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Abstract: Sandstone petrology, geochemistry, and detrital zircon U–Pb ages and trace elements are integrated to investigate the provenance of Middle Triassic strata from the Youjiang Basin, SW China. Variations in abundance of volcanic lithic fragments and ratios of Th/U, Zr/Sc and Th/Sc suggest that sandstones from the southwestern portion of the basin display less sedimentary recycling and have a lower felsic average source composition than time-equivalent strata from the central, eastern and northern portions of the basin. All sandstones exhibit an overall similar detrital zircon U–Pb age distribution pattern with major age groups at 1200–900Ma, 480–420Ma and 300–240Ma together with some Devonian–Carboniferous and Neoproterozoic grains. Combined with the compiled paleocurrents, the detrital zircon ages suggest multiple-sourced components. Pre-Devonian detrital zircons were likely derived from the recycled late Neoproterozoic–early Paleozoic clastic rocks and from magmatic and metamorphic rocks related to the early Paleozoic orogeny in the southeastern segment of the South China Craton. Late Paleozoic–Triassic detrital zircons together with the presence of well preserved volcanic lithic fragments were considered to indicate first-cycled detrital input from a subduction–collisional mountain belt to the southwest of the craton. These provenance data argue for an Indosinian mountain building event following the closure of a Paleo-Tethys branch ocean rather than for a thermotectonic reactivation event as recently proposed for the Indosinian orogeny in the southwestern China. In association with this orogeny the Youjiang Basin evolved into a foreland basin. [Copyright &y& Elsevier]

Abstract: Whole-rock geochemistry and zircon trace element and U-Pb age data for Late Permian–early Middle Triassic volcanogenic sedimentary rocks in SW China show a change from Large Igneous Province to subduction-related sources immediately before the Permian–Triassic boundary. Zircons from Late Permian samples give identical within-error ages to the adjoining Emeishan Large Igneous Province (LIP). The bulk-rock geochemistry of these Late Permian units shows no depletion in high field strength elements and is similar to the high-titanium basalts of the Emeishan. Six samples of latest Permian–earliest Triassic tuff and two earliest Middle Triassic tuffs samples yield U-Pb zircon ages at of ~252Ma and ~247Ma, respectively. These tuffs and interstratified volcanogenic sedimentary rocks show significant depletion in high field strength elements, akin to magmatic arc-related rocks. Zircons from the tuffs have Nb/Hf, Th/Nb and Hf/Th ratios similar to those from arc/orogenic-related settings and distinct from the zircons from the Late Permian samples which display within-plate/anorogenic characteristics. Our data demonstrate that there is a compositional change of the volcanogenic sediments across the Permian–Triassic boundary in South China. [Copyright &y& Elsevier]