Thermo‐tectonic history of the Northeast Sichuan Basin, Southwest China, using apatite fission‐track analysis, vitrinite reflectance, and basin modelling: Implications for hydrocarbon prospectivity

Abstract

Analysis of apatite fission‐track and vitrinite reflectance combined with 1‐D basin modelling was used to reconstruct the thermo‐tectonic history of the northeast Sichuan Basin, China. The study indicates that the basin has evolved through multi‐phase tectonic regimes involving a series of subsidence and tectonic uplift phases exerting significant control on the thermal history. Heating and cooling processes were largely related to deep burial and intense exhumation, respectively. Exhumation that extended from 122 to 2.5 Ma has resulted in at least 4 km of sedimentary removal. The rate of exhumation and removal (denudation) was found to have reached 58 and 35 m/Myr, respectively. The results show that the denudation magnitude is significantly higher in the eastern part reaching 5.5 km, compared with 2.2 km in the western part of the study area. The fission‐track ages demonstrate the occurrence of three cooling phases: initial‐gradually increasing (~120–70 Ma), stagnant (70–15 Ma), and rapid (15 Ma to present). This suggests that cooling was associated with different compressive thermo‐structural events that began in the mid‐Lower Cretaceous (~122 Ma) marking the subsidence climax period. With the sedimentary section approximating 8‐km thickness by the time of maximum burial, the modelled average maximum temperature and vitrinite reflectivity coefficient reached roughly 232°C, and 3.5% for the Lower Triassic Feixianguan Formation (T1f1), thus indicating the conditions of dry gas generation. The Meso‐Cenozoic thermo‐structural evolution that postdated the onset of hydrocarbon generation has been critical for the evolution of the petroleum play, including the Feixianguan Formation in the marine carbonates of the Early Triassic and the Xujiahe Formation in the non‐marine sandstones of the Upper Triassic. This resulted in the modification of primary hydrocarbon accumulations, mostly in the lower petroleum play, and development of secondary accumulation in the newly formed structural traps in the upper petroleum play. Therefore, accurate thermo‐tectonic history reconstruction is valuable for understanding the geological history and hydrocarbon prospectivity.