Early Cambrian high pressure/low temperature metamorphism in the southeastern Tarim craton in response to circum-Gondwana cold subduction  

作　　者：Qian Liu Toshiaki Tsunogae Guochun Zhao Sam Uthup Kazuki Takahashi Jinlong Yao Yu Wu Yigui Han Kei Ikehata 

机构地区：[1]State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China [2]Faculty of Life and Environmental Sciences,The University of Tsukuba,Ibaraki 305-8572,Japan [3]Department of Geology,University of Johannesburg,Auckland Park 2006,South Africa [4]Department of Earth Sciences,The University of Hong Kong,Pokfulam Road,Hong Kong,China [5]Beijing Research Institute of Uranium Geology,Beijing 100029,China

出　　处：《Geoscience Frontiers》2023年第4期72-88,共17页地学前缘（英文版）

基　　金：This work was financially supported by a National Natural Science Foundation of China Projects(41730213);a Grant-inAid for Scientific Research from Japan Society for the Promotion of Science(JSPS)to Prof.Toshiaki Tsunogae(18H01300)。

摘　　要：The circum-Gondwana subduction initiated by the early Cambrian has been suggested to reflect the establishment of the modern plate tectonics.The metamorphic rocks with low thermobaric(T/P)ratios indicative of cold subduction in the present tectonic regime have not been well investigated.To better understand the circum-Gondwana subduction and to test its possible link with the emergence of the modern plate tectonics,this study focused on blueschist-facies metamorphic rocks in the Altyn Tagh of the southeastern Tarim craton.Mineral assemblage and chemistry,phase equilibrium modelling,and quartz-in-garnet Raman elastic geobarometry reveal that the zoisite blueschist and glaucophane(Gln)-bearing quartz schist in northern Altyn Tagh were metamorphosed to lawsonite to epidote blueschistfacies at 520–545℃ and 16–19 kbar.It reflects high-pressure(HP)/low temperature(LT)metamorphism with low T/P ratios of<300℃/GPa and thermal gradients of<10℃/km.These blueschist-facies metamorphic rocks underwent rapid decompression starting at P-T conditions of<495℃ and<9.6 kbar during exhumation.Ar-Ar geochronology records paragonite Ar-Ar plateau ages of 520–506 Ma for the zoisite blueschist samples and phengite Ar-Ar plateau ages of 522–516 Ma for the Gln-bearing quartz schist samples,suggesting that the peak HP/LT metamorphism occurred prior to ca.522 Ma.Based on new results and available data from the major Gondwana blocks,cold subduction was suggested to profoundly operate along circum-Gondwana in the early Cambrian after the amalgamation of Gondwana.The extensive circum-Gondwana subduction represents the earliest global cold subduction in Earth’s history associated with the establishment of the modern plate tectonics,as directly recorded by the studied early Cambrian blueschist-facies metamorphic rocks and a dramatic drop in the mean T/P of metamorphism since the early Paleozoic.

关 键 词：Early Paleozoic High-pressure low temperature METAMORPHISM Cold subduction Tarim craton GONDWANA 

分 类 号：P542[天文地球—构造地质学]