河南南召地区上三叠统物源分析及其对秦岭印支期造山作用的沉积响应

The Indosinian orogeny of the Qinling orogen, resulted by the collision between the North China, Qinling and South China blocks, plays a key role to the formation of the China ancient continent, where the collision modal and subduction-collision transition are the fronting scientific problems. The Nanzhao Basin in the north Qinling Orogen developed a suite of Upper Triassic strata, and was regarded as an important part of the southern North China foreland basin system. Sediments from the Nanzhao Basin can, therefore, inform some vital information of the Qinling Orogen from the subduction to the collision. This project will focus on the Upper Triassic strata to deduce basin mountain interaction between the Qinling Orogen and the Nanzhao basin. Some practicable methods are carried out, including analysis on deposition system and filling characteristics, statistics of sandstone framework components, geochemical analysis of whole rock, U-Pb age, geochemical composition and Hf isotope of the detrital zircon, to reveal sedimentary records of the collision-uplift process of the Qinling Orogen, and depict the Triassic tectonic paleogeography of the boundary belt between the Qinling Orogen and the southern North China Block. The achievements will be further improvements on the research of the Indosinian mountain-basin interaction of the Qinling Orogen. Compared with the data from the surrounding basins of the Qinling Orogen, oblique or diachronogy collision will be discussed whether they happened between the South China and North China blocks, as well as the differential uplifting of the Qinling Orogen during the Late Triassic. The new understandings of the orogenic process of the Qinling Orogen will be applied to the discussion of the formation of the China ancient continent.

秦岭造山带印支期造山作用使华北、秦岭和华南板块最终拼合在一起，对中国古大陆的形成具有至关重要的意义。造山带碰撞造山的方式以及俯冲—碰撞转换的模式是目前研究的关键科学问题。南召晚三叠世沉积盆地位于秦岭造山带北缘，是华北南缘前陆盆地系统的重要组成部分，因此，盆地中的沉积物有可能记录了秦岭造山带从俯冲到碰撞造山的关键信息。项目将以南召盆地上三叠统为研究对象，进行盆山相互作用研究。通过系统的沉积体系与充填特征，砂岩骨架颗粒成分，全岩地球化学，碎屑锆石U-Pb年龄、微量元素及Hf同位素组成分析，揭示秦岭造山带造山—隆升过程及其在南召盆地中的沉积响应，重建华北—秦岭结合带三叠纪构造古地理，将丰富秦岭造山带印支期盆山相互作用研究的成果。通过秦岭造山带周缘盆地盆山过程的对比，分析秦岭造山带晚三叠世不规则边缘碰撞或斜向碰撞过程以及造山—隆升作用的空间差异，探讨秦岭造山带的造山过程在中国古大陆形成中的作用。

晚三叠世，秦岭造山带碰撞造山作用控制着两侧沉积盆地的形成和演化，盆地中的沉积物也记录了秦岭造山带造山的关键信息。然而，扬子北部盆地和华北南部盆地沉积记录却存在着明显差异，前者晚三叠世早期地层中存在大量来自秦岭造山带的沉积物，而后者同期地层中是缺乏的。这种差异是斜向碰撞方式产生的，还是造山带隆升作用存在南北差异，又或者与北秦岭内部晚三叠世南召盆地的形成有关。. 项目对河南南召盆地晚三叠世沉积体系、物源特征及盆山系统演化做了系统研究，取得了以下重要成果：（1）南召盆地上三叠统沉积环境经历了冲积扇→辫状河→湖泊三角洲→深湖及浊流沉积→三角洲相沉积的演化，可划分出三个充填阶段，分别代表了盆地的形成、发展与萎缩；（2）南召盆地上三叠统物源区主要为南秦岭、北秦岭和华北南缘，碎屑锆石指示了南秦岭在晚三叠世经历了由晚三叠世火山岩盖层到新元古代基底的剥蚀过程，而北秦岭的隆升方式也发生了由差异隆升（北秦岭南侧秦岭群的快速隆升）到均匀隆升（北秦岭整体隆升）的过程。华北南缘在晚三叠世后期加速隆升，可能成为控制华北南部前渊沉降的动力；（3）南召盆地上三叠统大量的火山物质记录逐渐消失，预示着火山活动的减弱，指示了秦岭造山带可能发生了由俯冲到碰撞的构造转换。（4）南召盆地上三叠统物源分析结果与华北盆地南部不一致，暗示它们是两个隔绝的盆地。但与扬子北部盆地物源数据较为一致，证明了华北南缘褶皱逆冲带的形成可能是产生扬子北部盆地和华北南部盆地沉积记录差异的原因。. 项目研究成果能为秦岭造山带碰撞造山过程提供沉积学依据，推动盆山系统沉积学的发展，也能为重建华北南缘古地理提供科学依据。