扬子陆块西缘古元古代火山-沉积建造的沉积学、年代学和地球化学研究

The Paleoproterozoic Dongchuan Group and its equivalents, the Dahongshan and Hekou Groups, in the western Yangtze Block, South China are important for the reconstruction of the supercontinent Columbia but are poorly studied. We have been working on Precambrian geology in the region in the past decade and have confirmed that these stratum are possibly formed at around 1.7Ga. In this project, we will carry out a detailed study of their ages and provenance in order to understand their temporal and spatial distributions. We will conduct detailed field and laboratory work on the clastic and volcanic rocks from these stratum, including whole-rock major and trace elements and Sr-Nd-Pb isotope analyses, and zircon U-Pb, and Hf isotopic analyses. The aims of this study will be 1) to determine the precise ages of their deposition; 2) to provide geochemical constraints on their provenance; 3) to understand their geodynamic setting, 4) to compare these stratum with those of similar ages from other continents and 5) ultimately to yield information about the possible re-construction of the Yangtze Block in the Columbia supercontinent.

东川群-大红山群-河口群是扬子陆块保持最好的一套古元古代火山－沉积建造，它包含完整的沉积岩和火山岩层序，为深入研究地质演化和构造背景提供了重要的天然地质条件。本项目拟对这套火山-沉积建造的形成和演化开展综合研究，运用高精度 锆石定年和原位 Hf 同位素等测试，并结合传统的碎屑岩物源分析方法，和全岩主、微量元素及 Sr-Nd-Pb 同位素分析，系统深入地研究这套火山-沉积建造的形成时限、沉积源区特征及其构造环境，并利用最新的资料与扬子北缘及其它克拉通已知的古元古代地层系统进行对比研究和整体研究，探讨扬子陆块前寒武纪演化历史。对扬子陆块在哥伦比亚超大陆中的重建有着重要的科学价值和意义。对于这些地层的研究不仅能够反映区域构造演化，而且对于理解成矿背景和成矿模式具有重要的指示意义。

本项目对位于扬子陆块西南缘的古元古代火山-沉积建造和与其相关的Fe-Cu矿床进行系统的沉积学、年代学和地球化学研究工作。研究表明古元古代东川群、大红山群和河口群为一套时代相近的裂谷系沉积,形成时序为1742Ma到1500 Ma,并伴生有具大陆裂谷型特点的基性岩浆岩。此系列沉积-岩浆活动与哥伦比亚(Columbia)超大陆的裂解基本同时，并且与澳大利亚北部以及劳伦大陆西北缘裂谷系在形成时间、沉积和岩浆作用以及演化历史等方面十分相似。扬子西缘古元古代铁、铜成矿事件主要分为~1.66 Ga和~1.1 Ga两期,分别对应于该区古元古代和晚中元古代大陆裂谷岩浆活动,为Columbia和Rodinia超级大陆旋回的产物。这些矿床在成因上也与印度西北部、澳大利亚北部相关Fe-Cu矿床相对应。