SUPERCONTINENTAL SCARS: VARIATIONS IN CRUSTAL STRUCTURE OF THE CENTRAL APPALACHIANS AND MID-ATLANTIC CONTINENTAL MARGIN

The surface geology of the eastern United States is extraordinary in its complexity. This complexity reflects a wide range of tectonic processes that have operated in the region over the past billion years, including episodes of subduction and rifting associated with two complete cycles of supercontinent assembly and breakup. A record of these processes is preserved in the geological units and topography we see at the surface today. It is largely unknown, however, how the crust and mantle lithosphere have responded to these tectonic forces over time, and whether and how the geological units preserved at the surface relate to deeper structures. In particular, the persistence of Appalachian topography through time remains a major outstanding problem in the study of landscape evolution. Also, structural variations within the modern Appalachians and rifted margin that were produced during the most recent supercontinent cycle are likely related to pre-existing structures that formed during the first cycle. We present preliminary crustal thickness estimates from receiver function and Bouguer gravity analysis, focusing on selected areas of the Mid-Atlantic Eastern US including: The transition zone between the modern northern and southern Appalachian mountains (Pennsylvania and southern New York); Virginia seismic zone; and the Mid-Atlantic rifted margin (Connecticut through Carolinas). Analysis of this data suggests that the crust is extremely complex and significantly layered, including within the Appalachian Fold and Thrust belt, as well as regions of ~7-10 km of mafic underplate beneath onshore abandoned rift basins associated with breakup of both supercontinents. Additionally, significant variations in crustal thickness appear to be preserved across short lateral distances throughout the Mid-Atlantic region. Overall, analysis of new EarthScope suggests that the crustal structure of the eastern US is significantly complicated, and variations in thickness and composition should be examined more closely for their effects on isostasy and dynamics.