东昆仑灶火河地区晚奥陶世侵入岩地球化学特征、锆石U-Pb年龄及其伸展构造环境的确定

灶火河地区位于东昆仑伯喀里克—香日德成矿带,为确定该区花岗闪长岩的形成时代、源区性质和构造背景,对其进行了LA-ICP-MS锆石U-Pb年代学和同位素及地球化学研究。结果显示岩体侵位时间为(449. 9±1. 4) Ma,属于晚奥陶世。岩石Si O2含量为71. 99%～63. 67%,Na2O含量为2. 61%～3. 43%、K2O含量为3. 56%～5. 81%,Al2O3含量为13. 31%～15. 28%,铝饱和指数A/CNK=0. 94～1. 04,介于偏铝质和过铝质之间。稀土元素分布模式为轻稀土富集,具弱负Eu异常。相对原始地幔明显富集Zr、Ga、Y和Hf等高场强元素并强烈亏损Ba、Sr、P和Ti等特征,Zr含量远高于该带内分异或者未分异的I型花岗岩,以上特征表明灶火河地区晚奥陶世侵入岩属A型花岗岩,结合岩石成岩年龄、地球化学特征以及区域构造演化,认为其为陆-陆碰撞或岛弧岩浆作用之后伸展构造环境下的花岗岩。

Geochemistry ziron U-Pb ages of Late Ordovician intrusive rocks in the Zaohuohe area, East Kunlun and determination of its extensional structural environment

The Zaohuohe area is located in the Bokalike-Xiangride metallogenic belt of the East Kunlun Mountains. To determine the formation age, source area and tectonic setting of the granodiorite in the area, LA-ICP-MS zircon U-Pb chronology and isotope and geochemistry research. The results show that the emplacement time of the rock mass is (449.9±1.4)Ma, belonging to the Late Ordovician. The content of SiO₂ in rock is 71.99%-63.67%, the content of Na₂O is 2.61%-3.43%, the content of K₂O is 3.56%-5.81%, the content of Al₂O₃ is 13.31%-15.28% aluminum saturation index A/CNK=0.94-1.04, Between partial aluminum and over-aluminum. The distribution pattern of rare earth elements is light rare earth enrichment with weak negative Eu anomalies. Compared with the original mantle, the high field strength elements such as Zr, Ga, Y and Hf are obviously enriched and the characteristics such as Ba, Sr, P and Ti are strongly depleted. The Zr content is much higher than the I-type granite with in-band differentiation or undifferentiation. The above characteristics indicate that the Late Ordovician intrusive rocks in the Zaohuohe area belong to the A-type granite. Combined with the diagenetic age, geochemical characteristics and regional tectonic evolution of the rock, the tectonic setting is the granite under the extensional tectonic setting after the land-continent collision or island arc magmatism.