Late Triassic Granites From the Quxu Batholith Shedding a New Light on the Evolution of the Gangdese Belt in Southern Tibet   总被引：2，自引：0，他引：2  

MENG Yuanku  XU Zhiqin  XU Yang  MA Shiwei 《《地质学报》英文版》2018,92(2):462-481

The Gangdese magmatic belt formed during Late Triassic to Neogene in the southernmost Lhasa terrane of the Tibetan plateau. It is interpreted as a major component of a continental margin related to the northward subduction of the Neo-Tethys oceanic slab beneath Eurasia and it is the key in understanding the tectonic framework of southern Tibet prior to the India-Eurasia collision. It is widely accepted that northward subduction of the Neo-Tethys oceanic crust formed the Gangdese magmatic belt, but the occurrence of Late Triassic magmatism and the detailed tectonic evolution of southern Tibet are still debated. This work presents new zircon U-Pb-Hf isotope data and whole-rock geochemical compositions of a mylonitic granite pluton in the central Gangdese belt, southern Tibet. Zircon U-Pb dating from two representative samples yields consistent ages of 225.3±1.8 Ma and 229.9±1.5 Ma, respectively, indicating that the granite pluton was formed during the early phase of Late Triassic instead of Early Eocene(47–52 Ma) as previously suggested. Geochemically, the mylonitic granite pluton has a sub-alkaline composition and low-medium K calc-alkaline affinities and it can be defined as an I-type granite with metaluminous features(A/CNK1.1). The analyzed samples are characterized by strong enrichments of LREE and pronounced depletions of Nb, Ta and Ti, suggesting that the granite was generated in an island-arc setting. However, the use of tectonic discrimination diagrams indicates a continental arc setting. Zircon Lu-Hf isotopes indicate that the granite has highly positive εHf(t) values ranging from +13.91 to +15.54(mean value +14.79), reflecting the input of depleted mantle material during its magmatic evolution, consistent with Mg~# numbers. Additionally, the studied samples also reveal relatively young Hf two-stage model ages ranging from 238 Ma to 342 Ma(mean value 292 Ma), suggesting that the pluton was derived from partial melting of juvenile crust. Geochemical discrimination diagrams also suggest that the granite was derived from partial melting of the mafic lower crust. Taking into account both the spatial and temporal distribution of the mylonitic granite, its geochemical fingerprints as well as previous studies, we propose that the northward subduction of the Neo-Tethys oceanic slab beneath the Lhasa terrane had already commenced in Late Triassic(~230 Ma), and that the Late Triassic magmatic events were formed in an active continental margin that subsequently evolved into the numerous subterranes, paleo-island-arcs and multiple collision phases that form the present southern Tibet.  相似文献   

Occurrence of the Iron–rich Melt in the Heijianshan Iron Deposit, Eastern Tianshan, NW China: Insights into the Origin of Volcanic Rock–hosted Iron Deposits     

LI Houmin  LI Lixing  DING Jianhu  LI Yanhe  SONG Zhe  MENG Jie  MA Yubo 《《地质学报》英文版》2018,92(2):666-681

Long-standing controversy persists over the presence and role of iron–rich melts in the formation of volcanic rock-hosted iron deposits. Conjugate iron–rich and silica–rich melt inclusions observed in thin-sections are considered as direct evidence for the presence of iron-rich melt, yet unequivocal outcrop-scale evidence of iron-rich melts are still lacking in volcanic rock-hosted iron deposits. Submarine volcanic rock-hosted iron deposits, which are mainly distributed in the western and eastern Tianshan Mountains in Xinjiang, are important resources of iron ores in China, but it remains unclear whether iron-rich melts have played a role in the mineralization of such iron ores. In this study, we observed abundant iron-rich agglomerates in the brecciated andesite lava of the Heijianshan submarine volcanic rock–hosted iron deposit, Eastern Tianshan, China. The iron-rich agglomerates occur as irregular and angular masses filling fractures of the host brecciated andesite lava. They show concentric potassic alteration with silicification or epidotization rims, indicative of their formation after the wall rocks. The iron-rich agglomerates have porphyritic and hyalopilitic textures, and locally display chilled margins in the contact zone with the host rocks. These features cannot be explained by hydrothermal replacement of wall rocks(brecciated andesite lava) which is free of vesicle and amygdale, rather they indicate direct crystallization of the iron-rich agglomerates from iron-rich melts. We propose that the iron-rich agglomerates were formed by open-space filling of volatile-rich iron-rich melt in fractures of the brecciated andesite lava. The iron-rich agglomerates are compositionally similar to the wall-rock brecciated andesite lava, but have much larger variation. Based on mineral assemblages, the iron-rich agglomerates are subdivided into five types, i.e., albite-magnetite type, albite-K-feldsparmagnetite type, K-feldspar–magnetite type, epidote-magnetite type and quartz-magnetite type, representing that products formed at different stages during the evolution of a magmatic-hydrothermal system. The albite-magnetite type represents the earliest crystallization product from a residual ironrich melt; the albite-K-feldspar-magnetite and K-feldspar-magnetite types show features of magmatichydrothermal transition, whereas the epidote-magnetite and quartz-magnetite types represent products of hydrothermal alteration. The occurrence of iron-rich agglomerates provides macroscopic evidence for the presence of iron-rich melts in the mineralization of the Heijianshan iron deposit. It also indicates that iron mineralization of submarine volcanic rock-hosted iron deposits is genetically related to hydrothermal fluids derived from iron-rich melts.  相似文献   

Geological and Geochemical Characteristics and Exploration Prospect of Coal‐Derived Tight Sandstone Gas in China: Case Study of the Ordos,Sichuan, and Tarim Basins     

ZOU Caineng  TAO Shizhen  HAN Wenxue  ZHAO Zhenyu  MA Weijiao  LI Changwei  BAI Bin  GAO Xiaohui 《《地质学报》英文版》2018,92(4):1609-1626

This work extensively investigated global tight sandstone gas, and geologically and geochemically analyzed the tight sandstone gas in China's Ordos, Sichuan, and Tarim basins. We compared typical tight sandstone gas in China with that in North America. We proposed six conditions for the formation of China's tight sandstone gas, and illustrated the geological characteristics of tight sandstone gas. In China, gas-bearing tight sandstones were mainly deposited in continental lake deltas and marine-terrigenous facies basin environments, associated with coal-measure strata, and were mostly buried deeper than 2000 m under a formation pressure of 20–30 MPa, with pressure coefficients varying from overpressure to negative pressure. In other countries, tight gas bearing sandstones were dominantly deposited in marine to marine-terrigenous facies environments, occurred in coal-measure strata, and were mostly buried shallower than 2000 m in low-pressure systems. We systematically analyzed tight sandstone gas in the Ordos, Sichuan, and Tarim basins in terms of chemical compositions, geochemical characteristics of carbon isotopes, origins, and sources. Tight sandstone gas in China usually has a hydrocarbon content of 95%, with CH4 content 90%, and a generally higher dry coefficient. In the three above-mentioned large tight sandstone gas regions, δ13 C1 and δ13 C2 mainly ranges from-42‰ to-28‰ and from-28‰ to-21‰, respectively. Type III coal-measure source rocks that closely coexist with tight reservoirs are developed extensively in these gas regions. The organic petrology of source rocks and the carbon isotope compositions of gas indicate that tight sandstone gas in China is dominantly coal-derived gas generated by coal-measure strata. Our analysis of carbon isotope series shows that local isotope reversals are mainly caused by the mixing of gases of different maturities and that were generated at different stages. With increasing maturity, the reversal tendency becomes more apparent. Moreover, natural gas with medium-low maturity(e.g., Xujiahe Formation natural gas in the Sichuan Basin) presents an apparent reversal at a low-maturity stage, a normal series at a medium-maturity stage, and a reversal tendency again at a high-maturity stage. Finally, we proposed four conditions for preferred tight sandstone gas "sweep spots," and illustrated the recoverable reserves, proven reserves, production, and exploration prospects of tight sandstone gas. The geological and geochemical characteristics, origins, sources, and exploration potential of tight sandstone gas in China from our research will be instructive for the future evaluation, prediction, and exploration of tight sandstone gas in China and abroad.  相似文献   

Zircon growth during subduction and exhumation metamorphism of mafic rocks, Aktyuz terrain, North Tiahshan, Kyrgyzstan     

DONG Hanwen  XU Zhiqin  YI Zhiyu  MA Zeliang 《《地质学报》英文版》2018,92(Z2):5-5

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Sedimentary Age of the Baoligaomiao Formation in the Zhanlantun Area,Inner Mongolia: Constraints by Fossil Assemblage and Zircon Geochronology     

QIN Tao  QIAN Cheng  LI Linchuan  JIANG Bin  SUN Wei  NA Fuchao  SI Qiuliang  MA Yongfei  ZANG Yanqing 《《地质学报》英文版》2018,92(3):1251-1254

正Objective The Baoligaomiao Formation is widely distributed from the East Wuqi to Zhanlantun area in the Xing'an Mongolian orogenic belt(Tian Shugang et al.,2016;Wei et al.,2017).This formation contains abundant Angara biological fossils which exhibit diachronism  相似文献   

LA–ICP–MS U–Pb Geochronology of Detrital Zircon in the Guanzhong Basin, China and Its Tectonic Response     

DONG Min  WANG Zongxiu  DONG Hui  MA Licheng  ZHANG Linyan 《《地质学报》英文版》2018,92(3):1257-1261

正Objective The Guanzhong Basin in the transitional zone of the Qinling orogenic belt and the southern margin of the Ordos Basin has been extensively studied in recent years.Although some results have been obtained,some problems such as whether the materials from the North China craton and the Qinling orogenic belt are detrital sedimentary rocks of the Guanzhong Basin still remain unresolved.  相似文献   

U-Pb Ages of the Late Early Cretaceous Magmatic Rocks  in the Zhalantun Area of Inner Mongolia     

QIN Tao  LI Linchuan  QIAN Cheng  SUN Wei  MA Yongfei  ZANG Yanqing 《《地质学报》英文版》2019,93(1):233-235

A great deal of early-to-mid Early Cretaceous magmatic activities have been recorded in the Zhalantun area of Inner Mongolia,while the late Early to Late Cretaceous magmatic rocks have been barely reported(Guo et al.,2018;Zhang Xiangxin et al.,2017).At present,only a few Late Cretaceous magmatic activities were reported in the Arongqi area,such as volcanic rocks of the Gushanzhen Formation.However,the Gushanzhen Formation lacks accurate isotopic age,and contemporaneous intrusive rocks has not been reported yet.In this work,we collected the volcanic rocks from the Gushanzhen Formation and contemporaneous intrusive rocks in the Zhanlantun and nearby,and aim to figure out the formation ages of volcanic rocks of the Gushanzhen Formation and accompanied intrusive rocks by analyzing zircon U-Pb isotopes(Fig.1).  相似文献   

Early Permian Strata Exist in the Olongbluk Block     

SUN Jiaopeng  JIANG Wan  MA Licheng  XIAO Zhouxuan 《《地质学报》英文版》2019,93(2):481-482

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Weak Summer Monsoon during the Early Holocene Inferred from the Dingxi Lujiagou Floodplain Lake-Eolian Sand Rhythm due to Solar Impacting     

ZHANG Wanyi  ZHANG Huirong  MA Yuan  WANG Xiaoyu  Steffen MISCHKE  ZHANG Chengjun 《《地质学报》英文版》2019,93(3):778-779

正Objective Precipitation was the highest in the loess plateau during the Early Holocene 10–8 ka BP even to the period 10–3.0 ka BP in the Kesang cave stalagmite westward Tianshan, Xinjiang, based on large numbers of records from paleoclimatic proxies(An et al., 2000; Zhang et al., 2009; Zhang et al., 2018). However, we discovered at first time that floodplain lake-eolian stratigraphical rhythm complex  相似文献   

Late Cretaceous Foraminiferal Biostratigraphy in Gongza, Tingri, Southern Tibet     

LI Qi  LI Guobiao  LI Xinf  WANG Tieyang  LI Yuewei  ZHANG Wen Yuan  XIE Dan  Li Xingpeng  MA Xuesong  SHI Wei  GUO Baojie 《《地质学报》英文版》2019,93(Z2):259-260

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