Latest Paleozoic-Early Mesozoic basin-range interactions in South Tian Shan (northwest China) and their tectonic significance: Constraints from detrital zircon U-Pb ages
Résumé
Since the Late Cenozoic, the Tian Shan area, as for most ranges in continental Asia is rejuvenated by the far-field effects of the India-Asia collision. However, the tectonic processes that affected the area prior to the Cenozoic are still poorly known, especially in the South Tian Shan block. An extensive record of this earlier tectonic history is provided by the thick Paleozoic to Mesozoic sedimentary sequences preserved in the Kapushaliang and Heiyingshan sections in southern Tian Shan. U-Pb (LA-ICP-MS) dating of detrital zircons from eight sandstone samples from these two close sections ranging in age from latest Paleozoic to Early Mesozoic is used to investigate changes in sediment provenance through time and to correlate them with major tectonic phases in the range. The results show that the detrital zircons are mostly magmatic in origin, with some minor metamorphic input. The U-Pb detrital zircon ages range widely from 224 to 3320 Ma and can be statistically divided into four main groups: 224-250 Ma (4%), 251-380 Ma (40%), 380-520 Ma (35%) and 545-3320 Ma (21%). Data analysis associated to already published sedimentary and geochronology information indicate that the zircons were largely derived from the Tian Shan area to the north since the Permian initiation of the basin. From latest Paleozoic to Early Mesozoic, the sediment provenance and basin-range pattern evolution of South Tian Shan can be generally divided into two stages: (1) during Early Permian, the South Tian Shan basin was in a half-graben most probably post-orogenic extensional context. (2) From Late Permian to Early Jurassic times, the South Tian Shan became a passively subsiding basin, with a geographically wider source area characterized by a relatively low topography.