<p>Understanding how ancient mantle plume residues modify lithospheric structure and influence tectonic deformation remains challenging, especially in plume-peripheral regions where basalts are not exposed at the surface. Here, we present magnetotelluric imaging across the Huayingshan Fault in the outer zone of the Permian Emeishan large igneous province, China. The resistivity model reveals a vertically extensive high-resistivity structure beneath the fault that coincides with high seismic velocities and high density, and is most consistently interpreted as the crystallized product of mantle-derived basaltic melts from the Emeishan plume. We use upper-mantle-scale geodynamic simulations to examine how plume-driven melting and plume-derived material interact with lithospheric heterogeneity. While these models do not explicitly simulate small-scale melt extraction or crustal emplacement, they suggest that pre-existing lithospheric heterogeneity can shape the lateral redistribution of plume-derived material. We infer that residual plume material crystallized in situ within the fault zone formed a low-permeability, mechanically strong lithospheric barrier that may impede or redirect crustal-fluid migration. This plume-reinforced lithosphere may promote stress localization on its northwestern side, where present-day earthquakes are preferentially clustered. Together, these results suggest that plume-modified lithosphere can preserve a long-lived structural imprint that modulates crustal-fluid migration and continental deformation.</p>