青海塔塔棱河中上游地区花岗岩地球化学和年代学研究

摘要

The granitic rocks from the Upper-middle Reaches of Tataleng River in Qinghai are mainly porphyritic monzonitic granite,monzonitic granite,granitic porphyry and porphyritic syengranite,which are syengranite,rapakiwi granite,granodiorite porphyry and quartz diorite.Geochemical study of these granitic rocks indicate that they are characterized by peraluminous (A/ CNK =1.10～1.26) and high-K (K2O ＞ Na2O),belonging to calc-alkaline series (σ=1.22～ 2.22) and S-type granite.LA-MC-ICP-MS zircon U-Pb results show that their ages are 440.4 + 1.4Ma.Tectonie setting discrimination diagram suggests that these granitic rocks were formed in post-collision tectonic environment.The comprenensive analysis indicates that the Early Silurian granite was formed by the partial melting of continental crust that caused by the extrusion of South Qilian block,when the South Qilian block was subducted and collided with the Quanji block in the continent-continent convergence stage.%青海塔塔棱河中上游地区花岗岩类主要岩石类型为斑状二长花岗岩、二长花岗岩、花岗斑岩和斑状正长花岗岩,其次为正长花岗岩、环斑花岗岩、花岗闪长斑岩和石英闪长岩.岩石地球化学研究表明,该区花岗岩具有过铝质(A/CNK值为1.10～1.26)、高钾(K2O＞Na2O)特征,属于钙碱性系列(σ为1.22～2.22),具S型花岗岩特征.LA-MC-ICP-MS锆石U-Pb测定结果,显示该区花岗岩年龄为(440.4±1.4)Ma.构造环境判别形成于后碰撞构造环境.综合分析后认为,早志留世花岗岩应当是陆陆汇聚时,南祁连陆块发生俯冲,与全吉地块发生碰撞,南祁连地块遭受挤压导致陆壳部分熔融而形成的产物.