黔北普宜地区晚三叠世二桥组砂岩碎屑锆石U-Pb年龄、重矿物分析及地质意义

普宜地区位于上扬子腹地——四川盆地东南缘,区内晚三叠世碎屑岩记录了上扬子前陆盆地演化信息,是研究盆地东缘盆山耦合的理想对象.二桥组主要由三角洲平原-三角洲前缘相砂岩组成,交错层理恢复的物源主要来自东侧,砂岩岩屑主要由岩浆岩岩屑和变质岩岩屑组成,碎屑重矿物主要由锆石、电气石、金红石、白钛石、黄铁矿、锐钛矿、石榴子石、铬铁...

Implications of detrital zircon U- Pb ages and analysis of heavy minerals from sandstone of the Late Triassic Erqiao Formation in Puyi area, North Guizhou

The Puyi area is located in the Middle of upper Yangtze, southeast margin of Sichuan basin. The Late Triassic clasolite record the evolution information of the upper Yangtze foreland basin, which is an ideal object for studying the coupling relationships between sedimentary basins and orogenic belts in the eastern margin of the basin. The Erqiao Formation is mainly composed of delta sandstone. The provenance of cross bedding restoration is mainly from the East. Sandstone detrital are mainly composed of magmatic detrital and metamorphic detrital. Detrital heavy minerals are mainly composed of zircon, tourmaline, rutile, albite, pyrite, garnet, chromite and anatase. In this paper, we determined the zircon tourmaline chemical composition and U- Pb isotope from sandstone of the Erqiao Formation by means of electron microprobe and LA- ICP- MS, further studied the provenance of the Erqiao Formation, and discussed the evolution of the upper Yangtze basin in Late Triassic. The chemical composition of tourmaline shows that it is mainly composed of magnesium tourmaline and black tourmaline, which comes from granite, meta- sandstone, slate etc. The zircon U- Pb ages show detrital zircons of the Erqiao Formation mainly have five peaks at 2662~2380 Ma, 2077~1688 Ma, 840~722 Ma, 475~412 Ma and 293~246 Ma. The first two age peaks account for the largest proportion, showing the characteristics of multiple provenances. Combined with sandstone detrital composition and tourmaline chemical composition, it is inferred that the provenance is mainly from the Neoproterozoic recycle sedimentary area in Fanjingshan area of the Jiangnan orogenic belt. Some provenances may be provided by Kongling area in the north of Yangtze, and a small amount by the Caledonian pyroclastic rocks, the Indosinian- Hercynian Emeishan basalt and contemporaneous intrusive rocks and tuffs. It shows that the front uplift belt of the upper Yangtze foreland basin continued to move southeast in the Late Triassic, and the Jiangnan orogenic belt became the front uplift belt in the middle and late stage, providing the main provenances for the southeast of the basin.