西藏雅江缝合带混杂岩中OIB型基性岩的年代学研究及对新特提斯洋扩张时限的制约

新特提斯洋的扩张时限的准确厘定是理解现今洋-陆格局的先决条件，对于建立板块构造理论的基本时间框架具有重要意义。现有研究对新特提斯洋扩张时限的约束较为有限，关键在于缺乏有效的地质载体。西藏南部的雅鲁藏布江缝合带是新特提斯洋消亡的遗迹，缝合带南缘混杂岩中的OIB型基性岩来源于新特提斯洋中的海山或洋岛，因此是约束新特提斯洋扩张时限的突破口。雅江混杂岩中OIB型基性岩以玄武岩为主，无法通过传统的锆石U-Pb定年手段测定其形成时间。因此，本项目拟利用创新性的“锆石原位离子探针U-Pb定年技术”，准确厘定雅江缝合带典型地段混杂岩中OIB型基性岩的形成时代，为约束新特提斯洋的扩张时限提供重要资料和研究思路。“锆石原位离子探针U-Pb定年技术”在本项目的成功应用也将为基性岩的年代学研究提供重要技术借鉴。

Determining the spreading duration of the Neo-Tethys Ocean, which is critical for understanding modern tectonic framework and plate tectonics theory, is limited by the lack of petological proxies. OIB-type basic rocks within the mélange from the Yarlung Zangbo suture zone (southern Tibet) are relics of seamounts and ocean islands from the Neo-Tethys Ocean. Determining the formation age of these OIB-type basic rocks, hence, is the key to understand the spreading duration of the Neo-Tethys Ocean. However, OIB-type basic rocks are mostly basalts, which are inapplicable to traditional zircon U-Pb dating methods. Therefore, this project uses “Zircon In-situ SIMS U-Pb Dating”, which is the newest method to analyze the age of basalt, to determine the formation age of the OIB-type basic rocks within the Zhongba mélange from the Yarlung Zangbo suture zone and for further constraint on the spreading duration of the Neo-Tethys Ocean. The application of this new method in this project can also provide important examples for geochronology of basic rocks.