中文摘要：

盐场北山英云闪长岩位于柴达木盆地北缘西端青海冷湖地区。岩体Si2O〉56%（62.86%～64.83%）,A12O3〉15%,MgO〈3%（含量为1.73%～1.96%）,Mg#=33.4～37.0,小于50。Sr〉400×10-6（平均为409×10-6）,Y〈18×10-6（Y=3.09×10-6～6.6×10-6）,Yb〈1.9×10-6（Yb=0.4×10-6～0.58×10-6）,具有埃达克岩地球化学特征;Na2O/K2O=2.39～2.73,富Na贫K,Eu、Sr正异常（δEu=1.22～1.44）,属O型埃达克岩。岩体富集大离子亲石元素（K、Rb、Sr、Ba）,亏损高场强元素（Nb、Ta、P）,具火山弧型花岗岩特征。LA-ICP-MS锆石U-Pb测年结果表明,岩体形成于263±2 Ma。结合区域地质背景和岩石地球化学特征,认为柴达木盆地北缘西端埃达克质花岗岩可能产于与俯冲有关的活动大陆边缘火山弧环境,是俯冲板片直接熔融的产物。进而揭示中二叠世末柴达木盆地北缘地区处于洋陆俯冲的构造演化阶段。

英文摘要：

The Yanchangbeishan tonalite is located in the Lenghu area of Qinghai in the west segment of the north margin of Qaidam. The petrochemical and geochemical study shows that the masses are characteristic of adakite,that is High Sr（〉400×10-6,409μg/g in average）,low Y（varies from 3.09 to 6.6μg/g）,Yb（varies from 0.4to 0.58μg/g）,Si2O〉56%（ranging from 62.86%to 64.83%）,A12O3〉15%（ranging from 17.25% to 18.15%）,MgO〈3%（ranging from 1.73% to 1.96%）,Mg#〈50（ranging from 33.4to 37.0）.Meanwhile,they are enriched in Na and depleted in K（Na2O/K2O=2.39～2.73）,Eu and Sr positive anomaly,displaying characteristics of O-type adakitic rock. Moreover,geochemical analysis shows that these samples are depleted in HFSEs（Nb,Ta,P）intensively,enriched in LILEs（K,Rb,Rb,Ba）,reflecting the characteristics of arc granite.LA-ICPMS zircon U-Pb dating suggests that the formation age of the rock is 263±2 Ma.On the basis of the regional geological background and the geochemical characteristics of the masses,we consider the adakitic granite of the western segment of the northern margin of Qaidam may form in a volcanic arc setting of active continental margin underneath subduction and the product of melting of plate subduction.Our study further reveals that the northern margin of Qaidam was in a tectonic evolution stage of oceanic crust subduction during middle Permian epoch.