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

AVILA, P.; DÁVILA, F.M.

JOURNAL OF GEODYNAMICS

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2020

0264-3707

The southernmost South America has been affected by the subduction of a oceanic seismic ridge, which began to subduct below southern Patagonia at ~14 Ma. This led to the formation of an 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 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, mainly before and after the slab windows formation. This allowed us to estimate the isostatic and dynamic adjustment over time and its 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 topographic, 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 conclusive question on the connection slab windows and asthenospheric upwelling flows with surface uplifting.