MODIFICATION OF CRUST AND MANTLE LITHOSPHERE BENEATH THE SOUTHERN PART OF THE EASTERN NORTH AMERICAN PASSIVE MARGIN (Invited Presentation)

The eastern North American margin (ENAM) represents an iconic passive margin, which was developed by a sequence of rifting events during the breakup of supercontinent Pangaea at ~230 Ma. Rifting-associated magmatic events have been observed, along with apparent magnetic and gravity anomalies. Thus, the ENAM serves as a superb location to studythe impact of syn- and post-rifting tectonism on lithospheric modification. Using an advanced seismic imaging method, we construct a detailed crustal and upper mantle model beneath the southeastern United States. We identify a clear change in the crustal thickness over a transitional zone from ocean to continent. Beneath the transitional crust, the upper mantle has a relatively lower seismic speed in comparison with its surroundings. We also discover a low-velocity column within the upper mantle beneath West Virginia where two volcanos are located. We propose that the transitional oceanic-continental crust was formed due to crustal extension during rifting. The mantle lithosphere underlying the transitional crust could have been partially melted or thermally and chemically altered after the rifting process. The rising flow of asthenosphere (a weak layer beneath the rigid lithosphere) might result in partial melting of the upper mantle beneath the continental interior, which can explain the presence of volcanoesin West Virginia.