HR: 0830h
AN: T31F-0901    [PDF]
TI: Revising the Triassic Unroofing History of the Qinling-Dabie Collisional Orogenic Belt: New Detrital Zircon Provenance Data from the Songpan-Ganzi Complex Turbidites, West-Central China
AU: * Weislogel, A L
EM: amyw@stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences 450 Serra Mall Braun Hall, Building 320 Stanford University, Stanford, CA 94305-2115 United States
AU: Graham, S A
EM: graham@pangea.stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences 450 Serra Mall Braun Hall, Building 320 Stanford University, Stanford, CA 94305-2115 United States
AU: Wooden, J L
EM: jwooden@usgs.gov
AF: U.S. Geological Survey, U. S. Geological Survey 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Chang, E Z
EM: edmund@pangea.stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences 450 Serra Mall Braun Hall, Building 320 Stanford University, Stanford, CA 94305-2115 United States
AU: Yang, H
AF: Sichuan Bureau of Geological and Ore Examination, 88 West Jianmenlu, Mianyang City, 621000 China
AB: Approximately 300 new U-Pb SHRIMP ages were obtained from detrital zircons recovered from six samples of the Songpan-Ganzi Complex (SGC), a succession of turbidites over 10 km thick covering an area of 220,000 km2 in the Sichuan province of west-central China. Situated 2000 km along structural strike of the Late Triassic-Late Jurassic Qinling-Dabie orogen, a collisional belt produced by the suturing of the North China block (NCB) with the South China block (SCB), the SGC exists as the prime, yet unproven, candidate for the ultimate sink of Qinling-Dabie derived detritus. Age spectra recorded by two samples from the northeastern zone and two samples from the central zones of the SGC record an initial source of early Paleozoic rocks of the SCB during the late Middle Triassic/early Late Triassic; by the late Late Triassic zircon age spectra are dominated by a 1900 Ma population derived from the NCB. This data represents the most statistically robust zircon provenance data set and contradicts a previous interpretation of another data set of less than 50 U-Pb ages of detrital zircon crystals recovered from two Middle Triassic samples and one Upper Triassic sample of the central zone of the SGC that were interpreted to indicate a provenance shift from the mid-Proterozoic rocks of the NCB to a dominantly 750-850 Ma source derived from rocks of the SCB. Age spectra from samples collected from the western zone of the SGC indicate a dominantly Proterozoic source with no Triassic grains, which is inconsistent with the previous interpretation that the western SGC turbidites were sourced by a contemporaneous volcanic arc. Geobarometric data indicate that ultrahigh pressure metamorphic rocks exposed within the Qinling-Dabie orogen were at or near the surface by 200-230 Ma; however, the SGC as a whole does not contain a large population of Late Triassic zircons that would indicate a Qinling-Dabie orogen source. Instead, the abundant Early and Late Proterozoic grains suggest the SGC records erosion of the SCB, perhaps prior to collision of the SCB with the NCB, followed by unroofing of more than 100 km of NCB crust to expose the Qinling-Dabie UHP rocks as suturing of the NCB and SCB progressed.
DE: 1035 Geochronology
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 9320 Asia
DE: 9609 Mesozoic
SC: Tectonophysics [T]
MN: 2003 Fall Meeting