically analysed. Result shows that the total cation concentration of deep-groundwaters are significantly different between geology, and the average values are decreased in the order of the sedimentary rock (66.7 meq l -1 ), volcanic rock (43.0 meq l -1 ), accretionary complex (24.6 meq l -1 ), and plutonic rock (11.0 meq l -1 ). The average pH does not show the major difference between geology whereas the highest average temperature is found in volcanic rock. In addition, the all four major cations (Na, K, Mg, and Ca) show the highest average concentrations in sedimentary rock, within the highest average concentrations of major anions for Cl, SO 4 , and HCO 3 are found in sedimentary rock, volcanic rock and accretionary complex, respectively, indicating the difference of the influence on the anions varied with geology. The distribution of deep-groundwater that are dominated by each major anions implied that SO 4 -type groundwater in volcanic rocks are formed by the influence of Neogene volcanic rock (Green tuff). In addition, HCO 3 -type groundwater in accretionary complex found from Kinki to Shikoku regions are formed by the addition of CO 2 gases supplying not only from surface soil and carbonate minerals but from deep underground. (author)

  2. Volcanic Supersites as cross-disciplinary laboratories

    Science.gov (United States)

    Provenzale, Antonello; Beierkuhnlein, Carl; Giamberini, Mariasilvia; Pennisi, Maddalena; Puglisi, Giuseppe

    2017-04-01

    surface between the top of the vegetation and the rock matrix in active volcanic areas and Volcanic Supersites.

  3. Geologic setting of the St. Catherine basement rocks, Sinai, Egypt

    OpenAIRE

    Abdel Maksoud, M. A. [محمد علي عبدالمقصود; Khalek, M. L. Abdel; Oweiss, K. A.

    1993-01-01

    St. Catherine area, some 900 km in size, is dominated by basement rocks Encompassing old continental gneisses, metasediments, greenstone belt, calc-alkaline granites (G-II-granites), rift-related volcanics (RV), and anorogenic within plate granites (G-III-granites). The greenstone belt is composed of subduction-related volcanics (SV) intercalated with metasediments. These volcanics split into older group (moderately metamorphosed) and younger group (slightly metamorphosed). The calc-alkaline ...

  4. Quaternary basaltic volcanism in the Payenia volcanic province, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina

    primitive basalts and trachybasalts but also more evolved samples from the retroarc region and the larger volcanoes Payún Matrú and Payún Liso are presented. The samples cover a broad range of compositions from intraplate lavas similar to ocean island basalts to arc andesites. A common feature found...... are isotopically similar to the Andean Southern Volcanic Zone arc rocks and their mantle source possibly resembled the source of South Atlantic N-MORB prior to addition of fluids and melts from the subduction channel. However, it must have been more enriched than the estimates of depleted upper mantle from...... the lithosphere is thinnest and possibly in areas of elevated mantle temperatures. The pyroxenite melts formed at deeper levels react with the surrounding peridotite and thereby changes composition leading to eruption of melts which experienced variable degrees of melt-peridotite interaction. This can presumably...

  5. Self-potential anomalies preceding tectonic and volcanic crises

    International Nuclear Information System (INIS)

    Patella, D.

    1993-01-01

    In this paper I consider a possible physical mechanism capable of explaining self-potential anomalies, which are currently observed on the ground surface prior to tectonic and volcanic activities. A rock cracking-fluid diffusion-charge polarization model is described. The electrical charge polarization is assumed to be the electrokinetic effect due to invasion of fluid into new fissures, which open inside a stressed rock material because of dilatancy, in the case of tectonic activity, and of the rising of a magma intrusion in the case of volcanic activity. (author). 10 refs, 2 figs

  6. Rock Art

    Science.gov (United States)

    Henn, Cynthia A.

    2004-01-01

    There are many interpretations for the symbols that are seen in rock art, but no decoding key has ever been discovered. This article describes one classroom's experiences with a lesson on rock art--making their rock art and developing their own personal symbols. This lesson allowed for creativity, while giving an opportunity for integration…

  7. Late Miocene marine tephra beds : recorders of rhyolitic volcanism in North Island, New Zealand

    International Nuclear Information System (INIS)

    Shane, P.; Black, T.; Eggins, S.; Westgate, J.

    1998-01-01

    A deep-sea sequence of 72 rhyolitic tephra beds, now exposed at Mahia Peninsula in the Hawke's Bay region of the east coast, North Island, New Zealand, provides a record of Late Miocene volcanism of the Coromandel Volcanic Zone (CVZ): the precursor to large-scale explosive volcanism of the Quaternary Taupo Volcanic Zone (TVZ). The geochemical signature of the glasses in the Miocene tephra has been protected from hydrothermal alteration and prolonged subaerial exposure that have affected proximal CVZ deposits. The tephra beds are primarily eruption-driven sediment gravity flows that have been emplaced into a trench-slope basin, some 300 km from active volcanoes. Their occurrence is consistent with long-distance fluvial transport followed by a point-source discharge into the deep-sea environment, and has no implications for the paleogeographic location of the basins relative to the volcanic arc. The tephra beds are calc-alkaline rhyolites with SiO 2 contents in the range 72-78 wt% (recalculated on a volatile-free basis), and are broadly similar to glassy rocks of the CVZ. Their major oxide, trace element, and REE compositions are indistinguishable from glasses of TVZ rhyolites. The trace element and REE compositional variability in the Late Miocene tephra beds, which were erupted over an estimated duration of c. 0.5-2.4 m.y. is no greater than that of large silicic eruptives of the last 350 ka, and is suggestive of a long-lived source and/or similar magmatic processes. However, the individual tephra beds are products of discrete homogeneous magma batches. New fission track ages of the Miocene tephra beds suggest the main period of volcaniclastic deposition occurred in the interval c. 9-7 Ma. This corresponds well with the initiation of rhyolitic volcanism in the CVZ at c. 10 Ma, and a major period of caldera formation that took place to c. 7 Ma. The ages suggest a sediment accumulation rate of between 0.23 and 1.2 m/ka (av. 0.4 m/ka), and a frequency of eruption of

  8. Rock burst governance of working face under igneous rock

    Science.gov (United States)

    Chang, Zhenxing; Yu, Yue

    2017-01-01

    As a typical failure phenomenon, rock burst occurs in many mines. It can not only cause the working face to cease production, but also cause serious damage to production equipment, and even result in casualties. To explore how to govern rock burst of working face under igneous rock, the 10416 working face in some mine is taken as engineering background. The supports damaged extensively and rock burst took place when the working face advanced. This paper establishes the mechanical model and conducts theoretical analysis and calculation to predict the fracture and migration mechanism and energy release of the thick hard igneous rock above the working face, and to obtain the advancing distance of the working face when the igneous rock fractures and critical value of the energy when rock burst occurs. Based on the specific conditions of the mine, this paper put forward three kinds of governance measures, which are borehole pressure relief, coal seam water injection and blasting pressure relief.

  9. The relational of Mesozoic volcanism to uranium mineralization in Guyuan-Hongshanzi area

    International Nuclear Information System (INIS)

    Wu Rengui; Xu Zhe; Yu Zhenqing; Jiang Shan; Shen Kefeng

    2011-01-01

    Based on the time of Mesozoic volcanism,the characteristic of major and trace element, and REE pattern of the volcanic rocks in Guyuan-Hongshanzi area, The Mesozoic volcanism can be divided into the early cycle and later cycle during the Early Cretaceous, and it's magma series is classified in two sub-series, one is alkaline series of trachyte dominated and another is subalkaline series of rhyolite dominated. The relations between Mesozoic volcanism and uranium mineralization is mainly shown in four aspects: (1) Uranium mineralization controlled by the coexist of two magma series; (2) Uranium mineralization controlled by superhypabyssal porphyry body in later cycle volcanism during the Early Cretaceous; (3) The porphyry body close to uranium mineralization,bearing the genesis characteristics of crust-mantle action; and (4) High Si and K content in the chemical composition of the mineralization volcanic rocks. (authors)

  10. New evidence of effusive and explosive volcanism in the Lower Carboniferous formations of the Moroccan Central Hercynian Massif: Geochemical data and geodynamic significance

    Science.gov (United States)

    Ntarmouchant, A.; Smaili, H.; Bento dos Santos, T.; Dahire, M.; Sabri, K.; Ribeiro, M. L.; Driouch, Y.; Santos, R.; Calvo, R.

    2016-03-01

    The Azrou-Khénifra basin, located in the SE sector of the Moroccan Central Hercynian Massif of the Western Meseta of Morocco comprises volcanic and volcanoclastic rocks where two magmatic sequences can be distinguished: i) the Dhar Lahmar Sequence, composed of Upper Visean basaltic lava flows and pyroclastic deposits; and ii) the Kef Al Asri Sequence, composed of Visean - Serpukhovian intermediate to acid rocks. A continuous spatial and temporal evolution between the two volcano-sedimentary sequences was observed during the detailed geological work performed in the studied area. Petrography and geochemical studies additionally suggest a continuous compositional evolution from the more basic magmatic rocks to the intermediate/acid rocks, which implies a cogenetic magmatic differentiation controlled by crystal fractionation (with minor crustal assimilation) of a calc-alkaline trend magmatic suite. The inferred magmatic evolution is consistent with a geodynamic environment of an orogenic zone within an active continental margin setting. This partly explosive Visean - Serpukhovian volcanism, identified for the first time in the Western Meseta of Morocco, displays very similar petrographic and geochemical characteristics to its Eastern Meseta analogues, which implies that the emplacement of these magmatic rocks must have occurred in similar collisional geodynamic settings for both major geological domains, further constraining the evolution of this major crustal segment within the Carboniferous events that shaped the Hercynian Orogeny.

  11. Thermal vesiculation during volcanic eruptions.

    Science.gov (United States)

    Lavallée, Yan; Dingwell, Donald B; Johnson, Jeffrey B; Cimarelli, Corrado; Hornby, Adrian J; Kendrick, Jackie E; von Aulock, Felix W; Kennedy, Ben M; Andrews, Benjamin J; Wadsworth, Fabian B; Rhodes, Emma; Chigna, Gustavo

    2015-12-24

    Terrestrial volcanic eruptions are the consequence of magmas ascending to the surface of the Earth. This ascent is driven by buoyancy forces, which are enhanced by bubble nucleation and growth (vesiculation) that reduce the density of magma. The development of vesicularity also greatly reduces the 'strength' of magma, a material parameter controlling fragmentation and thus the explosive potential of the liquid rock. The development of vesicularity in magmas has until now been viewed (both thermodynamically and kinetically) in terms of the pressure dependence of the solubility of water in the magma, and its role in driving gas saturation, exsolution and expansion during decompression. In contrast, the possible effects of the well documented negative temperature dependence of solubility of water in magma has largely been ignored. Recently, petrological constraints have demonstrated that considerable heating of magma may indeed be a common result of the latent heat of crystallization as well as viscous and frictional heating in areas of strain localization. Here we present field and experimental observations of magma vesiculation and fragmentation resulting from heating (rather than decompression). Textural analysis of volcanic ash from Santiaguito volcano in Guatemala reveals the presence of chemically heterogeneous filaments hosting micrometre-scale vesicles. The textures mirror those developed by disequilibrium melting induced via rapid heating during fault friction experiments, demonstrating that friction can generate sufficient heat to induce melting and vesiculation of hydrated silicic magma. Consideration of the experimentally determined temperature and pressure dependence of water solubility in magma reveals that, for many ascent paths, exsolution may be more efficiently achieved by heating than by decompression. We conclude that the thermal path experienced by magma during ascent strongly controls degassing, vesiculation, magma strength and the effusive

  12. Geothermal surveys in the oceanic volcanic island of Mauritius

    Science.gov (United States)

    Verdoya, Massimo; Chiozzi, Paolo; Pasqua, Claudio

    2017-04-01

    Oceanic island chains are generally characterised by young volcanic systems that are predominately composed of basaltic lavas and related magmatic products. Although hot springs are occasionally present, the pervasive, massive, recent outpourings of basaltic lavas are the primary manifestation of the existence of geothermal resources. These islands may have, in principle, significant potential for the exploitation of geothermal energy. In this paper, we present results of recent investigations aimed at the evaluation of geothermal resources of the island of Mauritius, that is the emerging portion of a huge submarine, aseismic, volcanic plateau extending in the SW part of the Indian Ocean. The plateau is related to a long-lived hotspot track, whose present-day expression is the active volcano of La Réunion Island, located about 200 km SW of Mauritius. The island does not show at present any volcanic activity, but magmatism is quite recent as it dates from 7.8 to 0.03 Myr. Geochemical data from water samples collected from boreholes do not indicate the presence of mature water, i.e. circulating in high-temperature geothermal reservoirs, and argue for short-term water-rock interaction in shallow hydrogeological circuits. However, this cannot rule out that a deep magmatic heat source, hydraulically insulated from shallow aquifers, may occur. To evaluate the geothermal gradient, a 270-m-deep hole was thus drilled in the island central portion, in which the most recent volcanic activity (0.03 Myr) took place. Temperature-depth profiles, recorded after complete thermal equilibration, revealed a thermal gradient of 40 mK/m. Attempts of extracting additional thermal information were also made by measuring the temperature in a 170-m-deep deep water hole, no longer used. The results were consistent with the gradient hole, i.e. pointing to a weak or null deep-seated thermal anomaly beneath Mauritius and low geothermal potential. The deep thermal process (mantle plume) invoked

  13. Electrostatic phenomena in volcanic eruptions

    Energy Technology Data Exchange (ETDEWEB)

    Lane, S J; James, M R; Gilbert, J S, E-mail: s.lane@lancaster.ac.uk [Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ (United Kingdom)

    2011-06-23

    Electrostatic phenomena have long been associated with the explosive eruption of volcanoes. Lightning generated in volcanic plumes is a spectacular atmospheric electrical event that requires development of large potential gradients over distances of up to kilometres. This process begins as hydrated liquid rock (magma) ascends towards Earth's surface. Pressure reduction causes water supersaturation in the magma and the development of bubbles of supercritical water, where deeper than c. 1000 m, and water vapour at shallower depths that drives flow expansion. The generation of high strain rates in the expanding bubbly magma can cause it to fracture in a brittle manner, as deformation relaxation timescales are exceeded. The brittle fracture provides the initial charge separation mechanism, known as fractoemission. The resulting mixture of charged silicate particles and ions evolves over time, generating macro-scale potential gradients in the atmosphere and driving processes such as particle aggregation. For the silicate particles, aggregation driven by electrostatic effects is most significant for particles smaller than c. 100 {mu}m. Aggregation acts to change the effective aerodynamic behaviour of silicate particles, thus altering the sedimentation rates of particles from volcanic plumes from the atmosphere. The presence of liquid phases also promotes aggregation processes and lightning.

  14. Local stresses, dyke arrest and surface deformation in volcanic edificesand rift zones

    Directory of Open Access Journals (Sweden)

    L. S. Brenner

    2004-06-01

    Full Text Available Field studies indicate that nearly all eruptions in volcanic edifices and rift zones are supplied with magma through fractures (dykes that are opened by magmatic overpressure. While (inferred dyke injections are frequent during unrest periods, volcanic eruptions are, in comparison, infrequent, suggesting that most dykes become arrested at certain depths in the crust, in agreement with field studies. The frequency of dyke arrest can be partly explained by the numerical models presented here which indicate that volcanic edifices and rift zones consisting of rocks of contrasting mechanical properties, such as soft pyroclastic layers and stiff lava flows, commonly develop local stress fields that encourage dyke arrest. During unrest, surface deformation studies are routinely used to infer the geometries of arrested dykes, and some models (using homogeneous, isotropic half-spaces infer large grabens to be induced by such dykes. Our results, however, show that the dyke-tip tensile stresses are normally much greater than the induced surface stresses, making it difficult to explain how a dyke can induce surface stresses in excess of the tensile (or shear strength while the same strength is not exceeded at the (arrested dyke tip. Also, arrested dyke tips in eroded or active rift zones are normally not associated with dyke-induced grabens or normal faults, and some dykes arrested within a few metres of the surface do not generate faults or grabens. The numerical models show that abrupt changes in Young's moduli(stiffnesses, layers with relatively high dyke-normal compressive stresses (stress barriers, and weak horizontal contacts may make the dyke-induced surface tensile stresses too small for significant fault or graben formation to occur in rift zones or volcanic edifices. Also, these small surface stresses may have no simple relation to the dyke geometry or the depth to its tip. Thus, for a layered crust with weak contacts, straightforward

  15. Volcanism on Io

    Science.gov (United States)

    Davies, Ashley Gerard

    2014-03-01

    Preface; Introduction; Part I. Io, 1610 to 1995: Galileo to Galileo: 1. Io, 1610-1979; 2. Between Voyager and Galileo: 1979-95; 3. Galileo at Io; Part II. Planetary Volcanism: Evolution and Composition: 4. Io and Earth: formation, evolution, and interior structure; 5. Magmas and volatiles; Part III. Observing and Modeling Volcanic Activity: 6. Observations: thermal remote sensing of volcanic activity; 7. Models of effusive eruption processes; 8. Thermal evolution of volcanic eruptions; Part IV. Galileo at Io: the Volcanic Bestiary: 9. The view from Galileo; 10. The lava lake at Pele; 11. Pillan and Tvashtar: lava fountains and flows; 12. Prometheus and Amirani: Effusive activity and insulated flows; 13. Loki Patera: Io's powerhouse; 14. Other volcanoes and eruptions; Part V. Volcanism on Io: The Global View: 15. Geomorphology: paterae, shields, flows and mountains; 16. Volcanic plumes; 17. Hot spots; Part VI. Io after Galileo: 18. Volcanism on Io: a post-Galileo view; 19. The future of Io observations; Appendix 1; Appendix 2; References; Index.

  16. Eos Chaos Rocks

    Science.gov (United States)

    2006-01-01

    11 January 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows light-toned, layered rock outcrops in Eos Chaos, located near the east end of the Valles Marineris trough system. The outcrops occur in the form of a distinct, circular butte (upper half of image) and a high slope (lower half of image). The rocks might be sedimentary rocks, similar to those found elsewhere exposed in the Valles Marineris system and the chaotic terrain to the east of the region. Location near: 12.9oS, 49.5oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Southern Summer

  17. A model for Nb-Zr-REE-Ga enrichment in Lopingian altered alkaline volcanic ashes: Key evidence of H-O isotopes

    Science.gov (United States)

    Dai, Shifeng; Nechaev, Victor P.; Chekryzhov, Igor Yu.; Zhao, Lixin; Vysotskiy, Sergei V.; Graham, Ian; Ward, Colin R.; Ignatiev, Alexander V.; Velivetskaya, Tatyana A.; Zhao, Lei; French, David; Hower, James C.

    2018-03-01

    Clay-altered volcanic ash with highly-elevated concentrations of Nb(Ta), Zr(Hf), rare earth elements (REE), and Ga, is a new type of critical metal deposit with high commercial prospects that has been discovered in Yunnan Province, southwest China. Previous studies showed that the volcanic ashes had been subjected to hydrothermal fluids, the nature of which, however, is not clear. Here we show that the volcanic ashes were originated from alkaline magmatism, followed by a continuous hydrothermal-weathering process. Heated meteoric waters, which were sourced from acidic rains and mixed with CO2 from degassing of the Emeishan plume, have caused partial, but widespread, acidic leaching of Nb, Ta, Zr, Hf, REE, and Ga into ground water and residual enrichment of these elements, along with Al and Ti, in the deeply altered rocks. Subsequent alteration occurring under cooler, neutral or alkaline conditions, caused by water-rock interaction, resulted in precipitation of the leached critical metals in the deposit. Polymetallic mineralization of similar origin may be found in other continental regions subjected to explosive alkaline volcanism associated with deep weathering in humid conditions.

  18. The structural architecture of the Los Humeros volcanic complex and geothermal field, Trans-Mexican Volcanic Belt, Central Mexico

    Science.gov (United States)

    Norini, Gianluca; Groppelli, Gianluca; Sulpizio, Roberto; Carrasco Núñez, Gerardo; Davila Harris, Pablo

    2014-05-01

    The development of geothermal energy in Mexico is a very important goal, given the presence of a large heat anomaly, associated with the Trans-Mexican Volcanic Belt, the renewability of the resource and the low environmental impact. The Quaternary Los Humeros volcanic complex is an important geothermal target, whose evolution involved at least two caldera events, that alternated with other explosive and effusive activity. The first caldera forming event was the 460 ka eruption that produced the Xaltipan ignimbrite and formed a 15-20 km wide caldera. The second collapse event occurred 100 ka with the formation of the Zaragoza ignimbrite and a nested 8-10 km wide caldera. The whole volcano structure, the style of the collapses and the exact location of the calderas scarps and ring faults are still a matter of debate. The Los Humeros volcano hosts the productive Los Humeros Geothermal Field, with an installed capacity of 40 MW and additional 75 MW power plants under construction. Recent models of the geothermal reservoir predict the existence of at least two reservoirs in the geothermal system, separated by impermeable rock units. Hydraulic connectivity and hydrothermal fluids circulation occurs through faults and fractures, allowing deep steam to ascend while condensate flows descend. As a consequence, the plans for the exploration and exploitation of the geothermal reservoir have been based on the identification of the main channels for the circulation of hydrothermal fluids, constituted by faults, so that the full comprehension of the structural architecture of the caldera is crucial to improve the efficiency and minimize the costs of the geothermal field operation. In this study, we present an analysis of the Los Humeros volcanic complex focused on the Quaternary tectonic and volcanotectonics features, like fault scarps and aligned/elongated monogenetic volcanic centres. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of

  19. 'Escher' Rock

    Science.gov (United States)

    2004-01-01

    [figure removed for brevity, see original site] Chemical Changes in 'Endurance' Rocks [figure removed for brevity, see original site] Figure 1 This false-color image taken by NASA's Mars Exploration Rover Opportunity shows a rock dubbed 'Escher' on the southwestern slopes of 'Endurance Crater.' Scientists believe the rock's fractures, which divide the surface into polygons, may have been formed by one of several processes. They may have been caused by the impact that created Endurance Crater, or they might have arisen when water leftover from the rock's formation dried up. A third possibility is that much later, after the rock was formed, and after the crater was created, the rock became wet once again, then dried up and developed cracks. Opportunity has spent the last 14 sols investigating Escher, specifically the target dubbed 'Kirchner,' and other similar rocks with its scientific instruments. This image was taken on sol 208 (Aug. 24, 2004) by the rover's panoramic camera, using the 750-, 530- and 430-nanometer filters. The graph above shows that rocks located deeper into 'Endurance Crater' are chemically altered to a greater degree than rocks located higher up. This chemical alteration is believed to result from exposure to water. Specifically, the graph compares ratios of chemicals between the deep rock dubbed 'Escher,' and the more shallow rock called 'Virginia,' before (red and blue lines) and after (green line) the Mars Exploration Rover Opportunity drilled into the rocks. As the red and blue lines indicate, Escher's levels of chlorine relative to Virginia's went up, and sulfur down, before the rover dug a hole into the rocks. This implies that the surface of Escher has been chemically altered to a greater extent than the surface of Virginia. Scientists are still investigating the role water played in influencing this trend. These data were taken by the rover's alpha particle X-ray spectrometer.

  20. The Dalradian rocks of Scotland: an introduction

    OpenAIRE

    Stephenson, David; Mendum, John R.; Fettes, Douglas J.; Leslie, A. Graham

    2013-01-01

    The Dalradian Supergroup and its basement rocks, together with younger plutons, underpin most of the Grampian Highlands and the islands of the Inner Hebrides between the Highland Boundary and Great Glen faults. The Dalradian is a mid-Neoproterozoic to early-Ordovician sequence of largely clastic metasedimentary rocks, with some volcanic units, which were deformed and metamorphosed to varying degrees during the Early Palaeozoic Caledonian Orogeny. Sedimentation of the lower parts of the Da...

  1. Volcanic deformation in the Andes

    Science.gov (United States)

    Riddick, S.; Fournier, T.; Pritchard, M.

    2009-05-01

    We present the results from an InSAR survey of volcanic activity in South America. We use data from the Japanese Space Agency's ALOS L-band radar satellite from 2006-2009. The L-band instrument provides better coherence in densely vegetated regions, compared to the shorter wave length C-band data. The survey reveals volcano related deformation in regions, north, central and southern, of the Andes volcanic arc. Since observations are limited to the austral summer, comprehensive coverage of all volcanoes is not possible. Yet, our combined observations reveal volcanic/hydrothermal deformation at Lonquimay, Llaima, Laguna del Maule, and Chaitén volcanoes, extend deformation measurements at Copahue, and illustrate temporal complexity to the previously described deformation at Cerro Hudson and Cordón Caulle. No precursory deformation is apparent before the large Chaitén eruption (VEI_5) of 2 May 2008, (at least before 16 April) suggesting rapid magma movement from depth at this long dormant volcano. Subsidence at Ticsani Volcano occurred coincident with an earthquake swarm in the same region.

  2. Geologic Map of the Bodie Hills Volcanic Field, California and Nevada: Anatomy of Miocene Cascade Arc Magmatism in the Western Great Basin

    Science.gov (United States)

    John, D. A.; du Bray, E. A.; Blakely, R. J.; Box, S.; Fleck, R. J.; Vikre, P. G.; Rytuba, J. J.; Moring, B. C.

    2011-12-01

    The Bodie Hills Volcanic Field (BHVF) is a >700 km2, long-lived (~9 Ma) but episodic, Miocene eruptive center in the southern part of the ancestral Cascade magmatic arc. A 1:50,000-scale geologic map based on extensive new mapping, combined with 40Ar/39Ar dates, geochemical data, and detailed gravity and aeromagnetic surveys, defines late Miocene magmatic and hydrothermal evolution of the BHVF and contrasts the subduction-related BHVF with the overlying, post-subduction, bimodal Plio-Pleistocene Aurora Volcanic Field (AVF). Important features of the BHVF include: Eruptions occurred during 3 major eruptive stages: dominantly trachyandesite stratovolcanoes (~14.7 to 12.9 Ma), mixed silicic trachyandesite, dacite, and rhyolite (~11.3 to 9.6 Ma), and dominantly silicic trachyandesite to dacite domes (~9.2 to 8.0 Ma). Small rhyolite domes were emplaced at ~6 Ma. Trachyandesitic stratovolcanoes with extensive debris flow aprons form the outer part of BHVF, whereas silicic trachyandesite to rhyolite domes are more centrally located. Geophysical data suggest that many BHVF volcanoes have shallow plutonic roots that extend to depths ≥1-2 km below the surface, and much of the Bodie Hills may be underlain by low density plutons presumably related to BHVF volcanism. BHVF rocks contain ~50 to 78% SiO2 (though few rocks have Bodie Hills at ~10 Ma, but the composition and eruptive style of volcanism continued unchanged for 2 Ma. However, kinematic data for veins and faults in mining districts suggest a change in the stress field from transtensional to extensional approximately coincident with cessation of subduction. The Bodie Hills are flanked to the east, north, and west by sedimentary basins that began to form in the late Miocene (locally >11 Ma). Fine to coarse sedimentary deposits within the BHVF include stream deposits in channels that cut across the hills and were partly filled by ~9.4 Ma Eureka Valley Tuff erupted 20 km to the northwest. Shallow dips and preservation of

  3. Research into basic rocks types

    International Nuclear Information System (INIS)

    1993-06-01

    Teollisuuden Voima Oy (TVO) has carried out research into basic rock types in Finland. The research programme has been implemented in parallel with the preliminary site investigations for radioactive waste disposal in 1991-1993. The program contained two main objectives: firstly, to study the properties of the basic rock types and compare those with the other rock types under the investigation; secondly, to carry out an inventory of rock formations consisting of basic rock types and suitable in question for final disposal. A study of environmental factors important to know regarding the final disposal was made of formations identified. In total 159 formations exceeding the size of 4 km 2 were identified in the inventory. Of these formations 97 were intrusive igneous rock types and 62 originally extrusive volcanic rock types. Deposits consisting of ore minerals, industrial minerals or building stones related to these formations were studied. Environmental factors like natural resources, protected areas or potential for restrictions in land use were also studied

  4. The 2007 Nazko, British Columbia, earthquake sequence: Injection of magma deep in the crust beneath the Anahim volcanic belt

    Science.gov (United States)

    Cassidy, J.F.; Balfour, N.; Hickson, C.; Kao, H.; White, Rickie; Caplan-Auerbach, J.; Mazzotti, S.; Rogers, Gary C.; Al-Khoubbi, I.; Bird, A.L.; Esteban, L.; Kelman, M.; Hutchinson, J.; McCormack, D.

    2011-01-01

    On 9 October 2007, an unusual sequence of earthquakes began in central British Columbia about 20 km west of the Nazko cone, the most recent (circa 7200 yr) volcanic center in the Anahim volcanic belt. Within 25 hr, eight earthquakes of magnitude 2.3-2.9 occurred in a region where no earthquakes had previously been recorded. During the next three weeks, more than 800 microearthquakes were located (and many more detected), most at a depth of 25-31 km and within a radius of about 5 km. After about two months, almost all activity ceased. The clear P- and S-wave arrivals indicated that these were high-frequency (volcanic-tectonic) earthquakes and the b value of 1.9 that we calculated is anomalous for crustal earthquakes but consistent with volcanic-related events. Analysis of receiver functions at a station immediately above the seismicity indicated a Moho near 30 km depth. Precise relocation of the seismicity using a double-difference method suggested a horizontal migration at the rate of about 0:5 km=d, with almost all events within the lowermost crust. Neither harmonic tremor nor long-period events were observed; however, some spasmodic bursts were recorded and determined to be colocated with the earthquake hypocenters. These observations are all very similar to a deep earthquake sequence recorded beneath Lake Tahoe, California, in 2003-2004. Based on these remarkable similarities, we interpret the Nazko sequence as an indication of an injection of magma into the lower crust beneath the Anahim volcanic belt. This magma injection fractures rock, producing high-frequency, volcanic-tectonic earthquakes and spasmodic bursts.

  5. Lithium, boron and chloride in volcanics and greywackes in Northland, Auckland and the Taupo Volcanic Zone

    International Nuclear Information System (INIS)

    Reyes, A.G.; Trompetter, W.J.

    1998-01-01

    During magmatic differentiation processes B preferentially partitions into the glassy mesostasis of rhyolite and andesite. The behaviour of Li, on the other hand, varies with the silica content of the rock. Lithium, B, Cl and water contents increase proportionally with the silica concentration of the volcanic rocks. Their relative proportions in andesites of the Taupo Volcanic Zone (TVZ) appear to reflect the nature of the underlying crust, the dip of the subducting slab and hence the depth and temperature of magma generation. The B/Li ratios of rhyolites associated with the northern Rotorua and Okataina eruptive centres yield lower B/Li ratios than those from Maroa and Taupo centres in the south, where the slab subducts at a shallower angle. Apparently, volcanics associated with a younger subduction event as in the TVZ, contain and retain more Cl, yielding lower Li/Cl ratios for the TVZ than Northland-Auckland basalts. The B/Li ratio of greywackes from the Torlesse terrane ( 1.4). In geothermal wells in Ngawha, hydrothermal alteration yields higher B/Li ratios of >2.8 for Waipapa terrane sedimentary rocks. The Li/Cl ratios for average South and North Island greywackes are similar and may reflect similar degrees of metamorphism. In general, the relative Li, B and Cl contents in greywackes are dictated by the composition of the detrital fragments, the clay fraction, the type of clays and the metamorphic grade. During hydrothermal alteration of rhyolite in the TVZ, Cl always partitions into solution while Li and B have an affinity for the rock. However, more Li remains in the rock than B at any given temperature. The distribution coefficients of Li and B between water and rock increase with increasing temperature. The partitioning of Li between rock and solution in TVZ hydrothermal systems is mainly dictated by temperature, whereas the mass distribution coefficient for B is related to the tectonic setting. An increase in relative Li of the rock is associated with the

  6. Volcanic signals in oceans

    KAUST Repository

    Stenchikov, Georgiy L.

    2009-08-22

    Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean integrates volcanic radiative cooling and responds over a wide range of time scales. The associated processes, especially ocean heat uptake, play a key role in ongoing climate change. However, they are not well constrained by observations, and attempts to simulate them in current climate models used for climate predictions yield a range of uncertainty. Volcanic impacts on the ocean provide an independent means of assessing these processes. This study focuses on quantification of the seasonal to multidecadal time scale response of the ocean to explosive volcanism. It employs the coupled climate model CM2.1, developed recently at the National Oceanic and Atmospheric Administration\\'s Geophysical Fluid Dynamics Laboratory, to simulate the response to the 1991 Pinatubo and the 1815 Tambora eruptions, which were the largest in the 20th and 19th centuries, respectively. The simulated climate perturbations compare well with available observations for the Pinatubo period. The stronger Tambora forcing produces responses with higher signal-to-noise ratio. Volcanic cooling tends to strengthen the Atlantic meridional overturning circulation. Sea ice extent appears to be sensitive to volcanic forcing, especially during the warm season. Because of the extremely long relaxation time of ocean subsurface temperature and sea level, the perturbations caused by the Tambora eruption could have lasted well into the 20th century.

  7. Geochronology and petrology of OIB-type lavas from the central part of the Mexican Volcanic Belt

    International Nuclear Information System (INIS)

    Hasenaka, Toshiaki; Yoshida, Takeyoshi; Uto, Kozo; Uchiumi, Shigeru

    1995-01-01

    In Mexican Volcanic Belt, typical continental margin arc volcanic activities have occurred accompanying the subduction of Rivera Plate and Cocos Plate into North American Plate. It has been known by recent geochemical research that the oceanic island type magma which does not show the characteristic chemical composition of subduction zone has extruded. In order to investigate the relation of the development of volcanic belt in continental margin are with the change of wide area tectonics, and to impose important limit on magma formation models, it is important to know the state of production of oceanic island type magma in continental margin arc and the age of its activities. In this report, the results of the K-Ar age measurement for the oceanic island type lava produced in the middle of Mexican Volcanic Belt are shown, and the geochemical features of those samples are clarified. The state of production and the petrography of oceanic island type igneous rock samples are explained. The K-Ar age measurement experiment and the results are reported. The chemical composition of oceanic island type lava determined by photon activation process and fluorescent X-ray analysis is shown. (K.I.)

  8. Geomechanical rock properties of a basaltic volcano

    Directory of Open Access Journals (Sweden)

    Lauren N Schaefer

    2015-06-01

    Full Text Available In volcanic regions, reliable estimates of mechanical properties for specific volcanic events such as cyclic inflation-deflation cycles by magmatic intrusions, thermal stressing, and high temperatures are crucial for building accurate models of volcanic phenomena. This study focuses on the challenge of characterizing volcanic materials for the numerical analyses of such events. To do this, we evaluated the physical (porosity, permeability and mechanical (strength properties of basaltic rocks at Pacaya Volcano (Guatemala through a variety of laboratory experiments, including: room temperature, high temperature (935 °C, and cyclically-loaded uniaxial compressive strength tests on as-collected and thermally-treated rock samples. Knowledge of the material response to such varied stressing conditions is necessary to analyze potential hazards at Pacaya, whose persistent activity has led to 13 evacuations of towns near the volcano since 1987. The rocks show a non-linear relationship between permeability and porosity, which relates to the importance of the crack network connecting the vesicles in these rocks. Here we show that strength not only decreases with porosity and permeability, but also with prolonged stressing (i.e., at lower strain rates and upon cooling. Complimentary tests in which cyclic episodes of thermal or load stressing showed no systematic weakening of the material on the scale of our experiments. Most importantly, we show the extremely heterogeneous nature of volcanic edifices that arise from differences in porosity and permeability of the local lithologies, the limited lateral extent of lava flows, and the scars of previous collapse events. Input of these process-specific rock behaviors into slope stability and deformation models can change the resultant hazard analysis. We anticipate that an increased parameterization of rock properties will improve mitigation power.

  9. Global volcanic emissions: budgets, plume chemistry and impacts

    Science.gov (United States)

    Mather, T. A.

    2012-12-01

    Over the past few decades our understanding of global volcanic degassing budgets, plume chemistry and the impacts of volcanic emissions on our atmosphere and environment has been revolutionized. Global volcanic emissions budgets are needed if we are to make effective use of regional and global atmospheric models in order to understand the consequences of volcanic degassing on global environmental evolution. Traditionally volcanic SO2 budgets have been the best constrained but recent efforts have seen improvements in the quantification of the budgets of other environmentally important chemical species such as CO2, the halogens (including Br and I) and trace metals (including measurements relevant to trace metal atmospheric lifetimes and bioavailability). Recent measurements of reactive trace gas species in volcanic plumes have offered intriguing hints at the chemistry occurring in the hot environment at volcanic vents and during electrical discharges in ash-rich volcanic plumes. These reactive trace species have important consequences for gas plume chemistry and impacts, for example, in terms of the global fixed nitrogen budget, volcanically induced ozone destruction and particle fluxes to the atmosphere. Volcanically initiated atmospheric chemistry was likely to have been particularly important before biological (and latterly anthropogenic) processes started to dominate many geochemical cycles, with important consequences in terms of the evolution of the nitrogen cycle and the role of particles in modulating the Earth's climate. There are still many challenges and open questions to be addressed in this fascinating area of science.

  10. Volcanism and Tectonics of the Central Deep Basin, Sea of Japan

    Science.gov (United States)

    Lelikov, E. P.; Emelyanova, T. A.; Pugachev, A. A.

    2018-01-01

    The paper presents the results of a study on the geomorphic structure, tectonic setting, and volcanism of the volcanoes and volcanic ridges in the deep Central Basin of the Sea of Japan. The ridges rise 500-600 m above the acoustic basement of the basin. These ridges were formed on fragments of thinned continental crust along deep faults submeridionally crossing the Central Basin and the adjacent continental part of the Primorye. The morphostructures of the basin began to submerge below sea level in the Middle Miocene and reached their contemporary positions in the Pliocene. Volcanism in the Central Basin occurred mostly in the Middle Miocene-Pliocene and formed marginal-sea basaltoids with OIB (ocean island basalt) geochemical signatures indicating the lower-mantle plume origin of these rocks. The OIB signatures of basaltoids tend to be expressed better in the eastern part of the Central Basin, where juvenile oceanic crust has developed. The genesis of this crust is probably related to rising and melting of the Pacific superplume apophyse.

  11. Areal and time distributions of volcanic formations on Mars

    International Nuclear Information System (INIS)

    Katterfeld, G.N.; Vityaz, V.I.

    1987-01-01

    The analysis of igneous rock distribution has been fulfilled on the basis of the geomorphological map of Mars at scale 1:5,000,000, according to data obtained from interpretation of 1:2,000,000 scale pictures of Mariner 9, Mars 4, Mars 5, Viking 1 and 2. Areological areas are listed as having been distinguished as the stratigraphic basis for a martian time scale. The area of volcanic eruptions and the number of eruptive centers are calculated on 10 x 10 deg cells and for each areological eras. The largest area of eruptive happening at different times is related with Tharsis tectonic uplift. The study of distribution of igneous rock area and volcanic centers number on 10 deg sectors and zones revealed the concentration belts of volcanic formations

  12. Areal and time distributions of volcanic formations on Mars

    Science.gov (United States)

    Katterfeld, G. N.; Vityaz, V. I.

    1987-01-01

    The analysis of igneous rock distribution has been fulfilled on the basis of the geomorphological map of Mars at scale 1:5,000,000, according to data obtained from interpretation of 1:2,000,000 scale pictures of Mariner 9, Mars 4, Mars 5, Viking 1 and 2. Areological areas are listed as having been distinguished as the stratigraphic basis for a martian time scale. The area of volcanic eruptions and the number of eruptive centers are calculated on 10 x 10 deg cells and for each areological eras. The largest area of eruptive happening at different times is related with Tharsis tectonic uplift. The study of distribution of igneous rock area and volcanic centers number on 10 deg sectors and zones revealed the concentration belts of volcanic formations.

  13. Volcanism Studies: Final Report for the Yucca Mountain Project

    International Nuclear Information System (INIS)

    Crowe, Bruce M.; Perry, Frank V.; Valentine, Greg A.; Bowker, Lynn M.

    1998-01-01

    This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. An assessment of the risk of future volcanic activity is one of many site characterization studies that must be completed to evaluate the Yucca Mountain site for potential long-term storage of high-level radioactive waste. The presence of several basaltic volcanic centers in the Yucca Mountain region of Pliocene and Quaternary age indicates that there is a finite risk of a future volcanic event occurring during the 10,000-year isolation period of a potential repository. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The risk of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt ( than about 7 x 10 -8 events yr -1 . Simple probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Amargosa Valley. The sensitivity of the disruption probability to the location of northeast boundaries of volcanic zones near the Yucca Mountain sit

  14. Recreating Rocks

    DEFF Research Database (Denmark)

    Posth, Nicole R

    2008-01-01

    Nicole Posth and colleagues spent a month touring South African rock formations in their quest to understand the origin of ancient iron and silicate layers.......Nicole Posth and colleagues spent a month touring South African rock formations in their quest to understand the origin of ancient iron and silicate layers....

  15. Martian volcanism: A review

    International Nuclear Information System (INIS)

    Carr, M.H.

    1987-01-01

    Martian volcanism is reviewed. It is emphasized that lava plains constitute the major type of effusive flow, and can be differentiated by morphologic characteristics. Shield volcanoes, domes, and patera constitute the major constructional landforms, and recent work has suggested that explosive activity and resulting pyroclastic deposits may have been involved with formation of some of the small shields. Analysis of morphology, presumed composition, and spectroscopic data all indicate that Martian volcanism was dominantly basaltic in composition

  16. Soil gas radon and volcanic activity at El Hierro (Canary Islands) before and after the 2011-2012 submarine eruption

    Science.gov (United States)

    Barrancos, J.; Padilla, G.; Hernandez Perez, P. A.; Padron, E.; Perez, N.; Melian Rodriguez, G.; Nolasco, D.; Dionis, S.; Rodriguez, F.; Calvo, D.; Hernandez, I.

    2012-12-01

    El Hierro is the youngest and southernmost island of the Canarian archipelago and represents the summit of a volcanic shield elevating from the surrounding seafloor at depth of 4000 m to up to 1501 m above sea level. The island is believed to be near the present hotspot location in the Canaries with the oldest subaerial rocks dated at 1.12 Ma. The subaerial parts of the El Hierro rift zones (NE, NW and S Ridges) are characterized by tightly aligned dyke complexes with clusters of cinder cones as their surface expressions. Since July 16, 2011, an anomalous seismicity at El Hierro Island was recorded by IGN seismic network. Volcanic tremor started at 05:15 hours on October 10, followed on the afternoon of October 12 by a green discolouration of seawater, strong bubbling and degassing indicating the initial stage of submarine volcanic eruption at approximately 2 km off the coast of La Restinga, El Hierro. Soil gas 222Rn and 220Rn activities were continuously measured during the period of the recent volcanic unrest occurred at El Hierro, at two different geochemical stations, HIE02 and HIE03. Significant increases in soil 222Rn activity and 222Rn/220Rn ratio from the soil were observed at both stations prior the submarine eruption off the coast of El Hierro, showing the highest increases before the eruption onset and the occurrence of the strongest seismic event (M=4.6). A statistical analysis showed that the long-term trend of the filtered data corresponded closely to the seismic energy released during the volcanic unrest. The observed increases of 222Rn are related to the rock fracturing processes (seismic activity) and the magmatic CO2 outflow increase, as observed in HIE03 station. Under these results, we find that continuous soil radon studies are important for evaluating the volcanic activity of El Hierro and they demonstrate the potential of applying continuous monitoring of soil radon to improve and optimize the detection of early warning signals of future

  17. Multiple edifice-collapse events in the Eastern Mexican Volcanic Belt: The role of sloping substrate and implications for hazard assessment

    Science.gov (United States)

    Carrasco-Nunez, Gerardo; Diaz-Castellon, Rodolfo; Siebert, L.; Hubbard, B.; Sheridan, M.F.; Rodriguez, Sergio R.

    2006-01-01

    The Citlalte??petl-Cofre de Perote volcanic chain forms an important physiographic barrier that separates the Central Altiplano (2500??masl) from the Gulf Coastal Plain (GCP) (1300??masl). The abrupt eastward drop in relief between these provinces gives rise to unstable conditions and consequent gravitational collapse of large volcanic edifices built at the edge of the Altiplano. Eastward sloping substrate, caused by the irregular configuration of the basement rocks, is the dominant factor that controls the direction of collapsing sectors in all major volcanoes in the region to be preferentially towards the GCP. These collapses produced voluminous debris avalanches and lahars that inundated the well-developed drainages and clastic aprons that characterize the Coastal Plain. Large catastrophic collapses from Citlalte??petl, Las Cumbres, and Cofre de Perote volcanoes are well documented in the geologic record. Some of the avalanches and transformed flows have exceptionally long runouts and reach the Gulf of Mexico traveling more than 120??km from their source. So far, no direct evidence has been found for magmatic activity associated with the initiation of these catastrophic flank-collapses. Apparently, instability of the volcanic edifices has been strongly favored by very intense hydrothermal alteration, abrupt topographic change, and intense fracturing. In addition to the eastward slope of the substrate, the reactivation of pre-volcanic basement structures during the Late Tertiary, and the E-W to ENE-SSW oriented regional stress regimes may have played an important role in the preferential movement direction of the avalanches and flows. In addition to magmatic-hydrothermal processes, high amounts of rainfall in the area is another factor that enhances alteration and eventually weakens the rocks. It is very likely that seismic activity may be the principal triggering mechanism that caused the flank collapse of large volcanic edifices in the Eastern Mexican Volcanic

  18. Low-pressure evolution of arc magmas in thickened crust: The San Pedro-Linzor volcanic chain, Central Andes, Northern Chile

    Science.gov (United States)

    Godoy, Benigno; Wörner, Gerhard; Kojima, Shoji; Aguilera, Felipe; Simon, Klaus; Hartmann, Gerald

    2014-07-01

    Magmatism at Andean Central Volcanic Zone (CVZ), or Central Andes, is strongly influenced by differentiation and assimilation at high pressures that occurred at lower levels of the thick continental crust. This is typically shown by high light to heavy rare earth element ratios (LREE/HREE) of the erupted lavas at this volcanic zone. Increase of these ratios with time is interpreted as a change to magma evolution in the presence of garnet during evolution of Central Andes. Such geochemical signals could be introduced into the magmas be high-pressure fractionation with garnet on the liquidus and/or assimilation from crustal rocks with a garnet-bearing residue. However, lavas erupted at San Pedro-Linzor volcanic chain show no evidence of garnet fractionation in their trace element patterns. This volcanic chain is located in the active volcanic arc, between 22°00‧S and 22°30‧S, over a continental crust ˜70 km thick. Sampled lavas show Sr/Y and Sm/Yb ratios Chile. We relate our geochemical observations to shallow crustal evolution of primitive magmas involving a high degree of assimilation of upper continental crust. We emphasize that low pressure AFC- (Assimilation Fractional Crystallization) type evolution of the San Pedro-Linzor volcanic chain reflects storage, fractionation, and contamination of mantle-derived magmas at the upper felsic crust (<40 km depth). The ascent of mantle-derived magmas to mid-crustal levels is related with the extensional regime that has existed in this zone of arc-front offset since Late-Miocene age, and the relatively thin portion of mafic lower crust observed below the volcanic chain.

  19. New insight from noble gas and stable isotopes of geothermal/hydrothermal fluids at Caviahue-Copahue Volcanic Complex: Boiling steam separation and water-rock interaction at shallow depth

    Science.gov (United States)

    Roulleau, Emilie; Tardani, Daniele; Sano, Yuji; Takahata, Naoto; Vinet, Nicolas; Bravo, Francisco; Muñoz, Carlos; Sanchez, Juan

    2016-12-01

    We measured noble gas and stable isotopes of the geothermal and hydrothermal fluids of the Caviahue-Copahue Volcanic Complex (CCVC), one of the most important geothermal systems in Argentina/Chile, in order to provide new insights into fluid circulation and origin. With the exception of Anfiteatro and Chancho-co geothermal systems, mantle-derived helium dominates in the CCVC fluids, with measured 3He/4He ratios up to 7.86Ra in 2015. Their positive δ15N is an evidence for subducted sediment-derived nitrogen, which is commonly observed in subduction settings. Both He-N2-Ar composition and positive correlation between δD-H2O and δ18O-H2O suggest that the fluids from Anfiteatro and Chancho-co (and partly from Pucon-Mahuida as well, on the southern flank of Copahue volcano) represent a meteoric water composition with a minor magmatic contribution. The Ne, Kr and Xe isotopic compositions are entirely of atmospheric origin, but processes of boiling and steam separation have led to fractionation of their elemental abundances. We modeled the CCVC fluid evolution using Rayleigh distillation curves, considering an initial air saturated geothermal water (ASGW) end-member at 250 and 300 °C, followed by boiling and steam separation at lower temperatures (from 200 °C to 150 °C). Between 2014 and 2015, the CCVC hydrogen and oxygen isotopes shifted from local meteoric water-dominated to andesitic water-dominated signature. This shift is associated with an increase of δ13C values and Stotal, HCl and He contents. These characteristics are consistent with a change in the gas ascent pathway between 2014 and 2015, which in turn induced higher magmatic-hydrothermal contribution in the fluid signature. The composition of the magmatic source of the CCVC fluids is: 3He/4He = 7.7Ra, δ15N = + 6‰, and δ13C = - 6.5‰. Mixing models between air-corrected He and N suggest the involvement of 0.5% to 5% of subducted sediments in the magmatic source. The magmatic sulfur isotopic

  20. Experimental leaching of uranium from tuffaceous rocks

    International Nuclear Information System (INIS)

    Goodell, P.C.; Trentham, R.C.

    1980-07-01

    The premise to be tested in this work is that felsic volcanic rocks particularly ash-flow tuffs, can serve as source rocks for certain uranium deposits. The applicability of this idea to several geologic environments is investigated. A genetic model is developed dealing with the behavior of uranium during and subsequent to ash-flow tuff deposition. It is based upon previously described investigations, geologic logic, data presented here, and speculation. Ash-flow tuff sequences described in the literature show significant alkali element variation, particularly in thick tuff units. Some variation is attributed to initial magma variations, whereas additional change may be produced during cooling and degassing of the tuff. Uranium variations have been documented in tuff sequences which are assumed to represent magmatic compositions. Uranium may be released during the initial degassing, during hydrothermal alteration, and/or during later diagenesis. Experimental studies have been designed and carried out to simulate natural leaching conditions such as might occur during diagenesis. Synthetic ground waters have been pumped through pulverized uraniferous vitrophyres. Major and minor element contents have been determined. The most significant chemical changes take place quickly, within a matter of days. Several starting and product leachant solutions were analyzed fluorimetrically for uranium. They show significant increases in uranium contents, from less than 1 ppB at the start to greater than 10 ppB maximu. Such leachant solutions might be significant transport agents of uranium given geologic time. Leaching at low temperatures appears to involve a thin surface reaction and diffusion layer. Both dissolution and ion exchange influence the leachant composition. It is also concluded that glassy ash-flow tuffs may serve as uranium source rocks during low temperature diagenetic changes

  1. The Valle de Bravo Volcanic Field. A monogenetic field in the central front of the Mexican Volcanic Belt

    Science.gov (United States)

    Aguirre-Diaz, G. J.; Jaimes-Viera, M. D.; Nieto-Obreg¢n, J.; Lozano-Santacruz, R.

    2003-12-01

    The Valle de Bravo volcanic field, VBVF, is located in the central-southern front of the Mexican Volcanic Belt just to the southwest of Nevado de Toluca volcano. The VBVF covers 3,703 square Km and includes at least 122 cinder cones, 1 shield volcano, several domes, and the 2 volcanic complexes of Zitacuaro and Villa de Allende. Morphometric parameters calibrated with isotopic ages of the volcanic products indicate four groups or units for the VBVF, Pliocene domes and lava flows, undifferentiated Pleistocene lava flows,> 40 Ka cones and lavas, 40 to 25 Ka cones and lavas, 25 to 10 Ka cones and lavas, and < 10 Ka cones and lavas. Whole-rock chemistry shows that all products of the VBVF range from basaltic andesites to dacites. No basalts were found, in spite of many units are olivine-rich and large some with large weight percent contents of MgO, 1 to 9. There is the possibility that some or all of the olivines in some samples could be xenocrysts. Some andesites are high in Sr, 1000 to 1800 ppm, that correlates with relatively high values of Ba, Cr, Ni, Cu, CaO and MgO. Y and Nb have the typical low values for orogenic rocks. The only shield volcano of the VBVF has a base of 9 Km, and its composition is practically the average composition of the whole field. Stratigraphycally, it is one of the earlier events of the VBVF. Compared with other volcanic fields of the Mexican Volcanic Belt, it lacks basalts and alkalic rocks. All volcanism of this field is calcalkaline

  2. Rock pushing and sampling under rocks on Mars

    Science.gov (United States)

    Moore, H.J.; Liebes, S.; Crouch, D.S.; Clark, L.V.

    1978-01-01

    Viking Lander 2 acquired samples on Mars from beneath two rocks, where living organisms and organic molecules would be protected from ultraviolet radiation. Selection of rocks to be moved was based on scientific and engineering considerations, including rock size, rock shape, burial depth, and location in a sample field. Rock locations and topography were established using the computerized interactive video-stereophotogrammetric system and plotted on vertical profiles and in plan view. Sampler commands were developed and tested on Earth using a full-size lander and surface mock-up. The use of power by the sampler motor correlates with rock movements, which were by plowing, skidding, and rolling. Provenance of the samples was determined by measurements and interpretation of pictures and positions of the sampler arm. Analytical results demonstrate that the samples were, in fact, from beneath the rocks. Results from the Gas Chromatograph-Mass Spectrometer of the Molecular Analysis experiment and the Gas Exchange instrument of the Biology experiment indicate that more adsorbed(?) water occurs in samples under rocks than in samples exposed to the sun. This is consistent with terrestrial arid environments, where more moisture occurs in near-surface soil un- der rocks than in surrounding soil because the net heat flow is toward the soil beneath the rock and the rock cap inhibits evaporation. Inorganic analyses show that samples of soil from under the rocks have significantly less iron than soil exposed to the sun. The scientific significance of analyses of samples under the rocks is only partly evaluated, but some facts are clear. Detectable quantities of martian organic molecules were not found in the sample from under a rock by the Molecular Analysis experiment. The Biology experiments did not find definitive evidence for Earth-like living organisms in their sample. Significant amounts of adsorbed water may be present in the martian regolith. The response of the soil

  3. Art Rocks with Rock Art!

    Science.gov (United States)

    Bickett, Marianne

    2011-01-01

    This article discusses rock art which was the very first "art." Rock art, such as the images created on the stone surfaces of the caves of Lascaux and Altimira, is the true origin of the canvas, paintbrush, and painting media. For there, within caverns deep in the earth, the first artists mixed animal fat, urine, and saliva with powdered minerals…

  4. Lunar cryptomaria: Physical characteristics, distribution, and implications for ancient volcanism

    Science.gov (United States)

    Whitten, Jennifer L.; Head, James W.

    2015-02-01

    Cryptomaria, lunar volcanic deposits obscured by crater and basin impact ejecta, can provide important information about the thermal and volcanic history of the Moon. The timing of cryptomare deposition has implications for the duration and flux of mare basalt volcanism. In addition, knowing the distribution of cryptomaria can provide information about mantle convection and lunar magma ocean solidification. Here we use multiple datasets (e.g., M3, LOLA, LROC, Diviner) to undertake a global analysis to identify the general characteristics (e.g., topography, surface roughness, rock abundance, albedo, etc.) of lunar light plains in order to better distinguish between ancient volcanic deposits (cryptomaria) and impact basin and crater ejecta deposits. We find 20 discrete regions of cryptomaria, covering approximately 2% of the Moon, which increase the total area covered by mare volcanism to 18% of the lunar surface. Comparisons of light plains deposits indicate that the two deposit types (volcanic and impact-produced) are best distinguished by mineralogic data. On the basis of cryptomaria locations, the distribution of mare volcanism does not appear to have changed in the time prior to its exposed mare basalt distribution. There are several hypotheses explaining the distribution of mare basalts, which include the influence of crustal thickness, mantle convection patterns, asymmetric distribution of source regions, KREEP distribution, and the influence of a proposed Procellarum impact basin. The paucity of farside mare basalts means that multiple factors, such as crustal thickness variations and mantle convection, are likely to play a role in mare basalt emplacement.

  5. Late Cretaceous transition from subduction to collision along the Bangong-Nujiang Tethys: New volcanic constraints from central Tibet

    Science.gov (United States)

    Liu, De-Liang; Shi, Ren-Deng; Ding, Lin; Zou, Hai-Bo

    2018-01-01

    This study deals with arc-type and subsequent bimodal volcanic rocks interbedded with (late) Cretaceous sedimentary formations near Gaize, central Tibet that shed new light on the Tethyan evolution along the Bangong-Nujiang suture. Unit I consists of trachyandesites interbedded with fine-grained sandstone, slate, and limestone. Zircon dating on a trachyandesite sample yields a 206Pb/238U age of 99 ± 1 Ma. The trachyandesites are characterized by strong enrichment in LILE but depletion in HFSE, low zircon saturation temperatures (TZr = 642-727 °C), and high oxygen fugacity (Δ FMQ = - 0.67-0.73), indicating their arc affinities. Unit II comprises a bimodal basalt-rhyolite suite interbedded with coarse-grained sandstone and conglomerate. Zircon dating on two rhyolitic samples yield 206Pb/238U ages of 97.1-87.0 Ma. In contrast with Unit I trachyandesites, Unit II basalts and rhyolites exhibit OIB-like trace element patterns, high temperatures (T = 1298-1379 °C for basalts, TZr = 855-930 °C for rhyolites), and low oxygen fugacity (Δ FMQ = - 3.37 - 0.43), suggesting that Unit II bimodal volcanic rocks probably formed in an extensional setting. The Sr-Nd isotopes of both Unit I (87Sr/86Sri = 0.7052-0.7074, εNd(t) = - 2.21-1.02) and Unit II (87Sr/86Sri = 0.7057-0.7098, εNd(t) = - 3.22-0.88) rocks are similar to mantle-wedge-derived volcanic rocks within the southern Qiangtang block. The parental magma of Unit I trachyandesites was formed by fluid induced melting of the mantle wedge above the subducted Bangong-Nujiang Tethyan slab, and contaminated by crustal materials during MASH process within a deep crustal hot zone; and Unit II bimodal volcanic rocks were derived by melting of upwelling asthenosphere and a mildly metasomatized mantle wedge during the Lhasa-Qiangtang collision. We propose that the transition from the Bangong-Nujiang Tethyan subduction to the Lhasa-Qiangtang collision occurred during the Late Cretaceous in central Tibet.

  6. Palaeomagnetic constraints on the age of Lomo Negro volcanic eruption (El Hierro, Canary Islands)

    Science.gov (United States)

    Villasante-Marcos, Víctor; Pavón-Carrasco, Francisco Javier

    2014-12-01

    A palaeomagnetic study has been carried out in 29 cores drilled at six different sites from the volcanic products of Lomo Negro eruption (El Hierro, Canary Islands, Spain). Systematic thermal and alternating field demagnetization of the samples' natural remanent magnetization revealed a northward, stable palaeomagnetic direction similar in all the samples. Rock magnetic experiments indicate that this palaeomagnetic component is carried by a mixture of high-Ti and low-Ti titanomagnetite crystals typical of basaltic lithologies that have experienced a significant degree of oxyexsolution during subaerial cooling. The well constrained palaeomagnetic direction of Lomo Negro lavas was used to perform a palaeomagnetic dating of the volcanic event, using the SHA.DIF.14k global geomagnetic model restricted for the last 3000 yr. It can be unambiguously concluded that Lomo Negro eruption occurred well before the previously proposed date of 1793 AD, with three different age ranges being statistically possible during the last 3 ka: 115 BC-7 AD, 410-626 AD and 1499-1602 AD. The calibration of a previously published non-calibrated 14C dating suggests a XVI c. date for Lomo Negro eruption. This conclusion leaves open the possibility that the seismic crisis occurred at El Hierro in 1793 AD was related to an intrusive magmatic event that either did not reach the surface or either culminated in an unregistered submarine eruption similar to the one occurred in 2011-2012 at the southern off-shore ridge of the island.

  7. Sphene and zircon in the Highland Range volcanic sequence (Miocene, southern Nevada, USA): Elemental partitioning, phase relations, and influence on evolution of silicic magma

    Science.gov (United States)

    Colombini, L.L.; Miller, C.F.; Gualda, G.A.R.; Wooden, J.L.; Miller, J.S.

    2011-01-01

    Sphene is prominent in Miocene plutonic rocks ranging from diorite to granite in southern Nevada, USA, but it is restricted to rhyolites in coeval volcanic sequences. In the Highland Range volcanic sequence, sphene appears as a phenocryst only in the most evolved rocks (72-77 mass% SiO2; matrix glass 77-78 mass% SiO2). Zr-in-sphene temperatures of crystallization are mostly restricted to 715 and 755??C, in contrast to zircon (710-920??C, Ti-in-zircon thermometry). Sphene rim/glass Kds for rare earth elements are extremely high (La 120, Sm 1200, Gd 1300, Lu 240). Rare earth elements, especially the middle REE (MREE), decrease from centers to rims of sphene phenocrysts along with Zr, demonstrating the effect of progressive sphene fractionation. Whole rocks and glasses have MREE-depleted, U-shaped REE patterns as a consequence of sphene fractionation. Within the co-genetic, sphene-rich Searchlight pluton, only evolved leucogranites show comparable MREE depletion. These results indicate that sphene saturation in intruded and extruded magmas occurred only in highly evolved melts: abundant sphene in less silicic plutonic rocks represents a late-stage 'bloom' in fractionated interstitial melt. ?? 2011 Springer-Verlag.

  8. Rock Physics

    DEFF Research Database (Denmark)

    Fabricius, Ida Lykke

    2017-01-01

    Rock physics is the discipline linking petrophysical properties as derived from borehole data to surface based geophysical exploration data. It can involve interpretation of both elastic wave propagation and electrical conductivity, but in this chapter focus is on elasticity. Rock physics is based...... on continuum mechanics, and the theory of elasticity developed for statics becomes the key to petrophysical interpretation of velocity of elastic waves. In practice, rock physics involves interpretation of well logs including vertical seismic profiling (VSP) and analysis of core samples. The results...

  9. Descartes region - Evidence for Copernican-age volcanism.

    Science.gov (United States)

    Head, J. W., III; Goetz, A. F. H.

    1972-01-01

    A model that suggests that the high-albedo central region of the Descartes Formation was formed by Copernican-age volcanism was developed from Orbiter photography, Apollo 12 multispectral photography, earth-based spectrophotometry, and thermal IR and radar data. The bright surface either is abundant in centimeter-sized rocks or is formed from an insulating debris layer overlying a surface with an abundance of rocks in the 1- to 20-cm size range. On the basis of these data, the bright unit is thought to be a young pyroclastic deposit mantling older volcanic units of the Descartes Formation. Since the Apollo 16 target point is only 50 km NW of the central part of this unit, evidence for material associated with this unique highland formation should be searched for in returned soil and rock samples.

  10. Comparison of hydrothermal alteration patterns associated with porphyry Cu deposits hosted by granitoids and intermediate-mafic volcanic rocks, Kerman Magmatic Arc, Iran: Application of geological, mineralogical and remote sensing data

    Science.gov (United States)

    Yousefi, Seyyed Jabber; Ranjbar, Hojjatollah; Alirezaei, Saeed; Dargahi, Sara; Lentz, David R.

    2018-06-01

    The southern section of the Cenozoic Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran, known as Kerman Magmatic Arc (KMA) or Kerman copper belt, is a major host to porphyry Cu ± Mo ± Au deposits, collectively known as PCDs. In this study, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and spectral angle mapper (SAM) method, combined with field data, mineralogical studies, and spectral analysis are used to determine hydrothermal alteration patterns related to PCDs in the KMA. Gossans developed over some of these porphyry type deposits were mapped using Landsat 8 data. In the NKMA gossans are more developed than in the SKMA due to comparatively lower rate of erosion. The hydrothermal alteration pattern mapped by ASTER data were evaluated using mineralogical and spectral data. ASTER data proved to be useful for mapping the hydrothermal alteration in this semi-arid type of climate. Also Landsat 8 was useful for mapping the iron oxide minerals in the gossans that are associated with the porphyry copper deposits. Our multidisciplinary approach indicates that unlike the PCDs in the northern KMA that are associated with distinct and widespread propylitic alteration, those in the granitoid country rocks lack propylitic alteration or the alteration is only weakly and irregularly developed. The porphyry systems in southern KMA are further distinguished by development of quartz-rich phyllic alteration zones in the outer parts of the PCDs that could be mapped using remote sensing data. Consideration of variations in alteration patterns and specific alteration assemblages are critical in regional exploration for PCDs.

  11. Constructional Volcanic Edifices on Mercury: Candidates and Hypotheses of Formation

    Science.gov (United States)

    Wright, Jack; Rothery, David A.; Balme, Matthew R.; Conway, Susan J.

    2018-04-01

    Mercury, a planet with a predominantly volcanic crust, has perplexingly few, if any, constructional volcanic edifices, despite their common occurrence on other solar system bodies with volcanic histories. Using image and topographical data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, we describe two small (Earth and the Moon. Though we cannot definitively conclude that these landforms are volcanic, the paucity of constructional volcanic edifices on Mercury is intriguing in itself. We suggest that this lack is because volcanic eruptions with sufficiently low eruption volumes, rates, and flow lengths, suitable for edifice construction, were highly spatiotemporally restricted during Mercury's geological history. We suggest that volcanic edifices may preferentially occur in association with late-stage, postimpact effusive volcanic deposits. The European Space Agency/Japan Aerospace Exploration Agency BepiColombo mission to Mercury will be able to investigate further our candidate volcanic edifices; search for other, as-yet unrecognized edifices beneath the detection limits of MESSENGER data; and test our hypothesis that edifice construction is favored by late-stage, low-volume effusive eruptions.

  12. Petrographic and Geochemical Investigation of Andesitic Arc Volcanism: Mount Kerinci, Sunda Arc, Indonesia

    Science.gov (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.

    2014-12-01

    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

  13. Volcanic hazards to airports

    Science.gov (United States)

    Guffanti, M.; Mayberry, G.C.; Casadevall, T.J.; Wunderman, R.

    2009-01-01

    Volcanic activity has caused significant hazards to numerous airports worldwide, with local to far-ranging effects on travelers and commerce. Analysis of a new compilation of incidents of airports impacted by volcanic activity from 1944 through 2006 reveals that, at a minimum, 101 airports in 28 countries were affected on 171 occasions by eruptions at 46 volcanoes. Since 1980, five airports per year on average have been affected by volcanic activity, which indicates that volcanic hazards to airports are not rare on a worldwide basis. The main hazard to airports is ashfall, with accumulations of only a few millimeters sufficient to force temporary closures of some airports. A substantial portion of incidents has been caused by ash in airspace in the vicinity of airports, without accumulation of ash on the ground. On a few occasions, airports have been impacted by hazards other than ash (pyroclastic flow, lava flow, gas emission, and phreatic explosion). Several airports have been affected repeatedly by volcanic hazards. Four airports have been affected the most often and likely will continue to be among the most vulnerable owing to continued nearby volcanic activity: Fontanarossa International Airport in Catania, Italy; Ted Stevens Anchorage International Airport in Alaska, USA; Mariscal Sucre International Airport in Quito, Ecuador; and Tokua Airport in Kokopo, Papua New Guinea. The USA has the most airports affected by volcanic activity (17) on the most occasions (33) and hosts the second highest number of volcanoes that have caused the disruptions (5, after Indonesia with 7). One-fifth of the affected airports are within 30 km of the source volcanoes, approximately half are located within 150 km of the source volcanoes, and about three-quarters are within 300 km; nearly one-fifth are located more than 500 km away from the source volcanoes. The volcanoes that have caused the most impacts are Soufriere Hills on the island of Montserrat in the British West Indies

  14. Rocking pneumonia

    OpenAIRE

    Rijkers, Ger T.; Rodriguez Gomez, Maria

    2017-01-01

    Ever since Chuck Berry coined the term “rocking pneumonia” in his 1956 song “Roll over Beethoven”, pneumonia has been mentioned frequently in modern blues and rock songs. We analyzed the lyrics of these songs to examine how various elements of pneumonia have been represented in popular music, specifically the cause of pneumonia, the risk groups, comorbidity (such as the boogie woogie flu), the clinical symptoms, and treatment and outcome. Up to this day, songwriters suggest that pneumonia is ...

  15. Major-element geochemistry of the Silent Canyon--Black Mountain peralkaline volcanic centers, northwestern Nevada Test Site: applications to an assessment of renewed volcanism

    International Nuclear Information System (INIS)

    Crowe, B.M.; Sargent, K.A.

    1979-01-01

    The Silent Canyon and Black Mountain volcanic centers are located in the northern part of the Nevada Test Site. The Silent Canyon volcanic center is a buried cauldron complex of Miocene age (13 to 15 m.y.). Black Mountain volcanic center is an elliptical-shaped cauldron complex of late Miocene age. The lavas and tuffs of the two centers comprise a subalkaline-peralkaline association. Rock types range from quartz normative subalkaline trachyte and rhyolite to peralkaline commendite. The Gold Flat Member of the Thirsty Canyon Tuff (Black Mountain) is a pantellerite. The major-element geochemistry of the Black Mountain--Silent Canyon volcanic centers differ in the total range and distribution of SiO 2 , contents, the degree of peralkalinity (molecular Na 2 O + K 2 O > Al 2 O 3 ) and in the values of total iron and alumina through the range of rock types. These differences indicate that the suites were unrelated and evolved from differing magma bodies. The Black Mountain volcanic cycle represents a renewed phase of volcanism following cessation of the Timber Mountain--Silent Canyon volcanic cycles. Consequently, there is a small but numerically incalculable probability of recurrence of Black Mountain-type volcanism within the Nevada Test Site region. This represents a potential risk with respect to deep geologic storage of high-level radioactive waste at the Nevada Test Site

  16. Fire effects on rock images and similar cultural resources [Chapter 5

    Science.gov (United States)

    Roger E. Kelly; Daniel F. McCarthy

    2012-01-01

    Throughout human global history, people have purposely altered natural rock surfaces by drilling, drawing, painting, incising, pecking, abrading and chiseling images into stone. Some rock types that present suitable media surfaces for these activities are fine-grained sandstones and granites, basalts, volcanic tuff, dolomites, and limestones. Commonly called rock...

  17. Carbon and Noble Gas Isotopes in the Tengchong Volcanic Geothermal Area, Yunnan, Southwestern China

    Institute of Scientific and Technical Information of China (English)

    XU Sheng; Shun'ich NAKAI; Hiroshi WAKITA; WANG Xianbin

    2004-01-01

    Carbon and noble gas isotope analyses are reported for bubbling gas samples from the Tengchong volcanic geothermal area near the Indo-Eurasian suture zone. All samples contain a resolvable component of mantle-derived 3He.Occurrence of mantle-derived 3He coincides with surface volcanism. However, 3He occurs over a larger geographic area than do surface volcanics. δ13C values for CO2 and CH4 vary from -33.4 ‰ to 1.6 ‰ and from -52.8 ‰ to -2.8 ‰,respectively. He and C isotope systematics indicate that CO2 and CH4 in the CO2-rich gases originated predominantly from magmatic component mixed with crustal CO2 produced from carbonate. However, breakdown of organic matter and nearsurface processes accounts for the CH4 and CO2 in N2-rich gases. 3He/4He ratio distribution pattern suggests that mantlederived He and heat sources of high-temperature system in central Tengchong originate from a hidden magma reservoir at subsurface. CO2-rich gases with the highest 3He/4He ratio (5.2 Ra) may be representative of the Tengchong magmatic component. Compared with MORB, this relative low 3He/4He ratio could be fully attributed to either deep crustal contamination, or radioactive aging, or past contamination of the local mantle by U- and Th-rich subducted crustal material.However, a combination of low 3He/4He, high radiogenic 4He/40Ar ratio and identical CO2/3He and δ13Cco2 relative to MORB may suggest addition of prior subductedd crsustal material (ca 1%-2%) to the MORB reservoir around 1.3 Ga ago,which is essentially compatible with the LIL-elements, and Sr-Nd-Pb isotopes of volcanic rocks.

  18. Timing and composition of continental volcanism at Harrat Hutaymah, western Saudi Arabia

    Science.gov (United States)

    Duncan, Robert A.; Kent, Adam J R; Thornber, Carl; Schliedler, Tyler D; Al-Amri, Abdullah M

    2016-01-01

    Harrat Hutaymah is an alkali basalt volcanic field in north-central Saudi Arabia, at the eastern margin of a large Neogene continental, intraplate magmatic province. Lava flow, tephra and spatter cone compositions in the field include alkali olivine basalts and basanites. These compositions contrast with the predominantly tholeiitic, fissure-fed basalts found along the eastern margin of the Red Sea. The Hutaymah lava flows were erupted through Proterozoic arc-associated plutonic and meta-sedimentary rocks of the Arabian shield, and commonly contain a range of sub-continental lithospheric xenoliths, although the lavas themselves show little indication of crustal contamination. Previous radiometric dating of this volcanic field (a single published K–Ar age; 1.8 Ma) is suspiciously old given the field measurement of normal magnetic polarity only (i.e. Brunhes interval, ≤ 780 Ka). We report new age determinations on 14 lava flows by the 40Ar–39Ar laser step heating method, all younger than ~ 850 Ka, to better constrain the time frame of volcanism, and major, trace and rare earth element compositions to describe the chemical variation of volcanic activity at Harrat Hutaymah. Crystal fractionation was dominated by olivine ± clinopyroxene at a range of upper mantle and crustal pressures. Rapid ascent and eruption of magma is indicated by the array of lower crustal and lithospheric xenoliths observed in lava flows and tephra. Modeling suggests 1–7% melting of an enriched asthenospheric mantle source occurred beneath Harrat Hutaymah under a relatively thick lithospheric cap (60–80 km).

  19. Groundwater flow in a relatively old oceanic volcanic island: The Betancuria area, Fuerteventura Island, Canary Islands, Spain

    Energy Technology Data Exchange (ETDEWEB)

    Herrera, Christian, E-mail: cherrera@ucn.cl [Universidad Católica del Norte, Av. Angamos 0610, Antofagasta (Chile); Custodio, Emilio [Department of Geo-Engineering, Technical University of Catalonia (UPC), Barcelona (Spain)

    2014-10-15

    The island of Fuerteventura is the oldest of the Canary Islands' volcanic archipelago. It is constituted by volcanic submarine and subaerial activity and intrusive Miocene events, with some residual later volcanism and Quaternary volcanic deposits that have favored groundwater recharge. The climate is arid, with an average rainfall that barely attains 60 mm/year in the coast and up to 200 mm/year in the highlands. The aquifer recharge is small but significant; it is brackish due to large airborne atmospheric salinity, between 7 and 15 g m{sup −2} year{sup −1} of chloride deposition, and high evapo-concentration in the soil. The average recharge is estimated to be less than about 5 mm/year at low altitude and up to 10 mm/year in the highlands, and up to 20 mm/year associated to recent lava fields. Hydrochemical and water isotopic studies, supported by water table data and well and borehole descriptions, contribute a preliminary conceptual model of groundwater flow and water origin in the Betancuria area, the central area of the island. In general, water from springs and shallow wells tends to be naturally brackish and of recent origin. Deep saline groundwater is found and is explained as remnants of very old marine water trapped in isolated features in the very low permeability intrusive rocks. Preliminary radiocarbon dating indicates that this deep groundwater has an apparent age of less than 5000 years BP but it is the result of mixing recent water recharge with very old deep groundwater. Most of the groundwater flow occurs through the old raised volcanic shield of submarine and subaerial formations and later Miocene subaerial basalts. Groundwater transit time through the unsaturated zone is of a few decades, which allows the consideration of long-term quasi-steady state recharge. Transit times are up to a few centuries through the saturated old volcanics and up to several millennia in the intrusive formations, where isolated pockets of very old water may

  20. The effects of naturally occurring impurities in rock salt

    Indian Academy of Sciences (India)

    Author Affiliations. Alina-Mihaela Badescu1 Alexandra Saftoiu2. University POLITEHNICA of Bucharest, Splaiul Independen¸tei 313, Sector 6, Bucharest 060042, Romania; IFIN-Horia Hulubei, Str. Reactorului No. 30, P.O. Box MG-6, Bucharest-Magurele, Romania ...

  1. The effects of naturally occurring impurities in rock salt

    Indian Academy of Sciences (India)

    Askaryan effect [1] travel through salt, and so the propagation medium has a ... where the real part is the relative permittivity and the imaginary part is the ... When a time-varying field is applied, the complex electronic polarizability is given by.

  2. Petrologic Aspects of Seamount and Guyot Volcanism on the Ancestral Mesozoic Pacific Plate: a Review

    Science.gov (United States)

    Natland, J. H.

    2007-12-01

    Hundreds of large seamounts and guyots are widely scattered almost in a "shotgun-blast" arrangement in an area about the size of the United States west of the Mississippi River on the Mesozoic Pacific plate between the Mariana Trench and the Gilbert Islands. Most of these formed between ~160-100 Ma while the Pacific plate was surrounded by spreading ridges and growing outward in all directions. There is little to no indication that the seamounts and guyots formed along linear seamount chains; existing radiometric-age data show no age progressions. The volcanoes appear to have formed in response to a uniform stress configuration across the plate, which was either not moving or moving very slowly at the time (1, 2), much like the modern Antarctic plate. When the growing plate started to encounter subduction systems in the western Pacific at ~90 Ma, consistent stress patterns began to develop, and the broad linear Gilbert and Line volcanic ridge systems began to form. Even then, however, considerable overlapping of volcanism occurred, and only the most general age progressions are evident in existing data. Petrologic data from samples obtained from dozens of volcanic summits by dredging and beneath several carbonate platforms by drilling reveal considerable diversity in development of differentiated alkalic magmatic lineages rooted in diverse parental basaltic rocks. These include transitional, alkalic and basanitic compositions, with differentiates of hawaiite, mugearite, trachyte and one phonolite. Many of the basaltic rocks are partly to significantly transformed by alteration under oxidative conditions (dredged rocks) and both oxidative and non-oxidative conditions (drilled rocks). This can make estimations of mantle geochemical provenance difficult. Nevertheless, the province has been linked by backtracking techniques to the modern SOPITA region of the South Pacific (3), and its rocks show enrichments in trace elements and isotopic characteristics similar to

  3. Volcanic hazards and public response

    Science.gov (United States)

    Peterson, Donald W.

    1988-05-01

    Although scientific understanding of volcanoes is advancing, eruptions continue to take a substantial toll of life and property. Some of these losses could be reduced by better advance preparation, more effective flow of information between scientists and public officials, and better understanding of volcanic behavior by all segments of the public. The greatest losses generally occur at volcanoes that erupt infrequently where people are not accustomed to dealing with them. Scientists sometimes tend to feel that the blame for poor decisions in emergency management lies chiefly with officials or journalists because of their failure to understand the threat. However, the underlying problem embraces a set of more complex issues comprising three pervasive factors. The first factor is the volcano: signals given by restless volcanoes are often ambiguous and difficult to interpret, especially at long-quiescent volcanoes. The second factor is people: people confront hazardous volcanoes in widely divergent ways, and many have difficulty in dealing with the uncertainties inherent in volcanic unrest. The third factor is the scientists: volcanologists correctly place their highest priority on monitoring and hazard assessment, but they sometimes fail to explain clearly their conclusions to responsible officials and the public, which may lead to inadequate public response. Of all groups in society, volcanologists have the clearest understanding of the hazards and vagaries of volcanic activity; they thereby assume an ethical obligation to convey effectively their knowledge to benefit all of society. If society resists, their obligation nevertheless remains. They must use the same ingenuity and creativity in dealing with information for the public that they use in solving scientific problems. When this falls short, even excellent scientific results may be nullified.

  4. The Geology And Geochemistry Of Zona Uranium Occurence, Upper Benue Trough; N.E. Nigeria

    International Nuclear Information System (INIS)

    Ogunleye, P.O.; Okujeni, C.D.

    1993-01-01

    The Zona uranium is located at the NE flank of the Peta syncline, which is an arm of the Middle Gongola Basin. The hostreok- the Cretaceous Bima sandstone bears the imprint of more than two preore tectonic episodes which are thought to have resulted from reactivation of paleolineaments in the basement since the Pan African Orogeny. The mineralized zone occurs at point of intersection of a set of NE-SW trending shear zone and N-S fracture system. The centre of the ore zone exhibits intense alteration features such as sericitization, ferruginization, silification, remobilization and powdering of the rock matrix. These alteration features diminish progressively from the core to the periphery of the ore zone. The main uraniferous minerals identified are phosphouranylite and meta-autunite. These occur mainly absorbed to iron oxides, in silicified veinlets and partly disseminated in the matrix of the sandstone. Evaluation of the analytical data of 9 elements in 67 rock samples suggest a close link between ferruginization and enrichment of uranium. A model involving the leaching of the uranium from conceal volcanics (rhyolites) and granites at depths by heated groundwater residual magmatic solutions is proposed

  5. The Geology And Geochemistry Of Zona Uranium Occurence, Upper Benue Trough; N.E. Nigeria.

    Energy Technology Data Exchange (ETDEWEB)

    Ogunleye, P O [Centre For Energy Research And Training, Ahmadu Bello University, Zaria (Nigeria); Okujeni, C D [Department Of Geology, Ahmadu Bello University, Zaria (Nigeria)

    1994-12-31

    The Zona uranium is located at the NE flank of the Peta syncline, which is an arm of the Middle Gongola Basin. The hostreok- the Cretaceous Bima sandstone bears the imprint of more than two preore tectonic episodes which are thought to have resulted from reactivation of paleolineaments in the basement since the Pan African Orogeny. The mineralized zone occurs at point of intersection of a set of NE-SW trending shear zone and N-S fracture system. The centre of the ore zone exhibits intense alteration features such as sericitization, ferruginization, silification, remobilization and powdering of the rock matrix. These alteration features diminish progressively from the core to the periphery of the ore zone. The main uraniferous minerals identified are phosphouranylite and meta-autunite. These occur mainly absorbed to iron oxides, in silicified veinlets and partly disseminated in the matrix of the sandstone. Evaluation of the analytical data of 9 elements in 67 rock samples suggest a close link between ferruginization and enrichment of uranium. A model involving the leaching of the uranium from conceal volcanics (rhyolites) and granites at depths by heated groundwater residual magmatic solutions is proposed.

  6. Influences on the variability of eruption sequences and style transitions in the Auckland Volcanic Field, New Zealand

    Science.gov (United States)

    Kereszturi, Gábor; Németh, Károly; Cronin, Shane J.; Procter, Jonathan; Agustín-Flores, Javier

    2014-10-01

    Monogenetic basaltic volcanism is characterised by a complex array of eruptive behaviours, reflecting spatial and temporal variability of the magmatic properties (e.g. composition, eruptive volume, magma flux) as well as environmental factors at the vent site (e.g. availability of water, country rock geology, faulting). These combine to produce changes in eruption style over brief periods (minutes to days) in many eruption episodes. Monogenetic eruptions in some volcanic fields often start with a phreatomagmatic vent-opening phase that later transforms into "dry" magmatic explosive or effusive activity, with a strong variation in the duration and importance of this first phase. Such an eruption sequence pattern occurred in 83% of the known eruption in the 0.25 My-old Auckland Volcanic Field (AVF), New Zealand. In this investigation, the eruptive volumes were compared with the sequences of eruption styles preserved in the pyroclastic record at each volcano of the AVF, as well as environmental influencing factors, such as distribution and thickness of water-saturated semi- to unconsolidated sediments, topographic position, distances from known fault lines. The AVF showed that there is no correlation between ejecta ring volumes and environmental influencing factors that is valid for the entire AVF. In contrary, using a set of comparisons of single volcanoes with well-known and documented sequences, resultant eruption sequences could be explained by predominant patterns of the environment in which these volcanoes were erupted. Based on the spatial variability of these environmental factors, a first-order susceptibility hazard map was constructed for the AVF that forecasts areas of largest likelihood for phreatomagmatic eruptions by overlaying topographical and shallow geological information. Combining detailed phase-by-phase breakdowns of eruptive volumes and the event sequences of the AVF, along with the new susceptibility map, more realistic eruption scenarios can be

  7. Igneous rocks formed by hypervelocity impact

    Science.gov (United States)

    Osinski, Gordon R.; Grieve, Richard A. F.; Bleacher, Jacob E.; Neish, Catherine D.; Pilles, Eric A.; Tornabene, Livio L.

    2018-03-01

    Igneous rocks are the primary building blocks of planetary crusts. Most igneous rocks originate via decompression melting and/or wet melting of protolith lithologies within planetary interiors and their classification and compositional, petrographic, and textural characteristics, are well-studied. As our exploration of the Solar System continues, so too does the inventory of intrusive and extrusive igneous rocks, settings, and processes. The results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected, and will continue to affect, all planetary objects with a solid surface, whether that be rock or ice. It is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact. The goal of this review is to provide an up-to-date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact. Following a brief overview of the basics of the impact process, we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes. While the process may differ, we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin. Such impact melt rocks, as they are termed, can display lobate margins and cooling cracks, columnar joints and at the hand specimen and microscopic scale, such rocks can display mineral textures that are typical of volcanic rocks, such as quench crystallites, ophitic, porphyritic, as well as features such as vesicles, flow textures, and so on. Historically, these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin. This raises the question as to how to distinguish between an impact versus an endogenic origin for igneous-like rocks on other planetary bodies where fieldwork and sample analysis may not

  8. Review of the petrology of the Auckland Volcanic Field

    International Nuclear Information System (INIS)

    Smith, I.E.M.; McGee, L.E.; Lindsay, J.M.

    2009-01-01

    Research has long shown that the petrology of suites of volcanic rock can be used to define and understand the fundamental parameters of the magmatic systems that feed volcanoes. The geochemistry of volcanic rocks provides information about the nature of the source rocks, depths and amounts of melting, the processes that act on magmas as they rise to the surface and, most importantly, the rates of these processes. In turn, the answers to fundamental petrological questions can provide input to important questions concerning volcano hazard scenarios and hazard mitigation challenges. The multi-disciplinary DEVORA research programme, launched in 2008, is a GNS Science-University of Auckland collaboration with the aim of DEtermining VOlcanic Risk in Auckland. One of its main themes is the development of an integrated geological model for the Auckland Volcanic Field (AVF) by investigating the physical controls on magma generation, ascent and eruption though detailed structural and petrological investigations. A key data set underpinning this theme is a comprehensive geochemical database for the rocks of the AVF. This report, Review of the Petrology of the Auckland Volcanic Field, is a synthesis and commentary of all petrological and geochemical data currently available for the AVF. It represents one of several reports carried out as part of the 'synthesis' phase of DEVORA, whereby existing data from previous work is collated and summarised, so that gaps in current knowledge can be appropriately addressed. In this report we utilise published and unpublished sources to summarise the petrological data available up to May 2009, and identify where new data and approaches will improve our understanding of the magmatic system which feeds the field. (author). 53 refs., 7 figs., 2 tabs.

  9. Post-Laramide and pre-Basin and Range deformation and implications for Paleogene (55-25 Ma) volcanism in central Mexico: A geological basis for a volcano-tectonic stress model

    Science.gov (United States)

    Tristán-González, Margarito; Aguirre-Díaz, Gerardo J.; Labarthe-Hernández, Guillermo; Torres-Hernández, José Ramón; Bellon, Hervé

    2009-06-01

    At central-eastern Mexico, in the Mesa Central province, there are several ranges that were formed after the K/T Laramide compression but before the Basin and Range peak extensional episodes at middle-late Oligocene. Two important volcano-tectonic events happened during this time interval, 1) uplift of crustal blocks exhuming the Triassic-Jurassic metamorphic sequence and formation of basins that were filled with red beds and volcanic sequences, and 2) normal faulting and tilting to the NE of these blocks and fanglomerate filling of graben and half-graben structures. The first event, from late Paleocene to early Eocene, was related to NNE and NNW oriented dextral strike-slip faults. These faults were combined with NW-SE en echelon faulting in these blocks through which plutonism and volcanism occurred. The second event lasted from early Oligocene to early Miocene and coincided with Basin and Range extension. Intense volcanic activity occurred synchronously with the newly-formed or reactivated old fault systems, producing thick sequences of silicic pyroclastic rocks and large domes. Volcano-tectonic peaks occurred in three main episodes during the middle-late Oligocene in this part of Mexico, at about 32-30 Ma, 30-28 Ma, and 26-25 Ma. The objectives of this work is to summarize the volcano-tectonic events that occurred after the end of the Laramide orogeny and before the peak episodes of Basin and Range faulting and Sierra Madre Occidental Oligocene volcanism, and to discuss the influence of these events on the following Oligocene-Miocene volcano-tectonic peak episodes that formed the voluminous silicic volcanism in the Mesa Central, and hence, in the Sierra Madre Occidental. A model based upon geological observations summarizes the volcanic-tectonic evolution of this part of Mexico from the late Paleocene to the Early Miocene.

  10. Ash production by attrition in volcanic conduits and plumes.

    Science.gov (United States)

    Jones, T J; Russell, J K

    2017-07-17

    Tephra deposits result from explosive volcanic eruption and serve as indirect probes into fragmentation processes operating in subsurface volcanic conduits. Primary magmatic fragmentation creates a population of pyroclasts through volatile-driven decompression during conduit ascent. In this study, we explore the role that secondary fragmentation, specifically attrition, has in transforming primary pyroclasts upon transport in volcanic conduits and plumes. We utilize total grain size distributions from a suite of natural and experimentally produced tephra to show that attrition is likely to occur in all explosive volcanic eruptions. Our experimental results indicate that fine ash production and surface area generation is fast (eruption column stability, tephra dispersal, aggregation, volcanic lightening generation, and has concomitant effects on aviation safety and Earth's climate.

  11. Ponds, Flows, and Ejecta of Impact Cratering and Volcanism: A Remote Sensing Perspective of a Dynamic Moon

    Science.gov (United States)

    Stopar, Julie D.

    Both volcanism and impact cratering produce ejecta and associated deposits incorporating a molten rock component. While the heat sources are different (exogenous vs. endogenous), the end results are landforms with similar morphologies including ponds and flows of impact melt and lava around the central crater. Ejecta from both impact and volcanic craters can also include a high percentage of melted rock. Using Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) images, crucial details of these landforms are finally revealed, suggesting a much more dynamic Moon than is generally appreciated. Impact melt ponds and flows at craters as small as several hundred meters in diameter provide empirical evidence of abundant melting during the impact cratering process (much more than was previously thought), and this melt is mobile on the lunar surface for a significant time before solidifying. Enhanced melt deposit occurrences in the lunar highlands (compared to the mare) suggest that porosity, target composition, and pre-existing topography influence melt production and distribution. Comparatively deep impact craters formed in young melt deposits connote a relatively rapid evolution of materials on the lunar surface. On the other end of the spectrum, volcanic eruptions have produced the vast, plains-style mare basalts. However, little was previously known about the details of small-area eruptions and proximal volcanic deposits due to a lack of resolution. High-resolution images reveal key insights into small volcanic cones (0.5-3 km in diameter) that resemble terrestrial cinder cones. The cones comprise inter-layered materials, spatter deposits, and lava flow breaches. The widespread occurrence of the cones in most nearside mare suggests that basaltic eruptions occur from multiple sources in each basin and/or that rootless eruptions are relatively common. Morphologies of small-area volcanic deposits indicate diversity in eruption behavior of lunar basaltic

  12. Rock mass evaluation for predicting tunnel constructability in the preliminary investigation stage. Phenomena causing difficult tunneling and rockburst prediction

    International Nuclear Information System (INIS)

    Shin, Koichi; Sawada, Masataka; Inohara, Yoshiki; Shidahara, Takumi; Hatano, Teruyoshi

    2011-01-01

    For the selection of the Detailed Investigation Areas for HLW disposal, predicting the tunnel constructability is one of the requirements together with assessing long-term safety. This report is the 1st of the three papers dealing with the evaluation of tunnel constructability. This paper deals with the geological factors relating to difficult tunneling such as squeezing, rockburst, and others. Also it deals with the prediction of rockburst. The 2nd paper will deal with the prediction of squeezing. The 3rd paper deals with the engineering characteristics of rock mass through rock mass classification. This paper about difficult tunneling has been based upon analysis of more than 500 tunneling reports about 280 tunnel constructions. The causes of difficult tunneling are related to (1) underground water, (2) mechanical properties of the rock, or (3) others such as gas. The geological factors for excessive water inflow are porous volcanic product of Quarternary, fault crush zone and hydrothermally altered zone of Green Tuff area, and degenerated mixed rock in accretionary complex. The geological factors for squeezing are solfataric clay at Quarternary volcanic zone, fault crush zone and hydrothermally altered zone of Green Tuff area, mudstone and fault crush zone of sedimentary rock of Neogene and later. Information useful for predicting rockburst has been gathered from previous reports. In the preliminary investigation stage, geological survey, geophysical survey and borehole survey from the surface are the source of information. Therefore rock type, P-wave velocity from seismic exploration and in-situ rock stress from hydrofracturing have been considered. Majority of rockburst events occurred at granitic rock, excluding coal mine where different kind of rockburst occurred at pillars. And P-wave velocity was around 5 km/s at the rock of rockburst events. Horizontal maximum and minimum stresses SH and Sh have been tested as a criterion for rockburst. It has been

  13. Geothermal and volcanism in west Java

    Science.gov (United States)

    Setiawan, I.; Indarto, S.; Sudarsono; Fauzi I, A.; Yuliyanti, A.; Lintjewas, L.; Alkausar, A.; Jakah

    2018-02-01

    Indonesian active volcanoes extend from Sumatra, Jawa, Bali, Lombok, Flores, North Sulawesi, and Halmahera. The volcanic arc hosts 276 volcanoes with 29 GWe of geothermal resources. Considering a wide distribution of geothermal potency, geothermal research is very important to be carried out especially to tackle high energy demand in Indonesia as an alternative energy sources aside from fossil fuel. Geothermal potency associated with volcanoes-hosted in West Java can be found in the West Java segment of Sunda Arc that is parallel with the subduction. The subduction of Indo-Australian oceanic plate beneath the Eurasian continental plate results in various volcanic products in a wide range of geochemical and mineralogical characteristics. The geochemical and mineralogical characteristics of volcanic and magmatic rocks associated with geothermal systems are ill-defined. Comprehensive study of geochemical signatures, mineralogical properties, and isotopes analysis might lead to the understanding of how large geothermal fields are found in West Java compared to ones in Central and East Java. The result can also provoke some valuable impacts on Java tectonic evolution and can suggest the key information for geothermal exploration enhancement.

  14. Co-Occurring Disorders

    Science.gov (United States)

    ... the mental health field. Alcohol and Drug Abuse, Addiction and Co-occurring Disorders: Co-occurring Disorders and ... 500 Montgomery Street, Suite 820 Alexandria, VA 22314 Phone (703) 684.7722 Toll Free (800) 969.6642 ...

  15. Modeling volcanic ash dispersal

    CERN Multimedia

    CERN. Geneva

    2010-01-01

    The assessment of volcanic fallout hazard is an important scientific, economic, and political issue, especially in densely populated areas. From a scientific point of view, considerable progress has been made during the last two decades through the use of increasingly powerful computational models and capabilities. Nowadays, models are used to quantify hazard...

  16. Source rock

    Directory of Open Access Journals (Sweden)

    Abubakr F. Makky

    2014-03-01

    Full Text Available West Beni Suef Concession is located at the western part of Beni Suef Basin which is a relatively under-explored basin and lies about 150 km south of Cairo. The major goal of this study is to evaluate the source rock by using different techniques as Rock-Eval pyrolysis, Vitrinite reflectance (%Ro, and well log data of some Cretaceous sequences including Abu Roash (E, F and G members, Kharita and Betty formations. The BasinMod 1D program is used in this study to construct the burial history and calculate the levels of thermal maturity of the Fayoum-1X well based on calibration of measured %Ro and Tmax against calculated %Ro model. The calculated Total Organic Carbon (TOC content from well log data compared with the measured TOC from the Rock-Eval pyrolysis in Fayoum-1X well is shown to match against the shale source rock but gives high values against the limestone source rock. For that, a new model is derived from well log data to calculate accurately the TOC content against the limestone source rock in the study area. The organic matter existing in Abu Roash (F member is fair to excellent and capable of generating a significant amount of hydrocarbons (oil prone produced from (mixed type I/II kerogen. The generation potential of kerogen in Abu Roash (E and G members and Betty formations is ranging from poor to fair, and generating hydrocarbons of oil and gas prone (mixed type II/III kerogen. Eventually, kerogen (type III of Kharita Formation has poor to very good generation potential and mainly produces gas. Thermal maturation of the measured %Ro, calculated %Ro model, Tmax and Production index (PI indicates that Abu Roash (F member exciting in the onset of oil generation, whereas Abu Roash (E and G members, Kharita and Betty formations entered the peak of oil generation.

  17. Scaling properties of planetary calderas and terrestrial volcanic eruptions

    Directory of Open Access Journals (Sweden)

    L. Sanchez

    2012-11-01

    Full Text Available Volcanism plays an important role in transporting internal heat of planetary bodies to their surface. Therefore, volcanoes are a manifestation of the planet's past and present internal dynamics. Volcanic eruptions as well as caldera forming processes are the direct manifestation of complex interactions between the rising magma and the surrounding host rock in the crust of terrestrial planetary bodies. Attempts have been made to compare volcanic landforms throughout the solar system. Different stochastic models have been proposed to describe the temporal sequences of eruptions on individual or groups of volcanoes. However, comprehensive understanding of the physical mechanisms responsible for volcano formation and eruption and more specifically caldera formation remains elusive. In this work, we propose a scaling law to quantify the distribution of caldera sizes on Earth, Mars, Venus, and Io, as well as the distribution of calderas on Earth depending on their surrounding crustal properties. We also apply the same scaling analysis to the distribution of interevent times between eruptions for volcanoes that have the largest eruptive history as well as groups of volcanoes on Earth. We find that when rescaled with their respective sample averages, the distributions considered show a similar functional form. This result implies that similar processes are responsible for caldera formation throughout the solar system and for different crustal settings on Earth. This result emphasizes the importance of comparative planetology to understand planetary volcanism. Similarly, the processes responsible for volcanic eruptions are independent of the type of volcanism or geographical location.

  18. Mobilization of arsenic and other naturally occurring contaminants in groundwater of the Main Ethiopian Rift aquifers.

    Science.gov (United States)

    Rango, Tewodros; Vengosh, Avner; Dwyer, Gary; Bianchini, Gianluca

    2013-10-01

    This study investigates the mechanisms of arsenic (As) and other naturally occurring contaminants (F(-), U, V, B, and Mo) mobilization from Quaternary sedimentary aquifers of the Main Ethiopian Rift (MER) and their enrichment in the local groundwater. The study is based on systematic measurements of major and trace elements as well as stable oxygen and hydrogen isotopes in groundwater, coupled with geochemical and mineralogical analyses of the aquifer rocks. The Rift Valley aquifer is composed of rhyolitic volcanics and Quaternary lacustrine sediments. X-ray fluorescence (XRF) results revealed that MER rhyolites (ash, tuff, pumice and ignimbrite) and sediments contain on average 72 wt. % and 65 wt. % SiO2, respectively. Petrographic studies of the rhyolites indicate predominance of volcanic glass, sanidine, pyroxene, Fe-oxides and plagioclase. The As content in the lacustrine sediments (mean = 6.6 mg/kg) was higher than that of the rhyolites (mean: 2.5 mg/kg). The lacustrine aquifers of the Ziway-Shala basin in the northern part of MER were identified as high As risk zones, where mean As concentration in groundwater was 22.4 ± 33.5 (range of 0.60-190 μg/L) and 54% of samples had As above the WHO drinking water guideline value of 10 μg/L. Field As speciation measurements showed that most of the groundwater samples contain predominantly (~80%) arsenate-As(V) over arsenite-As(III) species. The As speciation together with field data of redox potential (mean Eh = +73 ± 65 mV) and dissolved-O2 (6.6 ± 2.2 mg/L) suggest that the aquifer is predominantly oxidative. Water-rock interactions, including the dissolution of volcanic glass produces groundwater with near-neutral to alkaline pH (range 6.9-8.9), predominance of Na-HCO3 ions, and high concentration of SiO2 (mean: 85.8 ± 11.3 mg/L). The groundwater data show high positive correlation of As with Na, HCO3, U, B, V, and Mo (R(2) > 0.5; p groundwater indicates that Fe-oxides and oxyhydroxides minerals were saturated

  19. Petrologic and geochemical characterization and mineralization of the metavolcanic rocks of the Heib Formation, Kid Metamorphic Complex, Sinai, Egypt

    Directory of Open Access Journals (Sweden)

    Ibrahim H. Khalifa

    2011-07-01

    Full Text Available Metavolcanic rocks hosting base metal sulphide mineralization, and belonging to the Kid Metamorphic Complex, are exposed in the Samra-Tarr area, Southern Sinai. The rocks consist of slightly metamorphosed varicolored porphyritic lavas of rhyolite-to-andesite composition, and their equivalent pyroclastics. Geochemically, these metavolcanics are classified as high-K calc-alkaline, metaluminous andesites, trachyandesites, dacites, and rhyolites. The geochemical characteristics of these metavolcanics strongly point to their derivation from continental crust in an active continental margin. The sulphide mineralization in these metavolcanics occurs in two major ore zones, and is represented by four distinct styles of mineralization. The mineralization occurs either as low-grade disseminations or as small massive pockets. The associated hydrothermal alterations include carbonatization, silicification, sericitization and argillic alterations. The base metal sulphide mineralization is epigenetic and was formed by hydrothermal solutions associated with subduction-related volcanic activity.

  20. Basaltic Diatreme To Root Zone Volcanic Processes In Tuzo Kimberlite Pipe (Gahcho Kué Kimberlite Field, NWT, Canada)

    Science.gov (United States)

    Seghedi, I.; Kurszlaukis, S.; Maicher, D.

    2009-05-01

    Tuzo pipe is infilled by a series of coherent and fragmental kimberlite facies types typical for a diatreme to root zone transition level. Coherent or transitional coherent kimberlite facies dominate at depth, but also occur at shallow levels, either as dikes or as individual or agglutinated coherent kimberlite clasts (CKC). Several fragmental kimberlite varieties fill the central and shallow portions of the pipe. The definition, geometry and extent of the geological units are complex and are controlled by vertical elements. Specific for Tuzo is: (1) high abundance of locally derived xenoliths (granitoids and minor diabase) between and within the kimberlite phases, varying in size from sub-millimeter to several tens of meters, frequent in a belt-like domain between 120-200 m depth in the pipe; (2) the general presence of CKC, represented by round-subround, irregular to amoeboid-shaped clasts with a macrocrystic or aphanitic texture, mainly derived from fragmentation of erupting magma and less commonly from previously solidified kimberlite, as well as recycled pyroclasts. In addition, some CKC are interpreted to be intersections of a complex dike network. This diversity attests formation by various volcanic processes, extending from intrusive to explosive; (3) the presence of bedded polymict wall- rock and kimberlite breccia occurring mostly in deep levels of the pipe below 345 m depth. The gradational contact relationships of these deposits with the surrounding kimberlite rocks and their location suggest that they formed in situ. The emplacement of Tuzo pipe involved repetitive volcanic explosions alternating with periods of relative quiescence causing at least partial consolidation of some facies. The volume deficit in the diatreme-root zone after each eruption was compensated by gravitational collapse of overlying diatreme tephra and pre-fragmented wall-rock xenoliths. Highly explosive phases were alternating with weak explosions or intrusive phases, suggesting

  1. Developing International Guidelines on Volcanic Hazard Assessments for Nuclear Facilities

    Science.gov (United States)

    Connor, Charles

    2014-05-01

    tremendous challenge in quantitative volcanic hazard assessments to encompass alternative conceptual models, and to create models that are robust to evolving understanding of specific volcanic systems by the scientific community. A central question in volcanic hazards forecasts is quantifying rates of volcanic activity. Especially for long-dormant volcanic systems, data from the geologic record may be sparse, individual events may be missing or unrecognized in the geologic record, patterns of activity may be episodic or otherwise nonstationary. This leads to uncertainty in forecasting long-term rates of activity. Hazard assessments strive to quantify such uncertainty, for example by comparing observed rates of activity with alternative parametric and nonparametric models. Numerical models are presented that characterize the spatial distribution of potential volcanic events. These spatial density models serve as the basis for application of numerical models of specific phenomena such as development of lava flow, tephra fallout, and a host of other volcanic phenomena. Monte Carlo techniques (random sampling, stratified sampling, importance sampling) are methods used to sample vent location and other key eruption parameters, such as eruption volume, magma rheology, and eruption column height for probabilistic models. The development of coupled scenarios (e.g., the probability of tephra accumulation on a slope resulting in subsequent debris flows) is also assessed through these methods, usually with the aid of event trees. The primary products of long-term forecasts are a statistical model of the conditional probability of the potential effects of volcanism, should an eruption occur, and the probability of such activity occurring. It is emphasized that hazard forecasting is an iterative process, and board consideration must be given to alternative conceptual models of volcanism, weighting of volcanological data in the analyses, and alternative statistical and numerical models

  2. Volcanic ash in ancient Maya ceramics of the limestone lowlands: implications for prehistoric volcanic activity in the Guatemala highlands

    Science.gov (United States)

    Ford, Anabel; Rose, William I.

    1995-07-01

    In the spirit of collaborative research, Glicken and Ford embarked on the problem of identifying the source of volcanic ash used as temper in prehistoric Maya ceramics. Verification of the presence of glass shards and associated volcanic mineralogy in thin sections of Maya ceramics was straightforward and pointed to the Guatemala Highland volcanic chain. Considering seasonal wind rose patterns, target volcanoes include those from the area west of and including Guatemala City. Joint field research conducted in 1983 by Glicken and Ford in the limestone lowlands of Belize and neighboring Guatemala, 300 km north of the volcanic zone and 150 km from the nearest identified ash deposits, was unsuccessful in discovering local volcanic ash deposits. The abundance of the ash in common Maya ceramic vessels coupled with the difficulties of long-distance procurement without draft animals lead Glicken to suggest that ashfall into the lowlands would most parsimoniously explain prehistoric procurement; it literally dropped into their hands. A major archaeological problem with this explanation is that the use of volcanic ash occurring over several centuries of the Late Classic Period (ca. 600-900 AD). To accept the ashfall hypothesis for ancient Maya volcanic ash procurement, one would have to demonstrate a long span of consistent volcanic activity in the Guatemala Highlands for the last half of the first millennium AD. Should this be documented through careful petrographic, microprobe and tephrachronological studies, a number of related archaeological phenomena would be explained. In addition, the proposed model of volcanic activity has implications for understanding volcanism and potential volcanic hazards in Central America over a significantly longer time span than the historic period. These avenues are explored and a call for further collaborative research of this interdisciplinary problem is extended in this paper.

  3. Relationship between natural radioactivity and rock type in the Van lake basin - Turkey

    International Nuclear Information System (INIS)

    Tolluoglu, A. U.; Eral, M.; Aytas, S.

    2004-01-01

    The Van Lake basin located at eastern part of Turkey. The Van lake basin essentially comprises two province, these are namely Van and Bitlis. The former geochemistry research indicated that the uranium concentrations of Van lake water and deep sediments are 78-116 ppb and 0.1-0.5 ppm respectively. Uranium was transported to Van Lake by rivers and streams, flow through to outcrops of Paleozoic Bitlis Massive, and young Pleistocene alkaline/calkalkaline volcanic rocks. This study focused on the revealing natural radioactivity and secondary dispersion of radioactivity related to rock types surface environments in the Van Lake Basin. The Van Lake Basin essentially subdivided into three different parts; the Eastern parts characterized by Mesozoic basic and ultra basic rocks, southern parts dominated by metamorphic rocks of Bitlis Massive, Western and Northwestern parts covered by volcanic rocks of Pleistocene. Volcanic rocks can be subdivided into two different types. The first type is mafic rocks mainly composed of basalts. The second type is felsic rocks represented by rhyolites, dacites and pumice tuff. Surface gamma measurements (cps) and dose rate measurements (μR/h) show different values according to rock type. Surface gamma measurement and surface dose rate values in the basaltic rocks are slightly higher than the average values (130 cps, 11 μR/h). In the felsic volcanic rocks such as rhyolites and dacites surface gamma measurement values and surface dose rate values, occasionally exceed the background. Highest values were obtained in the pumice tuffs. Rhyolitic eruptions related to Quaternary volcanic activity formed thick pumice (natural glassy froth related to felsic volcanic rocks and exhibit spongy texture) sequences Northern and Western part of Van Lake basin. The dose rate of pumice rocks was measured mean 15 μR/h. The highest value for surface gamma measurements was recorded as 200 cps. The pumice has very big water capacity, due to porous texture of

  4. Intellektuaalne rock

    Index Scriptorium Estoniae

    2007-01-01

    Briti laulja-helilooja ja näitleja Toyah Willcox ning Bill Rieflin ansamblist R.E.M. ja Pat Mastelotto King Krimsonist esinevad koos ansamblitega The Humans ja Tuner 25. okt. Tallinnas Rock Cafés ja 27. okt Tartu Jaani kirikus

  5. Using Volcanic Lightning Measurements to Discern Variations in Explosive Volcanic Activity

    Science.gov (United States)

    Behnke, S. A.; Thomas, R. J.; McNutt, S. R.; Edens, H. E.; Krehbiel, P. R.; Rison, W.

    2013-12-01

    VHF observations of volcanic lightning have been made during the recent eruptions of Augustine Volcano (2006, Alaska, USA), Redoubt Volcano (2009, Alaska, USA), and Eyjafjallajökull (2010, Iceland). These show that electrical activity occurs both on small scales at the vent of the volcano, concurrent with an eruptive event and on large scales throughout the eruption column during and subsequent to an eruptive event. The small-scale discharges at the vent of the volcano are often referred to as 'vent discharges' and are on the order of 10-100 meters in length and occur at rates on the order of 1000 per second. The high rate of vent discharges produces a distinct VHF signature that is sometimes referred to as 'continuous RF' radiation. VHF radiation from vent discharges has been observed at sensors placed as far as 100 km from the volcano. VHF and infrasound measurements have shown that vent discharges occur simultaneously with the onset of eruption, making their detection an unambiguous indicator of explosive volcanic activity. The fact that vent discharges are observed concurrent with explosive volcanic activity indicates that volcanic ejecta are charged upon eruption. VHF observations have shown that the intensity of vent discharges varies between eruptive events, suggesting that fluctuations in eruptive processes affect the electrification processes giving rise to vent discharges. These fluctuations may be variations in eruptive vigor or variations in the type of eruption; however, the data obtained so far do not show a clear relationship between eruption parameters and the intensity or occurrence of vent discharges. Further study is needed to clarify the link between vent discharges and eruptive behavior, such as more detailed lightning observations concurrent with tephra measurements and other measures of eruptive strength. Observations of vent discharges, and volcanic lightning observations in general, are a valuable tool for volcano monitoring, providing a

  6. Morfologia e classificação taxonômica de neossolos e saprolitos derivados de rochas vulcânicas da Formação Serra Geral no Rio Grande no Sul Morphology and taxonomy classification of neossolos and saprolites derived from volcanic rock of the Serra Geral formation in Rio Grande do Sul, Brazil

    Directory of Open Access Journals (Sweden)

    Fabrício de Araújo Pedron

    2009-02-01

    low potential for agricultural use. Consequently the morphological description of Neossolos in the field is also hampered, particularly in terms of contacts between soil, saprolite and rock, and their classification in the Brazilian Soil Classification System. The purpose of this study was: to define morphologically the contact between soil, saprolite and rock in Neossolos; generate data of the saprolite layer and test an inclusion in the suborder Neossolos Litólicos and Neossolos Regolíticos; and evaluate the diagnostic attributes and classes available in the Brazilian Soil Classification System for the of Neossolos Litólicos and Regolíticos derived from volcanic rocks of the Serra Geral formation in Rio Grande do Sul, State, Brazil. Five profiles of litho-climosequence were analyzed. The contacts were characterized based on the straight shovel excavation test associated to analyses of saprolite fracture and weathering classes. The contacts related to the presence of saprolite layers identified in the profile are not taken into consideration in the Brazilian Soil Classification System. Diagnostic attributes for the classification of Neossolos Regolíticos were proposed as well as a change of the term from "Regolítico" to "Saprolítico". New classes were also suggested for the third categorical level, based on information such as soil position and saprolite contact, excavation resistance and cracking level of the material. The proposed diagnostic attributes and classes allowed a more adequate classification of Neossolos derived from volcanic rocks in the State of Rio Grande do Sul.

  7. Igneous Rocks

    Science.gov (United States)

    Doe, Bruce R.

    “Igneous Rocks was written for undergraduate geology majors who have had a year of college-level chemistry and a course in mineralogy … and for beginning graduate students. Geologists working in industry, government, or academia should find this text useful as a guide to the technical literature up to 1981 and as an overview of topics with which they have not worked but which may have unanticipated pertinence to their own projects.” So starts the preface to this textbook.As one who works part time in research on igneous rocks, especially as they relate to mineral deposits, I have been looking for such a book with this avowed purpose in a field that has a choking richness of evolving terminology and a bewildering volume of interdisciplinary literature. In addition to the standard topics of igneous petrology, the book contains a chapter on the role of igneous activity in the genesis of mineral deposits, its value to geothermal energy, and the potential of igneous rocks as an environment for nuclear waste disposal. These topics are presented rather apologetically in the preface, but the author is to be applauded for including this chapter. The apology shows just how new these interests are to petrology. Recognition is finally coming that, for example, mineral deposits are not “sports of nature,” a view held even by many economic geologists as recently as the early 1960's; instead they are perfectly ordinary geochemical features formed by perfectly ordinary geologic processes. In fact, the mineral deposits and their attendant alteration zones probably have as much to tell us about igneous rocks as the igneous rocks have to tell us about mineral deposits.

  8. Mainshock-Aftershocks Clustering Detection in Volcanic Regions

    Science.gov (United States)

    Garza Giron, R.; Brodsky, E. E.; Prejean, S. G.

    2017-12-01

    Crustal earthquakes tend to break their general Poissonean process behavior by gathering into two main kinds of seismic bursts: swarms and mainshock-aftershocks sequences. The former is commonly related to volcanic or geothermal processes whereas the latter is a characteristic feature of tectonically driven seismicity. We explore the mainshock-aftershock clustering behavior of different active volcanic regions in Japan and its comparison to non-volcanic regions. We find that aftershock production in volcanoes shows mainshock-aftershocks clustering similar to what is observed in non-volcanic areas. The ratio of volanic areas that cluster in mainshock-aftershocks sequences vs the areas that do not is comparable to the ratio of non-volcanic regions that show clustering vs the ones that do not. Furthermore, the level of production of aftershocks for most volcanic areas where clustering is present seems to be of the same order of magnitude, or slightly higher, as the median of the non-volcanic regions. An interesting example of highly aftershock-productive volcanoes emerges from the 2000 Miyakejima dike intrusion. A big seismic cluster started to build up rapidly in the south-west flank of Miyakejima to later propagate to the north-west towards the Kozushima and Niijima volcanoes. In Miyakejima the seismicity showed a swarm-like signature with a constant earthquake rate, whereas Kozushima and Niijima both had expressions of highly productive mainshock-aftershocks sequences. These findings are surprising given the alternative mechanisms available in volcanic systems for releasing deviatoric strain. We speculate that aftershock behavior might hold a relationship with the rheological properties of the rocks of each system and with the capacity of a system to accumulate or release the internal pressures caused by magmatic or hydrothermal systems.

  9. The Online GVP/USGS Weekly Volcanic Activity Report: Providing Timely Information About Worldwide Volcanism

    Science.gov (United States)

    Mayberry, G. C.; Guffanti, M. C.; Luhr, J. F.; Venzke, E. A.; Wunderman, R. L.

    2001-12-01

    The awesome power and intricate inner workings of volcanoes have made them a popular subject with scientists and the general public alike. About 1500 known volcanoes have been active on Earth during the Holocene, approximately 50 of which erupt per year. With so much activity occurring around the world, often in remote locations, it can be difficult to find up-to-date information about current volcanism from a reliable source. To satisfy the desire for timely volcano-related information the Smithsonian Institution and US Geological Survey combined their strengths to create the Weekly Volcanic Activity Report. The Smithsonian's Global Volcanism Program (GVP) has developed a network of correspondents while reporting worldwide volcanism for over 30 years in their monthly Bulletin of the Global Volcanism Network. The US Geological Survey's Volcano Hazards Program studies and monitors volcanoes in the United States and responds (upon invitation) to selected volcanic crises in other countries. The Weekly Volcanic Activity Report is one of the most popular sites on both organization's websites. The core of the Weekly Volcanic Activity Report is the brief summaries of current volcanic activity around the world. In addition to discussing various types of volcanism, the summaries also describe precursory activity (e.g. volcanic seismicity, deformation, and gas emissions), secondary activity (e.g. debris flows, mass wasting, and rockfalls), volcanic ash hazards to aviation, and preventative measures. The summaries are supplemented by links to definitions of technical terms found in the USGS photoglossary of volcano terms, links to information sources, and background information about reported volcanoes. The site also includes maps that highlight the location of reported volcanoes, an archive of weekly reports sorted by volcano and date, and links to commonly used acronyms. Since the Weekly Volcanic Activity Report's inception in November 2000, activity has been reported at

  10. The composition and structure of volcanic rifted continental margins in the North Atlantic: Further insight from shear waves

    Science.gov (United States)

    Eccles, Jennifer D.; White, Robert S.; Christie, Philip A. F.

    2011-07-01

    Imaging challenges caused by highly attenuative flood basalt sequences have resulted in the understanding of volcanic rifted continental margins lagging behind that of non-volcanic rifted and convergent margins. Massive volcanism occurred during break-up at 70% of the passive margins bordering the Atlantic Ocean, the causes and dynamics of which are still debated. This paper shows results from traveltime tomography of compressional and converted shear wave arrivals recorded on 170 four-component ocean bottom seismometers along two North Atlantic continental margin profiles. This traveltime tomography was performed using two different approaches. The first, a flexible layer-based parameterisation, enables the quality control of traveltime picks and investigation of the crustal structure. The second, with a regularised grid-based parameterisation, requires correction of converted shear wave traveltimes to effective symmetric raypaths and allows exploration of the model space via Monte Carlo analyses. The velocity models indicate high lower-crustal velocities and sharp transitions in both velocity and Vp/Vs ratios across the continent-ocean transition. The velocities are consistent with established mixing trends between felsic continental crust and high magnesium mafic rock on both margins. Interpretation of the high quality seismic reflection profile on the Faroes margin confirms that this mixing is through crustal intrusion. Converted shear wave data also provide constraints on the sub-basalt lithology on the Faroes margin, which is interpreted as a pre-break-up Mesozoic to Paleocene sedimentary system intruded by sills.

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

    Science.gov (United States)

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

    2016-04-01

    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

  12. Hot rock energy projects : Australian context

    Energy Technology Data Exchange (ETDEWEB)

    Goldstein, B.A.; Malavazos, M. [Society of Petroleum Engineers, Richardson, TX (United States); Hill, A.J.; Coda, J. [Primary Industries and Resources South Australia, Adelaide (Australia)]|[Australian Geothermal Energy Group, Adelaide (Australia); Budd, A.R.; Holgate, F.L. [Australian Geothermal Energy Group, Adelaide (Australia)]|[Geoscience Australia, Adelaide (Australia)

    2008-10-15

    The Australia Geothermal Energy Group is an alliance of companies, government agencies and research organizations with an interest in promoting geothermal energy use. Hot rocks (HR) geothermal energy is a valued addition to the portfolio of safe, secure and competitive energy supplies because it offers the potential of inexhaustible geothermal heat energy with zero emissions. Australia's vast HR resources have attracted global interest and government support for HR projects, which call upon integrated expertise from the petroleum minerals and power industries. Funding from the Australian government is aimed at reducing critical, sector-wide uncertainties and equates to nearly 25 per cent of the cost of the private sector's field efforts to date. A national HR resource assessment and a road-map for the commercialization of Australian HR plays will be published in 2008 to help in the decision making process by portfolio managers. The challenges and prospects for HR projects in Australia were presented. It has been estimated that converting only 1 per cent of Australia's crustal energy from depths of 5 km and 150 degrees C to electricity would supply 26,000 years of Australia's 2005 primary power use. The factors that distinguish Australian HR resources include abundant radioactive granites and areas of recent volcanic activity; and, Australia is converging with Indonesia on a plate scale resulting in common, naturally occurring subhorizontally fractured basement rocks that are susceptible to hydraulic fracture stimulation. Most projects are focused on HR to develop enhanced or engineered geothermal systems (EGS) to fuel binary power plants. Approximately 80 percent of these projects are located in South Australia. 14 refs., 3 tabs., 3 figs.

  13. Explosive Volcanic Activity at Extreme Depths: Evidence from the Charles Darwin Volcanic Field, Cape Verdes

    Science.gov (United States)

    Kwasnitschka, T.; Devey, C. W.; Hansteen, T. H.; Freundt, A.; Kutterolf, S.

    2013-12-01

    Volcanic eruptions on the deep sea floor have traditionally been assumed to be non-explosive as the high-pressure environment should greatly inhibit steam-driven explosions. Nevertheless, occasional evidence both from (generally slow-) spreading axes and intraplate seamounts has hinted at explosive activity at large water depths. Here we present evidence from a submarine field of volcanic cones and pit craters called Charles Darwin Volcanic Field located at about 3600 m depth on the lower southwestern slope of the Cape Verdean Island of Santo Antão. We examined two of these submarine volcanic edifices (Tambor and Kolá), each featuring a pit crater of 1 km diameter, using photogrammetric reconstructions derived from ROV-based imaging followed by 3D quantification using a novel remote sensing workflow, aided by sampling. The measured and calculated parameters of physical volcanology derived from the 3D model allow us, for the first time, to make quantitative statements about volcanic processes on the deep seafloor similar to those generated from land-based field observations. Tambor cone, which is 2500 m wide and 250 m high, consists of dense, probably monogenetic medium to coarse-grained volcaniclastic and pyroclastic rocks that are highly fragmented, probably as a result of thermal and viscous granulation upon contact with seawater during several consecutive cycles of activity. Tangential joints in the outcrops indicate subsidence of the crater floor after primary emplacement. Kolá crater, which is 1000 m wide and 160 m deep, appears to have been excavated in the surrounding seafloor and shows stepwise sagging features interpreted as ring fractures on the inner flanks. Lithologically, it is made up of a complicated succession of highly fragmented deposits, including spheroidal juvenile lapilli, likely formed by spray granulation. It resembles a maar-type deposit found on land. The eruption apparently entrained blocks of MORB-type gabbroic country rocks with

  14. The geology and mechanics of formation of the Fort Rock Dome, Yavapai County, Arizona

    Science.gov (United States)

    Fuis, Gary S.

    1996-01-01

    The Fort Rock Dome, a craterlike structure in northern Arizona, is the erosional product of a circular domal uplift associated with a Precambrian shear zone exposed within the crater and with Tertiary volcanism. A section of Precambrian to Quaternary rocks is described, and two Tertiary units, the Crater Pasture Formation and the Fort Rock Creek Rhyodacite, are named. A mathematical model of the doming process is developed that is consistent with the history of the Fort Rock Dome.

  15. National volcanic ash operations plan for aviation

    Science.gov (United States)

    ,; ,

    2007-01-01

    The National Aviation Weather Program Strategic Plan (1997) and the National Aviation Weather Initiatives (1999) both identified volcanic ash as a high-priority informational need to aviation services. The risk to aviation from airborne volcanic ash is known and includes degraded engine performance (including flameout), loss of visibility, failure of critical navigational and operational instruments, and, in the worse case, loss of life. The immediate costs for aircraft encountering a dense plume are potentially major—damages up to $80 million have occurred to a single aircraft. Aircraft encountering less dense volcanic ash clouds can incur longer-term costs due to increased maintenance of engines and external surfaces. The overall goal, as stated in the Initiatives, is to eliminate encounters with ash that could degrade the in-flight safety of aircrews and passengers and cause damage to the aircraft. This goal can be accomplished by improving the ability to detect, track, and forecast hazardous ash clouds and to provide adequate warnings to the aviation community on the present and future location of the cloud. To reach this goal, the National Aviation Weather Program established three objectives: (1) prevention of accidental encounters with hazardous clouds; (2) reduction of air traffic delays, diversions, or evasive actions when hazardous clouds are present; and (3) the development of a single, worldwide standard for exchange of information on airborne hazardous materials. To that end, over the last several years, based on numerous documents (including an OFCMsponsored comprehensive study on aviation training and an update of Aviation Weather Programs/Projects), user forums, and two International Conferences on Volcanic Ash and Aviation Safety (1992 and 2004), the Working Group for Volcanic Ash (WG/VA), under the OFCM-sponsored Committee for Aviation Services and Research, developed the National Volcanic Ash Operations Plan for Aviation and Support of the

  16. Backprojection of volcanic tremor

    Science.gov (United States)

    Haney, Matthew M.

    2014-01-01

    Backprojection has become a powerful tool for imaging the rupture process of global earthquakes. We demonstrate the ability of backprojection to illuminate and track volcanic sources as well. We apply the method to the seismic network from Okmok Volcano, Alaska, at the time of an escalation in tremor during the 2008 eruption. Although we are able to focus the wavefield close to the location of the active cone, the network array response lacks sufficient resolution to reveal kilometer-scale changes in tremor location. By deconvolving the response in successive backprojection images, we enhance resolution and find that the tremor source moved toward an intracaldera lake prior to its escalation. The increased tremor therefore resulted from magma-water interaction, in agreement with the overall phreatomagmatic character of the eruption. Imaging of eruption tremor shows that time reversal methods, such as backprojection, can provide new insights into the temporal evolution of volcanic sources.

  17. Monitoring and forecasting Etna volcanic plumes

    Directory of Open Access Journals (Sweden)

    S. Scollo

    2009-09-01

    Full Text Available In this paper we describe the results of a project ongoing at the Istituto Nazionale di Geofisica e Vulcanologia (INGV. The objective is to develop and implement a system for monitoring and forecasting volcanic plumes of Etna. Monitoring is based at present by multispectral infrared measurements from the Spin Enhanced Visible and Infrared Imager on board the Meteosat Second Generation geosynchronous satellite, visual and thermal cameras, and three radar disdrometers able to detect ash dispersal and fallout. Forecasting is performed by using automatic procedures for: i downloading weather forecast data from meteorological mesoscale models; ii running models of tephra dispersal, iii plotting hazard maps of volcanic ash dispersal and deposition for certain scenarios and, iv publishing the results on a web-site dedicated to the Italian Civil Protection. Simulations are based on eruptive scenarios obtained by analysing field data collected after the end of recent Etna eruptions. Forecasting is, hence, supported by plume observations carried out by the monitoring system. The system was tested on some explosive events occurred during 2006 and 2007 successfully. The potentiality use of monitoring and forecasting Etna volcanic plumes, in a way to prevent threats to aviation from volcanic ash, is finally discussed.

  18. The Elusive Evidence of Volcanic Lightning.

    Science.gov (United States)

    Genareau, K; Gharghabi, P; Gafford, J; Mazzola, M

    2017-11-14

    Lightning strikes are known to morphologically alter and chemically reduce geologic formations and deposits, forming fulgurites. A similar process occurs as the result of volcanic lightning discharge, when airborne volcanic ash is transformed into lightning-induced volcanic spherules (LIVS). Here, we adapt the calculations used in previous studies of lightning-induced damage to infrastructure materials to determine the effects on pseudo-ash samples of simplified composition. Using laboratory high-current impulse experiments, this research shows that within the lightning discharge channel there is an ideal melting zone that represents roughly 10% or less of the total channel radius at which temperatures are sufficient to melt the ash, regardless of peak current. The melted ash is simultaneously expelled from the channel by the heated, expanding air, permitting particles to cool during atmospheric transport before coming to rest in ash fall deposits. The limited size of this ideal melting zone explains the low number of LIVS typically observed in volcanic ash despite the frequent occurrence of lightning during explosive eruptions.

  19. ROCK GLACIERS IN THE KOLYMA HIGHLAND

    Directory of Open Access Journals (Sweden)

    A. A. Galanin

    2012-01-01

    Full Text Available Based on remote mapping and field studies inGrand Rapids, Tumansky,Hasynsky,Del-Urechen Ridges as well as Dukchinsky and Kilgansky Mountain Massifs there were identified about 1160 landforms which morphologically are similar to the rock glaciers or they develop in close association with them. Besides tongue-shaped cirque rock glaciers originated due to ablation, a large number of lobate-shaped slope-associated rock glaciers were recognized. Significant quantity of such forms are developing within the active neotectonic areas, in zones of seismic-tectonic badland and in association with active earthquakes-controlling faults. Multiplication of regional data on volcanic-ash-chronology, lichenometry, Schmidt Hammer Test, pollen spectra and single radiocarbon data, most of the active rock glaciers were preliminary attributed to the Late Holocene.

  20. Volcanic eruptions on Io

    Science.gov (United States)

    Strom, R. G.; Schneider, N. M.; Terrile, R. J.; Hansen, C.; Cook, A. F.

    1981-01-01

    Nine eruption plumes which were observed during the Voyager 1 encounter with Io are discussed. During the Voyager 2 encounter, four months later, eight of the eruptions were still active although the largest became inactive sometime between the two encounters. Plumes range in height from 60 to over 300 km with corresponding ejection velocities of 0.5 to 1.0 km/s and plume sources are located on several plains and consist of fissures or calderas. The shape and brightness distribution together with the pattern of the surface deposition on a plume 3 is simulated by a ballistic model with a constant ejection velocity of 0.5 km/s and ejection angles which vary from 0-55 deg. The distribution of active and recent eruptions is concentrated in the equatorial regions and indicates that volcanic activity is more frequent and intense in the equatorial regions than in the polar regions. Due to the geologic setting of certain plume sources and large reservoirs of volatiles required for the active eruptions, it is concluded that sulfur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes.

  1. Spatial variability of damage around faults in the Joe Lott Tuff Member of the Mount Belknap Volcanics, southwestern Utah

    Science.gov (United States)

    Okubo, C. H.

    2012-12-01

    In order to yield new insight into the process of faulting in fine-grained, poorly indurated volcanic ash, the distribution of strain around faults in the Miocene-aged Joe Lott Tuff Member of the Mount Belknap Volcanics, Utah, is investigated. Several distinct styles of inelastic strain are identified. Deformation bands are observed in tuff that is porous and granular in nature, or is inferred to have been so at the time of deformation. Where silicic alteration is pervasive, fractures are the dominant form of localized strain. Non-localized strain within the host rock is manifest as pore space compaction, including crushing of pumice clasts. Distinct differences in fault zone architecture are observed at different magnitudes of normal fault displacement, in the mode II orientation. A fault with cm-scale displacements is manifest as a single well-defined surface. Off-fault damage occurs as pore space compaction near the fault tips and formation of deformation band damage zones that are roughly symmetric about the fault. At a fault with larger meter-scale displacements, a fault core is present. A recognizable fault-related deformation band damage zone is not observed here, even though large areas of the host rock remain porous and granular and deformation bands had formed prior to faulting. The host rock is instead fractured in areas of pervasive alteration and shows possible textural evidence of fault pulverization. The zones of localized and distributed strain have notably dif