SKS Splitting and Upper Mantle Anisotropy Beneath the Southern New England Appalachians: Constraints From the Dense SEISConn Array

Abstract

AbstractThe geology of southern New England reflects subduction and terrane accretion during the Appalachian Orogeny and rifting during the breakup of Pangea. The presence of a low‐velocity seismic anomaly in the upper mantle beneath New England suggests the possible presence of vertical mantle flow (upwelling). It remains poorly understood how the lithosphere beneath southern New England was deformed by past tectonic events; furthermore, the details of the present‐day mantle flow field remain elusive. Observations of seismic anisotropy have the potential to constrain both past and present upper mantle deformation. Here, we present SK(K)S splitting observations at stations of the Seismic Experiment for Imaging Structure Beneath Connecticut array, a deployment of 15 broadband seismic stations across northern Connecticut. This linear array crosses a number of major terrane boundaries and traverses the Mesozoic Hartford Rift Basin in its central portion; its dense station spacing affords an opportunity to probe anisotropic structure on length scales that are relevant for the complex geology of southern New England. We find evidence for average fast splitting directions that are generally parallel to the absolute motion of the North American Plate, but in a few specific regions they are aligned with local tectonic boundaries. We document a striking decrease in splitting delay times (measured at low frequencies) from 0.9 s at the western end of the array to 0.2 s at the eastern end. We discuss several scenarios that might explain this observation, and explore the implications of our measurements for both present‐day mantle flow and past lithospheric deformation beneath southern New England.