DECONSTRUCTING THE LATE TRIASSIC SONGPAN-GANZI TURBIDITE COMPLEX, CENTRAL CHINA: COMBINING GEOCHRONOMETRIC AND GEOCHEMICAL PROVENANCE APPROACHES

The Songpan-Ganzi complex of central China is composed of deformed and metamorphosed Middle-Late Triassic turbidites that presently cover >200,000 km² of the eastern Tibet plateau. Detrital zircon-grain U-Pb ages from Ladinian-middle Carnian samples of the northeastern part of the complex exhibit a large component of Paleoproterozoic grains; coeval samples in the east-central area are dominated by Paleozoic zircon grain-ages, and a coeval sample in the southeasternmost area bears significant Paleozoic, Neoproterozoic, and Paleoproterozoic zircon-grain age populations. In contrast, late Carnian to Norian samples across the complex contain significant abundances of Paleoproterozoic zircon grains, with Neoproterozoic zircon grains abundant in most samples. Despite variation in detrital zircon-grain age signatures, mudstone geochemical signatures are consistent throughout the eastern part of the complex and indicate derivation from an evolved, fractionated source rock. Turbidites of the northeastern part of the complex exhibit southwest-directed paleocurrent indicators and are interpreted to have a source area composed of upper crustal crystalline and sedimentary rocks in the Qinling-Dabie collisional orogen to the east. Ladinian to middle Carnian turbidites in the east-central area exhibit south- to southwest-oriented paleocurrent indicators and are interpreted to contain detritus derived primarily from upper crustal Paleozoic rocks of the Qinling-Dabie orogen core; subsequent late Carnian to Norian turbidites record the introduction of a major Precambrian zircon-grain component and a shift to west-directed paleocurrent indicators, signaling a change in drainage pattern and/or basin configuration. Southeasternmost samples exhibit an overall different provenance signature that may reflect input of material derived from the arc systems along the Jinshajiang suture to the south. Provenance of the eastern Songpan-Ganzi complex turbidites differs from turbidites in the northwestern Songpan-Ganzi complex/Bayan Har region, which reportedly exhibit geochemical signatures consistent with an East Kunlun arc/orogen source. Altogether, the Songpan-Ganzi complex may preserve up to four separate depositional elements that were amalgamated through basin closure and collapse.