Numerical simulation study on the thermal effect of Emeishan basaltic magma in the Sichuan Basin

Sichuan Basin is an important petroliferous basin in China, of which the southwest is located in the outer zone of the Emeishan large igneous province. The influence of Permian Emeishan basaltic magma on the thermal history of Sichuan Basin and the thermal evolution of hydrocarbon source rocks has always been of great concern. In recent years, paleothermometric results from the basin have revealed the presence of high paleo-heat flow (75 similar to 85 mW center dot m(-2)), and even ultra-high paleo-heat flow (97-414 mW center dot m(-2)) in some parts of the basin during the Permian, which are thought to be related to the thermal effect of Emeishan basaltic magma. In order to understand the genetic mechanism of the high- and ultra-high paleo-heat flow and the thermal effect of basaltic magma overflowing to the surface on hydrocarbon source rocks and the strata of Permian and below, the thermal effect of Permian Emeishan basaltic magma has been simulated by two-dimensional finite element method, and the following conclusions have been drawn: (1) The disturbance of high-temperature mantle plume head at the bottom of the lithosphere and the high-temperature basaltic magma extruded into the base of the crust disturbed the surface heat flow less than 5 mW center dot m(-2) and 20 mW center dot m(-2), respectively, in a short time (within 4 Ma), neither of which can explain the Permian abnormal paleo-heat flow in the Sichuan Basin. (2) The paleo-heat flow is related to the magma intruded into the interior of the crust. Magma of different forms at the depth of 7 '17 km may cause the formation of high or ultra-high paleo-heat flow. The thickness of the horizontal magma chamber causing the ultra-high paleo-heat flow is 2 similar to 10 km, and the surface of the chamber is between 6 similar to 12 km from the surface. (3) The thicker the overlying magma and the shallower the underlying stratum, the greater the thermal disturbance of the magma to the stratum, and the greater the impact on the hydrocarbon source rocks. For example, when the overlying magma is 300 m thick, the maximum temperature rise caused in the strata at depths of 300 m (Permian), 800 m (Ordovician), 1250 m (Cambrian) and 2000 m (Sinian) is 241 degrees C, 77 degrees C, 40 degrees C and 19 degrees C, respectively, and the time required is 2100, 6100, 11700 and 25600 years. (4) The existence of phase change heat cannot be ignored for the Permian and Ordovician strata, for example, the phase change heat generated by 300 m thick magma can increase the temperature of the Permian strata by up to 55 degrees C.