豫西地区中元古代物源—沉积体系及其大地构造演化

Assembly and breakup history of the Columbia supercontinent were recorded by the source-to-sink system and tectonic evolution of the Mesoproterozoic of the North China Craton (NCC). However, little consensus has been reached regarding the stratigraphy correlation between the southern and central NCC due to the complicated-developed Mesoproterozoic sediments in the southern NCC, thus, Mesoproterozoic tectonic evolution of the NCC could not be further constrained. In view of this, 5~6 representative Mesoproterozoic sections outcropped in the three stratigraphic provinces of the southern NCC will be selected for the following studies. Initially, analysis of lithological features, structural characteristics and typical facies marks basing on the field survey of selected sections will be conducted for reconstructing sedimentary environment evolution. Besides, provenance and tectonic setting will be discussed, combining with sandstone grain framework components and whole-rock geochemistry. Furthermore, depositional age and provenance features are constrained by zircon and authigenic minerals, such as monazite and xenotime, U-Pb dating and Hf isotopic composition. Finally, a provenance-deposition system model of the Mesoproterozoic in the southern NCC will be set up for reconstruction of tectonic evolution. This project could reveal the tectonic-depositional response of the Mesoproterozoic in southern NCC, lay a foundation for the Mesoproterozoic stratigraphy correlation, and provide further insights into understanding the Mesoproterozoic tectonic evolution of the NCC.

中元古代华北克拉通沉积地层的源—汇体系及大地构造演化过程记录了Columbia超大陆聚合与裂解的过程，然而由于华北南缘中元古界沉积地层发育复杂，限制了华北南缘和中部中元古界沉积—构造特征的对比研究，无法进一步约束华北中元古代的大地构造演化。本项目选取华北南缘豫西地区三个地层小区出露的5~6条典型中元古界剖面为研究对象，通过地层剖面详测，分析岩石学特征、结构构造特征和典型相标志等，恢复其沉积环境演化过程；利用砂岩骨架颗粒成分、全岩地球化学研究母岩性质与物源构造背景；运用锆石及自生成岩矿物独居石和磷钇矿U-Pb年代学、Hf同位素等限定沉积地层的时代和源区性质；建立华北南缘中元古代物源-沉积体系模式，进而恢复其大地构造演化过程。该研究能揭示华北南缘中元古界构造-沉积响应过程，为华北克拉通中元古代地层对比奠定基础，进而深入研究华北克拉通中元古代大地构造演化。

中元古代华北克拉通沉积地层的源-汇体系及大地构造演化过程记录了Columbia超大陆聚合与裂解的过程，然而由于华北南缘中元古界沉积地层发育复杂，限制了华北南缘和中部中元古界沉积—构造特征的对比研究。本项目通过对华北南缘典型中元古界沉积特征和物源特征的综合分析，建立华北南缘中元古代物源-沉积体系模式，恢复其大地构造演化过程。. 自下而上，熊耳群大古石组为辫状河三角洲-湖泊系统，记录了熊耳裂谷早期“欠补偿”阶段；熊耳群不同火山岩沉积夹层可从附近太古代—古元古代变质杂岩以及熊耳火山岩中获得碎屑补给，此时盆地由喷发熔岩、少量火山碎屑岩和间歇性沉积岩补偿，盆地沉降速度相对较慢。兵马沟组主要沿裂谷边缘断裂带附近星点分布，主要由下部为冲积扇沉积，上部为滨岸沉积组成，代表了熊耳裂谷火山-沉积岩系向被动大陆边缘沉积过渡的地层，物质来源为克拉通结晶基底。汝阳群和洛峪群及其相当地层整体为一套滨-浅海的硅质碎屑-碳酸盐岩沉积地层，可以识别出潮坪相、泻湖相、滨岸相、陆棚相和碳酸盐台地沉积相，可以在大陆岛弧到被动大陆边缘背景的广泛范围内获取碎屑。华北南缘的罗圈组是在寒冷干燥向温暖湿润过渡的古气候下形成的冰川至冰水沉积物，揭示新元古代末期华北板块经历了气候变暖冰川消融的沉积过程。推测罗圈组构造背景是大陆岛弧，物源主要来源于华北克拉通早前寒武纪基底岩石。. 综合来看，华北南缘的中元古界垂向上总体为一个陆相河流碎屑岩-海陆过度相火山/沉积岩-滨浅海碎屑岩-台地碳酸盐岩的连续演化的大的海侵序列，受华北克拉通南部熊耳火山事件和后期发育的被动陆缘碎屑-碳酸盐台地控制。熊耳群（1.78~1.73 Ga）、兵马沟组和汝阳群–洛峪群（1.74~1.61Ga）具有统一的伸展裂谷背景，没有强烈的构造挤压作用，代表了一个大陆裂谷盆地的不同演化阶段。