西昆仑大红柳滩地区花岗岩类侵位时代与成因OA北大核心CSTPCD

In the West Kunlun orogenic belt,there are well developed Triassic granitoids that may be associated with pegmatite Li(Be)mineralization.In order to constrain its geological characteristics,petrogenesis,and their impact on pegmatitic lithium(beryllium)mineralization.In this paper,petrology,mineralogy,geochemistry and geochro-nology studies were carried out for the Bailongshan diorite,Fulugou diorite and Dahongliutan two-mica granite from the Dahongliutan district.Geochemical analyses reveal that the Bailongshan diorite and Fulugou diorite are significantly rich in MgO,CaO and TiO2,and belong to metaluminous-peraluminous,high-K calc-alkaline series.Based on a comprehensive review of available whole-rock Sr-Nd and zircon Lu-Hf data,we propose that the Bail-ongshan diorite and Fulugou diorite have a source region characterized by low clay content(possibly dominated by sandstone)and potential contributions from juvenile crust.The whole rock Zr saturation temperatures are 762～795℃(averaged at 781℃)for the Bailongshan and 769～773℃(averaged at 771℃)for the Fulugou diorites.Am-phibole thermobarometry yields temperatures of 718～760℃(averaged at 734℃)and pressure of 125～208 MPa(averaged at 151 MPa)for the Bailongshan diorite,and 729～776℃(averaged at 741℃)and 133～231 MPa(averaged at 176 MPa)for the Fulugou diorite.Zircon LA-ICPMS U-Pb dating reveals an emplacement age of(213.67±0.61)Ma(MSWD=1.4,n=39)for the Bailongshan diorite and(211.73±1.02)Ma(MSWD=1.9,n=14)for the Fulugou diorite.In case of the Dahongliutan two-mica granite,there are abundant aluminum-rich minerals such as tourmaline,muscovite and garnet.The two-mica granite has higher SiO2 and K2O,but lower MgO,CaO and TiO2 in comparison to the Bailongshan and Fulugou diorites,and belongs to peraluminous,high K calc-alkaline series.By contrast,the Dahongliutan two-mica granite is mainly sourced from partial melting of pelitic rocks.Its Zr saturation temperature falls into the range of 755～773℃(averaged at 764℃).The zircons hosted by two-mica granite commonly have inherited nuclei,and their U-Pb ages are extremely variable,ranging from 207 Ma to 2490 Ma.The youngest magmatic zircon constrains the emplacement at(211.20±1.1)Ma(MSWD=0.34,n=10).Subsequently,these magmatic zircons were enveloped by hydrothermal overgrowth rims,and the U-Pb age con-strains the magmatic-hydrothermal event to have occurred at(185.10±0.89)Ma(MSWD=4,n=5),possibly re-cording a later hydrothermal event induced by the emplacement of barren pegmatite.The Dahongliutan area con-currently developed I-type and S-type granites,formed under conditions of medium temperature(734～781℃)and pressure(151～176 MPa),with magma-hydrothermal activity lasting～33 Ma,providing favorable conditions for the formation of super large pegmatite deposits.