Uplift and exhumation events and thermochronological constraints at the end of Triassic in southwestern Ordos Basin

The regional sedimentary hiatus of large sedimentary basins records the important events of basin and tectonic environment evolution, which is an important basis and time scale for basin-range response comparison, and often has significance for tectonic dynamics and petroleum geology study. Ordos Basin is one of the most important large energy basins, located in the western North China Plate. At the end of Triassic, Ordos Basin had suffered its first large-scale sedimentary hiatus and exhumation since the basin was formed in Mesozoic, which significantly reformed the paleogeomorphology of Yanchang Formation in the Middle-Late Triassic, controlled the sedimentary pattern and reservoir distribution in the Early Jurassic, and had important impact on the basin evolution and distribution of mineral resources. Based on geological characteristics and a large number of drilling data, as well as the apatite fission track thermochronological data, this paper focuses on the sedimentary hiatus at the southwest of Ordos Basin to determine the temporal and spatial characteristics of its uplift and denudation, furthermore, it also discusses the geodynamic environment of its development in combination with the regional structural study. The results indicate that the uplift and denudation of this area at the end of Triassic is strong in the southwest and weak in the northeast, and the stratum of Yanchang Formation in the southwest is incomplete in a larger range, with a denudation thickness up to more than 1000m. The sedimentary paleogeomorphology of pre-Jurassic is generally characterized by a highland in the southwest and a low depression in the northeast. The time of uplift starts from 205 ~ 190Ma and last until Middle Jurassic (about 160Ma), with a cooling rate greater than 1°C/Myr. The uplift and denudation events can involve a wider area in southwestern margin of Ordos Basin. It had a good spatio-temporal coupling relationship with the rapid uplift and cooling events occurring in the Qinling orogenic belt at the same period, and it is a response and record to the regional geodynamic environment transformation of the Qinling orogenic belt. This study enriches and develops the influence of tectonic events at the end of Triassic on the North China Craton, and has certain practical significance for the new ideas for further exploration and evaluation of hydrocarbon and coal resources in this area.