Implications of geochemical and gravity data for the nature of strata beneath the Blue Ridge-Piedmont thrust sheet, USA

The nature of the rock beneath the Blue Ridge-Piedmont (BRP) decollement is inferred from a combined geochemical and geophysical study of the Grandfather Mountain window (GMW). Gravity modeling and geochemistry show the GMW is probably underlain by a duplex of rift-related rocks and crystalline basement, rather than a duplex composed of carbonate rocks. Geochemical results suggest that some of the rocks beneath the present day GMW were near peak metamorphic temperatures at ≈ 300 Ma. This age for peak temperatures plus structural relations in the GMW are broadly consistent with the rocks and age of peak temperatures in the Pine Mountain terrane, where the BRP decollement is exposed. Comparison of the gravity profiles for the GMW with other BRP structural culminations suggest that they, too, are underlain by similar rocks. This model of a duplex of rift-related rocks and crystalline basement implies ≥ 40 km less shortening for the Southern Appalachians than the carbonate duplesx model.