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Baddeleyite and Zircon U-Pb Dating of Badu Diabase in the Nanpanjiang Basin and Its Tectonic Significance

W.-J. Xia 1, 2, 3 Q.-R. Yan 2 Z.-J. Ziang 4 L. Xia 2 W. Jiang 2 B. Zhou 2 L. Deng 2
3 Géodynamique - UMR7327
INSU - CNRS - Institut national des sciences de l'Univers, UO - Université d'Orléans : UMR7327, BRGM - Bureau de Recherches Géologiques et Minières (BRGM), ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327 : UMR7327
Abstract : The Nanpanjiang basin is the biggest terrigenous clasitic basin developed on the southwest margin of the South China block. The tectonic setting of the Nanpanjiang Basin during its formation, the onset time and the mechanism of the basin's opening have been long debated. These debates obstruct our understanding on the evolution of the Indochina orogen. Inside the Nanpanjiang basin, in addition to the Triassic deposition, some Paleozoic carbonatites were also outcropped, which developed into faulted blocks of the basement during the basin stretching. Around the Paleozoic carbonate faulted blocks, some stratoid or veined diabase were outcropped. As the initial record of the basin evolution, the diabase is a perfect research target for studying the age and geodynamics of the basin's opening. In this study, the diabase samples were acquired near to Badu Town, Tianlin County, Guangxi, which is in the southeastern part of the Nanpanjiang Basin. The U-Pb dating was conducted with Cameca IMS 1280 on the baddeleyite and zircon concentrated from the diabase samples. The results yielded the weighted mean 206Pb/238U ages of (269.3±4.2) Ma (N=15, MSWD=0.27) and (265.0±2.9) Ma (N=8, MSWD=0.02), respectively. This result demonstrates that the Badu diabase emplaced during the Wordian, Middle Permian (265.1~268.8 Ma), and indicates that the Nanpanjiang Basin was stretching during this period. Besides this magmatic event dated by this study, a later mafic magmatic event continued widely in the Nanpanjiang basin during the Late Permian to the Early Triassic (258~248 Ma). Sedimentologic study suggests that, from the Late Permian to the Early Triassic, the sedimentary environment of the Nanpanjiang basin changed from calci-clastic platform to turbidite fan. All these facts suggest that the Nanpanjiang Basin experienced extension during the Middle Permian to Early Triassic.
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Submitted on : Monday, September 23, 2019 - 9:52:25 AM
Last modification on : Wednesday, October 14, 2020 - 4:12:58 AM

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W.-J. Xia, Q.-R. Yan, Z.-J. Ziang, L. Xia, W. Jiang, et al.. Baddeleyite and Zircon U-Pb Dating of Badu Diabase in the Nanpanjiang Basin and Its Tectonic Significance. Acta Geoscientica Sinica, Science Press, 2019, 40 (2), pp.265-278. ⟨insu-02294050⟩

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