Mantle deformation records fossil convergent upwelling at Perm Anomaly

Abstract

How low-velocity anomalies in the lower mantle influence convective flow, and their broader role in mantle dynamics, remain a topic of ongoing debate. One such anomaly, located roughly beneath the Russian city of Perm, is exceptionally well sampled by core-traversing seismic phases. We investigate seismic anisotropy, propagation- and polarization direction-dependent seismic wave speeds caused by deformation, within and around the Perm Anomaly at a sharp lateral resolution. Here we show a quasi-symmetric pattern of strong seismic anisotropy delineating the boundary of the Perm Anomaly, and linear streaks of strong anisotropy pointing towards the boundary. Geodynamic modeling experiments suggest such patterns of anisotropy are signatures of convergent upwelling mantle flow; 'frozen-in' fossilized deformation of ancient origin is a plausible explanation supported by geodynamic modeling. Furthermore, we detect seismic anisotropy within the anomaly indicative of internal deformation, though it is substantially weaker than that observed near the edges.