Geochronology and geochemistry of Late Triassic Baerdaling granitoids in West Kunlun orogenic belt and its constraints on the post-collision tectonic evolution of Paleo-Tethys
Early Mesozoic magmatic rocks are widespread in the West Kunlun orogenic belt,and their formation is genetically linked to the subduction-collision of the Paleo-Tethys Ocean.However,the concrete tectonic evolution process of Paleo-Tethys Ocean remains controversial.Granitoids in the Baerdaling area are the part of Muztagata complex pluton,the largest complex in the West Kunlun orogenic belt,thus that is critical significance to decode the evolution of Paleo-Tethys.This study discusses their genesis,magma sources and ages through petrology,geochemistry and LA-ICP-MS zircon U-Pb chronology.Baerdaling granitoids mainly consist of granodiorite,monzogranite and syenogranite.The zircon U-Pb weighted mean 206Pb/238U age of corresponding lithology respectively are 237Ma,233Ma and 231 Ma,which invaded in the early stage of Late Triassic.The whole-rock geochemical data show that Baerdaling granitoids with high Al2O3,alkali and low MgO are classified as metaluminium-slightly peraluminium and high potassium-calcium alkaline granitoids.The high rock differentiation index(67.3～81.1)suggest the magmatic evolution is dominated by crystallization differentiation and highly differentiated Ⅰ-type granite.Rare earth elements are characterized by obviously high LREE/HREE ratios and weak to medium negative Eu with right-leaning pattern.Trace elements are obviously enriched with Rb,Th,U,Zr and Hf while depletion of Ba,Nb,Sr,P and Ti.In addition,Baerdaling granitoids have low Nb/Ta(7.2～16.7)and Zr/Hf(28.4～40.3),high Rb/Sr(0.2～1.4)and La/Ta(20.0～56.4),which indicate that the source of rocks was mainly derived from the crust material with minor amount of mantle magma.Combined with regional geological evolution,we conclude that Baerdaling granitoids were formed in the post-collision environment in the early stage of Late Triassic,which may be related to the transformation of Paleo-Tethys from the compressive of main collision to the extension of post-collision.This result also indicates that the time limit for the begin of the post-collision extension of Paleo-Tethys should be no later than 237 Ma.
万方数据
维普
