阿尔金北缘西尤勒滚萨依二长花岗岩体地球化学特征、LA-ICP-MS锆石U-Pb年龄及其地质意义

Geochemical feature, LA-ICP-MS zircon U-Pb dating and the geological significance of West Youlegunsayi monzogranite in North Altyn

西尤勒滚萨依二长花岗岩体位于阿尔金北缘米兰—金雁山地块北侧,紧邻北阿尔金俯冲碰撞杂岩带。通过对岩体进行岩石学、岩石地球化学及同位素年代学研究,探讨阿尔金北缘晚奥陶世的岩浆作用及构造演化。研究表明,岩石具高SiO_(2)(70.27%~77.24%),A/CNK=0.69~1.03,w(K_(2)O)=4.36%~5.57%,为准铝质高钾钙碱性系列。岩石富集轻稀土而亏损重稀土,亏损大离子亲石元素Sr、Ba、Eu、U、Th,弱富集—亏损高场强元素Nb、Ta、P、Ti。岩石CIPW标准矿物中没有刚玉,P_(2)O_(5)与SiO_(2)呈负相关,且Zr-TiO2判别图解位于I型花岗岩区域以及岩体边部发育暗色闪长岩包体,表明岩体为I型花岗岩。岩体锆石U-Pb同位素年龄为(449±3.6)Ma,为晚奥陶世。岩体与北阿尔金洋向南俯冲碰撞密切相关,是同碰撞阶段的产物。

West Youlegunsayi monzogranite is located in the North of Milan-Jinyanshan block in North Altyn, close to the Northern Altyn subduction-collision complex rock. Through the study of petrology, petrogeochemistry and isotopic chronology of the rock body, the late Ordovician magmatism and tectonic evolution in the northern margin of Altyn are discussed. The research result shows that the rocks have high SiO_(2)(70.27%-77.24%), A/CNK=0.69-1.03, rich K_(2)O(4.36%-5.57%), belonging to high-K calc-alkaline series and quasi-aluminous rock series. The rocks are rich in LREE and depleted in HREE, depleted in large ion lithophile elements(Sr, Ba, Eu, U, Th) and weakly enriched and depleted in high field strength elements(Nb, Ta, P, Ti). There is no corundum in CIPW standard mineral of the rock, P_(2)O_(5)is negatively correlated with SiO_(2), and Zr-TiO2discrimination diagram is located in I-type granite area and dark diorite xenoliths are developed at the edge of the rock mass, indicating that the rock mass belongs to I-type granite. The zircon U-Pb isotopic age of the rock body is(449 ± 3.6) Ma, belonging to the Late Ordovician. The formation of the rock body is closely related to the southward subduction and collision of the North Altyn Ocean, and it is the product of the same collision stage.