河口地层独居石Th(U)-Pb年龄对长江贯通时限的约束

新生代长江水系调整、东西贯通时限是国内外学者共同关注的问题。长江发展演化的复杂性在近一个世纪的河流沉积地貌学研究中得到充分的认识,但在贯通时限问题上难以形成共识。河口地层中碎屑独居石的电子探针Th(U)-Pb年龄较好地限定长江东西贯通的时间在2.58MaBP前后。随着碎屑矿物微区分析技术的发展,锆石、独居石年代学和微区特征将成为研究流域演化、构造运动的主要手段。

CONSTRAINTS ON THE YANGTZE RIVER RUNNING-THROUGH TIME, USING Th (U)-Pb DATING OF MONAZITE

Neogene Yangtze drainage adjustment and timing of the Yangtze River running due east and due west have attracted great attention at home and abroad.Complexities of Yangtze drainage evolution have been well acknowldeged after studies of fluival sedimentology and geomorphology over a century,but the timing of the Yangtze formation is not well constrained.31 monazite samples from late Cenozoic deposits in the Yangtze River estuary were analyzed with electron microprobe dating technique.The statistical treatment of Th(U)-Pb ages revealed that the Yangtze River extended its drainage westward to the upper reach,especially through the Tibetan Pleteau around 2.58 MaBP.Following great progress in micro-analysis techniques of single detrital minerals,geochronology and micro-features of zircon and monazite will become a major method to study large drainage evolution and tectonic activities in the drainage basins.