Anatomy of a Passive Continental Margin: Deep Structure of Transitional Crust and the Source of the East Coast MagneticAnomaly

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Numerous MCS, magnetic and gravity surveys have concentrated on determining fundamental structural features of the US East Coast continental margin. Unfortunately, firm constraints on the nature of rifting, tectonic subsidence, thinning and early volcanism have all been hampered by the difficulty of imaging the deepest "rift-stage" crust that underlies several margin- parallel basins. A recent MCS program profiled the Carolina Trough, and 8 OBHs were deployed along two margin-perpendicular lines. Drs. Holbrook and Purdy have begun processing these data. The present award will allow them to continue full wavefield imaging and 2D ray trace modeling that will improve velocity structure and imaging of the vertical-incidence MCS profiles. In addition, support is provided to prepare for an additional series of OBH deployments along a similar margin transect offshore Chesapeake Bay. This is tentatively scheduled for the Spring or Summer of 1990. Specific goals of both experiments are to determine Moho geometry, basement depths, and various features of the intervening rift-stage crust. Examples of the latter include along-strike variations in thickness, width, and velocity of rift-stage crust, as well as internal structure, reflection character, and nature of the lateral boundaries with "normal" continental and oceanic crust.