藏北聂荣微陆块新元古代-寒武纪构造演化

Located in the juncture of the South Qiangtang Block and Gangdise Block, the Nyainrong microcontinent is the only tectonic block that has a large outcrop of crystalline basement, and it is one of the most favorable areas for understanding and researching early formation and evolution of the Qinghai-Tibet Plateau. Existing geochronology research data on the microcontinent basement orthogneiss fully confirmed magmatic events on the microcontinent in the Neoproterozoic and Cambrian. There were probably closely related to the evolution of the Rodinia Supercontinent or Gondwana land respectively. Currently, the study of crystalline basement is limited, mainly aiming at the geochronology of basement gneisses, and the obtained ages are not consistent. Systematic study about the cause of the rock formation is insufficient, and tectogenetic environment of the basement gneiss is rarely discussed. All these hamper the understanding of the tectonic evolution of the microcontinent to some extent. The project has further study and improve the Neoproterozoic-Cambrian lithostratigraphic units through the isotope chronology, geochemistry, isotope of Neoproterozoic-Cambrian magmatic activity, and through the tectonic environment, metamorphism and provenance of the Precambrian Zharen group and Nyainrong group. We further explore rational and effective measures to Neoproterozoic and Cambrian tectonic evolution of the Nyainrong microcontinent with the regional geologic characters, and under the big background of the global supercontinent aggregation and cracking. Inverting the evolutionary history of the Nyainrong microcontinent is critical to the understanding of the Qinghai-Tibet Plateau’s early formation and evolution.

聂荣微陆块处于羌南－保山板块与冈底斯板块结合部位，是藏北地区大范围出露结晶基底的构造块体，是认识和研究青藏高原早期形成与演化最为有利的地区之一。研究表明微陆块上发育新元古代和寒武纪的岩浆活动，并推测其分别与罗迪尼亚大陆和冈瓦纳大陆的演化密切相关。目前关于微陆块基底岩石的研究程度仍然较低，主要是针对正片麻岩的同位素定年研究，获得的年龄数据尚不统一，尤其缺乏其岩石成因和岩石地层的系统研究，在一定程度上制约了对微陆块构造演化的认识。本课题通过对新元古代-寒武纪岩浆活动的年代学、地球化学、同位素研究以及对前寒武系扎仁岩群和聂荣岩群形成的构造环境、变质作用和物源区研究，进一步建立和完善微陆块新元古代-寒武纪岩石地层系统。在全球超大陆聚合与裂解事件的背景下，结合区域地质研究，进一步有效探讨微陆块在新元古代-寒武纪的构造演化。这对认识青藏高原早期形成演化具有重要而深远的科学意义。

聂荣微陆块是藏北地区大范围出露结晶基底的构造块体，处于羌南-保山板块与冈底斯板块的结合部位，是研究青藏高原早期形成与演化的重要窗口。本课题对微陆块广泛出露的片麻岩进行了锆石U－Pb年代学和同位素地球化学研究。片麻岩的野外产状、矿物组成、结构构造以及全岩地球化学特征研究表明，片麻岩样品原岩均为中酸性侵入岩，锆石的微量元素示踪、成因分析表明锆石是典型岩浆锆石。结合已有年代学研究，聂荣岩群可以解体为新元古代片麻岩（843-820Ma）、寒武纪片麻岩（517-488Ma）、中生代花岗片麻岩（185-170Ma），建立了聂荣微陆块构造－岩浆演化的年代学格架，将微陆块上的岩浆活动分为新元古代、寒武纪、中生代三个演化阶段。地球化学研究表明，新元古代片麻岩和寒武纪片麻岩的原岩均具有火山弧花岗岩的特点。通过区域对比研究，初步认为聂荣微陆块在新元古代与扬子板块可能更具亲缘性，新元古代岩浆作用是罗迪尼亚超大陆裂解初期伸展背景下的产物。到寒武纪初，随着微陆块向印度大陆北缘的持续汇聚造成了寒武纪I型花岗岩的侵位，微陆块早期的结晶基底最终形成。