滇黔桂“金三角”地区晚三叠世地层碎屑物源示踪

Tracing of detrital provenance of Late Triassic Strata in the"Golden Triangle"area of Yunnan,Guizhou and Guangxi

三叠系是滇黔桂分布最广泛的岩系,赋存卡林型金矿等各种低温矿产。在前人研究基础上,运用LA-ICP-MS分析技术,对滇黔桂“金三角”地区的碎屑锆石进行了U-Pb测年。结果显示,大部分锆石具岩浆环带,Th/U值大于0.4,锆石U-Pb年龄集中在308~396 Ma、440~680 Ma、727~930 Ma、1004~1266 Ma、1400~1880 Ma、2360~2724 Ma六个区段。通过对比研究区及周围地块的碎屑锆石年龄分布特征,结合研究区岩相古地理、古海流及古流向,综合分析认为,研究区物源以越北古陆为主,同时湘粤桂构造山系和云开地区也可能提供了部分物源。该物源印证了古特提斯洋在印支期逐渐闭合,华南陆块与印支地块沿松马缝合带发生碰撞。

Triassic strata are most widely distributed rock series in Yunnan,Guizhou and Guangxi,and host various low-temperature mineral resources such as Carlin type gold deposits.Previous studies of the Triassic stratigraphic provenance in this area are quite rich;nevertheless,they are mainly concentrated on the Early and Middle Triassic strata,but lack the data on clastic provenance of late Triassic strata.Therefore,on the basis of previous studies,the U-Pb age of detrital zircons in the study area was measured by LA-ICP-MS analysis technology.The results show that most zircons have magmatic zones with Th/U ratios higher than 0.4.The U-Pb ages of zircons are concentrated in 308~396 Ma,440~680 Ma,727~930 Ma,1004~1266 Ma,1400~1880 Ma and 2360~2724 Ma.By comparing the age distribution characteristics of detrital zircons between the study area and the surrounding blocks and in combination with the lithofacies palaeogeography,palaeo-ocean current and palaeo-current,the authors hold that the provenance of the study area was mainly from the North Vietnam Palaeocontinent.At the same time,the tectonic mountain system of Hunan,Guangdong,Guangxi and Yunkai area probably also provided some provenances.The provenance proves that the Paleo-Tethyan Ocean was closed gradually during the Indosinian period,and the South China block collided with the Indosinian block along the Songma suture zone.