Detrital zircon U-Pb geochronological and depositional records of the Mesozoic-Cenozoic profile in the southern Junggar Basin, northwest China, and their responses to basin-range tectonic evolution

For the Mesozoic and Cenozoic outcrop profile in the southern Junggar Basin(northern piedmont of Tianshan), northwest China, four sandstone samples were chosen, and their detrital zircon U-Pb isotopes were measured by LA-ICP-MS method. Based on geochronology, provenance and tectonic attribute analysis of the detrital zircons, this research further explores sedimentary crust evolution and its geodynamic mechanism of the Tianshan and adjacent basins. The paper shows that the Middle Jurassic detrital zircons in the southern Junggar Basin are characterized by relatively wide and complex U-Pb ages between 160 Ma and 490 Ma: including one main age peak in 310~260 Ma and five minor age peaks in 180~160 Ma, 240~210 Ma, 370~340 Ma, 450~390 Ma and 490~460 Ma, respectively. The Upper Jurassic detrital zircon U-Pb ages distribute in relatively narrow range of 400~250 Ma: minor age peaks in 340~315 Ma beside one main age peak in 310~260 Ma. The Upper Cretaceous-Paleogene detrital zircon U-Pb ages tend to single peak, that is, ranging in 310~260 Ma. The above evidences illustrate four phases to basin-range tectonic evolution existed in the study area. Stable and weak tectonic activity developed in the Middle-Late Triassic-Middle Jurassic period, with main watershed occurred in the southern Tianshan. Regional and whole uplift became evident in the Late Jurassic-Early Cretaceous period, with main watershed north migrating in the Tianshan, which mostly resulted from long-distance effect of the Eurasia-Lhasa collision event. Following to relatively weakening tectonic activity in the Late Cretaceous-Paleogene period, the most intensive uplift of Tianshan area occurred in Neogene, which gradually resulted in distinctive watershed systems in the north and south Tianshan, respectively. Therefore, the southern Junggar Basin began to accept relatively single provenance type from the north Tianshan after Early Cretaceous, and this provenance constitution for the southern Jungar Basin-fill reserved up to the present in spite of the Neogene intensive uplift of Tianshan responsive for the Eurasia-India collision event.