宜昌砾石层重矿物组合特征及物源示踪分析  

Heavy Mineral Characteristics of the Yichang Gravel Layers and Provenance Tracing

作　　者：康春国[1,2] 李长安[3,4] 张玉芬[1] 邵磊[3] 江华军[3] 

机构地区：[1]中国地质大学地球物理与空间信息学院,武汉430074 [2]哈尔滨学院,哈尔滨150086 [3]中国地质大学地球科学学院,武汉430074 [4]中国地质大学生物地质与环境地质国家重点实验室,武汉430074

出　　处：《地质学报》2014年第2期254-262,共9页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40971008)资助的成果

摘　　要：广泛分布于宜昌至枝江-松滋-带的宜昌砾石层，对江汉平原乃至长江中游的地层划分、地貌演化、古环境变迁以及长江的形成与演化等研究具有重要意义。本研究在课题组前期研究的基础上，以本区内最具代表性的6个剖面为研究对象，对0．125～0．063mm粒级粉细砂质沉积物的重矿物特征进行了分析，结果显示宜昌代表性剖面砾石层细颗粒粉砂质沉积物的重矿物组合基本一致：锆石-绿帘石-白钛石-赤褐铁矿-钛铁矿-磁铁矿。源一汇分析表明，重矿物组成所指示的源区原岩类型除了三峡地区的还有长江三峡以西的金沙江、岷江、嘉陵江及乌江流域；经与长江及江汉平原西缘各河流的重矿物组合比较发现，宜昌砾石层的稳定重矿物组合特征与现代长江河漫滩和低矮阶地沉积物的重矿物组合一致。综合分析认为宜昌砾石层是于早更新世长江贯通三峡时形成的冲积扇，结合前人对宜昌砾石层形成时代的研究，推断三峡贯通的时间应该在1．0MaBP左右。The Yichang gravel layers distribute largely at the Yichang, Zhiiiang and Songzi area, which have important significance for the research of stratigraphic division, geomorphic evolution, ancient environmental changes of the Jianghan Plain and the middle Yangtze River, even formation and evolution of the Yangtze River. Based on previous research of our studying team,a total of six profiles were chosen in this paper. Here,heavy mineral characteristics of very fine sand fraction （63-125μm） was selected from bulk samples were analyzed. The results revealed that heavy mineral assemblages of the fine-grained sediments from the gravel layers are almost the same which meant zircon, epidote, leucoxene, hematite- limonite,ilmenite and magnetite. Relation of the source to sink shows source rock types reflected by heavy mineral assemblages distributed primarily in the Jinshajiang,Minjiang and Wujiang drainage basin,besides Western Three Gorges. Meantime heavy mineral assemblages of the sediments are similar to those of the modern Yangtze and the low-terrace sediments, which is showed by comparison the heavy mineral assemblage with the modern Yangtze and the main rivers in the Jianghan Plain. Based on the comprehensive analysis above, together with the early research on formation age of the Yichang gravel layers,we conclude that the Yichang gravel layers were the alluvial fan formed when the Yangtze River cut through the Three Gorges in the Early Pleistocene,approximately 1.0Ma BP.

关 键 词：宜昌砾石层 重矿物 物源示踪 三峡贯通 早更新世 

分 类 号：P575[天文地球—矿物学]