THERMAL, MAGMATIC, AND STRESS EFFECTS OF FLAT SUBDUCTION IN MEXICO AND CHILE: A 2D THERMO-MECHANICAL MODELING STUDY

Flat slabs are expected to affect the thermal, magmatic, and stress status of upper plates and the entire subduction systems. We investigate the implication of flat subduction in Mexico and Chile by using 2D thermo-mechanical models. The Chilean model features a thick and cold continental lithosphere and a relatively dry oceanic lithosphere, resulting in a low magma fraction of peridotite melting. This configuration induces strong compressional stress in the top of the upper plate and subduction interface, indicating strong coupling in Chilean flat subduction system. In contrast, the Mexican model features a thinner and warmer continental lithosphere and a more hydrated oceanic lithosphere, resulting in a continuous volcanic arc with the melting source evolving along the slab. The peridotite is the primary source of the melting before the slab becomes flat. After the slab becomes flat, the mantle wedge is too cold for peridotite melting. The dominant source of the melting shifts to subducted sediment, leading to the formation of adakitic magma. The upper plate does not undergo significant compression or extension process in the model, indicating a weakly-coupled state in Mexican flat subduction system. Our findings provide valuable insights into the distinct thermal and stress responses of the upper plates in these two contrasting flat subduction systems in Mexico and Chile.