Thesis defense of Carlos Fernández-García

Deformation processes of lateral slab tearing. Contributions from analogue modelling and perspectives for the Mediterranean tectonics

Abstract

Slab breakoff is a tectonic model that has been proposed to explain geological and geophysical observations such as: exhumation of metamorphic rocks, magmatism or regional uplift. This manuscript presents the results from four-dimensional (4D, space and time) analogue experiments of slab breakoff. Different configurations for the subducting plate and the orientation of the oceanic-continental transition (OCT) have been tested over a hundred of experiments. In scenarios where the OCT is parallel to the trench, breakoff occurs between 250-280 km depth, while in opposite scenarios, it occurs on a larger range from 160 to 345 km. The timing of breakoff may also vary accordingly to the initial geometry of the subduction zone: from almost instantaneous when the OCT is parallel to the trench, to 8.6-10.6 Ma after onset of continental subduction for other geometries. I investigated the impact of slab breakoff on subduction along oceanic basins bounded by STEP faults and OCT has also been investigated. When the interface is weak (STEP faults scenario) there is a significant increase in the trench retreat in the model that presents a long oceanic corridor. According to the experiments, the evolution of the topographic signal during breakoff is determined by eduction of continental lithosphere, gradual isostatic adjustments during breakoff, and mantle upwelling. With no breakoff or continental subduction, no topographic variations are seen at the surface. Finally, in the models related to subduction along oceanic basins, the trench retreat velocity becomes almost null when the continental positively buoyant material subducts along the embayment margins, highliting mantle deformation processes. I discussed the possible implications of these results for natural subduction zones, in particular for the Western Mediterranean.