A new ophiolitic mélange containing boninitic blocks in Alxa region:Implications for Permian subduction events in southern CAOB  

作　　者：Rongguo Zheng Jinyi Li Wenjiao Xiao Lijia Wang 

机构地区：[1]Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China [2]Xinjiang Research Center for Mineral Resources,Xinjiang Institute of Ecology and Geography,Chinese Academy of Sciences,Urumqi 830011,China [3]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [4]CAS Center for Excellence in Tibetan Plateau Earth Science,Chinese Academy of Sciences,Beijing 100101,China [5]University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Geoscience Frontiers》2018年第5期1355-1367,共13页地学前缘（英文版）

基　　金：jointly supported by the National Natural Science Foundation of China (Nos. 41502214 and 41230207);the Outlay Research Fund of Institute of Geology, Chinese Academy of Geological Sciences (J1706);the CPSF-CAS Joint Foundation for Excellent Postdoctoral Fellows (Grant No. 2015LH0049);the China Postdoctoral Foundation funded project (No. 2016M590990);the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (No. XDB18020203);the Key Research Program of Frontier Sciences, CAS (QYZDJ-SSW-SYS012)

摘　　要：The Alxa region, located in the southernmost part of Central Asian Orogenic Belt, is a key region for understanding the tectonic processes associated with the closure of the Paleo-Asian Ocean. Issues of late Paleozoic tectonic settings and tectonic unit divisions of the Alxa region still remain controversial. In this study, we report a new ophiolitic mélange named the Tepai ophiolitic mélange in the northern Alxa region, northwest of Alxa Youqi. The tectonic blocks in the Tepai ophiolitic mélange are mainly composed of serpentinized peridotites, serpentinites, mylonitized gabbros, gabbros, basalts, and quartzites, with a matrix comprising highly deformed clastic rocks. A gabbro exhibits a zircon LA-ICP-MS Ue Pb age of278.4 ± 3.3 Ma. Gabbros exhibit high Mg O and compatible element contents, but extremely low TiO_2,totally rare earth element and high field strength element contents. These rocks exhibit light rare earth element depleted patterns, and display enriched in large-ion lithophile elements and depleted in high field strength elements. Boninite-like geochemical data show that they were formed in a subductionrelated environment, and derived from an extremely depleted mantle source infiltrated by subduction-derived fluids and/or melts. The Tepai ophiolitic mélange exhibits similar zircon U-Pb-O isotopic compositions and whole-rock geochemical characteristics to those of the Quagan Qulu ophiolite.Therefore, we propose that the Tepai ophiolitic mélange may have been the western continuation of the Quagan Qulu ophiolite. Our new finding proves the final closure of the Paleo-Asian Ocean might have taken place later than the early Permian.The Alxa region, located in the southernmost part of Central Asian Orogenic Belt, is a key region for understanding the tectonic processes associated with the closure of the Paleo-Asian Ocean. Issues of late Paleozoic tectonic settings and tectonic unit divisions of the Alxa region still remain controversial. In this study, we report a new ophiolitic mélange named the Tepai ophiolitic mélange in the northern Alxa region, northwest of Alxa Youqi. The tectonic blocks in the Tepai ophiolitic mélange are mainly composed of serpentinized peridotites, serpentinites, mylonitized gabbros, gabbros, basalts, and quartzites, with a matrix comprising highly deformed clastic rocks. A gabbro exhibits a zircon LA-ICP-MS Ue Pb age of278.4 ± 3.3 Ma. Gabbros exhibit high Mg O and compatible element contents, but extremely low TiO_2,totally rare earth element and high field strength element contents. These rocks exhibit light rare earth element depleted patterns, and display enriched in large-ion lithophile elements and depleted in high field strength elements. Boninite-like geochemical data show that they were formed in a subductionrelated environment, and derived from an extremely depleted mantle source infiltrated by subduction-derived fluids and/or melts. The Tepai ophiolitic mélange exhibits similar zircon U-Pb-O isotopic compositions and whole-rock geochemical characteristics to those of the Quagan Qulu ophiolite.Therefore, we propose that the Tepai ophiolitic mélange may have been the western continuation of the Quagan Qulu ophiolite. Our new finding proves the final closure of the Paleo-Asian Ocean might have taken place later than the early Permian.

关 键 词：Alxa REGION CAOB OPHIOLITE LA-ICP MS U-Pb Oxygen isotope 

分 类 号：P534.46[天文地球—古生物学与地层学] P587[天文地球—地质学]