Sample records for mafic microgranular enclaves

  1. Mafic microgranular enclaves (MMEs) in amphibole-bearing granites of the Bintang batholith, Main Range granite province: Evidence for a meta-igneous basement in Western Peninsular Malaysia

    Quek, Long Xiang; Ghani, Azman A.; Chung, Sun-Lin; Li, Shan; Lai, Yu-Ming; Saidin, Mokhtar; Amir Hassan, Meor H.; Muhammad Ali, Muhammad Afiq; Badruldin, Muhammad Hafifi; Abu Bakar, Ahmad Farid


    Mafic microgranular enclaves (MMEs) with varying sizes are a common occurrence in porphyritic amphibole-bearing granite of the Bintang batholith, which is part of the Main Range granite province. The MMEs of the amphibole-bearing granite are significant as they are related to the I-type granitoids within the Main Range granite province. Petrographic observations indicate the MMEs are mantled with coarse mafic crystals on the rim and contain similar minerals to the host (biotite + plagioclase + K-feldspar + pyroxene + amphibole), but in different proportions. Geochemical analyses indicate the MMEs are shoshonitic with mg# comparable to the granite host. Substantial similarities exist between the MMEs and granite with regards to the normalized rare earth element patterns and trace elements variation diagrams. The MMEs and granite are not completely coeval as the MME zircon U-Pb age (224.3 ± 1.2 Ma) is slightly older than its granite host zircon U-Pb age (216.2 ± 1.0 Ma). The age difference is also observed from the unusual 500 m-long Tiak MME and another amphibole-bearing granite sample from the south of the pluton, which yield 221.8 ± 1.1 Ma and 217.4 ± 1.0 Ma respectively. The oldest inherited zircons found in the MME and granite are 2.0 Ga and 1.3 Ga respectively, while the oldest xenocrystic zircons found in the MME and granite are 2.5 Ga and 1.5 Ga respectively. Identical negative εHf(t) values from zircon U-Pb and Lu-Hf analysis for a MME-granite pair indicates the rocks were generated from a similar, ancient source in the basement. Combining the results, we suggest that incongruent melting of an ancient protolith played an important part in the evolution of the MMEs and granite and the MMEs characteristics are best explained as restite. The zircon Hf model age (two-stage) and the I-type peritectic and restitic mineral assemblages in the MMEs further describe the protolith as Early Proterozoic-Late Archean (≈2.5 Ga) meta-igneous rock. This shows the

  2. Petrochemical composition characteristics of mafic microgranular enclaves in granites in SE China and their significance.%华南花岗岩暗色微粒包体的岩石化学组成特征及其意义

    彭卓伦; Rodney Grapes; 庄文明; 张献河


    Inhomogeneous enclave is the most popular type in the marie microgranular enclave (MME) of gran ites in SE China, which is generally with a dark or more mafic tim. The lithologic units in the rim of MME range from monzonite to quartz monzonite and to monzodiorite, while those in the core from quartz monzodior ite to tonalite. A MME generally has decreasing Si and Ca contents and Na/K ratios, and increasing K, Al,Ti, P and Fe+Mg contents from its core to rim, indicating that the MMEs should have been mainly derived from restites of the partial melting rock. Further research revealed that the composition of restite in granites varies in the direction of increasing biotite as the melting degree of the rock increases and the biotite-rich en claves should be the final product of rock melting process.%对华南诸多花岗岩体暗色微粒包体的野外调查表明, 非均一包体是包体中最普遍的类型,常具有暗色基性边.岩石化学分析结果表明,包体边缘的岩性为二长岩-石英二长岩-二长闪长岩,中心则为石英二长闪长岩-英云闪长岩.从包体中心到边缘,具有Si、Ca含量和Na/K比值降低,K、Al、Ti、P和Fe+Mg含量升高的变化趋势,揭示包体应来自岩石部分熔融的残余熔渣.进一步研究还表明,花岗岩中残余熔渣(暗色包体)的组分随着岩石熔融程度升高而向黑云母增多的方向演化,暗示富云包体应是岩石熔融演化至末阶段的产物.

  3. Mineralogy and geochemistry of microgranular enclaves in Palaeoproterozoic Malanjkhand granitoids, central India: evidence of magma mixing, mingling, and chemical equilibration

    Kumar, Santosh; Rino, Vikoleno


    Palaeoproterozoic ( ca 2,480 Ma) felsic magmatism of Malanjkhand region of central Indian Precambrian shield, referred to as Malanjkhand granitoids (MG), contain xenoliths of country rocks and mesocratic to melanocratic, fine-grained porphyritic microgranular enclaves (ME). The shape of ME is spheroidal, ellipsoidal, discoidal, elongated, and lenticular, varying in size from a few centimeters to about 2 m across. The contact of ME with the host MG is commonly sharp, crenulate, and occasionally diffuse, which we attribute to the undercooling and disaggregation of ME globules within the cooler host MG. The ME as well as MG show hypidiomorphic texture with common mineral Hbl-Bt-Kfs-Pl-Qtz assemblage, but differ in modal proportions. The variation in minerals' composition, presence of apatite needles, elongated biotites, resorbed plagiclase, ocellar quartz, and other mafic-felsic xenocrysts strongly oppose the restite and cognate origins of ME. Compositions of plagioclases (An3-An29), amphiboles (Mg/Mg+Fe2+=0.55-0.69), and biotites (Mg/Mg+Fe2+=0.46-0.60) of ME are slightly distinct or similar to those of MG, which suggest partial to complete equilibration during mafic-felsic magma interactions. Al-in-amphibole estimates the MG pluton emplacement at ca 3.4 ± 0.5 kbar, and therefore, magma mixing and mingling must have occurred at or below this level. The FerightleftharpoonsMg substitution in biotites of ME and MG largely suggests subduction-related, calc-alkaline metaluminous (I-type) nature of felsic melts. Most major and trace elements against SiO2 produce near linear variation trends for ME and MG, probably generated by the mixing of mafic and felsic magmas in various proportions. Trace including rare earth elements patterns of ME-MG pairs, however, show partial to complete equilibration, most likely governed by different degrees of elemental diffusion. The available evidence supports the model of ME origin that coeval mafic (enclave) and felsic (MG) magmas produced

  4. Igneous banding, schlieren and mafic enclaves in calc-alkaline granites: The Budduso pluton (Sardinia)

    Barbey, P.; Gasquet, D.; Pin, C.; Bourgeix, A. L.


    This study deals with the origin of igneous layering in plutons, and, especially, the extent layering is related to mafic-silicic magma interactions. The Budduso pluton (Sardinia) shows three main scales of organization. (i) Large scale lithological variations correspond to three main magmatic units, with differentiation increasing from the Outer (hornblende-bearing biotite granodiorite/monzogranite) to the Middle (biotite monzogranite) and the Inner (leucomonzogranite) units. The striking homogeneity of 87Sr/ 86Sr initial ratios (0.7090 ± 4) and ɛNd(t) values (- 5.6 ± 0.1) strongly suggests that magma isotopic equilibration was achieved prior to emplacement, whereas mixing/mingling structures observed within the pluton reflect second-stage processes involving broadly cogenetic components. (ii) Metre to decametre-scale igneous layering may be isomodal or modally-graded, locally with cross-layering. Biotite and plagioclase compositions are similar in both biotite-rich and quartzofeldspathic layers, as are the trace-element patterns which differ only by relative abundances. This precludes an origin by fractional crystallization. A penetrative submagmatic fabric superimposed on the layering and corresponding mainly to flattening can be ascribed to interference between pluton growth and regional deformation. (iii) Composite layering and schlieren are commonly associated to mafic microgranular enclaves, locally within synmagmatic shear zones or disrupted synplutonic dykes. In that case, there is a progressive shift in biotite XFe values from the core of enclave (˜ 0.65) to the host monzogranite (˜ 0.72): schlieren in the monzogranite show biotite XFe values similar to that of the host rock, whereas schlieren close to mafic enclaves show lower XFe values (˜ 0.69) towards those of enclave rims. These features can be ascribed to three main processes: (i) assembly of differentiated (± mixed/mingled) magmatic pulses; (ii) local hydrodynamic sorting related to density

  5. Petrogenesis of Eocene granitoids and microgranular enclaves in the western Tengchong Block: Constraints on eastward subduction of the Neo-Tethys

    Zhao, Shao-wei; Lai, Shao-cong; Qin, Jiang-feng; Zhu, Ren-Zhi


    Eocene granitic and related igneous rocks in the western Tengchong Block are considered to be the result of eastward subduction of Neo-Tethyan oceanic lithosphere beneath the Tengchong Block. In this paper we show that the granitic and mafic rocks in the western Tengchong Block exhibit a systematic compositional variation from west to east, with Na-rich granodiorites in the Nabang area (west) that differ from coeval high-K calc-alkaline granodiorites in the Bangwan area (east), and with tholeiitic mafic rocks in the Nabang area that differ from shoshonitic mafic microgranular enclaves (MMEs) in granodiorites of the Bangwan area. In addition, high-silica biotite granites were intruded into the granodiorites in the Bangwan area. The host granodiorites, MMEs, and biotite granites in the Bangwan area yield zircon U-Pb ages of ca. 50 Ma. The MMEs have relatively low SiO2 contents (53.1-64.95 wt%) and Mg# values (37-45), and high K2O (4.14-5.02 wt%) and ∑ REE contents (331-509 ppm); the MMEs contain acicular apatites that indicate quenching. The host granodiorites also have high K2O (4.48-5.95 wt%) and ∑ REE compositions (320-459 ppm), and together with the MMEs they are enriched in Th but depleted in Nb and Ti. The Sr-Nd-Pb isotopic compositions of the host granodiorites and the MMEs are similar, with εHf(t) values of - 1.0 to - 10.8 and 3.3 to - 11.1, respectively. The geochemical data and igneous textures suggest that the MMEs represent a mafic magma that was derived from the partial melting of mantle pyroxenite, with the melting induced by the influx of fluids/melts from the recycling of sediments in the subducted slab. The mafic melts then caused the partial melting of lower crustal tonalitic rocks to produce granodioritic magma that was subsequently mixed with mafic magma. The biotite granites have relatively high SiO2 contents and low Mg# values that indicate a purely crustal origin and derivation from the partial melting of upper crustal metagraywacke. The

  6. Arc dacite genesis pathways: Evidence from mafic enclaves and their hosts in Aegean lavas

    Zellmer, G. F.; Turner, S. P.


    Mafic enclaves are commonly found in intermediate arc magmas, and their occurrence has been linked to eruption triggering by pre-eruptive magma mixing processes. New major, trace, Sr-Nd and U-Th isotope data of rocks from Nisyros in the Aegean volcanic arc are presented here. Pre-caldera samples display major and trace element trends that are consistent with fractionation of magnetite and apatite within intermediate compositions, and zircon within felsic compositions, and preclude extensive hybridization between mafic and felsic magmas. In contrast, post-caldera dacites form a mixing trend towards their mafic enclaves. In terms of U-series isotopes, most samples show small 238U excesses of up to ˜ 10%. Mafic enclaves have significantly higher U/Th ratios than their dacitic host lavas, precluding simple models that relate the mafic and felsic magmas by fractionation or aging alone. A more complicated petrogenetic scenario is required. The post-caldera dacites are interpreted to represent material remobilized from a young igneous protolith following influx of fresh mafic magma, consistent with the U-Th data and with Sr-Nd isotope constraints that point to very limited (Santorini in the same arc, there are many geochemical similarities between the two volcanic centers during the petrogenesis of the pre-caldera samples. However, striking differences are apparent for the post-caldera lavas: in Nisyros, dacites show geochemical and textural evidence for magma mixing and remobilization by influx of mafic melts, and they erupt as viscous lava domes; in Santorini, evidence for geochemical hybridization of dacites and mafic enclaves is weak, dacite petrogenesis does not involve protolith remobilization, and lavas erupt as less viscous flows. Despite these differences, it appears that mafic enclaves in intermediate Aegean arc magmas consistently yield timescales of at least 100 kyrs between U enrichment of the mantle wedge and eruption, on the upper end of those estimated

  7. Experimental and textural constraints on mafic enclave formation in volcanic rocks

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


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

  8. Middle Triassic magma mixing in an active continental margin: Evidence from mafic enclaves and host granites from the Dewulu pluton in West Qinling, central China

    Huang, X.; Mo, X.; Yu, X.


    The Qinling-Dabie-Sulu orogen was formed through the collision of the North and South China blocks, but the precise timing of the closure of the Paleo-Tethys ocean between the two blocks remains debated. Large volumes of Triassic granites associated with mafic microgranular enclaves (MMEs) were emplaced in the Qinling terrane. This paper presents field observations, petrography, geochronology and geochemistry of the MMEs and their host granites from the Dewulu pluton in West Qinling. The host rocks comprise granodiorite and granodioritic porphyry, and the The MMEs range in composition from gabbroic diorite to diorite. Zircon LA-ICP-MS U-Pb ages suggest that the granites and MMEs were coeval at ca. 245 Ma. The granites are relatively enriched in LILE and depleted in HFSE, and have evolved Sr-Nd-Pb and zircon Hf isotopic compositions [initial 87Sr/86Sr = 0.7070-0.7076, ɛNd(t) = -7.5 to -6.8, ɛHf(t) = -8.2 to -4.2], indicative of an origin from the amphibolitic lower crust. The near-primitive gabbro-dioritic MMEs bear a remarkable geochemical resemblance to the high-magnesium andesite (HMA), such as moderate SiO2 (~55 wt.%), low FeOT/MgO (~0.75), high Cr (268-308 ppm) and MgO (8.58-8.77 wt.%) with Mg# of ~70. Additionally, they exhibit lower initial 87Sr/86Sr, higher ɛNd(t) and ɛHf(t), and more radiogenic Pb isotopes than the dioritic MMEs which share similar isotopic compositions with the granites. These features, together with the presence of the specific minerals in the MMEs (e.g., felsic xenocrysts and acicular apatite), point to mixing process between the lower crust-derived magmas and the melts produced by the reaction of the subducting sediment-derived components and the overlying mantle. Taking into account the regional occurrence of synchronous plutonic-volcanic complexes (250-234 Ma) ranging from basaltic to granitic variants, we suggest that the Dewulu pluton formed in an active continental margin in response to the local extension triggered by the

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

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


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


    KURT, Hüseyin; Kerim KOÇAK; ASAN, Kürşad; KARAKAŞ, Mustafa


    Biotite granitoid contain mainly quartz, biotite, plagioclase, K-feldspar, muscovite as main phases with minor amphiboles, and apatite, zircon, allanite and chlorite and serisite as accessory components. In contrast, enclaves are composed mainly of plagioclase, amphibole, augite, biotite, with accessory sphene, zircon and calcite and epidote. The granitoids including enclaves with metaluminous composition, display chemical and mineralogical characteristics of S-type granitoids, such as peralu...

  11. The Pan-African calc-alkaline granitoids and the associated mafic microgranular enclaves (MME around Wadi Abu Zawal area, North Eastern Desert, Egypt: geology, geochemistry and petrogenesis

    Asran Mohamed Asran


    Full Text Available Introduction: The area around Wadi Abu Zawal is occupied by gneisses-migmatites, island arcs metavolcanics, Dokhan volcanics, Hammamat sediments, intrusive rocks of granitic and gabbroic composition and dyke swarms.Materials and Methods: The present work concerning on the geology, geochemistry and petrogenesis of the MME and the host granitoid rocks of that area. The analytical methods for major and trace elements of some representative samples were carried out by XRF technique at the Institute of BGR in Hannover, Germany.Results: Mineralogically, MME are composed mainly of plagioclase, hornblende, biotite and quartz with accessory of sphene, acicular apatite and opaque oxides, while chlorite and epidote are secondary ones. Whereas Abu Zawal granitoid rocks are subsolvus and consist of variable contents of plagioclase, K-feldspar, quartz, and biotite, with accessory sphene, zircon and opaque oxides, typical of I-type granites. The studied Abu Zawal area represents part of the northeastern Egypt which formed by regional crustal extension and magmatic-arc regimes during Pan-African orogenic event.The MME display major, trace element contents and tectonic setting comparable with the end members of (GDT and (IAG of the Eastern Desert which produced (by fractionation from a mantle-derived tholeiitic magma in an island-arc tectonic environment. Abu Zawal granitoid rocks exhibit trace element characteristics of volcanic-arc granites, and formed in an Andean-type setting.Conclusions: On the variation diagrams, major and trace element contents of the MME and granitoid rocks display conspicuous gap and two distinct trends one for the MME, (IAG and the other for the Abu Zawal granitoid rocks, which indicates that they are not genetically related and suggest the crustal source for the host granitoid rock.

  12. Evolution by Replenishment Fractional Crystallization (RFC) of Midproterozoic Magmatic Enclaves in Granites of the Eastern Llano Uplift, central Texas, U.S.A

    Smith, R. K.; Gray, W.


    The Llano Uplift is a gentle structural dome exposing both island-arc and continental margin blocks emplaced along the southern margin of Laurentia during the Grenville orogeny (locally the Llano orogeny). These ~1370 to 1230 Ma metaigneous and metasedimentary rocks were subsequently intruded by a number of ~1119 to 1070 Ma post-to syntectonic granitic plutons collectively known as the Town Mountain Granite. The eastern most of these plutons (Lone Grove, Kingsland, and Marble Falls plutons) contain sparse microgranular magmatic enclaves of intermediate composition (56-68 wt.% SiO2). The enclaves display sharp borders in contact with the host granite suggesting magma quenching with little or no physical exchange between host granite and enclave magma. The origin of the enclave magma(s) is uncertain, as no synchronous mafic to intermediate rocks are exposed in the Uplift. New major- and trace-element analyses are providing clues as to the possible origins and evolution of the enclave magmas. Numerical modeling reveals that neither fractional crystallization nor simple mixing can explain the trace-element trends. However, assuming source magmas similar to primitive continental arc andesites, the trends can be adequately replicated by a replenishment fractional crystallization(RFC) model. The model assumes that replenishment/hybridization events are accompanied by 20%-30% fractionation of plagioclase + clinopyroxene + magnetite. Modeling further reveals that results are relatively insensitive to the number of replenishment events (from 50 to 1000), as well as perturbations in the mineral percentages, suggesting that RFC is a very plausible and robust explanation for the chemical evolution of the enclaves. As suggested by Weibe et al. (1997), RFC and lack of magma exchange may be indicative of enclave magma ponding and hybridization at the base of the host granite magma chamber, followed by occasional dispersment into the host granite. Origin from a primitive

  13. A LA-ICP-MS study of minerals in the Rocche Rosse magmatic enclaves: Evidence of a mafic input triggering the latest silicic eruption of Lipari Island (Aeolian Arc, Italy)

    Davì, Marcella; De Rosa, Rosanna; Barca, Donatella


    The volcanic products of Lipari Island (Aeolian Arc, Italy) younger than 10 ka are mostly aphyric rhyolitic pumices and obsidians emitted during unusual strombolian-type eruptions, which ended with the emplacement of lava flows. The last volcanic activity on the island dates back to 1230 ± 40 AD, with the extrusion of Rocche Rosse (RR) obsidian lava flow. Recently, mafic enclaves of latitic to trachytic composition have been identified and an evolution process between these enclaves and the rhyolitic magma has been documented in detail [Davì, M., 2007. The Rocche Rosse rhyolitic lava flow (Lipari, Aeolian Islands): magmatological and volcanological aspects. Plinius, supplement to the European Journal of Mineralogy 33, 1-8]. In this work textural and trace-element investigation of mineral phases of the RR enclaves, such as crystals of clinopyroxene, olivine, plagioclase, alkali-feldspar and biotite, was carried out to delineate the most recent feeding system of the island, since such a reconstruction could be significant in terms of hazard forecasting. The results indicate that most of the mineral phases are reversely or oscillatory zoned with respect to both major and trace elements, suggesting an early crystallization under low fO 2 conditions from melts of intermediate composition, followed by a later growth from a more mafic (presumably shoshonitic-basaltic) magma than that from which their cores crystallized. Crystals of magnesium-rich pyroxene and forsteritic-rich olivine are indicative of the presence of this shoshonitic basaltic magma. Based on microanalytical data, it is suggested here that the feeding system of recent Lipari volcanic activity was characterized by a shoshonitic-basaltic magma originating from a deep reservoir, which may have evolved and stopped in the crust, generating zoned magma chambers at different depths, in which latitic and rhyolitic magmas reside. The sudden arrival of a new input of mafic melt may have interacted with these

  14. Geochemistry and Petrogenesis of Gouli Mafic Enclaves and Their Host Rocks in Eastern Kunlun%东昆仑沟里地区暗色包体及其寄主岩石地球化学特征及成因

    陈广俊; 孙丰月; 李碧乐; 王冠; 钱烨; 许庆林; 刘国才


    The authors report petrographical and whole-rock geochemical data of the host diorite and mafic microgranular enclaves(MMEs)within the Asiha diorite pluton at Gouli area in eastern Qinghai East Kunlun,and ascertain their petrogenesis and tectonic setting.The Asiha diorite pluton contains abundant MMEs which are mainly amphibole gabbro.The MMEs display igneous-texture and some of them are characterized by plastic flow deformation.The MMEs have plagioclase,amphibole and quartz xenocrysts and acicular apatite, which belongs to petrographical characteristics of magma mixing. Authors systematically studied petrological and geochemical characteristics of the host rocks and the MMEs,and conclude that both are meta-aluminous,high-K calc-alkaline series-shoshonitic series rocks. The selected major oxides of the MMEs and the host rocks show a linear correlation in Harker diagrams. In addition, Al2 O3/K2 O CaO/K2 O and SiO2/CaO K2 O/CaO identical oxide ratio denominator covariant diagram of the MMEs and their host rocks also show a linear correlation,which indicate their composition change is related to the magma mixing and mingling.Trace elements data show that they are both enriched in large ion lithophile elements (Rb,K)and depleted in high field strength elements (Nb,Ta,P and Ti).The MMEs are characterized by low SiO2 contents (SiO2=50.70% 53.88%), high MgO,Fe2O3 and CaO contents,as well as a higher Mg# value (Mg#=0.52 0.59),which indicates that the primary magma was derived from the partial melting of the mantle wedge.The Rb/Sr ratio of the host rocks varies from 0.22 to 0.27,which is close to but less than average values of the earth crust.The Nb/Ta ratio of the host rocks varies from 14.5 to 15.2,which is between the average values of the crust and mantle,suggesting that the magma of the host rocks is mainly from crust and experienced magma mixing.Combined with regional tectonic evolution and discrimination of tectonic setting,we suggest that the Asiha diorite pluton

  15. Chronological and geochemical studies of granite and enclave in Baimashan pluton, Hunan, South China


    Zircon LA-ICP-MS U-Pb dating reveals that the Baimashan Pluton is composed mainly of late Indosinian (204.5±2.8 Ma-209.2±3.8 Ma) biotite granodiorites/monzonitic granites (LIGs) and early Yanshanian (176.7±1.7 Ma) two-micas monzonitic granites (EYGs),and the coeval (203.2±4.5 Ma-205.1±3.9 Ma) mafic microgranular enclaves (MMEs) are generally found in the former.In addition,the ages of cores within zircons from LIGs and MMEs ranging from 221.4±4.0 Ma to 226.5±4.1Ma provide evidence of multistage magma intrusion during Indosinian in the study area.Measured 3010±20.6 Ma of inherited zircon age suggests that there may be recycling Archaean curstal material in existence in this area.LIGs and EYGs share some similar geochemical features: subalkaline and peraluminous granites,enrichment of Th,U,K,Ta,Zr,Hf and LREE but depletion of Ba,Nb,P,Ti and Eu,low εNd(t) values but high (87Sr/86Sr)i ratios,and old T2DM (ca.1.9-2.0 Ga).The behaviors of incompatible elements and REE are mainly dominated by fractional crystallization of plagioclase,K-feldspar,ilmenite and apatite,but that of Sr isotope mainly controlled by EC-AFC.They are crust-sourced and derived from partial melting of paleo-Proterozoic metagreywackes and related to biotite dehydration melting.LIGs are formed in post-collisional tectonic setting as crustal local extension and thinning during late Indosinian.But EYGs may be evolved products of congeneric granitic magma with LIGs formed in late Indoinian,which were emplaced again when crust underwent extensive thinning and extension in post-orogenic tectonic setting during Yanshanian in SC after undergoing EC-AFC.MMEs should be cognate enclaves and derived from liquid immiscibility of host magma.

  16. Textural analysis of magmatic enclaves from the Kameni Islands, Santorini, Greece

    Martin, Victoria M.; Holness, Marian B.; Pyle, David M.


    The Kameni Islands have been the focus of historic volcanic activity on Santorini, Greece. The islands comprise a series of dacite lavas, the erupted compositions of which have remained approximately constant for the last ˜2200 years. The dacite lava flows of Nea Kameni contain a variety of mafic enclaves, distinguished by differences in texture, composition and mechanical behaviour. The mafic enclaves represent chilled fragments of mafic magma that crystallised rapidly on contact with the cooler, more silicic host magma. The absence of chilled margins on the enclaves suggests that the replenishing magma initially formed a dense layer at the base of the chamber. Groundmass textures are interpreted as an indication of the degree of undercooling between the enclaves and the host. Groundmass textural information obtained from the enclaves has been used to determine the relative volumes of replenishing magmas injected into the host magma before eruption, which indicates that the volume of erupted magma is directly proportional to the volume of replenishing magma emplaced in the chamber prior to eruption, which thus may act as a potential eruption trigger. The variety of replenishing magmas implies the existence of a complex conduit and chamber system beneath Santorini volcano. Andesitic enclaves with linear crystal size distributions are thought to have originated as an aphyric andesitic melt expelled from a crystal mush by filter-pressing. Disequilibrium phenocryst assemblages in the lavas and phenocryst-bearing enclaves provide evidence for the entrainment and recycling of older phenocryst populations.

  17. Origins of Early Mesozoic granitoids and their enclaves from West Kunlun, NW China: implications for evolving magmatism related to closure of the Paleo-Tethys ocean

    Wang, Chao; Liu, Liang; Korhonen, Fawna; Yang, Wen-Qiang; Cao, Yu-Ting; He, Shi-Ping; Zhu, Xiao-Hui; Liang, Wen-Tian


    Early Mesozoic granitoids and microgranular enclaves (MEs) are widespread in the West Kunkun, northwestern Tibetan plateau, and record the tectonic evolution of Eurasia-Tethys in this area. This study reports geochemistry, zircon U-Pb and Hf isotopic data for a suite of granitoids and their MEs from the Middle Triassic Bulunkou pluton (BP) and the Late Triassic Akazishan pluton (AP) from the West Kunlun. LA-ICP-MS U-Pb zircon dating of a sample from the BP host monzogranite and an enclave, as well as a AP monzogranite, yielded ages of 236 ± 2, 230 ± 7 and 208 ± 1 Ma, respectively. The BP monzogranite and its enclaves from the northwestern part of the West Kunlun are mainly weakly peraluminous granites characterised by relatively high Rb, Th, Rb/Sr (2.64-9.03) and HREE contents, and low Mg#, Sr/Y and negative Eu anomalies. Zircons from the BP monzogranite have ɛHf(t) values from -5.7 to -1.6. Zircons from enclaves of the BP show more variable ɛHf(t) values from -4.1 to 3.8. We consider that the BP granites are likely to have been formed by partial melting of metasedimentary rocks at shallow crustal depth, and their enclaves, composed of quartz + biotite + plagioclase + garnet + K-feldspar, are relics from the melting of a source at middle crustal depths. The AP host and its enclaves from the southeastern part of the West Kunlun have low Rb, Rb/Sr (0.15-1.90) and weakly negative Eu anomalies but high HREE contents indicating limited fractionation of plagioclase without residual garnet in their source. The inferred protolith is an intermediate igneous rock in the middle or lower crust. MEs hosted in the AP have high Mg# (39.7-45.0) and Nb and weakly negative Eu anomalies, as well as high Sr, P and Ti, corresponding to a medium-K basaltic rock, which may have originated from mixing of partial melting of metasomatised mantle wedge that has been modified by upwelling asthenospheric mantle and crustal melting in the deep source. Post-collisional southeasternward

  18. Commodification of transitioning ethnic enclaves.

    Terzano, Kathryn


    This literature review examines the changing roles of ethnic enclaves, the question of their authenticity, and their value as commodified spaces, giving special attention to Little Italy neighborhoods in the United States. Understanding the roles of ethnic enclaves requires some understanding about immigrants' identities. For some theorists, immigrants become blended into society over the course of generations; for other theorists, descendants of immigrants sometimes retain their cultural heritage and traits, helping form a multicultural or pluralist society. In the traditional sense, ethnic enclaves consist of both ethnic residents and ethnic businesses (such as restaurants, shops, and grocers). One way that ethnic enclaves change is when the area experiences a demographic shift, and people from outside the ethnic group move their residences and businesses to the neighborhood, resulting in the area becoming diversified in people and businesses. A second way that an ethnic enclave changes is when the ethnic group shrinks, but the shops and other businesses remain, resulting in the area becoming diversified in residents but not businesses. This latter situation may encourage commodification of the neighborhood's ethnic identity, where a municipality or business association seeks to preserve an enclave's ethnic reputation for tourism purposes. This commodification has implications for many individuals and groups within the enclave as well as outside of it.

  19. Commodification of Transitioning Ethnic Enclaves

    Terzano, Kathryn


    This literature review examines the changing roles of ethnic enclaves, the question of their authenticity, and their value as commodified spaces, giving special attention to Little Italy neighborhoods in the United States. Understanding the roles of ethnic enclaves requires some understanding about immigrants’ identities. For some theorists, immigrants become blended into society over the course of generations; for other theorists, descendants of immigrants sometimes retain their cultural heritage and traits, helping form a multicultural or pluralist society. In the traditional sense, ethnic enclaves consist of both ethnic residents and ethnic businesses (such as restaurants, shops, and grocers). One way that ethnic enclaves change is when the area experiences a demographic shift, and people from outside the ethnic group move their residences and businesses to the neighborhood, resulting in the area becoming diversified in people and businesses. A second way that an ethnic enclave changes is when the ethnic group shrinks, but the shops and other businesses remain, resulting in the area becoming diversified in residents but not businesses. This latter situation may encourage commodification of the neighborhood’s ethnic identity, where a municipality or business association seeks to preserve an enclave’s ethnic reputation for tourism purposes. This commodification has implications for many individuals and groups within the enclave as well as outside of it. PMID:25431441

  20. Commodification of Transitioning Ethnic Enclaves

    Kathryn Terzano


    Full Text Available This literature review examines the changing roles of ethnic enclaves, the question of their authenticity, and their value as commodified spaces, giving special attention to Little Italy neighborhoods in the United States. Understanding the roles of ethnic enclaves requires some understanding about immigrants’ identities. For some theorists, immigrants become blended into society over the course of generations; for other theorists, descendants of immigrants sometimes retain their cultural heritage and traits, helping form a multicultural or pluralist society. In the traditional sense, ethnic enclaves consist of both ethnic residents and ethnic businesses (such as restaurants, shops, and grocers. One way that ethnic enclaves change is when the area experiences a demographic shift, and people from outside the ethnic group move their residences and businesses to the neighborhood, resulting in the area becoming diversified in people and businesses. A second way that an ethnic enclave changes is when the ethnic group shrinks, but the shops and other businesses remain, resulting in the area becoming diversified in residents but not businesses. This latter situation may encourage commodification of the neighborhood’s ethnic identity, where a municipality or business association seeks to preserve an enclave’s ethnic reputation for tourism purposes. This commodification has implications for many individuals and groups within the enclave as well as outside of it.

  1. Microgranitoid Enclaves in Some I—and S—type Granites from Southern China

    周金城; 陶仙聪; 等


    The three I-type plutons of Guantian(GT),Guidong(GD),Shangbao(SB)and the two S-type plutons of Xucun(XC)and Xiuning(XN) as well as their microgranitoid enclaves in southern China have been studied,Restite in the Motianling(MT) metasomatic granite in this area is described in this paper as well,Microgranitoid enclaves in the I-type granitoids may be divied into autoliths and schlierens which have marked differences both in petrography and geochemistry.In the S-type granitoids,schlierens are the major microgranitoid enclaves,but autoliths are rare.The metasomatic granite contains only restite without other enclaves.The microgranitoid enclaves and their host rocks have close ∈Nd(T)values and the same minerals within them are similar in composition.The microgranitoid enclaves,in general,don't represent the products of mixing of the syn-plutonic foreign mafic magma and the host acidic magma.They are the records of the evolution of intermediate-acidic magma itself.The formation of autoliths is related to the interdiffusion of different constituents in magma.Schlierens are the products of immiscible fractionation of the magma.

  2. Magmatic Enclaves in Granitic Rocks: Paragons or Parasites?

    Clemens, John; Stevens, Gary; Elburg, Marlina


    Granitic rocks form the fundamental building blocks of Earth's continents and provide us with a wide range of resources, so their formation is worth trying to understand. Fine-grained, igneous-textured microgranular enclaves of tonalitic to monzogranitic composition (ME) are common in granitic rocks and their origins have been hotly debated, with some workers suggesting that ME are not igneous. These ME have been studied intensively enough that we are now certain that they are of igneous origin - globules of mingled and quenched magma. Although a mantle connection is evident in many cases, their ultimate origin (including where in the lithosphere they originate) is still debated. This contribution explores the systematics of chemical variation in ME and their host granites, with the aim of uncovering any systematics in their behaviour and modelling the processes that have led to the variations that we measure, comparing host-rock series to their respective ME series. As always, the hope is that the study of ME may lead to improved understanding and modelling of the processes that are responsible for the formation of the host granitic magmas. Using variations between the molecular quantities Ti and M (Fe+Mn+Mg), we demonstrate that the petrogenetic processes that operated within a diverse group of S- and I-type granitic host magmas and their ME suites are dissimilar. Variations within the granitic series result from a variety of what might be called 'orderly' processes, resulting in linear or curvilinear trends in chemical variation diagrams. In contrast, processes that affected the ME series commonly resulted in scattered, chaotic variations. Even in cases in which an ME series displays more orderly variation, it can be shown that the hypothesis of simple mixing between a parent enclave magma and its host granitic magma, to produce the overall variations, cannot be supported. ME magmas had vastly smaller volumes compared with their host granitic magmas. Thus, they

  3. La deliberación de enclave

    Agustin, Oscar Garcia


    La configuración de la esfera pública puede ampliarse a través de los distintos mecanismos de deliberación que ofrece Internet. De este modo, desde los enclaves deliberativos, opiniones extremas pueden entrar en debate con otras opiniones vertidas desde otros enclaves y espacios más generales. En...

  4. La deliberación de enclave

    Agustin, Oscar Garcia


    La configuración de la esfera pública puede ampliarse a través de los distintos mecanismos de deliberación que ofrece Internet. De este modo, desde los enclaves deliberativos, opiniones extremas pueden entrar en debate con otras opiniones vertidas desde otros enclaves y espacios más generales. En...

  5. Ethnic Enclaves and Immigrant Labour Market Outcomes

    Damm, Anna Piil

    This study investigates empirically how residence in ethnic enclaves affects labour market outcomes of refugees. Self-selection into ethnic enclaves in terms of unobservable characteristics is taken into account by exploitation of a Danish spatial dispersal policy which randomly disperses new ref...

  6. Enclave Compositions Indicate Multiple Felsic Components at Chaos Crags, Lassen Volcanic National Park, California

    Schmidt, E. R.; Hammersley, L. C.; Clynne, M. A.


    Chaos Crags, located in Lassen Volcanic National Park, is a series of 6 rhyodacite domes that exhibit dramatic evidence of magma mixing. Mafic enclaves from the Chaos Crags form two distinct textural groups: a finer-grained group containing abundant plagioclase crystals from the host rhyodacite, and a coarser-grained group generally lacking host phenocrysts. Enclave samples were collected from Dome B of the Chaos Crags with the intent of obtaining complete suites of the two textural groups. Geochemical data for the enclaves shows a weak correlation between texture and geochemistry. Notably, the geochemical data also shows two distinct chemical trends that appear to represent mixing with two different felsic components. The dominant trend shows mixing between the host rhyodacite and the mafic end member. The second trend is interpreted to result from mixing between the mafic end member and a cryptic felsic component that is distinct from the host rhyodacite. Modeling of major oxides, selected trace elements and rare earth elements suggests that, although the two clusters of enclaves mix towards different felsic end members, they appear start from the same mafic end member, which has a composition of approximately: SiO2 51.84%, CaO 10.45%, K2O 0.69%, P2O5 0.10%, MgO 5.35%, Na2O 2.8%, FeO 8.25%, Fe2O3 1.84%, Al2O3 19.47% and TiO2 0.76%, a composition common in the Lassen region. Preliminary modeling results indicate that, at 75% SiO2, the cryptic felsic component has a composition of: K2O 5.25%, P2O5 1.2%, Na2O 8.25%, Al2O3 14.65%, Fe2O3 0.18%, FeO 0.88% and TiO2 1.46%, with negligible amounts of CaO and MgO. At 70% SiO2 this composition is approximately: K2O 4.3%, P2O5 0.95%, Na2O 7.05%, Al2O3 15.66%, TiO2 1.31%, FeO 2.51% and Fe2O3 0.55% with negligible amounts of CaO and MgO. It is likely that this previously unrecognized mixing trend represents crustal contamination of the mafic end member. A suite of samples with compositions intermediate between these two trends

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

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


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

  8. Fractal Analysis of Enclaves as a New Tool for Estimating Rheological Properties of Magmas During Mixing: The Case of Montaña Reventada (Tenerife, Canary Islands)

    Albert, Helena; Perugini, Diego; Martí, Joan


    The volcanic unit of Montaña Reventada on the island of Tenerife (Canary Islands, Spain) is an example of magma mingling and mixing in which the eruptive process was triggered by an intrusion of basanite into a phonolite magma chamber. The eruption started with emplacement of a basanitic scoria deposit followed by emplacement of a phonolitic lava flow characterized by the presence of mafic enclaves. These enclaves represent approximately 1 % of the outcrop and are basanitic, phono-tephritic and tephri-phonolitic in composition. The morphology of each enclave is different, varying from rounded to complex finger-like structures usually with cuspate terminations. In this study we quantified textural heterogeneity related to the enclaves generated by the mixing process and thus provided a new perspective on the 1100 Ad Montaña Reventada eruption. The textural study was performed by use of fractal geometry methods and the results show that the logarithm of the viscosity ratio between the phonolitic magma and the enclaves ranges between 0.39 and 0.81, with a mode at 0.49. This enables us to infer the water content is 2-2.5 wt% for the phonolitic magma and 1.5-2 wt% for the basanitic magma and the enclaves.

  9. Down syndrome with microgranular variant of acute promyelocytic leukemia in a child: a case report

    Jain Deepali


    Full Text Available Abstract Background Acute promyelocytic leukemia (APL accounts for less than 10% of pediatric AML. Cases of APL in Down syndrome (DS have been described in the literature rarely and it is rarer still to find the microgranular variant (M3v of APL in trisomy 21 patients. Case presentation We present a case of a five-year-old female with Down syndrome diagnosed with acute promyelocytic leukemia (APL. She came to our hospital with bleeding manifestations. Blood and bone marrow examination revealed promyelocytes showing a few fine granules and occasional Auer rods. Based on this morphology and cytochemistry, a diagnosis of APL microgranular variant (M3v was made. Conclusion This case report emphasizes the importance of a high index of suspicion in the diagnosis of acute promyelocytic leukemia microgranular variant in Down syndrome.

  10. Water-driven undercooling during the interaction of mafic and felsic magmas

    Pistone, M.; Blundy, J. D.; Brooker, R. A.; Hinton, R.


    Mantle-derived mafic magmas are often invoked as a mechanism to transfer heat, mass and volatiles to felsic plutons that reside in the Earth's crust. This process has been suggested as a means of sustaining shallow magmatic bodies and triggering volcanic eruptions. Various field observations suggest that mafic water-rich magmas might intrude a viscous felsic crystal-rich mush. This scenario might be expected to produce water advection from the crystallizing mafic magma to the felsic magma, leading to an increase of melt fraction in the felsic mush and subsequent mobilization whilst the mafic magma is simultaneously quenched. To investigate certain features of this scenario we conducted 24-hour experiments to establish the petrological evolution of a water-saturated (4 wt.% H2O in the interstitial melt) dacitic crystal mush (50-80 vol.% quartz crystals) subject to a volatile supply released from a water-saturated (≥ 6 wt.% H2O) andesitic magma at 950 °C and 500 MPa (15 km depth). Run products were characterised by SEM, EPMA, SIMS and Raman. Our results show unidirectional solidification textures (comb layering) as crystal nucleate at the mafic-felsic interface and grow into the mafic end-member. This is a direct effect of isothermal undercooling that results from a change in liquidus temperatures of the interacting magmas with changing water content. This is the first study exploring felsic-mafic magma interaction under "natural conditions" and shows that textures associated with mafic-felsic interactions found in the field may not be simply cooling-driven in origin. These experiments allow us to explore some essential concepts for understanding the origin of mafic enclaves, how volatiles contribute to crystal mush remobilisation within the Earth's crust and can trigger explosive volcanic eruptions during recharge of mafic inputs into felsic reservoirs, and how degassing processes might be traced by textural features that indicate the direction of volatile

  11. The influence of volatiles on the interaction of mafic and felsic magmas

    Pistone, M.; Jarvis, P.; Blundy, J. D.


    and crystallinity prior to interaction. Moreover, the results demonstrate the striking chemical and microstructural similarity between the run products and what observed in the textures of natural enclaves within felsic host rocks. This research is fundamental for understanding numerous, well-documented physico-chemical processes such as: magma mixing/mingling, alkali migration, formation of mafic enclaves, magma defrosting or partial melting of crystal mushes and their rheological remobilization within the Earth's crust.

  12. Ethnic Enclaves and Immigrant Labor Market Outcomes

    Damm, Anna Piil


    Spatial concentration of ethnic groups may theoretically have positive or negative effects on the economic performance of those groups. I examine the effects of the ethnic enclave size on labor market outcomes of immigrants. I account for ability-sorting into ethnic enclaves by exploiting a Danish...... increase in the ethnic enclave size increases annual earnings by 18 percent on average, irrespective of skill level. Third, the paper proposes an explanation for the earnings gain of ethnic enclave members. Enclave members benefit from more access to ethnic networks because ethnic networks disseminate job...

  13. Deep-derived enclaves (belonging to middle-lower crust metamorphic rocks) in the Liuhe-Xiangduo area,eastern Tibet: Evidence from petrogeochemistry

    WEI Qirong; LI Dewei; ZHENG Jianping; WANG Jianghai


    Petrological and geochemical studies of deep-derived enclaves from the Liuhe-Xiangduo area, eastern Tibet, showed that the enclaves involve five types of rocks, i. e. , garnet diopsidite, garnet amphibolite, garnet hornblendite, amphibolite and hornblendite, whose main mineral assemblages are Grt+Di + Hbl, Grt+ Pl + Hbl + Di, Grt + Hbl + Pl, Pl + Hbl, and Hbl + Bt, respectively. The enclaves exhibit typical crystalloblastic texture, and growth zones are well developed in garnet (Grt) in the enclaves. In view of major element geochemistry, the deep-derived enclaves are characterized by high MgO and FeO * ,ranging from 12.00% to 12.30% and 8.15% to 10.94%, respectively. The protolith restoration of metamorphic rocks revealed that the enclaves belong to ortho-metamorphic rocks. The REE abundances vary over a wide range, and ∑ REE ranges from 53.39 to 129.04 μg/g. The REE patterns slightly incline toward the HREE side with weak LREE enrichment. The contents of Rb, Sr, and Ba range from 8.34 to 101μg/g, 165 to 1485 μg/g, and 105 to 721 μg/g, respectively. The primitive mantle-normalized spider diagrams of trace elements show obvious negative Nb, Ta, Zr and Hf anomalies. Sr-Nd isotopic compositions of the enclaves indicated that the potential source of deep-derived enclaves is similar to the depletedmantle, and their (87Sr/86Sr) i ratios vary from 0.706314 to 0.707198, (147Nd/144Nd)i ratios from 0.512947 to 0.513046, and εNd(T) values from + 7.0 to +9.0, respectively. The potential source of the enclaves is obviously different from the EM2-type mantle from which high-K igneous rocks stemmed(the host rocks), i.e. , there is no direct genetic relationship between the enclaves and the host rocks.Deep-derived enclaves in the host rocks belong to mafic xenoliths, and those in the Liuhe-Xiangduo area,eastern Tibet, are some middle-lower crust ortho-metamorphic rocks which were accidentally captured at20-50 km level by rapidly entrained high-temperature high-K magma

  14. Mafic replenishment of multiple felsic reservoirs at the Mono domes and Mono Lake islands, California

    Bray, Brandon; Stix, John; Cousens, Brian


    The Mono Basin has been the site of frequent volcanic activity over the past 60,000 years, including the emplacement of the Mono domes and Mono Lake islands. The Mono Basin lavas are the youngest and most poorly understood products of the Long Valley Volcanic Field. We have undertaken a study of Mono Basin volcanism encompassing whole-rock major and trace element, Sr, Nd, Pb, and O isotopic, and electron microprobe glass, plagioclase, and amphibole analyses. Variations in major and trace elements suggest that fractional crystallization of feldspar (Sr, K2O), apatite (P2O5), titanomagnetite (V), zircon (Zr), and allanite (La, Ce) has influenced the evolution of the Mono Basin lavas. Field observations, petrography, and chemistry together demonstrate that injection of more mafic magma is a common process throughout the Mono Basin. Mafic enclaves of the Mono domes are stretched and rounded, with chilled margins between enclave and host rhyolite. Thin sections reveal millimeter-scale inclusions of rhyolite in the enclaves and vice versa along the host-enclave border. Paoha Island dacite has glass with 67-72 wt% SiO2 and contains microscopic clots of more mafic glasses, with SiO2 contents as low as 64 wt%. Isotopically, the June Lake and Black Point basalts and the Mono dome enclaves represent the least evolved material in the Long Valley Volcanic Field, with 87Sr/86Sri 0.5126. The silicic Mono Lake lavas and Mono dome rhyolites display a significant crustal component, with 87Sr/86Sri >0.7058 and 143Nd/144Nd 19 and δ18O >+6.5‰. The Mono Lake lavas generally are younger and less evolved than the Mono domes, with enrichment in trace elements including Ba and Sr accompanied by lower 143Nd/144Nd and higher 206Pb/204Pb. This implies that the Mono domes and the Mono Lake lavas are derived from different magma batches, if not from separate magma chambers. There is no systematic relationship between the degree of chemical evolution and the lava ages, indicating that several

  15. Kosmin granodiorite and its variable enclaves

    Gruszczyńska, Joanna; Pietranik, Anna


    Kośmin granodiorite represents Variscan magmatic activity in Poland, Sudetes. It is ca. 335 Ma and can be correlated with a similar magmatic episode in Czech Republic, Germany and Austria [1]. The geochemical data such as high contents of MgO and K2O, enrichment in LILE, high ratios of LREE/HREE, enrichment in Cr and Ni and low Na2O contents are similar to other K-rich intrusions in the Bohemian Massif [1]. Kośmin granodiorite contains variable dioritic, sjenitic and monzodioritic enclaves which potentially record processes of magma generation and differentiation typical for potassic magmatism. Three analyzed samples of the host granodiorite have similar composition (58 wt. % SiO2, 5 wt. % MgO, 4 wt. % K2O, 43 ppm Ni, 470 ppm Sr, 9 La/LuN). The mineral composition is dominated by K-feldspar and plagioclase, with subordinate hornblende, biotite, quartz and zircon and apatite as accessory minerals. An in plagioclase varies from 33 to 42% and average SrO content in plagioclase is ca. 650-850 ppm. The enclaves in the granodiorite can be divided into 3 groups according to their mineralogy and chemical composition: (1) Monzodiorites are the dominating type and are characterized by a range of chemical compositions (50-55 wt. % SiO2, 6-10 wt. % MgO, 4-5 wt. % K2O, 30-200 ppm Ni, 300-450 ppm Sr, 5-11 La/LuN). They consist of plagioclase, pyroxene, amphibole, biotite, K-feldspar, quartz and often contain variable amounts of plagioclase phenocrysts. The phenocrysts have variable An contents from 32 to 70%, but the highest An is observed in thin (ca. 100 μm) patchy zones close to the plagioclase rims. The SrO contents in plagioclase are ca. 900 ppm and are sometimes higher in the patchy zones up to 1100 ppm. The structure and chemical composition of phenocrysts is consistent with their crystallization in the host granodioritic magma and later transport and resorption in the monzodioritic magma. (2) Syenites comprise ca. 10% of enclaves and are characterized by very high K2O

  16. Microgranular acute promyelocytic leukemia: a distinct clinical, ultrastructural, and cytogenetic entity

    Golomb, H.M.; Rowley, J.D.; Vardiman, J.W.; Testa, J.R.; Butler, A.


    Three patients with acute leukemia, disseminated intravaslar coagulation, and a specific acquired chromosome abnormality (t(15;17)) were found by transmission electron microscopy to have the typical distribution of granules seen in promyelocytes. However, the average granule sizes were 120, 170 and 180 nm, respectively, for the three patients, significantly less than the 250-nm resolution of light microscopy. We regard the leukemia in these three patients as comprising a distinct clinical, ultrastructural, and cytogenetic entity that we have chosen to all microgranular acute promyelocytic leukemia.

  17. Timing of Magma Mixing in the Gangdisê Magmatic Belt during the India-Asia Collision:Zircon SHRIMP U-Pb Dating

    MO Xuanxue; DONG Guochen; ZHAO Zhidan; GUO Tieying; WANG Liangliang; CHEN Tao


    Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Quxu batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Quxu batholith, and subsequent zircon SHRIMP Ⅱ U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock,mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma,49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.

  18. Enclave Projects: What Are They and What Can Be Done?

    Virginia Alzina; Elizabeth Davidsen; Anne Deruyttere; Rodolfo Huici; Javier Jiménez; Juan Antonio Ketterer; Robert Montgomery; Gijs Nolet


    This report analyzes the advantages and disadvantages of including positive social actions in enclave projects after appropriate mitigation and compensation policies are in place, and addresses both the question of the mandatory or optional nature of these actions and the question of the responsible executing and financing agent or agents. The report defines enclave projects, reviews the experience of international financial institutions, the privatesector and the IDB with including positive ...

  19. Short-term evaluation of non-absorbable microgranular hydroxyapatite infiltration in the guinea pig subepidermal abdominal region

    A.P. Xavier


    Full Text Available Non-absorbable microgranular hydroxyapatite was infiltrated into the subepidermal abdominal region of guinea pigs in order to assess the possibility of using this material to correct deficiencies in orbital volume. Microgranular hydroxyapatite (2.0 ml was subepidermally infiltrated into the abdominal region of 20 guinea pigs. The animals were divided into four experimental groups of 5 animals each, which were killed 7 (G1, 15 (G2, 30 (G3 and 60 (G4 days after infiltration. The area and the largest and smallest diameters of the nodules formed by infiltration were evaluated at the site of infiltration and histological examination was performed. The mean granuloma area was similar in all groups. Histopathological examination showed that the material remained isolated from surrounding tissues by a pseudocapsule that became denser throughout the experiment. A host reaction started with young fibroblastic tissue that evolved to dense tissue until cartilaginous tissue was formed in G4, progressively advancing towards the center of the granuloma from G1 to G4. Non-absorbable microgranular hydroxyapatite is an inert material that was well tolerated by the animals studied, with maintenance of the infiltrated volume, and may perhaps be useful to fill anophthalmic cavities.

  20. Short-term evaluation of non-absorbable microgranular hydroxyapatite infiltration in the guinea pig subepidermal abdominal region.

    Xavier, A P; Schellini, S A; Aragon, F F; Padovani, C R; Taga, E M


    Non-absorbable microgranular hydroxyapatite was infiltrated into the subepidermal abdominal region of guinea pigs in order to assess the possibility of using this material to correct deficiencies in orbital volume. Microgranular hydroxyapatite (2.0 ml) was subepidermally infiltrated into the abdominal region of 20 guinea pigs. The animals were divided into four experimental groups of 5 animals each, which were killed 7 (G1), 15 (G2), 30 (G3) and 60 (G4) days after infiltration. The area and the largest and smallest diameters of the nodules formed by infiltration were evaluated at the site of infiltration and histological examination was performed. The mean granuloma area was similar in all groups. Histopathological examination showed that the material remained isolated from surrounding tissues by a pseudocapsule that became denser throughout the experiment. A host reaction started with young fibroblastic tissue that evolved to dense tissue until cartilaginous tissue was formed in G4, progressively advancing towards the center of the granuloma from G1 to G4. Non-absorbable microgranular hydroxyapatite is an inert material that was well tolerated by the animals studied, with maintenance of the infiltrated volume, and may perhaps be useful to fill anophthalmic cavities.

  1. Supported Employment: Report of a Successful Enclave Model: Research Note.

    Warth, Sue


    Three men and three women with moderate intellectual handicaps but no work experience outside sheltered workshops were employed by the Royal Australian Mint in the first enclave project in the Australian Capital Territory. Significant worker wages and improved independence and self-esteem were noted, and social security savings of over $7000…

  2. Ethnic enclaves and middleman minorities: alternative strategies of immigrant adaptation?

    Cobas, J A


    This article examines 2 modes or strategies of immigrant adaptation: middleman minorities and ethnic enclaves. Although they have been discussed as if they were disjointed and mutually exclusive, the authors challenge this view. Middleman minorities 1) tend to be self-employed or to work for a coethnic, 2) are usually concentrated in small business, 3) tend to rely on the in-group for resources, and 4) fill a "status gap" in the receiving society. Ethnic enclaves depend on 3 features: 1) recent coethnic arrivals spend a tour of duty at the worst jobs, 2) coethnics provide ethnic entrepreneurs with consumer markets, 3) ethnic businesses rely on each other to supply their operating needs. Ethnic enclaves are concentrated and spatially identifiable. For this study, the authors collected data in a survey of the Cuban exile community of San Juan, Puerto Rico. The sample selection procedure yielded a total of 261 individuals, 220 of whom were interviewed. 10 predictions found in the middleman minority and ethnic enclave perspectives were checked against the researchers' data. 4 of these predictions are hld in common by both approaches: 1) eomployment in an ethnic enterprise increases subsequent chances of self-employment, 2) ethnic firms rely on the in-group for business resources, 3) coethnic workers represent an asset to the ethnic entrepreneur in that they occupy important positions requiring the employer's trust, and 4) there is business competition between locals and minority members. As predicted by the middleman strategy, Cuban businesses in Puerto Rico tend not to be immediately productive and there is no evidence of spatial concentration of these businesses. However, fitting the enclave approach, these firms do not dominate certain business lines, Cuban entrepreneurs do not appear to be sojourners, and they tend to have business backgrounds. The middleman perspective is supported in that some elements of the local elite favor Cuban exiles. Thus, there is no

  3. Progress in Enclave Tourism Study of Overseas:A Literature Review

    Liu Aili; Liu Jiaming; Liu Min


    In response to the"isolated island"phenomenon emerging from the development of tourist resorts in China,this paper reviews the study of enclave tourism overseas,which has similar features to the resort"island".Based on the literatures related to enclave tourism from Tourism Management and Annals of Tourism Research,this paper reviews the study of enclave tourism from the following aspects:definition discussion,theoriesused,causation of enclaves,characteristics and impacts of enclave tourism.The understanding of the overseas researches on enclavetourism would provide instructions for the study on the problems of Chinese resorts,such as enclavity and"island effects",and suggest measures for the sustainable development of resorts in China.This paper is divided into three sections.Section 1 briefly introduces the development of enclave tourism in developing countries and the outline of enclave tourism study.Section 2 elaborates on the content of enclave tourism research and givesdeep insights into the study on concepts,characteristics,causations and effects respectively,which is the key part of this paper,Section 3 concludes the review and proposes suggestions for the enclave tourism study in China.

  4. P-T history and geochemical characteristics of mafic granulites and charnockites from west of Periya, North Kerala, southern India

    Prakash, D.; Chandra Singh, P.; Arima, M.; Singh, Triveni


    The study region forms the northern part of Kerala (south India) and constitutes part of granulite-facies rocks of the exhumed Proterozoic south Indian Granulite Terrain (SGT). The SGT consists of a large variety of rock types with a wide range of mineral parageneses and chemical compositions, namely charnockite, mafic granulite, gneiss, schist, anorthosite, granite and minor meta-sedimentary rocks. Garnet-bearing mafic granulites occur as small enclaves within charnockites. We report for the first time P-T constraints on the prograde path preceding peak metamorphism in the northernmost part of Kerala. An increase of the Mg, Fe and decrease of Ca and Mn contents from the core towards the rim of garnet in the mafic granulites suggest prograde garnet growth. The prograde path was followed by peak metamorphism at a temperature of c. 800 °C and a pressure of c. 7.5 kbar as computed by isopleths of XMg garnet, XCa garnet and XAn plagioclase. The resorption of garnet in various reaction textures and the development of spectacular orthopyroxene-plagioclase, biotite-quartz and hornblende-plagioclase symplectites characterize the subsequent stages of metamorphism. The PT path is characteristically T-convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust. Diffusion modeling of Fe-Mg exchange between garnet and hornblende suggests a near-peak cooling rate of 10-70 °C/myr. Such cooling rates are too high to be accounted for by normal isostatic uplift and erosion and suggest that the terrain was tectonically exhumed. Charnockites are richer in SiO2 and lower in MgO and CaO when compared to mafic granulites. Their REE patterns are relatively flat and show prominent negative europium anomalies. The mafic granulites are metamorphosed tholeiitic basalts as revealed by major- and trace-element geochemistry.

  5. The genetic relationship between mafic dike swarms and plutonic reservoirs in the mesozoic of central chile (30°-33°45'S): insights from AMS and geochemistry

    Creixell, Christian; Parada, Miguel Ángel; Morata, Diego; Roperch, Pierrick; Arriagada, César


    Five mafic dike swarms between 30° and 33°45'S were studied for their geochemical signature and kinematics of magma flow directions by means of AMS data. In the Coastal Range of central Chile (33°-33°45'S), Middle Jurassic dike swarms (Concón and Cartagena dike swarms, CMDS and CrMDS, respectively) and an Early Cretaceous dike swarm (El Tabo Dike Swarm, ETDS) display the presence of dikes of geochemically enriched (high-Ti) and depleted (low-Ti) basaltic composition. These dikes show geochemical patterns that are different from the composition of mafic enclaves of the Middle Jurassic Papudo-Quintero Complex, and this suggests that the dikes were injected from reservoirs not related to the plutonic complex. The mantle source appears to be a depleted mantle for Jurassic dikes and a heterogeneous-enriched lithospheric mantle for Cretaceous dikes. In the ETDS, vertical and gently plunging magma flow vectors were estimated for enriched and depleted dikes, respectively, which suggest, together with variations in dike thickness, that reservoirs were located at different depths for each dike family. In the Elqui Dike Swarm (EDS) and Limarí Mafic Dike Swarm (LMDS), geochemical patterns are similar to those of the mafic enclaves of the Middle Jurassic plutons. In the LMDS, east to west magma flow vectors are coherent with injection from neighbouring pluton located to the east. In the EDS, some dikes show geochemical and magma flow patterns supporting the same hypothesis. Accordingly, dikes do not necessarily come from deep reservoir; they may propagate in the upper crust from coeval shallow pluton chamber.

  6. Enclaves de la transición y democracia chilena Enclaves of the Transition and Chilean Democracy



    Full Text Available Algunas de las dificultades del gobierno de Michelle Bachelet y la crisis más generalizada del gobierno de la Concertación han estado cada vez más vinculadas a variables de liderazgo, al agotamiento de la coalición con respecto a sus ideales básicos, o a la necesidad de diversos tipos de reformas institucionales. Este trabajo contempla la posibilidad de que el modelo mismo de transición, que ha sido considerado como tan exitoso, podría ser el origen de las dificultades que hoy invaden tanto la Concertación como la democracia chilena en general. Además, argumenta que la interacción del sistema electoral y la estructura de la competencia postautoritaria han obligado a una política elitista que ayuda a explicar las dificultades actuales que sufre la Concertación, y ha forzado una crisis generalizada de representación. Para elaborar este argumento el autor se basa en el trabajo de Manuel Antonio Garretón, sobre los enclaves autoritarios, señalando que hay ciertos enclaves de la transición que dificultan el desarrollo de una democracia representativa de calidad. Estos enclaves de transición incluyen: el cuoteo, control de la élite en la selección de candidatos y la política electoral, dominación de los partidos en la política, formulación de políticas elitista y extrainstitucional, y la intocabilidad del modelo económico heredado del gobierno de Pinochet.Some of the difficulties of Michelle Bachelet Government and the more generalized crisis of Chile's governing Concertacián coalition have increasingly been tied to leadership variables, the exhaustion of the coalition with respect to its core ideals, or the need for various types of institutional reform. This paper considers the possibility that the very model of transition which has been lauded as so successful might actually be at the root of the difficulties that today plague both the Concertación and Chilean democracy more generally. This paper argues that the

  7. Enclaves van leed en werkelijkheid; wiens trauma is 'Srebrenica' eigenlijk?

    B.G.J. de Graaff


    Full Text Available R. van den Boogaard, Zilverstad. De Haagse verduistering van het drama-SrebrenicaC. Banning, P. de Koning, Balkan aan de Noordzee. Over het Joegoslavië-tribunaal, over recht en onrechtH. Praamsma, J. Peekel, T. Boumans, Herinneringen aan Srebrenica. 171 SoldatengesprekkenE. Suljagic, E. Vulliamy, L. Haveric, Postcards from the grave, afterword by Vulliamy, E., translated by L. HavericL.P.C. Ruigrok, Journalism of attachment. Dutch newspapers during the Bosnian warA. van Loon, Vrouwen van SrebrenicaJ. VanIerberghe, Kroniek van onmacht. Sarajevo, Srebrenica... tien jaar later Bob de Graaff, Enclaves of truth and anguish; whose trauma is ‘Srebrenica’ anyway? In 2005,ten years after the fall of the so-called ‘safearea’ of Srebrenica where a Dutch UN-battalion had been deployed to deter a Serb attack on the Bosnian Muslim enclave, several books were published on the war in Bosnia-Herzogovina (1992-1995. These publications examined the war’s aftermath and the way in which people came to terms with it. The author shows how the different groups involved in the tragedy at the time  Bosnian Muslims and Dutch politicians, journalists and soldiers  – all had their own separate ways of committing their pain to memory, there by giving the impression that each one of them had a monopoly on the truth and that their traumatic experience was unique.

  8. Mafic Plinian eruptions: Is fast ascent required?

    Szramek, Lindsay Ann


    It has been hypothesized that for a Plinian eruption of mafic magma to occur, that magma must ascend rapidly from the chamber to cause it to fragment into a jet containing juvenile and nonjuvenile tephra. To determine how fast mafic Plinian magmas need to travel to the level of fragmentation, a number of decompression experiments were carried out on two hydrous mafic magmas, and the results are compared to the products of two well-documented mafic Plinian eruptions: the basaltic andesite Fontana eruption of Masaya (Nicaragua) and the hawaiite 122 B.C. eruption of Etna (Italy). Comparison of natural and experimental textures shows that the Fontana eruption can be replicated in the lab at decompression rates between 0.1 MPa s-1 and 0.2 MPa s-1. This decompression rate is faster than any previously determined experimentally rate for more silicic eruptions. The hawaiite was unable to be reproduced in the lab. The natural groundmass is highly crystalline, which would have raised the viscosity of the initial melt by 1-2 orders of magnitude, which may not be enough to cause fragmentation.

  9. Explosive mafic volcanism on Earth and Mars

    Gregg, Tracy K. P.; Williams, Stanley N.


    Deposits within Amazonia Planitia, Mars, have been interpreted as ignimbrite plains on the basis of their erosional characteristics. The western flank of Hecates Tholus appears to be mantled by an airfall deposit, which was produced through magma-water interactions or exsolution of magmatic volatiles. Morphologic studies, along with numerical and analytical modeling of Martian plinian columns and pyroclastic flows, suggest that shield materials of Tyrrhena and Hadriaca paterae are composed of welded pyroclastic flows. Terrestrial pyroclastic flows, ignimbrites, and airfall deposits are typically associated with silicic volcanism. Because it is unlikely that large volumes of silicic lavas have been produced on Mars, we seek terrestrial analogs of explosives, mafic volcanism. Plinian basaltic airfall deposits have been well-documented at Masaya, Nicaragua, and basaltic ignimbrite and surge deposits also have been recognized there. Ambrym and Yasour, both in Vanuatu, are mafic stratovolcanioes with large central calderas, and are composed of interbedded basaltic pyrocalstic deposits and lava flows. Zavaritzki, a mafic stratovolcano in the Kurile Islands, may have also produced pyroclastic deposits, although the exact nature of these deposits in unknown. Masaya, Ambrym and Yasour are known to be located above tensional zones. Hadriaca and Tyrrhena Paterae may also be located above zones of tension, resulting from the formation and evolution of Hellas basin, and, thus, may be directly analogous to these terrestrial mafic, explosive volcanoes.

  10. Bimodal magmatism during the Diego Hernández Formation, Tenerife, Canary Islands: genesis and eruption-triggering of phonolitic magmas during ongoing mafic volcanism

    Olin, P. H.; Wolff, J. A.; Edgar, C. J.; Cas, R.; Martí, J.


    The Diego Hernández Formation (DHF) represents the explosive eruption of nearly 70 cubic km of phonolite over approximately 200 k.y. from the Las Cañadas caldera on Tenerife. Four chemostratigraphic units are distinguished on the basis of trace element contents: DHF bs (represented by the 370 ka Fortaleza and 347 ka Roque Members), DHF I (319 ka Aldea, 309 ka Fasnia, and 268 ka Poris Members), DHF II (Arafo and 223 ka Caleta Members), and DHF III (Cruz Sequence and the 196 ka Abrigo Member); all named units involve plinian and/or ignimbrite components that devastated a significant fraction of the island [1]. These chemostratigraphic units demarcate two dominant compositional trends distinct in incompatible element contents, and in Nb/Ta and REE ratios. DHF bs and DHF III plot along a high-Nb trend, and DHF I and DHF II plot along a low-Nb trend, a feature consistent with divergent fractionation histories involving titanite. Mafic magma was an important component of the DHF magmatic system and flanking mafic volcanism was ongoing during DHF time. Major phonolitic eruptions are conformably bounded by basanitic lavas and scoria deposits. Mafic magmatic components are identifiable in many of the phonolitic pyroclastic deposits as mafic, mingled and banded pumices, or as quenched mafic enclaves. Mafic components in the Abrigo, Caleta, and Poris Members are nearly geochemically identical to the underlying scoria or lava, suggesting that flanking mafic volcanism may in some cases be associated with subcaldera intrusive events that remobilize phonolitic magma to trigger major explosive eruptions. We envisage that the DHF represents a time when the intrusion of mantle-derived mafic magma in the lower crust supplied heat sufficient for the generation of intermediate tephriphonolite and phonotephrite magmas via melting of gabbroic/basaltic crust. Some of these intermediate magmas evolved to phonolite by crystal fractionation, a scenario consistent with DHF III

  11. Effect of partial melting on Vp and Vs in crustal enclaves from Mazarrón (SE Spain)

    Ferri, Fabio; Burlini, Luigi; Cesare, Bernardo


    The combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust. Here we report the laboratory measurements for Vp and Vs obtained in varying conditions up to those exceeding the beginning of melting (950 °C at 500 MPa confining pressure) on two residual garnet-biotite-sillimanite-cordierite-spinel metapelitic enclaves recovered from the Neogene dacites of Mazarrón (SE Spain). The enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction. At 500 MPa, the experimental Vp ranges from 7.21 ÷ 7.46 km s- 1 at room temperature to 5.44 km/s at 950 °C. The mean Vs is 4.5 km/s at room temperature with shear-wave splitting of 0.25 ÷ 0.3 km/s, measured along three mutually orthogonal directions. When temperature increases, the Vs evidences a reversible slope change at about 650 °C, and the shear-wave splitting reduces to zero (isotropic material) at 850-950 °C, where the sample Vs is ~ 3.0 km/s. The Vp anisotropy is 7-10% up to 700 °C increasing to ~ 20% at 950 °C, while the Vs anisotropy continuously decreases with temperature from 5% to 7% at room temperature to zero at 950 °C. No mineral reactions are observed up to 650-700 °C; however, microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature. Between 850 °C and 950 °C, a new melting reaction is observed producing biotite + spinel + ilmenite + plagioclase + melt. At melting, the rock becomes isotropic for Vs, and Poisson's ratio increases to 0.30. Our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials. The evolution of Vp and Vs at melting conditions is compatible with the geophysical data of the area, supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the Alborán domain.

  12. Secure Enclaves: An Isolation-centric Approach for Creating Secure High Performance Computing Environments

    Aderholdt, Ferrol [Tennessee Technological Univ., Cookeville, TN (United States); Caldwell, Blake A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hicks, Susan Elaine [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Koch, Scott M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Naughton, III, Thomas J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pelfrey, Daniel S. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Pogge, James R [Tennessee Technological Univ., Cookeville, TN (United States); Scott, Stephen L [Tennessee Technological Univ., Cookeville, TN (United States); Shipman, Galen M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Sorrillo, Lawrence [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)


    High performance computing environments are often used for a wide variety of workloads ranging from simulation, data transformation and analysis, and complex workflows to name just a few. These systems may process data at various security levels but in so doing are often enclaved at the highest security posture. This approach places significant restrictions on the users of the system even when processing data at a lower security level and exposes data at higher levels of confidentiality to a much broader population than otherwise necessary. The traditional approach of isolation, while effective in establishing security enclaves poses significant challenges for the use of shared infrastructure in HPC environments. This report details current state-of-the-art in virtualization, reconfigurable network enclaving via Software Defined Networking (SDN), and storage architectures and bridging techniques for creating secure enclaves in HPC environments.

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

    Ashima Saikia; Bibhuti Gogoi; Mansoor Ahmad; Talat Ahmad


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

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

    Saikia, Ashima; Gogoi, Bibhuti; Ahmad, Mansoor; Ahmad, Talat


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

  15. Ethnic enclaves and gestational diabetes among immigrant women in New York City.

    Janevic, T; Borrell, L N; Savitz, D A; Echeverria, S E; Rundle, A


    Previous research has shown that immigrants living in their own ethnic enclave are at decreased risk of poor health outcomes, but this question has not been studied in relation to gestational diabetes, an important early marker of lifecourse cardiovascular health. We ascertained gestational diabetes, census tract of residence, and individual-level covariates for Sub-Saharan African, Chinese, South Central Asian, Non-Hispanic Caribbean, Dominican, Puerto Rican, Mexican, and Central and South American migrant women using linked birth-hospital discharge data for 89,703 singleton live births in New York City for the years 2001-2002. Using 2000 census data, for each immigrant group we defined a given census tract as part of an ethnic enclave based on the population distribution for the corresponding ethnic group. We estimated odds ratios for associations between living in an ethnic enclave and risk of gestational diabetes adjusted for neighborhood deprivation, percent commercial space, education, age, parity, and insurance status, using multilevel logistic regression. Overall, we found no effect of ethnic enclave residence on gestational diabetes in most immigrant groups. Among South Central Asian and Mexican women, living in a residential ethnic enclave was associated with an increased odds of gestational diabetes. Several explanations are proposed for these findings. Mechanisms explaining an increased risk of gestational diabetes in South Central Asian and Mexican ethnic enclaves should be examined.

  16. Constraints on aeolian sediment transport to foredunes within an undeveloped backshore enclave on a developed coast

    Kaplan, Kayla L.; Nordstrom, Karl F.; Jackson, Nancy L.


    Landforms present in undeveloped beach enclaves located between properties developed with houses and infrastructure are often left to evolve naturally but are influenced by the human structures near them. This field study evaluates how buildings and sand-trapping fences change the direction of wind approach, reduce wind speed, and restrict fetch distances for sediment entrainment, thereby reducing the potential for aeolian transport and development of dunes in enclaves. Field data were gathered in an 80 m long, 44 m deep beach enclave on the ocean shoreline of New Jersey, USA. Comparison of wind characteristics in the enclave with a site unaffected by buildings revealed that offshore winds in the enclave are reduced in strength and altered in direction by landward houses, increasing the relative importance of longshore winds. Vertical arrays of anemometers on the foredune crest, foredune toe and berm crest in the enclave revealed increasing wind speed with distance offshore, with strongest winds on the berm crest. Vertical cylindrical traps on the foredune crest, foredune toe, mid-backshore, berm crest and upper foreshore revealed the greatest rate of sediment transport on the berm crest. Sediment samples from the beach and from traps revealed limited potential for aeolian transport because of coarse grain sizes. Strong oblique onshore winds are common in this region and are normally important for transporting sand to dunes. The length of an enclave and the setback distance on its landward side determine the degree to which sediment delivered by oblique winds contributes to dune growth. The landward edge of the enclave (defined by a sand fence near the dune toe) is sheltered along its entire length from winds blowing at an angle to the shoreline of 25° or less. A foredune set back this distance in an enclave the length of an individual lot (about 20 m) would be sheltered at an angle of 57° or less, reducing the opportunity for dune building by onshore winds

  17. Sobre o sentido do trabalho fora do enclave de mercado

    Débora Paschoal Dourado

    Full Text Available Ao longo do processo civilizatório, o trabalho adquiriu significados diversos para a humanidade, assumindo formas peculiares de organização e materialidade de acordo com o contexto histórico. Na sociedade contemporânea, o trabalho tende a ocupar um lugar central na vida das pessoas. Com base no pressuposto de que os estudos sobre o trabalho fundamentam-se na atual concepção do trabalho moderno associado ao âmbito das empresas, propôs-se, na presente pesquisa, investigar qual(is o(s sentido(s que indivíduos atuantes em organizações fora do enclave do mercado - mais especificamente em organizações de cultura popular - atribuem ao trabalho. Para responder ao problema posto, utilizou-se o método qualitativo, mais propriamente a história oral, mediante entrevista narrativa com a dirigente de uma organização de cultura popular afro-brasileira. Encontraram-se indícios de que há uma possibilidade de trabalho distinta do modelo empresarial e de que categorias como espiritualidade, resistência, cidadania podem explicar seu sentido. O trabalho, para a protagonista da história pesquisada, é uma atividade autodeterminada, externa à relação dinheiro-mercadoria, que gera realização pessoal e da comunidade onde mora/trabalha.

  18. Peer-to-Peer Enclaves for Improving Network Defence

    David W. Archer


    Full Text Available Information about cyberthreats within networks spreads slowly relative to the speed at which those threats spread. Typical "threat feeds" that are commercially available also disseminate information slowly relative to the propagation speed of attacks, and they often convey irrelevant information about imminent threats. As a result, hosts sharing a network may miss opportunities to improve their defence postures against imminent attack because needed information arrives too late or is lost in irrelevant noise. We envision timely, relevant peer-to-peer sharing of threat information – based on current technologies – as a solution to these problems and as a useful design pattern for defensive cyberwarfare. In our setting, network nodes form communities that we call enclaves, where each node defends itself while sharing information on imminent threats with peers that have similar threat exposure. In this article, we present our vision for this solution. We sketch the architecture of a typical node in such a network and how it might interact with a framework for sharing threat information; we explain why certain defensive countermeasures may work better in our setting; we discuss current tools that could be used as components in our vision; and we describe opportunities for future research and development.

  19. 75 FR 69717 - In the Matter of: Edentify, Inc., Embryo Development Corp., Enclaves Group, Inc., Energytec, Inc...


    ..., Inc., Embryo Development Corp., Enclaves Group, Inc., Energytec, Inc., Enesco Group, Inc... securities of Embryo Development Corp. because it has not filed any periodic reports since the period...

  20. Immigrant Enclaves and Inadequate Prenatal Care among Mexican-origin Mothers.

    Noah, Aggie J


    This study is an investigation of the relationships between residing in different types of ethnic enclave neighborhoods and inadequate use of prenatal care among Mexican-origin mothers. A unique dataset was created using National Center for Health Statistics 2008 restricted-use detailed natality files, the 2005-2009 American Community Survey, and the Department of Health and Human Services Area Resource file. Hierarchical modeling was used. Mexican-origin mothers' residential contexts are associated with the inadequacy of their prenatal care utilization beyond their individual characteristics. Specifically, residing in Mexican immigrant enclaves is associated with increased odds of having inadequate use of prenatal care. In contrast, residing in other types of ethnic enclaves (Mexican/Hispanic ethnic enclaves) and non-Hispanic white neighborhoods is associated with decreased odds of having inadequate utilization of prenatal care even after the inclusion of contextual-level controls for individual characteristics, neighborhood socioeconomic status, and the availability of healthcare infrastructure resources. Residing in immigrant enclaves is important for understanding the inadequacy of prenatal care utilization for Mexican-origin mothers. These findings have policy implications for designing place-based programs to target certain residential contexts where women are at greater risk of having inadequate use of prenatal care.

  1. Mafic and related complexes in Galicia: an excursion guide

    Arps, C.E.S.; Calsteren, van P.W.C.; Hilgen, J.D.; Kuijper, R.P.; Tex, den E.


    In Galicia occur several polymetamorphic complexes that contain mafic and ultramafic rocks. Mafic volcanics and gabbros are situated in or near the complexes. An episode of metamorphism and granitization encompassed the generation of the volcanics and gabbros. Gravity surveys revealed the existence

  2. Mid-Paleozoic age of granitoids in enclaves within early Cretaceous granulites, Fiordland, southwest New Zealand

    Bradshaw, J.Y.; Kimbrough, D.L.


    Orthogneisses of granite, quartz monzonite, monzonite, and tonalite, occur locally as isolated enclaves within the Early Cretaceous granulite terrain (Western Fiordland Orthogneiss - WFO). Discordant U-Pb zircon isotopic data (seven fractions) from four granitoid samples from enclaves at George Sound, define an upper intecept age of 341??34 Ma that is interpreted as approximating the time of formation of the granitoid suite. The lower intercept age of 93??37 Ma is interpreted as approximating the time of zircon isotopic disturbance by major episodic Pb loss. The low 87Sr/ 86Sr initial ratio indicates that these mid-Paleozoic granitoids were derived from an isotopically primitive source. The granitoid enclaves within WFO show influences of several different sources. The granitoids provide evidence linking WFO to a mid-Palaeozoic country rock similar to the central Fiordland metasediments. -from Authors

  3. Discovery of Enclaves from Cenozoic Pulu Volcanic Rocks in West Kunlun Mountains and Its Geological Implications


    In this paper, we present the occurrence and mineral components of the enclaves firstly discovered in the Cenozoic Pulu volcanic rocks in west Kunlun Mountains, and propose that the enclave is accumulated by fractional crystallization within high-level magma chamber. In addition, the chemical compositions of its primary magma are calculated. The calculated compositions are similar to those of the Kangxiwa volcanic rocks that belong to the same volcanic belt in the Pulu volcanic region, suggesting their origin from the same source region. However, the temperatures and oxygen fugacity of magmas at high-level magma chamber decreased along with fractional crystallization.

  4. Microgranular variant of acute promyelocytic leukemia with der(17) ins(17;15): A case report and review of the literature



    Acute promyelocytic leukemia (APL) with variant translocations is rare. The patient of the present case report, a 2-year-old male with a microgranular variant of APL carrying der(17) ins(17;15) translocation, exhibited fever and epistaxis. The complete blood count showed marked leukocytosis with 72% atypical promyelocytes, anemia and thrombocytopenia. Conventional cytogenetic analysis of the bone marrow cells revealed a karyotype of 47, XY, add(3)(q29), −7, ins(17;15)(q12;q14q22),+21,+mar. The promyelocytic leukemia/retinoic acid receptor α (PML/RARα) rearrangement and insertion were confirmed by fluorescence in situ hybridization. The PML/RARα transcripts were not detected by the reverse transcription polymerase chain reaction, and the patient was diagnosed with microgranular variant M3 APL. The patient achieved remission after a 30-day treatment and was still in remission during a recent follow-up. The present findings suggest that the ins(17;15) variant in APL may not be associated with an unfavorable prognosis. In summary, we reported an extremely rare case of APL with der(17) ins(17;15) abnormality in a pediatric patient and reviewed the literature. PMID:26622430

  5. Does microgranular variant morphology of acute promyelocytic leukemia independently predict a less favorable outcome compared with classical M3 APL? A joint study of the North American Intergroup and the PETHEMA Group

    Tallman, Martin S.; Kim, Haesook T.; Montesinos, Pau; Appelbaum, Frederick R.; de la Serna, Javier; Bennett, John M.; Deben, Guillermo; Bloomfield, Clara D.; Gonzalez, Jose; Feusner, James H.; Gonzalez, Marcos; Gallagher, Robert; Gonzalez-San Miguel, Jose D.; Larson, Richard A.; Milone, Gustavo; Paietta, Elisabeth; Rayon, Chelo; Rowe, Jacob M.; Rivas, Concha; Schiffer, Charles A.; Vellenga, Edo; Shepherd, Lois; Slack, James L.; Wiernik, Peter H.; Willman, Cheryl L.; Sanz, Miguel A.


    Few studies have examined the outcome of large numbers of patients with the microgranular variant (M3V) of acute promyelocytic leukemia (APL) in the all-trans retinoic acid era. Here, the outcome of 155 patients treated with all-transretinoic acid-based therapy on 3 clinical trials, North American I

  6. Morphology and geochemistry of zircon: a case study on zircon from the microgranitoid enclaves

    汪相; KIENAST; Jean-Robert


    There are three types of zircon (i.e. Zircon A, Zircon B and Zircon C) in the microgranitoid enclaves from the Qingtian granite. Zircon A is of the smallest Ipr, Ipy and Iel values with the largest range of variations; Zircon C is of the largest Ipr, Ipy and Iel values with the smallest range of variations; and Zircon B is intermediate among the three types. The microprobe analysis of zircon demonstrates that the contents of trace elements (Hf, U, Y, Th) increase progressively with larger and larger variation from Zircon A through Zircon B to Zircon C. These characters snggest that the three types of zircon in the enclaves may have formed successively during the cooling process of enclave magma, corresponding to different sites along with the intrusion of enclave magma. Because of positive correlations of the UO2/HfO2 ratio with Ipr, the ThO2/Y2O3 ratio with Ipy, and the UO2/(ThO2 + Y2O3) ratio with Iel, it is suggested that the variation in zircon typology is caused

  7. The Effects of Age at Arrival and Enclave Schools on the Academic Performance of Immigrant Children

    Cortes, Kalena E.


    This paper analyzes the relationship between age at arrival and immigrant-receiving high schools (i.e., enclave schools) on the academic performance of first- and second-generation immigrant children using data from the Children of Immigrants Longitudinal Study (CILS). The CILS survey was conducted in two major immigrant-receiving cities in the…

  8. Mexican Entrepreneurs and Markets in the City of Los Angeles: A Case of an Immigrant Enclave.

    Alvarez, Robert M., Jr.


    Explores Mexican-American immigrant entrepreneurial activity in the wholesale produce industry in Los Angeles (California). This activity exhibits the primary characteristics defined for immigrant enclaves, a specific mode of incorporation into the economic sector of the U.S. Describes hierarchical elements of Mexican entrepreneurship that…

  9. Dialectics of Authentication: Performing 'Exotic Otherness' in a Backpacker Enclave of Dali, China

    Ateljevic, I.; Doorne, S.


    This paper explores dialectics of entrepreneurship and cultural consumption in the backpacker tourist enclave of 'Foreigner's Lane' in Dali, Yunnan Province, PR China, focusing on the role of ethnic identities and their representation. The discussion uses the performance metaphor to conceptualise to

  10. A Comparative Perspective on the Ethnic Enclave: Blacks, Italians, and Jews in New York City.

    Model, Suzanne


    Research among workers and entrepreneurs in three ethnic groups found that (1) ethnic employees in an enclave environment receive rewards in some ways superior to those available to their counterparts in the secondary sectors, and (2) special linkages exist between ethnic businesses that facilitate the prosperity of these companies in the…

  11. Notes sur la dimension immunitaire des enclaves pétrolières

    Nicolas Donner


    Full Text Available Cet article se propose de réfléchir aux modes d’installation des enclaves pétrolières en milieux difficiles ; il s’attache aux procédures qui visent à prémunir l’activité extractive du potentiel de perturbation et/ou d’hostilité dont recèlent ces milieux. Dans un premier temps, et en se penchant sur le cas d’enclaves installées dans des milieux naturels hostiles à la vie, on montre en quoi le mode d'organisation des espaces extractifs est un outil important de leur immunisation : il relève d’une « architecture du vide » (Sloterdijk qui, par la production d’un espace inclusif et autonome, permet d’affranchir l’activité des conditions et contingences des milieux où elle se déploie. Dans un second temps, on s’intéresse aux enclaves dépêchées dans des milieux « pleins » (peuplés et territorialisés, où les procédures d’immunisation s’enrichissent de mécanismes défensifs (systèmes de clôtures et interventionnistes (pratiques de développement durable. On discute enfin de l’émergence d’un paradigme éthique qui s’enchevêtre dans les stratégies visant à garantir la permanence des activités extractives.This paper considers the ways of establishing oil enclaves in difficult environments and it focuses on procedures that aim to safeguard the extractive activity from external disturbance and/or hostility. First, in addressing the case of enclaves located in extreme environments (hostile to life, we show that the organization of enclaves is an important tool of their immunization: by producing an inclusive and autonomous space, an "architecture of vacuum "(Sloterdijk allows to free the activity from the conditions and contingencies of the external environment. Secondly, we move to the case of enclaves established in environments that are inhabited and territorialized, where immunization procedures are enriched by defensive (fencing and intrusive mechanisms (sustainable practices

  12. Melt extraction in mush zones: The case of crystal-rich enclaves at the Sabatini Volcanic District (central Italy)

    Masotta, M.; Mollo, S.; Gaeta, M.; Freda, C.


    A peculiar feature of the Sabatini Volcanic District (SVD, central Italy) is the occurrence of crystal-poor pumices and crystal-rich enclaves within the same eruptive host-deposit. The stratigraphic sequence of pumices and enclaves indicates the tapping of a stratified magma chamber, where a crystal-poor phonolitic magma lay on top of a more primitive crystal-rich magma. The crystal-rich enclaves are genetically related to the pumices and record the evolution of a solidification front, in which a more differentiated melt was produced, extracted and eventually erupted. We collected and analyzed crystal-rich enclaves from one of the largest phonolitic eruptions at the SVD and used their petrological and geochemical features to reconstruct magma differentiation and crystal-melt separation in the solidification front. On this basis, three groups of enclaves have been identified: porphyritic enclaves, holocrystalline enclaves and sanidinites. The mineralogical variability faithfully reproduces the spatial and temporal evolution expected of a solidification front, from early-to-intermediate crystallization conditions (porphyritic and holocrystalline type) to the late stage of solidification (sanidinites), in which the percolation of a more differentiated melt through the crystal mush triggered the instability of the solidification front. Results from numerical models indicate that gravitational instability is the most efficient mechanism to explain melt extraction in mush zones of medium-sized (~ 10 km3), short-lived (~ 104 years) magma chambers.

  13. Formation and Significance of Magmatic Enclaves in From the 2006 Eruption of Augustine Volcano, Alaska

    Browne, B. L.; Vitale, M. L.


    Deposits from the 2006 eruption of Augustine Volcano, Alaska, record a complicated history of open system magmatic processes that produced a suite of intermediate (56.5 to 63.3% SiO2) lithologies containing rare and variably quenched basaltic to basaltic-andesite enclaves (49.5-57.3% SiO2). The eruption transitioned from an explosive phase (Jan 11-28) to a continuous phase (Jan 28-Feb 10) before ending following a month-long effusive phase in March. Whereas the explosive phase is dominated by a low-silica andesite (LSAS, 56.5-58.7% SiO2) lithology, high-silica andesite (HSA, 62.2-63.3% SiO2) is more common during the continuous phase and dense low-silica andesite (DLSA, 56.4-59.3% SiO2) occurs mostly during the effusive phase. Enclaves occur in all lithologies, although most commonly in DLSA and LSAS. Point-counting of enclaves in outcrop reveals an average abundance of Augustine Volcano record a complex and multi-step mixing and mingling scenario between intruding basalt and resident silicic mush, and possibly gabbroic cumulates/wall rock, that is inconsistent with any single currently employed mingling model (e.g., buoyant lift-off of vesiculated and undercooled basalt, prolonged undercooling of intruded basalt punctuated by subsequent intrusions, enclave dissagregation and ripening, or violent intrusion of bubbly basaltic plumes) that has been used to explain magmatic enclave formation at other arc systems characterized by lower magma temperature, higher crystallinity, and larger eruptive volumes (e.g., Unzen Volcano, Mt. Lassen, Soufriere Hills).

  14. Mineral chemistry, P-T-t paths and exhumation processes of mafic granulites in Dinggye, Southern Tibet

    LIU; Shuwen; ZHANG; Jinjiang; SHU; Guiming; LI; Qiugen


    The mafic granulites in Dinggye, as various scale lense-shaped enclaves within the high Himalayan crystalline rock series, occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System (STDS) and the Xainza-Dinggye normal fault system. The main lithological assemblage comprises garnet plagioclase pyroxenite, garnet two-pyroxene granulite, pyroxene garnet amphibolite and so on. The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution. The first metamorphic stage, the garnet+clinopyroxene+quart mineral assemblage (M1) was probably formed under eclogite facies, the second stage, the plagioclase+clinopyroxene symplectite mineral assemblage (M2) was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage, the third stage, the plagioclase+clinopyroxene+ hypersthene symplectite mineral assemblage (M3) was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage, plagioclase+hornblende mineral assemblage (M4) was formed by hydrolysis of earlier mineral assemblages during late uplifting. The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites, whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite. These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyroblasts (M1) could be formed at the eclogite facies, the early decompressive breakdown (M2) occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃, the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃ and M4 plagioglase+hornblende retrograde mineral assemblage was produced under

  15. [Raman spectra and its application of graphite enclaves in nephrite-jades in Xiuyan, Liaoning].

    Qiu, Zhi-li; Jiang, Qi-yun; Luo, Han; Qin, She-cai; Li, Liu-fen


    Xiuyan, Liaoning was an important locality of jade material of the Red Mountain Culture in the Neolithic Age in Chinese history where there are two types of raw material of nephrite jades, namely gravel nephrite jade (Hemo Yu in Chinese) and old nephrite jade (Lao Yu in Chinese). In the present paper, Laser Raman spectrum technique was applied to analyze the graphite enclaves in the nephrite jades of the two types of materials. The results show that the graphite enclaves in the two types of jades have different characteristics of Raman spectra, indicating that they probably were formed under different geological conditions, or originated from different ore-forming periods or were exploited from different section of ore body. Hence, laser Raman spectrum technique could be used as a supplementary measure for nondestructive detection to determine the occurrence of jades.

  16. Pseudotachylitic breccia in mafic and felsic rocks

    Kovaleva, Elizaveta; Huber, Matthew S.


    Impact-produced pseudotachylitic breccia (PTB) is abundant in the core of the Vredefort impact structure and was found in many pre-impact lithologies (e.g., Reimold and Colliston, 1994; Gibson et al., 1997). The mechanisms involved in the process of forming this rock remain highly debated, and various authors have discussed many possible models. We investigate PTB from two different rock types: meta-granite and meta-gabbro and test how lithology controls the development of PTB. We also report on clast transport between different lithologies. In the core of the Vredefort impact structure, meta-granite and meta-gabbro are observed in contact with each other, with an extensive set of PTB veins cutting through both lithologies. Microstructural analyses of the PTB veins in thin sections reveals differences between PTBs in meta-granite and meta-gabbro. In granitic samples, PTB often develops along contacts of material with different physical properties, such as a contact with a migmatite or pegmatite vein. Nucleation sites of PTB have features consistent with ductile deformation and shearing, such as sigmoudal-shaped clasts and dragged edges of the veins. Preferential melting of mafic and hydrous minerals takes place (e.g., Reimold and Colliston, 1994; Gibson et al., 2002). Refractory phases remain in the melt as clasts and form reaction rims. In contrast, PTB in meta-gabbro develop in zones with brittle deformation, and do not exploit existing physical contacts. Cataclastic zones develop along the faults and progressively produce ultracataclasites and melt. Thus, PTB veins in meta-gabbro contain fewer clasts. Clasts usually represent multi-phase fragments of host rock and not specific phases. Such fragments often originate from the material trapped between two parallel or horse-tail faults. The lithological control on the development of PTB does not imply that PTB develops independently in different lithologies. We have observed granitic clasts within PTB veins in meta

  17. Immigrant Arab adolescents in ethnic enclaves: physical and phenomenological contexts of identity negotiation.

    Kumar, Revathy; Seay, Nancy; Karabenick, Stuart A


    Ecologically embedded social identity theories were used to examine the risk and protective factors associated with the identity negotiation and adjustment of recent immigrant Arab (IA) adolescents to the United States residing in ethnic enclaves. Yemeni, Lebanese, and Iraqi 8th-graders (n = 45) from 4 ethnic enclave schools participated in focus-group interviews. In-depth analyses of interviews revealed that living in an ethnic enclave enhanced IA adolescents' feelings of belonging to the community. However, the new immigrant status coupled with country of origin determined the permeability of intergroup boundaries with well-established Arab and Arab American peers. Their identity negotiations and social identity salience (national, religious, and pan-Arab) were informed by transitional experiences from home to host country and the prevailing political and cultural tensions between the two, recognition of national hierarchy within the Arab community, perceptions of discrimination by the larger society, changed educational aspirations consequent to immigration, and current physical (school and community) and phenomenological contexts. Findings suggest that current theoretical perspectives should be extended to incorporate phenomenological representations of past spaces and places not currently occupied to understand adolescents' multifaceted identity. (c) 2015 APA, all rights reserved).

  18. Formación de un enclave transnacional en la ciudad de Santiago de Chile

    Carolina Stefoni


    Full Text Available La llegada de inmigrantes a Chile ha transformado distintos lugares de Santiago, siendo un caso emblemático el sector de Plaza de Armas, centro histórico de la ciudad aquí analizado. Se sostiene que la concentración de actividades comerciales y prácticas cotidianas de los migrantes configuran un enclave transnacional. El objetivo del artículo es ofrecer un modelo de análisis que permita reconocer, describir y comprender el carácter transnacional que puede adquirir un espacio como el que se encuentra en la ciudad de Santiago. Utilizando el caso de los cibercafés emplazados dentro del enclave, se analizarán las prácticas y relaciones sociales, así como las materialidades que circulan y se desarrollan de manera transfronteriza. El objetivo es analizar cómo estas tres dimensiones configuran un modo de habitar que logra construir el carácter transnacional que adquiere el enclave.

  19. Relamination of mafic subducting crust throughout Earth's history

    Maunder, Ben; van Hunen, Jeroen; Magni, Valentina; Bouilhol, Pierre


    Earth has likely cooled by several hundred degrees over its history, which has probably affected subduction dynamics and associated magmatism. Today, the process of compositional buoyancy driven upwelling, and subsequent underplating, of subducted materials (commonly referred to as ;relamination;) is thought to play a role in the formation of continental crust. Given that Archean continental crust formation is best explained by the involvement of mafic material, we investigate the feasibility of mafic crust relamination under a wide range of conditions applicable to modern and early Earth subduction zones, to assess if such a process might have been viable in an early Earth setting. Our numerical parametric study illustrates that the hotter, thicker-crust conditions of the early Earth favour the upward relamination of mafic subducting crust. The amount of relaminating subducting crust is observed to vary significantly, with subduction convergence rate having the strongest control on the volume of relaminated material. Indeed, removal of the entire mafic crust from the subducting slab is possible for slow subduction (∼2 cm/yr) under Archean conditions. We also observe great variability in the depth at which this separation occurs (80-120 km), with events corresponding to shallower detachment being more voluminous, and that relaminating material has to remain metastably buoyant until this separation depth, which is supported by geological, geophysical and geodynamical observations. Furthermore, this relamination behaviour is commonly episodic with a typical repeat time of approximately 10 Myrs, similar to timescales of episodicity observed in the Archean rock record. We demonstrate that this relamination process can result in the heating of considerable quantities of mafic material (to temperatures in excess of 900 °C), which is then emplaced below the over-riding lithosphere. As such, our results have implications for Archean subduction zone magmatism, for

  20. Post-collisional plutonism with adakitic signatures: The Triassic Yangba granodiorite (Bikou terrane, northern Yangtze Block)

    QIN Jiangfeng; LAI Shaocong; LI Yongfei


    The post-collisional Yangba granodiorite intruded into the Bikou metasedimentary-volcanic group, southern Mianlue Suture, central China. The host granodiorites contain many mafic microgranular enclaves which have acicular apatite, phenocrysts of host granodiorites, implying that the enclaves have been incorporated as magma globules into host granodioritic magma and undergone rapid cooling. The variation trends of major and trace elements between enclaves and host rocks suggest a mixing and mingling process with respect to their petrogenesis. The mafic microgranular enclaves are characterized by shoshonite with SiO2≤63%, σ (4.54-6.18)>3.3, high K2O content (4.22%-6.04%), K2O/Na2O>1; in the K2O-SiO2 diagram, all the samples plot in the shoshonite field, which are enriched in LILE and LREE, with obvious Nb, Ta negative anomalies, indicating a subducting fluid-metasomatised mantle source. Zircon LA-ICP-MS dating of the granodiorites yielded an age of 215.4±8.3 Ma, indicating they were formed during the late-orogenic or post-collisional stage (≤242±21 Ma) of the South Qinling Mountain Belt. The host granodiorites have many close compositional similarities to high-silica adakites from supra-subduction zone setting, but tend to have a higher concentration of K2O (3.22%-3.84%) and Mg#. Chondrite-normalized rare-earth element patterns are characterized by high ratios of (La/Yb)N, the extreme HREE depletion and a lack of significant Eu anomalies. In conjunction with the high abundances of Ba and Sr as well as the low abundances of Y and HREE, these patterns suggest a feldspar-poor, garnet ± amphibole-rich fractionation mineral assemblage. High Mg# values demonstrate that the host granodiorites were contaminated by enclave magma. On a whole, integrated geological and geochemical studies suggested the Yangba granodiorites and their mafic microgranular enclaves resulted from mixing of enriched mantle-derived shoshonitic magma and thickened lower crust-derived felsic




    ¿Cómo investigar nuestras prácticas como investigadores educativos desde un perspectiva posfundacional?, ¿cómo construir herramientas de intelección que den cuenta de las condiciones históricas y biográficas del sujeto que investiga en el campo de la educación? En este trabajo se apuesta por un sujeto de la biografía como sujeto discursivo-textual y político desde una mirada posfundacional, su conceptualización recupera las categorías discurso (Laclau) y texto (Derrida) como enclave teórico y...

  2. Historias transnacionales: nuevas interpretaciones de los enclaves en América Latina

    Catherine LeGrand


    Full Text Available Este ensayo revisa las nuevas direcciones en la investigación sobre “enclaves extranjeros” en América Latina, centrándose particularmente en las regiones bananeras de la United Fruit Company (UFCO en el Caribe y Centroamérica. Explora las preguntas y aproximaciones que orientan la “nueva historia de los enclaves” producida en universidades norteamericanas en los últimos quince años, las críticas que han surgido a dichos estudios y el giro contemporáneo en la mirada a las luchas por los recursos naturales.

  3. Another Mexican birthweight paradox? The role of residential enclaves and neighborhood poverty in the birthweight of Mexican-origin infants.

    Osypuk, Theresa L; Bates, Lisa M; Acevedo-Garcia, Dolores


    Examining whether contextual factors influence the birth outcomes of Mexican-origin infants in the US may contribute to assessing rival explanations for the so-called Mexican health paradox. We examined whether birthweight among infants born to Mexican-origin women in the US was associated with Mexican residential enclaves and exposure to neighborhood poverty, and whether these associations were modified by nativity (i.e. mother's place of birth). We calculated metropolitan indices of neighborhood exposure to Mexican-origin population and poverty for the Mexican-origin population, and merged with individual-level, year 2000 natality data (n=490,332). We distinguished between neighborhood exposure to US-born Mexican-origin population (i.e. ethnic enclaves) and neighborhood exposure to foreign-born (i.e. Mexico-born) Mexican-origin population (i.e. immigrant enclaves). We used 2-level hierarchical linear regression models adjusting for individual, metropolitan, and regional covariates and stratified by nativity. We found that living in metropolitan areas with high residential segregation of US-born Mexican-origin residents (i.e. high prevalence of ethnic enclaves) was associated with lower birthweight for infants of US-born Mexican-origin mothers before and after covariate adjustment. When simultaneously adjusting for exposure to ethnic and immigrant enclaves, the latter became positively associated with birthweight and the negative effect of the former increased, among US-born mothers. We found no contextual birthweight associations for mothers born in Mexico in adjusted models. Our findings highlight a differential effect of context by nativity, and the potential health effects of ethnic enclaves, which are possibly a marker of downward assimilation, among US-born Mexican-origin women. Copyright 2009 Elsevier Ltd. All rights reserved.

  4. Enacting trust: contract, law and informal economic relationships in a Spanish border enclave in Morocco

    Brian Campbell


    Full Text Available Small and removed from the Spanish mainland, the Enclave of Ceuta has always depended on flows of goods and labour out of the Moroccan hinterland, with individuals from different ethnic and religious groups forming informal, flexible and personal economic bonds based on mutual ‘confianza’ (trust. Since its entry into the European Union in 1986,the Spanish government has erected a border-wall around the enclave, and introduced new migration policies branding many informal workers within its borders as a threat to Spanish society. Based on my preliminary months of research, this paper compares the Ceutancontext with other research recently conducted on the topics of migration and borders in the Mediterranean region. It brings into focus key theoretical issues and assumptions that constantly emerge in such literature, particularly regarding the role of ‘a-cultural’ personal ties between migrants and locals in undermining State categories and ideology. This paper observes how the Ceutan case encourages us to expand our focuses and consequently problematise our understanding of crucial concepts such as ‘trust’ and ‘integration’.

  5. Anthropological Critique and Framing of Suburban Enclaves: Case of Neighbourhood X

    Butko Matej


    Full Text Available The main point of this article is conceptualization of newcomers within specific suburb in perimeter of Bratislava. The analysis with fruitful and extensive base of evidence provides a connection between the western suburban community theories and local actual and discursive strategies in various topics. The content of this article consists of analysis of bonding, residential and motivational strategies of newcomers, and a wide conceptualization of them, including a class concept and a bounding character of socialization. Additional analytical and evidential asset of this article is the perceptiveness that provides us the ‘other-than-actual’ evaluative perspective. This perception is provided by other inhabitants outside of the researched Neighbourhood X. This evidence, which is connected to the theory of leisure class consumption, is therefore the perceptive side of the core definition of enclaves in residentially excluded neighbourhood. This article offers conclusions of a specific field experience and broadens not only the existing suburban community theories, but also the works that try to conceptualise significant traits of suburban enclaves.

  6. Health and sexual status in an urban gay enclave: an application of the stress process model.

    Green, Adam Isaiah


    In this article, I apply the stress process model as a framework to understand sexual sociality and its impact on health among urban gay men in a large North American gay enclave. Data consisting of in-depth interviews with 70 gay men coupled with three years of fieldwork demonstrate a sexual status order that privileges caucasian, middle-class men in their twenties and early thirties, and that disadvantages black and Asian men, men over 40 years of age, and poor men. Men with low sexual status faced significant stressors in the form of avoidance from others, stigmatization, and rejection. These stressors, in turn, taxed personal resources, including self-esteem, sense of social support, and sense of control, and they also negatively affected emotional states in the form of depression and anxiety. Finally, some low status men were unable to consistently negotiate condom use as a consequence of a history of field stressors and diminished personal resources. The results suggest that more work on sexual status structures and their connection to health is needed, both within gay enclaves and across a broader spectrum of sexual subcultures.

  7. Contortionist bubbles in andesitic enclaves: implications for gas migration and phase segregation in crystal-rich magmas.

    Oppenheimer, J. C.; Cashman, K. V.; Rust, A.; Dobson, K. J.; Bacon, C. R.; Dingwell, D. B.


    In order to constrain gas migration behaviors in crystal-rich magmas, we compare results of analogue experiments to frozen structures in andesitic enclaves. In the analogue experiments air was injected into mixtures of syrup and particles sandwiched between glass plates. We observed a significant increase in bubble deformation and coalescence when particle fractions increased beyond a critical value (the random loose packing). At high particle fractions, bubble growth re-organized (compacted) the particles adjacent to the bubble walls. This caused liquid segregation into patches within the particle suspension and into large void spaces near the outer edge of experiments. We compare these experiments to void morphologies in a 58 x 70 x 73 cm andesitic enclave from silicic-andesite lava flows of Mt Mazama, Oregon (Bacon, 1986). This enclave is zoned, with a vesicle-rich center and a glass-rich rim, suggesting gas-driven melt segregation from the center to the rim. We use both 2D (optical microscopy and SEM) and 3D (X-ray tomography) techniques to image crystal textures and bubble shapes. The center of the enclave bears scattered patches of groundmass in the main phenocryst framework. These patches are similar to those observed in experiments, and thus melt segregation in the enclave may have occurred both toward the rim and toward these patches. Bubble morphologies reveal two main types of bubbles. (1) Lobate and finger-like bubbles, similar to the deformed bubbles in experiments, are found exclusively in the groundmass patches. They are also often associated with compacted crystal structures at the bubble walls. (2) Diktytaxitic textures - angular bubbles flattened against phenocrysts - are abundant in the crystal networks. These voids are entirely connected in 3D and formed the gas-rich center of the enclave. They likely represent a gas migration regime where the expanding gas front cannot deform the crystal structure but instead invades the pore-space between

  8. Trabajo y relaciones laborales en los enclaves minero-metalúrgicos de la Amazonia

    Josep Pont Vidal


    Full Text Available Abstract:  Labour and labour relations in the enclaves of metallurgical mining in the AmazonThis article is based upon an empirical study of  life and labour conditions in the metallurgical  mining enclaves of the eastern Amazon region.  From the perspective of civil society (associations  of workers, labour conditions are analysed according to interviews with workers and their  family members given outside the work sphere.  Using the method based on ‘grounded theory’, and specifically on the qualitative analysis of  theorization, a scheme of two levels has been  made: the ‘situational activity’ and the ‘subjectivization of the activity’. The first level, the ‘situational activity’, is centred in the sphere of the  organizations of workers and their perceptions  and strategies for action. The second level, the  ‘subjective of the activity’, addresses the subjective interpretations adopted by workers and their  families. Resumen:Este escrito se basa en un estudio empírico de las  condiciones de vida y relaciones laborales en los  enclaves minero-metalúrgicos de la Amazonia  oriental. En él se analizan las condiciones laborales desde la perspectiva de la sociedad civil (asociaciones de trabajadores, recurriendo para ello a  entrevistas con trabajadores y sus familias fuera  del ambiente de trabajo. A partir del método basado en la teorización anclada, y específicamente  en el denominado análisis cualitativo de teorización, se ha confeccionado un esquema de dos  niveles: la ‘actividad situacional’, y la ‘subjetivización de la actividad’. El primer nivel -la ‘actividad situacional’- se centra en la esfera de las  organizaciones de trabajadores y sus ideas y estrategias de acción. El segundo nivel -la ‘subjetivización de la actividad’- trata las interpretaciones  subjetivas adoptadas por los trabajadores y sus  familias.

  9. Magma Emplacement and Mafic-Felsic Magma Hybridisation: Structural, Microstructural and Geochemical Evidences From the Pan-African Negash Pluton, Northern Ethiopia



    The Negash pluton (50 sq. km) consists of late Pan-African, high-K, calc-alkaline granitoids intruded into low-grade metavolcanics and metasediments. This almost circular massif consists of monzogranites, granodiorites, monzodiorites, monzogabbros, and hybrid quartz monzodiorites. The rocks are enriched in LIL-elements, depleted in HFS-elements, have fractionated REE patterns, low 87Sr/86Sri (0.702344 - 0.703553) and 143Nd/144Ndi (0.512031 - 0.512133) ratios, positive ɛ Nd values (3.46 to 5.40), and Pan-African model Nd ages (0.83 to 1.08 Ga). These data, along with single zircon U-Pb dating, show that the pluton was emplaced at 608 Ma from primitive source (underplated material or juvenile island arc crust) with contamination by the country rocks. The pluton shows widespread mafic-felsic magma interactions of two types: (i) homogeneous and heterogeneous hybrid monzodiorites at the northwestern part; and (ii) mingled interfaces at the diorite-granodiorite contact zones in the Eastern and Southeastern parts. Detailed structural (using the method of the anisotropy of magnetic susceptibility) and microstructural studies have been applied to understand how these interactions occurred with respect to pluton construction. The monzodiorites constituting the northwestern part of the pluton, which are composed of complexly zoned plagioclases or unzoned plagioclase laths, euhedral hornblende with biotite cores and acicular apatites, are characterized by abundant net veining, synplutonic dikes, microgranitoid enclaves, and juxtaposed series of discrete mafic-felsic pulses of hybrid nature with vertical syn-emplacement structures. The mingled interfaces between the diorites and granodiorites, on the other hand, are characterized by lobate contacts with interfingering of diorites into granodiorites at the decametric scale, abundant inclined to horizontal granitic pipes, breccia dykes and veins, which are strongly enriched in megacrysts of K-feldspars, and numerous swarms of

  10. Geomechanical analyses to investigate wellbore/mine interactions in the Potash Enclave of Southeastern New Mexico.

    Ehgartner, Brian L.; Bean, James E. (Sandia Staffing Alliance, LLC, Albuquerque, NM); Arguello, Jose Guadalupe, Jr.; Stone, Charles Michael


    Geomechanical analyses have been performed to investigate potential mine interactions with wellbores that could occur in the Potash Enclave of Southeastern New Mexico. Two basic models were used in the study; (1) a global model that simulates the mechanics associated with mining and subsidence and (2) a wellbore model that examines the resulting interaction impacts on the wellbore casing. The first model is a 2D approximation of a potash mine using a plane strain idealization for mine depths of 304.8 m (1000 ft) and 609.6 m (2000 ft). A 3D wellbore model then considers the impact of bedding plane slippage across single and double cased wells cemented through the Salado formation. The wellbore model establishes allowable slippage to prevent casing yield.

  11. Mobilidad laboral geográfica en un antiguo enclave minero

    Camilo Contreras Delgado


    Full Text Available Este artículo examina los fa c t o res internos y externos a una localidad que son copartícipes en la estructuración y reestructuración de su mercado de trabajo local. A partir de la revisión de la historia social y económica del lugar, se destaca su tránsito de enclave minero a lugar de residencia de mineros y trabajadores de maquiladoras. En este caso, se presenta la constitución de los mercados de trabajo locales como un resultado del encuentro de las condiciones del lugar de residencia de los trabajadores y el lugar donde se encuentra el centro de trabajo. De aquí que la movilidad laboral geográfica aparezca como una de las tácticas de los sujetos ante una situación de desempleo.

  12. No-Enclave Percolation Corresponds to Holes in the Cluster Backbone

    Hu, Hao; Ziff, Robert M.; Deng, Youjin


    The no-enclave percolation (NEP) model introduced recently by Sheinman et al. can be mapped to a problem of holes within a standard percolation backbone, and numerical measurements of such holes give the same size-distribution exponent τ =1.82 (1 ) as found for the NEP model. An argument is given that τ =1 +dB/2 ≈1.822 for backbone holes, where dB is the backbone dimension. On the other hand, a model of simple holes within a percolation cluster yields τ =1 +df/2 =187 /96 ≈1.948 , where df is the fractal dimension of the cluster, and this value is consistent with the experimental results of gel collapse of Sheinman et al., which give τ =1.91 (6 ). This suggests that the gel clusters are of the universality class of percolation cluster holes. Both models give a discontinuous maximum hole size at pc, signifying explosive percolation behavior.

  13. Crafting a Democratic Enclave on the Cyberspace: Case Studies of Malaysia, Indonesia, and Singapore

    Yangyue Liu


    Full Text Available As an antithesis of “authoritarian enclave” which has been well-established in the comparative politics literature, “democratic enclave” points to the institution of a state or the unambiguous regulatory space in society “where the authoritarian regime’s writ is substantively limited and is replaced by an adherence to recognizably democratic norms and procedures” (Gilley 2010. In this sense, the Internet space, embodied by information and communication technologies, has great potential to play such a role, since its “inherited” properties of decentralization and anonymity would inevitably breach the authoritarian rules. However, a closer look at three Southeast Asian states, Malaysia, Singapore and the “New Order” Indonesia whose regimes were characterized by authoritarianism when Internet was initially developed, reveals different trajectories. In the “New Order” Indonesia and Malaysia, the governments consciously left the Internet space uncontrolled; the online media developed independently, vibrantly, and professionally, especially in the Malaysian case; and there were strong connections between online and offline contentious politics. These elements made the Internet space in Indonesia and Malaysia a successful case of democratic enclave. Based on these criteria, however, the Internet space in Singapore has not achieved similar status. This paper analyses the different outcomes of enclave creation on the cyberspace among these countries. It argues that elite conflict and the strength of civil society are the two major factors that shape the differences. In this sense, the political contexts are of great importance for the understanding of Internet’s political impacts.

  14. Cloning, expression, and characterization of β-mannanase from Bacillus subtilis MAFIC-S11 in Pichia pastoris.

    Lv, Junnan; Chen, Yiqun; Pei, Honglei; Yang, Wenhan; Li, Zhimin; Dong, Bing; Cao, Yunhe


    The β-mannanase gene (1,029 nucleotide) from Bacillus subtilis MAFIC-S11, encoding a polypeptide of 342 amino acids, was cloned and expressed in Pichia pastoris. To increase its expression, the β-mannanase gene was optimized for codon usage (mannS) and fused downstream to a sequence-encoding modified α-factor signal peptide. The expression level was improved by 2-fold. This recombinant enzyme (mannS) showed its highest activity of 24,600 U/mL after 144-h fermentation. The optimal temperature and pH of mannS were 50 °C and 6.0, respectively, and its specific activity was 3,706 U/mg. The kinetic parameters V max and K m were determined as 20,000 U/mg and 8 mg/mL, respectively, representing the highest ever expression level of β-mannanase reported in P. pastoris. In addition, the enzyme exhibited much higher binding activity to chitin, chitosan, Avicel, and mannan. The superior catalytic properties of mannS suggested great potential as an effective additive in animal feed industry.

  15. Preliminary insights into a model for mafic magma fragmentation

    Edwards, Matt; Pioli, Laura; Andronico, Daniele; Cristaldi, Antonio; Scollo, Simona


    Fragmentation of mafic magmas remains a poorly understood process despite the common occurrence of low viscosity explosive eruptions. In fact, it has been commonly overlooked based on the assumption that low viscosity magmas have very limited explosivity and low potential to undergo brittle fragmentation. However, it is now known that highly explosive, ash forming eruptions can be relatively frequent at several mafic volcanoes. Three questions arise due to this - What is the specific fragmentation mechanism occuring in these eruptions? What are the primary factors controlling fragmentation efficiency? Can a link between eruption style and fragmentation efficiency be quantified? We addressed these questions by coupling theoretical observations and field analysis of the recent May 2016 eruption at Mount Etna volcano. Within this complex 10-day event three paroxysmal episodes of pulsating basaltic lava jets alternating with small lava flows were recorded from a vent within the Voragine crater. The associated plumes which were produced deposited tephra along narrow axes to the east and south east. Sampling was done on the deposits associated with the first two plumes and the third one. We briefly characterise the May 2016 eruption by assessing plume height, eruption phases, total erupted masses and fallout boundaries and comparing them to previous eruptions. We also analyse the total grainsize distribution (TGSD) of the scoria particles formed in the jets. Conventional methods for obtaining grainsize and total distributions of an eruption are based on mass and provide limited information on fragmentation though. For this reason, the TGSD was assessed by coupling particle analyser data and conventional sieving data to assess both particle size and number of particle distributions with better precision. This allowed for more accurate testing of several existing models describing the shape of the TGSD. Coupled further with observations on eruption dynamics and eruption

  16. Textural and chemical consequences of interaction between hydrous mafic and felsic magmas: an experimental study

    Pistone, Mattia; Blundy, Jonathan D.; Brooker, Richard A.


    Mantle-derived, hydrous mafic magmas are often invoked as a mechanism to transfer heat, mass and volatiles to felsic plutons in the Earth's crust. Field observations suggest that mafic, water-rich magmas often intrude viscous felsic crystal-rich mushes. This scenario can advect water from the crystallising mafic magma to the felsic magma, leading to an increase in melt fraction in the felsic mush and subsequent mobilisation, at the same time as the mafic magma becomes quenched through a combination of cooling and water loss. To investigate such a scenario, we conducted experiments on a water-undersaturated (4 wt% H2O in the interstitial melt) dacitic crystal mush (50-80 vol% quartz crystals) subject to volatile supply from a water-saturated (≥6 wt% H2O) andesite magma at 950 °C and 4 kbar. Our experimental run products show unidirectional solidification textures (i.e. comb layering) as crystals nucleate at the mafic-felsic interface and grow into the mafic end-member. This process is driven by isothermal and isobaric undercooling resulting from a change in liquidus temperature as water migrates from the mafic to the felsic magma. We refer to this process as "chemical quenching" and suggest that some textures associated with natural mafic-felsic interactions are not simply cooling-driven in origin, but can be caused by exsolution of volatiles adjacent to an interface, whether a water-undersaturated felsic magma (as in our experiments) or a fracture.

  17. Draining mafic magma from conduits during Strombolian eruption

    Wadsworth, F. B.; Kennedy, B.; Branney, M. J.; Vasseur, J.; von Aulock, F. W.; Lavallée, Y.; Kueppers, U.


    During and following eruption, mafic magmas can readily drain downward in conduits, dykes and lakes producing complex and coincident up-flow and down-flow textures. This process can occur at the top of the plumbing system if the magma outgases as slugs or through porous foam, causing the uppermost magma surface to descend and the magma to densify. In this scenario the draining volume is limited by the gas volume outgassed. Additionally, magma can undergo wholesale backflow when the pressure at the base of the conduit or feeder dyke exceeds the driving pressure in the chamber beneath. This second scenario will continue until pressure equilibrium is established. These two scenarios may occur coincidently as local draining of uppermost conduit magma by outgassing can lead to wholesale backflow because the densification of magma is an effective way to modify the vertical pressure profile in a conduit. In the rare case where conduits are preserved in cross section, the textural record of draining is often complex and great care should be taken in interpreting bimodal kinematic trends in detail. Lateral cooling into country rock leads to lateral profiles of physical and flow properties and, ultimately, outgassing potential, and exploration of such profiles elucidates the complexity involved. We present evidence from Red Crater volcano, New Zealand, and La Palma, Canary Islands, where we show that at least one draining phase followed initial ascent and eruption. We provide a rheological model approach to understand gravitational draining velocities and therefore, the timescales of up- and down-flow cycles predicted. These timescales can be compared with observed geophysical signals at monitored mafic volcanoes worldwide. Finally, we discuss the implications of shallow magma draining for edifice stability, eruption longevity and magma-groundwater interaction.

  18. Insights into the Mount St. Helens Magma Plumbing System from Coarse-grained, Crystal-rich Enclaves

    Wanke, M.; Bachmann, O.; Ellis, B. S.; Guillong, M.; Clynne, M. A.; Pallister, J. S.


    Co-magmatic plutonic enclaves provide information about the conditions of magmatic storage and magmatic processes. The deposits of Mount St. Helens contain a variety of coarse-grained, crystal-rich enclaves, dominantly derived from the Tertiary basement. However, zircons in two enclaves returned ages of 5-108 ka (n=29) and 45-486 ka (n=16), overlapping with zircon ages from the volcanics. From textures and mineralogy, we define five enclave types, interpreted as crystal mush from the current magmatic system: hbl-gabbros with ad-cumulate structure (type 1), dioritic meso-cumulates with partly decomposed minerals (type 2), and dioritic rocks enriched in incompatible elements (type 3). All three occur in Pine Creek dacite domes ( 2900 BP), and comprise amphibole, plagioclase, orthopyroxene and oxides (±apatite and zircon) with variable amounts of residual melt. A heterad-cumulate (type 4) from 1980 dacite consists of olivine, plagioclase, ortho- and clinopyroxene (±oxides and apatite) with poikilitic overgrowth of amphibole. Inclusions of pyroxene-plagioclase-oxide-bearing crystal aggregates (type 5) are found in Late Pine Creek andesites ( 2600 BP). Compositional similarity between amphiboles in type 1 and 2 cumulates and those from their dacitic host rock suggests these cumulates co-erupted with their extracted melt. Modelled trace element compositions of coexisting liquids indicate that the high-Al amphibole cores (up to 14.5 wt.% Al2O3) crystallized from andesitic melts that are parental to the dacites. In contrast, andesites erupted during the same eruptive period lack amphibole suggesting drier/shallower crystallization resulting in the predominant fractionation of pyroxene seen in type 5 inclusions. Different cumulates represent residues from basaltic andesitic to dacitic melts. Mid to upper crustal pressures determined via barometry are consistent with crystallization within the bottle-shaped magma reservoir ( 7-20 km) imaged during the recent activity.

  19. Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block

    Xu, Wenjing; Xu, Xisheng; Zeng, Gang


    Several recent studies have documented that the silicic rocks (SiO2 > 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of ;hidden; large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of 22,000 km2. In contrast, exposures of mafic rocks total only 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial 87Sr/86Sr = 0.7041-0.7102; εNd(t) = - 8.4 to + 1.8; weighted mean zircon εHf(t) = - 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59-13.1 and 3.5-20.9, respectively), and variable Th/La ratios (0.11-0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (- 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial 87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.

  20. From National Enclaves to Supporting Offices: an Analysis of the 1999 Reform of European Commissioners’ Cabinets

    Renke Deckarm


    Full Text Available This article analyses the transformation of European commissioners’ private offices (cabinets from national enclaves to supporting offices. Structural changes were caused by a reform by then-Commission President Prodi in 1999. To analyse this reform, a typology based on management literature is developed. The reform is characterised as ‘big bang’: it was strategically planned by a leader, transformational and affected the entire cabinet system. The most important measures were that at least three nationalities and three Commission officials were required in cabinets. These and other measures anticipated changing demands towards cabinets caused by the 2004/7 enlargement and the Kinnock reforms. This article closes a gap in research on the Commission, in which cabinets are seldom analysed in their own right. It complements earlier evidence on change in cabinets by explaining why and how structural changes evoked a functional transformation. This contributes to the broader research agenda on change in the functioning of the Commission. Content analysis of primary sources (Prodi’s speeches and publications, expert interviews and a biographic database and recent academic publications contribute to the analysis.

  1. Oxygen isotope composition of mafic magmas at Vesuvius

    Dallai, L.; Cioni, R.; Boschi, C.; D'Oriano, C.


    The oxygen isotope composition of olivine and clinopyroxene from four plinian (AD 79 Pompeii, 3960 BP Avellino), subplinian (AD 472 Pollena) and violent strombolian (Middle Age activity) eruptions were measured to constrain the nature and evolution of the primary magmas of the last 4000 years of Mt. Vesuvius activity. A large set of mm-sized crystals was accurately separated from selected juvenile material of the four eruptions. Crystals were analyzed for their major and trace element compositions (EPMA, Laser Ablation ICP-MS), and for 18O/16O ratios. As oxygen isotope composition of uncontaminated mantle rocks on world-wide scale is well constrained (δ18Oolivine = 5.2 ± 0.3; δ18Ocpx = 5.6 ± 0.3 ‰), the measured values can be conveniently used to monitor the effects of assimilation/contamination of crustal rocks in the evolution of the primary magmas. Instead, typically uncontaminated mantle values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary magmas during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). Low δ18O values have been measured in olivine from Pompeii eruption (δ18Oolivine = 5.54 ± 0.03‰), whereas higher O-compositions are recorded in mafic minerals from pumices or scoria of the other three eruptions. Measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas, as also constrained by their trace element compositions. Data on melt inclusions hosted in crystals of these compositions have been largely collected in the past demonstrating that they crystallized from mafic melt, basaltic to tephritic in composition. Published data on volatile content of these melt inclusions reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting

  2. Oxygen isotope geochemistry of mafic magmas at Mt. Vesuvius

    Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano


    Pumice and scoria from different eruptive layers of Mt. Vesuvius volcanic products contain mafic minerals consisting of High-Fo olivine and Diopsidic Pyroxene. These phases were crystallized in unerupted trachibasaltic to tephritic magmas, and were brought to surface by large phonolitic/tephri-phonolitic (e.g. Avellino and Pompei) and/or of tephritic and phono-tephritic (Pollena) eruptions. A large set of these mm-sized crystals was accurately separated from selected juvenile material and measured for their chemical compositions (EPMA, Laser Ablation ICP-MS) and 18O/16O ratios (conventional laser fluorination) to constrain the nature and evolution of the primary magmas at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary melts during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). At Mt. Vesuvius, measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas. Trace element composition constrains the near primary nature of the phases. Published data on volatile content of melt inclusions hosted in these crystals reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth occurred in a reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali magmas from trachybasaltic melts. Accordingly, the δ18O variability and the trace element content of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. Low, nearly primitive δ18O values are observed for olivine from Pompeii eruption, although still

  3. Lithological Discrimination of the Mafic-Ultramafic Complex, Huitongshan, Beishan, China:Using ASTER Data

    Lei Liu; Jun Zhou; Dong Jiang; Dafang Zhuang; Lamin R Mansaray


    The Beishan area has more than seventy mafic-ultramafic complexes sparsely distributed in the area and is of a big potential in mineral resources related to mafic-ultramafic intrusions. Many mafic-ultramafic intrusions which are mostly in small sizes have been omitted by previous works. This research takes Huitongshan as the study area, which is a major district for mafic-ultramafic occur-rences in Beishan. Advanced spaceborne thermal emission and reflection radiometer (ASTER) data have been processed and interpreted for mapping the mafic-ultramafic complex. ASTER data were processed by different techniques that were selected based on image reflectance and laboratory emis-sivity spectra. The visible near-infrared (VNIR) and short wave infrared (SWIR) data were trans-formed using band ratios and minimum noise fraction (MNF), while the thermal infrared (TIR) data were processed using mafic index (MI) and principal components analysis (PCA). ASTER band ratios (6/8, 5/4, 2/1) in RGB image and MNF (1, 2, 4) in RGB image were powerful in distinguishing the subtle differences between the various rock units. PCA applied to all five bands of ASTER TIR imagery high-lighted marked differences among the mafic rock units and was more effective than the MI in differen-tiating mafic-ultramafic rocks. Our results were consistent with information derived from local geolog-ical maps. Based on the remote sensing results and field inspection, eleven gabbroic intrusions and a pyroxenite occurrence were recognized for the first time. A new geologic map of the Huitongshan area was created by integrating the results of remote sensing, previous geological maps and field inspection. It is concluded that the workflow of ASTER image processing, interpretation and ground inspection has great potential for mafic-ultramafic rocks identifying and relevant mineral targeting in the sparsely vegetated arid region of northwestern China.

  4. Afrikaners in post-apartheid South Africa: Inward migration and enclave nationalism

    Christi van der Westhuizen


    Full Text Available South Africa’s transition to democracy coincided and interlinked with massive global shifts, including the fall of communism and the rise of western capitalist triumphalism. Late capitalism operates through paradoxical global-local dynamics, both universalising identities and expanding local particularities. The erstwhile hegemonic identity of apartheid, ‘the Afrikaner’, was a product of Afrikaner nationalism. Like other identities, it was spatially organised, with Afrikaner nationalism projecting its imagined community (‘the volk’ onto a national territory (‘white South Africa’. The study traces the neo-nationalist spatial permutations of ‘the Afrikaner’, following Massey’s (2005 understanding of space as (1 political, (2 produced through interrelations ranging from the global to micro intimacies, (3 potentially a sphere for heterogeneous co-existence, and (4 continuously created. Research is presented that shows a neo-nationalist revival of ethnic privileges in a defensive version of Hall’s ‘return to the local’ (1997a. Although Afrikaner nationalism’s territorial claims to a nation state were defeated, neo-nationalist remnants reclaim a purchase on white Afrikaans identities, albeit in shrunken territories. This phenomenon is, here, called Afrikaner enclave nationalism. Drawing on a global revamping of race as a category of social subjugation, a strategy is deployed that is here called ‘inward migration’. These dynamics produce a privatised micro-apartheid in sites ranging from homes, to commercial and religious enterprises, to suburbs. Virtual white spaces in the form of Afrikaans media products serve as extensions of these whitened locales. The lynchpin holding it all together is the heteronormative, middle-class family, with consumption the primary mode of the generation of its white comfort zones.


    Marcos José Nogueira de Souza


    Full Text Available The semi-arid region of the Northeast of Brazil involves a surface area of 788,064 km², which corresponds to 48% of Northeast and 9.3% of Brazil. Through out systemic analysis of the relationship between geo-environmental components, it showed the relative natural context and of the humid and sub-humid renewable natural resources by northeastern States in the phytogeographic domain of caatingas. The referred areas are widely distributed in the semi-arid sertões, which ware sit in surfaces topographically elevated of mountain prominence with varied dimensions that are submitted to the influences of altitude meso-climates. They represent true "green islands" in the morphoclimatic domain of caatingas that recover semi-arid area in the inter-plateau and inter- mountain depressions. Based in this study, it can be verified that humid enclaves of the northeastern semi-arid presents innumerable common characteristics and certain conditions that are very specific. All they present better conditions of humidity and mild temperatures, which are heterogeneity of the region. In the geo-ecological context of the semi-arid region, represented by caatingas, there is the occurrence of exception environments that configures true humid and sub-humid enclaves. This work aims to establish an integrated analysis of the geo-environmental determined by the altitude and excess of water surplus during the rainy season. In general, they have good surface water resource potential and soil with average the high natural fertility. The primary vegetal covering of the majority of enclaves is strongly degraded due to the disordered use. In some cases, the degradation of soil reaches irreversible stages, which compromise the water resources, biodiversity and the well-being of the population.

  6. At the southern edge of the EU: Identity challenges affecting the Spanish enclaves of Ceuta and Melilla

    Castan Pinos, Jaume


    economic sphere to its south. Indeed, Ceuta and Melilla highlight the double standards of the EU, which was founded to build bridges across borders but at the same time has built barriers (in Ceuta and Melilla actual physical barriers) at its southern border which have underpinned the idea of fortress...... of fortress Europe. Thus, the anomalous geographical location of both Spanish cities exposes them to border and identity challenges as well as to a complex situation of interdependent concentric circles which involves the enclaves (first circle), Spain, Morocco (second circle) and the EU (third circle...

  7. High level triggers for explosive mafic volcanism: Albano Maar, Italy

    Cross, J. K.; Tomlinson, E. L.; Giordano, G.; Smith, V. C.; De Benedetti, A. A.; Roberge, J.; Manning, C. J.; Wulf, S.; Menzies, M. A.


    Colli Albani is a quiescent caldera complex located within the Roman Magmatic Province (RMP), Italy. The recent Via dei Laghi phreatomagmatic eruptions led to the formation of nested maars. Albano Maar is the largest and has erupted seven times between ca 69-33 ka. The highly explosive nature of the Albano Maar eruptions is at odds with the predominant relatively mafic (SiO2 = 48-52 wt.%) foiditic (K2O = 9 wt.%) composition of the magma. The deposits have been previously interpreted as phreatomagmatic, however they contain large amounts (up to 30%vol) of deep seated xenoliths, skarns and all pre-volcanic subsurface units. All of the xenoliths have been excavated from depths of up to 6 km, rather than being limited to the depth at which magma and water interaction is likely to have occurred, suggesting an alternative trigger for eruption. High precision geochemical glass and mineral data of fresh juvenile (magmatic) clasts from the small volume explosive deposits indicate that the magmas have evolved along one of two evolutionary paths towards foidite or phonolite. The foiditic melts record ca. 50% mixing between the most primitive magma and Ca-rich melt, late stage prior to eruption. A major result of our study is finding that the generation of Ca-rich melts via assimilation of limestone, may provide storage for significant amounts of CO2 that can be released during a mixing event with silicate magma. Differences in melt evolution are inferred as having been controlled by variations in storage conditions: residence time and magma volume.

  8. El enclave urbano, lógica socioespacial de la periferia urbanizada: sus efectos sobre la segregación residencial y la fragmentación urbana

    Guénola Capron


    Full Text Available La producción de las periferias metropolitanas en Latinoamérica se ha caracterizado por el desarrollo de enclaves urbanos, residenciales y comerciales. Estos enclaves abarcan tanto los grandes conjuntos urbanos de vivienda de interés social como fraccionamientos y conjuntos privados orientados a poblaciones de altos ingresos. Ambas periferias responden a razones sociales muy diferentes, pero con una misma lógica espacial: la del enclave, el cual profundiza el aislamiento y la distancia social con sus entornos, generando segregación y fragmentación. En esta investigación, se pretenden rescatar los procesos sociales y espaciales de ‘enclavamiento’ o de ‘insularización’ en dos casos: una urbanización cerrada del nororiente —Zona Esmeralda— y un conjunto urbano del oriente —San Buenaventura—, ambos limítrofes de la Zona Metropolitana del Valle de México.

  9. On Heterogeneous and Homogeneous Networks in a Multilayered Reality: Clashing Interests in the Ethnic Enclave of Lloret de Mar

    Hugo Valenzuela-García


    Full Text Available Over the last decade, the tourist destination of Lloret de Mar (Gerona, Spain has experienced an increasing concentration of souvenir stores owned by a population of Indian origin. Although Lloret de Mar is already a multicultural spot, Indians represent a small minority in Spain. In order to explain such a remarkable concentration and economic specialization in a low profit sector, we suggest the emergence of an ethnic enclave based on a triple articulation (entrepreneurs, employees and the local community. Our findings provide support for the mixed-embeddedness hypothesis, which contends that ethnic entrepreneurs in Europe need to rely on both the co-ethnic social networks and the linkages with the host society in order to run their business successfully. However, differential degrees of social integration amongst Indians themselves—clearly shown by the composition of their social networks—and between local dwellers and Indians suggest confronting interests amongst social agents in a highly complex and micro-social touristic site undergoing deep economic crisis. Throughout, a mixed-methods approach in the paper reveals the unequal social structure of the enclave, providing a better theoretical understanding of the difficulties and backgrounds in which minority migrant groups develop and expand their social relationships in the “host society”.

  10. Geochemistry of PGE in mafic rocks of east Khasi Hills, Shillong Plateau, NE India

    Sampa Hazra; Jyotisankar Ray; C Manikyamba; Abhishek Saha; S S Sawant


    The mafic rocks of east Khasi Hills of the Meghalaya Plateau, northeastern India, occur as an intrusive body which cut across the weakly metamorphosed Shillong Group of rocks. Other than Shillong Group of rocks, high grade Archaean gneissic rocks and younger porphyritic granites are also observed in the study area. The studied mafic rocks of east Khasi Hills cover an area of about 4 km2 and represent structurally controlled intrusion and varying grades of deformation. Structurally, these mafic rocks can be divided into massive type of mafic rocks, which are more or less deformation free and foliated type of mafic rocks that experienced deformation. Petrographically, this massive type can be classified as leuco-hornblende-gabbro whereas foliated type can be designated as amphibolite. On the basis of major oxide geochemistry, the investigated mafic rocks can be discriminated into high titanium (HT) (TiO2 > 2 wt%) and low titanium (LT) types (TiO2 < 2 wt%). Use of several geochemical variation diagrams, consideration of chondrite-normalized and mantle-normalized REE and PGE plots suggest role of magmatic differentiation (with almost no role of plagioclase fractionation) in a subduction controlled tectonic environment. The PGE trends of the studied rocks suggest relative enrichment of palladium group of PGE (PPGE) compared to iridium group PGE (IPGE). Critical consideration of Sm vs. La, Cu vs. La, Pd vs. La and Cu/Pd vs. La/Sm plots strongly favours generation of the parent magma at a columnar melting regime with batch melting of cylindrical column of the parent mantle to the tune of ∼25%. The characteristic PGE behaviours of the presently investigated mafic rocks of east Khasi Hills can be typically corroborated as `orogenic' (discordant) type. These rocks have an enriched mantle affinity with a co-magmatic lineage and they have been generated by slab-dehydration, wedge-melting and assimilation fractional crystallization process at a continental margin arc setting.

  11. Sapphirine-bearing high pressure mafic granulite and its implications in the south Altyn Tagh

    ZHANG Jianxin; MENG Fancong


    Sapphirine-bearing high pressure mafic granulites are recognized in the Bashiwake area of the south Altyn Tagh. Mafic granulites and associated peridotites occur as lenses within kyanite-bearing high pressure felsic granulites. Sapphirine occurs as intergrowths with corundum, spinel and Ca-rich plagioclase in symplectite in between garnet and clinopyroxene. Reaction textures and mineral compositions indicate that sapphirine-bearing symplectites formed by reactions consuming kyanite, garnet and clinopyroxene. Therefore, both petrographic observations and the mineral compositions suggest that these quartz-free mafic granulites had an eclogite origin with an assemblage of garnet + clinopyroxene + kyanite, which is estimated to be stable at T = 1000℃ and P≥2.1 Gpa. The sapphirine-bearing symplectites are resulted from isothermal decompression or decompression with slight cooling during exhumation of the host rock.

  12. Nb/Ta variations of mafic volcanics on the Archean-Proterozoic boundary: Implications for the Nb/Ta imbalance

    LIU Yongsheng; GAO Shan; WANG Xuance; HU Shenghong; WANG Jianqi


    The HFSE and REE of the Precambrian mafic volcanics from the North China craton demonstrate obvious A(Archean)-P(Proterozoic) boundary. The Neoarchean mafic vol-canics show weak correlation between HFSE and TiO2. Their superchondritic Nb/Ta ratio (18.8(1.2) could be attributed to partial melting of mantle peridotite in the presence of garnet. Compared with Neoarchean mafic volcanics, the Paleoproterozoic ones have higher HFSE contents and lower Nb/Ta ratio (15.6(2.9). The significantly elevated HFSE and REE contents of Paleoproterozoic mafic volcanics imply metasomatic enrichment of mantle source, in which Ti-rich silicates could be present as suggested by significant positive correlations between TiO2 and HFSE. The global database of Precambrian mafic volcanics shows a similar A-P boundary. 23 Archean mafic volcanic suites yield an average Nb/Ta ratio of 17.8(1.9 higher than or close to the PM value; Proterozoic mafic volcanics from 28 suites yield an average Nb/Ta ratio of 14.7(4.1 deficit could be mainly formed in post-Archean time. Archean mafic volcanics could be one of the geochemical reservoirs complementing the low Nb/Ta of the post-Archean continental crust and DM.

  13. Geochronology and Geochemistry of Mafic Dikes from Hainan Island and Tectonic Implications

    CAO Jianjin; HU Ruizhong; LIU Shen; XIE Guiqing


    In the present study, the major and trace element compositions, as well as Sr, Nd isotopic compositions and K-Ar age data in mafic dikes from Hainan Island, China, have been analyzed. Whole-rock K-Ar dating yielded a magmatic duration of 61-98 Ma for mafic dikes. Mafic dikes have a very high concentration of incompatible elements, for example, Ba, Rb, Sr, K, rare earth elements, and especially light rare earth elements (LREE), and negative anomalies of Nb, Ta, and Ti in the normalized trace element patterns. The initial ~(87)Sr/~(86)Sr ratios and εSr(t) of the mafic dikes are 0.70634-0.71193 and +27.7 to +112.2, respectively. In the ~(87)Sr/~(86)Sr versus εNd(t) diagram, the Hainan Island mafic dikes plot between fields for depleted mantle and enriched mantle type 2. All these characteristics show that the mantle (source region) of mafic dikes in this area experienced metasomatism by fluids relatively enriched in LREE and large ion lithophile elements. The genesis of Hainan Island mafic dikes is explained as a result of the mixing of asthenospheric mantle with lithospheric mantle that experienced metasomatism by the subduction of the Pacific Plate. This is different from the Hainan Island Cenozoic basaits mainly derived from depleted asthenospheric mantle, and possibly, minor metasomatised lithospheric mantle. This study suggests that the Mesozoic and Cenozoic lithospheric revolutions in Hainan Island can be divided into three stages: (1) the compression orogenesis stage before 98 Ma. The dominant factor during this stage is the subduction of the ancient Pacific Plate beneath this area. The lithospheric mantle changed into enriched mantle type 2 by metasomatism; (2) the thinning and extension stage during 61-98 Ma. The dominant factor during this stage is that the asthenospheric mantle invaded and corroded the lithospheric mantle; and (3) the large-scale thinning and extension stage after 61 Ma. The large-scale asthenospheric upwelling results in the strong

  14. Formación de un sistema productivo: los enclaves forestales de la región chaqueño-misionera (Siglos XIX-XX

    Bitlloch, Ruben E.


    Full Text Available The purpose of this paper is to describe the development process of a form of production organization centered on the timber-yerba mate mill and the sawmill-tannin factory. This kind of activity developed in the North East of Argentina during the last decades of the 19th century and the first half of the 20th century. The term enclave is used to designate these hubs of activity with a spatial as well as a socio-economical meaning. They tended to set up a kind of physical isolation or spatial enclosure. These enclaves spread out on lands that had been recently appropriated to the indigenous communities. There they built up a territorial domain to which they gave a certain configuration that changed as the conditions of the original form of production organization developed.

    El propósito de este trabajo es el de describir el proceso de desarrollo de una forma de organización de la producción que, teniendo como núcleo al obraje maderero-yerbatero y al aserradero-fábrica de tanino, tuvo lugar durante las últimas décadas del siglo XIX y la primera mitad del siglo XX en el nordeste Argentino. La denominación de enclave que le adjudicamos a estos núcleos de actividad posee un significado espacial y socio-económico ya que se caracterizaron por establecer una suerte de aislamiento físico o clausura espacial. Estos enclaves se explayaron espacialmente en un área recientemente apropiada a las comunidades indígenas configurando un dominio territorial al cual le fueron otorgando cierta configuración que fue cambiando al alterarse las condiciones en que se desenvolvía la forma de organización de la producción que le dio origen.

  15. Petrological and geochemical studies of ultramafic–mafic rocks from the North Puruliya Shear Zone (eastern India)

    Aditi Mandal; Arijit Ray


    Ultramafic and mafic rocks occur within a linear belt, trending nearly E–W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbronorite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic–ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47–81) and Al2O3 (5.5–17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic–ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic–ultramafic rocks of high grade terrain, Alaskan type ultramafic–mafic complex and ophiolites. It is observed that the ultramafic–mafic rocks of present study have similarity with Alaskan type complex.

  16. Petrological and Mineralogical Study of Enclaves in Plutons in the Typical Mining Districts of Tongling,Anhui and Its Bearing on the Process of Magmatism—Metallogeny



    Two types of enclaves occur in magmatic plutons in Tongling,Anhui.Enclaves of the first type are residuals of metamorphic rocks of high amphibolite facies,and those of the other type are magmatic rocks ranging from monzonitic to dioritic in composition. A combined petrological and mineralogical study has been carried out on the two types of enclaves in order to estimate their forming conditions and analyze their relations to their as to have an insight into the material sources of magmatic rocks and associated mineral deposits and give a clue to better understanding the mechanism of magmatism-metallogeny.This leads us to propose a new metallogenic model for strats-bound skarn-type ore deposits associated with a syntectic type of magmatic rocks.The new model can be simply summarized as partial melting of old metamorphic basement rocks at depth and accumulating,differentiating and positioning of magmas to form deep-level and shallow-level magma chambers,follower by mixing of different magmas associated with their crypto-explosion,migration of gas-bearing ore fluids and precipitation of metals in fluids within the magmas.

  17. Spatial greenstone-gneiss relationships: Evidence from mafic-ultramafic xenolith distribution patterns

    Glikson, A. Y.


    The distribution patterns of mafic-ultramafic xenoliths within Archaean orthogneiss terrain furnish an essential key for the elucidation of granite-greenstone relations. Most greenstone belts constitute mega-xenoliths rather than primary basin structures. Transition along strike and across strike between stratigraphically low greenstone sequences and xenolith chains demonstrate their contemporaneity. These terrains represent least deformed cratonic islands within an otherwise penetratively foliated deformed gneiss-greenstone crust. Whereas early greenstone sequences are invariably intruded by tonalitic/trondhjemitic/granodioritic gneisses, stratigraphically higher successions may locally overlap older gneiss terrains and their entrained xenoliths unconformably. The contiguity of xenolith patterns suggests their derivation as relics of regional mafic-ultramafic volcanic crustal units and places limits on horizontal movements between individual crustal blocks.

  18. A primitive mantle source for the Neoarchean mafic rocks from the Tanzania Craton

    Y.A. Cook; I.V. Sanislav; J. Hammerli; T.G. Blenkinsop; P.H.G.M. Dirks


    Mafic rocks comprising tholeiitic pillow basalt, dolerite and minor gabbro form the basal stratigraphic unit in the ca. 2.8 to 2.6 Ga Geita Greenstone Belt situated in the NW Tanzania Craton. They outcrop mainly along the southern margin of the belt, and are at least 50 million years older than the supracrustal assemblages against which they have been juxtaposed. Geochemical analyses indicate that parts of the assemblage approach high Mg-tholeiite (more than 8 wt.%MgO). This suite of samples has a restricted compositional range suggesting derivation from a chemically homogenous reservoir. Trace element modeling suggests that the mafic rocks were derived by partial melting within the spinel peridotite field from a source rock with a primitive mantle composition. That is, trace elements maintain primitive mantle ratios (Zr/Hf ¼ 32e35, Ti/Zr ¼ 107e147), producing flat REE and HFSE profiles [(La/Yb)pm ¼ 0.9 e1.3], with abundances of 3e10 times primitive mantle and with minor negative anomalies of Nb [(Nb/La)pm ¼ 0.6e0.8] and Th [(Th/La)pm ¼ 0.6e0.9]. Initial isotope compositions (3Nd) range from 1.6 to 2.9 at 2.8 Ga and plot below the depleted mantle line suggesting derivation from a more enriched source compared to present day MORB mantle. The trace element composition and Nd isotopic ratios are similar to the mafic rocks outcropping w50 km south. The mafic rocks outcropping in the Geita area were erupted through oceanic crust over a short time period, between w2830 and w2820 Ma; are compo-sitionally homogenous, contain little to no associated terrigenous sediments, and their trace element composition and short emplacement time resemble oceanic plateau basalts. They have been interpreted to be derived from a plume head with a primitive mantle composition.

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

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


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

  20. Enclaves of opportunity or "ghettos of last resort?" Assessing the effects of immigrant segregation on violent crime rates.

    Feldmeyer, Ben; Harris, Casey T; Scroggins, Jennifer


    A growing body of research indicates that immigration to the U.S. has crime-reducing effects on aggregate levels of violence, which researchers have often attributed to the protective and revitalizing effects of immigrants settling in spatially concentrated neighborhoods. However, recent scholarship suggests that growing shares of the foreign-born population are bypassing these segregated immigrant enclaves and are dispersing more widely to other urban neighborhoods. Moreover, some scholars suggest that spatially isolating immigrant populations may not always be protective, but could actually contribute to social problems like crime, particularly in disadvantaged contexts. The current study offers one of the first analyses exploring the way that segregation of immigrant populations (relative to the U.S.-born) is related to year 2000 violent crime rates for nearly 500 census places in California and New York. Results of our analysis reveal no direct link between immigrant segregation and macro-level violence, but instead show that these effects are highly contextualized and depend on the resources present in locales. Specifically, immigrant segregation contributes to violence in highly disadvantaged places but is linked to lower violence in areas with greater resources.

  1. Population structure of the snail Buccinanops globulosum (Prosobranchia, Nassariidae) in San Matías Gulf, Patagonia Argentina: Isolated enclaves?

    Narvarte, Maite; Willers, Valeria; Avaca, María Soledad; Echave, María Eugenia


    In San Matías Gulf (Patagonia, Argentina), Buccinanops globulosum is typically distributed in two different areas: the intertidal-subtidal zone of Playa Villarino, where conch length reaches up to 60 mm, and the inner channel of San Antonio Bay, where individuals are not larger than 30 mm. It is suggested that both populations of B. globulosum constitute independent enclaves adapted to the local conditions and with a different population structure. This comparative study focuses on the population structure, sex ratios, growth, and size at maturity at the two sites. The data collected reveal that the individuals in San Antonio ranged from 5 to 29 mm whereas those in Villarino ranged from 4 to 61 mm. It was also observed that in San Antonio Bay, generally males outnumbered females whereas exactly the opposite occurred in Villarino. In addition, females were larger and showed a faster growth than males in both study areas. The number of egg capsules on each female ranged from 8 to 25 in San Antonio Bay and from 5 to 66 in Villarino. Size at maturity of females in San Antonio Bay was estimated at 14.47 mm and maximum estimated length at 6 years old was 33 mm. The same parameters in the individuals from Villarino were 45 and 65 mm, respectively. The comparative analysis of the above-mentioned features poses the question of whether these two populations represent either different species or different forms of the same species.

  2. Physical abrasion of mafic minerals and basalt grains: application to Martian aeolian deposits

    Cornwall, Carin; Bandfield, Joshua L.; Titus, Timothy N.; Schreiber, B. C.; Montgomery, D.R.


    Sediment maturity, or the mineralogical and physical characterization of sediment deposits, has been used to locate sediment source, transport medium and distance, weathering processes, and paleoenvironments on Earth. Mature terrestrial sands are dominated by quartz, which is abundant in source lithologies on Earth and is physically and chemically stable under a wide range of conditions. Immature sands, such as those rich in feldspars or mafic minerals, are composed of grains that are easily physically weathered and highly susceptible to chemical weathering. On Mars, which is predominately mafic in composition, terrestrial standards of sediment maturity are not applicable. In addition, the martian climate today is cold, dry and sediments are likely to be heavily influenced by physical weathering rather than chemical weathering. Due to these large differences in weathering processes and composition, martian sediments require an alternate maturity index. Abrason tests have been conducted on a variety of mafic materials and results suggest that mature martian sediments may be composed of well sorted, well rounded, spherical basalt grains. In addition, any volcanic glass present is likely to persist in a mechanical weathering environment while chemically altered products are likely to be winnowed away. A modified sediment maturity index is proposed that can be used in future studies to constrain sediment source, paleoclimate, mechanisms for sediment production, and surface evolution. This maturity index may also provide details about erosional and sediment transport systems and preservation processes of layered deposits.




    Based on the study of petrography and mineralogy, the enclaves in granitoids are parametamorphites of amphibolite facies and granulite facies, and the types of enclave rocks include hyperthene-granulite, geneiss, granulite and enclaves riched mica. The forming temperatures and pressures of amphibolite facies and granulite facies enclave rocks are 633℃, 460 MPa~550 MPa and 781~883℃, 530 MPa~710 MPa, respectively. The enclaves are remnants of rocks which partially melted to form granitoid magma. The genesis of enclave rocks of amphibolite facies and granulite facies in Darongshan and Shiwandashan regions is reginal dynamothermal metamorphism. In contrast, the genesis of enclave rocks of granulite facies in Yunkai region is thermal dome metamorphism.%据包体岩相学及矿物学研究,包体岩石为角闪岩相到麻粒岩相的副变质岩,岩石类型有麻粒岩、变粒岩、片麻岩和富云包体。角闪岩相包体形成的温度为633℃,压力为460 MPa~550 MPa;麻粒岩包体形成的温度为781℃~883℃,压力为530 MPa~710 MPa。包体为部分熔融形成寄主花岗岩岩浆的源区岩石残余。其中大容山—十万大山地区角闪岩相—麻粒岩相包体岩石为区域动热变质成因;云开大山地区麻粒岩包体岩石为热穹隆变质成因。

  4. Polarization of mafic and felsic rocks In the Skaergaard Layered Series (Invited)

    McBirney, A. R.; Johnston, A.; Webster, J. D.


    When it became apparent that plagioclase could never sink in a magma as iron rich and dense as that of the Skaergaard Intrusion, we were faced with the problem of explaining the formation of anorthositic layers, foundered blocks, and schlieren that consist almost entirely of plagioclase but were obviously stable on the floor of the intrusion. Sonnenthal (Jour. Pet., 1998, 39: 633-661) found that gabbroic blocks that fell from the roof series were originally more gabbroic and were altered metasomatically to anorthosites after they reached the floor were buried it the advancing front of crystallization. Their mafic components were expelled into the surrounding gabbro and replaced by plagioclase. Similar processes appear to have transformed parts of the Layered and Marginal Border Series into strongly polarized anorthosites and olivine pyroxenites. The studies of Filiberto and Treiman (Chem. Geol. 2009, 263: 50-68) of the effect of chlorine on the liquidus of basalts, together with our on-going experimental investigation of its effect on the system plagioclase-pyroxene, has opened new possibilities that may enable us to explain these enigmatic rocks. When Webster and his co-workers (Geoch Cosmoch. Acta, 2009, 73: 559-581) showed that, unlike water, chlorine is much more soluble in mafic silicate melts than felsic ones, these contrasting properties suggested that the effect of chlorine on the cotectic relations of plagioclase and pyroxene might be the opposite of that of water: it could depress the melting temperature of pyroxene just as water depressed that of plagioclase. Experiments currently underway at the American Museum of Natural History and University of Oregon are showing that this is indeed the case. Consider what might happen if a crystallizing gabbro were infiltrated by a chlorine-rich aqueous fluid of the kind that Larsen and Brooks (Jour. Pet., 1997, 35: 1651-79) have shown permeated the rocks while they were still at a high temperature. Flux melting

  5. Enclaves con espinela-corindon·sillimanita en rocas andesítico-dacíticas (Noguera, sierra de Albarracin. Teruel

    Aparicio, A.


    Full Text Available In intrusive dacitic-andesitic rocks, near Noguera de Albarracín, Iberian Mountains (Spain, there exist metamorphic inclusions with spinel, corundum, sillimanite, biotite and other interesting minerals, many of them indicating high T-P conditions (above 800° C and 5 Kb. The petrological studies indicate that such enclaves were built through a poliphasic process where various prograde and retrograde minerals were formed. A possible relationship between the metamorphic and the volcanic processes and both, metamorphic and volcanic, with the swelling-uplifting phenomenon, securely related with intrusive granitoids that took place in Albarracin area during last Hercynian times, is considered here.En un afloramiento intrusivo, constituído por rocas dacítico-andesíticas, al W de Noguera de Albarracín, existen enclaves de rocas metamórficas con espinela, corindón, sillimanita y otros minerales. Los estudios petrológicos indican que estos enclaves fueron originados en un proceso polifásico donde varias secuencias mineralógicas prógradas y retrógradas son reconocidas. Muchas de la paragénesis indican condiciones físicas de formación alrededor de los 800° C y los 5 Kb. Se plantea la posibilidad de la existencia de una relación entre el proceso metamórfico y el volcánico, y ambos asociados con el abombamiento cortical, posiblemente en relación con granitoides, que tuvo lugar en la Sierra de Albarracín durante el Paleozoico Superior.

  6. P-T-t Path of Mafic Granulite Metamorphism in Northern Tibet and Its Geodynamical Implications

    HU Daogong; WU Zhenhan; JIANG Wan; YE Peisheng


    Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (Mi) is preserved only in the granulites and represented by plagioclase+homblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of gamet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of horublende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of homblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of gamet+clinopyroxene+plagioclase+homblende were estimated at 769-905°C and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800°C and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708°C and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.

  7. Mutaciόn industrial en la Argentina: complejo electrόnico o conjunto de enclaves? Un analísis a traves del comercio exterior

    Azpiazu, Daniel; Basualdo , Eduardo; Nochteff, Hugo


    RésuméMutation industrielle : complexes électroniques ou enclaves ? Une analyse à travers le commerce extérieurLe complexe électronique en Argentine a connu la crise la plus profonde et la plus longue de son histoire lorsque se mettaient en place les politiques économiques élaborées après le coup d’Etat de mars 1976. Ces politiques ont provoqué un changement ou une restructuration de l’industrie dans un sens régressif : les entreprises productrices de biens intermédiaires, à forte intensité d...

  8. La figura del educador social en “aulas enclave: transición a la vida adulta” dentro del contexto escolar.


    A continuación, el presente documento pretende aproximar la figura del Educador Social al contexto escolar, involucrado en equipos de intervención multidisciplinar, complementando la labor de los maestros y profesores. En ningún momento se persigue descartar dicha figura en otros departamentos y términos intrínsecos de “La Escuela”, En este caso, se concreta la labor del Educador Social dentro de las Aulas Enclave de Transición a la Vida Adulta (TVA) en Educación Secundaria, reflejado...

  9. Petrología y geoquímica de rocas granitoides y enclaves asociados del batolito de los Pedroches (Macizo Ibérico)

    Donaire Romero, Teodosio


    El batolito de Los Pedroches está formado por importantes conjuntos plutónicos epizonales. Los litotipos plutónicos dominantes en cada uno de estos conjuntos son una granodiorita biotítica ±anfibol y un monzogranito biotítico ±cordierita porfídico de grano grueso a medio. Los datos petrográficos y geoquímicos presentados en este trabajo sugieren que los enclaves microgranitoides incluidos en granodioritas y monzogranitos no están relacionados con procesos de hibridación magmática, sino con la...

  10. Lithologic mapping of mafic intrusions in East Greenland using Landsat Thematic Mapper data

    Naslund, H. Richard; Birnie, R. W.; Parr, J. T.


    The East Greenland Tertiary Igneous Province contains a variety of intrusive and extrusive rock types. The Skaergaard complex is the most well known of the intrusive centers. Landsat thematic mapping (TM) was used in conjunction with field spectrometer data to map these mafic intrusions. These intrusions are of interest as possible precious metal ore deposits. They are spectrally distinct from the surrounding Precambrian gneisses. However, subpixel contamination by snow, oxide surface coatings, lichen cover and severe topography limit the discrimination of lithologic units within the gabbro. Imagery of the Skaergaard and surrounding vicinity, and image processing and enhancement techniques are presented. Student theses and other publications resulting from this work are also listed.

  11. El enclave urbano, lógica socioespacial de la periferia urbanizada y sus efectos sobre la segregación residencial y la fragmentación urbana

    Guénola Capron


    Full Text Available The production of the metropolitan peripheries in Latin America has been characterized by the development of urban, residential and commercial enclaves. These enclaves encompass both large urban housing projects of social interest and subdivisions and gated communities for high-income populations. Both peripheries respond to very different social reasons but have a common spatial logic: the enclave, which deepens the isolation and social distance with its surroundings, generating segregation and fragmentation. We seek to rescue the social and spatial processes of ‘enclosing’ or ‘insularity’ in two cases: a gated community in the northeast — Zona Esmeralda— and a social housing urban complex in the east —San Buenaventura—, both bordering the metropolitan area of the Mexico Valley

  12. Layered amphibolite sequence in NE Sardinia, Italy: remnant of a pre-Variscan mafic silicic layered intrusion?

    Franceschelli, Marcello; Puxeddu, Mariano; Cruciani, Gabriele; Dini, Andrea; Loi, Marilisa


    A banded amphibolite sequence of alternating ultramafic, mafic (amphibolite) and silicic layers, tectonically enclosed within Variscan migmatites, outcrops at Monte Plebi (NE Sardinia) and shows similarities with leptyno-amphibolite complexes. The ultramafic layers consist of amphibole (75-98%), garnet (0-20%), opaque minerals (1-5%) and biotite (0-3%). The mafic rocks are made up of amphibole (65-80%), plagioclase (15-30%), quartz (0-15%), opaque minerals (2-3%) and biotite (0-2%). The silicic layers consist of plagioclase (60-75%), amphibole (15-30%) and quartz (10-15%). Alteration, metasomatic, metamorphic and hydrothermal processes did not significantly modify the original protolith chemistry, as proved by a lack of K2O-enrichment, Rb-enrichment, CaO-depletion, MgO-depletion and by no shift in the rare earth element (REE) patterns. Field, geochemical and isotopic data suggest that ultramafic, mafic and silicic layers represent repeated sequences of cumulates, basic and acidic rocks similar to macrorhythmic units of mafic silicic layered intrusions. The ultramafic layers recall the evolved cumulates of Skaergaard and Pleasant Bay mafic silicic layered intrusions. Mafic layers resemble Thingmuli tholeiites and chilled Pleasant Bay mafic rocks. Silicic layers with Na2O: 4-6 wt%, SiO2: 67-71 wt% were likely oligoclase-rich adcumulates common in many mafic silicic layered intrusions. Some amphibolite showing a strong Ti-, P-depletion and REE-depletion are interpreted as early cumulates nearly devoid of ilmenite and phosphates. All Monte Plebi rocks have extremely low Nb, Ta, Zr, Hf content and high LILE/HFSE ratios, a feature inherited from the original mantle sources. The mafic and ultramafic layers show slight and strong LREE enrichment respectively. Most mafic layer samples plot in the field of continental tholeiites in the TiO2-K2O-P2O5 diagram and are completely different from N-MORB, E-MORB and T-MORB as regards REE patterns and Nd, Sr isotope ratios but show

  13. The discovery of the Neoarchean mafic dyke swarm in Hengshan and reinterpretation of the previous "Wutai greenstone belt"


    The structural mapping and section study indicate that the "greenstone belts" in the southern to central parts of Hengshan were intensively sheared and transposed mafic dyke swarm,which originally intruded into the Neoarchean grey gneiss and high-pressure granulite terrain(HPGT).The HPGT is characterized by flat-dipping structures,to the south it became steep and was cut by the Dianmen mafic dyke swarm.After high-pressure granulite-facies metamorphic event,the mafic dyke swarm occurred,and was associated with the extensional setting and reworked by the late strike-slip shearing.The zircon age dating proves that the Dianmen mafic dyke swarm was emplaced during the period between 2499±4 Ma and 2512±3 Ma,followed by late tectonothermal reworking.The Dianmen mafic dyke swarm further documents the extensional episode in the central to northern parts of North China Craton(NCC),providing the important constraint for the limit between Archean and Proterozoic and correlation between NCC and other cratonic blocks of the world.

  14. The discovery of the Neoarchean mafic dyke swarm in Hengshan and reinterpretation of the previous “Wutai greenstone belt”

    李江海; 张志强; 黄雄南


    The structural mapping and section study indicate thai the "greenstone belts" in the southern to central parts of Hengshan were intensively sheared and transposed mafic dyke swarm, which originally intruded into the Neoarchean grey gneiss and nigh-pressure granulite terrain (HPGT). The HPGT is characterized by flat-dipping structures, to the south it became steep and was cut by the Dianmen mafic dyke swarm. After high-pressure; granulite-facies metamorphic event, the mafic dyke swarm occurred, and was associated with the extensional setting and reworked by the late strike-slip shearing. The zircon age dating proves that the Dianmen mafic dyke swarm was emplaced during the period between 2499±4 Ma and 2512±3 Ma, followed by late tectonothermal reworking. The Dianmen mafic dyke swarm further documents the extensional episode in the central to northern parts of North China Craton (NCC), providing the important constraint for the limit between Archean and Proterozoic and correlation between NCC and other e

  15. Petrology and geochemistray of Imam-Zadeh Hashem mafic and ultramafic bodies, southern Guilan province

    Mojgan Salavati


    Full Text Available Mafic and ultramafic plutonic igneous bodies, with small and big outcrops, between Shemshak rock units (Jurassic are observed in east of Imam Zadeh Hashem, in southern Guilan province. Ultramafic cumulates consist of clinopyroxenite, and plagiofer clinopyroxenite, olivine clinopyroxenite, and mafic rocks, based on mineralogy consist of gabbros, olivine gabbros, biotite gabbros and amphibole gabbros. According to geochemical data, studied rocks have tholeiitic nature and in the tectonic setting diagrams, display arc characteristic. The chondrite normalized REE patterns show low enrichment in LREEs relative to HREEs. The negative Nb and Ti anomalies in primitive mantle and MORB-normalized multi-element diagrams of the rocks are characteristic of island arc magmas. Also, enrichment in LILE and depletion of HFSE may indicate a subduction-related tectonic setting. According to geological and geochemical evidence, Imam-Zadeh Hashem ultramafic and sub-alkaline gabbro rocks can be as a part of the Southern Caspian Sea Ophiolite sequence (SCO that formed in a suprasubduction tectonic system.

  16. Quantitative EPMA Compositional Mapping of NWA 2995: Characterization, and Petrologic Interpretation of Mafic Clasts

    Carpenter, P. K.; Hahn, T. M.; Korotev, R. L.; Ziegler, R. A.; Jolliff, B. L.


    We present the first fully quantitative compositional maps of lunar meteorite NWA 2995 using electron microprobe stage mapping, and compare selected clast mineralogy and chemistry. NWA 2995 is a feldspathic fragmental breccia containing numerous highland fine grained lithologies, including anorthosite, norite, olivine basalt, subophitic basalt, gabbro, KREEP-like basalt, granulitic and glassy impact melts, coarse-grained mineral fragments, Fe-Ni metal, and glassy matrix [1]. Chips of NWA 2995, representing these diverse materials, were analyzed by INAA and fused-bead electron-probe microanalysis (EPMA); comparison of analytical data suggests grouping of lunar meteorites NWA 2995, 2996, 3190, 4503, 5151, and 5152. The mean composition of NWA 2995 corresponds to a 2:1 mixture of feldspathic and mare material, with approximately 5% KREEP component [2]. Clast mineral chemistry and petrologic interpretation of paired stone NWA 2996 has been reported by Mercer et al. [3], and Gross et al. [4]. This study combines advances in quantitative EPMA compositional mapping and data analysis, as applied to selected mafic clasts in a polished section of NWA 2995, to investigate the origin of mafic lithic components and to demonstrate a procedural framework for petrologic analysis.

  17. Oxygen isotopes of some trondhjemites, siliceous gneisses, and associated mafic rocks

    Barker, F.; Friedman, I.; Hunter, D.R.; Gleason, J.D.


    Analyses of oxygen isotopes in whole-rock samples of 58 Precambrian and Phanerozoic trondhjemites and siliceous gneisses and of 28 cogenetic mafic to intermediate rocks from North America, Fennoscandia, and southern Africa give the following results: 1. (1) 47 trondhjemites, tonalites, and mostly Archean acidic gneisses that apparently are not isotopically disturbed show an overage ?? 15O of +7.3??? and a range of 5.2-8.9???; 11 other samples are slightly to moderately disturbed and show higher values; and 2. (2) the mafic rocks show a wide range of ??-values, from about 0-9??? but the undisturbed ones give an average ?? 18O of 5.2???. The ?? 18O values of the trondhjemitic intrusives and siliceous gneisses of similar composition are lower than those of most granitic rocks and support models for derivation of these rocks from basaltic parents. This approach, however, cannot be used to determine if individual bodies formed by differentiation or by partial melting. ?? 1976.

  18. K-Ar Geochronology of Mesozoic Mafic Dikes in Shandong Province, Eastern China:Implications for Crustal Extension

    LIU Shen; HU Ruizhong; ZHAO Junhong; FENG Caixia


    Based on K-Ar isotope analyses, Mesozoic mafic (and alkali ultramafic) dikes from western and eastern Shandong Province, China, are dated at 88.2±1.70 Ma to 169.5±3.7 Ma with the majority of ages ranging from 90 Ma to 140 Ma. The emplacement of the dikes suggests a major Yanshanian (Cretaceous) crustal extension in Shandong province.Together with other available age data, this study suggests four periods of crustal extension at about 80 Ma, 100 Ma, 120 Ma and 140 Ma, respectively. Besides the effect of collapse of the Yanshanian orogenic belt on the emplacement of the mafic dikes in Shandong in the Cretaceous, the mantle plume and the extensive left-lateral advection and extension of the Tanlu fault also have controlled the crustal extension and the emplacement of the mafic dikes in eastern Shandong and western Shandong, respectively.

  19. Geochronological Significance of the Post-Orogenic Mafic-Ultramafic Rocks in the Hongqiling Area of Jilin Province, Northeast China

    Zhang Guangliang; Wu Fuyuan


    Mafic-ultramafic complexes are widespread in Hongqiling in central Jinlin Province, NE China. The Hongqiling complex comprises pyroxenite, olivine websterite, lherzolite, gabbro and leucogabbro. Based on the latest geochronological results, these intrusions yield a zircon U-Pb age of about 216 Ma, implying that they emplaced in the late Triassic period and that the mafic-ultramafic complexes are post-orogenic in origin. These ages are coeval with the emplacement of A-type granites in the area, but slightly younger than syn-orogenic granitic magmatism. The composition of the parent magma during the equilibration of the accumulated olivine crystallizing is basaltic with high MgO, and it comes from depleted or juvenile lithospheric mantle, according to the results of trace elements and Sr-Nd isotopes. Amount of crustal material contaminated the magmatic source, implying that the mafic-ultramafic rocks originate from the mixing product of crust- and mantle-derived magma. Therefore, the magmatic source was contaminated by an amount of crustal material, and the subsequent crystal fractionation resulted in the Cu-Ni mineralization. Dynamic analyses indicate that, after the collision of the North China Craton and Jiamusi Massif, the lithospheric delamination during post-orogeny resulted in the upwelling of asthenosphere and the intruding of the mass and underplating of the mantle-derived magma, which led to the formation of the primary mafic-ultramafic magma due to the mantle-derived magma and partial melting of the lower crust. This result suggests that the mafic-ultramafic complexes belong to a typically important magmatic suite that evolved during post-orogenic processes, and they were exposed as maficultramafic dyke swarms that existed in the post-orogenic extension environment. It also implies that the orogenic process finished ultimately in this regional geological setting. The widespread occurrence of mafic-ultramafic complexes in the Xing'an-Mongolia Orogenic Belt

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

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


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

  1. ArcGIS studies and field relationships of Paleoproterozoic mafic dyke swarms from the south of Devarakonda area, Eastern Dharwar Craton, southern India: Implications for their relative ages

    Amiya K Samal; Rajesh K Srivastava; Lokesh K Sinha


    Google Earth Image and cross-cutting field relationships of distinct Paleoproterozoic mafic dykes from south of Devarakonda area in the Eastern Dharwar Craton has been studied to establish relative emplacement ages. The Devarakonda, covering an area of ∼700 km2, shows spectacular cross-cutting field relationships between different generations of mafic dykes, and is therefore selected for the present study. Although some recent radiometric age data are available for distinct Paleoproterozoic mafic dykes from the Eastern Dharwar Craton, there is no analogous age data available for the study area. Therefore, relative age relationships of distinct mafic dykes have been established for the study area using cross-cutting field relationships and GIS techniques, which shows slightly different picture than other parts of the Eastern Dharwar Craton. It is suggested that NE–SW trending mafic dykes are youngest in age (probably belong to ∼1.89 Ga dyke swarm), whereas NNW–SSE trending mafic dykes have oldest emplacement age. Further, the NNW–SSE mafic dykes are older to the other two identified mafic dyke swarms, i.e., WNW–ESE (∼2.18 Ga) and N–S trending (∼2.21 Ga) mafic dyke swarms, as dykes of these two swarms cross-cut a NNW–SSE dyke. It provides an evidence for existence of a new set of mafic dykes that is older to the ∼2.21 Ga and probably younger to the ∼2.37 Ga swarm. Present study also supports existence of two mafic dyke swarms having similar trend (ENE–WSW to NE–SW) but emplaced in two different ages (one is ∼2.37 Ga and other ∼1.89 Ga).

  2. Creep of mafic dykes infiltrated by melt in the lower continental crust (Seiland Igneous Province, Norway)

    Degli Alessandrini, G.; Menegon, L.; Malaspina, N.; Dijkstra, A. H.; Anderson, M. W.


    A dry mafic dyke from a continental lower-crustal shear zone in the Seiland Igneous Province (northern Norway) experienced syn-kinematic melt-rock interaction. Viscous shearing occurred at T ≈ 800 °C, P ≈ 0.75-0.95 GPa and was coeval with infiltration of felsic melt from adjacent migmatitic metapelites. The dyke has a mylonitic microstructure where porphyroclasts of orthopyroxene, clinopyroxene and plagioclase are wrapped by a fine-grained (4-7 μm) polyphase mixture of clinopyroxene + orthopyroxene + plagioclase + quartz + ilmenite ± K-feldspar ± apatite. Microstructural observations and electron backscatter diffraction analysis indicate that the porphyroclasts deformed by a combination of dislocation glide and fracturing, with only a limited record of dislocation creep, recovery and dynamic recrystallization. We identified diffusion creep as the dominant deformation mechanism in the mixture based on the small grain size, phase mixing and weak crystallographic preferred orientation of all phases (interpreted as the result of oriented grain growth during viscous flow). The polyphase mixture did not form by dynamic recrystallization or by mechanical fragmentation of the porphyroclasts, but rather by melt-rock interaction. Thermodynamic models indicate that the syn-kinematic mineral assemblage results from the chemical interaction between a pristine mafic dyke and ca. 10 vol.% of felsic melt infiltrating from the adjacent partially molten metapelites. Extrapolation of laboratory-derived flow laws to natural conditions indicates that the formation of interconnected layers of fine-grained reaction products deforming by diffusion creep induces a dramatic weakening in the mafic granulites, with strain rates increasing up to 2-3 orders of magnitude. The reaction weakening effect is more efficient than the weakening associated with melt-assisted diffusion creep in the presence of up to 10 vol.% of infiltrated melt without formation of fine-grained reaction products

  3. Mobile Security Enclaves


    Integrated Circuit Card Identifier IEC International Electrotechnical Commission IOS International Organization For Standardization IMEI...International Electrotechnical Commission (IEC) Standard IOS/IEC 7688. In general, each APDU contains specific instructions and data for both the SIM...13] L. Pesonen, “GSM Interception,” White Paper , University of Technology, Helsinki, pp. 2, 1999. 76 [14] A. Schoffl and M. Irger

  4. Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

    Tang, Ming; Chen, Kang; Rudnick, Roberta L


    The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago. Copyright © 2016, American Association for the Advancement of Science.

  5. Neogene to Recent Mafic Volcanism in Death Valley Reveals Architecture of Deep Mojavia Lithosphere

    Rämö, O. T.; Calzia, J.


    At 10-0 m.y., the evolution of the Death Valley region, SE California, was characterized by repeated extrusion of mafic and intermediate lavas. The volume of these lavas appears to have diminished with time, from the relatively extensive (now faulted) Sheephead, Death Valley, Shoshone, and Funeral basalts to small monogenic volcanic centers (Split Cinder Cone, Ubehebe). A common denominator of these lavas is their transitional alkaline character (in general, trachybasalts to trachydacites with Na > K), relatively low MgO (1.5 to 6 wt.%), varying Fe2O3(tot) (4 to 12 wt.%) and Ni (10 to 80 ppm). They are all strongly enriched in the LREE: Chondrite-normalized La/Yb varies between 10 and 28, with the earlier, more voluminous lavas being less enriched (10 to 18) than the youngest volcanics (27 to 28). The initial Nd isotope composition of the lavas is outstandingly varying and does not correlate with fractionation stage. Their epsilon-Nd values vary from -10 to -2 and none of them thus registers a major asthenospheric component. Overall, these transitional mafic magmas probably represent relatively low-degree melts from the subcontinental lithosphere underneath the cratonic Mojavia crust. The 147Sm/144Nd ratios of the lavas show a restricted range (0.0930 to 0.1140) and, together with the measured 143Nd/144Nd ratios of the lavas, define Meso- to Neoproterozoic depleted mantle model ages between 800 and 1200 Ma. These have now spatial control across the Death Valley region and are clearly lower than those measured for the exposed craton. This suggest that the Mojavia cratonic mantle lithosphere may be a random amalgamation of ultramafic domains that vary in the degree of metasomatism and rejuvenation.

  6. Evolution of the Antarctic Peninsula lithosphere: Evidence from Mesozoic mafic rocks

    Riley, T. R.; Curtis, M. L.; Flowerdew, M. J.; Whitehouse, M. J.


    New geochronology from a thick (> 800 m) basaltic succession along the eastern margin of the Antarctic Peninsula confirm a Middle Jurassic age (178 ± 1 Ma). This marginally postdates the adjacent Ferrar large igneous province of the Transantarctic Mountains and predates the extensive silicic volcanism of the Mapple Formation (~ 170 Ma) of the Antarctic Peninsula. The geochemistry of other rare, but broadly contemporaneous, basaltic successions of the Antarctic Peninsula, along with Cretaceous-age mafic dykes, are used to interpret the influences of lithospheric and asthenospheric mantle sources during the Mesozoic. Two significant high magmatic addition rate events occurred along the Antarctic Peninsula continental margin at 170 and 110 Ma and can be correlated to events along the South American Cordillera. These 'flare-up' events are characterised by extensive silicic (mostly ignimbrite) volcanism of the Chon Aike Province (V2 event: 170 Ma) and significant granitoid batholith emplacement of the Lassiter Coast intrusive suite (110 Ma). The 170 Ma event is exposed across large parts of the northern Antarctic Peninsula, whilst the 110 Ma event is more widespread across the southern Antarctic Peninsula. The basaltic volcanism described here precedes the 'flare-up' event at 170 Ma and has geochemical characteristics that indicate a thickened lithosphere prevailed. A major dyke swarm that followed the 170 Ma event indicates that extensive lithospheric thinning had occurred, which allowed the ascent of depleted mafic melts. The thinning was the direct result of widespread lower crustal/upper lithospheric melting associated with the silicic volcanism. In the southern Antarctic Peninsula, the lithosphere remained over thickened until the emplacement of the major batholiths of the Lassiter Coast intrusive suite at 110 Ma and was then immediately followed by the emplacement of more asthenosphere-like melts indicating extensive lithospheric thinning.

  7. The fate of mafic and ultramafic intrusions in the continental crust

    Roman, Alberto; Jaupart, Claude


    Geochemical and petrological data indicate that the bulk continental crust results from the fractionation of basaltic magmas followed by the foundering of residual mafic cumulates. Structural and geological evidence for foundering has been elusive and it is argued that it lies in the shapes of mafic intrusions that have been preserved in the crust. Numerical calculations of visco-elasto-plastic deformation induced by a dense intrusive body in continental crust have been carried out for a wide range of physical conditions. Three regimes are defined on the basis of the amount of dense material that remains at the original emplacement level as well as on the shape of the residual body. With strong encasing rocks, the intrusion deforms weakly in a sagging regime characterized by downwarping of the floor. At the other extreme, the intrusion sinks through weak surroundings, leaving behind a very small volume of material. In an intermediate regime, the intrusion does not sink wholesale and undergoes a dramatic change of shape. A residual body is preserved with a shape that depends on the aspect ratio of the initial intrusion. For aspect ratios of order one, the residual body is funnel-shaped above a thin and deep vertical extension. For the small aspect ratios that typify large igneous complexes such as the Bushveld, South Africa, the residual body is characterized by thick peripheral lobes with inward-dipping igneous layers and a thinner central area that has lost some of the basal cumulates. The transitions between these regimes depend on the rheology and temperature of encasing rocks.

  8. Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS

    Letícia Alexandre Redes

    Full Text Available The Taquaral Granite is located on southern Amazon Craton in the region of Corumbá, westernmost part of the Brazilian state of Mato Grosso do Sul (MS, near Brazil-Bolivia frontier. This intrusion of batholitic dimensions is partially covered by sedimentary rocks of the Urucum, Tamengo Bocaina and Pantanal formations and Alluvial Deposits. The rock types are classified as quartz-monzodiorites, granodiorites, quartz-monzonites, monzo and syenogranites. There are two groups of enclaves genetically and compositionally different: one corresponds to mafic xenoliths and the second is identified as felsic microgranular enclave. Two deformation phases are observed: one ductile (F1 and the other brittle (F2. Geochemical data indicate intermediate to acidic composition for these rocks and a medium to high-K, metaluminous to peraluminous calk-alkaline magmatism, suggesting also their emplacement into magmatic arc settings. SHRIMP zircon U-Pb geochronological data of these granites reveals a crystallization age of 1861 ± 5.3 Ma. Whole rock Sm-Nd analyses provided εNd(1,86 Ga values of -1.48 and -1.28 and TDM model ages of 2.32 and 2.25 Ga, likely indicating a Ryacian crustal source. Here we conclude that Taquaral Granite represents a magmatic episode generated at the end of the Orosirian, as a part of the Amoguija Magmatic Arc.

  9. Organización y Demandas del Movimiento Obrero en Centroamérica: Entre el Enclave Bananero y el Proceso de Reformas Sociales

    Yesenia Martínez García


    Full Text Available El surgimiento de las plantaciones bananeras y de los movimientos son procesos acompasados en la historia de Centroamérica y el Caribe de América Latina durante la primera mitad del Siglo XX. Lo que a continuación se expone es un panorama general sobre la organización y las agendas del movimiento obrero en Centroamérica desde un análisis historiográfico. Se trata de hilvanar los diferentes planteamientos y casos en la región; se contextualiza en la injerencia de los Estados Unidos y sus intereses económicos y políticos en Centroamérica, en un segundo periodo de la Reforma Liberal, y las conexiones con un Estado Moderno y Social. La historiografía centroamericana aporta mucho a esta problemática más desde enfoques económicos y políticos; han sido los académicos estadounidenses y costarricenses quienes más se han interesado por analizar la problemática desde perspectivas sociales y culturales. Ahora, tratamos de presentar un panorama comparativo, desde lo social.Palabras Clave: Centroamérica; Movimiento Obrero; Enclave Bananero y Reformas Sociales.Organization and Claims of Labor Movement in Central America: Between the Enclave Banana and Social ReformsAbstractThe emergence of the banana plantations and the movements are rhythmic processes in the history of Central America and the Caribbean Latin America during the first half of the twentieth century. What then is exposed is an overview of the organization and the agendas of the labor movement in Central America from a historiographical analysis. It is to weave the different approaches and cases in the region is contextualized in the interference of the United States and its economic and political interests in Central America, in a second period of liberal reform, and connections with a Modern State and Social. American historiography to this problem provides much more from economic and political approaches, scholars have been Americans and Costa Ricans who have been most

  10. Geological and Geochemical Characteristics of Early Cretaceous Mafic Dikes in Northern Jiangxi Province, SE China and Their Geodynamic Implications

    XIE Guiqing; HU Ruizhong; MAO Jingwen; LI Ruiling; CAO Jinjian; JIANG Guohao; QI Liang


    The development of Early Cretaceous mafic dikes in northern and southern Jiangxi allows an understanding of the geodynamic setting and characteristics of the mantle in southeast China in the Cretaceous. Geological and geochemical characteristics for the mafic dikes from the Wushan copper deposit and No. 640 uranium deposit are given in order to constrain the nature of source mantle, genesis and tectonic implications. According to the mineral composition,the mafic dikes in northern Jiangxi can be divided into spessartite and olive odinite types, which belong to slightly potassium-rich calc-alkaline lamprophyre characterized by enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), large depletion in high strength field elements (HSFE) and with negative Nb, Ta and Ti anomalies, as well as 87Sr/86Sr ratios varying from 0.7055 to 0.7095 and 143Nd/144Nd ratios varying from 0.5119 to 0.5122.All features indicate that the magma responsible for the mafic dikes was derived mainly from metasomatic lithosphere mantle related to dehydration and/or upper crust melting during subduction. Differences in geochemical characteristics between the mafic dikes in northern Jiangxi and the Dajishan area, southern Jiangxi were also studied and they are attributed to differences in regional lithosphefic mantle components and/or magma emplacement depth. Combining geological and geochemical characteristics with regional geological history, we argue that southeast China was dominated by an extensional tectonic setting in the Early Cretaceous, and the nature of the mantle source area was related to enrichment induced by asthenosphere upwelling and infiltration of upper crust-derived fluids responding to Pacific Plate subduction.

  11. Petrogenesis of the Alaskan-type mafic-ultramafic complex in the Makkah quadrangle, western Arabian Shield, Saudi Arabia

    Habtoor, Abdelmonem; Ahmed, Ahmed Hassan; Harbi, Hesham


    The Makkah quadrangle is a part of the Jeddah terrane in the Precambrian basement, Western Arabian Shield of Saudi Arabia. Gabal Taftafan mafic-ultramafic complex lies within the central part of the Makkah quadrangle. The Taftafan mafic-ultramafic complex is a well-differentiated rock association which comprises of dunite core, hornblende- and plagioclase-bearing peridotites, troctolite, clinopyroxenite and marginal gabbro, in a distinctive zonal structure. The bulk-rock geochemistry of the Taftafan mafic-ultramafic rocks is characterized by a tholeiitic/sub-alkaline affinity with high Mg in the ultramafic core (0.84) and is systematically decreased towards the marginal gabbro (0.60). The patterns of trace elements show enrichment in the fluid-mobile elements (Sr, Ba) and a pronounced negative Nb anomaly which reflect a hydrous parental magma generated in a subduction tectonic setting. The mafic-ultramafic rocks of the Taftafan complex have low total rare earth elements (REE) displaying sub-parallel patterns leading to the assumption that these rocks are comagmatic and are formed by fractional crystallization from a common magma type. The platinum-group elements (PGE) content of all rock types in the Taftafan complex is very low, with ∑ PPGE > ∑ IPGE; displaying slightly positive slopes of the PGE distribution patterns. The chemistry of ferromagnesian minerals is characterized by a high forsterite (Fo) olivine with wide range (Fo91-67), from ultramafic core to the marginal gabbro, Ca-rich diopsidic clinopyroxene, and calcic hornblende. Orthopyroxene is almost absent from all rock types, or very rare when present. Hornblende and Ca-plagioclase possess the longest crystallization history since they are present in almost all rock types of the complex. Spinels in the dunite and hornblende-bearing peridotite core show homogeneous composition with intermediate Cr# (0.53-0.67). Plagioclase-bearing peridotite and troctolite have two exsolved types of spinel; Al

  12. Phreatomagmatic explosive eruptions along fissures on the top of mafic stratovolcanoes with overlapping compound calderas

    Nemeth, Karoly; Geshi, Nobuo


    On near summit flank eruptions on stratovolcanoes it is commonly inferred that external water to have little or no influence on the course of the eruptions. Hence eruptions are typicaly "dry" that form spatter-dominated fissures and scoria cones. This assumption is based on that in elevated regions - especially on steep slopes - the hydrogeological conditions are not favourable to store large volume of ground water that can have effect on the eruptions. However there is some controversial trend of eruption progression from an early dry eruption below the summit that later turn to be phreatomagmatic as the eruption locus migrates toward the summit. The Suoana Ccrater on top of Miyakejima Island's mafic stratovolcano is a fine example to demonstrate such process. Suona Crater is the topmost crater of the 3 km long fissure aligned chain of small-volume volcanoes that formed in the 7th century flank of the summit region of the Miyakejima mafic stratovolcano. The oval shape crater of Suona (400 x 300 m) is surrounded by a tuff ring that developed over lava flows and epiclastic deposits accumulated in an older caldera forming about a tuff ring that is about 25 m in its thickest section with a basal consistent lava spatter dominated unit gradually transforming into a more scoria-dominated middle unit. A caldera-forming eruption in AD 2000 half-sectioned the Suona Crater exposing of its internal diatreme - crater in-fill - tephra rim succession providing a unique opportunity to understand the 3D architecture of the volcano. Toward the top of the preserved and exposed tuff ring section a clear gradual transition can be seen toward more abundance of chilled dark juvenile particles providing a matrix of a coarse ash that commonly hold cauliflower lapilli and bomb. This transition indicates that the eruption progressed from an early dry explosive phase such as lava fountaining to be a more Strombolian style explosive eruption that later on turned to be heavily influenced by

  13. Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating


    The protoliths of mafic-ultramafic plutons in the northern Dabie Mts. (NDM) (Hubei) include pyroxenite and gabbro. The zircon U-Pb dating for a gabbro suggests that emplacement of mafic magma took place in the post-collisional setting at the age of 122.9(0.6 Ma. It is difficult to obtain a reliable Sm-Nd isochron age, due to disequilibrium of the Sm-Nd isotopic system. Two hornblende 40Ar/39Ar ages of 116.1(1.1 Ma and 106.6(0.8 Ma may record cooling of metamorphism in the mafic-ultramafic plutons in Hubei below 500(C. The hornblende 40Ar/39Ar ages for the mafic-ultramafic rocks in Hubei are evidently 15-25 Ma younger than those for the same rocks in Anhui, indicating that there is a diversity of the cooling rates for the mafic-ultramafic rocks in Hubei and Anhui. The difference in their cooling rates may be controlled by the north-dipping normal faults in the NDM. The intense metamorphism occurring in the mafic-ultramafic rocks in Hubei may result from the Yanshanian magmatic reheating and thermal fluid action induced by the Cretaceous migmatization. The geochemical similarity of these mafic-ultramafic rocks wherever in Hubei and Anhui may be attributed to the same tectonic setting via an identical genetic mechanism.

  14. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania

    Bonin, Bernard; Tatu, Mihai


    The Guadalupian (Mid-Permian) Highiș massif (Apuseni Mountains, Romania) displays a bimodal igneous suite of mafic (gabbro, diorite) and A-type felsic (alkali feldspar granite, albite granite, and hybrid granodiorite) rocks. Amphibole is widespread throughout the suite, and yields markedly high chlorine contents. Three groups are identified: Cl-rich potassic hastingsite (2.60-3.40 wt% Cl) within A-type felsic rocks and diorite, mildly Cl-rich pargasite to hornblende (0.80-1.90 wt% Cl) within gabbro, and low F-Cl hornblende within gabbro and hybrid granodiorite. Coexisting biotite is either Cl-rich within diorite, or F-Cl-poor to F-rich within A-type felsic rocks. Chlorine and fluorine are distributed in both mafic phases, according to the F-Fe and Cl-Mg avoidance rules. The low-Ti contents suggest subsolidus compositions. Cl-rich amphibole within diorite and A-type felsic rocks yields a restricted temperature range - from 575 °C down to 400 °C, whereas mildly Cl-rich amphibole within gabbro displays the highest range - from 675 to 360 °C. Temperatures recorded by Cl-rich biotite within diorite range from 590 to 410 °C. Biotite within A-type felsic rocks yields higher temperatures than amphibole: the highest values- from 640 to 540 °C - are recorded in low-F-Cl varieties, whereas the lowest values- from 535 to 500 °C - are displayed by F-rich varieties. All data point to halogen-rich hydrothermal fluids at upper greenschist facies conditions percolating through fractures and shear zones and pervasively permeating the whole Highiș massif, with F precipitating as interstitial fluorite and Cl incorporating into amphibole, during one, or possibly several, hydrothermal episodes that would have occurred during a ~ 150 My-long period of time extending from the Guadalupian (Mid-Permian) to the Albian (Mid-Cretaceous).

  15. Evaluation of the Lithospheric Contribution to Southern Rio Grande Rift Mafic Melts

    Konter, J. G.; Crocker, L.; Anaya, L. M.; Rooney, T. O.


    As continental rifting proceeds, the accommodation of lithospheric thinning by mechanical extension and magmatic intrusion represents an important but poorly constrained tectonic process. Insight into role of the magmatic component may come from the composition of volcanic products, which can record magma-lithosphere interactions. The volcanic activity in continental rift environments is frequently characterized by bimodal associations of mafic and silicic volcanism with heterogenous lithospheric contributions. We present a new integrated data set from several mafic volcanic fields in the Rio Grande Rift, consisting of major and trace element compositions, as well as isotopes. This data set provides insight into asthenospheric melting processes and interactions with the overlying lithosphere. The melting processes and the related extensional volcanism is the result of foundering of the Farallon slab. Large volume silicic eruptions such as those in the Sierra Madre Occidental originate from a large contribution of lithospheric melting, with a subordinate asthenospheric contribution. In contrast, Late Tertiary and Quaternary basaltic volcanic fields in the Rio Grande Rift were likely sourced in the asthenosphere and did not reside in the lithosphere for substantial periods. As a result the region is the ideal natural laboratory to investigate the interaction of asthenospheric melts with the lithosphere. In particular the wide array of volcanic fields contain multiple xenolith localities, such as Kilbourne Hole, providing direct samples of lithosphere and crust. Although previous studies have focused on correlations between amount of extension related to Farallon slab foundering, volcanic compositions, and their mantle sources, we present data that suggest that some compositional signatures may pre-date current tectonic processes. Radiogenic isotope data from several volcanic fields in New Mexico show a converging pattern in Pb isotope compositions, focusing on the

  16. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.


    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  17. Geochronology and geochemistry of a suite of mafic rocks in Chencai area, South China: Implications for petrogenesis and tectonic setting

    Zhao, Lei; Zhai, Mingguo; Zhou, Xiwen; Santosh, M.; Ma, Xudong


    Paleozoic crust-mantle interaction and geodynamic setting of the South China Block have remained largely elusive due to the scarcity of mafic rock suites. Here we report data from a suite of mafic rocks including norite, mafic granulite, garnet-bearing amphibolite, biotite-bearing amphibolite, and amphibolite from the Chencai region in the northeastern Cathaysia Block of South China, that mostly record amphibolite to granulite facies metamorphism. U-Pb dating of zircons from the mafic granulite and biotite-bearing amphibolite show broadly coeval magmatism, and amphibolite- to granulite-facies metamorphism during 435-438 Ma. The garnet-bearing amphibolite also records metamorphism at 436 Ma and the magmatic age of its protolith is constrained to be between 436 Ma and 496 Ma. The norite has an emplacement age of 422 Ma. Geochemically, the amphibolite and granulite have high Al2O3 contents and belong to the high-alumina group. The garnet-bearing amphibolite belongs to the intermediate-alumina group, whereas the norite and biotite-bearing amphibolite belong to the low-alumina group. A cumulate origin is proposed for the norite with orthopyroxene as the main cumulus phase. Based on their similar trace element and Lu-Hf isotopic signatures, it is inferred that the protoliths of amphibolite and granulite belonging to high-alumina group were likely generated from the same source. Furthermore, their LREE enrichment relative to HREE, positive Eu anomaly, and negative Nb, Ta and Zr anomalies suggest derivation from the same enriched mantle source, perhaps in a continental arc environment. Zircons from the garnet-bearing amphibolite belonging to intermediate-alumina group have high positive ɛHf (t) values with a peak of + 14 and trace element signatures similar to N-MORB, suggesting a depleted asthenospheric mantle source. The rock suite from Chencai suggests formation in an active continental margin, with the garnet-bearing amphibolite representing relics of the Paleozoic

  18. Ubicación espacial de los negocios étnicos en Almería. ¿Formación de enclaves económicos étnicos?

    Arjona Garrido, Ángeles


    Full Text Available In Almeria it’s frequently common for businesses to be run by immigrants. They have created an economical system that has been changing the city’s scenery. This is due to the previously mentioned concentration of different communities within certain areas. The installation of their businesses has been assumedly due to a responsive demand in products that haven’t been satisfied within the autochthonous trade; therefore it symbolizes the search of employment alternatives to the segmentation of the labour market.

    The installation of businesses can be observed in different situations; the general framework we talk about is of the appearance of ethnic economy and from this starting point we analyse the middleman minorities, the entrepreneur of enclave or the ethnic enclave economy. In this paper, with the assistance of graphical representations of maps from the different cities of the province, we outline if these business groups have the sufficient training for ethnical economy enclaves.

    En Almería son cada vez más frecuentes los negocios regentados por inmigrados, se trata de un sistema económico creado por ellos mismos que está transformando el paisaje urbano. Es el resultado de la anterior concentración, en determinadas áreas, de distintas comunidades; la instalación de sus empresas supone la respuesta a una demanda de productos que no están satisfechos en el comercio autóctono y simbolizan, además, la búsqueda de alternativas laborales a la segmentación del mercado de trabajo.

    En la instalación de los negocios se pueden observar distintas situaciones: podemos hablar de la aparición de economías étnicas como marco general y, a partir de ahí, analizar las minorías intermediarias, los empresarios de enclave ó los enclaves económicos étnicos. En este trabajo, ayudados por la representación gráfica en planos de distintas ciudades de la provincia, planteamos si esta agrupación de negocios es

  19. Ca. 1.5 Ga mafic magmatism in South China during the break-up of the supercontinent Nuna/Columbia: The Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in western Yangtze Block

    Fan, Hong-Peng; Zhu, Wei-Guang; Li, Zheng-Xiang; Zhong, Hong; Bai, Zhong-Jie; He, De-Feng; Chen, Cai-Jie; Cao, Chong-Yong


    Secondary ion mass spectroscopy (SIMS) zircon and baddeleyite U-Pb ages, elemental, and Nd isotopic data are reported for the Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in western Yangtze Block, South China. The mafic intrusions are dated at 1494 ± 6 Ma (zircon U-Pb), 1486 ± 3 Ma (baddeleyite U-Pb) and 1490 ± 4 Ma (baddeleyite U-Pb). The intrusions are dominantly gabbros that experienced variable degrees of alteration. All the studied rocks are high-Ti and alkaline in composition, and exhibit light rare earth element enrichment and "humped" incompatible trace-element patterns with no obvious Nb-Ta depletion, similar to intraplate alkali basaltic rocks in continental flood basalt (CFB) and ocean island basalt (OIB) provinces. Negative ɛNd(T) values (- 0.97 to - 3.58) and fractionation of the HREE of these rocks indicate that they were derived from a time-integrated, slightly enriched asthenospheric mantle source with minor crustal contamination. Like other Fe-Ti oxide mineralized rocks in plume-related layered intrusions or large igneous provinces around the world, the Zhuqing gabbros likely occurred in an intraplate setting. The ~ 1.5 Ga mafic magmatism was likely part of the global 1.6-1.2 Ga anorogenic magmatism related to the break-up of the supercontinent Nuna/Columbia, suggesting that the Yangtze Block may have been a component of the supercontinent.

  20. Melanite garnet-bearing nepheline syenite minor intrusion in Mawpyut ultramafic–mafic complex, Jaintia Hills, Meghalaya

    Monoj Maitra; J S David; S Bhaduri


    Mawpyut igneous suite in Jaintia Hills of Meghalaya plateau comprises differentiated suite of ultramafic–mafic rocks. The complex differs from other ultramafic–alkaline–carbonatite igneous emplacements of Shillong plateau and Mikir Hills like Jesra, Sung, Samchampi complexes, by the absence of alkaline–carbonatite rocks as major litho-units. Melanite garnet-bearing nepheline syenite, occurs as late phase minor intrusion in Mawpyut igneous complex, posseses alkaline character and shows inubiquitous relation with the host ultramafic–mafic rocks. On the other hand, this alkaline intrusive bodies of the Mawpyut igneous complex shows chemico-mineralogical resemblance with garnet-bearing nepheline syenite, ijolite litho-members of Jesra, Sung, Samchampi complexes of the region. It is interpreted that melanite garnet-bearing nepheline syenite intrusion in Mawpyut is contemporaneous with Jesra, Sung, Samchampi ultramafic–alkaline–carbonatite complexes and the host rocks of Mawpyut complex is an earlier magmatic activity possibly from a comparatively least enriched source.

  1. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: What Is the Message?

    El Atrassi, F.; Debaille, V.; Mattielli, N. D. C.; Berger, J.


    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African Craton in Mauritania (Amsaga area). The Amsaga Archean Crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. Our main objectives aim to the identification of the mafic lithology origin and a better understanding of their role in the continental crust emplacement. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. The amphibolites are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. Two groups are distinct in their geochemical characteristics (major and trace elements), although both have tholeiitic basalt composition. The first group show LREE-enriched patterns and negative Nb-Ta anomalies. The second group is characterized by near-flat LREE patterns and flat HREE patterns. This second group clearly shows no Nb-Ta anomalies. The first group could be related to arc-like basalts, as it is many similarities with some Archean amphibolites probably formed in a supra-subduction zone, for instance the volcanic rocks from the southern edge of the Isua Supracrustal Belt. On the contrary, the second group has a MORB-like signature which is more unusual during the Archean. Different scenarios will be discussed regards to the Archean geodynamics.

  2. Petrogenesis of permian sulfide-bearing mafic-ultramafic intrusions insoutheast Chinese Altay and east Tianshan, NW China

    Gao, Jianfeng; 高剑峰


    The Central Asia Orogenic Belt is one of the largest accretionary orogenic belts in the world. In this belt, many sulfide‐bearing mafic‐ultramafic intrusions occur along faults, including the Kalatongke complex in southeast Chinese Altay and the Huangshandong intrusion in east Tianshan. The Kalatongke complex is a composite body including ~308Ma dioritic intrusion and 287Ma sulfide‐bearing mafic intrusion. The dioritic intrusion consists of biotite‐hornblende gabbro, diorite and quartz d...

  3. Suture Dynamics of the Banda Arc Collision Zone: Geochemical and Age Analysis of Ultramafic and Mafic Bodies in Timor, Indonesia

    Valenza, J. M.; Harris, R. A.; Spencer, C. J.; Hoiland, C. W.; Flores, J. A.


    New age and geochemical data confirm that most ultramafic bodies on the north coast of Timor are derived from the distal reaches of the Australian continental margin lower plate that was exhumed by extension during Late Paleozoic to Mesozoic rifting. The ultramafic bodies were accreted to Timor during Late Miocene to present arc-continent collision. One of the lherzolitic ultramafic bodies near Caicua was previously unknown, but yields clear isotopic indicators that it is kin to the Hili Manu mafic and ultramafic complex further to the west. Zircon grains from metagabbro of the Hili Manu complex have cores with mostly Early Permian ages and rims of Latest Miocene ages. Isotopic analysis indicates abyssal plain, or passive margin affinity of the Caicua ultramafic body. One important exception to this pattern are mafic and ultramafic bodies associated with the Ocussi volcanics, which yield Miocene and Pliocene ages and supra-subduction zone chemical signatures. The Ocussi body is clearly part of the upper plate of the collision and formed after collision initiated further to the east. It is also structurally higher than the Hili Manu complex and has no affinities with the Australian plate. This study documents that both the upper and lower plates of the active arc-continent collision contribute mafic and ultramafic rocks to the evolving suture zone between the Indo-Australian and Asian plates in the Banda Arc region.

  4. Petrogenesis and tectonic implications of the Neoproterozoic Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China

    Yang, Yi-Jin; Zhu, Wei-Guang; Bai, Zhong-Jie; Zhong, Hong; Ye, Xian-Tao; Fan, Hong-Peng


    Mafic-ultramafic dykes are important geological markers that can punctuate the onset of crustal extension during the breakup of a continent and provide valuable information on the mantle source. This study reports secondary ion mass spectroscopy zircon and baddeleyite U-Pb ages, elemental and Nd isotopic data for the Datian mafic-ultramafic dykes in the Panzhihua area, western Yangtze Block, SW China. Two kinds of rocks are confirmed: the picritic rock and the dolerite. Based on petrographic and geochemical features, the dolerite dykes are further subdivided into two groups: Group I mafic and Group II mafic dykes, which emplaced at 760 Ma (zircon U-Pb) and 800 Ma (zircon and baddeleyite U-Pb), respectively. All samples from the picritic rocks and the Group I mafic rocks show the features of high-Ti and alkaline basaltic magma in composition as well as "humped" trace element patterns, which are similar to those of typical alkaline basalts associated with continental rifts except for the slightly negative Nb-Ta anomalies. The Group II mafic rocks display the features of low-Ti and tholeiitic magma, moderately enriched in LILE and LREE, and characterized by distinctively negative Nb-Ta anomalies. The primary magmas of the picritic rocks and the Group I mafic rocks were generated from ca 25 % partial melting of an OIB-like, Nd isotopically depleted but incompatible elements relatively enriched mantle source within a garnet stable field. The Group II mafic rocks crystallized from crustal contaminated mafic magmas that were derived from a spinel-bearing sub-continental lithospheric mantle source, because of low ratios of La/Yb, Ti/Y and Sm/Yb. Geochemical features suggest that these groups of mafic-ultramafic dykes were formed in a continental rift setting, but derived from different mantle sources. In combination with other Neoproterozoic igneous rocks in the western margin of Yangtze Block, it is suggested that the Datian mafic-ultramafic dykes in the Panzhihua area

  5. Transfer of volatiles and metals from mafic to felsic magmas in composite magma chambers: An experimental study

    Guo, Haihao; Audétat, Andreas


    In order to determine the behavior of metals and volatiles during intrusion of mafic magma into the base of silicic, upper crustal magma chambers, fluid-rock partition coefficients (Dfluid/rock) of Li, B, Na, S, Cl, K, Mn, Fe, Rb, Sr, Ba, Ce, Cu, Zn, Ag, Cd, Mo, As, Se, Sb, Te, W, Tl, Pb and Bi were determined experimentally at 2 kbar and 850 °C close to the solidus of mafic magma. In a first step, volatile-bearing mafic glasses were prepared by melting a natural basaltic trachyandesite in the presence of volatile-bearing fluids at 1200 °C/10 kbar in piston cylinder presses. The hydrous glasses were then equilibrated in subsequent experiments at 850 °C/2 kbar in cold-seal pressure vessels, which caused 80-90% of the melt to crystallize. After 0.5-2.0 days of equilibration, the exsolved fluid was trapped by means of in-situ fracturing in the form of synthetic fluid inclusions in quartz. Both the mafic rock residue and the fluid inclusions were subsequently analyzed by laser-ablation ICP-MS for major and trace elements. Reverse experiments were conducted by equilibrating metal-bearing aqueous solutions with rock powder and then trapping the fluid. In two additional experiments, information on relative element mobilities were obtained by reacting fluids that exsolved from crystallizing mafic magma with overlying silicic melts. The combined results suggest that under the studied conditions S, Cl, Cu, Se, Br, Cd and Te are most volatile (Dfluid/rock >10), followed by Li, B, Zn, As, Ag, Sb, Cs, W, Tl, Pb and Bi (Dfluid/rock = 1-10). Less volatile are Na, Mg, K, Ca, Mn, Fe, Rb, Sr, Mo and Rb (Dfluid/rock 0.1-1), and the least fluid-mobile elements are Al, Si, Ti, Zr, Ba and Ce (Dfluid/rock <0.1). This trend is broadly consistent with relative element volatilities determined on natural high-temperature fumarole gases, although some differences exist. Based on the volatility data and measured mineral-melt and sulfide-melt partition coefficients, volatile fluxing in

  6. Enigmatic Late-Stage Textures In Mafic Cumulates: Skaergaard Intrusion, East Greenland.

    Stripp, G.; Holness, M.; Veksler, I.


    The complexities of slow solidification in deep-seated silicate liquid bodies are poorly understood. Late-stage melt migration, due to compaction of the crystal mush, drives re-crystallisation and metasomatism which can have significant effects on chamber-wide chemical evolution. In this contribution we present novel textural observations from mafic cumulates of the Skaergaard Layered Intrusion which may shed light on liquid movement during the last stages of solidification of the crystal mush. Previously undescribed mafic symplectites are widespread in the Skaergaard Layered Series, and comprise vermicular intergrowths of plagioclase and olivine, which may be replaced by clinopyroxene in the outer parts of the symplectite. The symplectites grow outwards from Fe-Ti oxide grains, consuming adjacent cumulus plagioclase. In the Middle Zone of the Layered Series (where symplectites are best developed) symplectite plagioclase adjacent to the Fe-Ti oxide grains contains 1.2 wt% FeOtot which decreases to 0.6 wt% FeOtot at the symplectite margin, compared to a ~ 0.35 wt% average for adjacent cumulus plagioclase. Symplectite plagioclase is up to 40 mol% more An-rich than the adjacent cumulus grains. Olivine compositions range from Fo45 to Fo32 along the growth direction of the symplectite, compared to ~ Fo44 for cumulus olivine at this level in the intrusion. Biotite commonly replaces olivine. Texturally- and compositionally-related patches of intergrown clinopyroxene and An-rich plagioclase occur locally on plagioclase triple junctions and plagioclase grain boundaries. Symplectites are present, but rare, in the lower parts of the Skaergaard Layered Series; increase significantly in volumetric importance in Lower Zone b; are very common in Middle Zone and disappear in UZ. The symplectites resemble those formed by hydrous partial melting of oceanic gabbros (Koepke et al., 2005) but important differences include the presence of clinopyroxene and Fe-rich plagioclase, and the

  7. Evolution of the East African rift: Drip magmatism, lithospheric thinning and mafic volcanism

    Furman, Tanya; Nelson, Wendy R.; Elkins-Tanton, Linda T.


    The origin of the Ethiopian-Yemeni Oligocene flood basalt province is widely interpreted as representing mafic volcanism associated with the Afar mantle plume head, with minor contributions from the lithospheric mantle. We reinterpret the geochemical compositions of primitive Oligocene basalts and picrites as requiring a far more significant contribution from the metasomatized subcontinental lithospheric mantle than has been recognized previously. This region displays the fingerprints of mantle plume and lithospheric drip magmatism as predicted from numerical models. Metasomatized mantle lithosphere is not dynamically stable, and heating above the upwelling Afar plume caused metasomatized lithosphere with a significant pyroxenite component to drip into the asthenosphere and melt. This process generated the HT2 lavas observed today in restricted portions of Ethiopia and Yemen now separated by the Red Sea, suggesting a fundamental link between drip magmatism and the onset of rifting. Coeval HT1 and LT lavas, in contrast, were not generated by drip melting but instead originated from shallower, dominantly anhydrous peridotite. Looking more broadly across the East African Rift System in time and space, geochemical data support small volume volcanic events in Turkana (N. Kenya), Chyulu Hills (S. Kenya) and the Virunga province (Western Rift) to be derived ultimately from drip melting. The removal of the gravitationally unstable, metasomatized portion of the subcontinental lithospheric mantle via dripping is correlated in each case with periods of rapid uplift. The combined influence of thermo-mechanically thinned lithosphere and the Afar plume together thus controlled the locus of continental rift initiation between Africa and Arabia and provide dynamic support for the Ethiopian plateau.

  8. Mafic-crystal distributions, viscosities, and lava structures of some Hawaiian lava flows

    Rowland, Scott K.; Walker, George P. L.


    The distribution patterns of mafic phenocrysts in some Hawaiian basalt flows are consistent with simple in situ gravitational settling. We use the patterns to estimate the crystal settling velocity and hence viscosity of the lava, which in turn can be correlated with surface structures. Numerical modeling generates theoretical crystal concentration profiles through lava flow units of different thicknesses for differing settling velocities. By fitting these curves to field data, crystal-settling rates through the lavas can be estimated, from which the viscosities of the flows can be determined using Stokes' Law. Lavas in which the crystal settling velocity was relatively high (on the order of 5 × 10 -4 cm/sec) show great variations in phenocryst content, both from top to bottom of the same flow unit, and from one flow unit to another. Such lava is invariably pahoehoe, flow units of which are usually less than 1 m thick. Lavas in which the crystal-settling velocity was low show a small but measurable variation in phenocryst content. These lavas are part of a progression from a rough pahoehoe to toothpaste lava to a'a. Toothpaste lava is characterized by spiny texture as well as the ability to retain surface grooves during solidification, and flow units are usually thicker than 1 m. In the thickest of Hawaiian a'a flows, those of the distal type, no systematic crystal variations are observed, and high viscosity coupled with a finite yield strength prevented crystal settling. The amount of crystal settling in pahoehoe indicates that the viscosity ranged from 600 to 6000 Pa s. The limited amount of settling in toothpaste lava indicates a viscosity greater than this value, approaching 12,000 Pa s. We infer that distal-type a'a had a higher viscosity still and also possessed a yield strength.

  9. Oceanic mafic magmatism in the Siletz terrane, NW North America: Fragments of an Eocene oceanic plateau?

    Phillips, Bethan A.; Kerr, Andrew C.; Mullen, Emily K.; Weis, Dominique


    The Siletz terrane, a predominantly mafic accreted oceanic terrane, is located in the Cascadia forearc region of Oregon, Washington and Vancouver Island. The terrane represents a late Palaeocene-Eocene large igneous province that consists of pillow lavas, massive flows and intrusive sheets. Previously it has been proposed that the Siletz terrane represents either an accreted oceanic plateau, hotspot island chain, backarc basin, island arc, or a sequence of slab window volcanics. A province-wide geochemical reassessment of the terrane, including new high precision Sr-Pb-Nd-Hf isotope data, has been used to assess the validity of the proposed tectonomagmatic models for the Siletz terrane. The trace element data show little evidence of crustal contamination, or an arc signature, and the samples have rare earth element (REE) patterns that are flat to light REE enriched. These features are similar to other oceanic plateaus such as the Ontong Java and the Caribbean. Initial isotope ratios range from 206Pb/204 Pb: 18.751 to 19.668, 207Pb/204Pb: 15.507 to 15.661, 208Pb/204Pb: 38.294 to 39.2128, 176Hf/177Hf: 0.28300 to 0.28316 (εHf: 9.0 to 14.5), 143Nd/144Nd: 0.51282 to 0.51299 (εNd: 5.0 to 8.1) and 87Sr/86Sr: 0.70302 to 0.70380. These data are consistent with a mantle source of the Siletz terrane that appears to have been heterogeneous and slightly enriched. The enriched signature has characteristics of both EM2 and HIMU components and this, combined with a calculated mantle potential temperature well above ambient mantle, indicates derivation of the Siletz magmatism from a mantle plume, possibly the Yellowstone Hotspot. We therefore conclude that the Siletz terrane represents an accreted oceanic plateau.

  10. Geochemistry and Petrogenesis of Neoarchean Metamorphic Mafic Rocks in the Wutai Complex

    L(U) Yongjun; LIU Shuwen; Guochun ZHAO; LI Qiugen; Jian ZHANG; LIU Chaohui; K. H. PARK; Y. S. SONG


    Neoarchean metamorphic mafic rocks in the lower and the middle Wutai Complex mainly comprise metamorphic gabbros, amphibolites and chlorite schists. They can be subdivided into three groups according to chondrite normalized REE patterns. Rocks in Group #1 are characterized by nearly flat REE patterns (Lan/Ybn=0.86-1.3), the lowest total REEs (29-52 ppm), and weak negative to positive Eu anomalies (Eun/Eun*=0.84-1.02), nearly flat primitive mantle normalized patterns and strong negative Zr(Hf) anomalies. Their geochemical characteristics in REEs and trace elements are similar to those of ocean plateau tholeiite, which imply that this group of rocks can represent remnants of Archean oceanic crust derived from a mantle plume. Rocks in Group #2 are characterized by moderate total REEs (34-116 ppm), LREE-enriched (Lan/Ybn=1.76-4.34) chondrite normalized REE patterns with weak Eu anomalies (Eun/Eun*=0.76-1.16), and negative Nb, Ta, Zr(Hf), Ti anomalies in the primitive mantle normalized spider diagram. The REE and trace element characteristics indicate that they represent arc magmas originating from a sub-arc mantle wedge metasomatized by slabderived fluids. Rocks in Group #3 are characterized by the highest total REEs (61-192 ppm), the strongest LREEs enrichment (Lan/Ybn=7.12-16) with slightly negative Eu anomalies (Eun/Eun*=0.81-0.95) in the chondrite normalized diagram. In the primitive mantle normalized diagram,these rocks are characterized by large negative anomalies in Nb, Ta, Ti, negative to no Zr anomalies.They represent arc magmas originating from a sub-arc mantle wedge enriched in slab-derived melts.The three groups of rocks imply that the formation of the Neoarchean Wutai Complex is related to mantle plumes and island-arc interaction.

  11. The Origin and Emplacement Patterns of Paleoproterozoic (2.5-1.8 Ga) Mafic/Ultramafic Magmatism

    Heaman, L. M.


    The Paleoproterozoic (~2.5-1.8 Ga) is a stunning period in Earth history where numerous giant dyke swarms were emplaced and can be found transecting Archean cratons worldwide, the onset of this magmatism follows closely the ~2.6 Ga stabilization of most Archean cratons. Based on conservative estimates, the volumes of basaltic magma produced in the Paleoproterozoic rival more contemporary LIPs (>1M km3). Often, only the root zones of Paleoproterozoic LIPs are preserved (mafic/ultramafic dyke swarms and layered mafic intrusions) so the complete erosion of the volcanic succession in many examples, the repeated emplacement of dyke swarms into zones of crustal weakness over protracted periods of time (e.g. >400 m.y.), and the fact that some Proterozoic LIPs are metamorphosed adds to the difficulty in deciphering their origin. Equally challenging is determining whether this period of voluminous outpouring of mafic magma could be the cause of several unique features of Earth evolution at this time; for example, triggering extreme climate conditions, initiating the abrupt increase in the oxygen content of the atmosphere, promoting the rapid production of banded iron formations, causing isobaric high-grade metamorphism and granite production in the lower crust, and contributing to substantial downward continental root growth through underplating of basaltic magma. Based on a compilation of more than 200 precise and accurate U-Pb dates for Paleoproterozoic mafic/ultramafic dykes, sills and layered mafic intrusions, at least three synchronous global events (~2.50, 2.23, and 1.88 Ga) and two active mantle-derived magmatic cycles can be identified in the period 2.5-1.8 Ga (2520-2370 and 2230-1820 Ma), with a distinct hiatus between 2370 and 2230 Ma. The beginning of each magmatic cycle is represented by the widespread emplacement of dyke swarms on several cratons within a relatively short time interval of ~20 m.y. In the Superior Province, Canada the onset of 2.52-2.50 Ga mafic

  12. Temporal magma dynamics during solidification of the mafic-silicic complex of Isle au Haut, Maine

    Patwardhan, Kaustubh

    The Isle au Haut Igneous Complex provides a unique opportunity to examine in detail the in situ physical and chemical interactions between contemporaneously emplaced mafic and silicic magmas. The complex contains a 600 m thick sequence of 11 alternating layers of gabbro and diorite (typically 15--40 m thick). Purely on the basis of density contrasts (2.65 g/cm 3 gabbro vs. 2.55 g/cm3 diorite), the entire system should have undergone wholesale instability and mixing; it is instead arrested in a grossly unstable state of interaction while molten. Chilled margins along the lower contacts of the gabbros and structural integrity of the diorite layers indicate that near liquidus gabbroic magma invaded partly crystalline, cooler diorite. Mineral assemblages, chemical analyses, and phase equilibria calculations indicate initial temperatures during emplacement of ˜1180°C (gabbro) and ˜1000°C (diorite). Conductive thermal models yield solidification timescales of 15--60 years for individual gabbro layers and about a thousand years for the entire complex. There is ample evidence for two phases of small-scale interfacial Rayleigh-Taylor type instabilities of dioritic melt into the gabbros. Phase I occurred immediately upon gabbro emplacement whereas evenly spaced, slender more silicic pipes represent a much later stage (Phase II). Pipe geometry and spacing, estimated viscosities of the gabbroic magma and silicic melt, and the sudden increase in silica near the upper contact of the diorite, all indicate a thin (˜18--53 cm) buoyant layer at the upper contact of the diorite as the source of the pipes. Compaction of the diorite produced this layer over a period of about ten years. Simultaneous solidification along the lower contact of the overlying gabbro, thickening inwards, increased viscosity enough to arrest pipe ascent after a few meters. Crystal size distribution (CSD) analyses of the gabbro layers yield crystal growth rates (G0 = 2--4 x 10-10 cm/s) and nucleation rates

  13. Hafnium-neodymium constraints on source heterogeneity of the economic ultramafic-mafic Noril'sk-1 intrusion (Russia)

    Malitch, K. N.; Belousova, E. A.; Griffin, W. L.; Badanina, I. Yu.


    The ultramafic-mafic Noril'sk-1 intrusion in Polar Siberia (Russia) hosts one of the world's major platinum-group-element (PGE)-Cusbnd Ni sulphide deposits. In situ Hf-isotope analyses of zircon and baddeleyite, combined with whole-rock Nd-isotope results, identify three distinct clusters of Hfsbnd Nd isotope values restricted to different lithological units (e.g., gabbro-diorite, unmineralised layered sequence gabbros, and mineralised portions, represented by ultramafic and taxitic-textured rocks). Hf-isotope signatures of zircon and baddeleyite from unmineralized mafic rocks (ɛHf from 7.3 ± 1.1 to 11.4 ± 0.3) reflect the dominant role of mantle-derived magmas and suggest that a juvenile mantle was one of the main sources for the ultramafic-mafic Noril'sk-1 intrusion. The less radiogenic Hf-isotope values for zircons from mineralised rocks (ɛHf from 4.9 ± 1.4 to 6.4 ± 1.2) and gabbro-diorite (ɛHf - 1.2 ± 1.9) are indicative of involvement of distinct source components, possibly equivalent to a subcontinental lithospheric mantle and a continental crust, respectively. The significant range in the initial 176Hf/177Hf values of unmineralised rocks and mineralised lithologies indicates interaction of distinct magma sources during formation of the Noril'sk-1 intrusion. Our new findings, in conjunction with whole-rock Nd-isotope results, imply that economic intrusions hosting PGE-Cusbnd Ni deposits of the Noril'sk area have a far more complex magmatic history than is commonly assumed.

  14. Mafic Volcanism Along the Sinaloa Coast, Mexico, and its Relation to the Opening of the Gulf of California

    Orozco Esquivel, T.; Ferrari, L.; Lopez Martinez, M.


    We report on new localities with mafic volcanism along the Sinaloa coast, which record changes in the magma generation processes along the eastern margin of the Gulf of California. South of Culiacán, Sinaloa, isolated outcrops of basaltic lavas built a ca. 60 km long belt aligned to the SE. The similarity in the mineralogy and composition of the lavas suggest that these outcrops could have been part of a single flow. Lavas contain abundant plagioclase (up to 3 mm), and olivine (up to 1.5 mm) phenocrysts, and scarce clinopyroxene, in a relatively coarse matrix. In multiement diagrams, the lavas show the negative Nb and Ta, and positive Pb and Sr anomalies characteristic of subduction related rocks. The age determination of these rocks is in process, nevertheless, rocks with similar compositions are known from ~11 Ma mafic dikes that outcrop in southern Sinaloa. The Pericos volcanic field, located about 25 km to the NW of Culiacán is composed by lava flows, shield volcanoes, and cinder cones of basaltic composition that cover an area of aprox. 20 x 32 km, and have a well preserved morphology suggestive of a Pliocene-Quaternary age. Lavas are porphyritic and contain olivine, plagioclase and clinopyroxene in a microcrystalline matrix. Some lava flows contain abundant megacrysts of green clinopyroxene (up to 8 cm), olivine (up to 1 cm), and/or plagioclase (up to 1 cm), or aggregates of olivine and clinopyroxene. Trace element abundances are remarkably uniform among all analyzed samples and are characteristic of intraplate magmas. Rocks with very similar composition, mineralogy, and also containing megacrysts, have been reported in the Pliocene Punta Piaxtla and Mesa Cacaxtla, located 200 km to the SSE at the Sinaloa coast. Those similarities indicate that mafic intraplate volcanism related to the opening of the Gulf of California is more broadly represented in the area than previously considered.

  15. Mapping the 3-D extent of the Northern Lobe of the Bushveld layered mafic intrusion from geophysical data

    Finn, Carol A.; Bedrosian, Paul A.; Cole, Janine; Khoza, Tshepo David; Webb, Susan J.


    Geophysical models image the 3D geometry of the mafic portion of the Bushveld Complex north of the Thabazimbi-Murchison Lineament (TML), critical for understanding the origin of the world's largest layered mafic intrusion and platinum group element deposits. The combination of the gravity and magnetic data with recent seismic, MT, borehole and rock property measurements powerfully constrains the models. The intrusion north of the TML is generally shallowly buried (generally modeled area of ∼160 km × ∼125 km. The modeled thicknesses are not well constrained but vary from ∼12,000 m, averaging ∼4000 m. A feeder, suggested by a large modeled thickness (>10,000 m) and funnel shape, for Lower Zone magmas could have originated near the intersection of NS and NE trending TML faults under Mokopane. The TML has been thought to be the feeder zone for the entire Bushveld Complex but the identification of local feeders and/or dikes in the TML in the models is complicated by uncertainties on the syn- and post-Bushveld deformation history. However, modeled moderately thick high density material near the intersection of faults within the central and western TML may represent feeders for parts of the Bushveld Complex if deformation was minimal. The correspondence of flat, high resistivity and density regions reflect the sill-like geometry of the Bushveld Complex without evidence for feeders north of Mokopane. Magnetotelluric models indicate that the Transvaal sedimentary basin underlies much of the Bushveld Complex north of the TML, further than previously thought and important because the degree of reaction and assimilation of the Transvaal rocks with the mafic magmas resulted in a variety of mineralization zones.

  16. Metallogenic Series Related to Permian Mafic Complex in North Xinjiang: Post-collisional Stage or Mantle Plume Result?

    WANG Yuwang; WANG Jingbin; WANG Lijuan; LONG Lingli


    There are four deposit types related to a Permian mafic complex in northern Xinjiang, i.e.,copper-nickel sulfide deposit, vanadic titanomagnetite deposit, magnetite (-cobalt) deposit and Cu-Ni-VTiFe composite deposit. The deposits are distributed spanning tectonic units with dose andconsecutive metallogenic ages. A transitional deposit type can occur among the end-member deposits.Trace elements of host rocks show that they can derive from similar source area. Hence, theyconstitute a particular metallogenic series related to a mafic-ultramafic complex that is also a symbolseries of the post-collisional stage of the Central Asia Metallogenic Province (CAMP). Themetallogenic ages of the series are between 260 Ma and 300 Ma throughout the Permian. Unlikemineralization from a mantle plume, the metallogenic period of this series spans at least 40 Ma.Compared with related deposits of the Emeishan mantle plume, the North Xinjiang series has asimilar ore-forming element assemblage but has preferably developed Cu-Ni sulfide deposits ratherthan vanadic titanomagnetite deposits. In concomitance with this series, North Xinjiang area hasdeveloped a set of syntectonic Au-Cu-Mo metailogenic series related to a felsic volcanic-intrusivecomplex, which might indicate that there is no direct relationship with mantle plume activity. Fromearly to late, i.e., the sequence of copper-nickel sulfide to magnetite (-cobalt) to vanadictitanomagnetite deposit, the host rock series evolves from mafic-ultramafic and tholeiite series tomafic and alkalic series, the ∑REE content tends to increase with increasing of REE fractionation, andsome of the trace elements (particularly LIL) also show an increasing tendency. The aboveevolutionary regularity possibly reflects a course where the magma source deepens and thermalinterface moves down, energy gradually exhausts, and neo-continentai crust forming in the post-collision stage tends to stabilize.

  17. Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites

    Tollari, N.; Baker, D. R.; Barnes, S.-J.


    Apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes. We investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes. Apatite saturation gives information about the formation of silicate rocks, and is of interest in explaining the formation of apatite-oxide-rich rocks (e.g. nelsonites comprising approximately, one-third apatite and two-third Fe-Ti oxide). Two models of formation are proposed for this rock type: crystal fractionation followed by accumulation of apatite and Fe-Ti oxides and liquid immiscibility. New experiments carried out with mafic compositions at 500 MPa confirm that the most important variables on phosphate saturation are SiO2 and CaO. Fluorine addition leads to apatite saturation at lower SiO2 and higher CaO concentrations. Comparison of our results with those of previous experimental studies on liquid-liquid immiscibility at upper-to-mid-crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid-liquid immiscibility in the petrogenesis of nelsonites and similar rocks. The liquid line of descent of three natural examples studied (the Sept-Îles intrusive suite, the anorthositic Complex of the Lac-St-Jean and the Skaergaard layered intrusion) do not cross the liquid-liquid immiscibility field before they reach apatite saturation. Thus, the apatite-oxide-rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and Fe-Ti oxides.

  18. Rb-Sr and Nd-Sr isotope geochemistry and petrogenesis of the Misho Mountains mafic dikes (NW Iran

    Maryam Ahankoub


    Full Text Available Introduction There are some theories about the Paleotethys event during the Paleozoic that have been proposed by geologists (Metcalfe, 2006. Some scientist offered some pieces of evidence about the northern margin of Gondwana (Zhu et al., 2010. The Paleotethys Ocean and Hercynian orogenic report first in Iran, have been Offered from the Morrow and Misho Mountain (Eftekharnejad, 1981. Misho Mountains is located between the north and south Misho faults and cause the formation of a positive flower structure (Moayyed and Hossainzade, 2011. There is theory about Misho southern fault as the best candidate of the Paleotethys suture zone (Moayyed and Hossainzade, 2011. Geochemistry and Sr –Nd isotopic data of the A2 granitic and Synite rocks of the East Misho, indicate that the magmatism post collision has occurred in the active continental margin by extensional zones of the following the closure of the Paleotethys (Ahankoub, 2012. Granite and syenite rocks have been cut by mafic dikes. Mafic dikes are often formed in extensional tectonic settings related to mantle plume or continental break –up (Zhu et al., 2009. In this paper, we use the geochemistry and Nd-Sr isotope data to determined petrogenesis, tectono-magmatic setting and age of Misho mafic dikes. Materials and methods After petrography study of 30 thin sections of mafic dike rocks, 8 samples were selected for whole-rock chemical analyses using ICP-MS and ICP-AES instruments by ACME Company in Vancouver, Canada. We prepared 6 sample For Sm-Nd and Rb-Sr analysis. Sr and Nd isotope ratios were measured with a thermal ionization mass spectrometer, VG Sector 54–30 at the Nagoya University. The isotope abundances of Rb, Sr, Nd, and Sm were measured by the ID method with a Finnigan MAT Thermoquad THQ thermal ionization quadrupole mass spectrometer at the Nagoya University. NBS987 and JNdi-1 were measured as natural Sr and Nd isotope ratio standards (Tanaka et al., 2000. Averages and 2σ errors

  19. Geochemical characteristics and tectonic setting of the Tuerkubantao mafic-ultramafic intrusion in West Junggar, Xinjiang, China

    Yufeng Deng


    Full Text Available Mineral chemistry, whole-rock major oxide, and trace element compositions have been determined for the Tuerkubantao mafic-ultramafic intrusion, in order to understand the early Paleozoic tectonic evolution of the West Junggar orogenic belt at the southern margin of the Central Asian orogenic belt. The Tuerkubantao mafic-ultramafic intrusion is a well-differentiated complex comprising peridotite, olivine pyroxenite, gabbro, and diorite. The ultramafic rocks are mostly seen in the central part of the intrusion and surrounded by mafic rocks. The Tuerkubantao intrusive rocks are characterized by enrichment of large ion lithophile elements and depleted high field strength elements relative to N-MORB. In addition, the Tuerkubantao intrusion displays relatively low Th/U and Nb/U (1.13–2.98 and 2.53–7.02, respectively and high La/Nb and Ba/Nb (1.15–4.19 and 37.7–79.82, respectively. These features indicate that the primary magma of the intrusion was derived from partial melting of a previously metasomatized mantle source in a subduction setting. The trace element patterns of peridotites, gabbros, and diorite in the Tuerkubantao intrusion have sub-parallel trends, suggesting that the different rock types are related to each other by differentiation of the same primary magma. The intrusive contact between peridotite and gabbro clearly suggest that the Tuerkubantao is not a fragment of an ophiolite. However, the Tuerkubantao intrusion displays many similarities with Alaskan-type mafic-ultramafic intrusions along major sutures of Phanerozoic orogenic belts. Common features include their geodynamic setting, internal lithological zoning, and geochemistry. The striking similarities indicate that the middle Devonian Tuerkubantao intrusion likely formed in a subduction-related setting similar to that of the Alaskan-type intrusions. In combination with the Devonian magmatism and porphyry mineralization, we propose that subduction of the oceanic slab has

  20. Variable sediment flux in generation of Permian subduction-related mafic intrusions from the Yanbian region, NE China

    Guo, Feng; Li, Hongxia; Fan, Weiming; Li, Jingyan; Zhao, Liang; Huang, Miwei


    This paper presents petrology, mineralogy, zircon U-Pb ages, and whole-rock major, trace element and Sr-Nd-Hf isotopic compositions of four Permian (273-253 Ma) subduction-related mafic intrusions (including the Qinggoushan and Qianshan gabbros, and the Wangqing and Shuguang diorites) from the Yanbian region, NE China, with aims to understand the role of subducted sediment flux in generation of arc mafic cumulates. These intrusions have mineral assemblages crystallized in water-saturated parental magmas and show variable degrees of crystal accumulation as observed in mafic cumulates in subduction zones. Mass-balance consideration indicates that their parental magmas were calc-alkaline with arc-type trace element features (enrichments in large ion lithophile elements (LILE) and light rare earth elements (LREE) and depletions in Nb-Ta). They also have Sr-Nd-Hf isotopic compositions, i.e., 87Sr/86Sr(i) = 0.7029-0.7047, εNd(t) = + 0.9 ~ + 6.8, εHf(t) = + 5.6 ~ + 14.6, similar to modern arc basalts. The parental magmas were likely derived from a mantle wedge variably metasomatized by sediment melt and fluid from the subducting paleo-Asian Oceanic slab. Combined trace elemental and isotopic modeling results suggest that the parental magma of Qinggoushan gabbro was formed through 5-20% melting of the mantle wedge with 1% and 1.5% additions of sediment fluid and sediment melt, respectively; 5-10% melting of the mantle wedge through inputs of 1% sediment fluid and 2% sediment melt produced the Qianshan gabbro; 10-20% melting of the mantle wedge with additions of 1% sediment fluid and 3% sediment melt formed the Wangqing diorite; whereas 5-20% melting of the mantle wedge through an input of 1.5% sediment melt produced the Shuguang diorite. The Hf-Nd isotopic array of the Yanbian Permian mafic intrusions reflected the existence of an Indian Ocean-type mantle, which was isotopically distinct from the Pacific-type mantle during early Paleozoic in the Central Asian Orogenic

  1. The Cerro Bitiche Andesitic Field: petrological diversity and implications for magmatic evolution of mafic volcanic centers from the northern Puna

    Maro, Guadalupe; Caffe, Pablo J.


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

  2. Global absorption center map of the mafic minerals on the Moon as viewed by CE-1 IIM data


    Determining the global distribution of minerals on the Moon has been an important goal of lunar science. Hyperspectral remote sensing is an important approach to acquiring minerals on the Moon on the global scale. The wavelength of the absorption band center is the key parameter for identifying minerals with reflectance spectra as well as remote sensing data. The global absorption center map of the mafic minerals of the Moon was produced for the first time with the Chang’E-1 IIM data. This map shows the global distribution of mafic minerals such as orthopyroxenes, clinopyroxenes, and olivine and even plagioclase feldspar of the Moon. The validation for some representative areas indicates that the global map is reliable and even more detailed than the results derived from Clementine-data. Moreover, our method is insensitive to the topography and viewing and illumination geometries. The global absorption band center map not only contributes to the lunar science research, but also has other implications to be further studied. Moreover, the preprocessing methods such as calibration and correction introduced in this study can be useful in other research with IIM data.

  3. East Scandinavian and Noril'sk plume mafic large igneous provinces of Pd-Pt ores: Geological and metallogenic comparison

    Mitrofanov, F. P.; Bayanova, T. B.; Korchagin, A. U.; Groshev, N. Yu.; Malitch, K. N.; Zhirov, D. V.; Mitrofanov, A. F.


    This paper compares the geological, geophysical, and isotopic geochemical data on the Paleoproterozoic East Scandinavian Pd-Pt province in the Baltic Shield and the Late Paleozoic Noril'sk Pd-Pt province in the Siberian Craton. Both provinces contain large magmatic PGE deposits: low-sulfide in the Baltic Shield and high-sulfide in the Siberian Craton. Multidisciplinary evidence shows that the East Scandinavian mafic large igneous province, which has a plume nature, is intracratonic and was not subjected to the crucial effect of subduction-related and other contamination processes, whereas the Noril'sk province is pericratonic with substantial crustal contamination of the intrusive processes. Low-sulfide Pd-Pt deposits dominate in the East Scandinavian province, while high-sulfide Ni-Cu-PGE deposits play the leading role in the Noril'sk province. The U-Pb, Sm-Nd, and Rb-Sr isotopic data indicate multistage and long-term (tens of millions of years) geological history of mafic large igneous provinces. The plume magmatism with specific geochemistry and metallogeny is probably related to lower mantle sources.

  4. Role of mafic and ultramafic rocks in drinking water quality and its potential health risk assessment, Northern Pakistan.

    Begum, Shaheen; Shah, Mohammad Tahir; Muhammad, Said; Khan, Sardar


    This study investigates the drinking water (groundwater and surface water) quality and potential risk assessment along mafic and ultramafic rocks in the Swat district of Khyber Pakhtunkhwa Provence, Pakistan. For this purpose, 82 groundwater and 33 surface water samples were collected and analyzed for physico-chemical parameters. Results showed that the majority of the physico-chemical parameters were found to be within the drinking water guidelines set by the World Health Organization. However, major cationic metals such as magnesium (Mg), and trace metals (TM) including iron (Fe), manganese (Mn), nickel (Ni), chromium (Cr) and cobalt (Co) showed exceeded concentrations in 13%, 4%, 2%, 20%, 20% and 55% of water samples, respectively. Health risk assessment revealed that the non-carcinogenic effects or hazard quotient values through the oral ingestion pathway of water consumption for the TM (viz., Fe, Cr and Mn) were found to be greater than 1, could result in chronic risk to the exposed population. Results of statistical analyses revealed that mafic and ultramafic rocks are the main sources of metal contamination in drinking water, especially Ni and Cr. Both Ni and Cr have toxic health effects and therefore this study suggests that contaminated sites should be avoided or treated for drinking and domestic purposes.

  5. Chemical weathering on Mars - Thermodynamic stabilities of primary minerals /and their alteration products/ from mafic igneous rocks

    Gooding, J. L.


    Chemical weathering on Mars is examined theoretically from the standpoint of thermodynamic equilibrium between primary rock-forming minerals and the atmospheric gases O2, H2O, and CO2. The primary minerals considered are those common to mafic igneous rocks and include olivine, pyroxene, plagioclase, magnetite, troilite, pyrrhotite, and apatite. The importance of kinetics and reaction mechanisms in controlling possible weathering processes on Mars is discussed within the limits of currently available data, and the possible influence of liquid water on Martian weathering processes is evaluated where appropriate. For gas-solid weathering of mafic igneous rocks at the Martian surface, it is concluded that upon attainment of thermodynamic equilibrium: (1) oxides and carbonates should dominate the mineral assemblage of weathering products; (2) hematite rather than goethite should be the stable mineral form of Fe (III); (3) FeSO4 or FeSO4.H2O could be the stable weathering product of iron sulfides in the absence of liquid water; and (4) kaolinite is apparently the only clay mineral that should be thermodynamically stable over all ranges of temperature and water-vapor abundance at the Martian surface.

  6. Why do mafic arc magmas contain ˜4wt% water on average?

    Plank, Terry; Kelley, Katherine A.; Zimmer, Mindy M.; Hauri, Erik H.; Wallace, Paul J.


    The last 15 yr have seen an explosion of data on the volatile contents of magmas parental to arc volcanoes. This has occurred due to the intense study of melt inclusions trapped in volcanic phenocrysts, aliquots of magma that have presumably escaped degassing during eruption. The surprising first-order result is the narrow range in H2O concentrations in the least degassed melt inclusions from each volcano. Nearly all arc volcanoes are sourced with mafic magmas that contain 2-6 wt% H2O. The average for each arc varies even less, from 3.2 (for the Cascades) to 4.5 (for the Marianas), with a global average of 3.9±0.4 wt% H2O. Significant variations occur from volcano to volcano within each arc, but the means are indistinguishable within one s.d. The narrow range and common average value for H2O are in stark contrast to the concentrations of most other subduction tracers, such as Nb or Ba, which vary by orders of magnitude. A modulating process, either in the crust or mantle, is likely responsible for the restricted range in the H2O contents of arc melt inclusions. One possibility is that melt inclusion H2O values reflect vapor saturation at the last storage depth in the crust prior to eruption. In this scenario, magmas rise from the mantle with variable H2O contents (>4 wt%), become vapor-saturated and start degassing, and continue to degas up until the depth at which they stall. If the stalling depths are ∼6 km, which is common for storage depths beneath volcanoes, magmas would be saturated at ∼4 wt% H2O, and melt inclusions, most of which become closed during further ascent, would thus record ≤4 wt% H2O. Another possibility is that the mantle melting process modulates water content in the melt such that magmas rise out of the mantle with ∼4 wt% H2O. A strong relationship between the water content of the source, H2O(o) and the degree of melting (F) maintains nearly constant water contents in the melt for a restricted range in mantle temperature. Magmas with

  7. Ultradepleted adcumulates from a late-stage mafic dyke of the Bayantsagaan layered intrusion, Mongolia

    Chistyakova, Sofya; Latypov, Rais


    It is commonly expected that late-stage dykes in mafic layered intrusions must be strongly enriched in all incompatible components that are concentrated in the evolved residual melt. Our recent study of one late-stage dyke from the Bayantsagaan layered intrusion (Mongolia) has revealed, however, that this is not always the case. This 11 cm thick dyke is composed of quite fresh, fully crystalline troctolite with no signs of chilling against host leucotroctolite. Texturally, both dyke and leucotroctolite are composed of medium-grained plagioclase-olivine-magnetite cumulate. The dyke is, however, finer-grained and more adcumulate than leucotroctolite as evident from a much less amount of intercumulus material mainly represented by interstitial amphibole (5 vol.% versus 10 vol.%). The dyke shows three distinctive geochemical features. Firstly, it is compositionally more evolved than leucotroctolite as indicated by notably lower real and normative An-content of plagioclase, whole-rock Mg-number and Cr and higher whole-rock TiO2. Secondly, despite of being more evolved, the dyke is notably depleted in all incompatible components (e.g. K2O, Y, REE). Their concentrations in the dyke are several times lower than in host leucotroctolite (e.g. 0.015 ppm versus 0.112 ppm for Dy). Thirdly, the dyke reveals internal reverse zonation with an inward increase in compatible MgO, TiO2 and normative An-content and a decrease in all incompatible components (e.g. REE). Such a distribution of incompatible components is indicative of an inward decrease in the amount of trapped melt, in other words, the dyke becomes inwards progressively more adcumulate. In layered intrusions, adcumulates are commonly attributed to the almost complete removal of interstitial liquid enriched in incompatible elements from cumulate pile by some primary cumulus (e.g. in situ growth) or post-cumulus processes (e.g. compaction, compositional convection, thermal migration). These processes are, however, not

  8. Multiple remote sensing data sources to assess spatio-temporal patterns of fire incidence over Campos Amazônicos Savanna Vegetation Enclave (Brazilian Amazon).

    Alves, Daniel Borini; Pérez-Cabello, Fernando


    Fire activity plays an important role in the past, present and future of Earth system behavior. Monitoring and assessing spatial and temporal fire dynamics have a fundamental relevance in the understanding of ecological processes and the human impacts on different landscapes and multiple spatial scales. This work analyzes the spatio-temporal distribution of burned areas in one of the biggest savanna vegetation enclaves in the southern Brazilian Amazon, from 2000 to 2016, deriving information from multiple remote sensing data sources (Landsat and MODIS surface reflectance, TRMM pluviometry and Vegetation Continuous Field tree cover layers). A fire scars database with 30 m spatial resolution was generated using a Landsat time series. MODIS daily surface reflectance was used for accurate dating of the fire scars. TRMM pluviometry data were analyzed to dynamically establish time limits of the yearly dry season and burning periods. Burned area extent, frequency and recurrence were quantified comparing the results annually/seasonally. Additionally, Vegetation Continuous Field tree cover layers were used to analyze fire incidence over different types of tree cover domains. In the last seventeen years, 1.03millionha were burned within the study area, distributed across 1432 fire occurrences, highlighting 2005, 2010 and 2014 as the most affected years. Middle dry season fires represent 86.21% of the total burned areas and 32.05% of fire occurrences, affecting larger amount of higher density tree surfaces than other burning periods. The results provide new insights into the analysis of burned areas of the neotropical savannas, spatially and statistically reinforcing important aspects linked to the seasonality patterns of fire incidence in this landscape. Copyright © 2017 Elsevier B.V. All rights reserved.

  9. Mafic rocks from Erinpura gneiss terrane in the Sirohi region: Possible ocean-floor remnants in the foreland of the Delhi Fold Belt, NW India

    M K Pandit; H De Wall; H Daxberger; J Just; M Bestmann; K K Sharma


    A small isolated mafic body occurs to the south of Sirohi near village Daba within the Neoproterozoic Erinpura Granite in the southern sector of the Proterozoic Delhi Fold Belt in NW India. This mafic body occurs close to a 100 m wide NE–SW trending shear zone (Daba Shear Zone) which overprints the felsic rock fabrics. Further south, a small mafic body near village Kui was also sampled which forms the southern limit of the Phulad Ophiolite Suite which is a 300 km long major NE–SW trending lineament, described as Western Margin Fault. Some of the lithological components of the Daba mafic body show locally preserved magmatic fabric but completely transformed mineralogies under lower amphibolites facies metamorphic conditions where two-stage deformation has been inferred. Magnetic fabric analysis underlines a general correspondence of structural elements in both felsic and mafic lithologies. Binary correlations of Zr with other high field strength elements underline fractionation as the main process in the evolution of Daba and Kui rocks. Geochemical characteristics indicate subalkaline tholeiitic basalt affinity for these mafic rocks. The trace element characteristics, such as enriched LIL elements, high Th, absence of negative Nb anomalies and depletion in compatible elements in Daba samples suggest an enriched mantle source and lower degree of melting. The trace and rare earth element characteristics for Kui (Th anomaly, Nb–Ta trough and less spiked patterns, flat REE trends) indicate derivation from a refractory mantle source affected by fluids derived from subduction. Distinct differences in trace and REE characteristics between Daba and Kui can be interpreted in terms of different stages of ophiolite development.

  10. Geochronology and Sr–Nd–Hf isotopic composition of the granites, enclaves, and dikes in the Karamay area, NW China: Insights into late Carboniferous crustal growth of West Junggar

    Di Li


    Full Text Available New whole-rock major and trace elements, and zircon U–Pb and Hf–Nd isotope compositions are reported for the Karamay dikes, enclaves, and host granites in the West Junggar, NW China. Zircon U–Pb dating of the Karamay pluton yields an age of 300.7 ± 2.3 Ma for the enclave and 300.0 ± 2.6 Ma for the host granite, which was intruded by dike with an age of 298 Ma. The host granites exhibit relatively low SiO2 contents and A/CNK and Ga/Al ratios, low initial 87Sr/86Sr ratios (0.703421–0.703526 and positive εHf(t (5.5–14.1 and εNd(t (7.3–8.1 values with a young model age, suggesting that they are I-type granites and were mainly derived from a juvenile lower crustal source. The enclaves and dikes belong to an andesitic calc-alkaline series and have high MgO concentrations at low silica content and positive εHf(t (7.6–13.2, 14.2–14.9 and εNd(t (6.8–8.3, ∼6.9 values. They are enriched in LILEs (Rb, Ba and U and LREE and depleted in HFSEs (Nb and Ta with insignificant negative Eu anomalies, indicating that the melts were derived from an enriched lithospheric mantle modified by subducted oceanic crust-derived melts and minor fluids, followed by fractional crystallization. The Karamay host granites and enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and lithospheric mantle-derived magmas, and were intruded by the unmixed dikes subsequently. The upwelling mantle through a slab window in an island arc environment might have triggered partial melting of the lithospheric mantle and its subsequent interaction with the granitic magma, further suggesting that the ridge subduction played an important role in the crustal growth of West Junggar.

  11. Eruption dynamics of the 7.7 ka Driftwood pumice-fall suggest mafic injection is a common eruption mechanism for Makushin Volcano, Alaska

    Lerner, A.; Crowley, P.; Hazlett, R. W.; Nicolaysen, K. E.


    Makushin Volcano on Unalaska Island, AK is potentially the most threatening volcano in the Aleutian chain, being close to the largest Aleutian towns of Dutch Harbor and Unalaska. This study reports the eruption chronology and triggering mechanism for the most recent highly explosive event, the 7.7 ka Driftwood Pumice-fall event. The Driftwood Pumice reaches thicknesses of over 2 m, and isopach contours estimate a total deposit volume of 0.3-0.9 km3, covering an area of at least 8100 km2. These reconstructions show an eruption on the scale of the 1980 Mt. St. Helens eruption, with a VEI of 4-5. In the field, the deposit was divided into four stratigraphic horizons from bottom to top, and tephra within these layers becomes systematically more mafic upward through the section, ranging from a basal low-SiO2 dacite (64 wt.% SiO2) to an upper medium-SiO2 andesite (61.5 wt.% SiO2). High-Ca plagioclase (An75-83) and high-Mg olivine (Mg69-75) grains within the pumice are in great disequilibrium with the dacitic glass (64-69 wt.% SiO2), suggesting their origin in a more mafic magma. Geochemical trends, disequilibrium mineral populations, and mineral zonation patterns within these plagioclase and olivine xenocrysts show evidence of magma mixing between a bulk siliceous magma chamber and a mafic injection. The amount of the mafic component increases upward within the deposit, ranging from 0-25% throughout the section. The mafic injection is calculated to have been ~110-200 °C hotter than the siliceous magma chamber. The thermal pulse provided by the injection likely initiated convection and volatile exsolution within the siliceous magma body, ultimately causing the Driftwood Pumice eruption. Diffusion rates based on the thickness of lower-Mg rim zonations (<10 µm thick rims of Mg64) in the olivine xenocrysts show a lag-time of ~1 year between the basaltic injection and the resulting eruption. Similar delays between mafic injections and eruptions are seen in numerous other

  12. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: Occurrence of Archean oceanic plateau

    El Atrassi, Fatima; Debaille, Vinciane; Mattielli, Nadine; Berger, Julien


    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African craton in Mauritania (Amsaga area). The Amsaga Archean crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. We report the results of a combined petrologic, Sm-Nd isotopic, major element and rare earth element (REE) study of the Archean amphibolites in the West African craton. This study was conducted in order to characterize these rocks, to constrain the time of their formation and to evaluate their tectonic setting and their possible mantle source. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. They are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. These amphibolites have tholeiitic basalt composition. On a primitive mantle-normalized diagram, they display fairly flat patterns without negative anomalies for either Eu or Nb-Ta. We have shown using Sm-Nd whole rock isotopic data that these amphibolites formed at 3.3 ±0.075 Ga. They have positive ɛNdi values (+5.2 ± 1.6). These samples show isotopically juvenile features, which rule out the possibility of significant contamination of the protolith magmas by ancient continental crust. Based on these geochemical data we propose that the tholeiitic basalts were formed in an oceanic plateau tectonic setting from a mantle plume source and that they have a

  13. Amphibole-rich intrusive mafic and ultramafic rocks in arc settings: implications for the H2O budget

    Tiepolo, M.; Langone, A.; Morishita, T.; Esna-Ashari, A.; Tribuzio, R.


    Although amphibole is rarely a phenocryst of arc lavas, many intermediate and silicic magmas in arc settings are considered residual after cryptic amphibole crystallization at mid-low crustal levels (e.g., Davidson et al., 2007). Amphibole-rich mafic and ultramafic intrusive rocks (hornblendites, amphibole-gabbros to amphibole-diorites) are reported worldwide in orogenic settings. These amphibole-rich plutonics could be the "hidden" amphibole reservoir invoked in the arc crust. They usually possess chemical and textural heterogeneities recording the magmatic processes occurring in the mid to low crust (e.g., Tiepolo et al., 2011). Being amphibole-rich, these intrusive rocks are an important source of information on the possible role played by amphibole in arc magma petrogenesis. In particular, for the capability of amphibole to incorporate H2O and elements with a marked affinity for the fluid phase, these rocks are also useful to track the origin and evolution of subduction related fluids. We present here geochemical and geochronologic data on amphibole-rich ultramafic intrusive rocks from different localities worldwide: i) Alpine Orogen (Adamello Batholith and Bregell intrusions); ii) Ross Orogen (Husky Ridge intrusion - Antarctica); iv) Japan Arc (Shikanoshima Island intrusion); v) Sanandaj-Sirjan Zone, Central Iran (Aligoordaz granitoid complex). The coupling of textural information, micro-chemical data and "in situ" zircon geochronology has allowed us to show that these ultramafic intrusive rocks share striking petrologic and geochemical similarities. They are thus the expression of a common magmatic activity that is independent from the age and from the local geological setting and thus related to a specific petrogenetic process. Amphibole-rich mafic and ultramafic intrusive rocks are retained a common feature of collisional-systems worldwide. Amphibole is thus expected to play a major role in the differentiation of arc magmas and in particular in the H2O

  14. Mafic and ultramafic inclusions along the San Andreas Fault System: their geophysical character and effect on earthquake behavior, California, USA

    Ponce, D. A.; Langenheim, V. E.; Jachens, R. C.; Hildenbrand, T. G.


    Mafic and ultramafic rocks along the San Andreas Fault System (SAFS) influence earthquake processes where their geologic setting often provides information on the tectonic evolution of these large-scale strike-slip faults. In the northern part of the SAFS, along the Hayward Fault (HF), inversion of gravity and magnetic data indicate that seismicity avoids the interior of a large gabbro body and mechanical models may be able to explain how this massive mafic block influences the distribution of stress. Aftershocks of the M6.7 1989 Loma Prieta earthquake are also spatially related to the distribution of a gabbro body, clustering along the SAF and terminating at the NW end of the gabbro body where it abuts the fault surface. Based on geophysical modeling and a three-dimensional view of the subsurface geology and seismicity, aftershocks do not occur in the interior of the buried gabbro body. In the southern part of the SAFS, aftershocks and ruptures of the M7.1 1999 Hector Mine and M7.3 1992 Landers earthquakes avoid the interior of a Jurassic diorite that extends to depths of approximately 15 km and was probably an important influence on the rupture geometry of the these earthquakes. Seismicity prior to the Landers earthquake also tend to avoid the diorite, suggesting that it affects strain distribution. The San Jacinto Fault (SJF), a discontinuity within the Peninsular Ranges batholith (PRB), separates mafic, dense, and magnetic rocks of the western PRB from more felsic, less dense, and weakly magnetic rocks of the eastern PRB. The geophysical gradients do not cross the SJF zone, but instead bend to the northwest and coincide with the fault zone. Because emplacement of the PRB presumably welded across this older crustal boundary, the SJF zone probably developed along the favorably oriented margin of the dense, stronger western PRB. Two historical M6.7 earthquakes may have nucleated along the PRB discontinuity suggesting that the PRB may continue to affect how strain

  15. The timing of compositionally-zoned magma reservoirs and mafic 'priming' weeks before the 1912 Novarupta-Katmai rhyolite eruption

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


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

  16. Geochronologic and geochemical constraints of the petrogenesis of Permian mafic dykes in the Wuding area, SW China: Implications for Fe-Ti enrichment in mafic rocks in the ELIP

    Fan, Hong-Peng; Zhu, Wei-Guang; Bai, Zhong-Jie; Yang, Yi-Jin


    Mafic dykes are widely distributed and well preserved in the Wuding area, SW China. The dykes are composed of fine-grained diabases, which are further subdivided into two groups (Group I and Group II). The rocks from Group I have relatively higher MgO (4.95-6.16 wt%) and lower TiO2 (2.26-2.78 wt%) contents than those from the Group II rocks (MgO = 4.04-4.58 wt%; TiO2 = 4.09-4.55 wt%). Two baddeleyite ages of 264 ± 3 Ma and 256 ± 5 Ma from the Wuding dykes suggest that the ages of these dykes are similar to the plutonic bodies and the associated volcanic rocks of the Emeishan large igneous province (ELIP). The compositions and isotopic signatures of the dykes are also similar to those of the ELIP volcanic rocks, indicating derivation from the same magmatic event at 260 Ma. The primary melts of the Wuding dykes were originated by partial melting of a long-term depleted OIB-like mantle source. The Group I dykes were mainly formed by wallrock assimilation and fractional crystallization processes. The magmas parental to the Group II rocks were much more evolved than the magma parental to the Group I rocks and probably produced by wallrock assimilation and fractional crystallization of the parent magma of the Group I rocks. The increasing enrichment of Fe and Ti from the Group I to the Group II rocks were attributed to a fractional crystallization process which may be an epitome of enrichment of Fe and Ti in the Fe-Ti rich mafic intrusions of the ELIP.

  17. Crustal thickening prior to 220 Ma in the East Kunlun Orogenic Belt: Insights from the Late Triassic granitoids in the Xiao-Nuomuhong pluton

    Xia, Rui; Wang, Changming; Deng, Jun; Carranza, Emmanuel John M.; Li, Wenliang; Qing, Min


    The East Kunlun Orogenic Belt (EKOB) played an important role in plate tectonics, magma generation, and crustal evolution. Late Triassic granodiorites and their mafic micro-granular enclaves (MMEs) from Xiao-Nuomuhong in the EKOB were studied for geochemistry and geochronology to constrain their petrogenesis. Zircon LA-ICP-MS dating indicates that the Xiao-Nuomuhong granodiorites are coeval with their MMEs (∼222 Ma). The granodiorites are high-K calc-alkaline rocks that are enriched in Rb, Th, U and LREE, and depleted in Cr, Ni and HFSE, with high Sr/Y ratios (82.2-85.3) and geochemically resemble the lower crust-derived adakites. The MMEs are also high-K calc-alkaline rocks, with high Al2O3 (16.8-18.8 wt.%), low Mg# (30-40), Nb, Zr and Hf, with weak negative Eu anomalies (Eu/Eu# = 0.8-0.9). We suggest the MMEs are mafic magmatic globules that were injected into the felsic host magma. The adakitic rocks from the Xiao-Nuomuhong pluton were generated by partial melting of thickened crust, while the primitive compositions of the MMEs were most likely from the lithospheric mantle beneath the EKOB. The Late Triassic Xiao-Nuomuhong pluton is important evidence that crustal thickening in the EKOB occurred prior to 220 Ma. The pluton is interpreted as the result of mixing between thickened lower crust-derived melts and lithospheric mantle-derived mafic melts and the protracted magmatic response to the break-off of the Paleo-Tethys oceanic slab at ∼232 Ma.

  18. Seismic constraints on a large mafic intrusion with implications for the subsidence mechanism of the Danish Basin

    Sandrin, Alessandro; Thybo, Hans


    Seismic refraction data from the ESTRID-1 profile are used for seismic velocity modeling along the strike of a large mafic intrusion in the Norwegian-Danish Basin, central Denmark. The P wave velocity structure identifies a ~8 km thick sedimentary succession with velocities between 1.8 and 5.7 km...... the magma probably intruded during only a few events and other similar structures cover much of the basin. An anomalously high velocity gradient (from 7.0 km/s in the middle crust to 7.7 km/s at 30-32 km depth) in the central part of the intrusion coincides with an interval without Moho reflections...

  19. Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials

    Fourny, Anaïs.; Weis, Dominique; Scoates, James S.


    Controlling the accuracy and precision of geochemical analyses requires the use of characterized reference materials with matrices similar to those of the unknown samples being analyzed. We report a comprehensive Pb-Sr-Nd-Hf isotopic and trace element concentration data set, combined with quantitative phase analysis by XRD Rietveld refinement, for a wide range of mafic to ultramafic rock reference materials analyzed at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. The samples include a pyroxenite (NIM-P), five basalts (BHVO-2, BIR-1a, JB-3, BE-N, GSR-3), a diabase (W-2), a dolerite (DNC-1), a norite (NIM-N), and an anorthosite (AN-G); results from a leucogabbro (Stillwater) are also reported. Individual isotopic ratios determined by MC-ICP-MS and TIMS, and multielement analyses by HR-ICP-MS are reported with 4-12 complete analytical duplicates for each sample. The basaltic reference materials have coherent Sr and Nd isotopic ratios with external precision below 50 ppm (2SD) and below 100 ppm for Hf isotopes (except BIR-1a). For Pb isotopic reproducibility, several of the basalts (JB-3, BHVO-2) require acid leaching prior to dissolution. The plutonic reference materials also have coherent Sr and Nd isotopic ratios (<50 ppm), however, obtaining good reproducibility for Pb and Hf isotopic ratios is more challenging for NIM-P, NIM-N, and AN-G due to a variety of factors, including postcrystallization Pb mobility and the presence of accessory zircon. Collectively, these results form a comprehensive new database that can be used by the geochemical community for evaluating the radiogenic isotope and trace element compositions of volcanic and plutonic mafic-ultramafic rocks.

  20. The origin of spheroidal patterns of weathering in the Pados-Tundra mafic-ultramafic complex, Kola Peninsula, Russia

    A.Y. Barkov


    Full Text Available We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of “normal spheroidal weathering” sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo 87. 5, which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. % are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96 formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts during a deuteric (autometasomatic alteration. In contrast, oikocrystic Opx (En 86.0 is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr are observed. We infer that (1 the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2 Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3 The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions.

  1. Geochemistry and zircon ages of mafic dikes in the South Qinling, central China: evidence for late Neoproterozoic continental rifting in the northern Yangtze block

    Zhu, Xiyan; Chen, Fukun; Liu, Bingxiang; Zhang, He; Zhai, Mingguo


    Neoproterozoic volcanic-sedimentary sequences of the southern Qinling belt, central China, were intruded by voluminous mafic dikes. secondary ion mass spectrometry zircon U-Pb dating indicates that these dikes were emplaced at 650.8 ± 5.2 Ma, coeval with mafic rocks occurring at the northern margin of the Yangtze block. The dikes are characterized by enrichment of large ion lithophile elements, high Ti contents (up to 3.73 wt%) and Nb/Ta ratios between 14.5 and 19.6, suggesting a mantle source of oceanic island basalt affinity. Initial 87Sr/86Sr ratios show positive correlation with SiO2 contents and negative correlation with Zr/Nb ratios, implying that these rocks were affected by crustal contamination during the magma ascend and emplacement process. The dikes have initial ɛ Nd values of +0.2 to +3.3, low 206Pb/204Pb ratios of 16.96-17.45, and moderate 87Sr/86Sr ratios of 0.7043-0.7076, likely pointing to the involvement of an enriched mantle source. The mafic dikes and coeval mafic volcanic equivalents in the South Qinling and the northern Yangtze are hypothesized to be related with the prolonged breakup of the supercontinent Rodinia, suggesting that continental rifting lasted until ca. 650 Ma.

  2. Petrogenesis and tectonic implications of Triassic mafic complexes with MORB/OIB affinities from the western Garzê-Litang ophiolitic mélange, central Tibetan Plateau

    Liu, Bin; Ma, Chang-Qian; Guo, Yu-Heng; Xiong, Fu-Hao; Guo, Pan; Zhang, Xin


    Although numerous Paleo-Tethyan ophiolites with mid-oceanic ridge basalts (MORB) and/or oceanic-island basalt (OIB) affinities have been reported in the central Tibetan Plateau (CTP), the origin and tectonic nature of these ophiolites are not well understood. The petrogenesis, mantle sources and geodynamic setting of the mafic rocks from these ophiolites are unclear, which is the main reason for this uncertainty. In this paper, we present new geochronological, mineralogical and Sr-Nd isotopic data for the Chayong and Xiewu mafic complexes in the western Garzê-Litang suture zone (GLS), a typical Paleo-Tethyan suture crossing the CTP. Zircon LA-ICP-MS U-Pb ages of 234 ± 3 Ma and 236 ± 2 Ma can be interpreted as formation times of the Chayong and Xiewu mafic complexes, respectively. The basalts and gabbros of the Chayong complex exhibit enriched MORB (E-MORB) compositional affinities except for a weak depletion of Nb, Ta and Ti relative to the primitive mantle, whereas the basalts and gabbros of the Xiewu complex display distinct E-MORB and OIB affinities. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The geochemical and Sr-Nd isotopic data reveal that the Chayong mafic rocks may have been derived from depleted MORB-type mantle metasomatized by crustal components and Xiewu mafic rocks from enriched lithospheric mantle metasomatized by OIB-like components. The ratios of Zn/Fet, La/Yb and Sm/Yb indicate that these mafic melts were produced by the partial melting of garnet + minor spinel-bearing peridotite or spinel ± minor garnet-bearing peridotite. We propose that back-arc basin spreading associated with OIB/seamount recycling had occurred in the western GLS at least since the Middle Triassic times, and the decompression melting of the depleted MORB-type asthenosphere mantle and partial melting of sub-continental lithosphere were metasomatized by plume

  3. Mafic granulite xenoliths in the Chilka Lake suite, Eastern Ghats Belt, India: evidence of deep-subduction of residual oceanic crust

    S. Bhattacharya


    Full Text Available Granulite xenoliths preserve key geochemical and isotopic signatures of their mantle source regions. Mafic granulite and pyroxinite xenoliths within massif-type charnockitic rocks from the Eastern Ghats Belt have recently been reported by us. The mafic granulite xenoliths from the Chilka Lake granulite suite with abundant prograde biotite are geochemically akin to Oceanic Island Basalt (OIB. They can be distinguished from the hornblende-mafic granulite xenoliths with signatures of Arc-derived basalt occurring in the other suites of the Eastern Ghats Belt. These two groups of xenoliths in the Paleoproterozoic Eastern Ghats Province have quite distinct Nd-model ages- 1.9 Ga and 2.5 Ga respectively, which may be interpreted as their crustal residence ages. Strong positive Nb anomalies, indicating subducted oceanic crust in the source, LREE enrichment and strongly fractionated REE pattern are key geochemical signatures attesting to their origin as OIB-type magma. Also low Yb and Sc contents and high (La / YbN ratios can be attributed to melting in the presence of residual garnet and hence at great depths (> 80 km. The variable enrichment in radiogenic 87Sr, between 0.70052 and 0.71092 at 1.9 Ga and less radiogenic 143Nd between ε-1.54 and 7.46 are similar to those of the OIBs compared to MORBs. As OIBs commonly contain some recycled oceanic crust in their sources, we suggest that the residue of the oceanic crust from a previous melting event (~ 2.5 Ga that produced the Arc-derived basalts (protoliths of hornblende-mafic granulite xenoliths could have subducted to great depths and mechanically mixed with the mantle peridotite. A subsequent re-melting event of this mixed source might have occurred at ca. 1.9 Ga as testified by the crustal residence ages of the biotite-mafic granulite xenoliths of the Chilka Lake granulite suite.

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

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


    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.

  5. Geochemistry and petrology of Late Cretaceous subvolcanic rocks (Macka-Trabzon) in the north of the eastern Black Sea region, NE-Turkey

    Aydin, Faruk


    In this study, geochronological, geochemical and isotopical data for the early Campanian subvolcanic rocks (Macka-Trabzon) in the north of the eastern Blacksea region, northeastern Turkey, have initially been presented with the aim of determining its magma source and geodynamic evolution. The subvolcanic rocks cutting the subduction-related Late Cretaceous volcano-sedimantary rocks in the region are characterized by several sills and dykes with columnar structures and they consist of amphibole-rich quartz-diorite and quartz-tonalite porphyries, with some dioritic mafic microgranular enclaves. The host rocks have a microgranular porphyritic texture, and they contain 15-25% phenocryst of plagioclase and amphibole and have a matrix that is composed primarily of fine-grained quartz, orthoclase, and plagioclase. Accessory apatite, zircon and Fe-Ti oxides are present in all of the rocks. Secondary minerals such as epidote, calcite, sericite and clays are sometimes observed in the matrix or as hydothermal alteration products of some amphibole and plagioclase phenocrysts. When compared to the host rocks, the magmatic enclaves without quartz are fine-grained, and they contain higher ferromagnesian phases and lower feldspar minerals. Ar-Ar geochronology studies on the amphibole separates reveal that the porphyries have a crystallization ages of 81±0.5 Ma. All samples show a high-K calc-alkaline differentiation trend and I-type features with metaluminous character. The rocks and magmatic enclaves are characterized by enrichment of LILE and depletion of HFSE with negative Nb, Ti, Zr and P anomalies. The chondrite-normalized REE patterns are not fractionated [(La/Yb)N = 9-11] and do not display Eu anomalies (Eu/Eu* = 0.7-0.9). The porphyritic rocks and their enclaves are almost isotopically similar. Sr-Nd isotopic data for all of the samples display initial Sr = 0.7085-0.7087, epsilon Nd (81 Ma) = -6.0 to -6.9, with TDM = 1.38-1.63 Ga. The lead isotopic ratios are (206Pb/204Pb

  6. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: Evidence from petrological and in situ Sr-Hf isotopic data

    Chen, C. J.; Chen, B.; Li, Z.; Wang, Z. Q.


    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle in a back-arc extensional regime. The principal geochemical signatures of these Mesozoic rocks include a high-K calc-alkaline affinity, high values of Mg#, high Sr-Ba abundances, high Sr/Y and La/Yb ratios, εNd(t) = - 13.1 to - 9.0, and ISr = 0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and amphibole, (2) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (3) the negative correlations between whole-rock Nd and Sr isotopic ratios, and (4) the significant differences in the values of εHf(t) (- 9.5 to - 26) within different zircons from the same intrusion.

  7. Secure Enclaves-Enabled Technologies


    solution. Recommendations There is the potential to exploit extremely lucrative opportunities utilizing our first- mover advantage in this...emerging market segment. However, there is still significant work to be completed. The SE Enabled browser extension application is still in the early

  8. ¿Culturas o enclaves?

    Renán Vega Cantor


    Full Text Available Culturas bananeras. Producción, consumo y transformaciones socioambientales. John Solurivita Randazzo (Traducción Siglo del Hombre Editores, Universidad Nacional de Colombia, Bogotá, 2013, 396 págs., il.

  9. From Enclave to Linkage Economies?

    Hansen, Michael W.

    and local enterprises by themselves will indeed produce linkages, the scope, depth and development impacts of linkages eventually depend on government intervention. Resource-rich African countries’ governments are aware of this and linkage promotion is increasingly becoming a key element...

  10. Portuguese Enclaves: The Invisible Minority.

    Smith, M. Estellie

    This paper presents the identity profile which emerged in investigations conducted in various Portuguese-American communities, offers an explanation for the nature of the profile, and discusses the implications of the data. The historical raison d'etre which underlies all cultural identities is stressed. Without an understanding and reasonably…

  11. En-clave de Sol

    Louis Manfield


    Full Text Available Ha pasado más de medio año desde que tuviera lugar el estallido reivindicativo del 16-M y las sucesivas explosiones en las que derivó este movimiento asambleario. Ninguno de los que asistieron a la manifestación del domingo, 15 de mayo, podía imaginarse que estaban pisando el centro de lo que iba a ser el escenario de la protesta colectiva más mediática de este país. Pero la Acampada ha sido algo más que el material de relleno para los medios de (desinformación y trend topic en redes sociales. Para los que nos dedicamos, en este caso, a la sociología, SOL se nos presenta como un juguete. Un sofisticado artefacto (su compleja y espesa red organizativa así lo atestiguan para poner a prueba, in situ y participando, la plasticidad y elasticidad social de la creatividad contestataria que ha convertido a un movimiento definido como indignado en un modelo autónomo de organización horizontal. Una cámara del tiempo donde el corto, el medio y largo plazo se entrecruzan con el corto, medio y largo alcance. Una ventana desde la que observar y anticipar el cambio que ya se está produciendo en el seno de la sociedad.

  12. Grain to outcrop-scale frozen moments of dynamic magma mixing in the syenite magma chamber, Yelagiri Alkaline Complex, South India

    M.L. Renjith


    Full Text Available Magma mixing process is unusual in the petrogenesis of felsic rocks associated with alkaline complex worldwide. Here we present a rare example of magma mixing in syenite from the Yelagiri Alkaline Complex, South India. Yelagiri syenite is a reversely zoned massif with shoshonitic (Na2O + K2O=5–10 wt.%, Na2O/K2O = 0.5–2, TiO2 <0.7 wt.% and metaluminous character. Systematic modal variation of plagioclase (An11–16 Ab82–88, K-feldspar (Or27–95 Ab5–61, diopside (En34–40Fs11–18Wo46–49, biotite, and Ca-amphibole (edenite build up three syenite facies within it and imply the role of in-situ fractional crystallization (FC. Evidences such as (1 disequilibrium micro-textures in feldspars, (2 microgranular mafic enclaves (MME and (3 synplutonic dykes signify mixing of shoshonitic mafic magma (MgO = 4–5 wt.%, SiO2 = 54–59 wt.%, K2O/Na2O = 0.4–0.9 with syenite. Molecular-scale mixing of mafic magma resulted disequilibrium growth of feldspars in syenite. Physical entity of mafic magma preserved as MME due to high thermal-rheological contrast with syenite magma show various hybridization through chemical exchange, mechanical dilution enhanced by chaotic advection and phenocryst migration. In synplutonic dykes, disaggregation and mixing of mafic magma was confined within the conduit of injection. Major-oxides mass balance test quantified that approximately 0.6 portions of mafic magma had interacted with most evolved syenite magma and generated most hybridized MME and dyke samples. It is unique that all the rock types (syenite, MME and synplutonic dykes share similar shoshonitic and metaluminous character; mineral chemistry, REE content, coherent geochemical variation in Harker diagram suggest that mixing of magma between similar composition. Outcrop-scale features of crystal accumulation and flow fabrics also significant along with MME and synplutonic dykes in syenite suggesting that Yelagiri syenite magma chamber had evolved

  13. Mafic dyke swarms of the Bastar Craton, central India: geochemistry, Sr-Nd isotopes and tectonic implications

    Liao, Chien-Yi; Shellnutt, J. Gregory; Raghvan Hari, Kosiyathu; Viswakarma, Neeraj


    The Archean Bastar Craton of central India which is demarcated by Godivari rift in the west, Mahanadi rift in the east, Narmada-Son rift in the north and the Eastern Ghats Mobile Belt in the south was intruded by several generations of mafic dyke swarms during the Precambrian, with most of the dykes NW-SE to WNW-ESE trending. The dyke swarms can be subdivided into three main groups: the Meso-Neoarchean sub-alkaline mafic dykes (BD1), Neoarchean to Paleoproterozoic boninite-norite dykes (BN) and Paleoproterozoic sub-alkaline mafic dykes (BD2). In the present work, an attempt has been made to constrain the petrogenesis and tectonic implications of the dykes in the Bhanupratapur area of central Bastar Craton. Petrographically, the dykes are metabasites / metadolerites that experienced hydrothermal alteration, as most of the samples are moderately to highly altered. Primary minerals were replaced but still retain the original igneous texture (ophitic). The least-altered samples contain orthopyroxene, plagioclase, secondary amphibole, secondary quartz and some euhedral Fe-Ti oxides. The dykes can be classified into two groups according to major element data. Petrographically, the two groups cannot be clearly distinguished. Group 1 is sub-alkaline basalt (SiO2 = 51 wt%) with low magnesium (MgO = 4.6 to 7.2 wt%), low Mg-number (Mg# ≤ 53) and higher titanium (TiO2 ≥ 0.83 wt%). Group 2 is sub-alkaline basaltic andesite and has boninitic characteristics with higher silica (SiO2 = 51 to 56 wt%), higher magnesium (MgO = 5.9 to 19.1 wt%), higher Mg-number (Mg# = 50 to 79) and lower titanium (TiO2 ≤ 0.8 wt%). The chondrite-normalized REE patterns of Group 1 show variability in the light rare earth elements (La/SmN = 1.2 to 2.4). Group 2 exhibit light rare earth element enrichment (La/YbN = 2.2 to 10.4). The Sm-Nd isochron age of Group 1 is approximately 1.9 Ga, with the initial 87Sr/86Sr ratios range from 0.7029 to 0.7058 and ɛNd(t) values range from-0.9 to +1.8. Group 1

  14. Petrogenesis of Bir Madi Gabbro-Diorite and Tonalite-Granodiorite Intrusions in Southeastern Desert, Egypt: Implications for Tectono-Magmatic Processes at the Neoproterozoic Shield

    M. A. OBEID


    Full Text Available The Neoproterozoic rocks of the Bir Madi area, south eastern desert, comprise a Metagabbro-Diorite Complex (GDC and a Tonalite-Granodiorite Suite (TGrS. The GDC has a weak tonalitic to strong calc-alkaline character and is made up of olivine gabbro, hornblende gabbro, diorite and monzodiorite. The olivine gabbro is characterized by abun-dance of augite and labradorite with pseudomorphic serpentine. The hornblende gabbro is mainly composed of horn-blende, labradorite, andesine and minor amounts of quartz with or without augite. The diorite consists essentially of andesine, hornblende, biotite and quartz. The GDC is compositionally broad, with a wide range of SiO2 (46-57 % and pronounced enrichment in the LILE (Ba and Sr relative to the HFSE (Nb, Y and Zr. The GDC rocks exhibit petrological and geochemical characteristics of arc-related mafic magmas, derived possibly from partial melting of a mantle wedge above an early Pan-African subduction zone of the Neoproterozoic Shield. The tonalite and granodiorite have a calc-alkaline affinity and show the geochemical signatures of I-type granitoids. The TGrS contains amphibolite enclaves and foliated gabbroic xenoliths. Based on the field evidence and geochemical data, the GDC and TGrS are not related to a single magma type through fractional crystallization. The presence of microgranular amphibolite enclaves in the tonalitic rocks suggest against their generation by partial melting of a mantle-derived basaltic source. The tonalitic magma originated from partial melting of an amphibolitic lower crust by anatexis process at a volcanic arc regime during construction of the Arabian-Nubian Shield. Fractional crystallization of K-feldspar and biotite gave more developed granodiorite variety from the tonalitic magma. The gabbroic xenoliths are similar in the chemical composition to the investigated metagabbros. They are incompletely digested segments from the adjacent metagabbro rocks incorporated into the

  15. Crystal Zoning Constrains on the Processes and Time Scales Involved in Monogenetic Mafic Volcanism (Tenerife, Canary Islands)

    Albert, H.; Costa Rodriguez, F.; Marti, J.


    Most of the historical eruptive activity in Tenerife has been relatively mafic and mildly-explosive monogenetic eruptions, and thus it seems that this activity is the most likely in the near future. Here we investigate the processes and time scales that lead to such eruptions with the aim to better interpret and plan for any possible unrest in the island. We focus on three historical eruptions: Siete Fuentes (December 31 1704-January 1705), Fasnia (January 5-January 13 1705) and Arafo (February 2-February 26 1705) issued from a 10 km long basaltic fissure eruption oriented N45E and covering an area of 10.4 km2. The erupted volume increases by 5-fold from the first to the last eruption. All magmas are tephritic, although the bulk-rock becomes more mafic with time due to accumulation of olivine with Cr-spinel inclusions, and clinopyroxene rather than to the appearance of a truly more primitive melt. Olivine core compositions of the three eruptions range between Fo79 and Fo87. Frequency histograms show three main populations: at Fo79-80, Fo80-82 and Fo84-87 displaying normal and reverse zoning. Thermodynamic calculations show that only cores with Fo80-82 are in equilibrium with the whole rock. Clinopyroxene phenocrysts can have large pools of matrix glass and show rims of different composition. Only the rims, with Mg#84-86, are in equilibrium with the whole-rock. Considering olivine cores and clinopyroxene rims in equilibrium we obtained a temperature range of 1150-1165°C, and MELTS calculations suggest pressures of 1 to 5 kbar. The variety of olivine core populations reflects mixing and mingling between three different magmas, and their proportions have changed with time from Siete Fuentes to Arafo. Most crystals have complex zoning profiles that record two events: (1) one of magma mixing/mingling at depth, (2) another of magma transport and ascent to the surface. Magma mixing at depth ranges from about 3 months to two years and is similar for the three eruptions

  16. Petrogenesis and tectonic setting of the Bondla mafic-ultramafic complex, western India: Inferences from chromian spinel chemistry

    Ishwar-Kumar, C.; Rajesh, V. J.; Windley, B. F.; Razakamanana, T.; Itaya, T.; Babu, E. V. S. S. K.; Sajeev, K.


    Crustal-scale shear/suture zones hold prime importance because they are one of the critical parameters used for paleogeographic configurations of supercontinental assemblies. The Kumta suture, located on the western margin of peninsular India, has been interpreted as the eastern extension of the Betsimisaraka suture zone of Madagascar. This suture separates the Karwar block (ca. 3200 Ma tonalite-trondhjemite-granodiorite (TTG) and amphibolite) in the west from a quartzite-dominated shelf that overlies ca. 2571 Ma quartzo-feldspathic gneisses of the Dharwar block in the east. The NW/SE-trending Bondla ultramafic-mafic complex, situated in the arc just west of the Kumta suture, comprises gabbro, troctolite, wehrlite, dunite, peridotite, pyroxenite, chromitite and chromian spinel-bearing serpentinite. In this paper, we study the chemistry of Cr-spinels in chromitites and serpentinites to help understand their paleo-tectonic environments. The Cr-spinel in Bondla chromitites and serpentinites shows variations in Cr# [Cr/(Cr + Al)] ranging from 0.54 to 0.58 and 0.56 to 0.64 respectively; also, the Mg# [Mg/(Mg + Fe)] varies from 0.56 to 0.67 and 0.41 to 0.63 respectively. The Cr-spinels in serpentinites have strong chemical zoning with distinctive ferrian chromite rims (Mg# 0.41-0.63), whereas the Cr-spinels in chromitites are generally homogeneous with only occasional weak zoning. The spinel-core crystallization temperature in the serpentinite is estimated to be above 600 °C (the spinel stability field was calculated for equilibrium with Fo90 olivine), which suggests the core composition is chemically unaltered. The Cr-spinels in all studied samples have low-Al2O3 (15-23 wt%) and moderate to high-Cr# (0.54-0.69), suggesting derivation from a supra-subduction zone arc setting. The chemistry of clinopyroxene in serpentinite indicates a wide range of crystallization temperatures from 969 °C to 1241 °C at 1.0 GPa. The calculated parental magma composition was similar to

  17. The Ni-Cu-PGE mineralized Brejo Seco mafic-ultramafic layered intrusion, Riacho do Pontal Orogen: Onset of Tonian (ca. 900 Ma) continental rifting in Northeast Brazil

    Salgado, Silas Santos; Ferreira Filho, Cesar Fonseca; Caxito, Fabrício de Andrade; Uhlein, Alexandre; Dantas, Elton Luiz; Stevenson, Ross


    The Brejo Seco mafic-ultramafic Complex (BSC) occurs at the extreme northwest of the Riacho do Pontal Orogen Internal Zone, in the northern margin of the São Francisco Craton in Northeast Brazil. The stratigraphy of this medium size (3.5 km wide and 9 km long) layered intrusion consists of four main zones, from bottom to top: Lower Mafic Zone (LMZ; mainly troctolite), Ultramafic Zone (UZ; mainly dunite and minor troctolite); Transitional Mafic Zone (TMZ; mainly troctolite) and an Upper Mafic Zone (UMZ; gabbro and minor anorthosite, troctolite, and ilmenite magnetitite). Ni-Cu-PGE mineralization occurs at the contact of the UZ with the TMZ, consisting of an up to 50 m thick stratabound zone of disseminated magmatic sulfides. An Mg-tholeiitic affinity to the parental magma is indicated by the geochemical fractionation pattern, by the magmatic crystallization sequence and by the elevated Fo content in olivine. A Smsbnd Nd isochron yielded an age of 903 ± 20 Ma, interpreted as the age of crystallization, with initial εNd = 0.8. Evidence of interaction of the BSC parental magma with sialic crust is given by the Rare Earth and trace element patterns, and by slightly negative and overall low values of εNd(900 Ma) in between -0.2 and +3.3. Contrary to early interpretations that it might constitute an ophiolite complex, based mainly on the geochemistry of the host rocks (Morro Branco metavolcanosedimentary complex), here we interpret the BSC as a typical layered mafic-ultramafic intrusion in continental crust, related to an extensional regime. The BSC is chrono-correlated to mafic dyke swarms, anorogenic granites and thick bimodal volcanics of similar age and tectonic setting in the São Francisco Craton and surrounding areas. Intrusion of the BSC was followed by continued lithospheric thinning, which led to the development of the Paulistana Complex continental rift volcanics around 888 Ma and ultimately to plate separation and the generation of new oceanic crust (Monte

  18. Characteristics and origin of mafic and ultramafic xenoliths in trachyandesite lavas from Heikongshan volcano,Tengchong,Yunnan Province,China


    The trachyandesite lavas from Heikongshan volcano of the Tengchong volcanic cluster, Yunnan Province contain relatively abundant mafic and ultramafic small xenoliths comprising mainly gabbro, pyroxenite and rare lherzolites, all less than 2.5 cm in size. Gabbro xenoliths are characterized by "open" texture represented by relatively abundant vesicles and ground-mass fillings, while pyroxenite xenoliths are characterized by equigranular and poikilitic texture. Their mineral compositions (clinopyroxene ± orthopyroxene ± plagioclase) are similar to those of phenocrysts in lavas, and their equilibration temperature (1000-1125°C) is consistent with the crystallization temperature of the phenocrysts (998-1108°C). Thus, the textures and compositions of these xenoliths are different from those of lower crustal and mantle xenoliths, and were derived from the magma chamber. Among them, the gabbroic xenoliths come from the crystal-bubble-liquid zone at the top of the magma reservoir, while the pyroxenite xenoliths come from the cumulates in the bottom of magma reservoir. The studied single lherzolite xenolith with porphyroclastic texture has similar mineral compositions to the mantle xenoliths from eastern China, and is considered to be of upper mantle origin. It was brought into magma reservoir by replenishment magma, and might have experienced a cooling event before eruption. The formation of xenoliths in trachyandesite flows largely reflects the ascent, storage, evolution and eruption processes of magma.

  19. Wild Plant Assessment for Heavy Metal Phytoremediation Potential along the Mafic and Ultramafic Terrain in Northern Pakistan

    Shah, Mohammad Tahir; Khan, Sardar; Saddique, Umar; Gul, Nida; Khan, Muhammad Usman; Malik, Riffat Naseem; Farooq, Muhammad; Naz, Alia


    This study investigates the wild plant species for their phytoremediation potential of macro and trace metals (MTM). For this purpose, soil and wild plant species samples were collected along mafic and ultramafic terrain in the Jijal, Dubair, and Alpuri areas of Kohistan region, northern Pakistan. These samples were analyzed for the concentrations of MTM (Na, K, Ca, Mg, Fe, Mn, Pb, Zn, Cd, Cu, Cr, Ni, and Co) using atomic absorption spectrometer (AAS-PEA-700). Soil showed significant (P metal uptake from the contaminated sites. Plant species such as Selaginella jacquemontii, Rumex hastatus, and Plectranthus rugosus showed multifold enrichment factor (EF) of Fe, Mn, Cr, Ni, and Co as compared to background area. Results revealed that these wild plant species have the ability to uptake and accumulate higher metals concentration. Therefore, these plant species may be used for phytoremediation of metals contaminated soil. However, higher MTM concentrations in the wild plant species could cause environmental hazards in the study area, as selected metals (Fe, Mn, Cr, Ni, Co, and Pb) have toxicological concerns. PMID:24078907

  20. Wild Plant Assessment for Heavy Metal Phytoremediation Potential along the Mafic and Ultramafic Terrain in Northern Pakistan

    Said Muhammad


    Full Text Available This study investigates the wild plant species for their phytoremediation potential of macro and trace metals (MTM. For this purpose, soil and wild plant species samples were collected along mafic and ultramafic terrain in the Jijal, Dubair, and Alpuri areas of Kohistan region, northern Pakistan. These samples were analyzed for the concentrations of MTM (Na, K, Ca, Mg, Fe, Mn, Pb, Zn, Cd, Cu, Cr, Ni, and Co using atomic absorption spectrometer (AAS-PEA-700. Soil showed significant (P<.001 contamination level, while plants had greater variability in metal uptake from the contaminated sites. Plant species such as Selaginella jacquemontii, Rumex hastatus, and Plectranthus rugosus showed multifold enrichment factor (EF of Fe, Mn, Cr, Ni, and Co as compared to background area. Results revealed that these wild plant species have the ability to uptake and accumulate higher metals concentration. Therefore, these plant species may be used for phytoremediation of metals contaminated soil. However, higher MTM concentrations in the wild plant species could cause environmental hazards in the study area, as selected metals (Fe, Mn, Cr, Ni, Co, and Pb have toxicological concerns.

  1. The growth and contamination mechanism of the Cana Brava layered mafic-ultramafic complex: new field and geochemical evidences

    Giovanardi, Tommaso; Girardi, Vicente A. V.; Correia, Ciro T.; Sinigoi, Silvano; Tassinari, Colombo C. G.; Mazzucchelli, Maurizio


    The Cana Brava complex is the northernmost of three layered complexes outcropping in the Goiás state (central Brasil). New field and geochemical evidences suggest that Cana Brava underwent hyper- to subsolidus deformation during its growth, acquiring a high-temperature foliation that is generally interpreted as the result of a granulite-facies metamorphic event. The increase along the stratigraphy of the incompatible elements abundances (LREE, Rb, Ba) and of the Sr isotopic composition, coupled with a decrease in ɛNd(790), indicate that the complex was contaminated by the embedded xenoliths from the Palmeirópolis Sequence. The geochemical data suggest that the contamination occurred along the entire magma column during the crystallization of the Upper Mafic Zone, with in situ variations determined by the abundance and composition of the xenoliths. These features of the Cana Brava complex point to an extremely similarity with the Lower Sequence of the most known Niquelândia intrusion (the central of the three complexes). This, together with the evidences that the two complexes have the same age (c.a. 790 Ma) and their thickness and units decrease northwards suggests that Cana Brava and Niquelândia are part of a single giant Brasilia body grown through several melt impulses.

  2. Geochemistry and Petrogenesis of the Wengeqi Mafic-Ultramafic Complex and Associated PGE Mineralization, Guyang County, Inner Mongolia, China

    Su, S.; Lesher, C.


    The Wengeqi complex in Guyang County, Inner Mongolia is one of several Paleozoic PGE-mineralized zoned mafic-ultramafic complexes along the north-central margin of the North China. The complex comprises pyroxenites, biotite pyroxenites, amphibole pyroxenites, gabbros, and amphibolites. Zircons extracted from pyroxenites yield a U-Pb SHRIMP age of 399 ± 4 Ma. Several 2-6m wide syngenetic websterite dikes contain 1-3 ppm total PGE and are dominated by pyrite- chalcopyrite-pyrrhotite-magnetite-(pentlandite) assemblages with minor sperrylite, sudburyite, and kotuskite. Textural relationships indicate that pyrite has replaced chalcopyrite and that magnetite has replaced pyrrhotite, suggesting alteration of an original of a S-rich oxidizing fluid. The mineralization is strongly enriched in Pd-Pt relative to Rh-Ru-Ir-Os, similar to that observed at New Rambler, Rathbun Lake, and Lac des Iles, but very different from the less fractionated compositions of magmatic PGE deposits. Textural, mineralogical, and geochemical relationships are inconsistent with retention of MSS in the source, fractional crystallization of chromite, or fractional crystallization of MSS, but are consistent with fluid-induced partial melting of sulfides and/or alteration by high-temperature (deuteric) hydrothermal fluids.

  3. Fluid Inclusion Study of Quartz Xenocrysts in Mafic Dykes from Kawant Area, Chhota Udaipur District, Gujarat, India

    Randive Kirtikumar


    Full Text Available Unusual mafic dykes occur in the proximity of the Ambadongar Carbonatite Complex, Lower Narmada Valley, Gujarat, India. The dykes contain dense population of quartz xenocrysts within the basaltic matrix metasomatised by carbonate-rich fluids. Plagioclase feldspars, relict pyroxenes, chlorite, barite, rutile, magnetite, Fe-Ti oxides and glass were identified in the basaltic matrix. Quartz xenocrysts occur in various shapes and sizes and form an intricate growth pattern with carbonates. The xenocrysts are fractured and contain several types of primary and secondary, single phase and two-phase fluid inclusions. The two-phase inclusions are dominated by aqueous liquid, whereas the monophase inclusions are composed of carbonic gas and the aqueous inclusions homogenize to liquid between 226°C and 361°C. Majority of the inclusions are secondary in origin and are therefore unrelated to the crystallization of quartz. Moreover, the inclusions have mixed carbonic-aqueous compositions that inhibit their direct correlation with the crustal or mantle fluids. The composition of dilute CO2-rich fluids observed in the quartz xenocrysts appear similar to those exsolved during the final stages of evolution of the Amba Dongar carbonatites. However, the carbonates are devoid of fluid inclusions and therefore their genetic relation with the quartz xenocrysts cannot be established.

  4. The growth and contamination mechanism of the Cana Brava layered mafic-ultramafic complex: new field and geochemical evidences

    Giovanardi, Tommaso; Girardi, Vicente A. V.; Correia, Ciro T.; Sinigoi, Silvano; Tassinari, Colombo C. G.; Mazzucchelli, Maurizio


    The Cana Brava complex is the northernmost of three layered complexes outcropping in the Goiás state (central Brasil). New field and geochemical evidences suggest that Cana Brava underwent hyper- to subsolidus deformation during its growth, acquiring a high-temperature foliation that is generally interpreted as the result of a granulite-facies metamorphic event. The increase along the stratigraphy of the incompatible elements abundances (LREE, Rb, Ba) and of the Sr isotopic composition, coupled with a decrease in ɛNd(790), indicate that the complex was contaminated by the embedded xenoliths from the Palmeirópolis Sequence. The geochemical data suggest that the contamination occurred along the entire magma column during the crystallization of the Upper Mafic Zone, with in situ variations determined by the abundance and composition of the xenoliths. These features of the Cana Brava complex point to an extremely similarity with the Lower Sequence of the most known Niquelândia intrusion (the central of the three complexes). This, together with the evidences that the two complexes have the same age (c.a. 790 Ma) and their thickness and units decrease northwards suggests that Cana Brava and Niquelândia are part of a single giant Brasilia body grown through several melt impulses.

  5. PGE distribution in the Chromite bearing mafic-ultramafic Kondapalli Layered Complex, Krishna district, Andhra Pradesh, India

    Meshram Tushar M.


    Full Text Available The Kondapalli Layered Complex (KLC is a dismembered mafic-ultramafic layered intrusion, mainly composed of gabbroic and anorthositic rocks with subordinate ultramafics and chromitite. Chromitite occurs as lenses, pods, bands and disseminations. Platinum group of minerals (PGMs occur as inclusions within chromite and silicates. The study indicates an inhomogeneous distribution of PGMs and distinct dominance of IPGEs over the PPGEs. The average ΣPGE content of chromite of KLC varies from 64 ppb to 576 ppb with Pt ranging from 5 to 495 ppb, Pd 5 to 191 ppb, Ir 3 to 106 ppb, Ru 3 to 376 ppb and Rh 3 to 135 ppb. The PGMs identified in the KLC indicate primary deposition of the IPGE, preceding chromite, indicating its orthomagmatic nature. Most of the PGM grains are usually below 10 μm. The identified PGMs are Laurite (RuS2, irarsite (Ir, As, S, iridosmine (Os, Ir, undetermined Os-Ir sulphide and Ru-Os-Ir-Zn alloys. Chromite also contains inclusions of pentlandite, millerite, chalcopyrite and pyrite. Study indicating that the KLC have orthomagmatic origin for PGE which are dominated by IPGE group and formed under surpa-subduction zone peridotite setting.

  6. Sm-Nd and zircon SHRIMP U-Pb dating of Huilanshan mafic granulite in the Dabie Mountains and its zircon trace element geochemistry

    HOU; Zhenhui; LI; Shuguang; CHEN; Nengsong; LI; Qiuli; LIU


    The mafic granulites from Huilanshan are outcropped on the center of the Luotian dome in the northern Dabie Mountains. The Sm-Nd isochron defined by granulite-facies metamorphic minerals (garnet + clinopyroxene + hypersthene) yields an age of 136(±)18 Ma indicating the early Cretaceous granulite-facies metamorphism. The cathodoluminescence (CL) images of zircons from the granulite show clearly core-mantle-rim structures. The zircon cores are characterized by typical oscillatory zoning and highly HREE enriched patterns, which suggests their magma origin. Some zircon cores among them with little Pb loss give SHRIMP U-Pb ages ranging from 753 to 780 Ma, which suggests that the protolith of Huilanshan granulite is Neoproterozoic mafic rocks. The zircon mantles usually cut across the oscillatory zone of the zircon cores have 3―10 times lower REE, Th, U, Y, Nb and Ta contents than the igneous zircon cores but have high common Pb contents. These characteristics suggest that they were formed by hydrothermal alteration of the igneous zircons. The part of zircon mantles with little Pb loss give a similar SHRIMP U-Pb age (716―780 Ma) to the igneous zircon cores, which implies that the hydrothermal events occurred closely to the magmatic emplacement. In view of the strong early Cretaceous magmatism in the Luotian dome, consequently, the Huilanshan mafic granulite was formed by heating of the Neoproterozoic mafic rocks in mid-low crust, which caused the granulite-facies metamorphism underneath the Dabie Mountains. The similarity between the granulite metamorphic age (136±18 Ma) defined by Sm-Nd isochron and K-Ar age of 123―127 Ma given by amphible from the gneiss in Luotian dome suggests a rapid uplifting of the Luotian dome, which may result in further exhumation of the ultrahigh pressure metamorphic rocks in the Dabie Mountains.

  7. Ordovician and Triassic mafic dykes in the Wudang terrane: Evidence for opening and closure of the South Qinling ocean basin, central China

    Nie, Hu; Wan, Xin; Zhang, He; He, Jian-Feng; Hou, Zhen-Hui; Siebel, Wolfgang; Chen, Fukun


    We report zircon ages and geochemical composition for mafic dykes that intruded Neoproterozoic volcanic-sedimentary sequences in the southern part of Wudang area, South Qinling. The results indicate that the dykes were emplaced during the Early Paleozoic (c. 460 Ma) and Early Mesozoic (c. 220 Ma). The dykes share similar major element composition, but have distinctive trace element pattern and Sr-Nd-Pb isotope distribution. Early Paleozoic mafic dykes are characterized by enrichment in LREEs, LILEs and HFSEs and EM II-type isotopic features. These geochemical features suggest derivation from an OIB-type mantle source that had undergone metasomatism during earlier subduction events. The Early Mesozoic mafic dykes can be subdivided into two distinct geochemical groups. Dykes of Group 1 are depleted in LREEs, LILEs and HFSEs and show depleted isotope compositions, indicating an origin by partial melting of asthenospheric mantle material. Dykes of Group 2 have high Rb-, Ba-, and K-contents and EM I-type isotopic features, suggesting input of lower crustal material to the magma source during Mesozoic subduction. We propose that the Early Paleozoic dykes are related to the opening of an oceanic basin separating South Qinling from the Yangtze Block, while the Early Mesozoic dykes were derived from partial melting of up-welling asthenosphere during the final amalgamation of these two blocks in the Early Mesozoic. A slab break-off model could explain not only the petrogenesis of the Mesozoic mafic dykes, but also the distinct geological features between the Dabie-Sulu and South Qinling orogens. We propose that slab break-off occurred at great depth in the Dabie-Sulu orogen and hence rare magmatism occurred. Whereas in South Qinling the break-off occurred at a shallow depth, the asthenospheric mantle material could rise further up into the overlying mantle where it experienced decompression and melting. As a consequence, crustal sections were heated up to produce extensive

  8. Hydration vs. oxidation: Modelling implications for Fe–Ti oxide crystallisation in mafic intrusions, with specific reference to the Panzhihua intrusion, SW China

    Geoffrey H. Howarth


    The H2O content of parent magmas for mafic layered intrusions associated with the ELIP is an important variable. H2O alters the crystallisation sequence of the basaltic magmas so that at high H2O and f(O2 Mt–Uv crystallises earlier than plagioclase and clinopyroxene. Furthermore, the addition of H2O to an anhydrous magma can explain silicate disequilibrium texture observed in the Fe–Ti oxide ore layers.

  9. Magmatic structure and geochemistry of the Luanga Mafic-Ultramafic Complex: Further constraints for the PGE-mineralized magmatism in Carajás, Brazil

    Mansur, Eduardo Teixeira; Ferreira Filho, Cesar Fonseca


    The Luanga Complex is part of the Serra Leste Magmatic Suite, a cluster of PGE-mineralized mafic-ultramafic intrusions located in the northeastern portion of the Carajás Mineral Province. The Luanga Complex is a medium-sized layered intrusion consisting of three main zones: i. the lower Ultramafic Zone comprising ultramafic adcumulates (peridotite), ii. the Transition Zone comprising interlayered ultramafic and mafic cumulates (harzburgite, orthopyroxenite and norite) and iii. the upper Mafic Zone comprising a monotonous sequence of mafic cumulates (norite) with minor orthopyroxenite layers. Several PGE-mineralized zones occur in the Transition Zone but the bulk of the PGE resources are hosted within a 10-50 meter thick interval of disseminated sulfides at the contact of the Ultramafic and Transition Zones. The compositional range of cumulus olivine (Fo78.9-86.4) is comparable to those reported for layered intrusions originated from moderate primitive parental magmas. Mantle normalized alteration-resistant trace element patterns of noritic rocks are fractionated, as indicated by relative enrichment in LREE and Th, with negative Nb and Ta anomalies, suggesting assimilation of older continental crust. Ni contents in olivine in the Luanga Complex (up to 7500 ppm) stand among the highest values reported in layered intrusions globally. The highest Ni contents in olivine in the Luanga Complex occur in distinctively PGE enriched (Pt + Pd > 1 ppm) intervals of the Transition Zone, in both sulfide-poor and sulfide bearing (1-3 vol.%) rocks. The origin of the PGE- and Ni-rich parental magma of the Luanga Complex is discussed considering the upgrading of magmas through dissolution of previously formed Ni-rich sulfide melts. Our results suggest that high Ni contents in olivine and/or orthopyroxene provide an additional exploration tool for Ni-PGE deposits, particularly useful for target selection in large magmatic provinces.

  10. Caribbean affinities of mafic crust from northern Colombia: preliminary geochemical results from basaltic rocks of the Sinu-San Jacinto belt

    Bustamante, C.; Cardona, A.; Valencia, V.; Weber, M.; Guzman, G.; Montes, C.; Ibañez, M.; Lara, M.; Toro, M.


    The petrotectonic characterization of accreted mafic remnants within the northern Andes and the Caribbean yield major insights on the growth and evolution of oceanic plates, as well as in the identification of the role of terrane accretion within the northern Andes orogeny. Within the northern termination of the Andes, in northern Colombia, several exposures of mafic and ultramafic rocks have been identified. However, extensive sedimentary cover and difficulties in field access have left the petogenetic analysis and tectonic implications of this rocks scarcely studied. Preliminary geochemical constrains from volcanic rocks obtained in outcrops and as clasts from a Paleocene-Eocene conglomerate indicate that the mafic rocks are mainly andesitic in composition, with well defined enrichment in Th and Ce and depletion in Nb and flat to weakly enriched LREE. These features suggest a relatively immature intra-oceanic volcanic arc setting for the formation of these rocks. Hornblende-dioritic dikes in peridotites also attest to the role of water in the magmatic evolution, and the affinity to a subduction related setting. The tectonic implications of this arc remnants and the relation between these rocks and other oceanic domains in the northern Andes suggest that the compositional and tectonic setting on the different accreted margins of the Caribbean plate are heterogeneous.

  11. Petrogenesis of the ∼500 Ma Fushui mafic intrusion and Early Paleozoic tectonic evolution of the Northern Qinling Belt, Central China

    Shi, Yu; Pei, Xiaoli; Castillo, Paterno R.; Liu, Xijun; Ding, Haihong; Guo, Zhichao


    The Fushui mafic intrusion in the Qinling orogenic belt (QOB) is composed of meta-gabbro, meta-gabbro-diorite, diorite, and syenite. Most of these rocks are metamorphosed under the upper greenschist facies to lower amphibolite facies metamorphism. Zircon separates from eight samples have LA-ICP-MS U-Pb ages of 497-501 Ma which are taken to be the emplacement age of magmas that formed the Fushui intrusion. Most of the zircon grains exhibit negative εHf values, correspond to TDM2 model ages of late Paleoproterozoic-early Mesoproterozoic or Neoproterozoic and suggest that the mafic rocks were most probably derived from mafic melts produced by partial melting of a previously metasomatized lithospheric mantle. The intrusion is not extensively contaminated by crustal materials and most chemical compositions of rocks are not modified during the greenschist to amphibolite-facies metamorhism. Rocks from the intrusion have primitive mantle-normalized trace element patterns with significant enrichment in light-REE and large ion lithophile elements (LILE) and depletion in high field-strength elements (HFSE). On the basis of the trace element contents, the Fushui intrusion was derived from parental magmas generated by environment and have been modified by fluids released from a subducting slab. The formation of the Fushui intrusion was related to the subduction of the Paleotethyan Shangdan oceanic lithosphere at ∼500 Ma.

  12. Late Mesozoic crust-mantle interaction and lower crust components in South China: A geochemical study of mafic granulite xenoliths from Cenozoic basalts

    YU; Jinhai; (于津海); XU; Xisheng; (徐夕生); ZHOU; Xinmin; (周新民)


    Mafic granulite xenoliths collected from Cenozoic basalts in SE China can be classified as magmatic granulite and cumulate granulite. Magmatic granulites are characterized by highly concentrated Al2O3, K2O, P2O5, Ba, Sr, Pb and REE, and low contents of Nb, Zr, Hf and Th, and have an incompatible element abundance pattern similar to that of continental arc basalts. Cumulate granulites aredepleted in K2O, P2O5, Rb, Cs and Ba. These granulite xenoliths were the products of crystallization and recrystallization of the basaltic magma underplating into crust-mantle boundary in Late Mesozoic. Sr and Nd isotopic compositions and variation trend of these mafic rocks are the result of crust-mantle mixing and controlled by assimilation and fractional crystallization process (AFC). However,trace element and major element variations were mainly controlled by fractionalcrystallization. The granulites are similar in geochemistry to surface Late Mesozoic gabbro and basalt in the study area, suggesting a close petrogenetic link between them. Late Mesozoic basaltic magma activities are the most important cause for the formation of extensive contemporaneous granite and rhyolite in the study area. This study and previous data indicate that the lower crust beneath South China is composed of a variety of Paleo- to Meso-proterozoic metamorphic rocks and Late Mesozoic mafic granulites.

  13. Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)

    Brueseke, Matthew E.; Hobbs, Jasper M.; Bulen, Casey L.; Mertzman, Stanley A.; Puckett, Robert E.; Walker, J. Douglas; Feldman, Josh


    The Southern Oklahoma Aulocogen (SOA) stretches from southern Oklahoma through the Texas panhandle and into Colorado and New Mexico, and contains mafic through silicic magmatism related to the opening of the Iapetus Ocean during the early Cambrian. Cambrian magmatic products are best exposed in the Wichita Mountains (Oklahoma), where they have been extensively studied. However, their ultimate derivation is still somewhat contentious and centers on two very different models: SOA magmatism has been suggested to occur via [1] continental rifting (with or without mantle plume emplacement) or [2] transform-fault related magmatism (e.g., leaky strike-slip faults). Within the SOA, the subsurface in and adjacent to the Arbuckle Mountains in southern Oklahoma contains thick sequences of mafic to intermediate lavas, intrusive bodies, and phreatomagmatic deposits interlayered with thick, extensive rhyolite lavas, thin localized tuffs, and lesser silicic intrusive bodies. These materials were first described in the Arbuckle Mountains region by a 1982 drill test (Hamilton Brothers Turner Falls well) and the best available age constraints from SOA Arbuckle Mountains eruptive products are ~ 535 to 540 Ma. Well cuttings of the mafic through intermediate units were collected from that well and six others and samples from all but the Turner Falls and Morton wells are the focus of this study. Samples analyzed from the wells are dominantly subalkaline, tholeiitic, and range from basalt to andesite. Their overall bulk major and trace element chemistry, normative mineralogy, and Srsbnd Nd isotope ratios are similar to magmas erupted/emplaced in flood basalt provinces. When compared with intrusive mafic rocks that crop out in the Wichita Mountains, the SOA well cuttings are geochemically most similar to the Roosevelt Gabbros. New geochemical and isotope data presented in this study, when coupled with recent geophysical work in the SOA and the coeval relationship with rhyolites, indicates

  14. Mafic magmas from Mount Baker in the northern Cascade arc, Washington: probes into mantle and crustal processes

    Moore, Nicole E.; Debari, Susan M.


    Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt of Park Butte (49.3-50.3 wt% SiO2, Mg# 64-65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of Lake Shannon (50.7-52.6 wt% SiO2, Mg# 58-62) and Sulphur Creek (51.2-54.6 wt% SiO2, Mg# 56-57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8-54.0 wt% SiO2, Mg# 68-70) and the HMA of Glacier Creek (58.3-58.7 wt% SiO2, Mg# 63-64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO2 suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite unit, Cathedral Crag (52.2-52.6 wt% SiO2, Mg# 55-58), is an Mg-poor differentiate of the Type 3 endmember. The calc

  15. Chemistry of amphiboles and clinopyroxenes from Euganean (NE Italy) cumulitic enclaves: implications for the genesis of melts in an extensional setting

    Bartoli, O.; Meli, S.; Sassi, R.; Magaraci, D.


    The magmatism of the Euganean Volcanic District (Veneto Volcanic Province, VVP) developed in the last phases of the Alpine orogenesis; the geochemical and geophysical data are consistent with an extensional geodynamic context (Milani et al., 1999). Cumulitic gabbroic enclaves occur within the Euganean trachytes, and Bartoli et al. (2008) pointed to their cogenetic origin with the Euganean host lavas. Sr isotopic data suggest that these cumulates derived from uncontaminated mantle-derived liquids. We analysed both cumulus and intercumulus amphiboles and clinopyroxenes by electron microprobe and LA-ICP-MS. The cumulus-intercumulus Cpx are diopsides and augites. The Mg#Cpx varies in a wide range (Mg#cumulus-Cpx= 0.74-0.84 and Mg#intercumulus-Cpx= 0.67-0.68). They show a MREE enrichment relative to LREE and HREE (LaN/SmN= 0.46-0.68 and TbN/YbN= 2.18-4.77). No significant Eu anomaly (Eu/Eu* = 0.78-1.23) was observed. On a chondrite-normalized spiderdiagram Cpx exhibits significant Pb and Co negative anomalies, and less evident negative anomalies for Sr and Zr. La, Sm and HREE increase, whereas Ba, Ti, Li and V decrease from core to rim. These Cpx exhibit high Cr contents (701-2958 ppm). Moreover, they display trace element differences when compared to Cpx from MORB gabbros. We analyzed also amphiboles: pargasites, edenites and kaersutites. In the cumulus Amph Mg# varies in the range 0.60-0.69, whereas in the intercumulus assemblage from 0.57 to 0.63. The high K2O and TiO2 contents are distinct from that of amphiboles in MORB gabbros. LREE are enriched relative to HREE (LaN/YbN = 5.07-7.56). Moreover, TbN/YbN = 2.50-4.02 indicates a HREE depletion relative to MREE. REE patterns lack a significant Eu anomaly (Eu/Eu* = 1.06-1.19). From core to rim Th and U decrease in cumulus crystals, but they increase in the intercumulus Amph. Ba (258-282 ppm) is enriched relative to other LILE and Nb-Ta are enriched relative to LREE. Cr varies in the range 423-594 ppm. The similar REE

  16. The 1.88 Ga Kotalahti and Vammala nickel belts, Finland: geochemistry of the mafic and ultramafic metavolcanic rocks

    Stephen J. Barnes


    Full Text Available The mafic and ultramafic volcanic rocks within the Svecofennian (1.88 Ga Kotalahti and Vammala Nickel Belts, Finland, are spatially associated and coeval with a suite of mineralized mafic–ultramafic intrusions. They have been divided into five suites based on major element geochemistry and spatial distribution: the Rantasalmi high- and low-Mg suites, the Vammala high-Mg suite, and the Rantasalmi, Kestilä and Pielavesi low-Mg suites. The Rantasalmi and Vammala high-Mg suites are very similar and probably comagmatic, and the Kestilä and Rantasalmi low-Mg suites are derived from them by a combination of fractionation and crustal assimilation. The Pielavesi suite is interpreted as an unrelated suite of island-arc affinity.On the basis of their trace element contents, the Kotalahti Belt intrusions are comagmatic with part of the analyzed volcanic rocks. In the Vammala Belt it is likely that the parent magmas to the intrusions and picrite magmas have a common mantle source but have evolved along distinct paths, and the picrites probably do not represent parent magmas tapped directly from the intrusions. Platinum-group element data show localised evidence for depletionby sulfide extraction. Vammala picrites are predominantly S-undersaturated, with the exception of lavas in the Stormi area. In the Kotalahti Belt the volcanic rocks are predominantlyS-undersaturated, while the volcanic rocks in the more northern part of the Belt are predominantly S-saturated. These spatial differences imply that the PGE contents of the metavolcanic rocks can be used as regional area selection criteria for intrusive nickel-copper-(PGE deposits within the Finnish Svecofennian.

  17. Petrological evidence for non-linear increase of magmatic intrusion rates before eruption at open vent mafic volcanoe

    Ruth, D. C. S.; Costa Rodriguez, F.


    The most active volcanoes on earth erupt in a yearly to decadal time scales, typically erupt mafic magmas and are open-vent systems with prominent degassing plumes (e.g. Mayon, Arenal, Llaima, Etna). Here we investigate the plumbing systems, dynamics, and processes that drive eruptions at these systems. These are key questions for improving hazard evaluation, and better understanding the unrest associated with these types of volcanoes. The petrology and geochemistry from six historical eruptions (1947-2006) of Mayon volcano (Philippines) shows that all lavas are basaltic andesite with phenocrysts of plagioclase + orthopyroxene (Opx) + clinopyroxene. Opx crystals show a variety of compositions and zoning patterns (reverse, normal or complex) with Mg# (= 100 *Mg/[Mg+Fe]) varying from 67 to 81. The simplest interpretation is that the low Mg# parts of the crystals resided on an upper crustal and crystal rich reservoir that was intruded by more primitive magmas from which the high Mg# parts of the crystals grew. Modelling Mg-Fe diffusion in Opx shows that times since magma injection and eruption range from a few days up to 3.5 years in all of the investigated eruptions. The longest diffusion times are shorter than the repose times between the eruptions, which implies that crystal recycling between eruptive events is negligible. This is a surprising result that shows that for each eruption a different part of the evolved crystal-rich plumbing system is activated. This can be due to random intrusion location or an irreversibility of the plumbing system that prevents multiple eruptions from the same crystal-rich part. Moreover, we find that the number of intrusions markedly increases before each eruption in a non-linear manner. Such an increased rate of intrusions with time might reflect non-linear rheological properties of the crystal-rich system, of the enclosing rocks, or the non-linear evolution of crystal-melt reaction-dissolution fronts during magma intrusions.

  18. An unusual occurrence of mafic accretionary lapilli in deep-marine volcaniclastics on 'Eua, Tonga: Palaeoenvironment and process

    Cunningham, J. K.; Beard, A. D.


    Reports of occurrences of accretionary lapilli on Earth, whether in historic time or in the geological record, are restricted to subaerial environments or to shallow marine environments when faunal evidence exists to determine palaeodepths. The proximity of the deep ocean to subduction zones/island arcs (where moist explosive volcanism conducive to ash aggregate formation is common) makes this surprising. In this paper, accretionary lapilli are reported within Middle Miocene mafic glass-rich volcaniclastics on 'Eua, the island closest to the Tonga Trench, a persistent high in the frontal arc basin. The glass in the accretionary lapilli has been subjected to advanced palagonitisation, but concentric layers marked by micro-aggregates containing shard-shaped particles survive to determine one group of occurrences as layered accretionary lapilli. The palaeoenvironment, as established by pelagic microfauna, is clearly deep marine, not less than 1600 m. The host rocks, typically gravel/sand in grain size, contain sedimentary structures (normal grading to inverse and normal-to-inverse grading, lack of grading, large-scale cross-bedding, slump bedding and sedimentary dykes) suggesting that the full spectrum of sediment gravity flow types, including less ordered debris flows, has been active. In an island arc environment, a range of sediment gravity flow types can be initiated, some by pyroclastic flows entering the sea. However, the thin beds of accretionary lapilli do not exhibit features of sediment gravity flow deposits or those of submarine pyroclastic flows. Possible transport processes must account for the matrix between the ash aggregates, which is either coarse-grained or absent. Modelling of particle descent times to 1600 m through a sea water column provides one explanation for the features displayed.

  19. Peridotites and mafic igneous rocks at the foot of the Galicia Margin: an oceanic or continental lithosphere? A discussion

    Korprobst, J.; Chazot, G.


    An ultramafic/mafic complex is exposed on the sea floor at the foot of the Galicia Margin (Spain and Portugal). It comprises various types of peridotites and pyroxenites, as well as amphibole-diorites, gabbros, dolerites and basalts. For chronological and structural reasons (gabbros were emplaced within peridotites before the continental break-up) this unit cannot be assigned to the Atlantic oceanic crust. The compilation of all available petrological and geochemical data suggests that peridotites are derived from the sub-continental lithospheric mantle, deeply transformed during Cretaceous rifting. Thus, websterite dykes extracted from the depleted MORB mantle reservoir (DMM), were emplaced early within the lithospheric harzburgites; subsequent boudinage and tectonic dispersion of these dykes in the peridotites, during deformation stages at the beginning of rifting, resulted in the formation of fertile but isotopically depleted lherzolites. Sterile but isotopically enriched websterites, would represent melting residues in the peridotites, after significant partial melting and melt extraction related to the thermal erosion of the lithosphere. The latter melts are probably the source of brown amphibole metasomatic crystallization in some peridotites, as well as of the emplacement of amphibole-diorite dykes. Melts directly extracted from the asthenosphere were emplaced as gabbro within the sub-continental mantle. Mixing these DMM melts together with the enriched melts extracted from the lithosphere, provided the intermediate isotopic melt-compositions - in between the DMM and Oceanic Islands Basalts reservoir - observed for the dolerites and basalts, none of which are characterized by a genuine N-MORB signature. An enriched lithospheric mantle, present prior to rifting of the Galicia margin, is in good agreement with data from the Messejana dyke (Portugal) and more generally, with those of all continental tholeiites of the Central Atlantic Magmatic Province (CAMP

  20. The chemical and isotopic differentiation of an epizonal magma body: Organ Needle pluton, New Mexico

    Verplanck, P.L.; Farmer, G.L.; McCurry, M.; Mertzman, S.A.


    Major and trace element, and Nd and Sr isotopic compositions of whole rocks and mineral separates from the Oligocene, alkaline Organ Needle pluton (ONP), southern New Mexico, constrain models for the differentiation of the magma body parental to this compositionally zoned and layered epizonal intrusive body. The data reveal that the pluton is rimmed by lower ??(Nd) (~-5) and higher 87Sr/86Sr (~0.7085) syenitic rocks than those in its interior (??(Nd) ~ 2, 87Sr/86Sr ~0.7060) and that the bulk compositions of the marginal rocks become more felsic with decreasing structural depth. At the deepest exposed levels of the pluton, the ??(Nd)~-5 lithology is a compositionally heterogeneous inequigranular syenite. Modal, compositional and isotopic data from separates of rare earth element (REE)-bearing major and accesory mineral phases (hornblende, titanite, apatite, zircon) demonstrate that this decoupling of trace and major elements in the inequigranular syenite results from accumulation of light REE (LREE)-bearing minerals that were evidently separated from silicic magmas as the latter rose along the sides of the magma chamber. Chemical and isotopic data for microgranular mafic enclaves, as well as for restite xenoliths of Precambrian granite wall rock, indicate that the isotopic distinction between the marginal and interior facies of the ONP probably reflects assimilation of the wall rock by ??(Nd) ~-2 mafic magmas near the base of the magma system. Fractional crystallization and crystal liquid separation of the crystally contaminated magma at the base and along the margins of the chamber generated the highly silicic magmas that ultimately pooled at the chamber top.

  1. Inventario de Hymenoptera (Hexapoda en El Ventorrillo: un rico enclave de biodiversidad en la Sierra de Guadarrama (España Central

    Nieves-Aldrey, José Luis


    Sierra de Guadarrama. Toda la zona está, sin embargo, bajo la potencial amenaza de impacto ambiental por la creciente presión humana y urbanística de la cercana urbe de Madrid. Se insta a los responsables de la conservación del Medio Ambiente en la Comunidad de Madrid a tomar medidas para garantizar la protección de este singular enclave de biodiversidad, y de su entorno, en la sierra madrileña. En este sentido, esperamos que este trabajo contribuya a apoyar la reciente propuesta de creación del Parque Nacional de la Sierra de Guadarrama.

  2. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros


    Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

  3. SIMS zircon ages and Nd isotope systematics of the 2.2 Ga mafic intrusions in northern and eastern Finland

    Eero Hanski


    Full Text Available Using the SIMS, ID-TIMS and Sm-Nd isotopic methods and the electron microprobe, we have studied several differentiated mafic intrusions of the c. 2.2 Ga gabbro-wehrlite association (GWA from four Paleoproterozoic schist belts and the Archean Kuhmo Greenstone Belt. Back-scattered electron images and electron microprobe analyses revealed that zircon crystals vary from well-preserved to turbid and highly altered with individual grains often displaying irregular, hydrated, CaO-bearing domains. In the most pristine domains, suitable for establishing the crystallization ages, SIMS 207Pb/206Pb ages fall in the range of 2210–2220 Ma, which is consistent with the most concordant ID-TIMS UPb ages. One of the studied intrusions that had previously yielded a conventional U-Pb date of less than 2.0 Ga, could be shown by spot analysis to belong to the 2.2 Ga family. In contrast to the well-preserved zircon domains, altered domains exhibit a variable and often strong U-Pb discordance up to 70 % and have distinctly lower 207Pb/206Pb ages. Some zircon grains record isotopic resetting at the time of the Svecofennian orogeny(ca. 1.8–1.9 Ga, while the most discordant ones project in the concordia diagram to late Paleozoic lower intercept ages indicating a relative recent Pb loss. The mineral chemistry of zircon suggests that the leakage of radiogenic Pb can be ascribed to an opensystembehavior related to hydrothermal alteration via action of CaCl2-bearing fluids.Common albitization of plagioclase in the GWA intrusions has caused this mineral to behave as an open system with regard to the Sm-Nd isotopic systematics. Despite this uncertainty, our Nd isotopic data indicate that the magma that produced the GWA intrusions in various parts of northern and eastern Finland was isotopically homogeneousand had an initial εNd(2220 Ma value of c. +0.6 precluding significant upper crustal contamination upon emplacement and subsequent fractional crystallization.

  4. Volatile contents of mafic-to-intermediate magmas at San Cristóbal volcano in Nicaragua

    Robidoux, P.; Aiuppa, A.; Rotolo, S. G.; Rizzo, A. L.; Hauri, E. H.; Frezzotti, M. L.


    San Cristóbal volcano in northwest Nicaragua is one of the most active basaltic-andesitic stratovolcanoes of the Central American Volcanic Arc (CAVA). Here we provide novel constraints on the volcano's magmatic plumbing system, by presenting the first direct measurements of major volatile contents in mafic-to-intermediate glass inclusions from Holocene and historic-present volcanic activity. Olivine-hosted (forsterite [Fo] 1500 μg/g) found in Nicaragua at Cerro Negro, Nejapa, and Granada. Models of H2O and CO2 solubilities constrain the degassing pathway of magmas up to 425 MPa ( 16 km depth), which includes a deep CO2 degassing step (only partially preserved in the MI record), followed by coupled degassing of H2O and S plus crystal fractionation at magma volatile saturation pressures from ∼ 195 to < 10 MPa. The variation in volatile contents from San Cristóbal MI is interpreted to reflect (1) Holocene eruptive cycles characterized by the rapid emplacement of basaltic magma batches, saturated in volatiles, at depths of 3.8-7.4 km, and (2) the ascent of more-differentiated and cogenetic volatile-poor basaltic andesites during historic-present eruptions, having longer residence times in the shallowest (< 3.4 km) and hence coolest regions of the magmatic plumbing system. We also report the first measurements of the compositions of noble-gas isotopes (He, Ne, and Ar) in fluid inclusions in olivine and pyroxene crystals. While the measured 40Ar/36Ar ratios (300-304) and 4He/20Ne ratios (9-373) indicate some degree of air contamination, the 3He/4He ratios (7.01-7.20 Ra) support a common mantle source for Holocene basalts and historic-present basaltic andesites. The magmatic source is interpreted as generated by a primitive MORB-like mantle, that is influenced to variable extents by distinct slab fluid components for basalts (Ba/La 76 and U/Th 0.8) and basaltic andesites (Ba/La 86 and U/Th 1.0) in addition to effects of magma differentiation. These values for the

  5. Reconstruction of P-T-t metamorphic conditions from symplectites: insights from Pouso Alegre mafic rocks (Brasília Belt, Brazil)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Hermann, Jörg; Pedrosa-Soares, Antônio Carlos; Dussin, Ivo; Aurélio Pinheiro, Marco; Bouvier, Anne-Sophie; Baumgartner, Lukas


    Reconstructing the metamorphic history of polycyclic tectono-metamorphic mafic rocks that preserve potential relicts of high-pressure metamorphism is challenging because such rocks are commonly retrogressed and rare in supercrustal sequences. However, pressure-temperature-time (P-T-t) information is required to obtain the paleo-geothermal gradients and thus to define those units as markers for suture zones. The mafic rocks from Pouso Alegre in the Meridional Brasília Orogen (SW-Brazil) outcrop as rare lenses within Sil-Grt gneisses, Amp-Grt orthogneisses and Bt granites. They are heavily weathered. They have previously been defined as "retro-eclogites", based on the characteristic symplectite texture and some mineralogical observations. They have been intepreted to mark the suture zone between the Paranapanema and São Francisco cratons, although no quantitative estimates of the pressure is available to support this conclusion. In this study we investigated in detail these samples to refine their P-T-t history. As commonly observed in retrogressed eclogites, the studied mafic rock shows symplectite and corona textures overprinting the former paragenesis of Garnet (Grt) - Clinopyroxene (Cpx) 1 - Amphibole (Amp) 1 - Rutile (Rt). Phase equilibrium modelling shows that this assemblage is stable at 690°C and 13.5 kbar, in line with Zr-in-rutile thermometry (720 ±30° C). Local compositions of the symplectite domains were used to retrieve the jadeite content of Cpx1. This low-Jd cpx is in line with the predictions of the model and confirms a maximum pressure of 14 kbar. The symplectite formed from the reaction Cpx1+Qz+H2O→Cpx2+Amp+Pl+Qz taking place at conditions of 600-750°C and <7 kbar. Zircon and monazite U-Th-Pb geochronology was performed for the mafic and surrounding rocks. Zircon core dates from the mafic rock spread along concordia from ca. 1.7 to 1.0 Ga with a cluster at 1520±17 Ma, which is interpreted as the protolith crystallization age. Zircon rim

  6. Early Jurassic subduction of the Paleo-Pacific Ocean in NE China: Petrologic and geochemical evidence from the Tumen mafic intrusive complex

    Guo, Feng; Li, Hongxia; Fan, Weiming; Li, Jingyan; Zhao, Liang; Huang, Miwei; Xu, Wenliang


    Subduction of the Paleo-Pacific Oceanic Plate is widely considered to have caused extensive Mesozoic magmatism, lithospheric deformation and mineralization in East Asia. However, it is still unclear when this subduction began. Here we report an Early Jurassic (~ 187 Ma) mafic intrusive complex (including olivine norite, gabbro, and diorite) from the Tumen area in NE China. The olivine norite contains a mineral assemblage of olivine, pyroxene, Ca-plagioclase, and hornblende that crystallized in a water-saturated parental magma. The rocks in the complex show variable degrees of plagioclase and ferromagnesian mineral accumulation as reflected by positive Sr and Eu anomalies in primitive mantle-normalized incompatible element patterns. Mass-balance calculations indicate that the parental magma was calc-alkaline with arc-type trace element features (i.e., large ion incompatible and light rare earth element enrichment and Nb-Ta depletion). It also had Sr-Nd-Hf isotopic compositions (87Sr/86Sr(i) = 0.7042 to 0.7044, εNd(t) = + 2.5 to + 3.5 and εHf(t) = + 8.4 to + 10.5) similar to those of modern arc basalts. The parental magma was likely derived from 5 to 20% melting of a mantle wedge metasomatized by an addition of 3-4% hydrous sediment melt from the subducting Paleo-Pacific Oceanic slab. The Tumen mafic intrusive complex, together with other contemporaneous mafic intrusions, I-type granitoids, and felsic lavas, constitutes an Early Jurassic N-S-trending arc magmatic belt that was formed by westward subduction of the Paleo-Pacific Ocean.

  7. Contamination in mafic mineral-rich calc-alkaline granites: a geochemical and Sr-Nd isotope study of the Neoproterozoic Piedade Granite, SE Brazil

    Leite Renato J.


    Full Text Available The Piedade Granite (~600 Ma was emplaced shortly after the main phase of granite magmatism in the Agudos Grandes batholith, Apiaí-Guaxupé Terrane, SE Brazil. Its main units are: mafic mineral-rich porphyritic granites forming the border (peraluminous muscovite-biotite granodiorite-monzogranite MBmg unit and core (metaluminous titanite-bearing biotite monzogranite BmgT unit and felsic pink inequigranular granite (Bmg unit between them. Bmg has high LaN/YbN (up to 100, Th/U (>10 and low Rb, Nb and Ta, and can be a crustal melt derived from deep-seated sources with residual garnet and biotite. The core BmgT unit derived from oxidized magmas with high Mg# (~45, Ba and Sr, fractionated REE patterns (LaN/YbN= 45, 87Sr/86Sr(t~ 0.710, epsilonNd(t ~ -12 to -14, interpreted as being high-K calc-alkaline magmas contaminated with metasedimentary rocks that had upper-crust signature (high U, Cs, Ta. The mafic-rich peraluminous granites show a more evolved isotope signature (87Sr/86Sr(t = 0.713-0.714; epsilonNd(t= -14 to -16, similar to Bmg, and Mg# and incompatible trace-element concentrations intermediate between Bmg and BmgT. A model is presented in whichMBmgis envisaged as the product of contamination between a mafic mineral-rich magma consanguineous with BmgT and pure crustal melts akin to Bmg.

  8. Compositional variability in mafic arc magmas over short spatial and temporal scales: Evidence for the signature of mantle reactive melt channels

    Rawson, Harriet; Keller, Tobias; Fontijn, Karen; Pyle, David M.; Mather, Tamsin A.; Smith, Victoria C.; Naranjo, José A.


    Understanding arc magma genesis is critical to deciphering the construction of continental crust, understanding the relationship between plutonic and volcanic rocks, and for assessing volcanic hazards. Arc magma genesis is complex. Interpreting the underlying causes of major and trace element diversity in erupted magmas is challenging and often non-unique. To navigate this complexity mafic magma diversity is investigated using sample suites that span short temporal and spatial scales. These constraints allow us to evaluate models of arc magma genesis and their geochemical implications based on physical arguments and recent model results. Young volcanic deposits (≲18 kyr) are analysed from the Southern Volcanic Zone (SVZ), Chile, in particular suites of scoria cones on the flanks of arc stratovolcanoes that have erupted relatively primitive magmas of diverse compositions. Our study is centred on the high-resolution post-glacial tephrochronological record for Mocho-Choshuenco volcano where tight age constraints and a high density of scoria cones provide a spatially well-resolved mafic magma dataset. Two compositional trends emerge from the data. Firstly, magmas from cones on the flanks of the main edifice become more mafic with distance from the central vent. This is attributed to fractional crystallisation processes within the crust, with distal cones sampling less differentiated magmas. Secondly, there is a set of cones with distinct major and trace element compositions that are more primitive but enriched in incompatible elements relative to the central system and other 'normal SVZ' magmas. This distinct signature - termed the 'Kangechi' signature - is observed at three further clusters of cones within the SVZ. This is attributed to greater preservation of the enriched melt signature arising from reactive melt transport within the mantle wedge. Our model has important implications for arc magma genesis in general, and in particular for the spatial and temporal

  9. A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

    Dai, Shifeng; Wang, Xibo; Chen, Wenmei [State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, (China); Li, Dahua [Research Center of State Key Laboratory of Coal Resources and Safe Mining, Chongqing 400042, (China); Chou, Chen-Lin [Illinois State Geological Survey (Emeritus), 615 East Peabody Drive, Champaign, IL 61820, (United States); Zhou, Yiping [Yunnan Institute of Coal Geology Prospection, Kunming 650218, (China); Zhu, Changsheng; Li, Hang [Research Center of State Key Laboratory of Coal Resources and Safe Mining, Chongqing 400042, (China); Zhu, Xingwei; Xing, Yunwei; Zhang, Weiguo; Zou, Jianhua [State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, (China)


    The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis. The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (S{sub p,d} 8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids. Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO{sub 2}/Al{sub 2}O{sub 3} (1.13) but a higher Al{sub 2}O{sub 3}/Na{sub 2}O (80.1) value and is significantly enriched in trace elements including Sc (13.5 {mu}g/g), V (121 {mu}g/g), Cr (33.6 {mu}g/g), Co (27.2 {mu}g/g), Ni (83.5 {mu}g/g), Cu (48.5 {mu}g/g), Ga (17.3 {mu}g/g), Y (68.3 {mu}g/g), Zr (444 {mu}g/g), Nb (23.8 {mu}g/g), and REE (392 {mu}g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO{sub 2}/Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3}/Na{sub 2}O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for

  10. New Elemental and Isotopic Data From Mafic Lavas on the Puna Plateau and Re-Examining the Geochemical Signature of Convective Lithospheric Removal in the Central Andes

    Murray, K. E.; Ducea, M. N.; Reiners, P. W.


    Foundering or delamination of the lower lithosphere into the convecting mantle is required by mass balance in convergent orogens such as the central Andes. In the central Andean volcanic zone (CVZ), late Miocene to Recent mafic lavas erupted on the Puna plateau are small volume fissure flows and cinder cones classically cited as evidence of convective lithospheric removal, in concert with a suite of observations including high surface elevation (>4000m) and anomalously thin lithosphere relative to other parts of the CVZ. Mafic lavas provide the best available geochemical window into the recent history of the upper mantle in this and other regions. However, an increasing number of elemental and isotopic data suggest that these melts are less distinct from the neighboring arc magmatism than originally predicted. This observation weakens the hypothesis that there is a distinct geochemical fingerprint for so-called delamination magmatism, while advancing our understanding of the size of delaminating bodies and the timescales over which they detach from the lithosphere and interact with the mantle wedge. In this contribution, we present elemental and radiogenic isotopic data from 20 newly sampled mafic lavas from the Puna plateau (24.5°S to 27°S). Preliminary major element analyses show that the Puna lavas are high-K to shoshonitic in composition, in broad agreement with other mafic lavas sampled though out the region. Several sampled flows contain xenotliths of granitoid composition, which likely represent the crustal end member that contributed to the more evolved lavas. Along with major, trace and rare earth element analyses, we will present 87Sr/86Sr and 143Nd/144Nd data to further characterize source regions of these melts. In sum, these data will allow us to (1) expand the spatial coverage of this dataset in the central Andes, (2) contribute to the effort to parse contributions from the subcontinental lithosphere, asthenosphere, subduction-related fluids, and

  11. Petrogenesis of the Dalongkai ultramafic-mafic intrusion and its tectonic implication for the Paleotethyan evolution along the Ailaoshan tectonic zone (SW China)

    Liu, Huichuan; Wang, Yuejun; Zi, Jian-Wei


    Layered ultramafic-mafic intrusions are usually formed in an arc/back-arc or intra-plate tectonic environment, or genetically related to a mantle plume. In this paper, we report on an ultramafic-mafic intrusion, the Dalongkai intrusion in the Ailaoshan tectonic zone (SW China), whose occurrence is closely associated with arc/back-arc magmatic rocks. The Dalongkai intrusion is composed of plagioclase-lherzolite, hornblende-peridotite, lherzolite and wehrlite at the bottom, cumulate plagioclase-pyroxenite at the middle part, changing to fine-grained gabbro towards the upper part of the intrusion, forming layering structure. Zircons from the plagioclase-pyroxenites and gabbros yielded U-Pb ages of 272.1 ± 1.7 Ma and 266.4 ± 5.8 Ma, respectively. The plagioclase-pyroxenites show cumulate textures, and are characterized by high MgO (25.0-28.0 wt.%; mg# = 80.6-82.3), Cr (1606-2089 ppm) and Ni (893-1203 ppm) contents, interpreted as early cumulate phases. By contrast, the gabbros have relatively lower mg# values (56.3-62.7), and Cr (157-218 ppm) and Ni (73-114 ppm) concentrations, and may represent frozen liquids. The plagioclase-pyroxenites and gabbros share similar chondrite-normalized REE patterns and primitive mantle-normalized trace element profiles which are analogous to those of typical back-arc basin basalts. The εNd(t) values for both rock types range from +2.20 to +4.22. These geochemical and isotopic signatures suggest that the Dalongkai ultramafic-mafic rocks originated from a MORB-like mantle source metasomatized by subduction-related, sediment-derived fluids. Our data, together with other geological evidence, indicate that the emplacement of the Dalongkai ultramafic-mafic intrusion most likely occurred in a back-arc extensional setting associated with subduction of the Ailaoshan Paleotethyan branch ocean during the Middle Permian, thus ruling out the previously speculated linkage to the Emeishan mantle plume, or to an intra-continental rift.

  12. Timing, mantle source and origin of mafic dykes within the gravity anomaly belt of the Taihang-Da Hinggan gravity lineament, central North China Craton

    Liu, Shen; Feng, Caixia; Feng, Guangying; Xu, Mengjing; Coulson, Ian M.; Guo, Xiaolei; Guo, Zhuang; Peng, Hao; Feng, Qiang


    Six mafic dyke swarms crop out in Hebei Province within the Taihang-Da Hinggan gravity lineament magmatic belt, China, and were sampled. Here, we present new zircon laser ablation-inductively coupled plasma-mass spectrometry U-Pb age, whole rock geochemical, and Sr-Nd-Pb-Hf isotopic data for the six areas where these mafic dykes occur. The mafic (dolerite) dykes formed between 131.6 ± 1.6 and 121.6 ± 1.1 Ma, and are enriched in the light rare earth elements (LREE), some of the large ion lithophile elements (LILE; e.g., Rb, Ba, and Sr) and Pb, and are depleted in Th, U, Nb and Ta; some samples are also depleted in Eu. The dykes have high initial 87Sr/86Sr ratios (0.7055-0.7057), negative εNd (t) values (-12.5 to -11.9), relatively constant Pb isotopic ratios ((206Pb/204Pb)i = 16.45-16.51, (207Pb/204Pb)i = 15.44-15.51, (208Pb/204Pb)i = 36.49-36.53), negative εHf (t) values (-18.2 to -15.1), and old Nd (TNdDM2; 2.17-2.47 Ga) and Hf (THfDM2; 2.28-2.33 Ga) model ages. These geochronological, geochemical, and isotopic data indicate that the dykes were derived from magmas generated by low to moderate degree partial melting (1.0%-10%) of an EM1-like garnet lherzolite mantle source; these magmas fractionated olivine, clinopyroxene, and hornblende prior to emplacement, and assimilated minimal amounts of crustal material. Several possible models have previously been proposed to explain the origin of Mesozoic magmatism in this region. However, here we propose a foundering model for these studied mafic dykes, involving the foundering of eclogite from thickened lower crust due to the collision between the Siberian Craton and the North China Craon.

  13. A high-pyrite semianthracite of Late Permian age in the Songzao Coalfield, southwestern China: Mineralogical and geochemical relations with underlying mafic tuffs

    Dai, S.; Wang, X.; Chen, W.; Li, D.; Chou, C.-L.; Zhou, Y.; Zhu, Chen; Li, H.; Zhu, Xudong; Xing, Y.; Zhang, W.; Zou, J.


    The No. 12 Coal (Late Permian) in the Songzao Coalfield, Chongqing, southwestern China, is characteristically high in pyrite and some trace elements. It is uniquely deposited directly above mafic tuff beds. Samples of coal and tuffs have been studied for their mineralogy and geochemistry using inductively coupled plasma-mass spectrometry, X-ray fluorescence, plasma low-temperature ashing plus powder X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray analysis.The results show that the minerals of the No. 12 Coal are mainly composed of pyrite, clay minerals (kaolinite, chamosite, and illite), ankerite, calcite, and trace amounts of quartz and boehmite. Kaolinite and boehmite were mainly derived from sediment source region of mafic tuffs. Chamosite was formed by the reaction of kaolinite with Fe-Mg-rich fluids during early diagenesis. The high pyrite (Sp,d=8.83%) in the coal was related to marine transgression over peat deposits and abundant Fe derived from the underlying mafic tuff bed. Ankerite and calcite were precipitated from epigenetic fluids.Chemical compositions of incompatible elements indicate that the tuffs were derived from enriched mantle and the source magmas had an alkali-basalt character. Compared to other coals from the Songzao Coalfield and common Chinese coals, the No. 12 Coal has a lower SiO2/Al2O3 (1.13) but a higher Al2O3/Na2O (80.1) value and is significantly enriched in trace elements including Sc (13.5??g/g), V (121??g/g), Cr (33.6??g/g), Co (27.2??g/g), Ni (83.5??g/g), Cu (48.5??g/g), Ga (17.3??g/g), Y (68.3??g/g), Zr (444??g/g), Nb (23.8??g/g), and REE (392??g/g on average). Above mineralogical compositions, as well as similar ratios of selected elements (e.g., SiO2/Al2O3 and Al2O3/Na2O) and similar distribution patterns of incompatible elements (e.g., the mantle-normalized diagram for incompatible elements and chondrite-normalized diagram for rare earth elements) of coal and tuff, indicated that

  14. Geology and petrology of a deep crustal zone from the Famatinian paleo-arc, Sierras de Valle Fértil and La Huerta, San Juan, Argentina

    Otamendi, J. E.; Vujovich, G. I.; de la Rosa, J. D.; Tibaldi, A. M.; Castro, A.; Martino, R. D.; Pinotti, L. P.


    and leucogranitic magmas, which together appear multiply-intruded by mafic sill/dike bodies. Within the tonalite- and granodiorite-dominated units, the less evolved mafic rocks occur as: (1) bodies tens of meters long, (2) chilled dikes and sills, and (3) microgranular inclusions (enclaves), supporting the inference that mafic magmatism was the main source for generating a vast volume of intermediate and silicic igneous rocks. Mass balance calculations and trace element systematics are combined to demonstrate that tonalites and granodiorites formed by concurrent closed-system fractional crystallization and open-system incorporation of paragneissic migmatites and/or anatectic leucogranites into the evolving igneous sequence. This study argues that the sequence of igneous rocks from Valle Fértil-La Huerta was formed as the result of complementary petrogenetic processes that operated concurrently at different levels of the Famatinian arc crust.

  15. Duration of a large Mafic intrusion and heat transfer in the lower crust: A SHRIMP U-Pb zircon Study in the Ivrea-Verbano Zone (Western Alps, Italy)

    Peressini, G.; Quick, J.E.; Sinigoi, S.; Hofmann, A.W.; Fanning, M.


    The Ivrea-Verbano Zone in the western Italian Alps contains one of the world's classic examples of ponding of mantle-derived, mafic magma in the deep crust. Within it, a voluminous, composite mafic pluton, the Mafic Complex, intruded lower-crustal, high-grade paragneiss of the Kinzigite Formation during Permian-Carboniferous time, and is now exposed in cross-section as a result of Alpine uplift. The age of the intrusion is still debated because the results of geochronological studies in the last three decades on different rock types and with various dating techniques range from 250 to about 300 Ma. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age determinations on 12 samples from several locations within the Mafic Complex were performed to better constrain the age of the igneous event. The results indicate a long history of magma emplacement and cooling, which reconciles the spread in previously published ages. The main intrusive phase took place at 288 ?? 4 Ma, causing a perturbation of the deep-crustal geotherm, which relaxed to the Sm-Nd closure temperature in garnet-free mafic rocks after about 15-20 Myr of sub-solidus cooling at c. 270 Ma. These results suggest that large, deep crustal plutons, such as those identified geophysically at depths of 10-20 km within extended continental crust (e.g. Yellowstone, Rio Grande Rift, Basin and Range) may have formed rapidly but induced a prolonged thermal perturbation. In addition, the data indicate that a significant thermal event affected the country rock of the Mafic Complex at about 310 Ma. The occurrence of an upper amphibolite- to granulite-facies thermal event in the Kinzigite Formation prior to the main intrusive phase of the Mafic Complex has been postulated by several workers, and is corroborated by other geochronological investigations. However, it remains uncertain whether this event (1) was part of a prolonged perturbation of the deep-crustal geotherm, which started long before the onset of

  16. Geochemistry and spatial distribution of late-Paleozoic mafic volcanic rocks in the surrounding areas of the Gonghe Basin: Implications for Majixueshan triple-junction and east Paleotethyan archipelagic ocean


    The late-Paleozoic mafic volcanic rocks occurring in the surrounding areas of the Gonghe basin are distributed in the A'nyêmaqên ophiolite zone, Zongwulong tectonic zone and Kuhai-Saishitang volcanic zone. The mafic volcanics in the A'nyêmaqên zone formed an ancient ridge-centered hotspot around the Majixueshan OIB, the Kuhai-Saishitang mafic rocks consist of E-MORB and continental rift basalts and the Zongwulong volcanic rocks are enriched N-MORB. The regionally low Nb/U and Ce/Pb ratios reflect the influence of the OIB material on the mafic magma source. From geochemistry, spatial distribution and tectonic relationship of the mafic rocks, an ancient triple-junction centered at the Majixueshan can be inferred. The existence of the Kuhai-Saishitang aulacogen may have provided a tectonic channel for the Majixueshan OIB materials metasomatizing the magma source for the Zongwulong rocks. The formation of the triple-junction and the rifting of the Zongwulong zone have separated the orogens and massifs in the region.

  17. Geochemical and mantle-like isotopic (Nd, Sr) composition of the Baklan Granite from the Muratdağı Region (Banaz, Uşak), western Turkey: Implications for input of juvenile magmas in the source domains of western Anatolia Eocene Miocene granites

    Aydoğan, M. Selman; Çoban, Hakan; Bozcu, Mustafa; Akıncı, Ömer


    The (late syn)- post-collisional magmatic activities of western and northwestern Anatolia are characterized by intrusion of a great number of granitoids. Amongst them, Baklan Granite, located in the southern part of the Muratdağı Region from the Menderes Massif (Banaz, Uşak), has peculiar chemical and isotopic characteristics. The Baklan rocks are made up by K-feldspar, plagioclase, quartz, biotite and hornblende, with accessory apatite, titanite and magnetite, and include mafic microgranular enclaves (MME). Chemically, the Baklan intrusion is of sub-alkaline character, belongs to the high-K, calc-alkaline series and displays features of I-type affinity. It is typically metaluminous to mildly peraluminous, and classified predominantly as granodiorite in composition. The spider and REE patterns show that the rocks are fractionated and have small negative Eu anomalies (Eu/Eu ∗ = 0.62-0.86), with the depletion of Nb, Ti, P and, to a lesser extent, Ba and Sr. The pluton was dated by the K-Ar method on the whole-rock, yielded ages between 17.8 ± 0.7 and 19.4 ± 0.9 Ma (Early Miocene). The intrusion possesses primitive low initial 87Sr/ 86Sr ratios (0.70331-0.70452) and negative ɛNd(t) values (-5.0 to -5.6). The chemical contrast between evolved Baklan rocks (SiO 2, 62-71 wt.%; Cr, 7-27 ppm; Ni, 5-11 ppm; Mg#, 45-51) and more primitive clinopyroxene-bearing monzonitic enclaves (SiO 2, 54-59 wt.%; Cr, 20-310 ppm; Ni, 10-70 ppm; Mg#, 50-61) signifies that there is no co-genetic link between host granite and enclaves. The chemical and isotopic characteristics of the Baklan intrusion argue for an important role of a juvenile component, such as underplated mantle-derived basalt, in the generation of the granitoids. Crustal contamination has not contributed significantly to their origin. However, with respect to those of the Baklan intrusion, the generation of the (late syn)- post-collisional intrusions with higher Nd(t) values from the western Anatolia require a much

  18. New paleomagnetic data from 1.80-1.75 Ga mafic intrusions of Fennoscandia and Sarmatia: implications for the late Paleoproterozoic paleogeography of Baltica and Laurentia

    Pisarevsky, Sergei; Lubnina, Natalia; Sokolov, Svetoslav; Bogdanova, Svetlana


    A series of recently dated 1.78-1.75 Ga lamprophyre and shoshonite intrusions are exposed north of Ladoga Lake in southern Karelia (Fennoscandia). We carried out a paleomagnetic study of these intrusions and an additional study of the coeval gabbro-dolerite Ropruchey sill near the Onega Lake. All studied rocks carry a stable primary remanence supported by positive contact tests. We also studied 14 mafic dykes and 1 mafic sill from Ukrainian shield (Sarmatia). Most of these intrusions have been dated or re-dated recently by U-Pb (baddeleyite) method at 1.80-1.75 Ga. Ukrainian dykes also carry a consistent stable bipolar remanence. Two positive contact tests suggest that this remanence is primary. A comparison of new and previously published paleomagnetic data shows a significant difference between Fennoscandian and Sarmatian 1.80-1.75 Ga paleopoles. This implies that the final assemble of Baltica by docking of Volgo-Sarmatia and Fennoscandia occurred after 1.75 Ga. Consequently these two parts of Baltica should be considered as independent blocks in pre-1.75 Ga paleogeographic reconstructions. Using late Paleoproterozoic paleomagnetic data from Laurentia together with geological constraints we have built a new kinematic paleogeographic model for Laurentia and Baltica in the Statherian.

  19. Triggers on sulfide saturation in Fe-Ti oxide-bearing, mafic-ultramafic layered intrusions in the Tarim large igneous province, NW China

    Cao, Jun; Wang, Christina Yan; Xu, Yi-Gang; Xing, Chang-Ming; Ren, Ming-Hao


    Three Fe-Ti oxide-bearing layered intrusions (Mazaertag, Wajilitag, and Piqiang) in the Tarim large igneous province (NW China) have been investigated for understanding the relationship of sulfide saturation, Platinum-group element (PGE) enrichment, and Fe-Ti oxide accumulation in layered intrusions. These mafic-ultramafic layered intrusions have low PGE concentrations (convecting mantle, without appreciable input of lithospheric mantle. The Mazaertag and Wajilitag intrusions have near-chondritic γOs(t) values (+13 to +60) against restricted ɛ Nd(t) values (-0.4 to +2.8), indicating insignificant crustal contamination. Rocks of the Piqiang intrusion have relatively low ɛ Nd(t) values of -3.1 to +1.0, consistent with ˜15 to 25 % assimilation of the upper crust. The rocks of the Mazaertag and Wajilitag intrusions have positive correlation of PGE and S, pointing to the control of PGE by sulfide. Poor correlation of PGE and S for the Piqiang intrusion is attributed to the involvement of multiple sulfide-stage liquids with different PGE compositions or sulfide-oxide reequilibration on cooling. These three layered intrusions have little potential of reef-type PGE mineralization. Four criteria are summarized in this study to help discriminate between PGE-mineralized and PGE-unmineralized mafic-ultramafic intrusions.

  20. Petrology of the Motaghairat mafic-ultramafic complex, Eastern Desert, Egypt: A high-Mg post-collisional extension-related layered intrusion

    Abdel Halim, Ali H.; Helmy, Hassan M.; Abd El-Rahman, Yasser M.; Shibata, Tomoyuki; El Mahallawi, Mahmoud M.; Yoshikawa, Masako; Arai, Shoji


    The geodynamic settings of the Precambrian mafic-ultramafic complexes in the Eastern Desert of Egypt have important bearing on understanding the geotectonic evolution of the Arabian Nubian Shield. We present a detailed petrological study on a layered mafic-ultramafic intrusion that is located at the contact between the Precambrian continental crust and the Miocene Red Sea oceanic crust. The Motaghairat layered intrusion consists of basal lherzolite, orthopyroxenite, troctolite, olivine gabbro and anorthosite on the top. Variations in modal mineralogy and mineral chemistry along with the chemical composition of these units suggest their derivation from a common high-Mg tholeiitic parent melt through fractional crystallization processes. The parental magma was derived from a metasomatised mantle source. The primitive mantle-normalized patterns of the calculated melts exhibit enrichment in U relative to Th and Ba relative LREE which indicate that the enriched lithospheric mantle source was metasomatised by fluids derived from a subducted oceanic crust rather than by a sediment melt. Geological and petrological evidences suggest that the layered Motaghairat intrusion was emplaced during post-orogenic extension following subduction break-off and lithospheric delamination after the collision between the amalgamated island arc terranes and the Saharan Metacraton. The heat source required to melt the metasomatised lithospheric mantle was derived from the upwelling of hot asthenosphere after the subduction-break-off.

  1. U-Pb isotopic geochemistry of the post-collisional mafic-ultramafic rocks from the Dabie Mountains--Crust-mantle interaction and LOMU component

    黄方; 李曙光; 周红英; 李惠民


    The U-Pb isotope geochemical study of the pyroxenite-gabbro intrusion in the Dabie Mountains shows that the post-collisional mafic-ultramafic rocks of the Dabie Mountains are characterized by relative high Pb contents, low U contents and low U/Pb ratios. These characters may be results of interaction between lithosphere or depleted asthenospheric mantle (DMM) and lower crust, but have nothing to do with mantle plume and subducted continental crust. It was first observed that some samples with lower 206Pb/204Pb and higher 207Pb/204Pb ratios show typical characters of the LOMU component. The Pb, Sr, and Nd isotopic tracing shows that three components are needed in the source of the Zhujiapu pyroxenite-gabbro intrusion. They could be old enriched sub-continental lithospheric mantle (LOMU component), lower crust and depleted asthenospheric mantle. The crust-mantle interaction process producing primitive magma of post-collisional mafic-ultramafic rocks in the Dabie Mountains could be described by a lithospheric delamination and magma underplating model. After continent-continent collision, delamination of the thickened lithosphere induced the upwelling of depleted asthenospheric mantle, which caused partial melting of asthenospheric mantle and residual sub-continental lithospheric mantle. The basaltic magma produced in this process underplated in the boundary between the crust and mantle and interacted with lower crust resulting in the geochemical characters of both enriched lithospheric mantle and lower crust.

  2. High-resolution seismic imaging of the Kevitsa mafic-ultramafic Cu-Ni-PGE hosted intrusion, northern Finland

    Malehmir, Alireza; Koivisto, Emilia; Wjins, Chris; Tryggvason, Ari; Juhlin, Christopher


    Kevitsa, in northern Finland, is a large nickel/copper ore body hosted by a massive mafic-ultramafic intrusion with measured and indicated resources of 240 million tons (cutoff 0.1%) grading 0.30% Ni and 0.41% Cu. Mining started in 2012 with an open pit that will extend down to about 550-600 m depth. The expected mine life is more than 20 years. Numerous boreholes are available in the area, but the majority of them are shallow and do not provide a comprehensive understanding of the dimensions of the intrusion. However, a number of boreholes do penetrate the basal contact of the intrusion. Most of these are also shallow and concentrated at the edge of the intrusion. A better knowledge of the geometry of the intrusion would provide a framework for near-mine and deep exploration in the area, but also a better understanding of the geology. Exact mapping of the basal contact of the intrusion would also provide an exploration target for the contact-type mineralization that is often more massive and richer in Ni-Cu than the disseminated mineralization away from the contact. With the objective of better characterizing the intrusion, a series of 2D profiles were acquired followed by a 3D reflection survey that covered an area of about 3 km by 3 km. Even though the geology is complex and the seismic P-wave velocity ranges between 5 to 8 km/s, conventional processing results show gently- to steeply-dipping reflections from depths of approximately 2 km to as shallow as 100 m. Many of these reflections are interpreted to originate from either fault systems or internal magmatic layering within the Kevitsa main intrusion. Correlations between the 3D surface seismic data and VSP data, based upon time shifts or phase changes along the reflections, support the interpretation that numerous faults are imaged in the volume. Some of these faults cross the planned open-pit mine at depths of about 300-500 m, and it is, therefore, critical to map them for mine planning. The seismic 3D

  3. Mineral reactions and strain localization in a sheared mafic granulite infiltrated by melt (Seiland Igneous Province, Norway)

    degli Alessandrini, Giulia; Menegon, Luca; Malaspina, Nadia; Dijkstra, Arjan; Anderson, Mark


    This study investigates the deformation mechanisms of a metagabbroic dyke experiencing syn-kinematic melt-rock interaction in a continental lower-crustal shear zone in the Seiland Igneous Province (northern Norway). Solid state shearing occurred at T ≈750-820 °C, P ≈0.75-0.95 GPa and was coeval with melt infiltration from dehydration melting of adjacent metasediments, as evident from thin leucosome veinlets within the dykes. The mylonite consists of cpx [Ca0.47,Mg0.35,Fe0.18]SiO3 + opx [Ca0.1,Mg0.5,Fe0.4]SiO3 + pl (An77Ab22Or1) porphyroclasts with localized grt and ilm coronas, embedded in a fine grained matrix of cpx + opx + pl + qtz + ilm ± kfs. Porphyroclasts range in size (diameter) between 25 to 650 μm, whereas the fine grain matrix is consistently below 10 μm (average 4-7 μm). Porphyroclasts show varying degrees of elongation, with the opx reaching aspect ratios of 1:16 and the cpx reaching rare maxima of 1:7. Cpx and pl porphyroclasts are micro-fractured and micro-boudinaged with fine-grained material infill. Texturally, opx porphyroclasts display a marked crystallographic preferred orientation (CPO) and activity of the {100} and minor {100} slip systems, whereas cpx and pl porphyroclasts are randomly oriented. All porphyroclasts have strong internal misorientations (undulatory and sweeping extinction) and lack recovery features (subgrains). The fine-grained polyphase matrix wrapping the porphyroclasts displays weak to absent CPO, with the exception of opx that shows a {100} poles-to-planes maxima perpendicular to the foliation. Based on the microstructure, we argue that a large part of the matrix is the product of metamorphic reactions in the presence of melt. To test this hypothesis, the interaction between the studied mafic dyke and an adjacent felsic leucosome was modelled using PerpleX for P-T conditions ranging between 7-9 kbar and 700-1000°C. Results show that the syn-kinematic mineral assemblage (opx + cpx + pl + qtz + ilm ± kfs) can be

  4. Emplacement and Solidification of Inter-Layerd Silicic and Mafic Magmas, Isle au Haut Igneous Complex, Maine

    Patwardhan, K.; Marsh, B. D.


    The Isle au Haut Igneous Complex, Maine, presents an intriguing association of basaltic and granitic rocks in the form of a composite layered sequence of alternating gabbroic and dioritic units. The 413 Ma complex may have formed by periodic replenishment or invasion of mafic magma into an evolving, more silicic magma chamber (Chapman & Rhodes, 1992; JVGR). The interaction of a denser magma overlying a less dense magma promotes Rayleigh-Taylor instabilities (RTI), resulting in overturning initiated through pipes and the eventual formation of a stable configuration of diorite over gabbro (Chapman & Rhodes, 1992; JVGR). Field exposures on the southern parts of the island covering a 160 m section through the sequence shows four gabbroic-dioritic pairs (i.e., gabbro over diorite) exhibiting strong interaction between the two in the forms of diapiric pipes of diorite intruding gabbro and gabbro pillows caught in diorite. It is clear that the two magmas were simultaneously molten, and this presents an opportunity to observe the physics and chemistry of interaction between gabbroic magma and partly molten diorite. Emplacement of denser, sill like gabbroic magma over solidifying, less dense dioritic magma may also have given rise to structures resembling load casts and flame structures common to sedimentary rocks. That the diorite was significantly solidified (e.g., ~55% crystals) at the time of intrusion of the gabbroic magma is reflected in field and textural relationships suggesting that overturning due to gravitational instability was initiated but did not go to completion. That is, the diorite was strong enough to act as a rigid medium for gabbro emplacement and subsequent support without wholesale mixing, but at the same time was weak enough to yield low density melt, perhaps through compaction, to undergo RTI at the interfaces and form extensive ensembles of diapiric pipes in the overlying gabbro. We examine the physics and chemistry of this process beginning with

  5. Integrated Experimental and Modeling Studies of Mineral Carbonation as a Mechanism for Permanent Carbon Sequestration in Mafic/Ultramafic Rocks

    Wang, Zhengrong [Yale Univ., New Haven, CT (United States); Qiu, Lin [Yale Univ., New Haven, CT (United States); Zhang, Shuang [Yale Univ., New Haven, CT (United States); Bolton, Edward [Yale Univ., New Haven, CT (United States); Bercovici, David [Yale Univ., New Haven, CT (United States); Ague, Jay [Yale Univ., New Haven, CT (United States); Karato, Shun-Ichiro [Yale Univ., New Haven, CT (United States); Oristaglio, Michael [Yale Univ., New Haven, CT (United States); Zhu, Wen-Iu [Univ. of Maryland, College Park, MD (United States); Lisabeth, Harry [Univ. of Maryland, College Park, MD (United States); Johnson, Kevin [Univ. of Hawaii, Honolulu, HI (United States)


    A program of laboratory experiments, modeling and fieldwork was carried out at Yale University, University of Maryland, and University of Hawai‘i, under a DOE Award (DE-FE0004375) to study mineral carbonation as a practical method of geologic carbon sequestration. Mineral carbonation, also called carbon mineralization, is the conversion of (fluid) carbon dioxide into (solid) carbonate minerals in rocks, by way of naturally occurring chemical reactions. Mafic and ultramafic rocks, such as volcanic basalt, are natural candidates for carbonation, because the magnesium and iron silicate minerals in these rocks react with brines of dissolved carbon dioxide to form carbonate minerals. By trapping carbon dioxide (CO2) underground as a constituent of solid rock, carbonation of natural basalt formations would be a secure method of sequestering CO2 captured at power plants in efforts to mitigate climate change. Geochemical laboratory experiments at Yale, carried out in a batch reactor at 200°C and 150 bar (15 MPa), studied carbonation of the olivine mineral forsterite (Mg2SiO4) reacting with CO2 brines in the form of sodium bicarbonate (NaHCO3) solutions. The main carbonation product in these reactions is the carbonate mineral magnesite (MgCO3). A series of 32 runs varied the reaction time, the reactive surface area of olivine grains and powders, the concentration of the reacting fluid, and the starting ratio of fluid to olivine mass. These experiments were the first to study the rate of olivine carbonation under passive conditions approaching equilibrium. The results show that, in a simple batch reaction, olivine carbonation is fastest during the first 24 hours and then slows significantly and even reverses. A natural measure of the extent of carbonation is a quantity called the carbonation fraction, which compares the amount of carbon removed from solution, during a run, to the maximum amount

  6. Integrated Experimental and Modeling Studies of Mineral Carbonation as a Mechanism for Permanent Carbon Sequestration in Mafic/Ultramafic Rocks

    Wang, Zhengrong [Yale Univ., New Haven, CT (United States); Qiu, Lin [Yale Univ., New Haven, CT (United States); Zhang, Shuang [Yale Univ., New Haven, CT (United States); Bolton, Edward [Yale Univ., New Haven, CT (United States); Bercovici, David [Yale Univ., New Haven, CT (United States); Ague, Jay [Yale Univ., New Haven, CT (United States); Karato, Shun-Ichiro [Yale Univ., New Haven, CT (United States); Oristaglio, Michael [Yale Univ., New Haven, CT (United States); Zhu, Wen-Iu [Univ. of Maryland, College Park, MD (United States); Lisabeth, Harry [Univ. of Maryland, College Park, MD (United States); Johnson, Kevin [Univ. of Hawaii, Honolulu, HI (United States)


    A program of laboratory experiments, modeling and fieldwork was carried out at Yale University, University of Maryland, and University of Hawai‘i, under a DOE Award (DE-FE0004375) to study mineral carbonation as a practical method of geologic carbon sequestration. Mineral carbonation, also called carbon mineralization, is the conversion of (fluid) carbon dioxide into (solid) carbonate minerals in rocks, by way of naturally occurring chemical reactions. Mafic and ultramafic rocks, such as volcanic basalt, are natural candidates for carbonation, because the magnesium and iron silicate minerals in these rocks react with brines of dissolved carbon dioxide to form carbonate minerals. By trapping carbon dioxide (CO2) underground as a constituent of solid rock, carbonation of natural basalt formations would be a secure method of sequestering CO2 captured at power plants in efforts to mitigate climate change. Geochemical laboratory experiments at Yale, carried out in a batch reactor at 200°C and 150 bar (15 MPa), studied carbonation of the olivine mineral forsterite (Mg2SiO4) reacting with CO2 brines in the form of sodium bicarbonate (NaHCO3) solutions. The main carbonation product in these reactions is the carbonate mineral magnesite (MgCO3). A series of 32 runs varied the reaction time, the reactive surface area of olivine grains and powders, the concentration of the reacting fluid, and the starting ratio of fluid to olivine mass. These experiments were the first to study the rate of olivine carbonation under passive conditions approaching equilibrium. The results show that, in a simple batch reaction, olivine carbonation is fastest during the first 24 hours and then slows significantly and even reverses. A natural measure of the extent of carbonation is a quantity called the carbonation fraction, which compares the amount of carbon removed from solution, during a run, to the maximum amount

  7. Variation of olivine composition in the volcanic rocks in the Songliao basin, NE China: lithosphere control on the origin of the K-rich intraplate mafic lavas

    Zhang, L.-Y.; Prelević, D.; Li, N.; Mertz-Kraus, R.; Buhre, S.


    Lithospheric thickness and the heterogeneity of the mantle lithosphere are two major parameters that play a role in determining the final composition of the mafic melts and their minerals. The Songliao basin in northeast China represents an ideal natural laboratory to study the effect of these two parameters on early Pliocene to Holocene K-rich mafic lavas (K2O > 4 wt.%; K2O/Na2O > 1). A series of Cenozoic volcanic edifices (Erkeshan, Wudalianchi, Keluo and Xiaogulihe) are tentatively divided into three groups (Group 1 - thin, Group 2 - middle, and Group 3 - thick) according to the lithosphere thickness. They are located in the northern region of the Songliao basin extending in a near north-south direction along a broad zone where the lithosphere thickness increases gradually. We present a detailed petrographical and geochemical study on olivine macrocrysts in combination with new geochemical data on their host lavas, including major and trace element abundances as well as Sr, Nd, and Pb isotopic signatures. Our ultimate aim is to quantitatively and qualitatively determine the role of lithospheric mantle thickness (named as "lid effect") and composition in the variation of mafic lavas and olivine composition. When corrected to Mg# = 0.72, a number of major elements in the lavas correlate with increasing lithospheric thickness (L): Si72 and Al72 decrease, whereas Mg72, Fe72, Ti72 and P72 increase. Sm/Yb ratios in the lavas increase, implying that lithospheric thickness exerts an important control. Group 3 mafic lavas are ultrapotassic (showing lamproite affinity) with K2O/Na2O > 4: their La/Sm and Pb isotope ratios deviate from the above correlations, indicating that the lavas from the thickest part of the basin exhibit the highest extent of metasomatic enrichment of the mantle source. Several parameters (e.g. [Ni], Ni/Mg, Ni/(Mg/Fe), Mn/Fe and Ca/Fe) in melt-related olivine from Group 1 and Group 2 lavas are controlled by variable lithosphere thickness. Olivine

  8. The Anfeg post-collisional Pan-African high-K calc-alkaline batholith (Central Hoggar, Algeria), result of the LATEA microcontinent metacratonization

    Acef, Kaissa; Liégeois, Jean Paul; Ouabadi, Aziouz; Latouche, Louis


    The Anfeg batholith (or composite laccolith) occupies a large surface (2000 km 2) at the northern tip of the Laouni terrane, just south of Tamanrasset in Hoggar. It is granodioritic to granitic in composition and comprises abundant enclaves that are either mafic microgranular enclaves (MME) or gneissic xenoliths. It intruded an Eburnian (≈2 Ga) high-grade basement belonging to the LATEA metacraton at approximately 608 Ma (recalculated from the U-Pb dating of [Tectonics 5 (1986) 955]) and cooled at approximately 4 kbar, with a temperature of about 750 °C. This emplacement occurred mainly along subhorizontal thrust planes related to Pan-African subvertical mega-shear zones close to the attachment zone of a strike-slip partitioned transpression system. Although affected by some LILE mobility, the Anfeg batholith can be ascribed to a high-K calc-alkaline suite but characterized by low heavy REE contents and high LREE/HREE ratios. The MME belong to the Anfeg magmatic trend while some xenoliths belong to Neoproterozoic island arc rocks. The Anfeg batholith defines a Nd-Sr isotopic initial ratios trend ( ɛNd/( 87Sr/ 86Sr) i from -2.8/0.7068 to -11.8/0.7111) pointing to a mixing between a depleted mantle and an old Rb-depleted granulitic lower crust. Both sources have been identified within LATEA and elsewhere in the Tuareg shield ( ɛNd/ 87Sr/ 86Sr) i of +6.2/0.7028 for the depleted mantle, -22/0.708 for the old lower crust. The model proposed relates the above geochemical features to a lithospheric delamination along the subvertical mega-shear zones that dissected the rigid LATEA former passive margin without major crustal thickening (metacratonization) during the general northward tectonic escape of the Tuareg terranes, a consequence of the collision with the West African craton. This delamination allowed the uprise of the asthenosphere. In turn, this induced the melting of the asthenosphere by adiabatic pressure release and of the old felsic and mafic lower crust

  9. Late Holocene hydrous mafic magmatism at the Paint Pot Crater and Callahan flows, Medicine Lake Volcano, N. California and the influence of H2O in the generation of silicic magmas

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


    This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive H2O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 14C years Before Present (14C years B.P.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H2O contents of 3 to 6 wt% H2O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding episodes of mafic magmatism (from 10,600 to ~3000 14C years B.P.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H2O (Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H2O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to the liquidus. These combined effects generate SiO2-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H2O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H2O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes.

  10. Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: Chapter I in Mineral deposit models for resource assessment

    Schulz, Klaus J.; Woodruff, Laurel G.; Nicholson, Suzanne W.; Seal, Robert R., II; Piatak, Nadine M.; Chandler, Val W.; Mars, John L.


    Magmatic sulfide deposits containing nickel (Ni) and copper (Cu), with or without (±) platinum-group elements (PGE), account for approximately 60 percent of the world’s nickel production. Most of the remainder of the Ni production is derived from lateritic deposits, which form by weathering of ultramafic rocks in humid tropical conditions. Magmatic Ni-Cu±PGE sulfide deposits are spatially and genetically related to bodies of mafic and/or ultramafic rocks. The sulfide deposits form when the mantle-derived mafic and/or ultramafic magmas become sulfide-saturated and segregate immiscible sulfide liquid, commonly following interaction with continental crustal rocks.

  11. Petrological and geochemical constraints on the origin of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc, NE Turkey

    Aydin, Faruk; Oguz, Simge; Baser, Rasim; Uysal, Ibrahim; Sen, Cüneyt; Karsli, Orhan; Kandemir, Raif


    Geological, petrographical and geochemical data of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc (EBMA), NE Turkey, provide new insights into the nature of the metasomatizing agents in subcontinental lithospheric mantle beneath the region during the late Mesozoic-early Tertiary. Mafic dykes from the Çaykara and Hayrat (Trabzon), and also Ikizdere (Rize) areas from the northern margin of the EBMA consist of basalts, dolerites, lamprophyres (basic member) and lesser basaltic andesites and trachyandesites (evolved member). All dykes have no deformation and metamorphism. The outcrops of these dykes vary, with thickness from 0.2 to 10 m. and visible length from 3 to 20 m. In general, the mafic dykes dip steeply and cut directly across the Kaçkar Pluton, and show NW- and NE-trending, roughly parallel to the orientations of the EBMA main faults. Most of the dyke samples display subaphyric to porphyritic texture with phenocrysts of plagioclase (up to 10%), clinopyroxene (5-20%), amphibole (5-15%), and some contain variable amount of biotite (5-20%), lesser quartz (1-2%), and minor euhedral zircon, apatite and Fe-Ti oxides. The basic members of the mafic dykes have SiO2 of 44.1-51.9%, MgO of 4.5-12.1%, and TiO2 >mostly 0.8% (up to 2.3%) with K2O+Na2O of 1.3-6.6% with mostly subalkaline character. They are relatively high in mg-number (0.45-0.73) and transition metals (V=171-376 ppm, Co=22-45 ppm, Ni=3-148 ppm, and Sc=21-49 ppm). The evolved members of the dykes exhibit relatively higher SiO2 (57.1-60.2%) and K2O+Na2O (5.6-9.0%), and lower MgO (2.2-5.9%) and TiO2 (0.5-0.8%) contents than those from the basic dykes. Also, these samples have slightly low mg-number (0.41-0.65) and transition metals (V=99-172 ppm, Co=9-22 ppm, Ni=1-43 ppm, and Sc=9-20 ppm). In the Harker diagrams, all samples of the mafic dykes form a continuous array, and exhibit similar geochemical characteristics. In general, SiO2 inversely correlates with MgO, Fe

  12. Dating sub-20 micron zircons in granulite-facies mafic dikes from SW Montana: a new approach using automated mineralogy and SIMS U-Pb geochronology

    Ault, A. K.; Mahan, K. H.; Flowers, R. M.; Chamberlain, K.; Appleby, S. K.; Schmitt, A. K.


    Geochronological data is fundamental to all tectonic studies, but a major limitation for many lithologies is a paucity of sizeable zircons suitable for conventional U-Pb techniques. In particular, mafic dike swarms provide important time markers for tectonometamorphic activity in Precambrian terranes, but commonly yield little or no zircon or baddeleyite sufficient for TIMS or standard ion-probe analysis of crystal separates. We apply a new approach involving in-situ automated mineralogy and high spatial resolution Secondary Ion Mass Spectrometry (SIMS) geochronology to a mafic dike swarm exposed in the Northern Madison Range of SW Montana. The dikes cross-cut early fabrics but are also variably deformed and metamorphosed to P-T conditions as high as 1.2 GPa and 850 C. The swarm emplacement age is inferred to be ca. 2.1 Ga based on similarities to dated dikes in the adjacent Tobacco Root Mountains. Resolving the timing of dike emplacement and high-grade metamorphism in the study area is important for understanding the extent of post-Archean modification to the northwest margin of the Wyoming craton. Identification and textural characterization of zircons were facilitated by in-situ automated mineralogical analysis, in contrast to a standard elemental X-ray mapping approach. Our technique uses an SEM-based platform coupling calibrated BSE data with X-ray data collected by multiple energy dispersive spectrometers to rapidly identify target accessory phases at high spatial resolution. Whole thin section search maps were generated in ~30 minutes at 4 µm pixel resolution. Our dike thin sections commonly contained >300 zircons in a variety of textural settings, with 80% having a short dimension 95% for 206Pb. SIMS data for 22 zircons from a granulite-facies mafic dike thin section define a chord with upper and lower intercepts of 1753.1 ± 9.5 Ma and 63.2 ± 7.9 Ma, respectively (2 sigma error, MSWD = 1.6). A positive correlation between U concentration and degree of

  13. Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust, Eastern Turkey: Implications for crustal thickening to delamination

    Karsli, Orhan; Dokuz, Abdurrahman; Uysal, İbrahim; Aydin, Faruk; Kandemir, Raif; Wijbrans, Jan


    Early Cenozoic (48-50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO 2 contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high ISr (0.70474-0.70640) and low ɛNd (50 Ma) values (- 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr-Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the

  14. Chemical and isotopic relationship of mafic and felsic magmas in a sub-volcanic reservoir: The Guadalupe Igneous Complex (GIC), Sierra Nevada, California

    Ratschbacher, B. C.; Paterson, S. R.; Putirka, K. D.


    It is commonly believed that the interaction of mafic and felsic melts in the form of mixing/mingling as well as their genetic link in the form of fractionation play an important role in the formation of continental crust. The combination of whole rock major element content and isotopic signature, as presented in this study, is a powerful tool to identify the origin and genetic relation of mafic and felsic melts in magmatic arc settings where new material is added to the crust. The GIC is part of the Jurassic Sierran magmatic arc exposed in the Western Metamorphic Belt and contains two main units consisting of mafic (up to 9 wt. % MgO and 49 to 56 wt. % SiO2) and felsic (around 75 wt. % SiO2) rocks, which locally mingled and mixed to different proportions at a shallow emplacement level. In the lower parts of the GIC, fine-grained gabbros gradually evolve into the overlying diorite to meladiorite unit. A mingling zone separates these mafic rocks from granites, granophyres and overlying rhyolites in the upper part of the complex. Major element whole rock analyses show that the GIC is bimodal with gabbros and granitoids acting as endmembers in SiO2, MgO and CaO contents. For Al2O3, Na2O and other element oxides, the different units strongly overlap in compositions. Recent work using single grain zircon U-Pb dating found ages for both the gabbros and the felsic part of the complex of 151 Ma within uncertainty (Saleeby et al., 1989; Ernst et al., 2009, and unpublished data from this study). These ages are in agreement with Rb-Sr data from each unit, which fall on a 152×7 Ma isochron and therefore imply closed-system evolution. Major oxide data show that assimilation of the exposed surrounding host rocks is unlikely and cannot serve as an assimilant to reproduce the observed felsic compositions from the gabbroic rocks. Sri, Nd and Pb systematics show that all units except for capping granophyres and rhyolites plot close together implying a shared parental melt, which is

  15. Sr-Nd-Pb isotopes of the Early Paleozoic mafic-ultramafic dykes and basalts from South Qinling belt and their implications for mantle composition


    Late Early Paleozoic mafic-ultramafic dykes and volcanic rocks from the South Qinling belt are characterized by eNd( t ) = +3.28―+5.02, (87Sr/86Sr)i=0.70341―0.70555, (206Pb/204Pb)i = 17.256―18.993, (207Pb/204Pb)i= 15.505―15.642, (208Pb/204Pb)i=37.125―38.968, △8/4=21.18―774.43, △7/4=8.11―18.82. These charac- teristics suggest that they derived from a Middle Neoproterozoic mantle with isotopic compositions of mixed HIMU, EMII and minor EMI components. We interpret that these rocks were melting products of depleted mantle modified by subducted ancient oceanic crust and continental margin sediments along the northern margin of Yangtze block during Early Neoproterozoic.

  16. The deep crustal structure of the mafic-ultramafic Seiland Igneous Province of Norway from 3-D gravity modelling and geological implications

    Pastore, Zeudia; Fichler, Christine; McEnroe, Suzanne A.


    The Seiland Igneous Province (SIP) is the largest complex of mafic and ultramafic intrusions in northern Fennoscandia intruded at ca. 580-560 Ma. The depth extent and the deep structure of the SIP are mainly unknown apart from three profiles modelled by gravity and refraction seismic data. Utilizing 3-D gravity modelling, a complex model of the deep subsurface structure of the SIP has been developed. The structure is presented in a multiprofile model ranging from the surface to the Moho. The mafic/ultramafic rocks of the SIP are modelled with densities of 3100 and 3300 kg m-3, the surrounding rocks by densities of 2700 and 2900 kg m-3 for upper and lower crust, respectively. This density model explains the pronounced positive Bouguer gravity anomaly of up to 100 mGal above background. Its minimum volume is estimated from the subsurface model to 17 000 km3 and as such we revise downwards the earlier estimations of 25 000 km3. The new subsurface model suggests that most of the SIP has a thickness between 2 and 4 km. An area with roots in an annular pattern is found and two deep-reaching roots have been identified located below the islands of Seiland and Sørøy. The depth of these roots is estimated to approximatively 9 km. The SIP is presently interpreted to be in the Caledonian Kalak Nappe Complex and the roots depth constrains its minimum thickness which is larger than earlier estimated. Furthermore, the rather undisturbed shape of the annular root pattern indicates that the SIP has not been subjected to strong tectonic reworking during the Caledonian orogeny.

  17. Mesoproterozoic island arc magmatism along the south-eastern margin of the Indian Plate: Evidence from geochemistry and zircon U-Pb ages of mafic plutonic complexes

    Subramanyam, K. S. V.; Santosh, M.; Yang, Qiong-Yan; Zhang, Ze-ming; Balaram, V.; Reddy, U. V. B.


    The Prakasam Igneous Province within the Nellore Schist Belt (NSB) preserves important imprints of mafic magmatism along the south-eastern margin of the Indian plate. Here we report petrology, geochemistry and zircon U-Pb age data from three gabbro plutons namely Purimetla, Kanigiri and P C Palle which intruded into the high grade rocks of the region. LA-ICP-MS U-Pb data on zircons from the three plutons reveal prominent late Mesoproterozoic ages of 1334 ± 15 Ma, 1338 ± 27 Ma and 1251.2 ± 9.4 Ma. The cumulative 207Pb/206Pb mean age of 1315 ± 11 Ma is interpreted to represent the timing of mafic magmatism in the Prakasam Igneous Province. These rocks show adcumulus to mesocumulus and poikilitic textures indicating fractional crystallization of plagioclase and clinopyroxenes in the Purimetla pluton whereas the Kanigiri and P C Palle intrusions possess hornblende and biotite suggesting the role of water during partial melting. The rocks show LREE enrichment (∑LREE/∑HREE = 2.2-15.0), marked Eu-anomalies (Eu/Eu∗ = 0.8-2.2) and fractionated patterns (LaN/YbN = 3-79). Primitive mantle normalised trace element spider diagrams indicate subduction modified arc signatures with LILE enrichment and depletion of Nb, Ti and Zr relative to Th and La. Tectonic discrimination diagrams show arc magmatic affinities for the three gabbro plutons consistent with subduction zone setting. We propose a tectonic model involving intra oceanic island arc accretion during late Mesoproterozoic along the eastern margin of the Indian continent.

  18. Structure and tectonic setting of the SE Sardinia mafic dyke swarm. Insights for the stress state during magma emplacement in the upper crust

    Martinez-Poza, Ana Isabel; Druguet, Elena


    The SE Sardinia mafic dyke swarm intruded in Permian times into the Late Variscan granitoids of the Sàrrabus massif. In order to characterize the structure of the dyke swarm and to assess the stress state and tectonic regime at the time of dyking, we have performed a multi-methodological study which encompasses paleostress analysis using the orientation distribution of dykes, estimation of crustal extension from dyke thickness/spacing ratios and true dilation direction from the matching geometry of offsets. The mean orientation of the dyke swarm is ∼N150°, with secondary main trends orientated ∼N77° and ∼N10°. The fracture network (mostly joints) exhibits multiple orientations grouped in four or more sets, being the orientation and density patterns in granitoid and dykes significantly different. Some of the pre-existing joints were exploited by the dykes, while others were reactivated as faults during and after dyke intrusion. The paleostress analysis yielded σ1 sub-vertical, indicating that an extensional tectonic regime predominated in the area during the emplacement of the dyke swarm. σ3 was sub-horizontal, sub-parallel to the mean NE-SW dilation direction. The inferred relative stress magnitudes are characterized by a σ1 much larger than the other two principal stresses. In this context, intrusion of the dyke swarm occurred under low magma pressure conditions and preferentially into a pre-existing joint nerwork during a regional extensional event. The SE Sardinian dyke swarm has been compared with other contemporary mafic dykes of the western Mediterranean region, by attempting to restore the effects of the Neogene and eo-Alpine rotational events. The reconstruction gives a complex crustal-scale pattern in terms of dyke orientation, a fact that could be partly attributed to differential rotations associated with localized strike-slip movements that might have operated coevally with regional extension or transtension during Permian times.

  19. Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication

    LING WenLi; REN BangFang; DUAN RuiChun; LIU XiaoMing; MAO XinWu; PENG LianHong; LIU ZaoXue; CHENG JianPing; YANG HongMei


    The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclas-tic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spec-trometry (LA-ICPMS). The results reveal that the Wudangshan volcanic sequence was formed at (755±3) Ma (a weighted mean from the 5 samples, MSWD=0.47), whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at (685:L±5) (2 samples, MSWD=0.36) and (679±J:3) Ma (MSWD=1.6), respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are identical to those of the bottom Liantuo and slightly older than those of the Nantuo Forms-tions, respectively, lower strata of the Nanhua (middle to late Neoproterozoic) stratotype section in eastern Three Gorges, Yangtze craton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830-780 Ma igne-ous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze craton before the Qinling Orogeny.

  20. Geochemistry of the Peramora Mélange and Pulo do Lobo schist: geochemical investigation and tectonic interpretation of mafic mélange in the Pangean suture zone, Southern Iberia

    Dahn, Dustin R. L.; Braid, James A.; Murphy, J. Brendan; Quesada, Cecilio; Dupuis, Nicole; McFarlane, Christopher R. M.


    The Peramora Mélange is part of an accretionary complex between the South Portuguese Zone (a fragment of Laurussia) and the Ossa Morena Zone (para-autochthonous Gondwana) and is an expression of the Pangean suture zone in southwestern Iberia. The suture zone is characterized by fault-bounded units of metasedimentary rocks, mélanges, and mafic complexes. Detailed geologic mapping of the Peramora Mélange reveals a complex pattern of imbricated schists and mafic block-in-matrix mélanges. Geochemical signatures of the Pulo do Lobo schist (PDL) are consistent with derivation from both mafic and continental sources. The mafic block-in-matrix mélange displays normal mid-ocean ridge basalt (NMORB) geochemical signature, juvenile Sm-Nd isotopic compositions, and a range of zircon ages similar to those observed in the PDL, suggesting a sedimentary component. Taken together, these data suggest a complex tectonic history characterized by erosion of a NMORB source, mélange formation, and imbrication during underplating occurring during the final stages of continent-continent collision.

  1. Geochemistry and origin of metamorphosed mafic rocks from the Lower Paleozoic Moretown and Cram Hill Formations of North-Central Vermont: Delamination magmatism in the western New England appalachians

    Coish, Raymond; Kim, Jonathan; Twelker, Evan; Zolkos, Scott P.; Walsh, Gregory J.


    The Moretown Formation, exposed as a north-trending unit that extends from northern Vermont to Connecticut, is located along a critical Appalachian litho-tectonic zone between the paleomargin of Laurentia and accreted oceanic terranes. Remnants of magmatic activity, in part preserved as metamorphosed mafic rocks in the Moretown Formation and the overlying Cram Hill Formation, are a key to further understanding the tectonic history of the northern Appalachians. Field relationships suggest that the metamorphosed mafic rocks might have formed during and after Taconian deformation, which occurred at ca. 470 to 460 Ma. Geochemistry indicates that the sampled metamorphosed mafic rocks were mostly basalts or basaltic andesites. The rocks have moderate TiO2 contents (1–2.5 wt %), are slightly enriched in the light-rare earth elements relative to the heavy rare earths, and have negative Nb-Ta anomalies in MORB-normalized extended rare earth element diagrams. Their chemistry is similar to compositions of basalts from western Pacific extensional basins near volcanic arcs. The metamorphosed mafic rocks of this study are similar in chemistry to both the pre-Silurian Mount Norris Intrusive Suite of northern Vermont, and also to some of Late Silurian rocks within the Lake Memphremagog Intrusive Suite, particularly the Comerford Intrusive Complex of Vermont and New Hampshire. Both suites may be represented among the samples of this study. The geochemistry of all samples indicates that parental magmas were generated in supra-subduction extensional environments during lithospheric delamination.

  2. Estructuras magmáticas en granitos Magmatic structures in granites

    Lucio P. Pinotti


    hospeda.Structural aspects of granites related to mechanisms for structures development and their timing of formation are still a subject of lively debate. Many authors suggest that structures generated during magmatic stages (i.e. from early magmatic flow with mineral grains suspended in melt to late magmatic grain-supported flow are only hardly preserved in granitic bodies. In this contribution, several magmatic structures in granitoid plutons from Sierras Pampeanas are showed, where small plutons and batholithic-sized bodies are both analysed. We discuss: a map-scale lithological variations, such as principal magmatic units, where magma dynamics are evidenced by mixing processes within magmatic chamber; b metre to decametre-scale magmatic layering that may be isomodal or modally-graded; c overprinting submagmatic structures indicating interplay between plutons or pluton internal units according to regional deformation; d composite magmatic layering and schlieren commonly associated to mafic microgranular enclaves, locally within synmagmatic shear zones. These structural features can be ascribed to three main processes: a assembly of differentiated magmatic pulses; b local hydrodynamic sorting related to density currents in a mush; c mechanical disruption and chemical hybridization of mafic magmas during ascent and emplacement; among others. The identification of preserved structures in granitoids, their timing and mechanisms of formation, as well as the structural dynamic of the surrounding crust, play a prominent role in proposing emplacement models for granitic plutons.

  3. The Upper Miocene magmatism of the Island of Elba (Central Italy): compositional characteristics, petrogenesis and implications for the origin of the Tuscany Magmatic Province

    Poli, Giampiero; Peccerillo, Angelo


    Late Miocene intrusive magmatism of the Island of Elba, Tuscany (central Italy), consists of stocks, laccoliths, sills, and dikes showing dominant monzogranite and granodiorite compositions, with minor leucogranitic dike-sill complexes, aplites and pegmatites. A few mafic rocks occur as dikes, and as microgranular enclaves hosted inside the main intrusions. The Elba magmatism belongs to the Tuscan Magmatic Province, an 8.5 to 0.3 Ma old association of mafic to felsic rocks, of mantle and crustal origin, cropping out in Tuscany and northern Latium. Major and trace element abundances of Elba rocks are extremely variable, testifying to complex origin and evolutionary history for magmas. 87Sr/86Sr (~ 0.708-0.723) and 143Nd/144Nd (~0.5121-0.5124) are close or within the field of upper continental crust, with mafic dikes showing the lowest Sr- and the highest Nd-isotope ratios. Petrological, geochemical and textural data of Elba igneous rocks are better explained by invoking a leading role for multiple mixing processes between crust-derived felsic magmas and mafic-intermediate melts of ultimate mantle origin, accompanied by fractional crystallisation. Proxies of crustal anatectic melts are represented by some highly radiogenic-Sr rocks from northern Monte Capanne pluton. Crustal magmas were formed by melting of sedimentary rocks, likely metagreywakes, at pressures exceeding 0.3 GPa. Mafic-intermediate magmas have calcalkaline to shoshonitic compositions and originated in an anomalous mantle, moderately contaminated by siliceous sediments. Selective enrichments in Sr, Ba and LREE are shown by some intermediate rocks (Orano dikes), revealing the occurrence of a distinct magma type at Elba. Similar compositions are also observed at Capraia island, San Vincenzo and Campiglia (southern Tuscany), suggesting a regional relevance for this magma type. Sr-Ba-LREE-rich rocks do not show obvious genetic relationships with other Tuscany magmas and may represent a distinct end

  4. Density and velocity relationships for digital sonic and density logs from coastal Washington and laboratory measurements of Olympic Peninsula mafic rocks and greywackes

    Brocher, Thomas M.; Christensen, Nikolas I.


    for each well log. We also present two-way traveltimes for 15 of the wells calculated from the sonic velocities. Average velocities and densities for the wells having both logs can be reasonably well related using a modified Gardner’s rule, with p=1825v1/4, where p is the density (in kg/m3) and v is the sonic velocity (in km/s). In contrast, a similar analysis of published well logs from Puget Lowland is best matched by a Gardner’s rule of p=1730v1/4, close to the p=1740v1/4 proposed by Gardner et al. (1974). Finally, we present laboratory measurements of compressional-wave velocity, shear-wave velocity, and density for 11 greywackes and 29 mafic rocks from the Olympic Peninsula and Puget Lowland. These units have significance for earthquake-hazard investigations in Puget Lowland as they dip eastward beneath the Lowland, forming the “bedrock” beneath much of the lowland. Average Vp/Vs ratios for the mafic rocks, mainly Crescent Formation volcanics, lie between 1.81 and 1.86. Average Vp/Vs ratios for the greywackes from the accretionary core complex in the Olympic Peninsula show greater scatter but lie between 1.77 and 1.88. Both the Olympic Peninsula mafic rocks and greywackes have lower shear-wave velocities than would be expected for a Poisson solid (Vp/Vs=1.732). Although the P-wave velocities and densities in the greywackes can be related by a Gardner’s rule of p=1720v1/4, close to the p=1740v1/4 proposed by Gardner et al. (1974), the velocities and densities of the mafic rocks are best related by a Gardner’s rule of p=1840v1/4. Thus, the density/velocity relations are similar for the Puget Lowland well logs and greywackes from the Olympic Peninsula. Density/velocity relations are similar for the Washington coastal well logs and mafic rocks from the Olympic Peninsula, but differ from those of the Puget Lowland well logs and greywackes from the Olympic Peninsula.

  5. Role of mantle-derived magma in genesis of early Yanshanian granites in the Nanling Range, South China: in situ zircon Hf-O isotopic constraints


    Although a number of petrographic observations and isotopic data suggest that magma mixing is common in genesis of many granite plutons, it is still controversial whether the mantle-derived magmas were involved in granites. We carried out in this study a systematic analysis of in situ zircon Hf-O isotopes for three early Yanshanian intrusions dated at ca. 160 Ma from the Nanling Range of Southeast China. The Qinghu monzonite has very homogeneous zircon Hf-O isotopic compositions, εHf(t) =11.6±0.3 and δ18O=5.4‰±0.3‰. In combination with whole-rock geochemical and Sr-Nd isotopic data, the parental magma of the Qinghu monzonite were likely derived from the partial melting of recently-metasomatized, phlogopite-bearing lithospheric mantle without appreciable crustal contamination. The Lisong and Fogang granites and the mafic microgranular enclaves (MME) within the Lisong granites have a wide range of zircon Hf-O isotopic compositions, with Hf and O isotopes being negatively correlated within each pluton. The Lisong MMEs were crystallized from a mantle-derived magma, similar to the parental magma of the Qinghu monzonite, with small amount of crustal assimilation. The Lisong and Fogang granites were formed by reworking of meta-sedimentary materials by mantle-derived magmas and mixing of the mantle-and sediment-derived melts to varying degrees. It is thus concluded that these two Yanshanian granites in the Nanling Range were formed associated with growth and differentiation of continental crust.

  6. Orogenic potassic mafic magmatism, a product of alkaline-peraluminous mixing ? Variscan 'calc-alkaline' rocks from the Central Iberian and Ossa Morena Zones, Central Spain.

    Scarrow, Jane H.; Cambeses, Aitor; Bea, Fernando; Montero, Pilar; Molina, José F.; Moreno, Juan Antonio


    Orogenic magmatic rocks provide information about mantle and crust melt-generation and -interaction processes. In this context, minor potassic mafic stocks which are formed of enriched mantle and crustal components and are common as late-orogenic intrusions in granitic plutons give insight into the timing of new crust formation and crustal recycling. Potassic mafic stocks are prevalent, albeit low volume, constituents of granite batholiths all through the European Variscan (350-280 Ma). In the Central Iberia Zone, Spanish Central System, crustal-melt, S-type, granitoid plutons are intruded by minor concomitant ultramafic-intermediate appinitic-vaugneritic stocks. Notwithstanding their whole-rock calc-alkaline composition, the stocks apparently did not have a subduction-related origin. Recent studies have attributed their genesis to mixing of alkaline mantle and peraluminous crustal melts. Their primary alkaline character, as indicated by amphibole and biotite mineral chemistry data, points, rather, towards an extension-related genesis. In the Ossa Morena Zone, south of the Central Iberian Zone, the igneous rocks also have a whole-rock calc-alkaline composition which has been considered to be the result of northward subduction of the South Portuguese Zone. Nevertheless, identification of a 'sill' of significant volume of mafic magma in the middle crust, the ´IBERSEIS reflective body', in a seismic profile across the Ossa Morena and South Portuguese Zones has cast doubt upon the calc-alkaline magmatism-subduction model; leading, instead, to the magmatism being attributed to intra-orogenic extension related to a mantle plume active from 340 Ma to 330 Ma. The aim here, then, is to reinvestigate the petrogenesis and age of the calc-alkaline rocks of the Ossa Morena Zone to determine their tectonomagmatic context be it subduction-, plume- or extension-related, and establish what they may reveal about mantle-crust interactions. Focussing, initially, on the Valencia del

  7. Multiple magmatism in an evolving suprasubduction zone mantle wedge: The case of the composite mafic-ultramafic complex of Gaositai, North China Craton

    Yang, Fan; Santosh, M.; Tsunogae, T.; Tang, Li; Teng, Xueming


    The suprasubduction zone mantle wedge of active convergent margins is impregnated by melts and fluids leading to the formation of a variety of magmatic and metasomatic rock suites. Here we investigate a composite mafic-ultramafic intrusion at Gaositai, in the northern margin of the North China Craton (NCC). The hornblende gabbro-serpentinite-dunite-pyroxenite-gabbro-diorite suite surrounded by hornblendites of this complex has long been considered to represent an ;Alaskan-type; zoned pluton. We present petrologic, mineral chemical, geochemical and zircon U-Pb and Lu-Hf data from the various rock types from Gaositai including hornblende gabbro, serpentinite, dunite, pyroxenite, diorite and the basement hornblendite which reveal the case of multiple melt generation and melt-peridotite interaction. Our new mineral chemical data from the mafic-ultramafic suite exclude an ;Alaskan-type; affinity, and the bulk geochemical features are consistent with subduction-related magmatism with enrichment of LILE (K, Rb, and Ba) and LREE (La and Ce), and depletion of HFSE (Nb, Ta, Zr, and Hf) and HREE. Zircon U-Pb geochronology reveals that the hornblendites surrounding the Gaositai complex are nearly 2 billion years older than the intrusive complex and yield early Paleoproterozoic emplacement ages (2433-2460 Ma), followed by late Paleoproterozoic metamorphism (1897 Ma). The serpentinites trace the history of a long-lived and replenished ancient sub-continental lithospheric mantle with the oldest zircon population dated as 2479 Ma and 1896 Ma, closely corresponding with the ages obtained from the basement rock, followed by Neoproterozoic and Phanerozoic zircon growth. The oldest member in the Gaositai composite intrusion is the dunite that yields emplacement age of 755 Ma, followed by pyroxenite formed through the interaction of slab melt and wedge mantle peridotite at 401 Ma. All the rock suites also carry multiple population of younger zircons ranging in age from Paleozoic to

  8. Petrogenesis and geodynamic setting of Early Cretaceous mafic-ultramafic intrusions, South China: A case study from the Gan-Hang tectonic belt

    Qi, Youqiang; Hu, Ruizhong; Liu, Shen; Coulson, Ian M.; Qi, Huawen; Tian, Jianji; Zhu, Jingjing


    A study using whole-rock major-trace elements and Sr-Nd isotopes as well as zircon U-Pb dating has been carried out on Early Cretaceous mafic-ultramafic intrusions from the Gan-Hang tectonic belt (GHTB), South China, to understand the origin of mantle sources and the sequential evolution of the underlying Late Mesozoic lithospheric mantle of this area. The study focused on two intrusions, one at Quzhou and the other at Longyou (see Fig. 1). They are primarily composed of mafic-ultramafic rocks with wide range of chemical compositions. The Quzhou mafic rocks have relatively narrow ranges of SiO2 (48.94-51.79 wt%), MgO (6.07-7.21 wt%), Fe2O3 (10.48-11.56 wt%), CaO (8.20-8.81 wt%), and Mg# (51.7-56.5) with relatively low K2O (0.56-0.67 wt%) and Na2O (3.09-3.42 wt%). By contrast, the ultramafic rocks from Longyou have distinct lower SiO2 (41.50-45.11 wt%) and higher MgO (9.05-9.90 wt%), Fe2O3 (12.14-12.62 wt%), CaO (8.64-10.67 wt%), and Mg# (59.5-61.1) with relatively higher K2O (1.32-1.75 wt%) and Na2O (4.53-5.08 wt%). They are characterized by Ocean Island Basalts (OIB)-type trace element distribution patterns, with a significant enrichment of light rare earth elements (LREE), large ion lithophile elements (LILE, i.e., Rb, Ba, K, and Sr) and high field strength elements (HFSE, i.e., Nb, Ta), and slight depletion of Th, U, Ti, and Y. The intrusions exhibit relatively depleted Sr-Nd isotope compositions, with (87Sr/86Sr)i range of 0.7035 to 0.7055 (143Nd/144Nd)i of 0.51264 to 0.51281 and εNd(t) values of + 3.0 to + 6.6. Zircon U-Pb dating of Longyou and Quzhou intrusions yields consistent magma emplacement ages of 129.0 ± 3.9 to 126.2 ± 2.4 Ma, respectively. The dating results are consistent with the peak of extension in Early Cretacerous throughout the Gan-Hang tectonic belt. Their magmas were principally derived from near-solidus partial melting of pyroxenites with different content of silica, and the pyroxenites were resulted from a juvenile SCLM peridotite

  9. Petrology and geochemistry of mafic and ultramafic cumulates occurring as xenoliths in volcanic rocks from Polish part of Central European Volcanic Province.

    Dajek, Michał; Matusiak-Małek, Magdalena; Puziewicz, Jacek; Ntaflos, Theodoros


    Mafic xenoliths coexisting with the peridotitic ones in rocks from Polish part of Cenozoic European Volcanic Province have been scarcely examined. (Bakun-Czubarow and Białowolska, 2003, Mineralogical Society of Poland- Spec. Pap. and references therein; Matusiak, 2006, Min. Polonica- Spec. Pap.; Puziewicz et al., 2011, JoP). In this study we present new results on mafic and ultramafic xenolithic rocks from the Wilcza Góra, Winna Góra, Góra Świątek, Mnisia Górka and Grodziec volcanic rocks in the Złotoryja-Jawor Volcanic Complex. The studied xenoliths are either plagioclase-free (clinopyroxenite, websterite) or plagioclase-bearing (anorthosite, gabbro, olivine-bearing gabbro and norite). Both the types may occur in the same volcanic rock. The cumulative xenoliths are smaller than peridotitic ones, blackish and show clear cumulative, coarse grained textures. Beside the rock-forming phases, the xenoliths occasionally contain spinel, sulfides and amphibole. Usually clinopyroxene grains occurring in gabbros are strongly corroded or disintegrated, while other phases are well-preserved. Contacts between xenolith and host volcanic rock are usually sharp with subhedral crystals of clinopyroxene growing at the xenolith surface. The mineral grains are usually zoned and chemical equilibrium between phases is scarce. Clinopyroxene in plagioclase-free rocks has composition of diopside with occasionally elevated Al, Ti and Cr contents. It's mg# varies from 0.89 to 0.79. It is slightly to moderately enriched in LREE; the REE patterns are concave, and the normalized values vary significantly between localities. It shows negative Sr anomaly, depth of Ti anomaly is variable. Orthopyroxene is Al-rich enstatite with mg# varying from 0.85 down to 0.75. Orthopyroxene in websterites is LREE depleted and show strong positive Ti and Zr-Hf anomalies. Opaques are ilmenite - Ti-magnetite solid solution and/or sulfides Clinopyroxene forming plagioclase-bearing rocks also has composition

  10. Geochemical (LA-ICP-MS) investigations of baddeleyite from the Palaeoproterozoic mafic and Palaeozoic alkaline intrusions in the Arctic part of the Baltic shield

    Drogobuzhskaya, Svetlana; Bayanova, Tamara; Novikov, Andrey


    Baddeleyite is a zirconium dioxide mineral, which is very important, but less common as zircon. While the zircon microelementary composition study is widely applicable, the baddeleyite geochemical features are poorly known. The first data on REE concentrations and distribution in baddeleyite were published in the past century. Baddeleyite is used as a geochronometer for dating mafic and alkaline rocks. It may be noted that the data on its geochemical composition are quite contradictory with a strongly varying Ce anomaly value and absent Eu anomaly in some samples. The new data on the elementary composition of baddeleyite (REE, Hf, U, Th, Y, and Ti) from the Monchegorsk pluton mafic rocks (2.5 Ga) and Kovdor and Vuoriyarvi deposits (380 Ma) was obtained. The sample morphology was studied using an electronic spectroscopy method (Hitachi S-430), and the position of local analysis on baddeleyite crystals was chosen based on analyzed optic images of minerals. The content of REE and other elements was measured using LA-ICP-MS technique on quadrupole mass-spectrometer ELAN 9000 DRC-e (Perkin Elmer) with laser evaporator UP-266 MACRO (New Wave Research) with a wave length of 266 nm for sampling. The laser ablation was made in argon atmosphere in a 35 and 70 μm diameter spot or when scanning to a line with a pulse repetition rate of 10 Hz and pulse energy of 14-15 J/cm2. The device was calibrated using the NIST SRM 612 standard with a REE, U, and Th concentration of about 40 ppm. The baddeleyite from reference rocks of mafic intrusions are characterized by medium concentrations of Hf (0.69-1.9 %), Th (7.6-21.1), REE (50.3-162), U (164-357), Y (5.0-149) ppm for the sample M-2 from Monchegorsk. Another rocks of alkaline intrusions are depleted in Th (0.25-5.9), REE (9.2-103), U (1.8-48.1), Y(2.9-65.9) ppm and Hf (0.20-1.9%) for the sample Bd-400 from Vuoriyarvi and Hf (0.18-1.3 %), Th (0.4-5.2), REE (2.1-17.7), U (4.2-32.6), Y(2.2-68.4) ppm for the samples Bd-300 and Bd-300

  11. Zircon geochronology and geochemistry of mafic xenoliths from Liaoning kimberlites:Track the early evolution of the lower crust, North China Craton

    ZHENG Jianping; YU Chunmei; LU Fengxiang; LI Huimin


    Mafic xenoliths from Paleozoic Fuxian kimberlites (Liaoning Province) mainly include garnet granulite, with minor pyroxene amphibolite, meta-gabbro and pyroxene syenite. The SiO2 contents of the xenoliths are from 47.3 wt% to 49.9 wt%. The granulites are mainly coarse-medium grained and reasonably with well-developed granoblastic (mostly polygonal)texture, contain the assemblage of garnet + plagioclase + pyroxene + K-feldspar ± phlogopite.The mineral assemblage of the amphibolites is plagioclase + pyroxene + amphibole ± K-feldspar,with the equilibrium temperature and pressure conditions of 744-821 ℃ and 0.76-0.88 GPa.The granulites are regarded as derivation from the lower crust depth (more than 29 km), below the amphibolites. Garnet granulites compositionally correspond to sub-alkalic basalt, and have wide ranges of Ni abundance (133-840 ppm), and Nb/Y (0.12-1.85), Nb/U (3.51-53.86) and Ta/U (0.38-2.48). The amphibolite and the syenite correspond to alkalic basalt. The Fuxian mafic xenoliths are regarded as the metamorphic product of the underplated magmas (including fractional crystallization or not) experienced the contamination with the pre-existed crustal components, and partly effected by kimberlitic magmas. The concordant ages of zircons for the gabbro (2610-2580 Ma) and the near-concordant upper intercept ages of zircons for the garnet granulite and pyroxene amphibolite (2578-2538 Ma) indicate that they are currently known as the oldest deep-seated xenoliths from the lower crust of the North China Craton. These ages recorded the formation of the united Eastern Block of the North China Craton, That is, Neoarchean (2.6-2.5 Ga) is an important continental crustal growth period of the North China Craton.The lower intercept age of the garnet granulite (1853 Ma) recorded an important tectonic thermal event in Paleoproterozoic. This event was probably related to collision of the East and West block,and resulted in the final assembly of the North China Craton

  12. Zircon geochronology and geochemistry of mafic xenoliths from Liaoning kimberlites: Track the early evolution of the lower crust, North China Craton

    ZHENG; Jianping; YU; Chunmei; LU; Fengxiang; LI; Huimin


    Mafic xenoliths from Paleozoic Fuxian kimberlites (Liaoning Province) mainly include garnet granulite, with minor pyroxene amphibolite, meta-gabbro and pyroxene syenite. The SiO2 contents of the xenoliths are from 47.3 wt% to 49.9 wt%. The granulites are mainly coarse-medium grained and reasonably with well-developed granoblastic (mostly polygonal)texture, contain the assemblage of garnet + plagioclase + pyroxene + K-feldspar ± phlogopite.The mineral assemblage of the amphibolites is plagioclase + pyroxene + amphibole ± K-feldspar,with the equilibrium temperature and pressure conditions of 744-821 ℃ and 0.76-0.88 GPa.The granulites are regarded as derivation from the lower crust depth (more than 29 km), below the amphibolites. Garnet granulites compositionally correspond to sub-alkalic basalt, and have wide ranges of Ni abundance (133-840 ppm), and Nb/Y (0.12-1.85), Nb/U (3.51-53.86) and Ta/U (0.38-2.48). The amphibolite and the syenite correspond to alkalic basalt. The Fuxian mafic xenoliths are regarded as the metamorphic product of the underplated magmas (including fractional crystallization or not) experienced the contamination with the pre-existed crustal components, and partly effected by kimberlitic magmas. The concordant ages of zircons for the gabbro (2610-2580 Ma) and the near-concordant upper intercept ages of zircons for the garnet granulite and pyroxene amphibolite (2578-2538 Ma) indicate that they are currently known as the oldest deep-seated xenoliths from the lower crust of the North China Craton. These ages recorded the formation of the united Eastern Block of the North China Craton, That is, Neoarchean (2.6-2.5 Ga) is an important continental crustal growth period of the North China Craton.The lower intercept age of the garnet granulite (1853 Ma) recorded an important tectonic thermal event in Paleoproterozoic. This event was probably related to collision of the East and West block,and resulted in the final assembly of the North China Craton

  13. Draped aeromagnetic survey in Transantarctic Mountains over the area of the Butcher Ridge igneous complex showing extent of underlying mafic intrusion

    Behrendt, John C.; Damaske, D.; Finn, C.A.; Kyle, P.; Wilson, T.J.


    A draped aeromagnetic survey over the area surrounding the Butcher Ridge igneous complex (BRIC), Transantarctic Mountains, was acquired in 1997-1998 as part of a larger Transantarctic Mountains Aerogeophysical Research Activity survey. The BRIC is a sill-like hypoabyssal intrusion ranging in composition from tholeiitic basalt to rhyolite. An 40Ar/39 Ar age of 174 Ma and the chemical character of the basaltic rocks show the BRIC to be part of the widespread Jurassic Ferrar suite of continental tholeiitic rocks, that extends for 3500 km across Antarctica. The aeromagnetic survey shows a horseshoe-shaped pattern of anomalies reaching amplitudes as great as 1900 nT generally associated with the bedrock topography where it is exposed. It is apparent that the high-amplitude anomaly pattern is more extensive than the 10-km-long exposed outcrop, first crossed by a single 1990 aeromagnetic profile. The highest-amplitude anomalies appear south of the profile acquired in 1990 and extend out of the survey area. The new aeromagnetic data allow determination of the extent of the interpreted Butcher mafic(?) intrusion beneath exposures of Beacon sedimentary rock and ice in the area covered, as well as beneath the small BRIC exposure. The magnetic anomalies show a minimum area of 3000 km2, a much greater extent than previously inferred. Magnetic models indicate a minimum thickness of ???1-2 km for a horizontal intrusion. However, nonunique models with magnetic layers decreasing in apparent susceptibility with depth are consistent with of a 4- to 8-km-thick layered intrusion. These magnetic models indicate progressively deeper erosion of the interpreted mafic-layered body from the south to north. The erosion has removed more magnetic upper layers that mask the magnetic effects of the lower less magnetic layers. The probable minimum volume of the intrusion in the area of the survey is ???6000 km3. An alternate, but less likely, interpretation of a series of dikes can also fit the

  14. The mafic rocks of Shao La (Kharta, S. Tibet): Ordovician basaltic magmatism in the greater himalayan crystallines of central-eastern Himalaya

    Visonà, Dario; Rubatto, Daniela; Villa, Igor M.


    In the Kharta area, east of Mount Everest, the Greater Himalayan Crystallines are significantly richer in mafic rocks than the surrounding areas, Sikkim-West Bhutan and Makalu-Cho Oyu. These rocks are lenses with a complex metamorphic history. The mafic lenses of Shao La, in the Greater Himalayan Sequence south of Kharta, are here considerated as dismembered dykes apparently escaped the Himalayan high-temperature metamorphism and only record a low-grade metamorphic event. They are calc-alkaline medium-K basalts to basaltic andesites, consisting of plagioclase (core 62% An and rim 55% An), augite (Wo 43-47En36 36-37Fs 16-20), hypersthene (Wo 1.6-3.3En 50-52Fs 46-48), and minor brown hornblende, biotite and ilmenite. They show strong enrichment in low ionic potential elements relative to high-field-strength elements, and only minor Ce and P enrichment with respect to MORB. Combined Sr-Nd systematics suggest contamination of a basic magma from a subcontinental mantle source with a small amount of crust (about 4 vol.%). This in turn indicates that the Shao La basalts and basaltic andesites have the geochemical fingerprint of a supra-subduction zone magma. U-Pb dating of zircon from one sample yielded an age of 457 ± 6 Ma for the crystallisation of the Shao La basic rocks, assigning them to the Cambro-Ordovician Bhimphedian orogenic event. The age and geochemical characteristics of the Shao La rocks are similar to those of the basic rocks of the Cambro-Ordovician Mandi pluton further west. This suggests the existence of an extensive supra-subduction zone magmatism along the Indian margin of Gondwana. Like the bimodal granite-gabbro magmatism in the Mandi-Kaplas area, the Shao La basic rocks are contemporaneous with the emplacement of granitic plutons in the Everest-Kharta area. This acid plutonism is interpreted as crustal melt triggered by the upwelling of metasomatised mantle in a back-arc setting. The age of basic and acidic plutonism in the Everest-Kharta area is

  15. Petrogenesis and ore genesis of the Permian Huangshanxi sulfide ore-bearing mafic-ultramafic intrusion in the Central Asian Orogenic Belt, western China

    Mao, Ya-Jing; Qin, Ke-Zhang; Li, Chusi; Xue, Sheng-Chao; Ripley, Edward M.


    The Permian Huangshanxi mafic-ultramafic intrusion hosts one of the two largest magmatic sulfide deposits in the Eastern Tianshan which is situated in the southern margin of the Central Asian Orogenic Belt. In this paper we use mineral compositions and whole-rock geochemical data to decipher the genetic relationship between magma evolution and sulfide mineralization. The Huangshanxi intrusion consists of three separate intrusive units. Important sulfide mineralization occurs in the base of the last intrusive unit, an elongated, layered ultramafic body composed of lherzolite at the bottom, olivine websterite in the middle and websterite at the top. Based on olivine-liquid equilibria and mass balance, the MgO and FeO contents in the parental magma for a lherzolite sample are estimated to be 8.71 and 8.36 wt.%, respectively. The Huangshanxi mafic-ultramafic intrusive rocks and the estimated "trapped liquids" for several olivine-orthopyroxene cumulate rocks all show light rare earth element enrichments relative to heavy rare earth elements and significant Nb depletions relative to Th and La, which are similar to the characteristics of coeval basalts in the region. The arc-like geochemical features are attributed to pre-Permian mantle metasomatism by slab-derived fluids. Partial melting of the previously-modified mantle is thought to have resulted from heating by upwelling asthenosphere associated with post-subduction lithosphere delamination or by mantle plume activity. The relationship between the Fo and Ni contents of olivine crystals from the Huangshanxi sulfide-poor ultramafic rocks (source mantle. Stratigraphic reversals in olivine Fo contents and bulk sulfide PGE tenors suggest that multiple magma replenishments occurred during the development of the Huangshanxi magmatic Ni-Cu sulfide deposit. The sulfide ore formation can be divided into two stages: a conduit stage during which immiscible sulfide droplets and olivine crystals were brought up by ascending magma

  16. The Late Pliocene mafic lavas from the Camusú Aike volcanic field (˜50°S, Argentina): Evidence for geochemical variability in slab window magmatism

    D'Orazio, M.; Innocenti, F.; Manetti, P.; Haller, M. J.; Di Vincenzo, G.; Tonarini, S.


    The Camusú Aike volcanic field (CAVF), part of the discontinuous N-S-trending belt of Cenozoic mafic lava formations that occur in a backarc position along extra-Andean Patagonia, is located in southern Patagonia (˜50°S, Santa Cruz province), approximately 70 km east of the extensive Meseta de las Vizcachas and just south of the upper Río Santa Cruz valley. The CAVF volcanics cover a surface of ˜200 km 2 and occur mainly as lava flows and scoria cones. They are subdivided into two groups: Group I volcanics are high-TiO 2, low-Mg# olivine-hypersthene-normative basalts and trachybasalts that erupted at about 2.9 Ma; Group II lavas are much less abundant, more primitive basaltic andesites that erupted at about 2.5 Ma. Both groups show a within-plate geochemical signature, though it is more marked in Group I lavas. The main geochemical characteristics, age, and location of CAVF volcanics are consistent with the slab window opening model proposed by different authors for the genesis of the Miocene-Recent mafic magmatism of Patagonia south of 46.5°S. The whole-rock geochemical and Sr-Nd isotope features of Group I lavas ( 87Sr/ 86Sr=0.7035-0.7037; 143Nd/ 144Nd=0.51288-0.51291) indicate a genetic link between these lavas and the primitive basalts in southernmost Patagonia (Pali Aike volcanic field and Estancia Glencross area), which have been interpreted as melting products of an isotopically depleted asthenosphere. The relatively evolved compositions of the erupted Group I magmas are modeled by a polybaric crystal fractionation process without significant involvement of crustal contamination. The more primitive Group II lavas are strongly depleted in incompatible elements, have slightly higher (LREE+Ba+Th+U)/HFSE ratios, and have more enriched Sr-Nd isotope compositions ( 87Sr/ 86Sr≈0.7039; 143Nd/ 144Nd≈0.51277) that are more akin to the Patagonian basalts farther to the north. The most likely explanation for the geochemical features of Group II lavas is the

  17. Rocas Verdes Ophiolite Complexes in the Southernmost Andes: Remnants of the Mafic Igneous Floor of a Back-arc Basin that Rifted the South American Continental Crust in the Late Jurrassic and Early Cretaceous

    Stern, C. R.


    The Rocas Verdes are an en echelon group of late Jurassic and early Cretaceous igneous complexes in the southernmost Andes. They consist of mafic pillow lavas, dikes and gabbros interpreted as the upper portions of ophiolite complexes formed along mid-ocean-ridge-type spreading centers. When secondary metamorphic affects are accounted for, the geochemistry of mafic Rocas Verdes rocks are similar to ocean-ridge basalts (MORB). The spreading centers that generated the Rocas Verdes rifted the southwestern margin of the Gondwana continental crust, during the start of break-up in the southern Atlantic, to form the igneous floor of a back-arc basin behind a contemporaneous convergent plate boundary magmatic arc. Late Jurassic and early Cretaceous sediments from both the magmatic arc on the southwest and the continental platform on the northeast of the basin were deposited in the Rocas Verdes basin, and these sediments are interbedded with mafic pillow lavas along the margins of the Rocas Verdes mafic complexes. Also, mafic dikes and gabbros intrude older pre-Andean and Andean lithologies along both flanks of the Rocas Verdes, and leucocratic country rocks are engulfed in the Rocas Verdes mafic complexes. These relations indicate that the Rocas Verdes complexes formed in place and are autochthonous, having been uplifted but not obducted, which may explain the lack of exposure of the deeper ultramafic units. Zircon U/Pb ages of 150+/-1 Ma for the Larsen Harbour Formation, a southern extension of the Rocas Verdes belt on South Georgia Island, and 138+/-2 Ma for the Sarmiento complex, the northernmost in the Rocas Verdes belt, indicate that this basin may have formed by "unzipping" from the south to the north, with the southern portion beginning to form earlier and developing more extensively than the northern portion of the basin. Paleomagnetic data suggest that the Rocas Verdes basin developed in conjunction with the displacement of the Antarctic Peninsula and opening of

  18. Dyke-sill relationships in Karoo dolerites as indicators of propagation and emplacement processes of mafic magmas in the shallow crust

    Coetzee, A.; Kisters, A. F. M.


    This paper describes the spatial and temporal relationships between Karoo-age (ca. 180 Ma) dolerite dykes and a regional-scale saucer-sill complex from the Secunda (coal mine) Complex in the northeastern parts of the Karoo Basin of South Africa. Unlike parallel dyke swarms of regional extensional settings, mafic dykes commonly show curved geometries and highly variable orientations, short strike extents and complex cross-cutting and intersecting relationships. Importantly, the dyke networks originate from the upper contacts of the first-order dolerite sill-saucer structure and are not the feeders of the saucer complex. Cross-cutting relationships indicate the largely contemporaneous formation of dykes and the inner sill and inclined sheets of the underlying saucer. Systematic dykes form a distinct boxwork-type pattern of two high-angle, interconnected dyke sets. The formation and orientation of this dyke set is interpreted to be related to the stretching of roof strata above elongated magma lobes that facilitated the propagation of the inner sill, similar to the ;cracked lid; model described for large saucer complexes in Antarctica. Dyke patterns generally reflect the saucer emplacement process and the associated deformation of wall rocks rather than far-field regional stresses.

  19. U-Pb zircon SHRIMP data from the Cana Brava layered complex: new constraints for the mafic-ultramafic intrusions of Northern Goiás, Brazil

    Giovanardi, T.; Girardi, V. A. V.; Correia, C. T.; Sinigoi, S.; Tassinari, C. C. G.; Mazzucchelli, M.


    The Cana Brava Complex is the northernmost and least well known layered intrusion of a discontinuous belt of mafic-ultramafic massifs within the Brasilia Belt, which also comprises theNiquelândia and Barro Alto complexes. Available geochronological data from a range of techniques (K/Ar, Ar/Ar, Rb/Sr, Sm/Nd and U/Pb) provide a range of possible ages (time span from 3.9 Ga to 450 Ma), hence a precise and reliable age for the Cana Brava Complex is still lacking. Also, preliminary isotopic and geochemical data of the Cana Brava Complex suggest a significant crustal contamination, which could have affected bulk-rock Sr and Nd systematics resulting in meaningless age determinations. In this paper, we present new U-Pb SHRIMP zircon analyses from four samples of different units of the Cana Brava Complexwhich suggest that the intrusion occurred during the Neoproterozoic, between 800 and 780 Ma, i.e. at the same age ofNiquelândia. Discordant older 206Pb/238U ages are provided by inherited zircons, and match the age of the metamorphism of the embedding Palmeirópolis Sequence.

  20. Plume-proximal mid-ocean ridge origin of Zhongba mafic rocks in the western Yarlung Zangbo Suture Zone, Southern Tibet

    He, Juan; Li, Yalin; Wang, Chengshan; Dilek, Yildirim; Wei, Yushuai; Chen, Xi; Hou, Yunling; Zhou, Aorigele


    The >2000 km-long Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet includes the remnants of the Mesozoic Neotethyan oceanic lithosphere, and is divided by the Zhada-Zhongba microcontinent into northern and southern branches in its western segment. Zircon U-Pb dating of a doleritic rock from the northern branch has revealed a concordant age of 160.5 ± 1.3 Ma. All of the doleritic samples from the northern branch and the pillow basalt and gabbro samples from the southern branch display consistent REE and trace element patterns similar to those of modern OIB-type rocks. The geochemical and Sr-Nd-Pb isotopic signatures of these OIB-type rocks from the western segment are identical with those of OIB-type and alkaline rocks from other ophiolite massifs along the central and eastern segments of the YZSZ, suggesting a common mantle plume source for their melt evolution. The enriched Sr-Nd-Pb isotopic character of the gabbroic dike rocks from the southern branch points to a mantle plume source, contaminated by subducted oceanic crust or pelagic sediments. We infer that the mafic rock associations exposed along the YZSZ represent the remnants of a Neotethyan oceanic lithosphere, which was developed as part of a plume-proximal seafloor-spreading system, reminiscent of the seamount chains along-across the modern mid-ocean ridges in the Pacific Ocean.

  1. Tectonic insights of the southwest Amazon Craton from geophysical, geochemical and mineralogical data of Figueira Branca mafic-ultramafic suite, Brazil

    Louro, Vinicius H. A.; Cawood, Peter A.; Mantovani, Marta S. M.; Ribeiro, Vanessa B.


    The Figueira Branca Suite is a layered mafic-ultramafic complex in the Jauru Terrane, southwest Amazon Craton. New lithological, geochemical, gamma-ray and potential field data, integrated with geological, isotope and paleomagnetic data are used to characterize this pulse of Mesoproterozoic extension-related magmatism. The Figueira Branca Suite formed through juvenile magma emplacement into the crust at 1425 Ma, coeval with the later stages of the Santa Helena Orogen. Gabbros and peridotite-gabbros display increasing enrichment of LREE, interpreted as evidence of progressive fractionation of the magma. Magnetic and gamma-ray data delimit the extent of magmatism within the suite to four bodies to the north of Indiavaí city. Modelling gravity and magnetic field data indicate that the anomalous sources are close to the surface or outcropping. These intrusions trend northwest over 8 km, with significant remanent magnetization that is consistent with published direction obtained through paleomagnetic data. The emplacement, mineralogy and geochemical signature point towards a back-arc extension tectonic framework in the later stages of the Santa Helena Orogen.

  2. Structural, Petrographic and Geochemical Characteristics of Mafic Dikes Intrusive in Metasedimentary Rocks of the Crixás Greenstone Belt, Goiás

    Hardy Jost


    Full Text Available Mafic dikes and stocks are a common feature in the Archean terrain of Goiás, Central Brazil, where they occur asswarms of 2.3 - 2.5 Ga within the granite-gneiss complexes (2.8 e 2.7 Ga, as well as intrusions related to the komatiite andbasalt flows of the greenstone belts lower stratigraphic units, but were unknown within the upper metasedimentary units.Detailed study of core sections from several drill-sites in the area of the Crixás greenstone belt gold deposits showed thatdike intrusion occurred after the main Paleoproterozoic deformation and metamorphism of the metasedimentary units,and literature data indicate that the magmatic zircons from the dikes yielded an age of 2,170 ± 17 Ma. Petrographic andgeochemical data show that they have the composition of epicratonic high-Ti diabases, which are similar to the largecontinental flood basalts of the Paraná Basin. The age of the intrusions may be correlated with the short time-interval of theRhyacian (2.20 to 2.17 Ga, during which successive localized episodes of mantle plume volcanism occurred on the Earth.

  3. New constraints on the geochronology and Sm-Nd isotopic characteristics of Bas-Drâa mafic dykes, Anti-Atlas of Morocco

    El Bahat, Abdelhakim; Ikenne, Moha; Cousens, Brian; Söderlund, Ulf; Ernst, Richard; Klausen, Martin B.; Youbi, Nasrrddine


    The Precambrian inliers of the Anti-Atlas belt across the southern part of Morocco contain numerous mafic dyke and sill swarms, which are thought to represent the erosional remnants of Proterozoic Large Igneous Provinces (LIPs). As part of an extended research campaign to date and characterize these LIPs, two amphiboles from one dyke within the Bas-Drâa inlier (western Anti-Atlas) yielded consistent 40Ar-39Ar ages of 611 Ma ± 1.3; i.e., evidence of magmatic activity during the Ediacaran (635-542 Ma). Furthermore, Nd isotope ratios and model ages identifies four groups of dykes within the Bas-Drâa inlier, all of which were derived from a previously enriched mantle reservoir with very low 143Nd/144Nd ratios (0.51065-0.51170) and corresponding εNd(t) values (-16.44 to -2.45). Such low Nd-ratios arguably reflect either a contribution of crustal components, such as the Paleoproterozoïc schisto-granitic basement, or metasomatic modification of the sub-continental lithospheric mantle.

  4. Context-Based Mobile Security Enclave


    Assisted Global Positioning System ADB Android Debugger API Application Programming Interface APK Android Application Package BSC Base Station...9 into a single Android Package file ( APK ) [6]. These APK files are how applications are stored on a device. D. SECURITY Android applications...application will be provided to the administrator as an APK (Android Package File), ready to install on the desired device. During installation, the

  5. Enclave urbanism in China: Consequences and interpretations

    Douglass, M.; Wissink, B.; Kempen, R. van


    Following reforms enacted since the late 1970s, domestic and foreign investments are resulting in a dramatic transformation of China’s landscape. The concentrated Maoist city with its cellular multifunctional work-unit structure is disappearing. In its place, cities now emerge as patchworks of mono-


    Martínez Cárdenas Rogelio


    Full Text Available Resumen: La región de los Altos de Jalisco es una zona turística basada en la religiosidad y principalmente en la devoción hacia la Virgen de la Inmaculada Concepción más conocida como “Virgen de San Juan de los Lagos”. Debido a la canonización que hizo el Papa Juan Pablo II de 25 mártires cristeros, han urgido en esta zona, nuevos centros de devoción religiosa. En el caso de Santa Ana de Guadalupe se estima que recibe alrededor de un millón de visitantes anualmente. Es sorprendente el crecimiento logrado por este último santuario. Se ha convertido en un importante centro de turismo religioso; lo asombroso es que está ubicada a 20 kilómetros de San Juan de los Lagos, segundo centro religioso del país, lo que hace aún más interesante la manera en que han podido integrarse estos dos sitios. Palabras clave: Turismo Religioso. Santuario. San Juan de los Lagos, Santo Toribio.

  7. Tectonic transition from Late Carboniferous subduction to Early Permian post-collisional extension in the Eastern Tianshan, NW China: Insights from geochronology and geochemistry of mafic-intermediate intrusions

    Zhang, Xiaoran; Zhao, Guochun; Eizenhöfer, Paul R.; Sun, Min; Han, Yigui; Hou, Wenzhu; Liu, Dongxing; Wang, Bo; Liu, Qian; Xu, Bing; Zhu, Chloe Yanlin


    The closure of the Junggar Ocean between the Central Tianshan and Junggar terranes is essential in understanding the final assembly of the southern Central Asian Orogenic Belt. This study presents new whole-rock geochemical, Sr-Nd and zircon U-Pb-Hf isotopic data for mafic-intermediate intrusions from the Central Tianshan block to provide robust constraints on the final closure of the ocean. LA-ICP-MS U-Pb dating on magmatic-type zircons yields weighted mean 206Pb/238U ages of ca. 310 Ma and ca. 290 Ma, which are interpreted as the crystallization ages of the intrusions. Petrographic and geochemical analyses of the Late Carboniferous mafic-intermediate rocks, characterized by typical subduction-related signatures, low Sm/Yb (plate. In contrast, the Early Permian mafic magmatism exhibits typical within-plate basalt affinities, such as high TiO2 (2.7-3.2 wt.%) contents, elevated Ti/V (86.0-115.1) and Zr/Y (4.9-9.3) ratios, OIB-like trace element patterns and high εNd(t) (+ 1.1 to + 4.5) and zircon εHf(t) (+ 3.0 to + 9.8) values. In association with previous investigations, we suggest that their protoliths were most probably derived from the partial melting of an asthenospheric mantle source in the garnet stability field, plausibly induced by asthenosphere upwelling during the slab break-off of the Junggar oceanic plate, which agrees well with the linear distributions of Permian mafic-ultramafic rocks in the Eastern Tianshan. Collectively, our data pinpoint a tectonic transition from oceanic subduction to post-collisional extension during Late Carboniferous to Early Permian time, probably triggered by the closure of the Junggar Ocean and subsequent arc-continent collision between the Central Tianshan and Junggar terranes that gave rise to the final assembly of the Eastern Tianshan.

  8. A back-arc setting for mafic rocks of the Honeysuckle Beds, southeastern N.S.W.: the use of trace and rare earth element abundances determined by INAA

    Dadd, K.A. [University of Technology, Sydney, NSW (Australia)


    Major, trace and rare earth elements abundance in mafic rocks of the Honeysuckle Beds was determined by x-ray fluorescence and neutron activation analysis . A comparison with typical mid-ocean ridge basalt compositions reveals an enrichment in light rare earths elements (Ba, Rb, and Th) and depletion in Nb, Ta and Ti, consistent with modifications of the source by subduction-related fluids. 9 refs., 6 figs.

  9. U-Pb zircon dating, geochemical and Sr-Nd-Hf isotopic compositions of mafic intrusive rocks in the Motuo, SE Tibet constrain on their petrogenesis and tectonic implication

    Pan, Fa-Bin; Zhang, Hong-Fei; Xu, Wang-Chun; Guo, Liang; Luo, Bi-Ji; Wang, Shuai


    Mafic intrusive rocks are widely exposed in the Motuo tectono-magmatic belt, southeast Lhasa terrane. LA-ICP-MS U-Pb zircon dating shows that they have magma crystallization ages of 69 and ca. 50 Ma. These mafic intrusive rocks are characterized by variable SiO2 (44.60-57.60 wt.%), high Al2O3 (17.19-20.86 wt.%), and low MgO (1.85-5.38 wt.%) with Mg# of 31-55. Their chemical composition is comparable with low-MgO high-Al basalts to basaltic andesites. They are enriched in LILEs (Rb, Ba, K) and LREE and depleted in HFSEs (Nb, Ta, Zr, Hf, Ti), with weakly evolved Sr-Nd-Hf compositions (whole-rock (87Sr/86Sr)0 = 0.7064 to 0.7086, εNd(t) = - 3.41 to + 1.22, and zircon εHf(t) = - 3.8 to + 6.4). The mafic rocks were derived from partial melting of metasomatized lithospheric mantle. Geochemical and Sr-Nd-Hf isotopic data show that they were insignificantly modified during magma emplacement. We provide a different secular evolution of the lithospheric mantle beneath the eastern part relative to the central part of the southern Lhasa terrane. Sr-Nd isotopic composition of the Motuo Late Cretaceous-Eocene mafic rocks argues that they were derived from partial melting of a relatively homogeneous and depleted lithospheric mantle. We propose that the Late Cretaceous delamination resulted in the replacement of ancient lithospheric mantle by the juvenile homogeneous lithospheric mantle in the eastern Lhasa terrane. The foundered ancient materials may subsequently re-fertilize the lithospheric mantle not only in the eastern Lhasa terrane but also in the surrounding areas.

  10. Subduction of fore-arc crust beneath an intra-oceanic arc: The high-P Cuaba mafic gneisess and amphibolites of the Rio San Juan Complex, Dominican Republic

    Escuder-Viruete, Javier; Castillo-Carrión, Mercedes


    The Rio San Juan metamorphic complex (RSJC) exposes a segment of a high-P accretionary prism, built during Late Cretaceous subduction below the intra-oceanic Caribbean island-arc. In this paper we present new detailed maps, tectonostratigraphy, large-scale structure, mineral chemistry, in situ trace element composition of clinopyroxene (Cpx), and bulk rock geochemical data for representative garnet-free peridotites and mafic metaigneous rocks of the Cuaba and Helechal tectonometamorphic units of the southern RSJC. The Cuaba subcomplex is composed of upper foliated amphibolites and lower garnet amphibolites, retrograded (coronitic) eclogites, and heterogeneous metagabbros metamorphosed to upper amphibolite and eclogite-facies conditions. The lenticular bodies of associated peridotites are Cpx-poor harzburgites. The underlying Helechal subcomplex is composed of Cpx-poor harzburgites, Cpx-rich harzbugites, lherzolites and rare dunites. The presented data allow us to argue that the Cuaba subcomplex: (a) represents tectonically deformed and metamorphosed crust of the Caribbean island-arc, (b) contains fragments of its supra-subduction zone mantle, and (c) includes different geochemical groups of mafic protoliths generated by varying melting degrees of diverse mantle sources. These geochemical groups include mid-Ti tholeiites (N-MORB), normal IAT and calc-alkaline rocks, low-Ti IAT, metacumulates of boninitic affinity, and HREE-depleted IAT, that collectively record a multi-stage magmatic evolution for the Caribbean island-arc, prior to the Late Cretaceous high-P metamorphism. Further, these mafic protoliths present comparable geochemical features to mafic igneous rocks of the Puerca Gorda Schists, Cacheal and Puerto Plata complexes, all of them related to the Caribbean island-arc. These relations suggest that the southern RSJC complex represents part of the subducted fore-arc of the Caribbean island-arc, which experienced initial subduction, underplating below the arc

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

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


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

  12. The behaviour of the extended HFSE group (Nb, Ta, Zr, Hf, W, Mo) during the petrogenesis of mafic K-rich lavas: The Eastern Mediterranean case

    Kirchenbaur, M.; Münker, C.


    In arc lavas, elements of the extended high field strength element group (HFSE; Nb, Ta, Zr, Hf, W, and Mo) are valuable tracers to unravel magma source processes. These elements can also help to identify residual mineral assemblages in subducting slabs and in the mantle. Most high-precision studies on HFSE behaviour to date only focused on intra-oceanic arc suites and data for mafic lavas of the K-rich series (medium-K, high-K and shoshonitic) are scarce. Arguably, K-rich series are the most incompatible element-rich end-members of subduction zone magmatism, and they often record sediment recycling into the mantle. Understanding HFSE fractionation in K-rich lavas can therefore provide important insight into the global HFSE budget. Here we present a comprehensive extended HFSE dataset obtained by isotope dilution on well-characterised K-rich lavas from the Eastern Mediterranean, also including subducting sediment samples drilled during DSDP Leg 13 and ODP Leg 160 South and West of Crete. The volcanic samples include mafic calc-alkaline lavas from the active Aegean Island arc (Santorini) and post-collisional Tertiary lavas from SE Bulgaria. The Santorini lavas record a hydrous sediment melt-mediated source overprint of a depleted mantle source by components from the subducting African plate. The Bulgarian lavas tap lithospheric mantle sources that were overprinted by fluid- and melt-like subduction components during Eocene subduction of the African Plate. The sediments in this study comprise silts/sands, marl oozes, limestones and clay-rich debris flows and approximate the bulk sediment subducted beneath the Hellenic arc. The marked enrichment of all HFSE in the lavas is controlled by the composition of the subducted sediments as shown by low 176Lu/177Hf (0.008630-0.02433) and Zr/Nb (11.3-29.4), combined with variable εHf (-3 to +11) and elevated W contents (up to 2.45 ppm) in the lavas. Nevertheless, the lavas display unfractionated ratios of Nb/Ta and Zr/Hf of 12

  13. Reactive transport modeling of ferroan dolomitization by seawater interaction with mafic igneous dikes and carbonate host rock at the Latemar platform, Italy

    Blomme, Katreine; Fowler, Sarah Jane; Bachaud, Pierre


    The Middle Triassic Latemar carbonate platform, northern Italy, has featured prominently in the longstanding debate regarding dolomite petrogenesis [1-4]. Recent studies agree that ferroan and non-ferroan dolomite replaced calcite in limestone during reactive fluid flow at altered mafic igneous dikes that densely intrude the platform. A critical observation is that ferroan dolomite abundances increase towards the dikes. We hypothesize that seawater interacted with mafic minerals in the dikes, leading to Fe enrichment in the fluid that subsequently participated in dolomitization. This requires that dolomite formation was preceded by dike alteration reactions that liberated Fe and did not consume Mg. Another requirement is that ferroan and non-ferroan dolomite (instead of other Fe- and Mg-bearing minerals) formed during fluid circulation within limestone host rock. We present reactive transport numerical simulations (Coores-Arxim, [5]) that predict equilibrium mineral assemblages and the evolution of fluid dolomitizing potential from dike crystallization, through dike alteration by seawater, to replacement dolomitization in carbonate host rock. The simulations are constrained by observations. A major advantage of the simulations is that stable mineral assemblages are identified based on a forward modeling approach. In addition, the dominant igneous minerals (plagioclase, clinopyroxene olivine and their alteration products) are solid solutions. Most reactive transport simulations of carbonate petrogenesis do not share these benefits (e.g. [6]). Predicted alteration mineral assemblages are consistent with observations on dikes and with ferroan and non-ferroan dolomite genesis. The simulation results also show that fluid dolomitizing potential (Mg/Ca and Fe/Mg) increases during dissolution of igneous solid solution minerals. Enrichment in fluid Fe concentration is sufficient to stabilize ferroan replacement dolomite. Consistent with field observations, ferroan dolomite

  14. Trace-element fingerprints of chromite, magnetite and sulfides from the 3.1 Ga ultramafic-mafic rocks of the Nuggihalli greenstone belt, Western Dharwar craton (India)

    Mukherjee, Ria; Mondal, Sisir K.; González-Jiménez, José M.; Griffin, William L.; Pearson, Norman J.; O'Reilly, Suzanne Y.


    The 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic-mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite-trondhjemite-granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)-peridotite-pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length ≈30-500 m; width ≈2-15 m) are hosted by the serpentinite-peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78-86 and moderate Mg# (100 Mg/(Mg + Fe2+)) of 45-55. In situ trace-element analysis (LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe3+# versus Ti/Fe3+# diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on major-element characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe-Ti-V-rich magnetite bands in layered intrusions, and magnetites from

  15. Time scales of the dynamics of mafic-silicic magma interaction during solidification of the Isle au Haut gabbro-diorite layered complex, Maine.

    Patwardhan, K.; Marsh, B. D.


    The opportunity to examine in detail the in situ physical and chemical interaction of juxtapositioned mafic and silicic magma is vital to understanding the general dynamics of interaction of basaltic and silicic magmas. The Isle au Haut Igneous Complex (413 Ma) is one of many along the coast of Maine exhibiting a clear silicic-mafic magmatic association in the form of a layered gabbro-diorite sequence emplaced within granitic country rock (Chapman and Rhodes 1992, Wiebe 1994, 2001). Although, purely on the basis of density contrasts, the entire system should have undergone wholesale instability and mixing, that it has not and is instead arrested in a grossly unstable state with many indications of interaction while molten, makes this an especially valuable sequence. The entire sequence (~600 m thick) has five pairs of gabbro-diorite layers with individual units typically 20-40 m (gabbro) and 15-35 m (diorite) thick. Based on the mineral assemblage, chemical analyses and phase equilibria, the initial temperatures at the time of emplacement of the two magmas were ~1180 oC (gabbro) and ~1020 oC (diorite). A conductive thermal model for the solidification of a typical gabbroic layer (~20 m) indicates a timescale on the order of a few years, whereas the whole complex solidified in about a thousand years. Essentially crystal-free gabbro invaded the partially crystallized and lower temperature diorite, forming a series of large horizontal 'fingers' or layers. Evidence of this process is in the form of distinct chilled margins of gabbro against diorite and that the gabbro has not fallen into the diorite in spite of its higher density. Yet the diorite has spawned fields of evenly spaced finger-like siliceous plumes (~6 cm radius) penetrating the gabbro to high levels at every interface, reaching to within ~2 m of the upper gabbro contact. The flattened plumes at this horizon, compositionally similar to the underlying undifferentiated diorite, represent an early stage of

  16. 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

    Dostal, Jaroslav; Jutras, Pierre


    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

  17. Zircon and baddeleyite from the economic ultramafic-mafic Noril'sk-1 intrusion (Russia): Hf-isotope constraints on source composition

    Malitch, K. N.; Belousova, E. A.; Badanina, I. Yu.; Griffin, W. L.


    The ultramafic-mafic Noril'sk-1 intrusion in the northwestern part of the Siberian Craton (Russia) represents one of three known Noril'sk-type, ore-bearing intrusions, which host one of the world's major economic sulphide platinum-group-element (PGE)-Cu-Ni deposits. Zircon and baddeleyite dated previously both by SHRIMP (i.e. 248.0 ± 3.7 Ma, Campbell et al. 1992) and ID-TIMS (251.1 ± 3.6 Ma, Kamo et al. 1996) have been restricted to one lithology (e.g. leucogabbro) of the Noril'sk-1 intrusion. To better constrain the age of igneous event and sources involved in its generation our multi-technique study utilized ten rock samples characteristic of unmineralized and mineralized lithologies. The rocks investigated comprise (from top to bottom) gabbro-diorite (sample N1-1), leucogabbro (N1-3), olivine-free gabbro (N1-2 and N1-4), olivine-bearing gabbro (N1-5), olivine gabbro (N1-6), plagiowehrlite and plagiodunite (N1-7), taxitic-textured rocks comprising melanotroctolite, olivine gabbro with relics of ultramafic rocks (N1-8, N1-9) and contact fine-grained gabbro (N1-10). Sulphide PGE-Cu-Ni ores occur in ultramafic (N1-7) and taxitic-textured rocks (N1-8 and N1-9), which have thickness of about 17 m, whereas the low-sulphide horizon of about 1 m thick occurs in the upper part of intrusion (N1-3). In situ U-Pb analyses of zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four zircon populations (Malitch et al. 2012). The U-Pb ages of baddeleyite and the defined zircon populations cover a significant time span, from Late Paleozoic to Early Mesozoic (e.g., 290 ± 2.8; 261.3 ± 1.6; 245.7 ± 1.1; 236.5 ± 1.8 and 226.7 ± 0.9 Ma). The established distribution of U-Pb ages implies that crystallization of baddeleyite and zircon corresponds to several stages of protracted evolution of ultramafic-mafic magmas at deep-seated staging chambers and/or probably characterizes interaction of distinct magmas during formation

  18. Volatile (sulphur and chlorine), major, and trace element geochemistry of mafic to intermediate tephras from the Chilean Southern Volcanic Zone (33-43°S)

    Wehrmann, Heidi; Hoernle, Kaj; Jacques, Guillaume; Garbe-Schönberg, Dieter; Schumann, Kai; Mahlke, Julia; Lara, Luis E.


    Here we present the first systematic investigation of volatile geochemistry along the Southern Volcanic Zone (SVZ) of Chile. Holocene olivine-hosted melt inclusions in the most mafic tephras sampled from 16 volcanoes along the volcanic front of the SVZ between 33°S and 43°S were analysed for pre-eruptive sulphur, chlorine, and major element contents. These results are combined with trace element compositions of the host whole rocks. The highest fractionation-corrected gas contents occur in the least-degassed melt inclusions from small monogenetic cones of Los Hornitos, Cabeza de Vaca, and Apagado from both the transitional and the southern-central SVZ, reaching ~3,000 μg/g S and 1,400 μg/g Cl, while the lowest abundances of ~1,100 μg/g S and ~600 μg/g Cl were found in the central SVZ at Volcán Lonquimay, Volcán Llaima, and Volcán Villarrica. Chlorine co-varies with trace element indicators for the degree of melting and/or source enrichment, such that the lowest Cl contents are found in high-degree melts from the most depleted mantle sources. The size of the volcanic edifices correlates inversely with Cl abundances in the melt. This could reflect more extensive degassing during ascent through the complex magma plumbing systems beneath the stratovolcanoes or greater dilution during larger degrees of melting of more depleted sources, or a combination of these factors. Compared to other subduction zones, the SVZ melt inclusions exhibit Cl and S abundances in the same range as most of those from the Central American and those from the Marianas arcs.

  19. High-Mg adakitic rocks and their complementary cumulates formed by crystal fractionation of hydrous mafic magmas in a continental crustal magma chamber

    Ma, Qiang; Xu, Yi-Gang; Zheng, Jian-Ping; Sun, Min; Griffin, William L.; Wei, Ying; Ma, Liang; Yu, Xiaolu


    Understanding how adakitic magmas form is important for understanding the formation of the continental crust. Generating such high-Sr/Y rocks by crystal fractionation of basalts/basaltic andesites in magma chambers has been proposed in a wide range of tectonic settings. However, the complementary cumulates predicted by this scenario have rarely been observed. The late Triassic (~ 227 Ma) Ningcheng complex from the North China Craton is composed of a websterite - (Ol -/Hbl-) pyroxenite - gabbro unit and a quartz-diorite unit. They are interpreted as the products (cumulates and derivative melts, respectively) of fractionation from hydrous mafic magmas at mid- to lower-crustal pressures (4.9 ~ 8.3 kbar). The quartz diorites are high-Mg intermediate rocks with moderate SiO2 (57.0 ~ 62.9 wt%), high Mg# (> 49) and adakitic trace element signatures, such as high Sr (≥ 636 ppm) and light rare earth elements (REEs), low Y (≤ 17 ppm) and heavy REEs (Yb ≤ 1.8 ppm), lack of obvious Eu anomalies, and high Sr/Y (≥ 31) and La/Yb (≥ 24)). These adakitic signatures reflect differentiation of hydrous mantle-derived magmas in the deep crust, leaving behind a plagioclase-free residual solid assemblage in the early stages, which is represented by the coeval websterite-pyroxenite complex. This study therefore not only demonstrates that hydrous crystal fractionation is an important mechanism to form adakitic rocks, but also presents an example of a preserved fractionating system, i.e. high-Sr/Y rocks and their complementary cumulates. A geochemical comparison is made between representative adakitic rocks formed by fractionation of hydrous magmas and Archean TTGs. It is suggested that crystal fractionation is an efficient process for making Phanerozoic high Sr/Y rocks but was not responsible for the formation of Archean granitoids.

  20. Mineralogical and numerical approaches to establish the pre-eruptive conditions of the mafic Licán Ignimbrite, Villarrica Volcano (Chilean Southern Andes)

    Lohmar, Silke; Parada, Miguel; Gutiérrez, Francisco; Robin, Claude; Gerbe, Marie Christine


    The Licán Ignimbrite represents a large explosive basaltic andesite event in the eruptive history of the Villarrica Volcano, an active stratovolcano of the Southern Andean Volcanic Zone. A mineralogical study of this ignimbrite indicates important disequilibrium features. Resoption textures were observed around Ca-rich (An74-92; Group 1) and more sodic (An35-44; Group 2) plagioclase phenocryst cores. Rims on these phenocrysts as well as microlites grew with an intermediate composition (An47-63; Group 3). Low- and high-Mg clinopyroxene and orthopyroxene phenocrysts were also identified; most of them showing reverse Mg zoning. Based on these mineralogical data and thermodynamic modeling, an increase of about 200 °C in temperature (from ~ 900-1000° to ~ 1100-1150 °C), a decompression of ~ 400 bar (equivalent to ~ 1.5 km) and a decrease in H2O content in the melt of ~ 1.6 wt.% are identified during crystallization. Addition of hot magma from below would have caused heating of the reservoir with the consecutive ascent of magma pulses, H2O exsolution and convective mixing (compositional and/or thermal mixing). A numerical model using the Finite Element Method was developed to assess the response of the Licán Ignimbrite reservoir upon conductive heating by 200 °C by mafic underplating; this model indicates a rapid (tens of years) temperature homogenization of this system, with ascending magma plumes with velocities as high as 6 m/h. Because the Licán Ignimbrite erupted at the end of the Pleistocene glaciation, glacial unloading could have also contributed to depressurization of the reservoir.

  1. Geological and petrological aspects of Ni-Cu-PGE mineralization in the early Paleoproterozoic Monchegorsk layered mafic-ultramafic complex, Kola Peninsula

    Sharkov, E. V.; Chistyakov, A. V.


    The Early Paleoproterozoic Monchegorsk Complex comprises two independent large layered mafic-ultramafic intrusions: the Monchegorsk pluton and the Main Range massif formed about 2.50 and 2.46 Ga ago, respectively. They are composed of similar cumulates, though they differ somewhat in the isotopic parameters of rocks, cumulate stratigraphy and derived from siliceous high-Mg series melts that arose in the same large long-living volcanic center. The economic syngenetic Ni-Cu-PGE sulfide mineralization related to the earlier Monchegorsk pluton is represented by two types of ores. The first type, pertaining to fractionation of the primary melt, is opposite to the reef formed due to injection of a special ore-bearing melt into the solidifying intrusive chamber. The primary magmatic mineralization is largely composed of Ni-Fe-Cu sulfides and Pd-Pt sulfides, bismuthides, and tellurides. Only small PGE and probably chromite occurrences are related to the Main Range massif. In the Mid-Paleoproterozoic (2.0-1.9 Ga), the complex was transformed into a collage of tectonic blocks confined to the regional fault zone. The Monchegorsk pluton was retained better, and only rocks of its southern framework were involved into tectonic and metamorphic reworking with the formation of economic metamorphic low-sulfide PGE mineralization with widespread Pd and Pt telluro-bismuthides, arsenides, stannides, antimonides, and selenides. The ore formation was accompanied by PGE redistribution and segregation of lenticular orebodies with diffuse contours. Thus, the Monchegorsk ore cluster is characterized by juxtaposition of unaltered primary magmatic deposits and those formed as a result of their metamorphism and distinguished from the former by structure and composition. The comparative study of these deposits opens up new possibilities for comprehending ore-forming processes in the same situations.

  2. Impingement of Deep Mantle-Derived Upwelling Beneath Northern, Subducted Extension of the East Pacific Rise and Palinspastically Restored Cenozoic Mafic Magmatism in Western North America

    Rowley, D. B.; Moucha, R.; Forte, A. M.; Mitrovica, J. X.; Simmons, N. A.; Grand, S. P.


    Reconstruction of the retrodicted whole mantle flow, based on presently imaged distribution of variations in seismic velocity and its correlation to density (Simmons et al. 2009), over the past 30 Ma, in the North American fixed frame of reference, reveals that the northern, now subducted, extension of the East Pacific Rise is coincident with mantle buoyancy arising from near the core-mantle boundary and extending to the base of the lithosphere (Moucha et al. 2009 GRL, in press). Divergence of the reconstructed flow near the surface is independent of the surface plate(s) and results in predicted geological manifestations distinct from those predicted by traditional plate driven models of flow. Most particularly the retrodicted flow-related dynamic topography results in progressive west to east sweep of surface uplift, that is now centered on the Colorado Plateau (Moucha et al. 2008, 2009 GRL, in press). In addition, and the primary focus of the current study is the relationship between this retrodicted mantle-wide flow and the history of magmatism within the western U.S. and adjacent Mexico. There is a close spatial correlation between the impingement of upwelling with palinspastic restored western North America (McQuarrie and Wernicke, 2005) and onset and distribution of magmatism, particularly of mafic compositions as revealed in the Navdat ( database. Although often attributed to effects of opening of a slab window (Snyder and Dickinson, 1979, McQuarrie and Oskins, 2008) associated with continued plate-driven separation, this model predicts active mantle flow induced upwelling and divergence resulting in mantle melting that sweeps across east-northeast across southern Basin and Range to the Rio Grande Rift with time and as seen in the distribution of magmatism in this region.

  3. Mafic sill/dykes intruding into late Maastrichtian-early Paleocene calciclastic units, NE-Turkey: Petrographical and geochemical features of latest magmatic activity before collision in the eastern Sakarya zone

    Aydin, Faruk; Oǧuz, Simge; Karsli, Orhan; Kandemir, Raif; Şen, Cüneyt; Uysal, İbrahim


    We present here new petrographical, mineralogical and whole-rock geochemical data for mafic sill/dykes intruding into late Maastrichtian-early Paleocene calciclastic units in the Düzköy (Trabzon) and Cankurtaran (Artvin) areas (NE Turkey) of the eastern Sakarya zone (ESZ) in order to decipher the latest magmatic activity in the final stage of subduction-related magmatism of the ESZ. U-Pb zircon dating for the mafic sill/dykes in the region yielded ages varying from 83.6 to 78.5Ma (i.e. Early Campanian). Mafic sill/dykes consist of mostly basalts and lesser basaltic-andesites with komatiitic basalts. Most of the dyke samples display aphyric to porphyritic texture with phenocrysts of plagioclase (mostly replaced by calcite), clinopyroxene (partly uralized), olivine (almost serpentinized), and amphibole (partly chloritized). Based on the MgO, Nb and Zr contents with Nb/Y ratio, the mafic dykes from Düzköy area are mainly classified as two subgroups (basalts and basaltic andesites) while those of Cankurtaran can be divided into three different groups (low- and high-Nb normal basalts and komatitic basalts). Düzköy basaltic dykes have higher MgO (3.8-7.8%) and lower Nb (3-4ppm) and Zr (53-62ppm) contents with Nb/Y ratio (˜0.2) than those of Düzköy basaltic-andesitic dykes (MgO: ˜1.8%, Nb: 6-15ppm, Zr: 106-145ppm, Nb/Y: 0.3-0.6). On the other hand, Cankurtaran mafic sill/dykes have relatively high MgO contents (˜4-20%). These sill/dykes with 15-20% of MgO and group 1 and 4.0-4.4% for group 2), Nb (3-14ppm for group 1 and 19-21ppm for group 2), Zr (94-111ppm for group 1 and 125-140ppm for group 2) contents, and Nb/Y ratio (˜0.2-0.8 for group 1 and (˜1.0-1.2 for group 2). Although the studied mafic sill/dykes have generally subalkaline composition, they show a geochemical character changing from mostly tholeiitic to rarely calc-alkaline and show typical features of late Cretaceous subduction-related magmatic rocks as in the ESZ. On the chondrite-normalized REE

  4. Petrogenesis of Late Mesozoic granitoids and coeval mafic rocks from the Jiurui district in the Middle-Lower Yangtze metallogenic belt of Eastern China: Geochemical and Sr-Nd-Pb-Hf isotopic evidence

    Xu, Yao-Ming; Jiang, Shao-Yong; Zhu, Zhi-Yong; Yang, Shui-Yuan; Zhou, Wei


    Large-scale Cu-Au mineralization is associated with the Late Mesozoic granitoids in the Jiurui district of the Middle-Lower Yangtze Mineralization Belt in Eastern China. To constrain the petrogenesis of these granitoids and coeval mafic rocks, a detailed geochemical and Sr-Nd-Pb-Hf isotopic study was performed. The Jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry. These granitoids are characterized by SiO2 and K2O contents of 58.8 wt.% to 68.6 wt.% and 1.9 wt.% to 5.7 wt.%, respectively. These granitoids show relatively high MgO contents (1.0 wt.% to 3.1 wt.%, average 2.1 wt.%) and high Mg# values (39 to 70, average 54). The Jiurui granitoids are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE), and compatible trace elements (Cr, Ni and V) but are relatively depleted in Nb, Ta, Y and Yb. These rocks show a negligible negative Eu anomaly (Eu/Eu* = 0.76-1.13, average 0.91) and nearly no negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7060 to 0.7092, and the ɛNd(t) values vary from - 5.4 to - 2.0. The granitoids show radiogenic Pb isotopic ratios with values of 206Pb/204Pb (17.93-18.21), 207Pb/204Pb (15.55-15.58), and 208Pb/204Pb (38.16-38.56) for the plagioclases. The zircon Hf isotopic compositions show ɛHf(t) values from - 11.8 to 2.4. The coeval mafic rocks consist of lamprophyre, diabase and fine-grained mafic dyke. These rocks are characterized by SiO2 contents ranging from 47.6 wt.% to 54.8 wt.%, with a negative Eu anomaly and a positive to negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7059 to 0.7071, and the ɛNd(t) values vary from - 3.8 to - 1.4. By comparing the geochemical and isotopic compositions of the Jiurui granitoids and the coeval mafic rocks, we conclude that the granitoids are similar to adakites that were likely related to the delamination processes, and the coeval mafic rocks may have originated directly from

  5. The Ilha Anchieta Quartz Monzonite: the southernmost expression of ca. 500 Ma post-collisional magmatism in the Ribeira Belt

    José M. Azevedo Sobrinho


    Full Text Available The Ilha Anchieta Quartz Monzonite (IAQM occupies most of the homonymous island in the coast of the state of São Paulo, and is intrusive into foliated rocks of the ~565 Ma Ubatuba Charnockite. The main petrographic variety is a porphyritic biotite-hornblende quartz monzonite with 2-4 cm tabular microcline megacrysts set in a medium-grained groundmass and magmatic foliation. Outcrop-scale structures indicate cumulative processes (modal and grain-size magmatic banding and interaction with basic magmas (mafic microgranular enclaves. Lithogeochemical data indicates that the main variety is intermediate to acid (S1O2 = 63-67%, alkali-calcic, metaluminous and magnesian (mg# ~30, showing moderate Sr (300-400 ppm and Ba (~1500 ppm contents and relatively high HFSE (Nb = 40 ppm; Zr = 550-700 ppm. The older charnockites are more silicic (S1O2 = 71-78%, ferroan(mg# = 12-16, and have very low Sr (13-80 ppm contents, resulting in Ba/Sr ratios remarkably higher than the IAQM (10 versus 4. LA-MC-ICPMS U-Pb zircon dating of the IAQM yielded 499.7 ± 5.9 Ma. This is the youngest magmatic age identified so far in the crystalline basement of the state of São Paulo, and indicates that the pluton is the southernmost expression of the post-collisional "G5" magmatism in the Ribeira Belt.O Quartzo Monzonito Ilha Anchieta (QMIA ocupa a maior parte da ilha homônima na região costeira do Estado de São Paulo, e é intrusivo em rochas foliadas do Charnockito Ubatuba (~565 Ma. A principal variedade petrográfica é um biotitahornblenda quartzo monzonito porfirítico com foliação magmática e megacristais tabulares de microclínio com 2-4 cm em matriz de granulação média. Estruturas em afloramento indicam processos cumuláticos (bandamento modal e granulométrico e interação com magmas básicos (enclaves microgranulares máficos. Dados geoquímicos indicam que a variedade principal é intermediária a ácida (SiO2 = 63-67%, tem caráter

  6. Petrology of Gameleira potassic lamprophyres, São Francisco Craton

    Jorge Plá Cid


    Full Text Available Gameleira lamprophyres are dykes and mafic microgranular enclaves associated with the shoshonitic Gameleira monzonite. This association belongs to the Paleoproterozoic alkaline magmatism from Serrinha nucleus, northeast Brazil. The liquidus paragenesis is diopside, pargasite, apatite and mica. Reverse zoning was identified in the groundmass alkali feldspar and was related to the undercooling of lamprophyric magma during the emplacement, with high growth rate of pargasite/edenite inducing disequilibrium between feldspars and liquid. Chemical data indicate that the lamprophyres are basic rocks (SiO2 3 wt% and potassic signature (K2O/Na2O ≈ 2. High contents of MgO and Cr are consistent with a signature of a primary liquid, and such concentrations, as well as Al, K, P, Ba, Ni- and light rare earth elements, are consistent with an olivine-free metasomatic mantle source enriched in amphibole, clinopyroxene and apatite. By contrast, the ultrapotassic lamprophyres from Morro do Afonso, contemporaneous alkaline ultrapotassic magmatism in Serrinha nucleus, were probably produced by melting of a clinopyroxene-phlogopite-apatite enriched-source. The identification of different mineral paragenesis in the source of potassic and ultrapotassic lamprophyres from Serrinha nucleus can contribute to the understanding of the mantle heterogeneities and tectonic evolution of this region.Os lamprófiros Gameleira são formados por diques e enclaves máficos microgranulares associados ao monzonito shoshonítico Gameleira. Esta associação pertence ao magmatismo alcalino Paleoproterozóico do núcleo Serrinha, nordeste do Brasil. A paragênese no liquidus é formada por diopsídio, pargasita, apatite e mica. Zonamento inverso foi identificado no feldspato alcalino da matriz e relacionado ao super-resfriamento do magma lamprofírico durante sua colocação, com alta taxa de crescimento da pargasita/edenita induzindo desequilíbrio entre os feldspatos e o l

  7. Mesozoic-Cenozoic mafic magmatism in Sanandaj-Sirjan Zone, Zagros Orogen (Western Iran): Geochemical and isotopic inferences from Middle Jurassic and Late Eocene gabbros

    Deevsalar, R.; Shinjo, R.; Ghaderi, M.; Murata, M.; Hoskin, P. W. O.; Oshiro, S.; Wang, K. L.; Lee, H. Y.; Neill, I.


    One of the consequences of Neo-Tethys ocean subduction beneath the Central Iranian Micro-continent (CIMC) is the development of rare gabbroic intrusions in the Malayer-Boroujerd Plutonic Complex (MBPC) located in the Sanandaj-Sirjan Zone (SaSZ) of the Zagros Orogenic belt. The MBPC is a suite of extensive felsic and lesser mafic magmatic products in the northern SaSZ with geochemical signatures of arc-like magmatism during the Middle Jurassic (Ghorveh-Aligudarz arc) and intraplate type in the Late Eocene. Middle Jurassic gabbros (non-cumulate and cumulate) have low-Ti concentrations (non-cumulates belong to common liquid line of descent, with complementary trace element patterns. Much of the variation between samples can be modeled by fractional crystallization (FC) of a common parent; only one cumulate gabbro from this suite exhibits isotopic evidence of contamination, probably by Rb-depleted crustal materials. The Late Eocene gabbros have relatively high-Ti (> 1 wt.%) and display isotopically depleted Sr-Nd values (initial 87Sr/86Sr: 0.7044-0.7087, εNd(t): 1.9 -+3.2, barring one crustally-contaminated sample). OIB-like trace element characteristics such as enriched HFSE, and only minor enrichment of LILE and LREE, reflect a within-plate character and asthenospheric source. Trace element modeling indicates small degree melting (fmelting: 0.05) of upper mantle lherzolite (garnet:spinel 3:1) followed by higher degree melting (fmelting: 0.15) at shallower depths (garnet:spinel 4.5:2). The Eocene parental magma underwent FC of olivine and clinopyroxene. We propose that Eocene asthenospheric upwelling was triggered by slab tearing in response to slab-rollback, which is elsewhere reported to have triggered a 'flare-up' of extension-related magmatism across Iran. Three stages of tectono-magmatic evolution in the Ghorveh-Aligudarz arc segment of the N-SaSZ are represented by: 1) arc-like magmatism during active subduction of the Neo-Tethys seaway at Middle Jurassic, 2

  8. Intensive hydration of the wedge mantle at the Kuril arc - NE Japan arc junction: implications from mafic lavas from Usu Volcano, northern Japan

    Kuritani, T.; Tanaka, M.; Yokoyama, T.; Nakagawa, M.; Matsumoto, A.


    The southwestern part of Hokkaido, northern Japan, is located at the junction of the NE Japan arc and the Kuril arc. The subducting Pacific plate under this region shows a hinge-like shape due to the dip change of the subducting plate along the trench. Because of the interest in this unique tectonic setting, this arc-arc junction has been the focus of extensive geophysical studies (e.g. Kita et al., 2010, Morishige and van Keken, 2014; Wada et al., 2015). This region is also known as an area in which magmatism has been intense; there are many active volcanoes such as Usu, Tarumae, and Komagatake, and large calderas including Toya, Shikotsu, and Kuttara. In this region, the temporal and spatial evolution of the volcanism and the chemical compositions of the volcanic rocks are well characterized (e.g. Nakagawa, 1992). However, the generation conditions of magmas have not been estimated for these volcanoes, probably because of the scarcity of basaltic products. Therefore, a possible link between the tectonic setting and the intense magmatism is still unclear. In this study, we carried out a petrological and geochemical study on mafic lavas (49.6-51.3 wt.% SiO2) from Usu Volcano, and estimated the conditions under which the magmas were generated. By application of a plagioclase-melt hygrometer to the plagioclase and the host magma, the water content of ~6.5 wt.% was obtained for the basaltic magma. Using this information, as well as the olivine maximum fractionation model (Tatsumi et al., 1983), the composition of the primary magma is estimated to be 47.9 wt.% SiO2, 15.1 wt.% MgO, and 4.1 wt.% H2O. Analyses using the multi-component thermodynamics suggest that the primary magma was generated in the source mantle with 0.9 wt.% H2O at 1310ºC and at 1.6 GPa. The water content of 0.9 wt.% of the source mantle is significantly higher than the estimates for the source mantle in the main NE Japan arc (hinge-like shape, and many fractures might have been developed in the slab

  9. Pre-eruptive volatile content of mafic magma from the 2.0-1.7 ka Castle Creek eruptive period, Mount St. Helens

    Rea, J.; Wallace, P. J.; Clynne, M. A.


    Among global convergent margins, the Cascade arc (Pacific Northwest, North America) has an atypically warm thermal profile due to the young age of the subducting ocean crust (≤10 Ma) and slow rate of subduction (3.5 cm/yr) in this region. Slab dehydration is thus expected to occur at relatively shallow subduction depths, resulting in high fluid fluxes in the mantle wedge below the forearc, with minimal addition of volatiles directly beneath the main volcanic front. Across-arc trends in magmatic volatiles should be most visible within particularly wide (E-W) portions of the active volcanic arc, such as are observed in Southern Washington, Central Oregon, and Northern California. As part of an ongoing study aimed at constraining variations in magmatic volatiles using monogenetic cinder cones across the Southern Washington Cascades, we analyzed the H2O and CO2 contents of olivine-hosted melt inclusions in basaltic scoria (Bu tephra) from the Castle Creek eruptive period (2.0-1.7 ka) of Mount St. Helens (MSH). The defining feature of this period is the first appearance of mafic magma at the surface, which initiated the modern Mount St. Helens and its variety of rock compositions (Mullineaux, 1996). Andesite, dacite, and basalt all were erupted during Castle Creek time, producing pyroclastic flows, surges, and tephra as well as lava flows. Our initial results show pre-eruptive H2O contents of 0.4-1.3 wt. % H2O and CO2 values that are below detection (<25-50 ppm). The morphology of the olivine crystals and their melt inclusions indicate relatively rapid crystallization. Given the low CO2 values, we conclude that the melt inclusions trapped partially degassed melts at relatively low pressure in a volcanic conduit or shallow storage reservoir. MSH represents the western extent of a stretch of volcanism extending ~100 km to the east; MSH magmas are thus expected to have high volatile contents relative to the other volcanic centers at this latitude.

  10. Emplacement age for the mafic-ultramafic plutons in the northern Dabie Mts. (Hubei): Zircon U-Pb, Sm-Nd and 40Ar/39Ar dating

    WANG; Jianghai


    [1]Zhang, Q., Ma, B. L., Liu, R. X. et al., A remnant of continental lithospheric mantle above a subduction zone: Geochemical constraints on ultramafic rocks from Raobazhai area in Anhui Province, Sci. in China, Ser. B, 1995, 38(12): 1522- 1529.[2]Zhai, M. G., Cong, B. L., Petro-tectonics of the Sulu-Dabie Shan metamorphic belt, Central and East China, Sci. in China, Ser. D, 1996, 39(3): 319-328.[3]Li, S. G., Hart, S. R., Zheng, S. G. et al., Timing of collision between the North and South China Blocks-- the Sm-Nd isotopic age evidence, Sci. in China, Ser. B, 1989, 32(11): 1393-1400.[4]Ni, Y. H., Li, S. G., Sm-Nd ages of the syn-collisional mafic-ultramafic intrusions in the Dabie Mountains, Chinese Sci. Bull., 1998, 43(2): 160-163.[5]Chen, D. G., Wu, Y. B., Xia, Q. K. et al., Sm-Nd ages for the Jiaoziyan gabbro pluton and the characteristics of Nd isotopes, Acta Geosci. Sinica, 1997, 18(Suppl.): 9-11.[6]Jahn, B. M., Wu, F. Y., Lo, C. H. et al., Crust-mantle interaction induced by deep subduction of the continental crust: geochemical and Sr-Nd isotopic evidence from post-collisional mafic-ultramafic intrusions of the northern Dabie complex, central China, Chem. Geol., 1999, 157: 119-146.[7]Li, S. G., Jagoutz, E., Zhang, Z. Q. et al., Structure of high-metamorphic belt in the Dabie mountains and its tectonic implications, Chinese Sci. Bull., 1995, 40(Suppl.): 138-140.[8]Zhang, R. Y., Liou, J. G., Tsai, C. H., Petrogenesis of a high-temperature metamorphic terrain: a new interpretation for the north Dabie Shan, central China, J. Metamorphic Geol., 1996, 14: 319-333.[9]Wang, J. H., The Early Evolution of the Dabie Complex, with Special Reference to the Genetic Mechanism of Migmatites, Wuhan: China University of Geosciences Press, 1991, 1-140.[10]Suo, S. T., Zhong, Z. Q., You, Z. D., Extensional deformation of post ultrahigh-pressure metamorphism and exhumation process of ultrahigh-pressure metamorphic rocks in the Dabie massif

  11. Late Eocene-Early Oligocene two-mica granites in NW Turkey (the Uludağ Massif): Water-fluxed melting products of a mafic metagreywacke

    Topuz, Gültekin; Okay, Aral I.


    hornblende, (iii) occurrence in a ductile strike-slip zone, and (iv) relatively low magma temperatures can be accounted for by water-fluxed melting of a metagreywacke source with substantial mafic component at middle to lower crustal depths.

  12. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: evidence from petrological and in situ Sr-Hf isotopic data

    Chen, Bin; Chen, ChangJian


    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model, and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle by subduction zone fluids in an extensional regime. The principal geochemical signatures of these Mesozoic rocks include a hydrous and high-K calc-alkaline affinity, high values of Mg#, high Sr abundances, high Sr/Y and La/Yb ratios, ɛNd(t)=-13.1 to -9.0, and ISr=0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and hornblende, (2) the increase in Ti and Al(IV) from hornblende cores to rims, and the overgrowths of high-Ca pyroxene around hornblende grains as well, indicative of episode of heating and rejuvenation of the magma chamber as a result of recharge of mafic magma, (3) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (4) negative correlations between whole-rock Nd and Sr isotopic ratios, and (5) the significant differences in the values of ɛHf(t) (-9.5 to -26) within different zircons from the same intrusion. We propose that underplating of hydrous basaltic magma from the metasomatized lithospheric mantle in the lower crust resulted in partial melting of the lower crustal rocks (Precambrian TTG gneisses and amphibolite/granulite) under water-saturated conditions, during which plagioclase decomposed, leaving hornblende-rich restites and

  13. Geochemistry, geochronology and zircon Hf isotopic study of peralkaline-alkaline intrusions along the northern margin of the North China Craton and its tectonic implication for the southeastern Central Asian Orogenic Belt

    Zhao, Pan; Jahn, Bor-ming; Xu, Bei; Liao, Wen; Wang, Yanyang


    A giant Permian alkaline magmatic belt has recently been identified in southern Inner Mongolia, along the northern margin of the North China Craton (NCC). This belt is mainly composed of syenite, quartz syenite, alkaline granite and mafic microgranular enclaves (MME)-bearing granodiorite. In order to study the petrogenesis and tectonic implications of these rocks, we undertook zircon U-Pb dating and geochemical analysis of two Permian alkaline plutons. The first Guangxingyuan Pluton occurs in the Hexigten area and is composed of MME-bearing tonalite, K-feldspar granite and syenite. The second Durenwuliji Pluton, located in the Xianghuangqi area, comprises syenite, quartz syenite and K-feldspar granite. Zircon U-Pb dating on tonalite, K-feldspar granite, syenite and quartz syenite from the two plutons yielded a tight range of ages from 259 to 267 Ma. The peralkaline-alkaline rocks show high abundance of total alkalis (K2O + Na2O = 7.9-12.9%) and K2O contents (3.9-8.0%), enrichment in large ion lithophile elements (LILE) and light rare earth element (LREE), and depletion of high field strength elements (HFSE). The associated tonalite and MMEs display I-type granitic geochemical affinity, with less total abundance of trace elements than the peralkaline-alkaline rocks. Zircon Hf isotopic analysis of the Guangxingyuan pluton yielded a large range of εHf(t) values from - 15.5 to + 6.7 and model ages (TDMC) from 781 to 2012 Ma. By contrast, the Hf isotopic data of the Durenwuliji pluton shows a small range of εHf(t) from + 6.2 to + 8.9 and TDMC from 667 to 816 Ma. The geochemical and Hf isotopic characteristics indicate that the parental magma was derived from a mixing of metasomatic mantle-derived mafic magma with different amount of crust-derived felsic magma, and followed by fractional crystallization. Considering previous tectonic studies in Inner Mongolia, a Permian post-orogenic extension was proposed to account for these peralkaline-alkaline intrusions following

  14. Early paleozoic granodioritic plutons in the Shedong W-Mo ore district, Guangxi, southern China: Products of re-melting of middle Proterozoic crust due to magma underplating

    Jiang, Xingzhou; Kang, Zhiqiang; Xu, Jifeng; Feng, Zuohai; Pang, Chongjin; Fang, Guicong; Wu, Jiachang; Xiong, Songquan


    The Shedong W-Mo ore district in the south-central Dayaoshan Uplift of Guangxi, southern China hosts the Baoshan and Pingtoubei deposits, both of which occur in granodioritic plutons. Zircon U-Pb dating of granodiorites and its mafic microgranular enclaves (MMEs) in the Baoshan deposit yielded ages of 439.8 ± 3.2 and 441.1 ± 2.2 Ma, respectively. Granodiorites have moderate SiO2 (54.5-63.0 wt.%) and high Al2O3 (15.4-17.8 wt.%) contents, wide variations in major element ratios, significant rare earth element fractionation, and small negative Eu anomalies. They are rich in Th, U, Zr, and Hf, and depleted in Ba, Nb, and Ti. Their initial 87Sr/86Sr, εNd(t), and εHf(t) values are in the range of 0.7086-0.7091, -5.2 to -6.6 and -6.3 to +1.6, respectively. Rounded or lenticular MMEs have relatively low silica and high mafic components, depletion in Eu, Sr, and Zr, and marked negative Eu anomalies. Rb/Sr and Nb/Ta ratios, and εNd(t) and εHf(t) values of the MMEs are higher than those of host granodiorites, indicating a different magmatic source. Zircon U-Pb dating of the unexposed granodiorite porphyry in the Pingtoubei deposit yielded an age of 440.0 ± 1.7 Ma. The granodiorite porphyries have high SiO2 and low K2O, FeOT, and MgO contents, with similar trace element features to the granodiorites at the Baoshan deposit, although the former has small negative Eu anomalies. Its initial 87Sr/86Sr values range from 0.7162 to 0.7173, εNd(t) values from -8.7 to -12.3, and εHf(t) values from -7.8 to +1.3, indicative of a crustal source. Nd and Hf two-stage model ages of the granodiorites, MMEs, and granodiorite porphyries have a narrow range between 1.3 and 2.2 Ga. We propose that the granodiorites and MMEs at the Baoshan deposit were produced through re-melting of middle Proterozoic crust as a result of underplating of mantle-derived magmas in a transitional compression-to-extension tectonic setting. Mantle-derived magmas provided the heat and material for the formation

  15. Geochemistry and age relationships of metamorphosed mafic sills from Sierra de Enmedio and Sierra de Carrascoy (Eastern Betic zone, Southeastern Spain

    Torres-Roldán, R. L.


    Full Text Available The presence of fairly abundant shallow-intrusive mafic bodies is a common feature of the almagride units, a recently defined group of tectonic elements of the Eastern Betic Zone whose paleogeographic and tectonic interpretation is particuIarly controversial. In this paper we focuse on the bulk geochemistry (including K/Ar data and possible age relationships of tbese rocks, and discuss them in view of their significance regarding possible tectonic framework of emplacement and subsequent crustal evolution. The analyses (49-55% SiO2 point to a derivation from tholeiitic magmas that interacted with continental crust, as indicated by enrichment in the less compatible elements, such as Ba, Rb, Th and K, whose amounts are similar to those of well known continental tholeiitic provinces. Thus, the magmatic event is inferred to have been generated in a tectonic environment comparable to that of continental rifts. Emplacement may have taken place in Upper Triassic to Middle Jurassic times, as bracketed by their intrusion within Triassic beds and one whole-rock KIAr date of 178±4 Ma from a less altered sample. Much younger analytical K/Ar ages, scattering between 41±5 and 57±2 Ma, are obtained from common samples, however, reflecting an Eocene or younger metamorphic event that caused partial recrystallisation under low-grade greenchist, to actinolite-pumpelIyite facies conditions. As compared to other mafic complexes in the Betics, the observed chemical evidence for crustal contamination makes the almagride metabasites more similar to those in the external zona (e.g. the so-calIed «opbites» than in tbe Nevado-Filábride Ensemble, thus being consistent with proposals that correlate these units with the Subbetic in the Murcia area.La frecuente presencia de cuerpos de metabasitas es una característica común de las unidades almágrides, un grupo de unidades tectónicas de la Zona Bética Oriental, de reciente definición, cuya interpretaci

  16. Brittle-ductile deformation effects on zircon crystal-chemistry and U-Pb ages: an example from the Finero Mafic Complex (Ivrea-Verbano Zone, western Alps)

    Langone, Antonio; José Alberto, Padrón-Navarta; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia


    A detailed structural, geochemical and geochronological survey was performed on zircon grains from a leucocratic dioritic dyke discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex. This latter is nowadays exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dyke consists mainly of plagioclase (An18-24Ab79-82Or0.3-0.7) with subordinate amounts of biotite, spinel, zircon and corundum. Both the leucocratic dyke and the surrounding meta-diorites show evidence of ductile deformation occurred under amphibolite-facies conditions. Zircon grains (up to 2 mm in length) occur mainly as euhedral grains surrounded by fine grained plagioclase-dominated matrix and pressure shadows, typically filled by oxides. Fractures and cracks within zircon are common and can be associated with grain displacement or they can be filled by secondary minerals (oxides and chlorite). Cathodoluminescence (CL) images show that zircon grains have internal features typical of magmatic growth, but with local disturbances. However EBSD maps on two selected zircon grains revealed a profuse mosaic texture resulting in an internal misorientation of ca. 10o. The majority of the domains of the mosaic texture are related to parting and fractures, but some domains show no clear relation with brittle features. Rotation angles related to the mosaic texture are not crystallographically controlled. In addition, one of the analysed zircons shows clear evidence of plastic deformation at one of its corners due to indentation. Plastic deformation results in gradual misorientations of up to 12o, which are crystallographically controlled. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections and designed to cover the entire exposed surface of selected grains. Such investigations revealed a strong

  17. A Late Carboniferous-Early Permian slab window in the West Junggar of NW China: Geochronological and geochemical evidence from mafic to intermediate dikes

    Yin, Jiyuan; Long, Xiaoping; Yuan, Chao; Sun, Min; Zhao, Guochun; Geng, Hongyan


    The Late Carboniferous to Early Permian is a critical period for the formation of particular high-temperature magmatic associations in West Junggar, NW China and the geodynamic processes of ridge subduction and related slab windows in the Central Asian Orogenic Belt. Mafic to intermediate dikes, exposed in the central and southeastern West Junggar extensively, mainly consist of Nb-enriched and magnesian suites. The Nb-enriched dikes (305 Ma) are characterized by high Nb contents (5.63-9.08 ppm) and large variations of major element contents, exhibiting high-K to medium-K calc-alkaline characteristics with high Na2O/K2O (1.33-3.85) and low Sr/Y (9-32) ratios. The dikes have moderate Mg# (44.6-52.9), LREE-rich and sub-horizontal HREE patterns ((La/Yb)N = 3.05-7.18; (Gd/Yb)N = 1.43-1.78) with weak Eu anomalies (Eu*/Eu = 0.81-1.10) and positive εNd (t) values (+ 5.2 to + 8.0), and likely originate from partial melting of mantle peridotite that was metasomatized by subducted sediment-derived melts and slab fluids. The medium-K magnesian dikes (305 Ma) are characterized by high MgO (3.05-7.28 wt.%), Cr (22.3-311 ppm) and Ni (32.6-199 ppm) contents and all plot in the field of high-Mg andesite. Some have very high Mg numbers (Mg# > 60), suggesting a primitive melt composition. These samples display positive Ba, Sr, K and negative Nb-Ta-Ti anomalies as well as strongly-depleted HREE patterns with weak positive Eu anomalies. They have high Sr/Y (27-126) and relatively high εNd (t) values (+ 6.0 to + 8.3), which suggest a similar petrogenesis as the Nb-enriched dikes, but were metasomatized by adakitic melts. The high-K magnesian dikes (284 Ma) are high-K calc-alkaline and have lower MgO (3.63-5.57 wt.%) compared with the medium-K suite. They have high Sr (422-819 ppm), Sr/Y (26-62) ratios and εNd (t) values (+ 7.0 to + 7.1) with relatively flat REE patterns ((La/Yb)N = 2.4-5.5), probably originating from partial melting of K-enriched mantle wedge peridotite metasomatized

  18. Tephra architecture, pyroclast texture and magma rheology of mafic, ash-dominated eruptions: the Violent Strombolian phase of the Pleistocene Croscat (NE Spain) eruption.

    Cimarelli, C.; Di Traglia, F.; Vona, A.,; Taddeucci, J.


    A broad range of low- to mid-intensity explosive activity is dominated by the emission of ash-sized pyroclasts. Among this activity, Violent Strombolian phases characterize the climax of many mafic explosive eruptions. Such phases last months to years, and produce ash-charged plumes several kilometers in height, posing severe threats to inhabited areas. To tackle the dominant processes leading to ash formation during Violent Strombolian eruptions, we investigated the magma rheology and the field and textural features of products from the 11 ka Croscat basaltic complex scoria cone in the Quaternary Garrotxa Volcanic Field (GVF). Field, grain-size, chemical (XRF, FE-SEM and electron microprobe) and textural analyses of the Croscat pyroclastic succession outlined the following eruption evolution: activity at Croscat began with fissural, Hawaiian-type fountaining that rapidly shifted towards Strombolian style from a central vent. Later, a Violent Strombolian explosion included several stages, with different emitted volumes and deposit features indicative of differences within the same eruptive style: at first, quasi-sustained fire-fountaining with ash jet and plume produced a massive, reverse to normal graded, scoria deposit; later, a long lasting series of ash-explosions produced a laminated scoria deposit. The eruption ended with a lava flow breaching the western-side of the volcano. Scoria clasts from the Croscat succession ubiquitously show micrometer- to centimeter-sized, microlite-rich domains (MRD) intermingled with volumetrically dominant, microlite-poor domains (MPD). MRD magmas resided longer in a relatively cooler, degassed zone lining the conduit walls, while MPD ones travelled faster along the central, hotter streamline, the two interminging along the interface between the two velocity zones. The preservation of two distinct domains in the short time-scale of the eruption was favoured by their rheological contrast related to the different microlite

  19. An example of post-collisional mafic magmatism: the gabbro-anorthosite layered complex from the Tin Zebane area (western Hoggar, Algeria)

    Aı̈t-Djafer, Saı̈da; Ouzegane, Khadidja; Paul-Liégeois, Jean; Kienast, Jean Robert


    The Tin Zebane gabbro-anorthosite layered mafic intrusion represented by plagioclase-rich cumulates forms a set of small lenticular to round-shaped mainly undeformed bodies intruding the Pan-African high-pressure metamorphic rocks from western Hoggar (Tuareg shield, southwest Algeria). The coarse-grained anorthosites are mainly made of slightly zoned bytownite (An 86-74) with the higher anorthite content at the cores. Anorthosites are interlayered with leucogabbros and gabbros that show preserved magmatic structures and with olivine gabbros characterised by coronitic textures. The primary assemblage in gabbros includes plagioclase (An 93-70), olivine (Fo 77-70), zoned clinopyroxene (En 43-48Fs 05-13Wo 41-49 with Al 2O 3 up to 4.3 wt.%) and rare orthopyroxene (En 73-78). Pyroxenes and olivine are commonly surrounded by Ca-amphibole. The olivine-plagioclase contact is usually marked by a fine orthopyroxene-Cr-spinel-amphibole symplectite. A magnesian pigeonite (En 70-75Fs 19-20Wo 6-10) is also involved in corona. The coronitic minerals have equilibrated with the primary mineral rims at P- T- aH2O conditions of 797 ± 42 °C for aH2O=0.5 and 808 ± 44 °C for aH2O=0.6 at 6.2 ± 1.4 kbar. The Tin Zebane gabbroic rocks are depleted in REE with a positive Eu anomaly, high Sr (>10 ∗ chondrite) and Al 2O 3 concentrations (17-33%) that support plagioclase accumulation with the extreme case represented by the anorthosites. The REE patterns can be modelised using plagioclase, clinopyroxene and orthopyroxene REE signature, without any role played by accessory minerals. High MgO content points to olivine as a major cumulate phase. Anorthositic gabbros Sr and Nd isotopic initial ratios are typical of a depleted mantle source (Sr i=0.70257-0.70278; ɛNd=+5.9 to +7.8). This isotopic signature is identical to that of the 10-km wide 592 Ma old dyke complex composed of alkaline to peralkaline granites and tholeiitic gabbros and one single bimodal complex can be inferred. The source

  20. Lower Devonian paleomagnetic dating of a large mafic sill along the western border of the Murzuq cratonic basin (Saharan metacraton, SE Algeria).

    El-M. Derder, Mohamed; Maouche, Said; Liégeois, Jean-Paul; Henry, Bernard; Amenna, Mohamed; Ouabadi, Aziouz; Bellon, Hervé; Bruguier, Olivier; Bayou, Boualem; Bestandji, Rafik; Nouar, Omar; Bouabdallah, Hamza; Ayache, Mohamed; Beddiaf, Mohamed


    The Murzuq basin located in central North Africa, in Algeria, Libya and Niger is a key area, delineating a relictual cratonic area within the Saharan metacraton (Liégeois et al., 2013). On its western border, we discovered a very large sill ("Arrikine" sill), with a thickness up to 250m and a minimum length of 35 km. It is made of mafic rocks and is interbedded within the Silurian sediments of the Tassilis series. In the vicinity, the only known post-Pan-African magmatism is the Cenozoic volcanism in the In Ezzane area. Further south in Niger, also along the SW border of the Murzuq basin, large Paleozoic dolerite (Carte géologique du Sahara central, 1962) are probably related to the "Arrikine" sill magmatism, as they are in the same stratigraphical position. Several hundred kilometers westward and southwestward of Arrikine, Paleozoic magmatic products are known: Carboniferous basic intrusives (346 Ma; Djellit et al., 2006) are located in the Tin Serririne basin and Devonian ring complexes (407 Ma; Moreau et al, 1994) in the Aïr Mountains. For the Arrikine sill, K/Ar data gave a rejuvenation age (326 Ma) related to a K-rich aplitic phase and the LA-ICP-MS U-Pb method on zircon showed that only inherited zircons are present (0.6 to 0.7, 2.0 and 2.7 Ga ages), pointing to ages from the underlying basement corresponding to the Murzuq craton covered by Pan-African sediments (Derder et al., 2016). By contrast, a well-defined paleomagnetic pole yielded an age of 410-400 Ma by comparison with the Gondwana Apparent Polar Wander Path (APWP). This age, similar to that reported for the Aïr complexes (Moreau et al., 1994), can be correlated with the deep phreatic eruption before Pragian time thought to be at the origin of sand injections, which gave circular structures observed on different borders of the Murzuq basin (Moreau et al,. 2012). This Lower Devonian magmatism had therefore a regional extension and can be related to a "Caledonian" transtensive reactivation of the

  1. Isotopic and trace element geochemistry of alkalic-mafic-ultramafic-carbonatitic complexes and flood basalts in NE India: Origin in a heterogeneous Kerguelen plume

    Ghatak, Arundhuti; Basu, Asish R.


    The Archean East Indian cratonic margin was affected by the Kerguelen plume (KP) ˜117 Ma, causing flood-basalt eruptions of the Rajmahal-Bengal-Sylhet Traps (RBST). The RBST cover ˜one million km2 in and around the Bengal Basin as alkalic-ultrabasic intrusives in the west and Sikkim in the north, and Sylhet basalts and alkalic-carbonatitic-ultramafic complexes in the Shillong plateau - Mikir hills farther east of the Rajmahal-Bengal Traps. We provide new Nd-Sr-Pb-isotopic and trace element data on 21 unreported discrete lava flows of the Rajmahal Traps, 56 alkalic-carbonatitic-mafic-ultramafic rocks from four alkalic complexes, and three dikes from the Gondwana Bokaro coalfields, all belonging to the RBST. The data allow geochemical correlation of the RBST with some contemporaneous Kerguelen Plateau basalts and KP-related volcanics in the southern Indian Ocean. Specifically, the new data show similarity with previous data of Rajmahal group I-II basalts, Sylhet Traps, Bunbury basalts, and lavas from the southern Kerguelen Plateau, indicating a relatively primitive KP source, estimated as: ɛNd(I) = +2, 87Sr/86Sr(I) = 0.7046, with a nearly flat time-integrated rare earth element (REE) pattern. We model the origin of the uncontaminated RBST basalts by ˜18% batch melting with a 2× chondritic KP source in the spinel-peridotite stability depths of 60-70 km in the mantle. The new geochemical data similar to the Rajmahal group II basalts indicate a light REE enriched average source at ɛNd(I) = -5, 87Sr/86Sr(I) = 0.7069. Our geochemical modeling indicates these lavas assimilated granulites of the Eastern Ghats, reducing the thickness of the continental Indian lithosphere. Lack of an asthenospheric MORB component in the RBST province is indicated by various trace element ratios as well as the Nd-Sr isotopic ratios. Three alkalic complexes, Sung, Samchampi, and Barpung in NE India, and one in Sikkim to the north are of two groups: carbonatites, pyroxenites, lamproites

  2. Formación de megacristales de feldespato potásico en el sector sur del batolito Cerro Aspero-Alpa Corral (32°40'S y 64°50'W, Sierras Pampeanas, Córdoba, Argentina

    Pinotti, L. P.


    Full Text Available The surrounding rocks of studied area are composed by a metamorphic sequence which includes gneisses, schists, amphibolites, marbles and heterogeneous migmatites in non-conformity intruded by a granitic pluton. All this sequence is dated as having late-Precambric to mid-Paleozoic age.Three facies, mostly of monzogranitic composition, were identified. This study focuses on the porphiric facies; detailed petroestructural studies being performed, the orientation of large microcline crystal and associated microgranular enclaves being measured.Different primary flow directions were determined with track variation of microcline megacrystal and enclaves from subvertical to nearly horizontal positions.These changes have been interpreted as a convective system within the pluton.The presence of a marked planar fabric in microcline megacrystals along with phenomena such a size-variation of crystal, synneusis, crystal trending at the enclave's border and crystal accumulation, proves their early magmatic origin. The enclaves show a cinematic of deformation produced by simple shear.El entorno encajante de la zona estudiada está integrado por una secuencia metamórfica que incluye gneises, esquistos, anfibolitas, calizas cristalinas y migmatitas heterogéneas, intruidas discordantemente por el plutón granítico. A este conjunto puede asignársele una edad precámbrica superior-paleozoica media.Se identificaron tres facies, en su mayoría de composición monzogranítica, diques micrograníticos a aplíticos y enclaves. En este trabajo se pone énfasis en la facies porfiroide efectuándose estudios petroestructurales de detalle, tomando como indicadores la orientación de los grandes cristales de microclina y enclaves microgranulares asociados.Se determinaron distintas direcciones de flujo primario con variaciones en la trayectoria de los megacristales de microclina y enclaves desde posiciones subverticales hasta aproximadamente horizontales. Estos cambios han

  3. 全球化下"跨国移民社会空间"的地方响应——以广州小北黑人区为例%The local response of transnational social space under globalization in urban China: A case study of African enclave in Guangzhou

    李志刚; 薛德升; 杜枫; 朱颖


    After a successful market reform featured by opening-up, urban China is facing a tremendous sociospatial restructuring in recent years. The rise of a new type of social space, i. e. , ethnic enclaves has been remarkable. Taking Xiaobei of Guangzhou City as a study case, this paper examines the response of local residents and communities. Method of triangulation is mainly used, along with both quantitative analysis such as questionnaire and logistics regression and qualitative analysis of semi-structured interviews, focus group and so on. As shown by the empirical study, a negative representation of African communities has been constructed in Guangzhou. Attitudes of local residents surveyed upon African en-claves do not show a consistent result of either acceptance or exclusion. Through a logistic regression, it is found that in terms of the variables of age, gender, educational attain-ments, the length of living time or religions, no variables can stand out to be significant.Employment, however, is important, while traders, workers or those involved in service sectors mainly put a positive attitude towards Africans, in contrast to professionals, self-employed or students. Moreover, interviews of traders in Xiaobei further disclose that in-teractions between local residents and Africans are an important determinant of the rela-tions, which, however, are purely economic-based rather than cultural or social based.According to a study of local media reports and website, it is found that the local state-owned newspapers produce a negative impact upon the representation of African enclaves.Critical comments upon criminal cases of African immigrants already engender an invisible wall between local residents and African communities. Based on the sprawl of information on the net, such negative attitudes towards African immigrants soared. Therefore, this in-dicates a transition of Xiaobei from initiative concentration of African traders to negative segregation. The future of

  4. The giant Dexing porphyry Cu-Mo-Au deposit in east China: product of melting of juvenile lower crust in an intracontinental setting

    Hou, Zengqian; Pan, Xiaofei; Li, Qiuyun; Yang, Zhiming; Song, Yucai


    The Dexing porphyry Cu-Mo-Au deposit in east China (1,168 Mt at 0.45 % Cu) is located in the interior of the South China Craton (SCC), made up of two lithospheric blocks, the Yangtze and Cathaysia blocks. The Cu-Mo-Au mineralization is associated with mid-Jurassic granodioritic porphyries with three high-level intrusive centers, controlled by a series of lineaments at the southeastern edge of the Yangtze block. Available age data define a short duration (172-170 Ma) of the felsic magmatism and the mineralization (171 ± 1 Ma). The deposit shows broad similarities with deposits in volcanoplutonic arcs, although it was formed in an intracontinental setting. Porphyries associated with mineralization are mainly granodiorites, which contain abundant phenocrysts (40-60 %) and carry contemporaneous microgranular mafic enclaves (MMEs). They are mainly high-K calc-alkaline and show geochemical affinities with adakite, characterized by relatively high MgO, Cr, Ni, Th, and Th/Ce ratios. The least-altered porphyries yielded relatively uniform ɛ Nd( t) values from -0.9 to +0.6, and wide (87Sr/86Sr)i range between 0.7046 and 0.7058 partially overlapping with the Sr-Nd isotopic compositions of the MMEs and mid-Jurassic mafic rocks in the SCC. Zircons from the porphyries have positive ɛ Hf( t) values (3.4 to 6.9), and low δ18O values (4.7 to 6.3 ‰), generally close to those of depleted mantle. All data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components (e.g., Neoproterozoic mafic arc magmas), triggered by invasion of contemporaneous mafic melts at Dexing. The MMEs show textural, mineralogical, and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas. These MMEs usually contain magmatic chalcopyrite, and have original, variable contents of Cu (up to 500 ppm). Their geochemical characteristics suggest that they were derived from an enriched mantle source, metasomatized by

  5. Melt inclusions in the olivine from the Nantianwan intrusion: Implications for the parental magma of Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions of the ∼260 Ma Emeishan large igneous province (SW China)

    Zhang, Le; Ren, Zhong-Yuan; Wang, Christina Yan


    Olivine-hosted melt inclusions provide an archive of the parental magma and early magma history that is unavailable from bulk-rock analyses of cumulates. For those olivine-bearing mafic-ultramafic intrusions, a combined in situ analysis of major elements and Pb isotopic compositions for the melt inclusions and host olivine crystals may provide an effective way to understand the nature of the parental magma of the intrusions. In this study, we take the Nantianwan intrusion in the Emeishan large igneous province (SW China) as an example to analyze the melt inclusions and the host olivine. The Nantianwan intrusion is mainly composed of gabbronorite, with minor olivine gabbro. The olivine crystals in the olivine gabbro have Fo contents varying from 81.1 to 89.2 and Ni from 0.05 to 0.30 wt.%. The melt inclusion hosted in the most Mg-rich olivine has 50.9 wt.% SiO2, 1.0 wt.% TiO2, 15.1 wt.% MgO and 2.9 wt.% Na2O + K2O, indicating that the parental magma of the intrusion was of high-Mg basaltic composition. The melt inclusions overall have 208Pb/206Pb ratios of 2.0567-2.1032 and 207Pb/206Pb of 0.8287-0.8481, similar to the Pb isotopic compositions of the Emeishan flood basalts and consistent with insignificant crustal contamination. Given that the Nantianwan intrusion contains the most Mg-rich olivine among the Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions in the Emeishan LIP, we infer that the composition of the melt inclusion in the most Mg-rich olivine from the Nantianwan intrusion may represent the least evolved parental magma of the Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions in the Emeishan LIP. This can be further used to constrain the magma process related to Ni-Cu-(PGE) sulfide mineralization.

  6. Petrogenesis of garnet in the Darongshan-Shiwandashan granitic suite of the South China Block and the metamorphism of the granulite enclave%华南大容山-十万大山花岗岩体中石榴石成因以及麻粒岩包体变质作用研究

    焦淑娟; 郭敬辉; 彭松柏


    Garnets from the Jiuzhou granitic pluton of the Darongshan-Shiwandashan suite have been distinguished into four types based on their different textural and chemical characteristics:magmatic,peritectic,residual/metamorphic grains,and the transform from peritectic to magmatic that confirms the dissolution-precipitation process.Two types of granulite enclaves are divided based on their different microdomainal mineral assemblages.Recognition of microdomainal mineral assemblages,determination of metamorphic stages,and reaction analyses,combined mineral chemistry with phase equilibria modeling are performed to constrain thermal evolution of the two types of granulite enclave in granite.The original conditions of the granulite enclaves are 800 ~ 830℃ and 7.2 ~ 8.0kbar,which is representative of the garnet-bearing assemblage,reflecting the late stage of the partial melting in the source.Opx + Crd reaction rim around garnet or biotite might be coeval with crystallization of cordierite,and formed at conditions of 810 ~ 860℃ and 4.6~ 5.2kbar.Further decompression results in the formation of Spl + Crd association at 850℃ and 3.1 ~ 3.8kbar.In combination of the obtained data,a clockwise P-T path is retrieved and characteristic of decompression associated with slightly heating and succedent isobaric cooling in response to ascent and emplacement of the host granitic magma.This study coupled with the available geochronological data from previous researches suggests that the petrogenesis of both granite and its granulite enclave is related to the anatexis of the crust during 250 ~260Ma,and might have been provided with heat source by the coeval Emeishan mantle plume.%根据石榴石不同的结构和化学特征,在大容山-十万大山岩套旧州岩体中共识别出四种不同成因类型的石榴石:岩浆型、转熔型、变质型和由于上升岩浆中溶解-再沉淀机制导致的从转熔型向岩浆型转变的过渡型石榴石.由于含不同的

  7. Magnetic properties of electroplated nano/microgranular NiFe thin films for rf application

    Zhuang, Y.; Vroubel, M.; Rejaei, B.; Burghartz, J.N.; Attenborough, K.


    A granular NiFe thin film with large in-plane magnetic anisotropy and high ferromagnetic-resonance frequency developed for radio-frequency integrated circuit (IC) applications is presented. During the deposition, three-dimensional (3D) growth occurs, yielding NiFe grains (ϕ ∼ 1.0 μm). Nanonuclei (ϕ

  8. Assessment of Various Kinetic Models for the Pyrolysis of a Microgranular Cellulose

    Burnham, A K; Capart, R; Khezami, L


    The kinetics of pyrolysis of a micro-crystalline cellulose in nitrogen were studied from TGA and DTG data, obtained with two different modes of heating: a dynamic mode at constant heating rates between 1 and 11 C/min and an isothermal mode at various temperatures, kept constant between 280 and 320 C. In isothermal mode, it appeared very clearly that the mass depletion shows a sigmoid profile characteristic of an auto-accelerated reaction process. This behavior is consistent with kinetics of nuclei-growth, well represented by the models of Avrami-Erofeev and of Prout-Tompkins type. All the other kinetic models commonly applied to the thermal decomposition of solids revealed unsatisfactory. The TGA and DTG data were thus found ideally simulated from a reaction scheme consisting in two parallel reactions, termed 1 and 2, each one described by the kinetic law: DX/DT = -A{sup -E/RT}x{sup n}(1-0.99x){sup n}. Reaction 1 is related to the bulk decomposition of cellulose and is characterized by the set of parameters: E{sub 1}= 202 kJ/mole; n{sub 1}=1; m{sub 1}=0.48. Reaction 2 is related to the slower residual decomposition, which takes place over approximately 350 C and affects only 16 % by weight of the raw cellulose. With m{sub 2} constrained to 1, the optimized parameters of this reaction were: E{sub 2}= 255 kJ/mole; n{sub 2}=22. Finally, the proposed model allowed to correctly fit not less than to 10 sets of ATG-DTG data, isothermal and dynamic.

  9. Evidence of enriched mantle in the Archaean beneath eastern Indian Singhbhum Craton: constraints from geochemistry and Sr-Nd isotopic studies of mafic-ultramafic rocks from Bangriposi, Orissa, India

    Mouli Chakraborti, Tushar; Ray, Arijit; Deb, Gautam Kumar; Chakrabarti, Ramananda; Banerjee, Anupam


    Mafic-ultramafic rocks around Bangriposi (22° 9' N; 86° 32' E) are found to have been emplaced within polydeformed metasedimentary rocks of Singhbhum Group, belonging to the North Singhbhum Mobile Belt (NSMB) assemblage. Recent studies have assessed Mesoarchaean ( 3.09 Ga) age of these rocks and categorized the ultramafic unit as ultrahigh-pressure obducted bodies. The rocks are exposed mainly in two separate locations- Layered gabbroic rocks are found in an area SE of Bangriposi, and a well foliated, N-S trending Cr-spinel bearing wehrlite body is found S of Bangriposi. The gabbroic body (dubbed as "Kuliana Gabbro") is modally layered, contains plagioclase, clinopyroxene and orthopyroxene, and shows petrographic evidence of adcumulus growth and textural coarsening mechanisms. Cr-spinel bearing wehrlite rocks are highly serpentinized, containing serpentinized olivine, clinopyroxene, phlogopite, Cr-spinel, magnetite, and displays textural evidence of tectonic deformation. Geochemically, the Kuliana gabbro shows effects of fractional crystallization, and has relatively unfractionated REE patterns. The ultramafic rocks have high LOI contents (8- 9.3 wt%), with low Mg# (0.72- 0.77), and LREE enriched REE patterns. Parental melt calculations of the Kuliana Gabbro rocks have yielded an enriched-MORB like liquid, a product of low degree partial melting (8- 30%) in garnet facies. Cr-spinel bearing wehrlite rocks on the other hand exhibit ample evidences of modal and cryptic metasomatism in the mantle depth. Presence of phlogopite, diopside as reaction rims around serpentinized olivine, lack of primary orthopyroxene and presence of apatite are considered effects of modal metasomatism. Elevated LREE contents define cryptic metasomatism, which is also conspicuously visible in LREE enriched patterns of clinopyroxene separates from wehrlite. The metasomatism in the mantle may be due to multiple events involving separate melts or a single event of re-fertilization by

  10. Decoupling of whole-rock Nd-Hf and zircon Hf-O isotopic compositions of a 284 Ma mafic-ultramafic intrusion in the Beishan Terrane, NW China

    Su, Ben-Xun; Qin, Ke-Zhang; Lu, Ying-Huai; Sun, He; Sakyi, Patrick Asamoah


    Abundant Permian mafic-ultramafic intrusions in the Beishan Terrane, NW China, are parts of the Tarim large igneous province. Among these intrusions, Luodong intrusion is composed of dunite, wehrlite and gabbro. These rocks have whole-rock Sr-Nd-Hf and zircon Hf-O isotope compositions that display significant decoupling. The decoupling of these generally well-correlated systems demonstrates contrasting evolving trends. Systematic compositional and mineralogical controls on decoupling have been investigated. Wehrlites and gabbros show MORB-like trace element patterns with negligible crustal contamination. They have high initial 143Nd/144Nd [ɛNd(t) = +6.6 to +11.2] and 176Hf/177Hf [ɛHf(t) = +12.2 to +16.9] and low initial 87Sr/86Sr [(87Sr/86Sr)i = 0.702949-0.704098] ratios and plot within the MORB field, indicating that their parental magmas were derived from a depleted mantle source. The enrichment features are present in the zircon crystals separated from the gabbro. These homogeneously unzoned zircon crystals have high U concentrations, low Th/U ratios and a U-Pb age of 284.0 ± 2.3 Ma. They are therefore interpreted as having formed rapidly in a highly fractionated/evolved magma. Their ɛHf(t) and δ18O values range from -9.3 to -6.7 and +10.25 ‰ to +11.42 ‰, respectively. The decoupling is linked with crustal contamination by ancient crust (probably Proterozoic schist in the Beishan Terrane) that occurred during zircon crystallization. However, the contamination signature in the whole-rock composition was soon overprinted by magma mixing process. The inference is evidenced by zoning textures preserved in plagioclase, clinopyroxene, spinel and particularly olivine, and the presence of coeval diabase dykes cutting through the intrusion. The isotope decoupling observed in this mantle-plume-related mafic-ultramafic intrusion supports the idea that Nd-Hf decoupling and Lu/Hf and Sm/Nd parent/daughter variations exist only on a small hand-size scale in a

  11. Rb-Sr isotopic composition of granites in the Western Krušné hory/Erzgebirge pluton, Central Europe: record of variations in source lithologies, mafic magma input and postmagmatic hydrothermal events

    Dolejš, David; Bendl, Jiří; Štemprok, Miroslav


    The late Variscan (327-318 Ma) Western Krušné hory/Erzgebirge pluton (Czech Republic and Germany) represents a multiply emplaced intrusive sequence ranging from low-F biotite monzogranites (with rare minor bodies of gabbrodiorites and granodiorites) to high-F topaz-zinnwaldite alkali-feldspar granites. This granite suite is characterized by progressively increasing concentrations of incompatible elements (Li, Rb, F), monotonous decrease in mafic components and compatible elements (FeOtot, MgO, TiO2, CaO, Sr) with increasing silica. Consequently, this leads to extreme variations in the Rb/Sr ratios (0.52 to 59), which impose highly variable 87Rb/86Sr and 87Sr/86Sr signatures. The low-F biotite monzogranites represent isotopically heterogeneous mixture with (87Sr/86Sr)323 = 0.707-0.709 between partial melts from the Saxothuringian metasediments and mantle-derived mafic precursors. The medium-F two-mica microgranites show variable (87Sr/86Sr)323 = 0.708-0.714, indicating involvement of multiple precursors and more mature crustal protoliths. The evolved high-F topaz-zinnwaldite alkali-feldspar granites were derived from a precursor with (87Sr/86Sr)320 = 0.707-0.708 at 324-317 Ma by differentiation, which produced the extreme Rb/Sr enrichment and variations. The Li/Rb ratios remain nearly constant (~0.5), thus insensitive to the degree of geochemical differentiation. In comparison to terrestrial variations, the high Li/Rb values indicate derivation of granitic magmas from predominantly sedimentary precursors, in accord with 7Li-6Li and 143Nd-144Nd isotope composition reported previously. The Rb-Sr element variations in each granite unit are sligthly different and indicate ascent and emplacement of separate magma batches, which do not form a single liquid line of descent. We consider the enrichment of granites in incompatible elements (Li, Rb, F) and compatible depletion of ferromagnesian components, CaO and Sr as a combined effect of multiple precursors, changes in

  12. The Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion, northeast of Beijing (North China): Implications for the mantle source of the giant Late Mesozoic magmatic event in the North China Craton

    Liu, Ping-Ping; Zhou, Mei-Fu; Yan, Dan-Ping; Zhao, Guo-Chun; Su, Shang-Guo; Wang, Xiao-Lin


    The Early Cretaceous Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion in the Yanshan Belt northeast of Beijing is coeval with the giant Late Mesozoic igneous province in the eastern part of the North China Craton (NCC). This magmatic event was associated with lithospheric thinning and thus the igneous rocks have been used to characterize the nature of the Mesozoic mantle beneath the NCC. The Shangzhuang mafic pluton intruded a large granodioritic complex and crystallized at ~ 850-872°C at a depth of 13-14 km. It is composed, from the base upward, of troctolite, Fe-Ti oxide-bearing gabbronorite and gabbro. Rocks from this intrusion have low initial 87Sr/86Sr ratios (0.7053-0.7058), negative initial εNd values (- 9.4 to - 10.7), highly differentiated LREE and nearly flat HREE patterns indicative of an EMI-like mantle source unaffected by upper crustal contamination. The occurrence of Fe-Ti oxide ore layers, magnetite-ilmenite exsolution lamellae in hornblende and high TiO2 contents of the silicate rocks indicate that they formed from Fe- and Ti-rich ferrobasaltic magmas, which may have been generated by addition of magmas from a deeper mantle source. The presence of orthopyroxene, high-Mg ilmenite (up to 8.5 wt %), hornblende, biotite and high oxygen fugacities calculated from coexisting titanomagnetite-ilmenite pairs can be explained by derivation from an enriched EMI-type mantle modified by fluids from a subducted slab and mixed with asthenospheric or deeper-mantle materials in an extensional setting. Exposure of the complex occurred during large-scale uplift (at least 13 km) and exhumation of the Yanshan orogenic belt in the Early Cretaceous. Chemical metasomatism triggered by water and enhanced by heat from a deep magma source may have played an important role in removing the ancient cratonic root, generating partial melting of the lithospheric mantle and producing coeval magmatic activity in the Mesozoic eastern NCC.

  13. Two stage mantle-derived granitic rocks and the onset of the Brasiliano orogeny: Evidence from Sr, Nd, and O isotopes

    Silva, Thyego R.; Ferreira, Valderez P.; Lima, Mariucha Maria C.; Sial, Alcides N.


    The elongate Monteirópolis batholith (270 km2) is composed of alkali feldspar granite to granodiorite, it is part of the Águas Belas-Canindé composite batholith and it intruded rocks of the Pernambuco-Alagoas Domain, northeastern Brazil. This batholith is bounded by the NNE-SSW-trending Jacaré dos Homens transpressional shear zone on its southwestern margin, and displays low-angle foliation, coeval to the development of a regional flat-lying foliation. Microgranular dioritic enclaves and amphibole-rich clots are abundant. The mineralogy of this pluton comprises biotite and amphibole as major accessory phases, and titanite and magmatic epidote as trace minerals. Major and trace element chemistry shows high SiO2, total alkalis, Ba and Sr, low Fe# and Nb contents, all of these conferring a high-K calc-alkaline character. The rocks are enriched in LREE and LILE and depleted in HFSE, and show fractionated chondrite-normalized REE patterns with Eu/Eu* = 0.67 to 1.25. Chondrite-normalized spidergrams show marked negative Nb-Ta and Ti anomalies, typical of subduction-related magmas. U-Pb SHRIMP zircon data yielded a crystallization age of 626 ± 4 Ma. Regional structures and U-Pb geochronological data for the Jacaré dos Homens transpressional shear zone suggest that shearing was initiated at ca. 640 Ma. Dilatational movements along this shear zone opened space for magma emplacement. The rocks in this batholith are characterized by slightly negative to slightly positive εNd values (- 0.78 to + 1.06), average Nd-model age of 1.0 Ga, low initial 87Sr/86Sr(626 Ma) values of 0.7050 to 0.7052, and low δ18O values (zircon) of + 5.00 to + 5.94‰ V-SMOW. A possible protolith, Tonian mantle-derived rocks in the lower continental crust, could have been partially melted by underplating of mantle-derived mafic magma during collision of the São Francisco Craton and the Pernambuco-Alagoas Domain during onset of the Brasiliano orogeny.

  14. Multiple rifting and alkaline magmatism in southern India during Paleoproterozoic and Neoproterozoic

    Renjith, M. L.; Santosh, M.; Satyanarayanan, M.; Rao, D. V. Subba; Tang, Li


    The Southern Granulite Terrane (SGT) in India preserves the history of tectonothermal events ranging from Paleoarchean to latest Neoproterozoic-Cambrian. Here we investigate alkaline magmatism possibly associated with rifting events in Paleoproterozoic and Neoproterozoic based on petrological, geochemical and zircon U-Pb and Lu-Hf isotopic studies on the alkaline complexes of Korangani (KGAC) and Kambamettu (KAC) in the Madurai Block of SGT. The mica pyroxenite which represents the first intrusive phase at KGAC crystallized from a mildly alkaline hydrous magma derived from a metasomatized mantle. The younger shoshonitic syenite was emplaced at 2533 ± 16 Ma, carries mafic microgranular enclaves, and shows trace-elements ratios consistent with magma mixing trend, and zircon εHf(t) values display mixed positive and negative values - 2.6 to 3.6 suggesting the mixing of adakite-like felsic crustal melt and non-adakitic mantle derived melt. In KAC, four distinct magmatic intrusions are identified: i) quartz-monzonite (emplaced at 2498 ± 16 Ma), an ultrapotassic adakitic rock derived from a carbonated alkali-rich lower crustal source with negative zircons εHf(t) values in zircon (- 8.0 to - 0.8); Y/Nb (> 1.2) and Th/Ce (0.03-0.8) ratios; lower Ni (< 30 ppm) and Cr (< 14 ppm) contents; ii) phlogopite-rich pyroxenite, crystallized from an alkali-rich basaltic parental magma derived from carbonate metasomatized mantle; iii) mantle derived high Ba-Sr carbonatite (emplaced at 2470 ± 15 Ma); and iv) shoshonitic peralkaline syenite rock (emplaced at 608 ± 6 Ma) with strong adakitic signature, low MgO (< 1 wt.%), Ni (12-5 ppm) and Cr (49-35 ppm) contents and negative zircon εHf(t) values (- 30.3 to - 27.3) and trough of Zr-Hf in spidergrams suggesting a carbonated alkali-rich garnet-bearing crustal source. The geochemical features and petrogenetic considerations of the felsic shoshonitic-ultrapotassic adakite-like rocks (syenite, quartz monzonite), mica-pyroxenites and

  15. Interaction of the lithospheric mantle and crustal melts for the generation of the Horoz pluton (Niğde, Turkey: whole-rock geochemical and Sr–Nd–Pb isotopic evidence

    Kerim Kocak


    Full Text Available The Horoz pluton includes granitic and granodioritic rocks, with widespread mafic microgranular enclaves (MMEs. Petrochemically, the rocks of the pluton show calc-alkaline to shoshonitic and metaluminous to slightly peraluminous composition. The rocks also exhibit an enrichment in large ion lithophile elements, e.g. Rb, K, and depletions of high field strength elements such as Y, Lu, and Mg#, Ni, with a slightly concave-upward rare earth element pattern. Both granitic and granodioritic rocks exhibit geochemical characteristics of tonalite, trondhjemite and granodiorite assemblages, possibly developed by the partial melting of a thickened lower crust. The granitoids have high concentrations of Na2O (2.6–4.5 wt%, Sr (347–599 ppm, intermediate-high (La/YbN (8.2–18.1, mostly >11 , Al2O3 (13.2–16.9 wt%, average 15.3 wt%, low MgO (0.2–1.4 wt%, average 0.84 wt% and Co (0.7–10.3 ppm. The MMEs include higher Na2O (4.5–5.5 wt%, Sr (389–1149 ppm, Al2O3 (16.9–19.2 wt%, average 17.8 wt%, MgO (1.4–4.4 wt%, average 2.75 wt% and Co (6.2–18.7 ppm contents in comparison with that of their hosts. There is a lack of negative Eu anomalies, except a few samples. Both host rocks and MMEs have a low initial 87Sr/86Sr ratio (respectively 0.7046–0.7051 and 0.7047–0.7058, low eNd value (–1.8 to –0.2 and –0.6 to 0.7 at 50 Ma and highly radiogenic 208Pb/204Pb ratios (39.43–39.47 and 39.39–39.54. Whole-rock chemistry and isotopic data suggest that parent magmas of both MMEs and their hosts have derived from melts of the mixing between the lithospheric mantle and crustal end members, than fractional crystallization processes in crustal levels.

  16. Geochemistry of the Topuk Pluton associated with the Kozbudaklar W-skarn deposit (Western Anatolia, Turkey): Implication for crystallization conditions

    Orhan, Ayşe; Demirbilek, Mehmet; Mutlu, Halim


    The Kozbudaklar scheelite-bearing skarn deposit in the Tavşanlı Zone, western Turkey, occurs at the contact between Eocene Topuk pluton and Triassic İnönü marble of calcic character. The Topuk pluton is medium-coarse grained, granodiorite in composition and has a hypidiomorphic equigranular texture. The host rock contains mafic microgranular enclaves (MME) of monzodiorite-monzogabbro composition and is interrupted by porphyritic granodiorite and granite-aplite vein rocks. The pluton is calk-alkaline, metaluminous and composed of I-type melt character. δ18O and δD compositions of silicate minerals from granodioritic host rock are 5.9-10.6‰ and -77.0 to -71.4‰ and conformable with the range of unaltered I-type granites. Trace element contents indicate that pluton is crystallized from mantle-derived magma interacted with continental crust in a volcanic arc or subduction related setting. Major and trace element concentrations of Topuk pluton are quite consistent with geochemical patterns of Cu-skarn granitoids. Results of mineral chemistry analysis of the pluton yield that plagioclases are of oligoclase-andesine, amphiboles are of magnesio-hornblende and biotites are of ferro-magnesian composition. Amphiboles and biotites of granodioritic host rock are represented by calc-alkaline, I-type melt composition evolved in a subduction environment. Based on the results of plagioclase-Al in hornblende and amphibole chemistry data from the pluton, two different stages are proposed for the magma crystallization. The first stage was developed in a relatively deeper environment (>15 km) under high pressure (>4 kbar) and low log ƒO2 (>-17.6) conditions which reflect fractional crystallization and magma-mixing depth of basaltic magma and these conditions are not correlated with scheelite mineralization. The second crystallization stage of magma which proceeded at shallow depths (-12.9 to -11.0) values are accompanied by high H2O contents (5.39-6.88 wt.%). High water

  17. Petrogenesis of the middle Jurassic appinite and coeval granitoids in the Eastern Hebei area of North China Craton

    Fan, Wenbo; Jiang, Neng; Xu, Xiyang; Hu, Jun; Zong, Keqing


    An integrated study of zircon U-Pb ages and Hf-O isotopic compositions, whole rock elemental and Sr-Nd isotope geochemistry was conducted on three lithologically diverse middle Jurassic plutons from the Eastern Hebei area of the North China Craton (NCC), in order to reveal both their petrogenesis and possible tectonic affinity. The three plutons have consistent magmatic zircon U-Pb ages from 167 ± 1 Ma to 173 ± 1 Ma. The Nianziyu pluton has typical characteristics of appinite with low SiO2 (43.7-52.6%), high Ca, Mg, Fe and H2O contents. It possesses subduction-related trace element patterns, enriched Nd-Hf isotopic signatures as well as elevated zircon δ18O values (6.2-7.2‰), arguing for an enriched mantle source metasomatized by fluids related to subduction. The Shuihutong monzogranites have high silica (SiO2 = 75.4-75.9%) and alkali contents, low Ca contents and striking negative Ba, Sr and Eu anomalies. Samples from the pluton have more evolved Nd-Hf isotopic values and are considered to be most likely derived from anatexis of ancient lower continental crust. Hybridization between mantle- and ancient lower crust-derived magmas is proposed for the mafic microgranular enclave-bearing Baijiadian granitoids, which are characterized by variable εNd (t) and εHf(t) values. Integrated with the regional geologic history, we suggest that the formation of the three middle Jurassic plutons were related to the subduction of the Paleo-Pacific ocean plate beneath the NCC. Their petrogenetic differences reflect complex magmatic processes in subduction settings involving melting of multiple sources, possible partly facilitated by fluid metasomatism and water-rich magma injection, accompanied with various degrees of magma mixing. The appearance of middle Jurassic appinitic rocks leads us to propose that the NCC destruction and lithosphere thinning were facilitated and controlled by the weakening of the lithospheric mantle after hydration because of the subduction of the

  18. Petrology of the shoshonitic Çambaşı pluton in NE Turkey and implications for the closure of the Neo-Tethys Ocean: Insights from geochemistry, geochronology and Sr-Nd isotopes

    Özdamar, Şenel; Roden, Michael F.; Billor, Mehmet Z.


    The Eastern Pontide Orogenic Belt (EPOB) is one of the well-preserved continental magmatic arcs in the Alpine-Himalayan Belt and consists of Paleozoic to Miocene plutonic bodies. This paper presents new geological, bulk-rock major and trace element analyses, biotite Ar-Ar ages and Sr-Nd isotope data on representative samples from the Çambaşı granitic body exposed in the northwestern part of the EPOB. Although the majority of the plutons in the EPOB show calc-alkaline affinity and I-type character, the Çambaşı pluton has a shoshonitic affinity and an I-type, metaluminous signature. The pluton is composed of mainly monzonite, quartz monzonite and granite bodies including monzo-dioritic mafic microgranular enclaves (MMEs). Excluding the MMEs, these rocks have 57.7-70.2 wt.% SiO2, 13.1-17.5 wt.% Al2O3, 3.06-3.64 wt.% Na2O, 3.66-5.92 wt.% K2O, 0.33-3.3 wt.% MgO and Mg# earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with small negative Eu anomalies and moderately fractioned REE patterns [average (La/Yb)N = 11.32]. Decreasing Fe2O3T, MgO, CaO, TiO2, Ba, Eu, and Sr with increasing SiO2 contents are consistent with fractional crystallization and can be related to fractionation of plagioclase, clinopyroxene, hornblende, apatite and Fe-Ti oxides. Initial 87Sr/86Sr ratios vary between 0.70470 and 0.70478, while those of 143Nd/144Nd lie between 0.51262 and 0.51263. Major, trace element and initial Sr-Nd homogeneity show that fractional crystallization played a key role in the evolution of the pluton. 40Ar/39Ar dating of four biotite samples from the pluton gave plateau ages of between 44.62 ± 0.1 Ma and 44.10 ± 0.0 Ma, which are interpreted as cooling ages of the plutonic rocks. We suggest that the Çambaşı pluton formed in a post-collisional extensional setting where partial melting of chemically enriched lithospheric mantle was controlled by lithospheric thinning and upwelling of asthenosphere that followed the closure of

  19. Mineral Chemistry and Crystallization Conditions of the Late Cretaceous Mamba Pluton from the Eastern Gangdese, Southern Tibetan Plateau

    Xiaowei Li; Xuanxue Mo; Mark Scheltens; Qi Guan


    The Late Cretaceous Mamba granodiorite belongs to a part of the Mesozoic Gangdese con-tinental magmatic belt. No quantitative mineralogical study has been made hitherto, and hence the depth at which it formed is poorly constrained. Here we present mineralogical data for the Mamba pluton, in-cluding host rocks and their mafic microgranular enclaves (MMEs), to provide insights into their overall crystallization conditions and information about magma mixing. All amphiboles in the Mamba pluton are calcic, withB(Ca+Na)>1.5, and Si=6.81–7.42 apfu for the host rocks and Si=6.77–7.35 apfu for the MMEs. The paramount cation substitutions in amphibole include edenite type and tschermakite type. Biotites both in the host rocks and the MMEs collectively have high MgO (13.19 wt.%–13.03 wt.%) contents, but define a narrow range of Al apfu (atoms per formula unit) variations (2.44–2.57). The oxygen fugacity es-timates are based on the biotite compositions cluster around the NNO buffer. The calculated pressure ranges from 1.2 to 2.1 kbar according to the aluminum-in-hornblende barometer. The computed pressure varies from 0.9 to 1.3 kbar based on the aluminum-in-biotite barometer which corresponds to an average depth of ca. 3.9 km. Besides, the estimates of crystallization pressures vary from 0.8 to 1.4 kbar based on the amphibole barometer proposed by Ridolfi et al. (2010), which can be equivalent to the depths ranging from 3.1 to 5.2 km. The MMEs have plagioclase oscillatory zonings and quartz aggregates, probably indi-cating the presence of magma mixing. Besides, core-to-rim element variations (Rb, Sr, Ba, and P) for the K-feldspar megacrysts serve as robust evidence to support magma mixing and crystal fractionation. This indicates the significance of the magma mixing that contributes to the formation of K-feldspar megacryst zonings in the Mamba pluton.

  20. Late Triassic syn-exhumation magmatism in central Qiangtang, Tibet: Evidence from the Sangehu adakitic rocks

    Liu, Han; Wang, Bao-di; Ma, Long; Gao, Rui; Chen, Li; Li, Xiao-bo; Wang, Li-quan


    The geodynamic setting of Late Triassic magmatic activity along the Longmu Co-Shuanghu suture zone (LSSZ) in central Qiangtang, Tibet is a matter of debate. This paper presents zircon LA-ICP-MS U-Pb ages, zircon Hf isotopic compositions, and whole-rock geochemical data for the Sangehu (SGH) granitic intrusion in central Qiangtang, and addresses the petrogenesis of Late Triassic magmatism, and the history of collision between the northern and southern Qiangtang terranes. The SGH pluton consists mainly of biotite adamellite with mafic microgranular enclaves (MMEs), and small amounts of K-feldspar granite. The biotite adamellite, MMEs, and K-feldspar granite give ages of 207.8 ± 3.0 Ma, 212.4 ± 31 Ma, and 211.6 ± 3.8 Ma, respectively. The MMEs show magmatic textures and acicular apatite, and are coeval with the host biotite adamellite, suggesting they were produced by magma mixing. All samples from the SGH pluton show high Sr and low Y contents, and positive Eu anomalies, similar to adakitic rocks. The high K2O contents and low Mg#, Cr, and Ni contents, and enriched Hf isotopic characteristics of the zircons indicate that these magmas were derived from the partial melting of thickened crust. However, the whole-rock geochemical data and zircon Hf isotopic compositions also reveal heterogeneity at the source. The combined magmatic and metamorphic records suggest that Triassic magmatic activity in central Qiangtang was closely related to the collision of the northern and southern Qiangtang terranes. The large-scale Late Triassic (225-200 Ma) magmatic event in central Qiangtang may have resulted from the breakoff of the Longmu Co-Shuanghu Tethys Ocean lithospheric slab in the early Late Triassic (236-230 Ma). The Late Triassic magmatic rocks, including adakitic rocks, are coeval with retrograde high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in central Qiangtang, and show characteristics of syn-exhumation magmatism. The early adakitic rocks (>220 Ma

  1. Sm-Nd data for mafic-ultramafic intrusions in the Svecofennian (1.88 Ga Kotalahti Nickel Belt, Finland – implications for crustal contamination at the Archaean/Proterozoic boundary

    Hannu V. Makkonen


    Full Text Available Sm-Nd data were determined for eight mafic-ultramafic intrusions from the Svecofennian (1.88 Ga Kotalahti Nickel Belt, Finland. The intrusions represent both mineralized and barren types and are located at varying distances from the Archaean/Proterozoic boundary.The samples for the 23 Sm-Nd isotope analyses were taken mostly from the ultramafic differentiates. Results show a range in initial εNd values at 1880 Ma from -2.4 to +2.0. No relationship can be found between the degree of Ni mineralization and initial εNd values, whilea correlation with the geological domain and country rocks is evident. The Majasaari and Törmälä intrusions, which have positive εNd values, were emplaced within the Svecofennian domain in proximity to 1.92 Ga tonalitic gneisses, which have previously yielded initialεNd values of ca. +3. In contrast, the Luusniemi intrusion, which has an εNd value of -2.4 is situated close to exposed Archaean crust. Excluding two analyses from the Rytky intrusion, all data from the Koirus N, Koirus S, Kotalahti, Rytky and Kylmälahti intrusions, withinerror limits, fall in the range -0.7 ± 0.3. The results support the concept of contamination by Archaean material in proximity to the currently exposed craton margin. The composition of the proposed parental magma for the intrusions is close to EMORB, with initialεNd values near +4.

  2. Rb-Sr geochronology and geochemical characteristics of mafic dikes in the Nova Lacerda and Conquista D'Oeste region, Mato Grosso, SW Amazonian Craton; Geocronologia Rb-Sr e caracteristicas geoquimicas dos diques maficos da regiao de Nova Lacerda e Conquista D'Oeste (MT), porcao sudoeste do Craton Amazonico

    Costa, Paulo Cesar Correa da; Matos, Joao Batista de [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Dept. de Recursos Minerais; Grupo de Pesquisas em Evolucao Crustal e Metalogenia Guapore, Cuiaba, MT (Brazil)], e-mail:, e-mail:; Girardi, Vicente Antonio Vitorio [Universidade de Sao Paulo (USP), SP (Brazil). Inst. de Geociencias. Dept. de Mineralogia e Geotectonica], e-mail:; Ruiz, Amarildo Salina [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Dept. de Geologia Geral; Grupo de Pesquisas em Evolucao Crustal e Metalogenia Guapore, Cuiaba, MT (Brazil)], e-mail:


    In the Nova Lacerda and Conquista D'Oeste regions, Mato Grosso State, SW part of the Amazonian Craton, mafic dikes trending NNW intrude the Nova Lacerda Granite (1462{+-}12 Ma), within the Jauru Domain, in the Rondonia-San Ignacio Province (1.55 - 1.3 Ga). The mafic swarm comprises diabases, metadiabases and amphibolites. Metadiabases originated from uralitization of diabases. These rocks have tholeiitic affinity and predominant basaltic composition. Some samples are andesi-basalts. The ages of diabases and metabasites are 1380 {+-} 32 Ma and 1330 {+-} 120 Ma respectively. Geochemical data indicate that the compositional variation of diabases and metadiadases is due to fractional crystallization of evolved tholeiitic magmas. The origin of the basaltic magmas is related to a heterogeneous mantle source. (author)

  3. Comment on "Geochemistry, petrogenesis and tectonic setting of the Samothraki mafic suite, NE Greece: Trace-element, isotopic and zircon age constraints" by N. Koglin, D. Kostopoulos & T. Reischmann [Tectonophysics 473, 53-68 (doi:10.1016/j.tecto.2008.10.028)

    Bonev, Nikolay; Stampfli, Gérard


    The work by Koglin et al. (Koglin, N., Kostopoulos, D., Reichmann, T., 2009. Geochemistry, petrogenesis and tectonic setting of the Samothraki mafic suite, NE Greece: Trace-element, isotopic and zircon age constraints. Tectonophysics 473, 53-68. doi:10.1016/j.tecto.2008.10.028), where the authors have proposed to nullify the scenario presented by Bonev and Stampfli (Bonev, N., Stampfli, G., 2008. Petrology, geochemistry and geodynamic implications of Jurassic island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic low-grade sequence, eastern Rhodope, Bulgaria. Lithos 100, 210-233) is here put under discussion. The arguments for this proposal are reviewed in the light of available stratigraphic and radiometric age constraints, geochemical signature and tectonics of highly relevant Jurassic ophiolitic suites occurring immediately north of the Samothraki mafic suite. Our conclusion is that the weak arguments and the lack of knowledge on the relevant constraints from the regional geologic information make inconsistent the proposal and the model of these authors.

  4. Geochemical and structural characterization of the Cruzeiro do Sul Granodiorite: neoproterozoic post-collisional shoshonitic magmatism within transcurrent shear zone, Quitéria region, Southernmost Brazil

    Daniel Knijnik


    Full Text Available The Cruzeiro do Sul Granodiorite is located in the Eastern portion of the Sul-rio-grandense shield. It forms one ENE-WSW elongate body of approximately 4 km² within a sinistral strike slip shear zone. The rocks were originally considered as part of the Arroio dos Ratos Complex, but they were recently mapped as a separate unit because igneous textures are widely preserved and they are intrusive in the gneissis complex rocks. The Cruzeiro do Sul Granodiorite is thus a porphyritic horblende-biotite granodiorite in a mafic-rich (M’ ~ 20, medium-grained matrix. The magmatic foliation is marked by the shape alignment of feldspar megacrystals and mafic minerals. A solid-state, mylonitic structure is well-developed mainly near the contacts. Leucocratic veins are found both concordant and discordant to the main foliation, and they may give rise to a composite banding within high-strain zones, together with elongate mafic microgranular enclaves and synplutonic dykes of tonalitic to dioritic composition. The mylonitic foliation trends EW to ENE-WSW with medium to steep dip, and contains a shallow plunging stretching lineation, which indicates a transcurrent kinematic for this shear zone. Structural evidences, such as the parallelism and progressive evolution of mylonitic foliation relative to the magmatic one, as well as the elongated form of granodioritic bodies and the concordant character of planar structures with the ENE shear zone, are interpreted as an indication of syntectonic emplacement. Moreover, the absence of metamorphic foliation reworked by mylonitic shows that the Cruzeiro do Sul Granodiorite registers only one phase of deformation, which would have occurred during their emplacement. Thus, we have concluded that the Cruzeiro do Sul Granodiorite has no relation with the EW transversal event, and low dip angle responsible for the deformation of Arroio dos Ratos Complex, but is linked to the transcurrent event of Dorsal de Canguçu Shear

  5. Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

    Danielson, Lisa R.; Metcalf, Rodney V.; Miller, Calvin F.; Rhodes Gregory T.; Wooden, J. L.


    The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the

  6. Geochemical and isotopic studies of the Lady of the Lake Intrusion and associated tobacco root Batholith: Constraints on the genetic relation between Cretaceous mafic and silicic magmatism in Southwestern Montana

    Sarkar, Arindam; Brophy, James G.; Ripley, Edward M.; Li, Chusi; Kamo, Sandra L.


    Small volumes of alkalic mafic intrusions are spatially associated with Cretaceous to Early Tertiary granodioritic to granitic intrusions in the batholithic province of southwestern Montana. The mafic rocks generally occur near the contacts of the Boulder, Pioneer, and Tobacco Root Batholiths with country rocks, but their genetic relation with the batholiths is uncertain. The Lady of the Lake Intrusion is a small layered body composed of melagabbro and gabbro that occurs along the south-central margin of the Tobacco Root Batholith near its contact with Archean country rocks. A diorite unit, spatially distinct from the granodiorite/quartz monzonite of the Batholith intrudes the gabbroic rocks of the Lady of the Lake Intrusion. Zircon crystals from the melagabbro and diorite units give U-Pb ages that are very similar to that of the Tobacco Root Batholith at 74.88 ± 0.17 Ma and 76.24 ± 0.08 Ma, respectively. Mineral chemistry, whole rock major and trace element compositions, and oxygen and sulfur isotope ratios have been utilized to evaluate the genetic relation between the Lady of the Lake Intrusion, the diorite, and the Tobacco Root Batholith. No significant variation in the composition of clinopyroxene is observed in different rock units of the Lady of the Lake Intrusion. Minor olivine with Fo 64 in the melagabbro unit is interpreted to represent early crystallization in the base of the intrusion. Whole rock major and trace element compositions, as well as results from modeling using the MELTS program, are consistent with the premise that the diorite was produced by fractional crystallization of the same magma that was parental to the gabbros of the Lady of the Lake Intrusion. Both whole rock chemistry and oxygen isotopes support the interpretation that the parental magma was an uncontaminated mantle-derived basaltic magma. In contrast, trace element and oxygen isotopes indicate that the quartz monzonitic and granodioritic rocks of the Tobacco Root Batholith and

  7. Ductile-brittle deformation effects on crystal-chemistry and U-Pb ages of magmatic and metasomatic zircons from a dyke of the Finero Mafic Complex (Ivrea-Verbano Zone, Italian Alps)

    Langone, Antonio; Padrón-Navarta José, Alberto; Ji, Wei-Qiang; Zanetti, Alberto; Mazzucchelli, Maurizio; Tiepolo, Massimo; Giovanardi, Tommaso; Bonazzi, Mattia


    A detailed microstructural, geochemical and geochronological study was performed on zircon grains from plagioclase-rich dioritic dykes discordantly intruded within meta-diorites/gabbros forming the External Gabbro unit of the Finero Mafic Complex (Italian Alps). This unit is exposed as part of a near complete crustal section spanning from mantle rocks to upper crustal metasediments (Val Cannobina, Ivrea-Verbano Zone, Italy). The leucocratic dykes consist mainly of plagioclase (An18-24Ab79-82Or0.3-0.7) with subordinate amounts of biotite and spinel defining melanocratic layers. Zircon and corundum are common accessory phases. Both the dykes and the surrounding meta-diorites/gabbros show evidence of ductile deformation under amphibolite-facies conditions. Zircon grains/fragments (up to 2 mm in length) occur as porphyroclasts surrounded by fine-grained plagioclase within the leucocratic domains and may occur within the melanocratic layers completely or partially surrounded by biotite and spinels. Fractures are common within zircon, define networks and have associated displacements occasionally and/or they can be filled by secondary minerals. Cathodoluminescence (CL) images reveal that zircon grains from the leucocratic layers show relicts of primary magmatic (i.e. oscillatory and or sector) zoning generally related with the crystal shapes or crystallographic orientation, whereas those from the melanocratic domains do not. In both cases, zircon shows secondary CL features, i.e. mosaic-like textures, due to deformation. EBSD maps confirmed a profuse mosaic texture, resulting in an internal misorientation of ca. 10°, generally associated with fractures. Locally, zircon shows clear evidence of crystal-plastic deformation at the edges, with a gradual misorientations of up to 12°, suggesting an origin prior fragmentation. Trace elements and U-Pb analyses were carried out by LA-ICP-MS directly on petrographic thin sections. Such in situ investigations revealed a strong

  8. U-Pb zircon geochronology and phase equilibria modelling of a mafic eclogite from the Sumdo complex of south-east Tibet: Insights into prograde zircon growth and the assembly of the Tibetan plateau

    Weller, O. M.; St-Onge, M. R.; Rayner, N.; Waters, D. J.; Searle, M. P.; Palin, R. M.


    The Sumdo complex is a Permian-Triassic eclogitic metamorphic belt in south-east Tibet, which marks the location of a suture zone that separates the northern and southern Lhasa terranes. An integrated geochronological and petrological study of a mafic eclogite from the complex has constrained its tectonometamorphic history and provides a case study of zircon growth in eclogite as a product of prograde dissolution-precipitation. In situ U-Pb geochronology indicates that the eclogite contains a single population of zircon with a crystallisation age of 273.6 ± 2.8 Ma. The morphology and chemistry of the zircon grains are consistent with growth by dissolution-precipitation of protolith magmatic zircon. The presence of zircon grains as inclusions in the cores of peak phases indicates that zircon dissolution-precipitation occurred during prograde metamorphism, and calculated pressure and temperature conditions over which mineral inclusions in zircon are stable suggest that the zircon most likely precipitated at 15.5-16.5 kbar and 500-560 °C. Subsequent peak metamorphism is calculated to have reached pressure-temperature conditions of 27 ± 1 kbar and 670 ± 50 °C. Previous studies, which have documented a range of peak metamorphic conditions from high- to ultrahigh-pressure at c. 266-230 Ma, indicate that the Sumdo complex is a composite belt that experienced protracted eclogite exhumation. The results of this study are consistent with this interpretation, and extend the age range of high-pressure metamorphism in the complex to over 40 Myr. Analysis of published pressure-temperature-time data indicates two systematic behaviours within this spread. First, peak metamorphic temperatures declined over time. Second, eclogite exhumation occurred in two discrete intervals: soon after formation, and during the demise of the subduction zone. The latter behaviour serves as a reminder that eclogite exhumation is the exception rather than the rule.

  9. 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)

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


    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.

  10. Comment on ;Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications;. Tectonophysics, 662, 219-242 (2015) by Ishwar-Kumar et al.

    Goncalves, Philippe; Brandt, Sönke; Nicollet, Christian; Tucker, Robert


    Determining the possible tectonic regimes active during the Neoproterozoic is crucial for the knowledge of the evolution of the super-continent Gondwana. In Madagascar, that occupies a key position in Gondwana, there is an on-going debate regarding the location of possible suture zones and the implications in terms of paleo-geography. Recognizing high-pressure to ultra-high pressure conditions in mafic rocks is commonly viewed as a strong argument for paleo-subduction zones. Ishwar-Kumar et al. (2015) report unusual high pressure conditions (24 kbar) in Neoproterozoic to Cambrian rocks from North-Central Madagascar (Andriamena Complex). They propose a geodynamic model in which exhumation of the high pressure terranes from up to 80 km to 40 km occurred via vertical extrusion during the collision of various crustal blocks after subduction and closure of an oceanic domain during the formation of Gondwana in the late Neoproterozoic to Cambrian. We question this model and in particular the (ultra-)high pressure conditions reported, because their estimation is based on a misinterpretation of the petrography and inaccurate thermodynamic modeling for the crucial metabasite sample. The authors suggest that garnet-quartz coronas around orthopyroxene and ilmenite coexist with clinopyroxene. The postulated garnet-clinopyroxene-quartz assemblage is interpreted to document an eclogite facies overprint. However, the presence of abundant plagioclase in the sample and the lack of high jadeite content in clinopyroxene clearly refute the postulated eclogite facies conditions. According to the presented photographs clinopyroxene is part of the rock matrix. We therefore suggest that the sample represents a common two-pyroxene granulite, formed at mid- to low-pressure granulite facies conditions of > 700 °C and Madagascar, this interpretation is not justified by the data presented by Ishwar-Kumar et al. (2015).

  11. 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.

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


    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.

  12. Petrography, geochemistry and geochronology of the host porphyries and associated alteration at the Tuwu Cu deposit, NW China: a case for increased depositional efficiency by reaction with mafic hostrock?

    Shen, Ping; Pan, Hongdi; Zhou, Taofa; Wang, Jingbin


    Tuwu is the largest porphyry copper deposit discovered in the Eastern Tianshan Mountains, Xinjiang, China. A newly recognized volcanic complex in the Early Carboniferous Qi'eshan Group at Tuwu consists of basalt, andesite, and diorite porphyry. The plagiogranite porphyry was emplaced into this complex at 332.8±2.5 Ma (U-Pb zircon SIMS determination). Whole-rock element geochemistry shows that the volcanic complex and plagiogranite porphyry formed in the same island arc, although the complex was derived by partial melting of the mantle wedge and the plagiogranite porphyry by partial melting of a subducting slab. The diorite and the plagiogranite porphyries have both been subjected to intense hydrothermal alteration and associated mineralization, but the productive porphyry is the plagiogranite porphyry. Three alteration and mineralization stages, including pre-, syn- and post-ore stages, have been recognized. The pre-ore stage formed a barren propylitic alteration which is widespread in the volcanic complex. The syn-ore stage is divided into three sub-stages: Stage 1 is characterized by potassic alteration with chalcopyrite + bornite + chalcocite; Stage 2 is marked by chlorite-sericite-albite alteration with chalcopyrite ± pyrite ± bornite; Stage 3 is represented by phyllic alteration with chalcopyrite + pyrite ± molybdenite. The post-ore stage produced a barren argillic alteration limited to the diorite porphyry. A specific feature of the Tuwu deposit is that the productive porphyry was emplaced into a very mafic package, and reaction of the resulting fluids with the ferrous iron-rich hostrocks was a likely reason that Tuwu is the largest porphyry in the district.

  13. Genesis of felsic plutonic magmas and their igneous enclaves

    Clemens, John D.; Maas, Roland; Waight, Tod Earle


    -type Pyalong pluton was emplaced, apparently along an east-west-orientated fracture zone. Around 367 Ma, the main I-type Baynton pluton intruded as numerous shallow-dipping sheets. The last plutonic event was the intrusion of the broad, thin, flat-lying, and crosscutting sheet of the I-type Beauvallet pluton...

  14. Punjabi Orchard Farmers: An Immigrant Enclave in Rural California.

    Gibson, Margaret A.


    Examines the adaptation patterns of Punjabi Sikh orchard farmers in rural California. Discusses the role of the following: (1) the historical context of immigration; (2) the immigrants' perceptions of their particular situation; (3) the group's cultural traditions; and (4) 1965 Immigration Act. (FMW)

  15. Urbanism in the Anthropocene: Ecological urbanism or premium ecological enclaves?

    Hodson, Michael; Marvin, Simon


    Earth scientists now argue that the current geological era should be re-named the anthropocene to better reflect the impact of humans in reshaping planetary ecology. Urbanism encompasses the social, economic and political processes most closely linked to the rapid transformation of habitats, destruction of ecologies, over use of materials and resources, and the production of pollutants and carbon emissions that threaten planetary terracide. Consequently, the key concern for 21st-century globa...

  16. Punjabi Orchard Farmers: An Immigrant Enclave in Rural California.

    Gibson, Margaret A.


    Examines the adaptation patterns of Punjabi Sikh orchard farmers in rural California. Discusses the role of the following: (1) the historical context of immigration; (2) the immigrants' perceptions of their particular situation; (3) the group's cultural traditions; and (4) 1965 Immigration Act. (FMW)

  17. Urbanism in the Anthropocene: Ecological urbanism or premium ecological enclaves?

    Hodson, Michael; Marvin, Simon


    Earth scientists now argue that the current geological era should be re-named the anthropocene to better reflect the impact of humans in reshaping planetary ecology. Urbanism encompasses the social, economic and political processes most closely linked to the rapid transformation of habitats, destruction of ecologies, over use of materials and resources, and the production of pollutants and carbon emissions that threaten planetary terracide. Consequently, the key concern for 21st-century globa...

  18. Low grade metamorphism of mafic rocks

    Schiffman, Peter


    Through most of this past century, metamorphic petrologists in the United States have paid their greatest attention to high grade rocks, especially those which constitute the core zones of exhumed, mountain belts. The pioneering studies of the 50's through the 80's, those which applied the principles of thermodynamics to metamorphic rocks, focused almost exclusively on high temperature systems, for which equilibrium processes could be demonstrated. By the 1980's, metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks. Of course, low grade metamorphic rocks - here defined as those which form at pressures and temperatures up to and including the greenschist facies - had been well known and described as well, initially through the efforts of Alpine and Circum-Pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts, and that they underlay large portions of accreted terranes, many of oceanic origins. But until the mid 80's, much of the effort in studying low grade rocks - for a comprehensive review of the literature to that point see Frey (1987) - had been concentrated on mudstones, volcanoclastic rocks, and associated lithologies common to continental mountain belts and arcs. In the mid 80's, results of the Deep Sea Drilling Project (DSDP) rather dramatically mitigated a shift in the study of low grade metamorphic rocks.

  19. Geochemistry and mineralogy of mafic Icelandic hyaloclastites

    Hudak, M. R.; Feineman, M. D.; Eyer, C.; Bindeman, I. N.; Sigmarsson, O.


    Hyaloclastite in the crust may be a cryptic contaminant contributing to some volatile-rich Icelandic basalts and in some places reach 2.5 km1. Hyaloclastites are highly fragmented composites of lithics, glass, and crystals in a palagonite matrix that form as a result of magma-ice or magma-water interactions. These rocks have high water content and porosity and a high initial glass content, which makes them susceptible to rapid alteration by ambient or hydrothermal waters and potentially fast digestion by magmas. Due to low density and ductility, they have the potential to stall ascending mantle-derived magmas to form sills, and in the process may contribute exotic volatile or fluid-mobile components. We have characterized the geochemistry and mineralogy of 18 hyaloclastite samples from the Reykjanes Peninsula (RP), Vestmannajyar, and the southern coast of Iceland. Major and trace elements were obtained using ICP-AES and ICP-MS, respectively, and mineralogy was determined by XRD. Loss on ignition is highly variable (0.44 - 15.7 wt.%) and positively correlated with alkali loss reflected in the Chemical Index of Alteration [34.8 - 51.3; CIA = Al2O3/(Al2O3+CaO+Na2O+K2O)]. Primitive mantle normalized multi-element plots for RP hyaloclastites are broadly similar to those for unaltered RP Holocene basalts. Two samples have trace element profiles resembling those of picrites in the region. The samples from the south coast and Vestmannaeyjar have OIB-like enrichments similar to local Holocene basalts. Five well-sorted hyaloclastite samples have broad humps in their XRD patterns from 20-50° 2q. These samples contain only primary magmatic mineral phases (plagioclase, olivine, and pyroxene), if any, while other hyaloclastites contain both primary phases and secondary alteration phases including halite, calcite, clays, chlorite, and zeolites. Preliminary O and H isotope investigation demonstrates large ranges in both parameters. Future work will include oxygen isotope analyses and bulk rock halogen leachates. 1. Marks, N., Zierenberg, R. A. & Schiffman, P. Strontium and oxygen isotopic profiles through 3 km of hydrothermally altered oceanic crust in the Reykjanes Geothermal System, Iceland. Chem. Geol. 412, 34-47 (2015).

  20. Viscosity of mafic magmas at high pressures

    Cochain, B.; Sanloup, C.; Leroy, C.; Kono, Y.


    While it is accepted that silica-rich melts behave anomalously with a decrease of their viscosity at increased pressures (P), the viscosity of silica-poor melts is much less constrained. However, modeling of mantle melts dynamics throughout Earth's history, including the magma ocean era, requires precise knowledge of the viscous properties of silica-poor magmas. We extend here our previous measurements on fayalite melt to natural end-members pyroxenite melts (MgSiO3 and CaSiO3) using in situ X-ray radiography up to 8 GPa. For all compositions, viscosity decreases with P, rapidly below 5 GPa and slowly above. The magnitude of the viscosity decrease is larger for pyroxene melts than for fayalite melt and larger for the Ca end-member within pyroxene melts. The anomalous viscosity decrease appears to be a universal behavior for magmas up to 13 GPa, while the P dependence of viscosity beyond this remains to be measured. These results imply that mantle melts are very pervasive at depth.

  1. Plutonismo del Ordovícico inferior en el sector norte de la sierra de Macón, provincia de Salta

    M. Koukharsky


    Full Text Available En el norte de la sierra de Macón, ubicada en el oeste de la Puna, aflora un complejo plutónico dominantemente granodiorítico cuyas composiciones extremas llegan a tonalitas y granitos. Hacia el oeste y norte de la sierra son comunes los enclaves microgranosos máficos, además de pseudodiques y pseudo cuerpos intrusivos de metavolcanitas sugiriendo que se encuentran los niveles más cercanos al techo. Edades K/Ar y Rb/Sr determinadas en la década del 70 en una roca granítica asignaban al Proterozoico superior la intrusión, y por correlaciones en diferentes trabajos se la había considerado del Ordovícico, Silúrico y Carbonífero. En este estudio se determinó la edad Ar/Ar en hornblenda en una de las rocas mas primitivas y frescas del complejo con un valor de 482,7 ±7,8 Ma. Esta edad se considera cercana a la de la intrusión, sobre la base de características petrográficas que indican un emplazamiento epizonal. La asociación litológica y los datos geoquímicos corresponden a rocas calcoalcalinas de arco volcánico. Un leve grado de alteración (cloritización-sericitización y deformación estructural de los últimos minerales en cristalizar (feldespato potásico y cuarzo, presentes en todas las muestras estudiadas, se asocian con esfuerzos compresivos vinculados a la orogenia oclóyica. Estas conclusiones se contraponen con el ambiente anorogénico extensional que había sido propuesto previamente por otros autores para el magmatismo que dio origen a estas rocas plutónicas.In northern Sierra de Macón, in the western sector of the Puna, is a plutonic complex composed dominantly of granodiorites, which grade in composition to tonalites and granites. Toward the west and north of the range, mafic microgranular enclaves are common, as well as pseudo-dikes and pseudo-intrusive bodies of metavolcanic rocks, suggesting levels near to the roof of the magma chambers. K/Ar and Rb/Sr ages determined in the 1970´s gave an Upper Proterozoic

  2. Characteristics and Magmatism of MaficUltramafic Layered Intrusions%镁铁质-超镁铁质层状岩体基本特征及岩浆作用

    夏昭德; 姜常义; 夏明哲; 凌锦兰; 卢荣辉


    Mafic- ultramafic layered intrusions can occur in various tectonic settings and have typical layered structure and prosodic structure. The magmatisms for layered rocks are mainly gravity differentiation, double-diffusive convection, compaction, assimilation contamination, and magma mixing. Gravitational differentiation well explains the vertical changes of rock types and variations of mineral composition in layered intrusions. Double-diffusive convection and magma mixing play an important role in the formation process of rhythmic beddings. Compaction plays a key role in the late stage of magma evolution for the formation of adcumulatic texture. Assimilation contamination can change the composition of magma,resulting in changes in the composition of magma differentiation. The types of crystal structures depend on the different activities of inter-cumulus liquid and penetration rate of crystal mush, and adcumulatic texture formation requires high permeability. When the inter-cumulus liquid is not active, it is favorable for the formation of ortho-cumulatic texture. Rock association and textures, mineral compositions and change rules are good records for magma differentiation process, magma supplying, and other information, which can be used to discuss the petro-genesis of layered intrusions: temperature and pressure conditions of magma, primitive magma and magmatic evolution.%镁铁质-超镁铁质层状岩体可以产于多种构造环境,岩体具有典型的层状构造和韵律结构.层状岩体形成时主要的岩浆作用有重力分异作用、双扩散对流作用、压实作用、同化混染和岩浆混合作用等,其中重力分异作用很好地解释了层状岩体垂向上岩石类型的变化和矿物组分的变化,双扩散对流作用和岩浆混合作用在韵律层理形成过程中起了很重要的作用,而压实作用对岩浆演化晚期阶段补堆晶结构的形成作用明显,同化混染作用可改变岩浆的成分,导致岩浆分

  3. 新疆北山地区罗东镁铁质-超镁铁质层状岩体岩石成因%Petrogenesis of Luodong mafic-ultramafic layered intrusion, Beishan region, Xinjiang

    凌锦兰; 夏明哲; 郭娜欣; 汪帮耀; 夏昭德; 姜常义


    罗东镁铁质-超镁铁质岩体位于塔里木板块东北部的新疆北山地区,岩体平面形态为眼球状,出露面积约2.1 km2.由纯橄岩、单辉橄榄岩、斜长二辉橄榄岩、橄榄二辉岩、方辉辉石岩、橄长岩、橄榄辉长岩、辉长岩、苏长辉长岩和淡色辉长岩组成,堆晶结构和堆晶韵律发育,属于层状岩体.岩浆演化过程中主要分离结晶/堆晶相是橄榄石和单斜辉石,此外还有斜长石、铬尖晶石和斜方辉石.岩石地球化学特征表明岩体与围岩之间的同化混染较弱.原生岩浆属于苦橄质岩浆(MgO=14.7%),并且具有高的岩浆结晶温度(1412℃).OIB型Nd、Sr同位素组成和高温苦橄质原生岩浆暗示,罗东岩体的形成可能与地幔柱活动有关,是地幔柱轴部部分熔融的产物.由此表明,塔里木板块东北部早二叠世幔源岩浆岩也应该隶属于塔里木大火成岩省.%Lens shaped Luodong mafic-ultramafic intrusion lies in Beishan region of Xinjiang in Northeastern Tarim Plate and covers an area of 2.1 km2. It consists of dunite, wehrlite, plagio-lherzolite, olivine websterite, peridotite pyroxenite, troctolite, olivine gabbro, gabbro, noritegabbro and leucogabbro. The Luodong intrusion is a layered intrusion with obvious cumulus textures and rhythmics. The mainly fractional crystallized or cumulated phases are olivine and clinopyroxene, together with minor plagioclase, orthopyroxene and Cr-spinel during magma evolution. The geochemical feature indicates weak crustal contamination. The primary magma is picritic with MgO contents up to 14.7% and high crystallization temperature of 1412 ℃. OIB-like Nd, Sr isotopic compositions and high temperature picritic primary magma indicate that Luodong intrusion may have an affinity with mantle plume and be formed by partial melting of axis plume. The Early Permain mantle-derived magmatic rocks in Northeastern Tarim Plate are thus a part of Tarim Large Igneous Province.

  4. Isotopic evidence for multiple contributions to felsic magma chambers

    Waight, Tod Earle; Wiebe, R.A.; Krogstad, E.J.


    by contemporaneous mafic magmas; the transition between the two now preserved as a zone of chilled mafic sheets and pillows in granite. Mafic components have highly variably isotopic compositions as a result of contamination either at depth or following injection into the magma chamber. Intermediate dikes...... with identical isotopic compositions to more mafic dikes suggest that closed system fractionation may be occurring in deeper level chambers prior to injection to shallower levels. The granitic portion of the pluton has the highest Nd isotopic composition (eNd=+3.0) of plutons in the region whereas the mafic...... lithologies have Nd isotopic compositions (eNd=+3.5) that are the lowest in the region and similar to the granite and suggestive of prolonged interactions and homogenization of the two components. Sr and Nd isotopic data for felsic enclaves are inconsistent with previously suggested models of diffusional...

  5. Microscopic analisys of porous microgranular bovine anorganic bone implanted in rat subcutaneous tissue Análise microscópica do osso bovino inorgânico microgranular implantado em subcutâneo de ratos

    Willian Fernando Zambuzzi


    Full Text Available The tissue response to porous bovine anorganic bone implanted in rat connective tissue was evaluated by subjective light microscopy analysis. Forty rats were divided into two groups: control (empty collagen capsules and test (collagen capsule filled with 0.1g biomaterial and killed 10, 20, 30 and 60 days after implantation. At 10 days, intense chronic inflammatory infiltrate consisting mainly of macrophages and inflammatory multinucleated giant cells (IMGC was observed. Neutrophils, plasma cells and lymphocytes were present in discrete amounts and slowly disappeared along the repair process. Porosity of the material was filled by reaction connective tissue exhibiting IMGC. The fibrosis was more intense after 60 days and clearly higher than the control group. Thus, the material did not cause any severe adverse reactions and did not stimulate the immune system. Based on the results it could be concluded that deproteinized bovine cancelous bone was well tolerated by rat connective tissue.A resposta tecidual ao osso inorgânico bovino medular implantado em subcutâneo de rato foi avaliada por análise subjetiva através de microscopia de luz. Quarenta ratos foram divididos em 2 grupos: controle (cápsulas vazias de colágeno e teste (cápsulas de colágeno contendo 0,1g do biomaterial e mortos 10, 20, 30 e 60 dias após a implantação. Histologicamente, aos 10 dias, observou-se infiltrado inflamatório crônico composto por macrófagos e Células Gigantes Multinucleadas Inflamatórias (IMGC. Neutrófilos, plasmócitos e linfócitos estavam presentes de maneira discreta, desaparecendo durante o processo de reparo tecidual. A porosidade do material foi preenchida pelo tecido conjuntivo reacional mostrando as IMGC. A fibrose foi mais intensa aos 60 dias e evidentemente superior ao grupo controle. Entretanto, o material não causou reações adversas severas, não estimulando a resposta imunológica. Baseado nos resultados encontrados, concluímos que o osso inorgânico bovino medular foi bem tolerado pelo tecido conjuntivo de rato.

  6. Efeitos de ciclos de umedecimento e secagem na reorganização da estrutura microgranular de latossolos Effects of wetting and drying cycles on the reorganization of the microgranular structure of latosols

    J. H. M. Viana


    Full Text Available Um experimento foi realizado em casa de vegetação com o objetivo de examinar as modificações provocadas por ciclos de umedecimento e secagem em amostras de Latossolos com diferentes mineralogias, em agregados integrais ou quando destruídos por moagem. Amostras de terra fina seca ao ar foram passadas em peneira de 1,0 mm e subdivididas em grupos: solo integral não moído e solo moído em almofariz e passado em peneira de 0,105 mm. O solo moído foi ainda subdividido em solo moído puro ou adicionado de ácido húmico purificado. Os materiais foram montados em cilindro de alumínio e submetidos a dez ciclos sucessivos de umedecimento e secagem, realizados por ascensão capilar, seguidos por secagem ao ar, com intervalo de sete dias entre cada ciclo. Após o término dos ciclos, os solos foram impregnados com resina de poliéster, montando-se seções finas para microscopia, as quais foram levadas para observação em microscópio ótico e fotografadas. As imagens obtidas foram digitalizadas, analisadas e quantificadas por meio do programa QUANTIPORO, desenvolvido no Departamento de Solos/Universidade Federal de Viçosa. Os resultados mostraram completa modificação na forma e no padrão da estrutura após a aplicação dos ciclos nos tratamentos que sofreram destruição de agregados por moagem. Essas mudanças foram atribuídas a uma reacomodação dos agregados fragmentados com a retração do plasma, que se seguiu ao processo de secagem. Todos os materiais estudados mostraram uma estrutura bem diferente da estrutura primária original destes solos. Não se observou qualquer tendência à reversão da estrutura após os dez ciclos, demonstrando que outros fatores, além dos físico-químicos e mineralógicos, devem ser invocados para explicar a gênese de microagregados em Latossolos.A greenhouse experiment was conducted to examine the structural modifications engendered by wetting-drying cycles in Latosol samples (Oxisols with different mineralogical properties submitted to dry grinding, compared with bulk samples. Air-dried soil samples were sieved through a 1.00 mm sieve and separated in two groups. One was kept as control group and the other ground in a mortar and sieved through a 0.105 mm sieve. This second was also split in two groups, one of which received particulate humic acid treatment. The materials were placed in aluminum columns, subjected to 10 weekly wetting cycles by capillarity followed by air-drying. At the end of the cycles, the samples were impregnated with polyester resin, cut in blocks and thin-sectioned for microscopy analysis. The sections were scrutinized under optical microscope, photographed, and the images digitalized, analyzed, and quantified with the Software QUANTIPORO. After the wetting and drying cycles, important alterations in both shape and structural pattern were observed in the ground samples. These changes were attributed to a re-organization of soil particles during the plasma shrinkage after the drying process. All materials presented a different structural pattern in relation to the original soil structure. No trend for reversion to the original structure was observed after the cycles. This indicates that other factors besides the physical-chemical and mineralogical should be considered to explain the genesis of Latosol microaggregates.

  7. High-Risk Microgranular Acute Promyelocytic Leukemia with a Five-Way Complex Translocation Involving PML-RARA

    Benjamin Powers


    Full Text Available Acute promyelocytic leukemia (APL is classically characterized by chromosomal translocation (15;17, resulting in the PML-RARA fusion protein leading to disease. Here, we present a case of a 50-year-old man who presented with signs and symptoms of acute leukemia with concern for APL. Therapy was immediately initiated with all-trans retinoic acid. The morphology of his leukemic blasts was consistent with the hypogranular variant of APL. Subsequent FISH and cytogenetic analysis revealed a unique translocation involving five chromosomal regions: 9q34, 17q21, 15q24, 12q13, and 15q26.1. Molecular testing demonstrated PML/RARA fusion transcripts. Treatment with conventional chemotherapy was added and he went into a complete remission. Given his elevated white blood cell count at presentation, intrathecal chemotherapy for central nervous system prophylaxis was also given. The patient remains on maintenance therapy and remains in remission. This is the first such report of a 5-way chromosomal translocation leading to APL. Similar to APL with chromosomal translocations other than classical t(15;17 which result in the typical PML-RARA fusion, our patient responded promptly to an ATRA-containing regimen and remains in complete remission.

  8. High-Risk Microgranular Acute Promyelocytic Leukemia with a Five-Way Complex Translocation Involving PML-RARA.

    Powers, Benjamin; Persons, Diane; Rao, Deepthi; Woodroof, Janet; Lin, Tara L


    Acute promyelocytic leukemia (APL) is classically characterized by chromosomal translocation (15;17), resulting in the PML-RARA fusion protein leading to disease. Here, we present a case of a 50-year-old man who presented with signs and symptoms of acute leukemia with concern for APL. Therapy was immediately initiated with all-trans retinoic acid. The morphology of his leukemic blasts was consistent with the hypogranular variant of APL. Subsequent FISH and cytogenetic analysis revealed a unique translocation involving five chromosomal regions: 9q34, 17q21, 15q24, 12q13, and 15q26.1. Molecular testing demonstrated PML/RARA fusion transcripts. Treatment with conventional chemotherapy was added and he went into a complete remission. Given his elevated white blood cell count at presentation, intrathecal chemotherapy for central nervous system prophylaxis was also given. The patient remains on maintenance therapy and remains in remission. This is the first such report of a 5-way chromosomal translocation leading to APL. Similar to APL with chromosomal translocations other than classical t(15;17) which result in the typical PML-RARA fusion, our patient responded promptly to an ATRA-containing regimen and remains in complete remission.

  9. Metasomatismo en ortoanfibolitas de la Faja máfica-ultramáfica del río de las tunas, Mendoza Metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt, Mendoza

    M. Florencia Gargiulo


    áticos y la secuencia de reemplazo observada en ellos, sugieren que tales asociaciones se generaron a causa de un proceso metasomático, acontecido en condiciones de bajo grado a una presión menor a 4 kbar, durante los estadios finales del ciclo de metamorfismo regional evidenciado en el área.In this contribution, petro-mineralogical and chemical evidences of metasomatism in orthoamphibolites from the Río de Las Tunas mafic-ultramafic belt in Frontal Cordillera of Mendoza province are provided. These orthoamphibolites integrate the metamorphic basement of the Frontal Cordillera and they belong to the Guarguaráz Metamorphic Complex. These rocks show mineral associations and textural relationships indicating disequilibrium conditions between some of the mineral phases. Hornblendic amphibole crystals show a reaction border with development of clinopyroxene (ferroan dioside; meanwhile the calcicplagioclase is mostly replaced by a fine-grained matrix integrated by the mineral association of garnet-epidotes.l -prehnite-pumpellyite- albite. The amphibole and clinopyroxene crystals are also partially replaced by pumpellyite and/or chlorite, meanwhile the matrix is slightly replaced by muscovite and calcite. Garnet compositions belong to the grossular-andradite series and their average composition is: Alm05Adr53Prp01Sps04Grs36Uv01. Some crystals with Cr2O3 content between 11.69-13.17 wt.% and with a subtle chemical zonation (uvarovitic core: Alm03Adr13Prp00Sps02Grs35Uv47 with more grossularic border: Alm03Adr12 Prp00Sps01Grs44Uv40 occur in relationship with magnetite crystals with up to 20% of the chromite component. Pressure estimations based on the compositional zoning of amphibole crystals gave values between 2.5-4.5 kbar. The observed mineral associations together with the textural and chemical characteristics of these rocks show that this kind of orthoamphibolites is completely different from the classical amphibolites of igneous protoliths outcropping in the study area

  10. 华北克拉通孔兹岩带中段大青山-乌拉山变质杂岩立甲子基性麻粒岩年代学及地球化学研究%Geochronological and geochemical study of the Lijiazi mafic granulites from the Daqingshan-Wulashan metamorphic complex, the central Khondalite Belt in the North China Craton

    刘平华; 刘福来; 蔡佳; 刘建辉; 施建荣; 王舫


    The Iijiazi mafic granulites are predominantly composed of Amp Cpx-Opx granulite, Grt-bearing Amp Cpx-Opx granulite and Bt Amp Cpx-Opx granulite, and have been found as irregular lenses and deformed dykes within the Al-rich gneisses and granitic gneisses in the Daqingshan-Wulashan metamorphic complex. The apparent207 Pb/206 Pb ages recorded by the metamorphic zircon domains with the middle-to low-pressure granulite-facies mineral inclusions of Cpx + Amp + Pl, which are consistent to the matrix-type metamorphic assemblages of the mafic granulites, range from 1933 ±39Ma to 1834 ±40Ma with a weighted mean age of 1892 ±7Ma, which are interpreted as the timing of the middle,-to low-pressure granulite-facies metamorphism of the mafic granulites. Mobile elements such as the large ion lithophile elements (K, Na, Sr, Rb) of the mafic granulites changed in significant levels, high field strength elements (such as Nb, Zr, Ti) and rare earth elements basically unchanged and keep stable during the metamorphic process. The Lijiazi mafic granulites from the Daqingshan complex belong to tholeiitic-basaltic rock series, with the concentrations of SiO2 at 45. 58% ~51. 40%, and Mg# value mainly ranging from 41 to 54. The composition of the rare earth elements of the mafic granulites is characterized by the flat, (La/Yb )CN =1. 30 ~ 1.51) with no Eu anomalies (Eu/Eu * = 0. 93 ~ 1. 04) on the chondrite-normalized patterns. All samples of the mafic granulites share obvious negative anomaly in Nb, Zr and Ti of the Phanerozoic island arc basalts. According to the geochemical and geochronological data of the Lijiazi mafic granulites, it is suggested that the protolith ages of the Lijiazi mafic granulites is 2450 ~ 1930Ma, the protoliths of the mafic granulites are undergone middle-to low-pressure granulite-facies metamorphism at ~ 1900Ma, the composition of the major and trace elements of the mafic granulites is characterized by the island arc tholeiitic basaltic rocks, and

  11. Condiciones físicas de formación de gabros ymigmatitas derivadas de rocas máficas en el centro de la Sierra de ValleFértil, San Juan Physical conditions for the formation ofgabbros and migmatites derived from mafic rocks in the center of Sierra deValle Fértil, San Juan

    AlinaM. Tibaldi


    resultadosexperimentales se demuestra que la transición desde rocas ígneas máficas amigmatitas máficas ocurrió por enfriamiento isobárico, y que el emplazamientocontinuo de magmas debió ser la fuente de calor que mantuvo la secuencia enfacies de granulitas sin dejar que el enfriamiento fuera rápido. Se interpretala geología del centro de la sierra de Valle Fértil como un ejemplo del núcleoplutónico-metamórfico del arco magmático Famatiniano donde el gradientemetamórfico anormalmente alto refleja que un volumen importante de magmasmáficos alcanzaban, y dominaban, en paleo-profundidades de entre 16 y 20kilómetros.A sequence of plutonicmafic rocks inter-stratified with both mafic- and metasedimentary-derivedmigmatites is found along the San Juan valley in the center of the Sierra deValle Fértil. This natural example shows the transition from igneous tometamorphic petrologic processes which occurred during the crystallization ofmafic magmas and the subsequent partial melting of crystallized gabbroic rocks.This work studies the mineralogical changes associate to this petrologictransition. Thermobarometric estimates based on amphibole-plagioclase indicatethat the mafic magmas crystallized at around 1100ºC and 5 ± 0.5 kbar. Theconditions under which gabbroic rocks were partially melted are estimated usingtwo pyroxenes thermometry and amphibole-plagioclase thermobarometry. Similarphysical conditions in the range between 740 and 840ºC and 5 to 6.5 kbar arerecovery from mineral assemblages in the mesosomes and leucosomes of maficmigmatites. The main mineral compositional changes that accompanied the partialprocess of the gabbroic rocks are: 1 depletion of aluminium content and Mg#ratio in pyroxenes; 2 depletion of anorthite mole fraction of theplagioclases; and 3 depletion of the Mg# ratio in amphiboles. These mineralcompositional variations are consistent with those found by experimentallymelting mafic protoliths. Experimental results showed that the temperature forpromoting

  12. SHRIMP zircon U-Pb and Re-Os dating of No. 10 intrusive body and associated ores in Pobei mafic-ultramafic belt of Xinjiang and its significance%新疆坡北基性-超基性岩带10号岩体SHRIMPU-Pb和矿石Re-Os同位素定年及其意义

    李华芹; 梅玉萍; 屈文俊; 蔡红; 杜国民


    Located in Beishan rift in the northeastern part of Tarim plate, the Pobei No. 10 mafic-ultramafic body in-truded into Early Carboniferous Hongliuyuan Formation. It is large in size and well differentiated, thus serving as one of the most important intrusive bodies in search for copper-nickel sulfides. According to its emplacement strata, it was previously thought that this intrusive body was formed in Late Carboniferous-Early Permian. The uthors performed dating by using such techniques as zircon U-Pb, disseminated ores Re-Os and Sr-Nd isotopic tracer with the purpose of systematic determination of the magmatie and mineralization ages, on such a basis, discussed the metallogenic significance of systematic differences between the ages dated by different isotopic sys-tems. Radiometric dating of the gabbro from the Pobei No. 10 mafic-ultramafie body yielded rather scattered zir-con age information, but obtained a main body zircon SHRIMP U-Pb age of (289± 13)Ma(95 % confidence, MSWD=4.9, n = 8), which is interpreted as the formation age of the host intrusive. The disseminated ores give an apparent Re-Os isochron age of (413 ± 20) Ma with an initial 187Os/188Os ratio of (0.226 ± 0.032). However, it is found that the apparent Re-Os isochron ages of disseminated ores are older than both the forma-tion age of the host intrusions and the ages of Pobei No. 10 mafic-ultramafic emplacement strata, which indicates that the apparent Re-Os isochron ages of disseminated ores are not reliable. It is suggested that the Pobei No. 10 mafic-ultramafic body and the deposit were formed at about 280 Ma ago. Because of heterogeneity in initial ~(187)Os/~(188)Os ratios of disseminated ores caused by crust contamination, the apparent dates older than the true age were obtained. Cu-Ni mineraliztion shows a close time-space relationship with the mafic-ultramafic intrusive body, implying a product of magmatic liquation. It is therefore concluded that the intrusion of Pobei No. 10 mafic

  13. Interaction between two contrasting magmas in the Albtal pluton (Schwarzwald, SW Germany): textural and mineral-chemical evidence

    Michel, Lorenz; Wenzel, Thomas; Markl, Gregor


    The magmatic evolution of the Variscan Albtal pluton, Schwarzwald, SW Germany, is explored using detailed textural observations and the chemical composition of plagioclase and biotite in both granite and its mafic magmatic enclaves (MMEs). MMEs probably formed in a two-step process. First, mafic magma intruded a granitic magma chamber and created a boundary layer, which received thermal and compositional input from the mafic magma. This is indicated by corroded "granitic" quartz crystals and by large "granitic" plagioclase xenocrysts, which contain zones of higher anorthite and partly crystallized from a melt of higher Sr content. Texturally, different plagioclase types (e.g. zoned and inclusion-rich types) correspond to different degrees of overprint most likely caused by a thermal and compositional gradient in the boundary layer. The intrusion of a second mafic magma batch into the boundary layer is recorded by a thin An50 zone along plagioclase rims that crystallized from a melt enriched in Sr. Most probably, the second mafic intrusion caused disruption of the boundary layer, dispersal of the hybrid magma in the granite magma and formation of the enclaves. Rapid thermal quenching of the MMEs in the granite magma is manifested by An30 overgrowths on large plagioclase grains that contain needle apatites. Our results demonstrate the importance of microtextural investigations for the reconstruction of possible mixing end members in the formation of granites.

  14. Petrología y geoquímica de las rocas máficas-ultramáficas del área río Las Águilas - arroyo de Los Manantiales, Provincia de San Luis Petrology and geochemistry of mafic-ultramafic rocks in the Las Águilas River-of the Manantiales stream area, San Luis

    G. Ferracutti


    Full Text Available Dada la carencia de información de campo detallada, se efectuó el mapeo y muestreo de los cuerpos máficos-ultramáficos aflorantes entre el río de Las Águilas y el arroyo de Los Manantiales en la provincia de San Luis. La escasa información de campo, petrográfica y geoquímica de las unidades de éste área dificultaba la vinculación entre las rocas aflorantes y aquellas reconocidas en los testigos de perforación. Los cuerpos ígneos de interés se hallan en contacto con el basamento metamórfico a través de fallas de alto ángulo de buzamiento y/o contactos intrusivos. En Las Higueras y Virorco, se identificaron afloramientos de rocas máficas-ultramáficas con textura magmática primaria de tipo estratificada no-uniforme de regularidad intermitente. El estudio de estos cuerpos generó un desafío particular debido a los procesos deformación, metamorfismo y alteración que los han afectado. Estos factores no solo modificaron la mineralogía de las rocas sino que ademas generaron bloques basculados reconocidos por la presencia de texturas de estratificación magmaticas cuya posición espacial no se corresponde con la magmática originaria. Los patrones de los elementos de tierras raras normalizados a condrita permiten identificar un proceso de diferenciación, con mayor enriquecimiento en los contenidos de tierras raras en las rocas más evolucionadas. En base a los contenidos de tierras raras de las rocas ultramáficas, se infiere que la cristalización magmática estuvo controlada por la presencia de olivino y ortopiroxeno.Geological mapping was completed in the area between Las Águilas River and the Manantiales stream in San Luis province due to the absence of a detailed geologic map of the mafic-ultramafic bodies which occur in this region. Also the lack of petrographic and geochemical information constituted a draw back when attempting to relate surface and subsurface rocks. In this contribution a geological map of the area and

  15. Tectonic breccia of the Cabo Frio area, State of Rio de Janeiro, Brazil, intruded by Early Cretaceous mafic dyke: evidence of the Pan-African brittle tectonism? Brecha tectônica da área de Cabo Frio - RJ, intrudida por dique máfico do Eocretáceo: evidência do tectonismo rúptil do Pan-Africano?

    Akihisa Motoki


    Full Text Available This paper presents the field descriptions and microscopic observations of a tectonic breccia in the basement gneiss of the Cabo Frio and Arraial do Cabo areas, State of Rio de Janeiro, Brazil, and its intrusive contact with the Early Cretaceous mafic dyke. At the sea cliff close to the Ilha do Japonês, there is an excellent contact outcrop between them. The tectonic breccia zone is 10 to 20m wide and has N30ºE direction. The breccia clasts are angular and characterized by auto-brecciation texture, and composed of breccia with similar aspect of the host tectonic breccia. The matrix is firmly consolidated by hydrothermalism and following silicification. The mafic dyke is 7 to 10m wide and of N45ºE direction. Along the contact, the dyke chilled margin featured by fine-grained basalt and prismatic joints can be observed. At the Conchas Beach and Arraial do Cabo city, there are four outcrops demonstrating the mafic dyke intrusion into the consolidated tectonic breccias. These outcrops prove that the tectonic breccias are older than the Early Cretaceous tholeiitic dykes. The fault breccias could have been formed during the brittle-phase tectonism of the last stage of the Pan-African Orogeny by hydrothermalism without magmatic activities, namely tectonic hydrothermalism. The existence of the clasts constituent of the breccia that are composed of breccia suggests that the fault movement and following hydrothermalism occurred repeatedly.Esse trabalho apresenta as descrições de campo e observações petrográficas de uma brecha tectônica no embasamento gnáissico das áreas de Cabo Frio e Arraial do Cabo, RJ, e seu contato intrusivo com um dique máfico do Eocretáceo. Na proximidade da ilha do Japonês, ocorre um excelente afloramento de contato entre esses litotipos. A zona da brecha tectônica tem 10 a 20 m de largura e tem direção de N30ºE. Os clastos da brecha são angulosos e caracterizados pela textura de auto-brechação, sendo similares

  16. Caracterización de rocas ultramáficas, máficas y metasedimentarias del cordón del Peñasco, Precordillera Occidental, Mendoza Characterization of ultramafic, mafic and metasedimentary rocks of the Cordón del Peñasco, western Precordillera, Mendoza

    Florencia L Boedo


    Full Text Available En el cordón del Peñasco, ubicado en el sector norte de la provincia de Mendoza, dentro del ámbito de la Precordillera Occidental, aforan metasedimentitas en contacto tectónico con una asociación máfica-ultramáfica. Dentro de las metasedimentitas en facies esquistos verdes se han reconocido dos asociaciones: metalimolitas carbonáticas y metaareniscas y metapelitas. Las rocas máficas-ultramáficas están representadas por serpentinitas derivadas de harzburgitas y dunitas, gabros bandeados metamorfizados en facies granulita; diabasas constituyendo diques o filones capa, metabasaltos amigdaloides y metahialoclastitas con bajo grado de metamorfismo. Se realizaron estimaciones termométricas en una granulita máfica (gabro bandeado utilizando el par granate-clinopiroxeno, obteniéndose temperaturas de 884°C. Las mismas permiten estimar que estos cuerpos experimentaron metamorfismo de alta temperatura, para posteriormente retrogradar a facies esquistos verdes, sobre la base de aspectos mineralógicos y texturales. Con respecto a las unidades metasedimentarias, el paleoambiente inferido para la unidad de metaareniscas y metapelitas corresponde a pie de talud continental con predominio de sedimentación gravitacional sobre la base de estructuras sedimentarias reconocidas. Mientras que la unidad de metalimolitas carbonáticas pertenecerían a un ambiente marino profundo. Estas unidades han sido asignadas al Eopaleozoico a partir de criterios estratigráficos y deformadas y metamorfizadas hacia fines del Devónico como consecuencia de la orogenia Chánica.In Cordón del Peñasco area, located in northern Mendoza province, western Precordillera, metasedimentites are in tectonic contact with a mafic-ultramafic association. The former have been under greenschist facies metamorphism and two associations have been recognized: carbonate metasiltstones and metasandstones and metapelites. The mafic-ultramafic association is represented by serpentinized

  17. Petrology of Oligocene Ghaleh Yaghmesh granitoids in the west of Yazd province

    Bahareh Fazeli


    calculation of amphibole minerals by Cameca SX50 microprobe device at the Oklahomacity University (Norman - USA. Results The studied plutonic rocks are dominated by plagioclase, orthoclase, quartz, amphibole (magnesio hornblende and actinolite hornblende, biotite, and pyroxene. Zircon, apatite, sphene, tourmaline and opaque minerals as the common accessory and chlorite, epidote and calcite are the secondary minerals. On the base of petrographic observation as well as mineral-chemistry and geochemical data, the granitoid massif is classified as I-type (magnetite series, calc – alkaline and metaluminous composition. The rocks under discussion are characterized by the high level of LILE (Ba, Sr, K and Cs and the negative anomaly of HFS elements (Ti, Nb, Zr and Y indicating the subduction related magmatism. The Ghaleh Yaghmesh granitoids are cogenetic and possibly developed in subduction zone related to active continental margin calc – alkaline volcanic arcs. Mixing process of acidic and basic magmas is likely involved in generation of the rocks being studied. Discussion The parent magma probably formed by partial melting of amphibolites with some sedimentary materials. Fractional crystallization of melt in the higher levels of crust gave rise to various rock types. Mantle – derived basaltic magmas emplaced into the lower crust most likely provide heat for partial melting Clemens et al., 2011(. Field evidences such as the presence of mafic microgranular enclaves having sharp boundaries with the host rocks (Zorpi et al., 1989; Didier, 1991, petrographic observations (similar mineralogy of MME and the host rock (Didier, 1991; Didier and Barbarin, 1991, the occurrence of accicular apatite (Zorpi et al., 1989; Didier, 1991, the corroded margin of amphibole and plagioclase (Zorpi et al., 1989; Shelley, 1993 and the abundance of biotite and hornblende in MME compared to the host rock (Ellis and Thompson, 1986 and geochemical criteria (range of silica from 51.35 to 70.78 indicate

  18. Tracing magma sources of three different S-type peraluminous granitoid series by in situ U-Pb geochronology and Hf isotope zircon composition: The Variscan Montes de Toledo batholith (central Spain)

    Merino Martínez, E.; Villaseca, C.; Orejana, D.; Pérez-Soba, C.; Belousova, E.; Andersen, T.


    Three distinct S-type peraluminous granitoid types have been identified within the Variscan Montes de Toledo batholith, located in the Central Iberian Zone (SW European Variscides): type-1, extremely high peraluminous restite-rich granitoids; type-2, highly peraluminous restite-bearing granitoids; and type-3, moderately peraluminous granitoids with mafic microgranular enclaves. Type-1 and type-2 granitoids are restricted to the western part of the batholith, whereas type-3 granites are mostly restricted to the eastern segment. There is a sequential youngering of emplacement age from type-1 (late-tectonic) to type-2 and type-3 granitoids (post-tectonic), extending the timing of the batholith formation for about 19 Ma between 316 and 297 Ma. Although the degree of peraluminousity of the different series could be related to different partial melting conditions or to the variable entrainment of restitic components (including the peritectic mineral assemblage of the melting reactions), whole-rock geochemical signatures and isotope zircon composition of the peraluminous granitoid types suggest contribution of different crustal sources. There is no evidence for the direct mantle-derived material contribution in the genesis of these peraluminous melts. Type-1 and type-2 granitoids contain mostly Archean to Neoproterozoic inherited zircons, whereas type-3 granites show preferentially Neoproterozoic (up to late Cryogenian) and Ordovician inheritance. The wide range of initial Hf isotope composition, ranging to highly radiogenic values (ƐHf up to + 10), of Neoproterozoic zircon inheritances in type-1 and type-2 granitoids suggests derivation from heterogeneous Neoproterozoic metasedimentary sources composed of both juveline and recycled crustal materials, similar in composition to the host Schist-Greywacke Complex metasediments. Trace-element modelling clearly suggests the involvement of metasediments similar to those mentioned from the southern part of the Central Iberian

  19. Brasiliano-age granitoids in the Sergipana Fold Belt, NE Brazil: the Coronel João Sá Pluton

    Mcreath, I.; Lafon, J. M.; Davison, I.; Chaves, J. M.; Conceiçāo, H.


    The Coronel João Sá pluton is a zoned Brasiliano-age, late- to post-tectonic intrusion in the Macururé schist domain of the Sergipana Foldbelt, Northeast Brazil. Biotite-hornblende granodiorite predominates, and flattened ultramafic to intermediate enclaves are present. Igneous orientations are present but fabrics produced by strong solid-state flattening are absent. Rb-Sr whole rock isochrons including enclaves and their host rocks yielded a probable intrusion age of 614 Ma which dates the waning phase of the dominant deformation which produced the F2 foliation of the Sergipana belt and is close to ages reported for late tectonic granites in other Brasiliano domains of Northeast Brazil. More radiogenic Sr (I Sr(614) = 0.71008 ± 52) is present in some felsic rocks, while less radiogenic Sr (I Sr(614) = 0.70814 ± 18) is mainly found in the more mafic core of the main body. Sr isotopic equilibrium between most enclaves and their host rocks was attained. Textural evidence, especially in the enclaves, shows that magma mixing occurred, but late biotite formation in the enclaves caused modifications of their chemical compositions. The geological, petrographical and isotopic evidence shows that the pluton was probably fed by a complex feeder system into the crust under extensional conditions. Variable upper crustal contamination was probably responsible for the isotopic heterogeneity of Sr.

  20. Geología y petrología del cuerpo Máfico-Ultramáfico Las Juntas, Sierra de Valle Fértil, Provincia de San Juan Geology and petrology of mafic-ultramafic body from Las Juntas, Valle Fértil, San Juan

    Baliani Ignacio


    Full Text Available En el centro de la sierra de Valle Fértil aflora un cuerpo lenticular orientado en forma aproximada N-S que se encuentra encajado en un basamento ígneo de naturaleza máfica-ultramáfica. La morfología y posición actual de dicho cuerpo se debe a su emplazamiento tectónico, y la fábrica magmàtica interna presenta rumbo similar al del cuerpo y buzante al este. Las rocas que conforman el cuerpo de Las Juntas exponen una variedad litológica con las siguientes composiciones: norita olivínica, gabro anfibólico, dunita, gabronorita anfibólica y peridotita anfibólica piroxénica. Se caracterizan por presentar un encapado ígneo a escala de afloramiento y textura cumular a escala de muestra de mano, mientras que la microtextura predominante en estas rocas es de tipo coronítica. La relación cogenética entre las rocas máficas y ultramáficas de Las Juntas es determinada por la composición de silicatos de Mg y Fe presentes en ellas. El coeficiente de intercambio Fe-Mg entre olivino y clinopiroxeno con el líquido muestra un magma con una relación de #Mg (Mg/Mg + Fe-2 alrededor de 0,6; siendo inferior a la esperada para magmas generados en el manto peridotítico. Esto demuestra que el magma formador de estas rocas se habría originado en el manto litosférico, posteriormente ascendido y emplazado en niveles inferiores de la corteza (20 - 25 km. Este proceso petrológico es característico de magmatismo asociado a subducción, y relacionado al arco magmático Famatiniano.An elongate body of mafic and ultramafic plutonic rock crops out in central Sierra de Valle Fértil. The igneous body was tectonically emplaced and its internal magmatic fabrics strike roughly north-south and dip to the east. Rocks in the body are different from their hosting plutonic rocks in showing a layered igneous structure associated with pristine cumulate textural features at all observational scales. The layered body is composed of gabbronorite cumulates, ultramafic

  1. Eruptive history of Mammoth Mountain and its mafic periphery, California

    Hildreth, Wes; Fierstein, Judy


    This report and accompanying geologic map portray the eruptive history of Mammoth Mountain and a surrounding array of contemporaneous volcanic units that erupted in its near periphery. The moderately alkaline Mammoth eruptive suite, basaltic to rhyodacitic, represents a discrete new magmatic system, less than 250,000 years old, that followed decline of the subalkaline rhyolitic system active beneath adjacent Long Valley Caldera since 2.2 Ma (Hildreth, 2004). The scattered vent array of the Mammoth system, 10 by 20 km wide, is unrelated to the rangefront fault zone, and its broad nonlinear footprint ignores both Long Valley Caldera and the younger Mono-Inyo rangefront vent alignment.

  2. Vesta Evolution from Surface Mineralogy: Mafic and Ultramafic Mineral Distribution

    DeSanctis, M. C.; Ammannito, E.; Palomba, E.; Longobardo, A.; Mittlefehldt, D. W.; McSween, H. Y; Marchi, S.; Capria, M. T.; Capaccioni, F.; Frigeri, A.; Pieters, C. M.; Ruesch, O.; Tosi, F.; Zambon, F.; Hiesinger, H.; Magni, G.; McFadden, L. A.; Raymond, C. A.; Russell, C. T.; Sunshine, J. M.


    Vesta is the only intact, differentiated, rocky protoplanet and it is the parent body of HED meterorites. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta. Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, a mineral that is a major component of the mantles of differentiated bodies, including Vesta. The HED parent body experienced complex igneous processes that are not yet fully understood and olivine and diogenite distribution is a key measurement to understand Vesta evolution. Here we report on the distribution of olivine and its constraints on vestan evolution models.

  3. Characteristics Research on Chromite from the Poyi Cu-Ni Sulfide-bearing Mafic-ultramafic Intrusions in the Beishan Block,Xinjiang%新疆北山坡-含铜镍镁铁-超镁铁质岩体铬铁矿特征研究

    柴凤梅; 夏芳; 陈斌; 卢鸿飞


    The Poyi maiic-ultramafic intrusion is one of the most important Cu-Ni bearing complexes in Beishan area. This intrusion is composed of peridotite, pyroxenite and gabbro. Chromites occurs in the peridotite as an enhedral, subhedral and anhedral accessory mineral. The characteristics of chromites suggested that the primary magma of the Poyi intrusions must have been mantle-derived S-undersaturated mafic magma derived from asthenosphere mantle source even related to mantle plume and have experienced two stages evolution to form this intrusion. Some chromites enclosed within olivine may be crystallized from the primary magma in the deep magma chamber, and others enclosed within pyroxene and being interstitial crystals may be formed from the olivine- and sulfide-laden crystal mush in the high-level magma chamber. The chromites formed in the early stage of magma evolution are very important for the Cu-Ni sulphide deposit.%坡-镁铁-超镁铁质岩体为新疆北山地区一重要的含铜镍硫化物的侵入体.该岩体主要由橄榄岩、辉石岩和辉长岩组成.铬铁矿主要以副矿物形式现于橄榄岩中.它们以自形-半自形以及它形存在于橄榄石颗粒间或其内,部分为辉石包裹,偶见其包裹橄榄石.结合电子探针研究,认为坡一岩体母岩浆是来源于软流圈地幔或者与地幔柱有关的基性岩浆,原生岩浆经过了两个阶段的演化形成了目前的坡一岩体.包裹于橄榄石中的铬铁矿为岩浆早期深部岩浆房中结晶的产物,其他形式存在的铬铁矿为富含橄榄石和铬铁矿“晶粥”的演化岩浆结晶的结果.铬铁矿的结晶对坡一铜镍矿床的形成具有重要的意义.

  4. Tectonic juxtaposition of crust and continental growth during orogenesis:Example from the Rengali Province, eastern India

    Sankar Bose a; Susmita Guha a; Gautam Ghosh a; Kaushik Das b; Joydip Mukhopadhyay a; c


    The southern boundary of the Singhbhum Craton witnessed multiple orogenies that juxtaposed thin slice of granulite suite of the Rengali Province against the low-grade granite-greenstone belt of the craton along the EeW trending Sukinda Thrust. The strong southerly dipping mylonitic foliation within the granulites along with the prominent down-dip mineral lineation, suggest a northerly-verging thrusting. Mylonitized charnockite at the contact zone contains enclaves of mafic and ultramafic granulite, whereas granitoid gneiss contains enclaves of pelitic granulite. Mafic granulite enclaves preserve an early (S1M) foliation that formed during D1M deformation. This rock, along with the host charnockite, were intensely deformed by the D2M thrusting event and resulting S2M foliation development in both rock suites. Geothermobarometric and pseudosection analyses show that the garnet-clinopyroxene-plagioclase-orthopyroxene-ilmenite-quartz assemblage in mafic granulite was stabilized at high-pressure and temperature conditions (10?12 kbar, 860 ?C) and was overprinted by a fine-grained assemblage of cli-nopyroxene-plagioclase ? hornblende that developed during decompression (down to 5.5e7.5 kbar). Matrix hornblende shows incipient breakdown to garnet-clinopyroxene-quartz intergrowth due to a granulite facies reworking. A contrasting P-T history is preserved in the pelitic granulite. The peak assemblage garnet-orthopyroxene-cordierite-quartz-rutile was stabilized at w6.0 kbar, 730 ?C which resulted from heating of the mid crust magma during the D2M thrusting. The contrasting P-T histories could result from the tectonic juxtaposition of lower- and mid-crustal section during the D2M event. Evidences of an early orogenic imprint within the mafic granulite imply involvement of deep continental crust during southward growth of the Singhbhum Craton.

  5. Tectonic juxtaposition of crust and continental growth during orogenesis: Example from the Rengali Province, eastern India

    Sankar Bose


    Full Text Available The southern boundary of the Singhbhum Craton witnessed multiple orogenies that juxtaposed thin slice of granulite suite of the Rengali Province against the low-grade granite-greenstone belt of the craton along the E–W trending Sukinda Thrust. The strong southerly dipping mylonitic foliation within the granulites along with the prominent down-dip mineral lineation, suggest a northerly-verging thrusting. Mylonitized charnockite at the contact zone contains enclaves of mafic and ultramafic granulite, whereas granitoid gneiss contains enclaves of pelitic granulite. Mafic granulite enclaves preserve an early (S1M foliation that formed during D1M deformation. This rock, along with the host charnockite, were intensely deformed by the D2M thrusting event and resulting S2M foliation development in both rock suites. Geothermobarometric and pseudosection analyses show that the garnet-clinopyroxene-plagioclase-orthopyroxene-ilmenite-quartz assemblage in mafic granulite was stabilized at high-pressure and temperature conditions (10−12 kbar, 860 °C and was overprinted by a fine-grained assemblage of clinopyroxene-plagioclase ± hornblende that developed during decompression (down to 5.5–7.5 kbar. Matrix hornblende shows incipient breakdown to garnet-clinopyroxene-quartz intergrowth due to a granulite facies reworking. A contrasting P-T history is preserved in the pelitic granulite. The peak assemblage garnet-orthopyroxene-cordierite-quartz-rutile was stabilized at ∼6.0 kbar, 730 °C which resulted from heating of the mid crust magma during the D2M thrusting. The contrasting P-T histories could result from the tectonic juxtaposition of lower- and mid-crustal section during the D2M event. Evidences of an early orogenic imprint within the mafic granulite imply involvement of deep continental crust during southward growth of the Singhbhum Craton.

  6. Magma Mixing Genesis of the Jinchang Quartz Diorite in West Qinling Orogen,Western China: Petrographical and Geochronological Constraints and Their Tectonic Implications%西秦岭金厂石英闪长岩的岩浆混合成因:岩相学和锆石U-Pb年代学证据及其构造意义

    刘志鹏; 李建威


    位于西秦岭南部的金厂石英闪长岩岩体内含有大量镁铁质暗色微粒包体,包体大多呈浑圆状和水滴状,部分呈不规则拉长状,与寄主岩的接触界线截然或呈渐变过渡关系.石英闪长岩中的磷灰石呈短柱状,而包体中的磷灰石则呈细长针状,反映基性岩浆的快速冷凝结晶.石英闪长岩中的斜长石发育振荡环带,核部的斜长石An低,而边部斜长石An先急剧上升,复又下降;核部与边部之间存在明显的间断,同时斜长石边部包裹有暗色矿物,指示其形成时可能有更基性的岩浆注入.寄主岩中的角闪石大多为普通角闪石和镁普通角闪石,属SiO2饱和型,而包体中角闪石一部分为镁普通角闪石,属SiO2饱和型,一部分为韭闪石、韭闪石质普通角闪石,属SiO2不饱和类型.包体中的角闪石自核部到边部,Al2O3与TiO2含量急剧下降,说明核部和幔部相对于边部形成于更高温的环境.寄主岩中黑云母部分为铁质黑云母,部分为镁质黑云母,而包体中黑云母均为镁质黑云母,在∑FeO/(∑FeO+MgO)对MgO图解上寄主岩与包体中黑云母均落入壳-幔混源区.寄主岩和包体中的锆石均为典型的岩浆锆石,LA-ICP- MS锆石U- Pb定年表明它们的形成年龄分别为212±2 Ma及215±1Ma(2σ),在误差范围内基本一致,证明二者同时形成.综合以上岩相学和年代学证据认为,金厂石英闪长岩和镁铁质暗色微粒包体是幔源基性岩浆和壳源酸性岩浆混合作用的产物,形成于秦岭造山带中三叠世造山后伸展环境.结合区域上的研究结果认为,中—晚三叠世时期的幔源岩浆底侵和下地壳部分熔融在西秦岭广泛存在.%The Jinchang quartz diorite pluton is located in the south part of western Qinling orogen, western China. Mafic microgranular enclaves (MMEs) are widespread in the pluton, and are mostly rounded or irregular elongated in morphology. They commonly have sharp to

  7. Comparison of host magmatic sulphide and oxide deposits of mafic-ultramafic intrusions and review the mineralizing process%寄主岩浆硫化物和氧化物矿床的镁铁质-超镁铁质岩体对比分析与成矿过程评述

    姜常义; 夏昭德; 凌锦兰; 夏明哲; 卢荣辉; 郭芳放


    Mafic-ultramafic intrusion is a main vector of magmatic sulfide (Ni-Cu-PGE) deposits and oxide (Fe-Ti-V-P) deposits in the world. The world's major magmatic sulfide deposits and magmatic oxide deposits can occur in large igneous provinces, cratonic rift zone areas or extension setting, stretching post-collisional environment of the folded belt The scale of host rock of magmatic sulphide deposits varies greatly (from 6x10 km to < 0. 1 km ), the rock associations have ultramafic rocks and mafic rocks, but their primary magma are mainly tholeiitic magma. The PGE deposits bearing Ni-Cu host mainly in large-scale stratified intrusions, while the Ni-Cu sulfide deposit occurs in small intrusions. Vanadium-titanium magnetite or magnetite deposits host mainly in layered gabbro complex and ilmenite-apatite deposits are host in layered intrusions with anorthosite-mangerite-chamockite associations. Although the rock composition varies greatly, but its primary magma belongs to tholeiitic. Host rock of sulphide deposit is relatively rich in Si, Mg, Cr, Ni, while host rock of oxide deposits is relatively rich in Fe-Ti-P-V, rock-forming mineral crystal chemistry also reflects the difference. The critical factor of the contrast is the pressure of magma generation, whereas the difference in the magma source and the extent of melting may only play a role in the local area. The view for the ore forming processes of magmatic sulfide deposits are represented by the Jinchuan model and magma conduit model, and that of oxide deposit by whether oxide and apatite are cumulates or crystals from immiscible oxide liquid. Comparative analysis shows that the mineralizing process is complex, and it may not be preferable that trying to use a model to interpret the process of all the similar deposits. There is no doubt that an appropriate redox environment is the necessary conditions for the formation of magmatic deposits. Accompanied by crystallization of magma and mineralizing process of change in

  8. Study on Enzymatic Hydrolyss to Starch Micro-granular a Maltodextrin%酶法制备玉米淀粉糊精的性质研究

    郝晓敏; 王遂


    以玉米淀粉为原料,分别以温度84℃、时间20 min、酶用量16 u/g的中温a-淀粉酶和以温度95℃、时间40 min、酶用量15 U/g的耐高温仅a-淀粉酶水解玉米淀粉制取糊精,并对得到的两种玉米淀粉糊精进行研究.结果表明,样品具有较小的粒径,X-射线衍射图谱保持了 A 型特征峰,持水性比原淀粉大,感官及其理化特性符合麦芽糖标准,有望成为脂肪代用品.

  9. Assessment laser phototherapy on bone defects grafted or not with biphasic synthetic micro-granular HA + β-tricalcium phosphate: histological study in an animal model

    Soares, Luiz Guilherme P.; Marques, Aparecida M. C.; Aciole, Jouber Mateus S.; Trindade, Renan; Santos, Jean N.; Pinheiro, Antônio Luiz B.


    Beside of biomaterials, Laser phototherapy has shown positive results as auxiliary therapy on bone repair. The aim of this study was to evaluate, through histological analysis, the influence of Laser phototherapy in the process of repair of bone defects grafted or not with Hydroxyapatite. Forty rats were divided into 4 groups each subdivided into 2 subgroups according to the time of sacrifice. Surgical bone defects were made on femur of each animal with a trephine drill. On animals of group Clot the defect was filled only by blood, on group Laser the defect filled with the clot and further irradiated. In group Biomaterial the defect was filled with HA + β-TCP graft. In group Laser + Biomaterial, the defect was filled with biomaterial and further irradiated. The irradiation protocols were performed every 48 hours during for 15 days. Animal death occurred after 15 and 30 days. The specimens were routinely processed and evaluated by light microscopy. Qualitative analysis showed that group Laser + Biomaterial was in a more advanced stage of repair at the end of the experimental time. It was concluded that the Laser irradiation improved the repair of bone defects grafted or not.

  10. Immigrant enclaves and obesity in preschool-aged children in Los Angeles County.

    Nobari, Tabashir Z; Wang, May-Choo; Chaparro, M Pia; Crespi, Catherine M; Koleilat, Maria; Whaley, Shannon E


    While neighborhood environments are increasingly recognized as important contributors to obesity risk, less has been reported on the socio-cultural aspects of neighborhoods that influence obesity development. This is especially true among immigrants, who may lack the necessary language skills to navigate their new living environments. In this study, we tested the hypothesis that young children of immigrants would be at lower obesity risk if they lived in neighborhoods where neighbors share the same language and culture. Using 2000 Census data and 2003-2009 data from the Special Supplemental Nutrition Program for Women, Infants and Children in Los Angeles County, we examined the relation between BMI z-scores in low-income children aged 2-5 years (N = 250,029) and the concentration of neighborhood residents who spoke the same language as the children's mothers. Using multi-level modeling and adjusting for child's gender and race/ethnicity, household education, neighborhood socioeconomic status, and year the child was examined, we found that percent of neighborhood residents who spoke the same language as the child's mother was negatively associated with BMI z-scores. This relation varied by child's race/ethnicity and mother's preferred language. The relation was linear and negative among children of English-speaking Hispanic mothers and Chinese-speaking mothers. However, for Hispanic children of Spanish-speaking mothers the relation was curvilinear, initially exhibiting a positive relation which reversed at higher neighborhood concentrations of Spanish-speaking residents. Our findings suggest that living in neighborhoods where residents share the same language may influence obesity-related behaviors (namely diet and physical activity) possibly through mechanisms involving social networks, support, and norms.

  11. Spain and Morocco: The Spanish Enclaves in North Africa, Potential Mediterranean Security Dilemma


    Economic News Service Weekly, XXXVI:31, p. 3, 19 January 1982. 34. 1979 exchange rate used was 69.91 pesetas per $1. Sources: Estadistica del Commercio...There also is detailed information on Ceuta (pp. 556-58) and Melilla (p. 559). 47. Rezette, p. 99. 48. Estadistica del Commercio Exterior de Espana


    . Amirian


    Full Text Available 800x600 Normal 0 false false false IN X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";} The aim of this research was to know the food security of farmer household, based on the availibility of staple food, access to food and  utilization of food of farmer household. The research design was cross-sectional study. The samples were consisted of 35 owner farmer, 12 yeoman, and 13 farmworker. Primary and secondary data was analyzed by Microsoft Excel and SPSS version 13 for windows. The result showed that 48.33% of husband and 78.33% of wife were 40 years old. As many as 66.67% of husband education and 70.00% of wife education were elementary school.  Most of the sample were farmers, 26.67% husband and 18.33% wife had additional work. The result showed, based on the availability of staple food, 70.00% of household catagorized as food secured. Based on the access to food, 65.00% of household catagorized as food secured, and based on the utilization of food, 56.70% of household catagorized as food secured. The conclusion of this research, 63.30% of household catagorized as food secured based on combination of three component of food security. There was a significant positive correlation (pproduction distributed to household with the availability of energy per capita per day. Key words: food security, household

  13. Foreign-born out-migration from new destinations: Onward or back to the enclave?

    Kritz, Mary M; Gurak, Douglas T; Lee, Min-Ah


    Immigrants have a markedly higher likelihood of internal mignation if they live in new destinations. This paper looks at why that pattern occurs and at how immigrants' out-migration to new versus traditional destinations responds to their labor market economic and industrial structure, nativity origins and concentration, geographic region, and labor market type. Confidential data from the 2000 and 1990 decennial censuses are used for the analysis. Metropolitan and non-metropolitan areas are categorized into 741 local labor markets and classified as new or traditional based on the nativity concentrations of immigrants from the 24 largest Asian, Caribbean and Latin American origins. The analysis shows that immigrants are less likely to migrate to new destinations if they live in areas of higher nativity concentration, foreign-born population growth, and wages but more likely to make that move if they are professionals, agricultural or blue collar workers, highly educated, fluent in English, and live in new destinations. While immigrants are more likely to migrate to new rather than traditional destinations that outcome differs sharply for immigrants from different origins and for some immigrants, particularly those from the Caribbean, the dispersal process to new destinations has barely started. Copyright © 2012 Elsevier Inc. All rights reserved.

  14. Owen Sound, Canadá (1815-1996. De enclave portuario colonial a ciudad provincial

    Monge, Fernando


    Full Text Available This paper focuses on Owen Sound's relation between the port and the settlement, and how the port played a major role in a town rising to the city status. Owen Sound history is, though important for Canadian history may be, an adequate case study of the role of ports in generating communities as well as of the preeminence of the human factor over the much emphasized locational analysis.

    Este artículo se centra en la relación existente entre el puerto y el asentamiento, así cómo el papel central que el puerto jugó en la conversión del pueblo en una ciudad. A pesar de la importancia que dicha ciudad tiene en la historia canadiense, Owen Sound es un buen caso de estudio para evaluar el papel de los puertos en la génesis de comunidades así como de la preeminencia del factor humano sobre los excesivamente valorados análisis locacionales.

  15. Federal enclaves: The community culture of Department of Energy cities Livermore, Los Alamos, Oak Ridge

    Moore, Patrick Kerry

    During the Second World War, the United States Government funded the research of nuclear fusion to create the first atomic weapons. To accomplish this task, the Manhattan Engineering District recruited scientists and engineers to remote sites in New Mexico, Tennessee, and Washington. During the five decades of the Cold War, the congressionally created Atomic Energy Commission, and later the Department of Energy (DOE), funded and operated numerous facilities throughout the United States. The mission of the facilities was to design and stockpile atomic weapons and to further the understanding of nuclear energy. This dissertation examines the influences of the United States federal government on three communities associated with these facilities, Los Alamos, New Mexico, Oak Ridge, Tennessee, and Livermore, California. As isolated secret cities, these environments each created complex community structures. This work identifies how, unlike other community settings, the influences of the federal government, both directly and indirectly, created distinctive patterns of behavior within the residents of each city. Examining these behaviors within the framework of the dissertation's chapters provides the necessary context to understand fully the community culture of these Department of Energy cities. This work addresses contemporary community settings in new ways. It approaches the topic broadly by examining five specific areas of community interaction: social, political, business and economic, educational, and ethical. Through the use of oral history methodology and techniques, the researcher captured significant information from respondents. This approach provides valuable insights to the behavior and interaction of the individual populations while revealing important insights all aspects of each town's community culture.

  16. Hydrocarbon-Rich Territories in Central Asia: Producing Countries, Exporting Enclaves or Transit Countries?

    Aurelia Mañé


    Full Text Available This article aims to qualify the different analyses and currents of opinion that are circulating with respect to Central Asia’s capacity to become one of the main exporters of hydrocarbons in the next decade. For this, it first examines whether or not, in quantitativeterms, the hydrocarbon-rich territories of Central Asia can become one of the main suppliers on a world scale; secondly, it explains why the countries of Central Asia will play a necessarily different role on the international energy scene than that played by the OPEC countries; and, finally, it indicates what the relevance of this area could be in the organisation (structure of the contemporary international energy scene. In this sense, it discusses not producing countries, but rather countries of passage.

  17. Lifeline From the Sky: The Doctrinal Implications of Supplying an Enclave From the Air


    contemporary changes affecting airlift support to en­ claves , leading to the final conclusion. From this conclusion, implications will be drawn for future...during a heated debate with Hitler and Gen­ eral Zeitzler, chief of the General Staff of the army on November 21. Göring was losing favor with Hitler

  18. Nanotecnología y los enclaves del conocimiento en Latinoamérica

    Edgar Zayago Lau; Guillermo Foladori; Mark Rushton


    Mucho se ha escrito sobre la nanotecnología en los últimos años, sobre todo en lo relacionado a su revolucionario significado para la ciencia y sus aplicaciones que, según se argumenta, plantean la posibilidad de cambiar profundamente el mundo en que vivimos. No obstante, muy poco se ha escrito acerca de cómo la nanotecnología se incorpora al contexto de la economía del conocimiento y las fuerzas impulsoras detrás de esta dinámica. En el artículo, los autores analizan la intención del Banco M...

  19. The Early Mediaeval manorial estate of Gars/Thunau, Lower Austria: An enclave of endemic tuberculosis?

    Teschler-Nicola, Maria; Novotny, Friederike; Spannagl-Steiner, Michaela; Stadler, Peter; Prohaska, Thomas; Irrgeher, Johanna; Zitek, Andreas; Däubl, Barbara; Haring, Elisabeth; Rumpelmayr, Kerstin; Wild, Eva Maria


    In recent decades, an increasing number of studies have aimed to shed light on the origin and spread of tuberculosis in past human populations. Here we present the results of a systematic palaeodemographic and palaeopathological survey of the Early Mediaeval population of Gars/Thunau (Lower Austria), which - at this stage - includes 373 individuals recovered at two archaeological sub-sites: a fortified settlement (including a necropolis) at the top of a hill - probably reserved for social and military elites; and a large riverine settlement at the foot of the hill, a so-called 'suburbium', where burials and an area of 'industrial' character were discovered. We recorded a great number of pathological alterations and a variety of 'classical' features of tuberculosis, such as vertebral destructions (Pott's disease) and joint destructions, and other pathological (unspecific) features probably linked with Mycobacterium tuberculosis infection (e.g. new bone formation at the inner surface of the ribs, endocranial alterations in the form of 'pits', and new bone formation at the cranial base). We hypothesize that the two contemporaneous (∼900-1000 AD) populations of Gars/Thunau differed not only in their social affiliation/condition, but also in the type and frequencies of their population-density-related infectious diseases (in particular tuberculosis). Moreover, we investigated the molecular genetic evidence of the causative organism in a few selected immatures exhibiting pathological changes at the inner wall of the cranium and discuss these findings in regard to the macroscopic features observed. Finally, we analysed carbon and nitrogen stable isotopes of both populations and strontium isotope ratios of the hill-top inhabitants in order to reconstruct certain aspects of diet and mobility to test our hypothesis concerning the specific social and/or military character of the site.

  20. Strong Ties, Weak Ties, and Human Capital: Latino Immigrant Employment outside the Enclave

    Pfeffer, Max J.; Parra, Pilar A.


    This study focuses on the role of social ties and human capital in the integration of Latino immigrants into the local economy. This analysis extends earlier research by focusing on more rural contexts with limited labor-market opportunities and less access to social resources provided by coethnics. We reconsider conclusions of previous studies by…

  1. Nanotecnología y los enclaves del conocimiento en Latinoamérica

    Edgar Zayago Lau


    Full Text Available Mucho se ha escrito sobre la nanotecnología en los últimos años, sobre todo en lo relacionado a su revolucionario significado para la ciencia y sus aplicaciones que, según se argumenta, plantean la posibilidad de cambiar profundamente el mundo en que vivimos. No obstante, muy poco se ha escrito acerca de cómo la nanotecnología se incorpora al contexto de la economía del conocimiento y las fuerzas impulsoras detrás de esta dinámica. En el artículo, los autores analizan la intención del Banco Mundial de desarrollar las Iniciativas Científicas Milenio como Centros de Excelencia en Latinoamérica, con el objetivo de incrementar la competitividad y promover el crecimiento económico, que son entendidos por el Banco Mundial como prerrequisitos del desarrollo. De igual forma, se exponen las implicaciones del régimen de patentes que terminan modificando la trayectoria de esta tecnología revolucionaria.

  2. Erotic Enclaves and Contested Beds: Gardens in Pu Songling’s Chuanqi Tales

    Lei Jin


    Full Text Available Abstract:             This article examines the literary garden depicted by Pu Songling (1640-1715 in his' Liaozhai zhiyi '聊齋誌異 (Liaozhai's records of the strange; 1766. These enchanted, deserted, and haunted gardens function as metaphors for the contested ground on which some key Ming-Qing intellectual issues are debated. The article examines Pu’s depiction of 'qing'情,an important concept reflecting the philosophical and literary trends of the time, and shows that in the process of constructing literary gardens, Pu challenges the intellectual issues of his time and dissolves the boundaries between normal and abnormal, reality and ideal, death and life, and order and disorder.

  3. Enclaves agrícolas modernos: el caso del jitomate mexicano en los mercados internacionales

    Alejandro Macías


    las nuevas exigencias de la producción flexible. Entre dichas características podemos considerar las siguientes: la creciente participación en el mercado de productos frescos de Estados Unidos, pero también la elevada concentración en dicho mercado y en ese tipo de oferta, sin existir mayor valor agregado; la dependencia externa que se tiene sobre la provisión de insumos y medios de producción, que hacen que esta industria quede supeditada a las decisiones estratégicas tomadas en el país consumidor. Así, también se destacan los procesos de integración económica entre los dos países surgidos de la conformación del bloque comercial de Norteamérica, donde no sólo hay relaciones de competencia entre las naciones sino también de complementariedad.

  4. 新疆东天山镁铁-超镁铁岩体中橄榄石成分特征及其成因意义:以黄山东和图拉尔根为例%Compositions of olivine from the mafic-ultramafic complexs in eastern Tianshan, Xinjiang and implications to petrogenesus: Examples from Huangshandong and Tulargen complexes

    刘艳荣; 吕新彪; 梅微; 惠卫东


    A dozen of mafic-ultramafic complexes related to copper-nickel sulphide mineralization were found in Eastern Tianshan, Xinjiang. This paper takes Huangshandong and Tulargen complexes for examples, and carries out mineral chemistry tests of fresh olivine from different lithologies. Electron microprobe analyses of olivine show that the Fo of olivine in hornblende-gabbro facies and ultramafic rock facies range from 67 to 73 and from 81 to 84, respectively; Ni contents range from 308 to 1762 ug/g in Huangshandong complex. Olivine crystals in the Tulargen complex have Fo numbers varying from 82 to 85, with Ni from 857 to 1818 μg/g. Modeling of olivine fractional crystallization and sulfide segregation show that the parental magma for Huangshandong complex has experienced 19% olivine fractional crystallization and extensive sulfide segregation (~0.3%). Re-equilibration of the early formed olivine crystals with trapped liquid can account for the variations of olivine compositions. The Tulargen complex has experienced 9% olivine fractional crystallization and extensive sulfide segregation (~0.5%).%新疆东天山发育有十多个与铜镍硫化物成矿有关的镁铁-超镁铁杂岩体,对选取于黄山东和图拉尔根岩体岩体内不同岩性中的新鲜橄榄石进行了矿物化学成分测试.黄山东岩体角闪辉长岩相的橄榄角闪辉长岩中橄榄石Fo为67~73,超镁铁岩相的角闪(斜长)橄榄岩、角闪二辉橄榄岩和斜长单辉橄榄岩中橄榄石Fo为81~84,Ni含量为308~1762 μg/g;图拉尔根岩体中橄榄石Fo为82~85,Ni含量变化范围为857~1818μg/g.利用最高Fo含量的橄榄石成分计算得到黄山东岩体母岩浆MgO为10.3%,图拉尔根岩体母岩浆MgO为11.47%.橄榄石分离结晶和硫化物熔离模拟结果显示,黄山东岩体发生了19%的橄榄石分离结晶,由橄榄石分离结晶导致硫化物熔离的程度约为0.3%,晶间硫化物熔浆的物质交换作用对黄山东橄榄石

  5. Mineralogía y termo-barometría de los Complejos máficos Sol de Mayo y Suya Taco, Norte de las Sierras de Comechingones, Córdoba Mineralogy and thermo-barometry of the Sol de Mayo and Suya Taco mafic complexes from northern Sierra de Comechingones, Córdoba

    Alina M. Tibaldi


    Full Text Available Este trabajo presenta un estudio detallado de la petrografía, mineralogía química y termo-barometría de dos complejos máficos que afloran al norte de la sierra de Comechingones. Se aplicaron un conjunto de termómetros y barómetros empíricos con el propósito de determinar los rangos de P y T absolutas de cristalización de estas rocas. Las temperaturas de equilibrio en pares de piroxenos (cpx-opx se estimaron usando tres termómetros independientes. Dos calibraciones termométricas (Wells 1977, Kretz 1982 dan resultados consistentes y razonables indicando que los piroxenos registran condiciones de cristalización magmática (920-1150ºC, mientras que la tercera calibración (Lindsley 1983 estima temperaturas muy inferiores. Esta discrepancia puede estar relacionada con el hecho de que la última calibración no sería aplicable a rocas que cristalizaron a partir de magmas ricos en hierro. Por su parte, la termometría Amph-Pl sugiere temperaturas de equilibrio comprendidas entre 750-850ºC, para composiciones típicas de núcleos, mientras que para composiciones representativas de los bordes de grano las temperaturas estimadas son significativamente inferiores (This work presents a detailed study including petrography, mineral chemistry and thermo-barometry of igneous rock from two mafic complexes that outcrop in the north portion of the sierra de Comechingones. The range of absolute P and T under which these rocks crystallized is retrieved using a set of empiric barometers and thermometers. The estimations of equilibrium temperature determined in pairs of pyroxenes (cpx-opx were performed through three independent thermometers. Two of the thermometric formulations (Wells 1977, Kretz 1982 yield consistent and reasonable results indicating that these phases record magmatic crystallizations conditions (920-1150ºC, whereas the third calibration by Lindsley (1983 gives lower temperatures. This discrepancy is thought to reflect the fact that

  6. Evolución metamórfica de los gabros coroníticos de El Arenal, faja máfica-ultramáfica El Destino-Las Águilas, sierra de San Luis Metamorphic evolution of the coronitic gabbrons of the El Arenal, El Destino-Las Aguilas, mafic-ultramafic belt, Sierra de San Luis

    N. Brogioni


    Full Text Available Las meta-melagabronoritas coroníticas se localizan en uno de los cuerpos de El Arenal, pertenecientes a la faja máfica-ultramáfica El Destino-Las Aguilas del flanco oriental de la sierra de San Luis. Son rocas de grano fino y representan fraccionados poco evolucionados, con alto contenido de Cr-Ni y [Mg/Mg+FeT++] comprendidas entre 0,72 y 0,75, derivados de un magma toleítico olivínico de bajo Ti, cuyo emplazamiento precedió a la deformación penetrativa y metamorfismo famatinianos. Las microestructuras en coronas alrededor de olivino magnesiano y anortita registran tres estadios metamórficos de crecimiento mineral bajo condiciones de facies granulita, anfibolita y esquistos verdes que tuvieron lugar durante el ascenso y enfriamiento lento del magma favorecido por las condiciones P-T elevadas, ca. facies anfibolita, propias del nivel cortical profundo de locación. Luego de una ligera alteración deutérica de los componentes primarios, que ahora se conservan como relictos, se produjeron las transformaciones mineralógicas y microestructurales metamórficas más significativas. La desestabilización del par olivino-plagioclasa durante el estadio granulítico dio lugar a la formación de coronas de Opx y de simplectitas de Cpx + Spl. La deshidratación de las rocas de caja adyacentes, causada por el desarrollo de reacciones metamórficas, permitió durante el estadio anfibolítico la incorporación de fluidos acuosos indispensables para la cristalización de hornblenda, tanto en coronas de Amp + Spl simplectíticos como reemplazando al Opx relicto. La mineralogía de menor temperatura es relacionable con la exhumación de las rocas y representaría la última etapa de la trayectoria evolutiva antihoraria experimentada por las mismas durante el Paleozoico inferior.The coronitic meta-melagabbronorites are part of the El Arenal bodies which belong to the El Destino-Las Aguilas mafic to ultramafic belt, outcroping on the eastern flank of the

  7. 东天山白石泉镁铁-超镁铁杂岩体的Nd-Sr-Os同位素成分及其对岩浆演化的意义%Nd-Sr-Os isotopic data of the Baishiquan mafic-ultramafic complex from East Tianshan, and implications for petrogenesis

    陈斌; 贺敬博; 陈长健; 木合塔尔·扎日


    本文报道东天山有铜镍硫化物矿化的白石泉镁铁-超镁铁杂岩体(分布在中天山地块北部)的微量元素和Nd-Sr-Os同位素成分,以探讨其地幔源区性质和壳幔相互作用过程.白石泉杂岩体的地球化学特征是富集大离子亲石元素和轻稀土元素,但亏损高场强元素.全岩Sr和Nd同位素初始比值变化较大,分别是(87Sr/86Sr)i =0.7032~0.7066和εNd(t)=5.6~-0.9,两者呈反相关关系.全岩Os含量在80×10-12~29×10-12之间,富含放射性成因Os(187 Os/188 Os=0.295~ 1.18).据此,得出结论:(1)白石泉杂岩体的母岩浆在上升侵位过程中,受到地壳物质的强烈混染,导致各岩石类型的Nd-Sr同位素成分变化很大和Os同位素成分富集放射性成因Os的特征,这与前人认为的白石泉岩体侵位过程中没有地壳混染作用的模式明显不同;(2)白石泉杂岩体的母岩浆来自被古生代俯冲带熔/流体交代过的年轻岩石圈地幔,这要求我们重新认识中天山前寒武地块的性质和规模.%We report trace elements and Nd-Sr-Os isotopic data for the Baishiquan mafic-ultramafic complex that occurs in the East Tianshan Mountains (in the northern part of the Mid-Tianshan Precambrian block) and is accompanied by Cu-Ni deposits, to understand its mantle source characteristics and processes of mantle-crustal interaction. Geochemically, the complex is characterized by enrichment of LILEs and depletion of HFSEs. The whole-rock Sr-Nd isotopic compositions of the Baishiquan complex vary significantly, with (87Sr/ 86Sr)i =0. 7032 ~0. 7066 and εNd(t) =5. 6 ~ -0. 9, and the Nd-Sr isotopic ratios are negatively correlated. The complex shows very radiogenic Os isotopic compositions, with (187Os/188Os)i =0.295~1. 18 and Os=80 ×l0-12 ~29 ×l0-12. Based on these data, we conclude that (1) the parent magma of the Baishiquan complex experienced significant crustal contamination during magma emplacement, as is revealed by the negatively

  8. 西南天山东德沟镁铁-超镁铁岩中尖晶石的矿物学特征及其地质意义%Mineralogy of spinel from mafic-ultramafic rocks in Dongdegou, southwestern Tianshan and its geological significance

    孔凡梅; 李旭平; 李守军; 吴苏


    中国西南天山东德沟镁铁-超镁铁岩出露于天山伊犁-中天山板块和塔里木板块之间的碰撞造山带中,岩石类型主要为(方辉)橄榄岩,且普遍经历了含水流体(熔体)的渗透交代作用,含有形态和成分变化复杂的尖晶石,表现为从红褐色到黄褐色、再到深绿色和浅绿色,尖晶石的Cr2O3和FeO的含量依次降低,Al2O3和MgO的含量逐渐增高.研究认为红褐色和黄褐色的铬尖晶是原生矿物,而绿色的镁铝尖晶石为次生矿物.原生铬尖晶石的Cr#为0.41~0.87,Mg#为0.21~0.61,且成分变化大,显示其可能具多期熔融的复杂成因;次生绿色的尖晶石形态不一、成分相对有较大变化,表明其至少形成于两个期次的变质作用或流体交代过程.原生铬尖晶石具有SSZ环境橄榄岩的特征,指示其寄主岩石可能是俯冲上板片地幔楔岛弧环境的橄榄岩残片.%The mafic-ultramafic rocks of Dongdougou are located in the orogenic belt between the Tarim plate and the Yili-central Tianshan plate, southwestern Tianshan. Harzburgite is the main type of peridotite, generally metasomatized by hydrous melt or fluid. It includes different types of spinels, being red-brown, brown, dark green, and light green in color. Cr2O3 and FeO decrease gradually whereas AI2O3 and MgO increase with the metasomatism. Studies indicate that red-brown and brown picotiles constitute the primary type, while green magnesium spinels possess the second place. The compositions of the primary picotiles are variable with Cr and Mgtt in the range of 0.41~0.87 and 0.21-0.61 respectively, which may indicate polyphase origin of melting. Secondary spinels have different shapes, and their compositions vary tremendously, exhibiting two stages of metasomatism or metamorphism. The primary picotiles have characteristics of peridotite in a subducting upper plate mantle wedge zone, which implies the host rocks might have been the fragments of peridotite from a SSZ

  9. Geochemical characteristics of platinum group elements and Re-Os isotopes of the Hongshishan Cu-Ni sulfide-bearing mafic-ultramafic intrusion in Beishan block of Xinjiang and their metallogenic significance%新疆北山红石山含铜镍镁铁-超镁铁质岩体PGE和Re-Os同位素地球化学特征及成矿意义

    夏芳; 柴凤梅; 陈斌; 卢鸿飞; 严玉圃


    The Pobei mafic-ultramafic belt is an impotant Ni-Cu sulfide metallogenic prospective province in Beis-han area, eastern Xinjiang. About 20 intrusions (e.g. , Bijiashan, Hongshishan, Cihai, Poyi, Poshi and Lu-odong) were recognized along the fault in this area and almost all the intrusions are associated with Ni-Cu sulf ide deposits. The Hongshishan mafic-ultramafic complexs are located in the eastern part of the Pobei mafic-ultramafic belt and the southern part of the Baidiwa-Yunihe fault in this area. They intruded into quartz schist of the Lower Carboniferous Hongliuhe Formation. They are mainly composed of dunite, peridotite, troctolite, pyrox-enite, olivine gabbro, gabbro and diorite. These rocks were emplaced in two stages. The first stage consists ofperidotite and olivine gabbro, and the second stage comprises gabbro and diorite. The dunite, pyroxene peri-dotite and troctolite are the host rocks for Ni-Cu sulfide ores. The platinum-group elements and Re-Os isotopic compositions of ore and rocks from the Hongshishan Ni-Cu sulfide-bearing mafic-ultramafic intrusions were analyzed, and the result shows that the total PGE content is quite low, ranging from 0.54×l0~9to 15.84×1CT9 and increasing with the increase of sulfide content. The PGE primitive mantle-normalized patterns display a positive slope and low fractionation between IPGE and PPGE. PGE, Cu and Ni are depleted relative to the primitive mantle with low and a narrow Pd/Ir range (3.19 - 10.5), indicating a weak influence of later hydrothermal alteration. Furthermore, the Ir displays positive correlations with Pt, Pd, Os, Ru and Rh, indicating a weak contribution of the fractionation and the partial melt to PGE depletion. The Cu/Pd ratios(73 × 103 ~ 1 670 × 103)and Ti/Pd ratios (87 × 103~2 857 × 103)of these rocks suggest that sulfur in the primary magmas had reached saturation, and immiscible sulfides droplets were segregated from silicate magmas before their emplacement The relationship between Ni

  10. Petrological, geochemical and isotopic investigations on a carbonate-dyke and enclosed pyroxenite xenoliths from Val Mastallone (Ivrea-Verbano Zone): evidence of a cumulate carbonatite in the lower crust?

    Galli, Andrea; Grassi, Daniele; Burg, Jean-Pierre; Schwab, Leo; Rickli, Jörg; Gianola, Omar


    The Ivrea-Verbano Zone (Italy/Switzerland) represents one of the best exposed mantle-crust sections worldwide. Its geological evolution has been governed by the Permian underplating of mantle-derived basic magmas („Mafic Complex") into the high-grade basement of the Southern Alps. In the Ivrea-Verbano Zone, marbles occur as concordant bodies or partly discordant carbonate-dykes. Generally, these dykes are constituted of calcite, diopside, scapolite, contain enclave of the host rocks and display sharp contacts to the host lithologies without evidences of alteration zones. In Val Mastallone, an up to 40 m thick carbonate-dyke with different characteristics occurs within mafic granulites. This dyke is composed of calcite, clinopyroxene and subordinate allanite and zircon. No scapolite is observed. The contacts to the host granulites are characterized by alteration zones composed of actinolite, chlorite, clinozoisite, plagioclase and calcite. The carbonate-dyke bears enclave of phlogopite-amphibole-apatite-rutile-ilmenite ± garnet or spinel clinopyroxenites. These rock type is not outcropping elsewhere in the proximity of the dyke, suggesting a significant transport. Host mafic granulite enclave are found exclusively at the margin of the dyke. Calcite dykelets rich in zircon, baddeleyite and other Ba, U, Th, REE-rich phases cut across the enclave. The carbonate-dyke shows an enrichment of LREE over HREE ((La/Yb)N = 14), with a Σ REE = 338 and Y/Ho = 27. On the chondrite-normalized REE abundances diagram, no Eu anomaly is observed. Mantle-normalized pattern shows strong negative anomalies at Cs, Rb, K, Pb, P, Zr, Hf, Ti and positive Ba, Th, Sr, Nd anomalies, similarly to the "world average carbonatites". Measured absolute trace element concentrations are lower than average carbonatites but significantly higher than typical limestones and similar to cumulate carbonatites found elsewhere in the world (e.g. India, China, Brazil). Grt-bearing clinopyroxenite enclave

  11. Sienogranitos leucocráticos do Domínio Macururé, Sistema Orogênico Sergipano, Nordeste do Brasil: Stock Glória Sul

    Joane Almeida da Conceição

    Full Text Available RESUMO: O Stock Glória Sul (SGS (41 km2 é arredondado e intrusivo na parte central do Domínio Macururé, no Sistema Orogênico Sergipano (SOS. Internamente o Stock é formado por vários tipos de sienogranitos leucocráticos (biotita sienogranito, sienogranito com muscovita e biotita e muscovita sienogranito. Os biotita sienogranitos apresentam abundância de enclaves máficos microgranulares que correspondem a sienitos e são ocasionais nos sienogranitos com muscovita e biotita. Os sienogranitos são metaluminosos, com termos mais evoluídos peraluminosos, posicionando-se no campo dos granitos do tipo I e exibem assinatura geoquímica cálcio-alcalino de alto K2O. Os enclaves sieníticos são metaluminosos e exibem assinatura shoshonítica. Os dados geoquímicos sugerem que as diferentes rochas presentes no SGS podem ser explicadas como produto da mistura entre um magma fortemente diferenciado e peraluminoso (≈ 73% SiO2 com outro máfico shoshonítico (≈ 56% SiO2, representado pelos enclaves. Os valores dos elementos traços são mais elevados nos enclaves do que nos granitos, tais como Ba (1.179 - 319 ppm, Rb (351 - 55,3 ppm, Y (16,7 - 1,6 ppm. Os padrões de elementos terras raras mostram variação de ∑38,58 - 299,21 ppm, LaN/YbN 12,57 - 137,22 e Eu/Eu* 0,72 - 1,94. O SGS, ante aos resultados obtidos neste estudo, evidencia que a granitogênese no Domínio Macururé (DM é complexa e que os sienogranitos leucocráticos que ocorrem bem distribuídos nesse domínio são pós-tectônicos e representam o produto de interação entre magmas riolíticos peraluminosos com magmas mantélicos shoshoníticos.

  12. Isotopic chronology and geological events of Precambrian complex in Taihangshan region

    刘树文; 梁海华; 赵国春; 华永刚; 简安华


    There are five major geological events in Precambrian complex, Taihangshan region determined by researching into geology and isotopic chronology of the complex. Basaltic magma erupted and quartz-dioritic to tonalitic magma intruded in earlier neo-Archaean, which formed horn-blende-plagiogneiss of Fuping gneiss complex and metamorphic mafic rock enclaves in TTG gneiss complex. Granulite fades metamorphism and emplacement of biotite-plagiogneiss occurred in late neo-Archaean. Extension and uplifting from the end of neo-Archaean to Paleoproterozoic era formed Chengnanzhuang large extensional deformation zones and metamorphic mafic veins emplaced into the deformation zones. Remobilization of Precambrian complex and tectonic uplifting in late Paleoproterozoic era formed Longquanguan ductile shear zone and emplacement of Nanying gneiss. Occurrence of regional granite pegmatite at the end of Paleoproterozoic era means the end of the Luliang movement.

  13. Isotopic chronology and geological events of Precambrian complex in Taihangshan region


    There are five major geological events in Precambrian complex, Taihangshan region determined by researching into geology and isotopic chronology of the complex. Basaltic magma erupted and quartz-dioritic to tonalitic magma intruded in earlier neo-Archaean, which formed hornblende-plagiogneiss of Fuping gneiss complex and metamorphic mafic rock enclaves in TTG gneiss complex. Granulite facies metamorphism and emplacement of biotite-plagiogneiss occurred in late neo-Archaean. Extension and uplifting from the end of neo-Archaean to Paleoproterozoic era formed Chengnanzhuang large extensional deformation zones and metamorphic mafic veins emplaced into the deformation zones. Remobilization of Precambrian complex and tectonic uplifting in late Paleoproterozoic era formed Longquanguan ductile shear zone and emplacement of Nanying gneiss. Occurrence of regional granite pegmatite at the end of Paleoproterozoic era means the end of the Lliang movement.

  14. 新疆北天山黄山东含铜镍矿镁铁-超镁铁岩体的岩石因:主量元素、微量元素和Sr-Nd同位素证据%Petrogenesis of the Huangshandong Ni-Cu Sulfide-Bearing Mafic-Ultramafic Intrusion, Northern Tianshan, Xinjiang: Evidence from Major and Trace Elements and Sr-Nd Isotope

    邓宇峰; 宋谢炎; 颉炜; 程松林; 李军


    本文对新疆黄山-镜儿泉铜镍成矿带中黄山东岩体进行了主量元素、微量元素和Sr-Nd同位素的研究,探讨了岩体成因和区域构造演化.黄山东岩体有三次岩浆侵入,第一次侵入形成了橄榄辉长岩、角闪辉长岩和闪长岩,构成岩体的主体,其中橄榄辉长岩位于岩体中部,角闪辉长岩位于岩体上部和下部,闪长岩沿岩体边缘分布;第二次侵入形成辉长苏长岩,呈岩墙状分布于岩体西端和西北部;第三次侵入岩石为二辉橄榄岩,位于岩体下部,为主要的赋矿岩相.黄山东岩体样品除橄榄辉长岩和角闪辉长岩TiO2含量之外主量元素投影点都处于橄榄石、单斜辉石、斜方辉石和斜长石矿物化学成分之间,指示它们主要由橄榄石、单斜辉石、斜方辉石和斜长石组成.与塔里木地区地幔柱成因二叠纪镁铁-超镁铁岩体相比,黄山东岩体亏损Nb、Ta、Ti等高场强元素,La、Ba、Th、U等不相容元素含量较低,ENd (t)较高(+7.32‰~+8.29‰),并且具有较低的Th/U比值(1.13~2.98)和Nb/U比值(2.53~7.02),较高的La/Nb比值(1.15~4.19)和Ba/Nb比值(37.7~79.8).这些特征与俯冲成因的火山岩和侵入岩相似,暗示其原始岩浆主要来源于受俯冲流体交代地幔的部分熔融,软流圈地幔的上涌可能为部分熔融提供了热源.%The major and trace elements and Sr-Nd isotopes of the Huangshandong mafic-ultramafic intrusion in the Huangshan-Jing'erquan magmatic Cu-Ni mineralization belt are discussed to constrain its formation and regional tectonic evolution. Three magmatic pulses of the Huangshandong intrusion have been identified. The first pulse formed olivine gabbro, hornblende gabbro and diorite, which constitute the main body of the complex, with olivine gabbro in the central section, hornblende gabbro in upper and lower parts, and olivine gabbro along the margin of the complex. The second pulse formed gabbronorite dykes occurring as

  15. The intrusion of new magma triggered the 2011-2012 unrest at Santorini: evidence from noble-gas isotopes

    Rizzo, A.; Barberi, F.; Carapezza, M.; Di Piazza, A.; Francalanci, L.; Sortino, F.; D'Alessandro, W.


    Santorini is one of the most famous active volcanoes of the world for its catastrophic explosive eruption that occurred during the Minoan civilization. Since then the Kameni eruptive centers that formed within the caldera erupted repeatedly until 1950. In 2011-2012 the volcano has been characterized by a seismic unrest, that was unprecedented at Santorini at least since the 1950 eruption, and that led to fear for an imminent eruption. Because more than 100,000 visitors are present on the island during the tourist season, and considering the eruptive potential of Santorini, it is crucial to evaluate the hazard of this volcano, which depends on the type of magma actually present in the volcanic system. With the aim to address this question, this research shows the first comparison between noble-gas isotope composition of the present fumarolic gases with that of fluid inclusions hosted in enclaves contained in the 1570 and 1925 AD dacitic magmas erupted at Nea Kameni. These enclaves are a portion of mafic magma batches that replenished the shallow chamber of the plumbing system hosting cooler and more silicic melts. Their Sr-Nd isotope ratios are quite similar to those measured in the host dacitic rocks, implying a common parental magma. Therefore, the analyzed enclaves may be considered representative of the historic magma erupted at Nea Kameni which could be still present in the volcano plumbing system feeding the crater fumaroles. The 3He/4He ratios of enclaves, once corrected for air contamination (3.1-3.6 Ra), partially overlap those of the gases (3.5-4.0 Ra) collected from Nea and Palea Kameni. The range of 3He/4He ratios (3.1-4.0 Ra) is appreciably lower than typical arc volcanoes (R/Ra ~7-8), implying that a contamination by 4He-rich fluids occurred either directly in the mantle and/or in the plumbing system. Comparison of 3He/4He and 4He/40Ar* ratios measured in enclaves with those of gases, as well as long-term monitoring of R/Ra in the latters, coherently

  16. Constraints on the Rates of Replenishment, Magma Mixing, and Crystal Recycling at Santorini Volcano, Greece

    Martin, V. M.; Davidson, J. P.; Morgan, D. J.; Jerram, D. A.


    Santorini is a young, active volcano, which preserves abundant evidence for open-system processes such as magma replenishment and crystal recycling, and thus represents an ideal system in which to study magma chamber dynamics. Santorini is the largest volcanic centre in the Aegean arc, with an eruptive history spanning more than 250,000 years over two eruptive cycles. The cycles are dominated by extended periods of effusive shield-building activity with occasional large-magnitude explosive eruptions, the Minoan eruption of ~3600 years ago being the most recent. Current activity consists of a phase of post-caldera reconstruction, focused recently on the intra-caldera Kameni islands. Microsampling to measure 87Sr/86Sr ratios of plagioclase cores indicates the presence of a complex plumbing system beneath Santorini. Large rhyodacitic deposits typically contain a mafic component, interpreted as the eruption trigger. In some cases, the mafic magma groundmass and phenocrysts are isotopically similar to their rhyodacite host; other deposits show the opposite, implying the coexistence of isotopically distinct magma batches. To add further complexity, plagioclase phenocrysts are in some cases in equilibrium with their groundmass while others show the reverse, implying modification due to crystal recycling or shallow mixing processes prior to eruption. Mafic enclaves in the recent Kameni lavas, again interpreted as the probable eruption trigger, provide some constraints on the rates of these recycling, mixing, and triggering processes. Glomerocrysts and xenocrysts of recycled gabbroic cumulate material are present in a number of Kameni enclaves. Isotopic and chemical disequilibrium between the cumulate crystals and the host indicate that these fragments are derived from pre- existing crystal mush piles pervaded by the replenishing melts as they migrated to shallow levels, creating disequilibrium between the cumulate mineral cores and the replenishing melts. 87Sr/86Sr isotope

  17. Erupted cumulate fragments in rhyolites from Lipari (Aeolian Islands)

    Forni, Francesca; Ellis, Ben S.; Bachmann, Olivier; Lucchi, Federico; Tranne, Claudio A.; Agostini, Samuele; Dallai, Luigi


    Over the last ~267 ky, the island of Lipari has erupted magmas ranging in compositions from basaltic andesites to rhyolites, with a notable compositional gap in the dacite field. Bulk geochemical and isotopic compositions of the volcanic succession, in conjunction with major and trace elemental compositions of minerals, indicate that the rhyolites were dominantly generated via crystal fractionation processes, with subordinate assimilation. Radiogenic (Sr, Nd, and Pb) and stable (O) isotopes independently suggest ≤30 % of crustal contamination with the majority of it occurring in mafic compositions, likely relatively deep in the system. Within the rhyolites, crystal-rich, K2O-rich enclaves are common. In contrast to previous interpretations, we suggest that these enclaves represent partial melting, remobilization and eruption of cumulate fragments left-over from rhyolite melt extraction. Cumulate melting and remobilization is supported by the presence of (1) resorbed, low-temperature minerals (biotite and sanidine), providing the potassic signature to these clasts, (2) reacted Fo-rich olivine, marking the presence of mafic recharge, (3) An38-21 plagioclase, filling the gap in feldspar composition between the andesites and the rhyolites and (4) strong enrichment in Sr and Ba in plagioclase and sanidine, suggesting crystallization from a locally enriched melt. Based on Sr-melt partitioning, the high-Sr plagioclase would require ~2300 ppm Sr in the melt, a value far in excess of Sr contents in Lipari and Vulcano magmas (50-1532 ppm) but consistent with melting of a feldspar-rich cumulate. Due to the presence of similar crystal-rich enclaves within the rhyolites from Vulcano, we propose that the eruption of remobilized cumulates associated with high-SiO2 rhyolites may be a common process at the A