Lithospheric thinning and dynamic uplift effects during slab window formation, southern Patagonia (45˚-55˚ S)

ÁVILA, PILAR; DÁVILA, FEDERICO M.

JOURNAL OF GEODYNAMICS

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 133

0264-3707

The southernmost South America has been affected by the subduction of an oceanic seismic ridge, which began to subduct below southern Patagonia at∼14 Ma. This scenario led to the formation of a slab window, which is still active and where hot buoyant asthenospheric mantle produced thermal anomalies and modifications in the lithospheric thicknesses. Meanwhile, from the Patagonian Andes to the Atlantic coast, an outstanding regional surface uplift took place, conducting to a moderated-elevation plateau formation. In this work we analyzed the causes of this long-wavelength surface elevation change using residual topography and uplift rate calculations, considering paleo-lithospheric states. We achieved this considering that the study area underwent a lithospheric thickness changes through time, before and after the slab window formation. This allowed us to estimate the isostatic and dynamic adjustment over time and their influences on the surface elevation changes. These rates were compared with geological and stratigraphic observations derived from a key elevation marker bed: The modern altitudes of Oligo-Miocene marine strata top, originally deposited close or below sea level, and placed at Present at hundreds of meters above sea level. Our residual topography calculations, that result from comparing isostatic and observed topography, indicates the dynamic topography contribution in the study region was very minor (if so) to null. The isostatic uplift, in turn, shows a remarkable fitting with the reconstruction of marine marker bed, suggesting a causative relationship. We can assert that Patagonian lithospheric thinning, particularly of the lithospheric mantle, by slab window formation, would have been enough to reproduce the modern elevations and surface uplift across the plateau from the Miocene to Present day. Our work opens a question on the model that connect slab windows, asthenospheric upwelling flows with surface uplifting. However, as shown by recent works, lithospheric changes might trigger small convection cells, which might produce local and small dynamic topography