胶南新元古代花岗片麻岩中淡色脉体的锆石年代学和稀土元素研究

Zircon Geochronology and REE in Leucosome of Neoproterozoic Granite Gneiss,Jiaonan Area

苏鲁造山带中出露了大面积的新元古代花岗片麻岩,这些花岗片麻岩中赋存规模不等、形态各异的变质岩包体,已有资料表明它们均受到印支期高压─超高压变质作用的强烈影响。在花岗片麻岩及包体中经常可见以白色为主的长英质淡色脉体,脉体通常较窄,宽度多在1厘米以内,少数可达几个厘米,它们一般随片麻理方向延展,亦可见切穿片麻理的淡色脉,通常认为这类淡色脉体是母岩部分熔融的产物。作者等对出露于山东诸城市石河头乡新元古代花岗片麻岩中淡色脉体的锆石年代学及地球化学进行了探索性研究,取得了宝贵的地质信息。研究结果表明,淡色脉体中锆石SHRIMP法U Pb年龄为(147.6±2.5)Ma,同时锆石具有高铀、极低钍和重稀土富集等特征。文中在简略介绍地质背景的基础上,着重对淡色脉体中锆石的特征、锆石微区年龄和REE测定结果的地质意义进行了讨论。

There are many metamorphic rock inclusions of different sizes and forms within the Neoproterozoic granitic gneiss that widely spread in the Su-Lu orogen. Both the metamorphic rock inclusions and the country rocks have subjected to Indo-Chinese Epoch HP-UHP metamorphism based on available data. White felsic leucosome is common within the granitic gneiss and the metamorphic rock inclusions. Generally the leucosome occurs in narrow veinlet mostly less than 1 cm in width, with minors of a few centimeters. The leucosome veinlets extend mostly parallel to gneissosity with a few penetrating the gneissosity in different angles. It is generally believed that the leucosome was generated during partial melting of its parent rock. The authors carried out U-Pb dating and geochemical research on zircons separated from the leucosome occurring in the Neoproterozoic granitic gneiss in Shihetou, Zhucheng City of Shandong Province. Significant geological information has been obtained. The research demonstrates that the SHRIMP U-Pb zircon age of the leucosome is （147.6 ± 2.5） Ma and that the zircon is high in U concentration, extremely low in Th concentration and enriches in heavy REE. This paper describes briefly the geological background of the leucosome and focuses on the discussion of the features of the zircons separated from the leucosome and then the geological significance of the in situ age and REE data.