西昆仑库地伟晶辉长岩和玄武岩锆石SHRIMP年龄:库地蛇绿岩的解体

Zircon SHRIMP Age Determination of the Giant-crystal Gabbro and Basalt in Küda, West Kunlun: Dismembering of the Küda Ophiolite

西昆仑“库地蛇绿岩“是中国西部地区研究程度较高的蛇绿岩之一。对这条蛇绿岩带的时代、构造背景至今存在很大分歧。笔者等在库地超镁铁岩体中 ,获得侵入于橄榄岩中的伟晶辉长岩锆石 SHRIMP年龄为5 2 5± 2 .9Ma,在库地一些克沟获得块状玄武岩锆石 SHRIMP年龄为 4 2 8± 19Ma,这表明库地超镁铁岩和库地一些克沟玄武岩不属于同一时代 ,因此它们可能形成的构造背景也存在差异 ,库地蛇绿岩应解体。

Küda Ophiolite” in West Kunlun is one of the most studied ophiolites in West China. Controversies on its age and tectonic significance exist among geologists till now. In this paper, by SHRIMP age determination, the zircon U Pb age of the giant crystal gabbro, which intrudes into the ultramfic complex, is 525±2.9Ma (MSWD=1.2), so the ultramafic complex, which is an important part of the Küda ophiolite, must older than this age. Zircon U Pb age of the basalt is 428±29Ma. The ages of the gabbro and the basalt argue that the ultramafic complex and the basalt in Küda were asynchronous and the Küda ophiolite should be dismembered. The age data in this paper supply new information to study the Paleozoic evolution in this area.