西昆仑苏纳克早古生代花岗岩锆石U-Pb年龄、地球化学特征及其地质意义

Zircon U-Pb Dating and Geochemical Characteristics of Early Paleozoic Granite in the Southern Sunake of West Kunlun,Northwest China and Their Geological Significances

苏纳克花岗岩位于西昆仑造山带库尔良裂谷带内,岩体岩性为黑云母二长花岗岩,其中侵入有花岗闪长岩脉。LA-ICP-MS锆石U-Pb定年结果显示,黑云母二长花岗岩和花岗闪长岩脉的结晶年龄分别为(477.0±2.1)Ma和(466.7±2.0)Ma,为早—中奥陶世岩浆活动的产物。苏纳克黑云母二长花岗岩主量元素组成具有高硅(SiO2含量(质量分数,下同)为72.75%~76.44%)、富碱(Na2O+K2O值为8.58%~9.12%)的特征,A/CNK值为1.02~1.11,为弱过铝质、高钾钙碱性系列。球粒陨石标准化稀土元素配分模式表现为平缓的右倾型特征,并呈“V”字型,且具有显著的负Eu异常。微量元素组成明显富集Rb、K等大离子亲石元素及Th、U等高场强元素,强烈亏损Ba、Sr、Eu、P、Ti等。整体上,苏纳克黑云母二长花岗岩具有高分异I型花岗岩的地球化学特征,是西昆仑早古生代原特提斯洋俯冲过程中的产物。

Sunake granite,located in Kuerliang rift zone of West Kunlun orogen,is composed of biotite monzogranite,in which granodiorite dikes are intruded.The LA-ICP-MS dating yields zircon U-Pb ages of(477.0±2.1)Ma and(466.7±2.0)Ma from the biotite monzogranite and granodiorite,respectively,which are the products of tectonic magmatism during Early-Middle Ordovician.The major elements of Sunake biotite monzogranite are characterized by high silica(the contents of SiO 2 are 72.75%-76.44%)and alkali(the contents of Na 2O+K 2O are 8.58%-9.12%)with the A/CNK of 1.02-1.11,showing that they are weakly peraluminous and high-K calc-alkaline series.The chondrite-normalized REE pattern presents a gentle right-leaning and“V”shape with significant negative Eu anomalies.The trace elements are enriched in Rb,K,Th and U,and evidently depleted in Ba,Sr,Eu,P and Ti.Overall,Sunake biotite monzogranite has the geochemical characteristics of high fractionated I-type granite,which is the product of Proto-Tethys Ocean subduction in West Kunlun during Early Paleozoic.