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Petrology,Zircon Chronology and Geochemistry of the Late Silurian Ophiolitic Mélanges and the Baiyunshan Forearc Complex in the Central Beishan Orogenic Belt,NE China

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Journal of Earth Science 2023年第2期34卷 444-455页

作者： Hou-Tian Xin Jian Tian Xue-Jian Teng Li-Xin Sun Guo-Zhen Zhang Yong Zhang Bang-Fang Ren Shenyang Center China Geological SurveyShenyang 110086China Tianjin Center China Geological SurveyTianjin 300170China

The WNW-ESE-trending Baiyunshan ophiolitic mélange is exposed in the central Beishan orogenic belt(BOB),between the Hongliuhe-Niujuanzi and Xichangjing ophiolitic mélanges in the west and east,*** we present new petrological,geochemical,and zircon U-Pb age data for the Baiyunshan ophiolitic mélange and metamorphosed lithic sandstones of“the Baiyunshan Formation”.The Baiyunshan ophiolitic mélange is characterized by a block-in-matrix structure,and the blocks of ultramafic-mafic rocks are mainly pyroxenites,dunites,gabbros,and minor *** U-Pb dating yielded an emplacement age of 424.2±3.7 Ma for the *** ultramaficmafic rocks have geochemical features of supra-subduction zone-type ophiolites,including low Ti contents(TiO2=0.01 wt.%–0.35 wt.%),negative Nb-Ta anomalies,and U-shaped rare earth element patterns with positive Eu anomalies(δEu=0.99–3.25).“The Baiyunshan Formation”is exposed to the north of the ophiolitic mélange,and comprises mainly meta-cherts in its lower part and metasandstones and marbles in its upper *** of basalt are locally dispersed in the sand-slate *** ages of detrital zircons in the metamorphosed lithic sandstones range from 521 to 464 Ma,with an age peak of 500 Ma,which is similar to those of the Gongpoquan arc in the *** central Beishan orogenic belt experienced continuous subduction of the Hongliuhe-Xichangjing oceanic lithosphere in the Late Silurian,which produced the Baiyunshan forearc complex and supra-subduction zone-type ophiolite.

关键词： Beishan orogenic belt the Hongliuhe-Xichangjing Ocean the ultramafic-mafic rocks Late Silurian ssz-type ophiolite Subduction and accretion geochemistry

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Formation Age and Tectonic Setting of the Muli Arc-ophiolite Complex in the South Qilian Belt, NW China

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Acta Geologica Sinica(English Edition) 2020年第S1期94卷 69-69页

作者： YAN Zhen FU Changlei Jonathan C.AITCHISON NIU Manlan Solomon BUCKMAN CAO Bo Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China School of Earth and Environmental Sciences University of QueenslandBrisbaneQld 4072Australia Department of Resources and Environment Hefei University of TechnologyHefei 230009China School of Earth and Environmental Science University of WollongongNSW 2522 Australia

The Qilian orogenic belt is the northernmost orogen of the Tethyan domain and connects the Altaids to the north. It contains an assembly of Precambrian micro-continental fragments, early Paleozoic island arcs, accretionary complexes, ophiolites, forearc and backarc basins, and high-pressure(HP) metamorphic rocks, indicating a long history of accretionary processes. Spatially, this orogen is adjacent to the Tarim, Qaidam, and North China blocks, which also extends into accretionary orogenic belts to the east and SW such as the Qinling and Kunlun belts. Abundant ophiolites in this orogen record the closure of an early Tethyan Ocean and amalgamations between micro-continents of North China, Qaidam, and Tarim. Thus, the ages and tectonic settings of these ophiolites within this belt provide important information regarding evolution of the Proto-Tethys Ocean and assembly of micro-continental blocks, which aids understanding of the spatial and temporal relationship of this orogen within the Tethyan realm. Dismembered ophiolites sporadically crop out along the northern margin of the South Qilian belt, and, from east to west, are locally referred to as the Lajishan, Gangcha, Muli, and Dadaoerji ophiolites. Much attention had been paid to these ophiolites, and several competing models for the tectonic evolution of this belt have been suggested. Considerable disagreement remains in respect of the temporal and spatial framework of the Qilian Orogen and details such as timing of subduction(s) and associated polarities, early collision events, and final closure of oceanic basins. In particular, the formation age and tectonic setting of Muli arc-ophiolite complex remains unknown, which limits understanding of the tectonics of the South Qilian belt and the history of the Proto-Tethys Ocean. The Muli arc-ophiolite complex is distributed over 20 km^2 west of the township of Muli in the western segment of the South Qilian Belt and consists of serpentinite, dunite, cumulate gabbro, ba

关键词： Muli arc-ophiolite complex ssz-type ophiolite Proto-Tethys Ocean Qilian Orogen

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