东昆仑卡尔却卡地区中志留世A型花岗岩岩石成因及构造环境

东昆仑造山带西部卡尔却卡地区出露大量似斑状二长花岗岩，对其展开岩相特征、锆石U-Pb年龄和岩石地球化学研究，结果显示，似斑状二长花岗岩年龄为425±2.3 Ma，表明其形成于中志留世。岩石具有高SiO2（69.0%~71.2%）和K2O（4.3%~5.54 %）含量，富集大离子亲石元素（Rb、K、Th和U），亏损高场强元素（Nb、Ta和Ti），强烈的负Eu异常（Eu/Eu*=0.40~0.51）特征。岩石较低的Cr、Ni含量（Cr=13.81×10-6~32.9×10-6，Ni=5.48×106~12.05×10-6）、低的Ce/Pb（2.01~4.19）和Nb/U（4.1~7.57）值，表明该岩体来自上地壳的部分熔融。岩体高10000Ga/Al值（3.22~3.42）、Zr+Nb+Ce+Y元素含量（459×10-6~656×10-6）和锆石饱和温度（827~881℃），表明其为A型花岗岩。构造图解和高的Y/Nb值（2.93~3.15）指示，该岩体为A2型花岗岩，形成于碰撞后伸展背景。结合区域岩浆岩的时空分布，表明东昆仑造山带从中志留世开始进入碰撞后伸展阶段。

Petrogenesis and tectonic setting of Middle Silurian A-type granite in Kaerqueka area,East Kunlun

A lot of porphyritic monzogranites are outcropped in the Kaerqueka area, west of the East Kunlun orogenic belt.Zircon U-Pb age and geochemistry of the porphyritic monzonites were studied.Zircon U-Pb dating yields an age of 425±2.3 Ma, indicating Middle Silurian.The rocks are characterized by high contents of SiO2(69.0%~71.2%) and K2O(4.3%~5.54%), enrichment of large ion lithophile element(Rb, K, Th and U), depletion of high field strength element(Nb, Ta and Ti), and strong Eu negative anomaly(Eu/Eu*=0.40~0.51).Their lower content of Cr, Ni(Cr=13.81×10-6~32.9×10-6, Ni=5.48×10-6~12.05×10-6) and the lower Ce/Pb (2.01~4.19) and Nb/U(4.1~7.57) values indicate that they were originated from partial melting of the upper crust.The high ratio of 10000Ga/Al (3.22~3.42), high contents of Zr+Nb+Ce+Y(459×10-6~656×10-6) and zircon saturation temperature(827~881℃) imply they belong to A-type granite.Tectonic diagram and high Y/Nb ratio(2.93~3.15) indicate that they are A2 type granites, and were formed in the post-collision extension setting.Combined with the spatial and temporal distribution of magmatic rocks in the region, it is suggested that the East Kunlun Orogen entered the post-collision extension stage from the Middle Silurian period.