Triassic temporal and spatial migration of the provenance along the South Ordos Basin: Insights into the tectonic evolution of Eastern Palaeo-Tethys Ocean

Abstract

Clarifying the role of mountain-building processes in the filling history of large hinterland basins is an essential aspect of basin–mountain system research. We consider the case of the Triassic South Ordos Basin (SOB) to clarify these points. Located in the south-western North China Block (NCB), the SOB which preserves the most complete Triassic deposition on the north of the Qinling Orogenic Belt (QB) is crucial for understanding the detailed tectonic processes of the QB. Sedimentological, petrological and zircon U–Pb geochronological signatures from the three parts (eastern, central and western) in the SOB indicate that the sediment source migrated both temporally and spatially. Stratigraphic correlation identified two fluvial progradational episodes from south to north in the fluvial–deltaic–lacustrine sedimentary system, one in the eastern SOB and the other in the central SOB. The Late Triassic detrital zircons in the central SOB with distinguishing Neoproterozoic ages were derived from the southern margin of the NCB and the QB. The western SOB exhibited the sediment source shifted from pre-Triassic North Qilian Belt sedimentary cover to basement from the Middle-to-Late Triassic based on a zircon age transition from ca. 2000 to ca. 430 Ma. Late Triassic sediment sources also included the southern margin of the NCB and the QB. Differing provenances from east to west were also confirmed using thin section and heavy mineral analyses. Regional comparisons of zircon age distributions in the eastern SOB with published data indicate that detritus from the QB was first transported to the eastern SOB and then to the central and western SOB. Spatiotemporal changes in the sediment source and sedimentary filling transitions in the three parts of the SOB suggest that the QB underwent asynchronous uplift that began in the east during the Early Triassic and propagated westward, reaching its maximum extent in the early Late Triassic.