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Mantle Flow Pattern Through the Patagonian Slab Window and Around the South America From Shear Wave Splitting Analysis

Session: Subduction Processes Along Latin America Subduction Zones II

Type: Oral

Date: 4/19/2021

Presentation Time: 02:30 PM Pacific

Description: 

It is well known that the physical state of the mantle (temperature, bulk composition, viscosity) controls the present-day surface topography and the stress distribution within the lithosphere. Locally, the slab geometry along a subduction zone also affects the mantle flow pattern and the mantle's properties. When a spreading ridge intersects a subduction zone, a slab window can be generated, and the mantle’s properties will be then modified. Patagonia is the perfect example of a spreading ridge intersecting 16 Myr ago a subduction zone and opening a window in the slab. The triple junction zone (Nazca, Antarctica, South America) splits a region with a strong seismic and volcanic hazard (northern part) to the southern region relatively quieter. Early studies with a poorly seismic network coverage support the idea of this slab window and its effect on the mantle flow pattern beneath South America. Recently, twenty-six broadband seismic stations were deployed in Southern Patagonia to fill the data gap between latitude 45^oS and 55^oS. From this new set, we analyze core phases SKS and SKKS in the context of shear wave splitting to characterize the azimuthal seismic anisotropy as a proxy of the mantle flow pattern in this region. Shear‐wave splitting parameters have been measured for using the minimum (transverse) energy method within the SplitRacer software package, which constrains the fast-polarization direction (phi) and the delay time (dt). We measure these two parameters and stack measurements to produce our final shear wave splitting datasets for each station. This new shear wave splitting set provides an extended view of the shear wave splitting in southern America and better constrain the mantle flow between the northern and southern Patagonia. This presentation will also compare recent seismic tomography studies (surface and body waves) in the region and discuss the potential effect of the slab on the mantle dynamic and surface expression.

Presenting Author: Walid Ben Mansour

Student Presenter: No

Authors