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Zhiguang Chen Lianchang Zhang Bo Wan Huaying Wu Nathan Cleven 《Ore Geology Reviews》2011,43(1):92-105
The Wunugetushan porphyry Cu–Mo deposit is located in the Manzhouli district of NE China, on the southern margin of the Mesozoic Mongol–Okhotsk Orogenic Belt. Concentric rings of hydrothermal alteration and Cu–Mo mineralization surround an Early–Middle Jurassic monzogranitic porphyry. The Cu–Mo mineralization is clearly related to the quartz–potassic and quartz–sericite alteration. Molybdenite Re–Os and groundmass 40Ar/39Ar of the host porphyry dates indicate that the ore-formation and porphyry-emplacement occurred at 177.6 ± 4.5 Ma and 179.0 ± 1.9 Ma, respectively. Geochemically, the host porphyry of the deposit is characterized by strong LREE/HREE fractionation, enrichment in LILE, Ba, Rb, U, Th and Pb, and depletion of HFSE, Nb, Ta, Ti and HREE. The Sr–Nd–Pb isotopic compositions of the porphyry display an varied initial (87Sr/86Sr)i ratio, a positive εNd(t) values and high 206Pb/204Pbt, 207Pb/204Pbt and 208Pb/204Pbt ratios. These data indicate that the magmatic source of the host porphyry comprised two end-members: lithospheric mantle metasomatized by fluids derived from the subducted slab; and continental crust. We infer that the primitive magma of the host porphyry was derived from crust–mantle transition zone. Based on regional geology and geochemistry of the host porphyry, the Wunugetushan deposit is suggested to form in a continental collision environment after closure of the Mongol–Okhotsk Ocean. 相似文献
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Permafrost is found on 63%of the territory of Mongolia. This paper provides evidence that the main influences on per-mafrost formation are meso and micro factors of climate and geographical location. R... 相似文献
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We identify and describe a series of east–west left-lateral strike-slip faults (named the Songino-Margats, the Hag Nuur, the Uliastay and the South Hangay fault systems) in the Hangay mountains of central Mongolia: an area that has little in the way of recorded seismicity and which is often considered as a rigid block within the India–Eurasia collision zone. The strike-slip faults of central Mongolia constitute a previously unrecognized hazard in this part of Mongolia. Each of the strike-slip faults show indications of late Quaternary activity in the form of aligned sequences of sag-ponds and pressure-ridges developed in alluvial deposits. Total bed-rock displacements of ∼3 km are measured on both the Songino-Margats and South Hangay fault systems. Bed-rock displacements of 11 km are observed across the Hag Nuur fault. Cumulative offset across the Uliastay fault systems are unknown but are unlikely to be large. We have no quantitative constraint on the age of faulting in the Hangay. The ≤20 km of cumulative slip on the Hangay faults might, at least in part, be inherited from earlier tectonic movements. Our observations show that, despite the almost complete absence of instrumentally recorded seismicity in the Hangay, this part of Mongolia is cut through by numerous distributed strike-slip faults that accommodate regional left-lateral shear between Siberia and China. Central Mongolia is thus an important component of the India–Eurasia collision that would be overlooked in models of the active tectonics based on the distribution of seismicity. We suggest that active faults such as those identified in the Hangay of Mongolia might exist in other, apparently aseismic, regions within continental collision zones. 相似文献
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Omar?GianolaEmail authorView author&#;s OrcID profile Max?W.?Schmidt Oliver?Jagoutz Oyungerel?Sambuu 《Contributions to Mineralogy and Petrology》2017,172(11-12):92
The ~ 570 Ma old Khantaishir ophiolite is built by up to 4 km harzburgitic mantle with abundant pyroxenites and dunites followed by ~ 2 km of hornblende-gabbros and gabbronorites and by a ~ 2.5 km thick volcanic unit composed of a dyke + sill complex capped by pillow lavas and some volcanoclastics. The volcanics are mainly basaltic andesites and andesites (or boninites) with an average of 58.2 ± 1.0 wt% SiO2, X Mg = 0.61 ± 0.03 (X Mg = molar MgO/(MgO + FeOtot), TiO2 = 0.4 ± 0.1 wt% and CaO = 7.5 ± 0.6 wt% (errors as 2σ). Normalized trace element patterns show positive anomalies for Pb and Sr, a negative Nb-anomaly, large ion lithophile elements (LILE) concentrations between N- and E-MORB and distinctly depleted HREE. These characteristics indicate that the Khantaishir volcanics were derived from a refractory mantle source modified by a moderate slab-component, similar to boninites erupted along the Izu-Bonin-Mariana subduction system and to the Troodos and Betts Cove ophiolites. Most strikingly and despite almost complete outcrops over 260 km2, there is no remnant of any pre-existing MORB crust, suggesting that the magmatic suite of this ophiolite formed on completely denudated mantle, most likely upon subduction initiation. The architecture of this 4–5 km thick early arc crust resembles oceanic crust formed at mid ocean ridges, but lacks a sheeted dyke complex; volcanic edifices are not observed. Nevertheless, low melting pressures combined with moderate H2O-contents resulted in high-Si primitive melts, in abundant hornblende-gabbros and in a fast enrichment in bulk SiO2. Fractional crystallization modeling starting from the observed primitive melts (56.6 wt% SiO2) suggests that 25 wt% pyroxene + plagioclase fractionation is sufficient to form the average Khantaishir volcanic crust. Most of the fractionation happened in the mantle, the observed pyroxenite lenses and layers in and at the top of the harzburgites account for the required cumulate volumes. Finally, the multiply documented occurrence of highly depleted boninites during subduction initiation suggests a causal relationship of subduction initiation and highly depleted mantle. Possibly, a discontinuity between dense fertile and buoyant depleted mantle contributes to the sinking of the future dense subducting plate, while the buoyant depleted mantle of the future overriding plate forms the infant mantle wedge. 相似文献
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Tsukada Kazuhiro Yamamoto Koshi Gantumur Onon Nuramkhaan Manchuk 《International Journal of Earth Sciences》2017,106(4):1429-1451
International Journal of Earth Sciences - In placing Japanese tectonics in an Asian context, variation in the Paleozoic geological environment is a significant issue. This paper investigates the... 相似文献
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The study of Paleoproterozoic rocks is crucial for understanding Earth's tectonic evolution during the time when most of the modern crust and ore deposits were formed. The rocks of the Brazilian Amazonian Craton record some of the most-complete and best-preserved Paleoproterozoic magmatic and volcanic episodes on Earth. Following previous investigations, we present new lithofaciological and stratigraphic records of the felsic rocks of the Tapajós Mineral Province (TMP) (~2–1.88 Ga) and the São Felix do Xingú region (SFX) (~1.88 Ga) which, combined with new petrological and geochronological data, help providing a more complete understanding of the tectonic, magmatic and volcanological evolution of the Amazonian Craton. This magmatism/volcanism is thought to be formed in a late-/post-orogenic to extentional regime confirmed by the new geochemical data presented here. The transition from late-convergent to extensional tectonic setting could register the beginning of the taphrogenesis that marked the Amazonian Craton throughout the Mesoproterozoic. The volcanological approach of this contribution can serve as a strategy for the modelling of the evolution of Precambrian volcano-sedimentary basins around the world. The large amount of rocks analyzed are divided into primary and secondary volcaniclastic products depending on if they resulted from a direct volcanic activity (pyroclastic) or processes that reworked pyroclastic fragments. Furthermore, the deposits are subdivided into massive and stratified, depending on their primary mechanisms of transport and emplacement. By confirming the results from previous studies, our study permits to depict a more precise paleo-environmental picture of the processes that occurred in the Amazonian Craton during the Late-Paleoproterozoic. In particular, the presence of large regional-scale fissural systems and caldera collapses produced large silicic explosive volcanic eruptions, also accompanied by the emission of large volume effusive products. Although studies on the Amazonian Craton are still scarce and controversial, the present study provides new evidence that this volcanism may have formed one of the largest Silicic Large Igneous Provinces (SLIP) on earth. Our data also confirm that at least two major Paleoproterozoic periods of formation of volcanic rocks exist in the Amazonian craton. This point is of great relevance for any future interpretation of the geological evolution of this craton. 相似文献
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Hf isotopes have proven invaluable in understanding the evolution of Earth's crust-mantle system, but their use in reconstructing tectonic environments, in many cases, remains equivocal. In this study, we introduce a new approach to predict the Hf isotopic evolutionary pattern for rifting and collision based on the integration of numerical models and 176Hf/177Hf isotopes. The geodynamic numerical models allow us to estimate the proportion of juvenile material added to the crust through time. On the basis of this proportion, we calculate changing 176Hf/177Hf ratios using mixing models. Predicted Hf isotopic patterns generated through this numerical approach imply that juvenile signals are observed during back-arc extension, whereas evolved signatures dominate collisional settings. We use this novel modeling approach in the case study region of the Halls Creek Orogen to elucidate its tectonic setting through time. In addition, the geochemical features of magmatic rocks in the case study region imply partial melting of a sub-arc mantle wedge with magma-crust interaction on ascent in a convergent margin setting. The links between predicted Hf isotopic evolution, geodynamic numerical models, whole rock geochemistry and measured zircon Hf isotopic evolution trend resolve three discrete stages in the tectonomagmatic development of the Halls Creek Orogen: (1) oceanic crust subduction; (2) back-arc formation with addition of juvenile mantle input; and (3) docking of the North Australian and Kimberley cratons resulting in the development of mixed-source magmatism formed in a collisional setting. We provide a new method to validate geodynamic models with isotopic datasets, which should lead to more rigorous understanding of crustal evolution. 相似文献
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The enigmatic appearance of cuboctahedral diamonds in ophiolitic and arc volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds that were grown from metal solvent requires a critical reappraisal. We have studied 15 diamond crystals and fragments from Tolbachik volcano lava flows, using Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), synchrotron X-ray fluorescence (SRXRF) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS). FTIR spectra of Tolbachik diamonds correspond to typical type Ib patterns of synthetic diamonds. In TEM films prepared using focused ion beam technique, we find Mn-Ni and Mn-Si inclusions in Tolbachik diamonds. SRXRF spectra indicate the presence of Fe-Ni and Fe-Ni-Mn inclusions with Cr, Ti, Cu, and Zn impurities. LA-ICP-MS data show variable but significantly elevated concentrations of Mn, Fe, Ni, and Cu reaching up to 70 ppm. These transition metal concentration levels are comparable with those determined by LA-ICP-MS for similar diamonds from Tibetan ophiolites. Mn-Ni (+Fe) solvent was widely used to produce industrial synthetic diamonds in the former USSR and Russia with very similar proportions of these metals. Hence, it appears highly probable that the cuboctahedral diamonds recovered from Kamchatka arc volcanic rocks represent contamination and are likely derived from drilling tools or other hard instruments. Kinetic data on diamond dissolution in basaltic magma or in fluid phase demonstrate that diamond does not form under the pressures and temperature conditions prevalent within the magmatic system beneath the modern-day Klyuchevskoy group of arc volcanoes. We also considered reference data for inclusions in ophiolitic diamonds and compared them with the composition of solvent used in industrial diamond synthesis in China. The similar inclusion chemistry close to Ni70Mn25Co5 for ophiolitic and synthetic Chinese diamonds scrutinized here suggests that most diamonds recovered from Tibetan and other ophiolites are not natural but instead have a synthetic origin. In order to mitigate further dubious reports of diamonds from unconventional tectonic settings and source rocks, we propose a set of discrimination criteria to better distinguish natural cuboctahedral diamonds from those produced synthetically in industrial environments and found as contaminants in mantle- and crust-derived rocks. 相似文献
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蒙古国查干苏布尔加和苏廷铜矿容矿斑岩体SHRIMP锆石U-Pb年龄——对南戈壁斑岩型铜矿成矿时代及成矿背景的约束 总被引：1，自引：1，他引：0
对蒙古国南戈壁地区查干苏布尔加和苏廷斑岩型矿床的容矿花岗岩进行SHRIMP锆石U-Th-Pb同位素测定,结果表明查干苏布尔加斑岩型铜钼矿床矿化花岗闪长岩的侵位年龄为368±4Ma,苏廷铜矿花岗岩的侵位年龄为333±4Ma,表明它们形成于不同的时代。结合已有资料提出,蒙古南戈壁地区发育2条时代不同的斑岩型铜矿带:一条为晚泥盆世,以欧玉陶勒盖和查干苏布尔加矿床为代表;另一条为中晚石炭世,以苏廷及曼达赫斑岩型矿床为代表。同时,结合区域资料,初步探讨了2条斑岩成矿带的成矿地质背景。 相似文献