The Wuyu Basin is bounded by the Gangdese Mountains to the north and the Yarlung Tsangpo River to the south, and is a representative basin to study the Cenozoic tectonism of the southern Tibet. The sedimentary strata in the Wuyu Basin include the Paleocene-Eocene Linzizong Group volcanics and the Oligocene Rigongla Formation (Fm.) volcanics, the Miocene lacustrine sediments of the Mangxiang Fm. and Laiqing Fm. volcanics, the late Miocene-Pliocene Wuyu Fm., and the Pleistocene Dazi Fm. Five sandstone samples from the Mangxiang Fm., Wuyu Fm. and Dazi Fm. and one modern Wuyu reiver sand sample were collected for detrital zircon U-Pb dating using the LA-ICP-MS method. Detrital zircon U-Pb ages in the Mangxiang Fm. show a large cluster at 45-80 Ma; those in the Wuyu Fm. show a large cluster at 8-15 Ma and a subsidiary cluster at 45-70 Ma; those in the Dazi Fm. show three large clusters at 45-65 Ma, 105-150 Ma and 167-238 Ma; and those in modern Wuyu river show a large cluster at 8-15 Ma and a subsidiary cluster at 45-65 Ma (Figure 1). Late Cretaceous-early Eocene zircons in all samples are consistent with the most prominent stage of magmatism of the Gangdese Mountains; the 8-15 Ma zircons in the Wuyu Fm. and modern Wuyu river are consistent with the magmatism of the Laiqing Fm.; and the Triassic-Jurassic zircons in the Dazi Fm. are consistent with the magmatism of the central Lhasa terrane. The results of detrital zircon U-Pb ages and sedimentary facies analyses in the Wuyu Basin indicate that the southern Tibetan Plateau suffered multi-stage tectonism-magmatism since the India-Asia collision: (1) Paleogene Linzizong Group-Rigongla Fm. volcanics; (2) tectonism-magmatism at ~15 Ma ended the lacustrine sediments of the Mangxiang Fm. and resulted in volcanism of the Laiqing Fm.; (3) tectonism at ~8 Ma resulted in the volcanic rocks of the Laiqing Fm. becoming one of the main provenances for the overlying Wuyu Fm.; (4) the Wuyu Basin formed braided river and received sediments from the central Lhasa terrane to its north at ~2.5 Ma. The geomorphic pattern of the southern Tibet has gradually formed since the Quaternary.
MENG Qingquan MENG Qingquan
The data includes natural remanence, thermal demagnetization and magnetic susceptibility anisotropy of paleomagnetic samples in altash section in Southwest Tarim. The data is mainly used for magnetic stratigraphy in altash section. Combined with the results of isotopic dating, the chronological framework of altash section is established according to the records of geomagnetic polarity reversal in rocks or sediments and the comparison with standard polarity columns. From 2020 to 2021, members of the research group mainly used drilling rigs to drill paleomagnetic directional samples on the profile at an interval of 1 m (back to the laboratory to be processed into a 2 cm cylinder), and collected directional hand samples in individual areas (back to the laboratory to be processed into a 2 cm * 2 cm * 2 cm cube). The paleomagnetic experimental testing instrument includes two parts: 1 Rock superconducting magnetometer is used to measure the remanence and rock magnetic parameters of paleomagnetic samples; 2. Mfk kappa bridge is used to measure the magnetic susceptibility and magnetic susceptibility anisotropy of geological samples. A total of 298 samples were selected at an interval of 10 m, of which 221 obtained stable remanence, with a success rate of 74%. According to the preliminary paleomagnetic results, the chronological framework of altash section in Southwest Tarim is established; After all the paleomagnetic results are tested, combined with the accurate isotopic age, the high-precision magnetic stratigraphic sequence in Southwest Tarim will be established.
ZHENG Hongbo
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