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Integrated Provenance Analysis of a Complex Orogenic Terrane: Mesozoic Uplift of the Bogda Shan and Inception of the Turpan-Hami Basin, NW China

2005; Society for Sedimentary Geology; Volume: 75; Issue: 2 Linguagem: Inglês

10.2110/jsr.2005.019

1938-3681

Todd J. Greene, Alan R. Carroll, M. A. Wartes, Stephan A. Graham, Joseph L. Wooden,

earthquake and tectonic studies

We employ petrographic and advanced geochemical tech- niques to better document the evolution of the Turpan-Hami basin based on the unique geologic histories of the arc terranes that served as potential sources of Turpan-Hami deposits. First, a provenance study of Permian through Cretaceous sandstone of the Turpan-Hami basin reveals temporal and spatial changes in dominant source ter- ranes that provided detritus to the basin. Volcanic-lithic-rich Upper Permian sandstone (mean Qm 19F18Lt63 ;Q p 7Lvm89Lsm4 ;Q m 48P39K13) followed by more quartzose compositions in Triassic sandstone (mean Qm 41F19Lt40 ;Q p 20Lvm75Lsm5 ;Q m 68P21K11) indicate progressive un- roofing of the extinct northern and central Tian Shan arc terranes to the south of Turpan-Hami. A sharp change to sedimentary-lithic-rich Lower Jurassic sandstone (mean Qm 47F16Lt37 ;Q p 16Lvm42Lsm42; Qm 75P12K13) overlain by a return to volcanic-lithic-rich Middle Ju- rassic sandstone (mean Qm 39F21Lt40 ;Q p 14Lvm51Lsm35 ;Q m 65P21K14) points to the initial uplift and unroofing of the largely andesitic Bogda Shan to the north, which first shed its sedimentary cover as it emerged to become the partition between the Turpan-Hami and southern Jung- gar basins. Second, geochronological, trace-element, and Sm-Nd isotopic varia- tions among granitoids in the late Paleozoic Tian Shan orogenic belt provide a further test of Mesozoic uplift of the Bogda Shan. On the basis of previous models of crustal compositions throughout the South, Central, and North Tian Shan, Bogda Shan, and East and West Jung- gar terranes, we infer that isotopically enriched granitic cobbles (av- erage eNdi 5 20.50, n 5 6) contained in Lower Triassic deposits in the north-central Turpan-Hami basin were derived from the continen- tal crustal Central Tian Shan terrane, south of Turpan-Hami, and not from the more oceanic North Tian Shan, Bogda Shan, and East and West Junggar terranes, north of the Turpan-Hami basin. We therefore infer that the ancestral Bogda Shan had not been uplifted by the Early Triassic, and that prior to this time, a unified Junggar-Turpan-Hami basin existed during Late Permian deposition of extensive lacustrine deposits.