龙门山前陆盆地南部晚三叠世沉积--物源体系及其构造动力学指示

The power source of the change from marine carbonate rock to terrestrial detrital rock in the Longmen Shan foreland basin during the late Triassic is the key point of the project, and the provenance system of the Xiaotangzi formation and Xujiahe formation in study area will be selected as the research object. Firstly, based on the predecessor research results, we will build the isochronal stratigraphic framework, and analyze the sedimentary face and the sedimentary environment. The dating of the zircons from the key stratigraphic and other methods will be used to analyze the provenance of the detrital sediments, and the provenance system and the palaeogeographic pattern of Longmen Shan foreland basin in each stage will be detailed. Then, the uplift process of the south of Longmen Shan could be estimated. Finally, we will dissect the Tectonic dynamic mechanism of the filling of detrital sediments in the south of the Longmen Shan foreland basin during the late Triassic. Based on the research conclusions about the palaeogeographic pattern of the center and northern of the Longmen Shan foreland basin, we will discuss the whole palaeogeographic pattern of the Longmen Shan foreland basin and the characteristics of regional geological structure.

本项目以晚三叠世龙门山前陆盆地南部由海相碳酸盐沉积向陆相碎屑沉积转变的动力来源为切入点，选取龙门山前陆盆地南部的上三叠统小塘子组和须家河组物源体系作为主要研究对象。首先结合前人研究成果，建立晚三叠世等时地层格架，并进行沉积相与沉积环境分析。然后对关键层位采用碎屑锆石U-Pb定年技术分析碎屑沉积物来源，并结合多种方法对各个阶段物源体系进行精确刻画，揭示晚三叠世龙门山前陆盆地南部古地理格局，标定龙门山南段隆升的隆升过程。在此基础上，详细剖析晚三叠世龙门山前陆盆地南部碎屑沉积物充填的动力机制，并结合前人对龙门山前陆盆地中北部古地理格局的研究结论，探讨晚三叠世龙门山前陆盆地的整体古地理格局、区域构造格局。

本项目以晚三叠世龙门山前陆盆地南部由海相碳酸盐沉积向陆相碎屑沉积转变的动力来源为切入点。我们对四川盆地西南缘三叠系地层开展了碎屑锆石U-Pb年代学分析，结合古流向数据及前人发表的四川盆地其它地区碎屑锆石年龄数据，认为早-中三叠世四川盆地碎屑物源主要来自康滇古陆的北段，而晚三叠世四川盆地碎屑物源主要来自松潘-甘孜地体、龙门山造山带和秦岭造山带。这种物源变化反映了在晚三叠世古特提斯洋闭合、龙门山及松潘-甘孜东部发生强烈构造缩短的背景下的古水系调整。另外，晚三叠世康滇基底北段由剥蚀区转变为沉降区并接受沉积，结合古流向及地层分布特征分析，认为康滇古陆北段的沉降可能是晚三叠世扬子板块、义敦岛弧和羌塘地体碰撞、持续汇聚的情况下，松潘-甘孜地体向东逆冲并负载到扬子西缘造成的。在对晚三叠世以来前陆盆地各阶段盆地结构进行刻画的基础上，进行弹性挠曲模拟反演，推断龙门山前陆盆地的前渊地区(四川盆地西部)岩石圈的Te值自晚三叠世以来具有逐渐减薄的趋势。这可能与松潘-甘孜地块下方广泛存在的软流圈热物质对四川盆地西部岩石圈下部的长期加热而导致的熔融有关，反映了地球深部动力学过程与地球表层盆地演化之间的耦合关系。