Sediment provenances of a Mesozoic intracontinental basin enclosed by multiple orogenic belts, Junggar Basin, NW China: insights from detrital ilmenite, Cr-spinel geochemistry, and zircon U–Pb geochronology

Abstract

ABSTRACT The Junggar Basin was an intracontinental basin enclosed by multiple orogenies in the Mesozoic. Unravelling the provenances development in the western Junggar Basin enclosed by the West Junggar Orogenic Belt (WJOB) and Tianshan Orogenic Belt (TSOB) would elucidate the exhumation history of these orogenic belts during the post-orogenic period. The TSOB includes Central Tianshan which includes a continental block with the Precambrian to early Palaeozoic metamorphic basements, while the WJOB includes Palaeozoic accretionary complexes. Given their contrasting geological histories, we use detrital garnets, metamorphic ilmenites, epidotes, and Precambrian zircons to distinguish the TSOB and detrital Cr-spinel to distinguish the WJOB. Combined with sedimentary analysis, palaeocurrents, heavy mineral data, seismic profiles, and zircon U-Pb geochronology, here we reconstruct a four-phase source-to-sink model. During the syn-rift phase, the southern basin was stably fed by the TSOB in the Triassic, evidenced by high Garnet-zircon index and stable single-peak Carboniferous detrital zircon age spectra. During the post-rift sag basin phase, the source-to-sink system experienced a significant change, because detrital zircon age spectra change into multiple peaks. During the transpressional basin phase, the WJOB replaced the TSOB as the dominant provenance in the late Middle Jurassic and the TSOB became the dominant provenance again in the Late Jurassic. Syndepositional volcanic materials provided a large amount of sediments. During the sag basin phase, lake transgression happened and the TSOB provenance could not reach the northern basin. We concluded that the WJOB experienced transpression and obvious denudation in the late Middle Jurassic, and the TSOB uplifted under transpression in the Late Jurassic. The transpression controlled the change of major provenances. The aridification in the Late Jurassic was recorded by the decrease in the Zircon-Tourmaline-Rutile index and the increase in epidotes and magnetites. The humidification in the Early Cretaceous was responded to by lake transgression and sediment recycling.