New long period magnetotelluric data across the southeastern Appalachians image deep crustal and upper mantle relics of prior orogenic events. Two-dimensional inversions of tensor decomposed impedances and magnetic transfer functions show: (1) Beneath the Appalachian mountains there is a sub-horizontal conductor at 15 - 20~km depth which dips to the southeast at the surface trace of the Brevard fault. (2) At the location of the Central Piedmont suture, there is a crustal conductor which dips towards the southeast, interpreted as a structure related to the Acadian suture. (3) Upper mantle conductors were found at 80 km depth northwest of the Blue Ridge and at 140 km depth southeast of the Eastern Piedmont. Between these, there is a northwest-dipping resistive gap, possibly representing the remnant structure of the Alleghanian collision.
(a) Conventional geologic section, (b) distribution of static shift, (c) final resistivity model, (d) simplified interpretation of the model