THE PROVENANCE OF EARLY CAMBRIAN SEQUENCES IN THE TARIM BASIN, NW CHINA: EVIDENCES FROM THE U-PB GEOCHRONOLOGY OF DETRITAL ZIRCON AND MONAZITE OF DEEP WELL SAMPLES

Abstract: The Tarim Basin is located in western China and is the largest petroleum-bearing sedimentary basin in China. Its ultra-long tectonic evolution history can be divided into the Proterozoic paleotrough marine phase, the Paleozoic platform stable development stage and the development stage of platform fault block in Mesozoic and Cenozoic, accompanied by multiple periods of magmatic events. Since the thickness of the sedimentary sequence in the Tarim Basin is greater than 10km, the burial depth of the Early Paleozoic strata in the basin is generally deep, and there are few available samples, resulting in a relatively weak study on the evolution. In order to understand the Cambrian source to sink and paleogeographical features and Precambrian basement nature of the Tarim Basin, we collected the Cambrian samples of the WNCN1 Well (3167m) in the NW margin and the ZH1 Well (7460m) in the Tazhong area, and then conducted a spatial comparison of different regions. U-Pb dating was carried out by LA-ICPMS on the detrital zircon (hardness 7.5~8) of stronger refractory nature and the less resistant monazite (hardness 5~5.5) in both samples. Combined with the geochronological achievements of the potential source area and surrounding orogenic belts, our results show that: Zircon (~1950Ma) and monazite (~1930Ma) from the WNCN1 have a similar U-Pb age spectrum, and the major source areas are the Wensu uplift in the west, the South Tianshan orogenic belt in the north, and the continental erosion source area in the Tabei uplift, which belongs to the near-source mixture source area. Compared with monazite (~1920Ma), the zircon (~750Ma and ~1850Ma) in the samples from the ZH1 has one more Neoproterozoic age peak. Therefore it is speculated that the Neoproterozoic zircon components have undergone recycling, and these components from the Iron Creek area and the Altyn area. Besides that, the Paleoproterozoic peaks (1.8~1.9 Ga) present in both detrital zircon and monazite may represent the Paleoproterozoic basement under the near-source Tazhong uplift. This research shows significant differences in provenance and paleogeographical setting between the two regions. At the same time it verifies that the combined study of detrital zircon and monazite can identify recycled provenances.