川西太阳河黑云母二长花岗岩的锆石U-Pb年龄、岩石地球化学特征及其地质意义

Zircon U-Pb Age and Geochemistry of the Taiyanghe Granitoid in Western Sichuan, China and Its Geological Significance

为揭示松潘-甘孜造山带构造演化及花岗岩成矿作用特征,对太阳河岩体进行了锆石U-Pb定年及地球化学研究。结果显示,岩性主要为黑云母二长花岗岩和黑云母花岗闪长岩,锆石U-Pb年龄为(206.7±1.3)Ma,表明岩体形成于中生代印支末期。岩石的A/CNK为1.01~1.15,具有较低的Sr含量,Rb/Sr值较低,为0.12~0.36。大离子亲石元素Rb、Ba相对富集,Sr元素则呈现出较为明显的负异常。高场强元素Nb、Hf、P亏损,La、Ce、Nd、Sm、Zr等呈正异常而明显富集。岩体稀土总量为238×10^-6~1057×10^-6,轻稀土富集,重稀土亏损。LaN/YbN值为39.85~192.16,δEu=0.64~0.92,δCe=0.89~1.06。岩石地球化学特征显示,该岩体具有过铝质S型花岗岩特征,源区为杂砂岩,形成于陆内汇聚一推覆造山阶段的后碰撞环境。

The Taiyanghe pluton is located in the eastern part of the Songpan-Ganzi orogenic belt.This pluton is mainly composed of biotite monzogranite and biotite granodiorite.LA-ICPMS zircon U-Pb age of biotite monzogranite is (206.7±1.3)Ma,which show that this pluton was emplaced at the end of Indosinian.The rocks have variable SiO2 from 53.26% to 73.84%,K2O/Na2O ratios from 0.63 to 1.91,A/CNK values from 1.01 to 1.15 and Sr contents from 325×10^-6 to 723×10^-6 with Rb/Sr ratios of 0.12 to 0.36.All rocks are relatively enriched in large ion lithophile elements (Rb and Ba, etc.),LREE and Zr and are depleted in Sr,Nb,Hf and P.The pluton have high rare earth elements (∑REE from 238×10^-6 to 1057×10^-6)and show strong fractionation of REE (LaN/YbN of 39.85 to 192.16)with slightly negative anomaly of Eu (δEu=0.64 to 0.92)and weakly Ce anomaly (δCe=0.89 to 1.06).Rock geochemistry show that the Taiyanghe granitoid is peraluminous S-type granite,which was derived from the partial melting of greywacke in post-orogenic setting.