HR: 1340h
AN: T23D-1638    [Abstracts]
TI: U-Pb Detrital Zircon Geochronology and Implications: the Mesozoic southern Ordos Basin, North Central China
AU: * Xie, X
EM: xiangyang@utig,ig.utexas.edu
AF: Institue for Geophysics, University of Texas at Austin 10100 Burnet Rd., Bldg. 196, Austin, TX 78758, United States
AU: * Xie, X
EM: xiangyang@utig,ig.utexas.edu
AF: Department of Geology and Geophysics, University of Wyoming 1000 E. University Ave., Laramie, WY 82071, United States
AU: Heller, P L
EM: heller@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming 1000 E. University Ave., Laramie, WY 82071, United States
AU: Chamberlain, K R
EM: kchamber@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming 1000 E. University Ave., Laramie, WY 82071, United States
AB: Two deformation belts — the Qinling orogenic belt (QOB) to the south and the Western Liupanshan thrust belt (WLTB) to the west, including the Qilian-Qaidam terrane (QQT) — control the evolution of the southern Ordos Basin during early Mesozoic time. U-Pb detrital zircon geochronology is used to identify provenance, reconstruct paleogeography, and document the relative timing of basin margin deformation. Two correlated strata same age samples of the Middle to Late Triassic Yanchang Fm. were collected from the southern and southwestern basin margin respectively. In total 258 zircon grains were analyzed using LA-ICP-MS. Three major age populations — 240–490 Ma, 1.8-2.0 Ga, and 2.2-2.8 Ga — characterize the detrital zircon grains of the Yanchang Fm. Regional geochronology studies show that the two oldest age groups match ages of basement rocks found in the underlying North China block. The younger age group can be subdivided into three distinctive groups: 240-300 Ma, 300-400, and 400-490 Ma. The youngest age group matches ages exposed to the west in the QQT, whereas the other two match grains from southern QOB source. In all samples detrital zircon from the WLTB source area overwhelms the QOB source, regardless of its proximity to either basin margin. This result suggests that either the source rock with the youngest zircon grains (e.g. 240- 490 Ma) from the QOB to the south have been eroded away and no longer existed, or simply the QOB, even during deformation, was never the dominant source of detrital zircon to the southern Ordos Basin. Probably some drainage systems far from the west combine with some local tributary systems from the south control the sedimentation in the south Ordos Basin during the middle to Late Triassic time. This is surprising in that most studies suggest that the QOB was a longer lived and more dominant tectonic feature in this part of China during early Mesozoic time. Furthermore, it also indicates that: 1) deformation in the QOB and WLTB began in Middle Triassic time in this area; and 2) the southern source area barely contributed sediment by Late Triassic time.
DE: 8103 Continental cratons
DE: 8110 Continental tectonics: general (0905)
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: 2007 Fall Meeting