【摘要】 碎屑锆石物源示踪是当今国际上研究大河演化的重要手段。通过对湖北省监利县周老镇钻孔中砂样Gsh6(86.76～88.58m)和Gsh10(126.22～128.42m)的碎屑锆石原位U-Pb年龄进行分析,并与周围可能源区的岩石年龄进行对比,发现Gsh6的U-Pb年龄主要可以分为11个年龄峰值:>3.0Ga,2490～2386Ma,2006～1784Ma,838～723Ma,654～625Ma,453～415Ma,257Ma,235Ma,212Ma,166Ma和<17Ma。Gsh10中碎屑锆石年龄表现出8个年龄峰值:>3.0Ga,2543～2273Ma,1979～1535Ma,835～723Ma,638Ma,451～423Ma,235Ma和212Ma。Gsh6比Gsh10多的3个年龄峰值表明长江流域面积逐渐扩大,其中257Ma的年龄峰值的出现表明峨眉山玄武岩已成为长江的源区,14.8±0.4Ma和16.5±0.3Ma锆石的出现,预示着长江源头已到达青藏高原。分析认为,Gsh6样沉积时(大约800kaB.P.),长江三峡已经贯通。更多还原

【Abstract】 U-Pb Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) analysis of detrital zircon in two sand samples from the Zhoulao borehole, which located at Zhoulao Town in the Jianli County( 112°59′E ,30°02′ N) , Hubei Province, are presented here. The two samples, named Gsh6 and Gshl0, situated at the depth of 86.76m to 88.58m,and 126.22m to 128.42m,respectively. The paleomagnetic age of the Gsh6 is ca. 800kaB. P. and the Gshl0 is ca. 1.2MaB. P. The Gsh6 yields age spectrum with significant groupings at > 3.0Ga,2490 ～2386Ma,2006 ～1784Ma, 838 ～ 723Ma,654 ～ 625Ma,453 ～ 415Ma,257Ma,235Ma,212Ma, 166Ma, and < 17Ma; while Gshl0 yields principal zircon populations with ages of > 3.0Ga,2543 ～ 2273Ma, 1979 ～ 1535Ma, 835 ～ 723Ma,638Ma,451 ～ 423Ma, 235Ma,and 212Ma,reflecting provenance chiefly from local sources in the Western Kongling terrain of the Western Hubei Province. The two sand samples have similar detrital zircon age profiles with three distinctive age peaks,e, g., < 17Ma, 166Ma,and 257Ma, interpreted to represent sources of the Tibet Plateau, the Emeishan Large Igneous Province (LIP) ,respectively. The 166Ma age peak is less known in the study area, more work will be done in the future. The three unique peaks in Gsh6 also indicate that the catchments of the Yangtze River were larger than that of the Gshl0 at the deposition time of the Gsh6. Age spectra are consistent with sedimentological and stratigraphic information. The Tibetan Plateau,situated at the upper reaches of the Yangtze River,was so active that any age of Cenozoic rocks could be found. There are two young zircons, aged 14. 8 ± 0.4Ma(Gsh6-50) and 16.5 ± 0.3Ma( Gsh6-18 ), which indicates that the source of the Yangtze River had reached the Tibetan Plateau at the deposition time of the Gsh6. The Emeishan Large Igneous Province (LIP)is located at the western margin of the Yangtze Craton, SW China. It consists of erosional remnants of voluminous mafic volcanic successions and numerous contemporaneous mafic and felsic intrusions. The big area of the Emeishan LIP can provide large quantity of zircons to the Jianghan Basin through the Yalongjiang River and the Minjiang River, both of which are the tributaries of Yangtze River. We speculate that the Eastern Tibetan Plateau and the Western Sichuan Province are one of the important provenances of zircons of those ages. The appearance of the 257Ma peak of Gsh6 suggests that lots of clastic sediments from the Emeishan LIP had been transported into the Jianghan Plain,at the deposition time of the Gsh6 of ca. 800kaB. P. Compare our result with the former studies, we find that the two sand samples show quite different age frequencies from the modern Hanjiang River sand. This implies that the Hanjiang River does not influence the sediments of the Zhoulao core from the depth of the 86m to 128m.更多还原