滇黔桂盆地碎屑物源的变化及其对古特提斯洋演化历史的启示

Changes of Detrital Provenance in Dianqiangui Basin and Its Enlightenment to the Evolution of Ancient Tethys Ocean

摘要:

古特提斯洋的构造与演化过程一直是研究热点，很多学者在其产生、扩张、俯冲及闭合的时间上持有不同观点。本次研究中，运用LAICPMS锆石UPb测年技术对滇黔桂盆地三叠纪罗楼组碎屑锆石、泥盆纪坡松冲组碎屑独居石进行分析测试，同时结合古生代以来碎屑物源的演化历史，以期确定出古特提斯洋开启与闭合的时间。锆石测试结果显示：者桑地区罗楼组碎屑锆石UPb年龄主要集中在308~396Ma，440~680Ma，727~930 Ma，1004~1266Ma，1400~1880Ma，2360~2724Ma；老寨湾地区坡松冲组碎屑独居石UPb年龄则主要集中在657~460Ma和998~798Ma。通过对比研究区与周围地块的年龄分布特征，联系研究区岩相古地理、古海流以及古流向等地质证据，发现滇黔桂盆地古生代时期碎屑物源在460Ma左右发生了变化，460Ma以前碎屑物源主要来自印度北部、喜马拉雅、拉萨、羌塘、海南岛、澳大利亚西部及江南造山带，460Ma以后碎屑物源主要来自越北古陆、湘粤桂构造山系，云开地区也可能提供了碎屑物源。

Abstract:

The structure and evolution of Ancient Tethys Ocean has always been a research hotspot. Many scholars hold different opinions on the timing of its generation, expansion, subduction and closure. In this study, by using LAICPMS zircon UPb dating technology, Triassic Luolou formation detrital zircon and Devonian Posongchong formation detrital monazite in Dianqiangui basin have been analyzed and tested. Combining with the evolutionary history of the detrital provenance since the Paleozoic era, the opening and closing time of Ancient Tethys Ocean has been determined. As showed by the zircon test, the UPb ages of detrital zircons from Luolou formation in Zhesang area are mainly concentrated in 308~396Ma, 440~680Ma, 727~930Ma, 1004~1266Ma, 1400~1880Ma and 2360~2724Ma. The UPb ages of detrital monazite from Posongchong formation in Laozhaiwan area are mainly concentrated in 657~460Ma and 998~798Ma. Through contrast of age distribution characteristics of the study area and surrounding blocks, and linking with geological evidences, such as lithofacies paleogeography, paleo-currents, and paleo-current directions, it is found that the source of the clastics in the Paleozoic period of Dianqiangui Basin has changed at about 460Ma. In the past, the detrital provenance mainly came from northern India, the Himalayas, Lhasa, Qiangtang, Hainan Island, western Australia and the Jiangnan orogenic belt. After 460Ma, the detrital provenance mainly came from Yuebei ancient land, Xiangyuegui tectonic mountain system and Yunkai area. It may also provide a source of debris.