东昆仑祁漫塔格地区玉古萨依基性超基性岩体成因及构造意义

Genesis and Tectonic Significance of the Yugusayi Basic-Ultrabasic Complex in Qimantage Area of East Kunlun

玉古萨依基性超基性杂岩体位于东昆仑造山带祁漫塔格山西段玉古萨依地区。岩体侵入于祁漫塔格群变质砂岩中,由北西至南东方向岩性由超基性向基性过渡,可见明显的层状分异现象,普遍蚀变较强,辉石岩为主要的堆晶相。杂岩体岩石整体属于钙碱性系列,都属于富铁质或铁质基性超基性岩,富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,稀土元素配分曲线为右倾型。微量元素特征显示不同岩石类型均为同源岩浆演化的产物。岩体中角闪辉长岩的锆石U-Pb年龄为406±2.6Ma,形成于早泥盆世早期。岩石地球化学特征显示岩体形成于板内伸展环境下,表明在该时期区域内已经为碰撞后的伸展阶段。本次研究发现该杂岩体应为祁漫塔格早古生代蛇绿构造混杂岩带中非蛇绿岩成因的镁铁-超镁铁质层状侵入体。

The Yugusayi basic-ultrabasic complex is located in the Yugusayi area of the western Qimantag section of the East Kunlun orogenic belt. The complex intruded into the metamorphic sandstone of Qimantag Group and transited from NW to SE to lithology from ultrabasic to basic. The obvious stratiform differentiation was observed, and the alteration was strong in general. Pyroxene was the main accumulative facies. Complex rocks as a whole belong to calc-alkaline series, which belong to iron-rich or iron-rich basic ultrabasic rocks, enrich light rare earth elements and large ion lithophile elements, deplete heavy rare earth elements and high field strength elements, and the distribution curve of rare earth elements is right-leaning. Trace element characteristics show that different rock types are the products of the evolution of homologous magma. The zircon U-Pb age of amphibole gabbro in the pluton is 406±2.6 Ma, which was formed in the early Devonian. Geochemical characteristics of the complex indicate that the rocks were formed in intra-plate extensional environment, indicating that the area was in post-collision extensional stage. It is found that the complex should be a mafic-ultramafic layered intrusive body of non-ophiolite origin in the Early Paleozoic ophiolitic tectonic melange belt of Qimantag.