Detrital record of sediment influx in the Triassic Chuxiong broken foreland basin in southeastern Tibetan Plateau

The Triassic Chuxiong basin represents a classic example of a foreland system that is thought to be associated with the closure of eastern branches of the Paleo-Tethys and subsequent Indosinian collision, yet how it was filled remains poorly understood. Here, we use paleocurrent measurements, sandstone petrology, and detrital zircon U-Pb geochronology to examine the patterns of basin fill. Paleocurrent reconstruction indicates that although some evidence exists for axial transport, the basin was mainly filled transversely with abundant sediment input from the Paleo-Tethyan suture to the west and the Kangdian High to the east. Qualitative determination of sandstone petrology shows that the lithic fragments contained within the Late Triassic strata are not of a uniform mode: volcanic lithics and glass grains are contained within nine Carnian and Rhaetian samples from the western part of the basin, but rarely observed in thirteen samples from the eastern basin. Similarly, detrital zircon U-Pb geochronology of sandstone samples from five sections reveals marked temporal and spatial changes in their age signatures that can be divided into three distinct types. Type-1 age spectra are represented by a narrow unimodal age probability peak at ca. 250 Ma that correlates with the Indosinian-aged arc sources developed along the Jinsha Jiang-Ailao Shan and Changning-Menglian sutures. Type-2 also shows a major zircon age population, but with a diagnostic peak at similar to 780 Ma that corresponds to the Neoproterozoic basement outcropped in Kangdian High. Type-3 is generally characterized by multimodal distribution with major populations of ca. 200-350 Ma, ca. 400-500 Ma, ca. 700-900 Ma, ca. 1750-2000 Ma, and ca. 2350-2600 Ma. Comparing our new data with existing age spectra for the Triassic strata across the western Yangtze and the Indochina blocks demonstrates that the Chuxiong basin was primarily filled by a magmatic arc along the Paleo-Tethyan suture zone during the Carnian, and mostly fed by a reorganized drainage system by incorporating the fold-thrust belt and uplifted foreland basement as source area when the basin expanded eastward through the Norian and Rhaetian as the basin-fill onlaps onto the basement of Kangdian High. The patterns of sediment dispersal of the Triassic Chuxiong basin not only provide a new example of the interplay between orogen and craton sediment input in the peripheral setting but also highlight that the local basement-cored uplifts may dominate the provenance of a broken foreland system during underthrusting.