青海玉树查涌地区高镁闪长岩年龄、岩石成因及构造背景
Age,Petrogenesis and Tectonic Implications of High-Mg Diorite in Chayong Region,Yushu,Qinghai

为了查明青海玉树查涌地区闪长岩岩石成因及形成的地球动力学背景，对其进行了岩相学、矿物电子探针分析、锆石LA-ICP-MS U-Pb年代学和岩石地球化学分析.闪长岩锆石LA-ICP-MS U-Pb年龄为230±2Ma，属于晚三叠世.电子探针分析结果显示，闪长岩中的斜长石具有正环带结构，核部斜长石属于倍长石或钙长石，边部属于中长石或拉长石；黑云母矿物成分为镁质黑云母，结晶温度介于647~688℃，侵位深度约为14.2~15.5km；角闪石属于钙质角闪石，显示壳幔混合成因的特点.岩石地球化学分析结果显示闪长岩具有富硅、富镁、高的Mg#值及较高含量的Cr和Ni，富集LILE和LREE，亏损HFSE，铕异常不明显，与高镁闪长岩中的赞岐岩相似.闪长岩中锆石的εHf(t)值为-10.4~-10.3和-6.4~-4.0，锆石Hf单阶段模式年龄(tDM1)为1021~1311Ma.分析研究表明闪长岩形成于俯冲带之上的地幔楔环境，为地幔橄榄岩与俯冲的洋壳板片部分熔融的富硅质熔体平衡反应形成的.结合区域地质演化认为晚三叠世古特提斯洋仍处于俯冲消减状态，查涌高镁闪长岩为金沙江洋向西俯冲消减过程中的产物.
This paper presents petrography, electron microprobe results, zircon U-Pb dating and geochemistry of diorites at Chayong, Yushu, Qinghai Province,with the aim of constraining its petrogenesis and geodynamic significance. The dating results indicate that the diorite formed in the Late Triassic (230±2Ma). Electronic Probe analysis results show that plagioclase has a band structure with bytownite and calciclase in the centre, andesine and labradorite on the edge. Biotite belongs to magnesia biotite, which crystallized at temperature of 647-688℃, at depth of 14.2-15.5km.Hornblende belongs to calcic amphibole and has the characteristics of crust-mantle mixing origin of the magma.The diorites contain high SiO2, MgO, Mg# values,Cr and Ni,enriched in large ion lithophile elements (LILEs) and light rare earth elements(LREEs), depleted in the high field strength elements (HFSE), which is similar with high Mg diorite. The εHf(t) values of zircons from the diorites vary from -10.4 to -10.3 and from -6.4 to -4.0, and their Hf one-stage model ages vary from 1021 to 1311Ma. They are likely formed from mantle peridotites by reacting with Si-rich melts released from subducted oceanic slab. Combined with regional tectonic evolution, it is suggested that the diorites might have been resulted from the subduction of Jinshajiang Ocean in the Late Triassic