Source and sink evolution of a Permian–Triassic rift–drift basin in the southern Central Asian Orogenic Belt: perspectives on sedimentary geochemistry and heavy mineral analysis

Abstract

Abstract How sedimentary processes, climate, diagenesis, and tectonism influence sediment composition during transport from source to sink remains an outstanding question. To evaluate these mechanisms, we collected more than 11,000 heavy minerals and 800 geochemical data from the Junggar Basin for principal component analysis, and heavy mineral assemblages and instability index studies. Multiple geochemical and mineralogical approaches show climatically influenced changes in weathering for the Middle–Late Triassic sedimentary rocks, while compositions of the Pennsylvanian–Early Triassic sedimentary rocks are mainly provenance-controlled. Moreover, a comparison of the Zr/Sc and Th/Sc ratios, chemical index of alteration and weathering index of Parker, together with relatively high stable heavy mineral contents, indicates that the Middle–Late Triassic sedimentary rocks underwent some sedimentary recycling. The diverse proxies show two pronounced source-to-sink system changes in the Bogda Mountains. During the Lopingian–Early Triassic epochs, the appearance of abundant epidote and high instability index suggest a source shift from the Central Tianshan Block to the North Tianshan Orogenic Belt (NTOB), which is interpreted as two pulses of uplift of the NTOB. The integrated techniques also show that the Bogda Mountains contained much epidote and pyrite with high instability index in the Middle–Late Triassic, while the NTOB piedmont had relatively lower unstable heavy mineral assemblages and instability index. We suggest that this change likely reflects the initial uplift of the Bogda Mountains. Although the upsection sediment composition could be influenced by weathering, sedimentary recycling, and diagenesis, multidisciplinary provenance studies can minimize these uncertainties and biases.