Meso-Cenozoic tectonothermal evolution of Ordos basin, central China: Insights from newly acquired vitrinite reflectance data and a revision of existing paleothermal indicator data

Thermal history reconstruction using paleogeothermal indicators, including vitrinite reflectance (Ro) and apatite fission track (AFT) dating in the Ordos basin indicates that the lower subsection, consisting of the Paleozoic to Middle Triassic sediments, reached its maximum paleotemperatures at the end of the Middle Triassic (T2) and experienced a paleogeothermal gradient of 42–63 °C/km with a mean of 49 ± 9 °C/km, while the upper subsection from the Late Triassic to Middle Jurassic, experienced its maximum paleotemperatures at the beginning of Late Jurassic (J3) and a paleogeothermal gradient of 25–39 °C/km with a mean of 31 ± 6 °C/km. Therefore, at least two heating events are recorded in the Ordos basin since the Mesozoic: the first and most intensive in Middle Triassic as recorded by the lower subsection, the other is a moderate Jurassic thermal event as recorded by the upper subsection. These heating events were followed by a Cenozoic rapid cooling starting at about 21 Ma. In the regional geodynamic context, the Triassic thermal event might be ascribed to hydrothermal activity related to the Triassic collision between the North China Block (NCB) and the South China Block (SCB); the Jurassic thermal event to the Pacific subduction and the Cenozoic rapid cooling event to the Indo-Asian collision, respectively.