No abstract

[1] The goal of this study is to better constrain anisotropy and mantle flow above and below the Nazca slab from 28 S to 42 S through modeling of shear wave splitting in local S, SKS and SKKS (SK(K)S) phases. Comparisons of local S splitting times and path lengths in the slab, mantle wedge, and upper plate indicate that splitting times for arc and back-arc stations are consistent with anisotropy in the mantle wedge, but long slab paths to fore-arc stations imply that slab anisotropy is also significant. SK(K)S shear wave splitting observations and models for sub-slab anisotropy show that significant anisotropy is present below the slab, and that the orientation of sub-slab anisotropy sometimes differs from anisotropy above the slab. Anisotropy both above the slab and below the slab in the South American subduction zone is consistent with mantle flow that is driven by a combination of entrainment with downgoing slab motion and flow complexity related to variations in slab shape and slab rollback.

To constrain mantle structure that might contribute to the topography of the southern Appalachian Mountains, Pn phases from regional earthquakes recorded in northern Georgia by EarthScope Southeastern Suture of the Appalachian Margin Experiment and Transportable Array stations were used to solve for shallow mantle P wave velocities. Mantle velocities vary laterally, with values of 7.6-7.8 km/s beneath the higher elevations of the Blue Ridge terrane and northwestern flank of the Inner Piedmont terranes and values of 8.3-8.5 km/s farther south where elevation is lower. The zone of low-velocity mantle could represent a source of buoyancy that helps to support the higher elevations, in addition to the root of thickened crust that also exists beneath the mountains.