Abstract:

The east Qinling Orogen had experienced intracontinental orogenic tectonics since the Late Triassic, which formed a series of intermountain basins. The intracontinental evolution involved mainly intensive uplifting and magmatism. We took the Luonan and Shanyang basins in the east Qinling as a case study to analyze the sedimentary filling characteristics, to determine the phases of deformation on stratigraphic structures, and to constrain the Mesozoic-Cenozoic intracontinental evolution of the east Qinling Orogen. The results show that: (1) In Late Cretaceous,major faults of the Luonan and Shanyang basins were subjected to N-S-directed sinistral transtensional movement. Therefore, the basin basement had been activated via the N-S-trending fault depression. Intrusions in the detrital provenance region had been strongly uplifted, and then denudated and cooled, and the detritus were transported to the nearby basins. Various sedimentary systems (fan delta, lake and alluvial fan)were developed in the basins.(2)During Paleocene to Oligocene, sedimentation in the basins gradually waned. The deep faults had controlled the basinal development, as supported by structural evidence and apatite fission-track calculation results.Transtentional tectonics continued to wane, and we proposed that the Luonan and Shanyang basins may have been affected by non-E-W-directed compression, which suppressed the transtentional movement.

Key words: east Qinling orogenic belt, intermontane basin, sedimentary filling characteristic, apatite fission track, tectonic deformation