吉林中部四合屯组安山岩锆石U-Pb定年、地球化学特征及其地质意义OACHSSCD

To further investigate the effect of oceanic plate subduction on the modification of the lithospheric mantle in the Xing'an-Mongolia Orogenic Belt,this study focuses on the andesite from Sihetun Formation in central Jilin Province.We conducted LA-ICP-MS zircon U-Pb dating and whole-rock geochemical studies.The weighted average 206 Pb/238 U age of magma-related zircons from the andesite is 223.6±2.1 Ma,indicating that the andesite formed in the Late Triassic.The andesite has a SiO2 content ranging from 57.60％to 64.50％,total alkali(Na2O+K2O)content from 4.20％to 7.20％,Al2O3 content from 15.39％to 17.35％,TFe2O3 content from 5.45％to 7.24％,and TiO2 content from 0.87％to 1.43％.It also has relatively high MgO(2.05％to 4.24％),Cr(37.7×10-6 to 92.2×10-6),and Mg#values(41 to 54),classifying it as calc-alkaline.The andesite samples are enriched in large ion lithophile elements(e.g.,Rb,K,Sr)and light rare earth elements(LREEs),depleted in high field strength elements(e.g.,Nb,Ta,Ti)and heavy rare earth elements(HREEs),exhibiting a slight negative Eu anomaly(δEu=0.70 to 0.98).These geochemical features suggest that the andesite from Sihetun Formation likely originated from the mantle wedge modified by subduction fluids,with further fractional crystallization of minerals such as apatite,plagioclase,and hornblende during magma evolution.In combination with regional geological data,these observations suggest that the formation of the andesite from Sihetun Formation in central Jilin Province was closely related to a post-collisional extensional tectonic setting triggered by the final closure of the Paleo-Asian Ocean.Influenced by the prolonged subduction of the Paleo-Asian Ocean,the mantle wedge magma source region of the Late Triassic andesite from Sihetun Formation in central Jilin Province,eastern Xing'an-Mongolia Orogenic Belt,still preserves the geochemical signature of early plate subduction.