The Alleghanian Southern Appalachian Piedmont: A transpressional model

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Abstract
Alleghanian dextral transpression produced multiple strike‐slip shear zones forming a contractional mega‐duplex in the central and southern Appalachian Piedmont. Structural upwelling along the zones is identifiable as crustal arching on seismic reflection profiles that roughly corresponds to the Piedmont gravity high. The structural upwelling coincides both temporally and spatially with areas of peak Alleghanian plutonism and metamorphism. The compositionally bimodal plutons generally occur in or around the fault zones and are isotopically primitive. Geobarometry of cognate xenocryst inclusions of coexisting plagioclase and pyroxene from a granitoid indicates 8–11 kbar or 31‐ to 42.5‐km depth to proposed source region. This depth roughly corresponds to the pre‐erosional location of multiple reflections beneath the arches on seismic profiles that are interpreted as the Moho. The granitoids are proposed to have formed by partial melting of the lowermost crust through heat from mafic intrusions and decompression resulting from crustal arching beneath the strike‐slip faults. The granitoids ascended along the strike‐slip faults and were emplaced in or near them. The crustal arching and melting processes appear to be important mechanisms in the development of strike‐slip orogens.