Thermal-rheological effects induced by crustal magmatic underplating and implications for Emeishan Large Igneous Province

Magmatic underplating plays a critical role in the growth and evolution of the continental crust. Here we employ 2-D numerical simulation to investigate the thermal-rheological effects of magmatic underplating and the influences of magmatic temperature and water content on crustal thickening due to magmatic underplating. Our models are constrained with the available petrological-geochemical and geophysical data from the Emeishan Large Igneous Province (ELIP). We compare the model predictions with the temporal evolution of the surface heat flow in the ELIP, and estimate the potential temperature and initial melting depth of the magmatic underplating beneath the inner zone of the ELIP. The results show that: 1) The dissipation of the thermal perturbation caused by magmatic underplating depends on the initial thickness of magmatic intrusion. For example, it requires similar to 150Myr to dissipate the heat inputted by a large magmatic intrusion (1300 degrees C and 20-km thick), while this time scale reduces to similar to 50Myr for a small-size magmatic intrusion (1300 degrees C and 5-km thick). 2) The magmatic underplating causes the lithospheric bulk strength to decrease significantly at the early stage. Then it restores gradually as the thermal decay proceeds. When the lithosphere returns to thermal equilibrium state again, its strength becomes even stronger than its pre-intrusion value. This indicates that magmatic underplating not only can contribute to crustal thickening, but also can eventually strengthen the lithosphere. 3) Our models also demonstrate that the initial magmatic temperature plays a more influential role than the magmatic water content in crustal thickening. The application of our models to the ELIP suggests that the crustal underplating, as revealed by recent geophysical studies, is likely caused by a large magmatic intrusion originated from a magmatic chamber with potential temperature over 1500 degrees C seated at a depth deeper than 200 km, and it's heat would take more than one hundred Million years to dissipate.