The Geochemistry Of Xiaoyanglong、Xiatiemor And Tectonic Significance In The North Qilian

The researched area is suited in Yanglong village, Qilian County, Qinghai Province in the upstream of Tuolai River. On the basis of field regional geological survey, we attempt to study the tectonic setting, genetic mechanism of rock bodies and tectonic significance of early Paleozoic granite.Early Paleozoic island-arc granite widely developed in the researched area, with the age of462+2.8Ma(Xiaoyanglong rock-body) belonging to Middle Ordovician. The rock associations are mainly granite-adamellite-pladorite, belonging to middle-potassium calc-alkaline series. The standardized microelement spider diagram indicates a coincident distribution model of three rock bodies, displaying strong enrichment of large ion lithophile elements (LILE) Rb, Th, U, K and Pb and depletion of high field strength element(HFSE, Nb, Ta, Ti), showing the characteristics of island-arc magmatic rocks. The relative depletion of large large ion lithophile elements Sr and Ba indicates the magmas has undergone separation and evolution.Petrology and lithogeochemistry researches indicate the characteristics of island-arc granite relate to the subduction of oceanic plate, reflecting Northern Qilian Mountain existed as an active continental margin in early Paleozoic.Based on regional researched results, we conclude that early Paleozoic granites in Northern Qilian Mountain are the products of Northern Qilian Oceanic Plate subducting down to Northern China Plate from SW to NE. Xiaoyanglong and Dandeer rock-bodies show characteristics of S-type granites, reflecting they may be formed by partial melting of Middle Qilian continental crust, whereas, Tiemoer rock-body displays characteristics of I-type granite, showing it may be formed by partial melting of subducted oceanic crust.