A study on the late Indosinian tectonic activity of the south part of Longmenshan: constraints from structural analyses and detrital zircon chronology

The Indosinian tectonic event played an important role in the formation and evolution of the Longmenshan thrust belt. In order to depict the structural characteristic of the southern section of the Longmenshan thrust belt during the late Indosinian epoch, integration of structural analysis and forward modeling of seismic section and detrital zircon U-Pb chronology analyses from the piedmont belt are used in this study. The results show that, the provenance of the syntectonic sediments from the southern section of the Longmenshan thrust belt was affinity to the Songpan-Ganzi block, thus most likely from the Qinling Orogenic Belt and the recycling of the folded Middle to Lower Triassic strata of Songpan-Ganzi block. The balanced restoration of the seismic section reveals a. 1.7 km shortening at the southern section of the Longmenshan thrust belt, which is weaker than that of middle and north part of Longmenshan thrust belt. Combined with the regional geological data, the tectonic activity of Longmenshan thrust belt during Indosinian was migrated from north to south, thus the piedmont zone of southern section of the Longmenshan thrust belt can receive material from the recycled Middle to Lower Triassic of Songpan-Ganzi block.