Provenance study of the Xujiahe Formation in northern Sichuan Basin and its implications for the source to sink systems during the Late Triassic, China

Numerous studies have investigated the provenance of the Upper Triassic Xujiahe Formation, but there are still controversies concerning the provenance of this formation in the northern part of the Sichuan Basin. This research combines sandstone grain point-counting, heavy mineral assemblage analysis, and electron microprobe measurements of heavy mineral compositions to examine the provenance of the Xujiahe Formation in the Guangyuan, Wangcang, Nanjiang, and Tuhuang sections located in the northern part of the Sichuan Basin. The results show that the sandstone composition, unstable heavy mineral type and garnet composition are similar for samples from Guangyuan, Wangcang, Nanjiang sections, characterized by abundance of garnet and chromian spinel. Garnet types are predominantly almandine and pyrope, which are mainly derived from amphibolite-to granulite-facies metasedimentary rocks. In contrast, samples from the Tuhuang section are characterized by lack of chromian spinel and existence of pyroxene, with garnet of almandine type and derivation from intermediate-acidic magmatic rocks, and with pyroxene of augite and diopside types and derivation from alkaline-subalkaline volcanic arc basalt magma or subalkaline oceanic floor basalt magma. Comprehensive analysis shows that the provenance of the Guangyuan, Wangcang, and Nanjiang sections includes Triassic turbidites from the Songpan-Ganzi Fold Belt and west Qinling Orogen and Paleozoic strata in the Longmenshan thrust belt. The Tuhuang section, by contrast, receive sediment from the North China Block and Qinling Orogen. These findings, in combination with previous provenance and sedimentary studies, support the existence of two distinct source to sink systems in the northern part of the Sichuan Basin during the Late Triassic. The provenance study of the Xujiahe Formation also demonstrates the limitation of the detrital zircon U–Pb method and underscores the importance of the combination of multiple provenance analysis methods for the effective discrimination of complex source to sink systems.