宜昌第四纪砾石层钾长石主、微量元素物源研究及其地质意义

位于长江三峡出口的宜昌地区分布着一套第四纪砂砾石层，详细记录了区域内古环境变迁以及长江的形成与演化，但这些砾石层何时与长江上游物质建立物源关系一直存在较大争议。而钾长石是河流沉积物中常见的矿物，其地球化学元素组成在不同区域内存在显著差异，是进行河流物源对比研究的理想矿物。基于此，利用激光剥蚀电感耦合等离子质谱仪（LA-ICP-MS）对宜昌第四纪砾石层和宜昌以上长江流域开展碎屑钾长石原位主微量元素和主成分（PCA）分析，结合砾石层已发表的地层沉积年龄，综合区域内已发表的研究结果，系统对比分析宜昌砾石层与长江上游物质建立物源联系的时间，结果表明在1.15 Ma时宜昌砾石层和长江流域存在物源关系；在0.75 Ma时随着长江上游水系的拓展与调整，有新物源区的物质进入长江。这些物源变化现象，主要体现了1.2~0.7 Ma期间长江流域受东亚和南亚夏季风的气候影响出现的沉积过程。 

Provenance study on geochemical elements of detrital K-feldspar in Quaternary gravel layer in Yichang and its geological significance

The Yichang area located at the exit of the Three Gorges is covered with a set of thick Quaternary gravel layers, recording the evolution of the paleoenvironment and the formation of the Yangtze River. However, there has been a great dispute over the time when the Yangtze River materials in the upper reaches entered the western margin of the Jianghan Basin. K-feldspar is a common mineral in fluvial sediments, and its geochemical element compositions are significantly different in different regions, making it an ideal mineral for the fluvial provenance study. In this case, we utilized the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to analyze the elementary compositions of detrital K-feldspar grains (n=340) on the gravel layers of the Yichang area and the upper reaches of the Yangtze River. In combination of principal component analysis (PCA) with formation sedimentary ages of gravel layers, we discussed the time when they established the provenance connection. The results show that the provenance connection has been established since 1.15 Ma and a new provenance area appeared at 0.75 Ma, suggesting that the Yangtze River drainage was strongly influenced by the East and South Asian summer monsoon during the period of 1.2~0.7 Ma.