南米仓山变质岩变质时代及地质意义

Metamorphic Age and Geological Significance of Metamorphic Rock in the South Micang Mts

通过对汪家坪岩组的两件黑云斜长变粒岩变质岩样品进行LA-ICP-MS锆石U-Pb年代学研究,获得的^(206)Pb/^(238)U年龄介于843.3~904.9Ma之间,最古老的年龄达1138.46±16.7Ma,表示南米仓山结晶基底在新元古代早期曾发生过强烈的构造-岩浆活动;具有变质锆石特征的样品,获得的年龄数据表明南米仓山地区在新元古代发生过两期变质作用,早期的变质作用峰值年龄约为810.0~900.0Ma,代表着晋宁末期华北大陆板块与扬子板块逐渐对接拼合,古秦岭洋壳迅速向南北两侧俯冲消减事件;晚期变质作用发生在约为550.0~760.0Ma,记录了这一阶段的澄江期岩浆热事件引起的接触变质事件。

The zircon U-Pb dating for 2 biotite-plagioclase granulite samples from the Wangjiaping Complex in the south Micangshan crystallization basement gives ^（206）Pb/^（238） U ages ranging from 843.3 Ma to 904.9 Ma. Some zircon grains from the samples show clear rhythmic bands characteristic of magmatic genesis. These indicate that strong tectonic-magmatic activity and 2 metamorphic stages took place in the south Micang Mts during the early Neoproterozoic. The early metamorphism took place during 810~900 Ma, indicating gradual butting and jointing of the north China plate with the Yangtze plate at the end of the Jinning period, and rapid subduction of the ancient Qinling to the north and south sides. While late metamorphism occurred dyring 550~760 Ma, recording the contact metamorphism caused by the magmatic thermal events in Chengjiang period.