Arc migration driven by subduction dynamics: a possible origin for the Chon Aike magmatic province

The spatial-temporal evolution of volcanic arcs provides valuable insights into the deep melting processes occurring in the mantle wedge. The dehydration of the subducting slab is key because these fluids directly affect the melting temperatures of the mantle wedge. Fluids in this region (partial melts and released fluids from the slab) migrate to the corner of the wedge, where pressure/temperature conditions are optimal for magma production. Changes in the locus of the volcanic arc can be thus related to the position or changes in the physicochemical properties of the mantle wedge at depths, which is drastically dependent on subduction dynamics in time. The dip of the subducting slab is one of the key factors affecting the relative location of the mantle wedge, which can migrate the volcanic arc several hundreds of kilometers into the continent during flat slabs periods. However, the transition to a normal subduction angle or even processes such as slab break-off will migrate the mantle wedge, and the volcanic arc, to the trench and potentially generating large magmatic provinces in the lifespan of an active margin.

The scope of this preliminary study is to track the location of the magmatic arc in time driven by different subduction styles (e.g., low/high angle subduction, slab break-off) and the generation of magmatic provinces in the continent. We conducted a series of 2D geodynamics models using the code I2ELVIS feeded with ad hoc thermodynamic pseudosection modelling with the Perple_X software, to reproduce different subduction angles and the transition between them. The timings and mechanisms of the arc migration is applied to the well-documented exposure of Jurassic igneous rocks along the Antarctic Peninsula and Patagonia in the Chon Aike magmatic province. Recent debate postulates an active margin origin of these rocks, which is supported by geochemical signatures of typical slab-dehydration reactions and a mixed magmatic source that resided in the continental crust. Even though, the subduction dynamics are not constrained, the location and age of these rocks suggest several episodes of arc migration during the Jurassic, making this an exceptional study case to understanding the mechanisms of arc migration and the role of subduction dynamics.

Preliminary results of our modelling tracked the position of the mantle wedge by the presence of partial melts and the maximum depth of dehydration of the subducting slab. Explored scenarios consisted on periods of flat slab subduction triggered by the subduction of aseismic ridges and the return to a normal subduction. During the flat slab period, we also tested the generation of slab break-off, which induced local mantle upwelling and melting. Finally, we expect to reproduce the magmatic history of Antarctic Peninsula and Patagonia in the Jurassic to support the active margin hypothesis for the generation of the Chon Aike magmatic province.