SEISMIC EVIDENCE FOR MAGMATISM OFFSHORE CAPE HATTERAS, EAST NORTH AMERICAN MARGIN

The assisting role of magma in continental lithosphere break-up and subsequent passive margin evolution has long been recognized, although details of magma localization along the rifted margin are still debated. Evidence of magma along passive margins comes from upper crustal seaward dipping reflectors (SDRs) interpreted as packages of volcanics, and high velocity anomalies in the lower crust, interpreted as intruded mafic magmas. Early estimates of magma volumes emplaced along the East North America Margin (ENAM) derived from sparse profiles imaging SDRs proximal to the wide, high amplitude, positive East Coast magnetic anomaly (ECMA), suggested that the margin might be a Large Igneous Province. Newly acquired multichannel seismic (MCS) reflection data around Cape Hatteras, North Carolina, both parallel and perpendicular to the strike of the margin allow to re-evaluate these estimates, to capture the short-scale magmatic segmentation of the margin, and to assess the syn-rift role of magmatism.

The new MCS data acquired across the continental slope are particularly challenging because the combination of water depth and steep bathymetric change produces water reverberations that obscure or mimic SDRs. The profiles are also severely affected by the northward moving Gulf Stream, which causes feathering of the streamer by as much as 60º. Data processing focused primarily on mitigating the effect of feathering using a hybrid 2-3D geometry, and on multiples attenuation using a combination of Surface Related Multiple Elimination (SRME) and Tau-P domain filtering. Resulting images of the dip profile show clear reflectors at 4.5s Two Way Travel Time (twtt) traceable from the margin shelf to 6.5s twtt beneath the continental slope. These packages are interpreted as SDRs, and appear to be thinner than SDRs on legacy profiles to the north and south of Cape Hatteras. Processed lines parallel to the margin show undulating, southward dipping reflectors at ~9-9.5s twtt (~20 km depth), which we preliminarily interpret as top of the high velocity lower crust, as constrained by coincident wide-angle refraction profiles. Here we present the interpretation of the newly processed data, a new estimate of the extent of SDRs, and a correlation of the SDRs structures with the ECMA along the margin.