Controlling And Indication Of The Eruption Of Emeishan Large Igneous Province To The Upper Permian-Mesozoic Source-Sink System In Southwest Sichuan

The Emeishan Large Igneous Province(ELIP)with an age of ～260Ma,plays an important role in understanding the sedimentary processes,environmental changes,and mineralization in the Upper Yangtze region.The palaeogeomorphology of the ELIP has been proved to be a significant sediment source for the southwest China area since its eruption.With the unique zircon crystallization ages,the ELIP turns out to be a useful source tracer to reveal the provenance changes and the related tectonic events.In this study,we focus on the late Permian-Mesozoic strata in the southwest Sichuan Basin and performed sedimentology,petrology and detrital zircon age analyses.By combing with previous studies,the regional source-to-sink system and related tectonic events during the late Permian-Mesozoic in the southwest Sichuan Basin have been well reconstructed in the study.The following conclusions are drawn:(1)The characteristics of sandstone clastic components show that the late Permianearly Triassic sandstone samples are dominated by low-maturity clastic components,with basalt fragments,and quartz content is about 15%.The late Permian clastic grains are dominated by a large amount of basalt fragments,reflecting the provenance from the ELIP.The small amount of glauconite indicates a neritic environment.And the quartz minerals content of sandstone samples from late Triassic to late Cretaceous is about 50%,with minor feldspar and volcanic fragments,indicating that the sediments are mainly cyclic materials.(2)According to the detrital zircon U-Pb chronology,the late Permian sandstone samples yield U-Pb ages of ca 257 Ma in the Xinqiao Town section of Meigu County,while the early Triassic Feixianguan Formation shows age peaks of ～523Ma,～768Ma,～959Ma,and the peak age of ～257Ma disappeared.Since the Late Triassic,the peak age of ～257Ma appear again.The early Triassic Feixianguan Formation in the Laodongcun section of Tianquan County is characterized by a single peak age of～258Ma.The middle Triassic Jialingjiang Formation is characterized by a single peak age of ～833Ma,and the peak age of ～257Ma basically disappears.Sandstone samples from the late Triassic to late Cretaceous yield similar age distributions with peak ages of ～270Ma,～436Ma,～820Ma,～1840Ma,and 2500 Ma.(3)Combined with the characteristics of sandstone detrital components and detrital zircon U-Pb age distribution of Xinqiao Town Section and Laodongcun Section in southwest Sichuan,the provenance of the late Permian strata in the southwest Sichuan Basin can be revealed to be the ELIP.During the early Triassic,samples from the Xinqiao Town section did not exhibit similar zircon ages of the ELIP,while samples from the Laodongcun Section show similar zircon ages of the ELIP.During the middle Triassic,no similar zircon ages of the ELIP are recorded in both sections.Since the late Triassic,the zircon ages of the ELIP can be observed again,indicating that the ELIP has been uplifted and denuded again and fed sediments to the southwest Sichuan Basin.A peak age of ～200Ma can be observed in the samples of the middle Triassic-Mesozoic strata,indicating a new provenance from the Sanjiang Orogenic Belt in the southwest Sichuan Basin.(4)Sedimentary process reconstruction,and provenance analyses suggest that the ELIP has greatly influenced the southwest Sichuan Basin.During the late Permianearly Triassic,the ELIP was an important provenance of the southwest Sichuan Basin.However,from the upper part of the early Triassic to the middle Triassic,the ELIP did not contribute to the deposition of the southwest Sichuan,which may reflect the gradual disappearance of the ancient highland of the ELIP caused by the large-scale denudation and transgression.During the late Triassic to Cretaceous,the ELIP fed sediments to the southwest Sichuan Basin again,indicating the uplift and denudation which can be strongly related to the tectonic events of the Sanjiang Orogenic belt.This also indicates that the Sanjiang Orogenic Belt in southwest China at least started large-scale orogenesis in the late Triassic,and the buried ELIP by late sediments was thrust and uplifted to become the provenance again.