长江三角洲地区TZK3孔碎屑锆石U-Pb年龄及其物源意义

DETRITAL ZIRCON U-Pb AGES AND ITS PROVENANCE SIGNIFICANCE IN THE TZK3 CORE FROM THE YANGTZE RIVER DELTA

以TZK3孔的磁性地层学为基础,结合沉积物的岩性、结构构造及锆石年龄谱系特征,探讨沉积物的物质来源及长江贯通的时限。古地磁结果表明:96.7 m、263.3 m、603.75 m分别对应B/M界线、M/G界线、晚上新世/早上新世的界线(3.58 Ma)。锆石年龄谱系数据显示,TZK3孔的U-Pb锆石年龄主要分为5组:100～300 Ma,400～500 Ma,700～850 Ma,1800～2000 Ma,2400～2600 Ma。其中3.7 Ma的锆石年龄谱相对简单,以白垩纪(100～150 Ma)为主,物质主要来自于长江中下游的火山盆地,为近源沉积。TZK3孔3.04 Ma以来,锆石年龄谱变得复杂且主峰相对较多,表明物源区更广且加入了远源的成分。3.04 Ma的锆石年龄谱中开始出现峨眉山玄武岩年龄段(251～260 Ma)的锆石,表明在此时期长江上游的物质就已到达了长江三角洲地区,即长江贯通的时限为3.04～3.7 Ma。

Based on the magnetic stratigraphy of TZK3 core, the lithology, structural structure and zircon age characteristics of sediments were studied to explore the material source of sediments and running through time limit of the Yangtze River. The paleomagnetic results show that 96.7 m, 263.3 m and 603.75 m are B/M boundary, M/G boundal7 and boundal7 in the Pliocene, respectively. The plot of U-Pb age spectra for concordant zircons shows that the U-Pb zircon ages of the TZK3 Core are divided into five groups： 100 -300 Ma, 400 -500 Ma, 700 -850 Ma, 1800 -2000 Ma, 2400 -2600 Ma. The age spectrum of 3.7 Ma is relatively simple, mainly in the Cretaceous （100 - 150 Ma） , and the materials are mainly from the volcanic basin in the middle and lower reaches of the Yangtze River. The zircon age spectrum becomes complex and there are relatively rrlore main peaks since 3.04 Ma, indicating that the source area is wider and far-source components are involved. The appearance of zircons from the Emeishan basaltic age （251 - 260 Ma） in the zircon age of 3.04 Ma, indicating that the material in the upper reaches of the Yangtze River has reached the Yangtze River Delta region in this period. So the running through time limit of the Yangtze River is 3.04 - 3.7 Ma.