西昆仑甜水海地体早寒武世花岗岩浆作用及其构造意义

瓦仍孜拉甫岩体和阿依里西岩体出露于西昆仑造山带的甜水海地体中。LA-ICP-MS锆石U-Pb定年表明，阿依里西岩体的花岗质斑岩的侵位年龄为（530±6）Ma，瓦仍孜拉甫岩体的黑云母二长花岗质片麻岩的侵位年龄为（515±2）Ma，都形成于早寒武世。岩石地球化学特征表明，阿依里西岩体中花岗质斑岩的SiO2含量为67.7%~69.4%，具有较高的Mg#值（44~46），A/CNK值为0.81~0.93；K2O含量为2.15%~3.02%，呈钙碱性至高钾钙碱性特征；其εHf（t）值为-3.3~-0.8；以轻重稀土分异较为明显，富集Cs、Rb、K、Th、Zr、Hf、Y等元素，而亏损Ba、Nb、Ta、Sr、P和Ti等元素为特点，是由幔源岩浆与壳源岩浆发生混合作用而成。瓦仍孜拉甫岩体黑云母二长花岗质片麻岩的SiO2含量高其变化范围为75.0%~76.3%，Mg#值比较低，为18~26；A/CNK值为1.01~1.30，K2O含量为4.31~4.98，表现为高钾钙碱性、过铝质特征，其εHf（t） 值为+2.5~+4.3；属于高分异I型花岗岩，源于高钾钙碱性的安山岩和玄武质安山岩的部分熔融。根据这些地球化学特征，结合西昆仑不同地质单元中早古生代花岗岩体的分布特征、地质年代学和岩石成因特征，研究认为这2个花岗质岩体形成于岛弧环境，其为进一步深入研究西昆仑造山带早古生代的构造演化过程提供了新的地质资料。

Magmatism and Tectonic Implications of Early Cambrian Granitoid Plutons in Tianshuihai Terrane of the Western Kunlun Orogenic Belt,Northwest China

The Ayilixi and Warengzilafu plutons are located in the Tianshuihai terrane of the Western Kunlun Orogenic Belt (WKOB).Detailed LA-ICP-MS zircon U-Pb dating has yielded the crystallization ages of ca. (530±6) Ma and ca. (515±2) Ma for the Ayilixi pluton and Warengzilafu pluton, respectively, signifying their formation in Cambrian. The Ayilixi rocks are high-K calc-alkaline to shoshonitic granite porphyries, with a limited range of SiO2 (67.7%~69.4%), high Mg# (44~46), A/CNK ratios (0.81~0.93) and K2O (2.15%~3.02%). They are also marked by negative εHf(t) values of -3.3 to -0.8, obviously fractionated between light and heavy rare earth element, enrichments in Cs, Rb, K, Th, Zr, Hf, Y, and depletions in Ba, Nb, Ta, Sr, P, T. They are considered to have been most likely derived from magma mixing processes by mantle-derived magma and crustal magmatic melt. The Warengzilafu biotite monzonitic granite gneisses are high-K calc-alkaline and peraluminous. Compared to the rocks of the Ayilixi pluton, they generally have higher SiO2 (75.0%~76.3%), lower Mg# (18~26), with higher A/CNK ratios (1.01~1.30) and positive εHf(t) values of +2.5 to +4.3. Elemental and isotopic data suggest that the Warengzilafu rocks are highly fractionated I-type granites, which were mainly generated by partial melting of high-K calc-alkaline andesite and basaltic andesite. The two plutons represent the early Cambrian magmatism under island-arc setting in Tianshuihai terrane, which are related to the subduction of Proto-Tethys.