Provenance and Tectonic Setting of the Songpan‐Ganzi Complex in the Tibetan Plateau: Insights From the Monte Carlo Unmixing Modeling With Age Spectra and Isotopes

Abstract The triangular Songpan‐Ganzi complex (SGC), the largest turbiditic basin in the Tibetan Plateau, is a key area for understanding the source‐to‐sink process of a trapped basin during the closure of a paleo‐ocean. However, the diversity of age spectra of detrital zircons in this complex was generally neglected in previous study, resulting in hot debates on provenance and tectonic setting of the SGC. Rather than local homogeneity (e.g., depocenters) as previously suggested, at least four categories of age spectra with different age peak associations over the whole SGC can be recognized from the clustering analysis based on our new and previously published detrital zircon data from the SGC. The Monte Carlo unmixing models from four categories of turbidite in the SGC and surrounding terranes/orogens and magmatites reveal that turbidites in the SGC were shaped by the mixing of diverse source combinations with varying degrees. The modeling results were supported by the Hf isotope based on the consistency between the four categories of turbidite and corresponding simulated source associations. Given the diversity of age spectra of turbidites in the whole SGC, previous published paleocurrent data and other geologic facts, we proposed an alternative model in which the internal ocean circulation drove the mixing of different proportions of sources around and transported the mixed sediments to scatter and fill at the scope of the whole SGC during the Mid‐Late Triassic period. This detritus‐filling pattern supports a remnant‐ocean basin model, which provides a feasible solution to the formation of trapped basins in fossil orogens.