江汉盆地新生代早期河流演化研究:来自地表河流和盆地钻孔碎屑锆石U-Pb年龄的约束

Early Cenozoic drainage evolution in the Jianghan Basin:Constraints from detrital zircon U-Pb ages of surface rivers and cores in the basin

大型河流的演化是构造-气候相互作用的结果,对其开展演化历史研究是揭示地球深部动力过程对地表过程影响的关键切入点。保存于江汉盆地的新生代地层详细记录了汉江、长江等大型河流的演化信息。通过对汉江流域进行系统的碎屑锆石U-Pb年龄分析(n=690),结合前人在江汉盆地主要汇入河流发表的锆石U-Pb年龄数据,将其与江汉盆地内早始新世沉积钻孔的锆石U-Pb年龄数据进行了对比。结果表明,汉江下游的碎屑锆石U-Pb年龄物质组成混合了秦岭西部、大巴山和秦岭东部的河流碎屑物质信号,采用其下游干流样品的锆石U-Pb年龄组成进行物源对比更具有代表性;江汉盆地早始新世的碎屑物质主要来自秦岭和大别山,这主要归结为江汉盆地内部断陷与这些造山带的隆升形成显著的地势差异,为大型河流发育奠定基础;发源于武陵山和黄陵背斜的河流此时并不是江汉盆地中部、东部和南部凹陷的物质供给河流;黄陵背斜以西的长江在早始新世未进入江汉盆地。总体而言,江汉盆地在新生代早期的沉积物源以近源造山带为主,是对盆地周缘造山带隆升和类季风气候的沉积响应。

The evolution of large rivers is closely linked to the interactions between tectonic and climatic processes.Understanding the evolutionary history of these rivers is crucial for uncovering the influence of deep dynamic processes on the Earth's surface.In the Jianghan Basin,the preserved Cenozoic strata provide valuable insights into the evolutionary history of the Han and Yangtze Rivers.By conducting a systematic analysis of detrital zircon U-Pb ages(n=690)in the Hanjiang River Basin,the sediments in the lower reaches of the Hanjiang River contain a mixture of fluvial detrital signals from the Qinling and Dabie mountains.The detrital zircon U-Pb ages of these samples from the lower reaches of the Hanjiang River are more representative for determining their provenance.We have compared these new data with previously published fluvial sedimentary zircon U-Pb ages from the Jianghan Basin,as well as detrital zircon U-Pb ages from drilling cores obtained from Early Eocene strata in the basin.Provenance analysis reveals that the detrital material in the Jianghan Basin during the Early Eocene was primarily derived from the Qinling-Dabie Mountains.This can be attributed to the significant difference in elevation between the depression within the Jianghan Basin and the surrounding uplifted orogenic belts,which provided the necessary conditions for the development of large rivers.It is important to note that the Wuling Mountain and Huangling Anticline rivers did not serve as the main sources of sediment supply for the central,eastern,and southern depressions of the Jianghan Basin during this time period.Additionally,the Yangtze River,located west of the Huangling Anticline,did not flow into the Jianghan Basin in the Early Eocene.Overall,the sediments in the Jianghan Basin were predominantly proximal deposits sourced from the adjacent orogenic belt,which can be attributed to the exhumation of the orogenic belt and a monsoon-like climate in the early Cenozoic era.