INITIAL RESULTS FROM THE EASTERN NORTH AMERICA MARGIN COMMUNITY SEISMIC EXPERIMENT ONSHORE ACTIVE SOURCE SEISMIC DATA

Onshore, active source seismic data were collected along two dip lines in the summer of 2015 on the mid-Atlantic coast for the Eastern North American Margin (ENAM) Community Seismic Experiment (CSE), funded by the NSF GeoPRISMS program as part of the Rift Initiation and Evolution (RIE) Initiative. The study area includes the Carolina terrane, Piedmont, and Atlantic Coastal plain in eastern North Carolina and southeastern Virginia. Data were acquired using a total of 11 explosions, five on the northern profile and six on the southern profile, and recorded using 720 Reftek-125 “Texans” with a 250 m spacing along each ~220 km profile. This instrument spacing yields crustal refraction (Pg) arrivals along each entire profile, Moho reflection (PmP) arrivals on offsets greater than 100 km, and Moho refraction (Pn) arrivals on offsets greater than 180 km. Additionally, intracrustal reflection arrivals (Pi_xP) were recorded from several shots. These Pi_xP arrivals may reveal intracrustal structures and can aid in determining the location and arrangement of known Triassic-aged basins. Preliminary 2-D velocity models along both profiles reveal a crustal thickness between 35-40 km and show a high velocity (>7.0 km/s) layer at the base of the crust. This feature may represent magmatic underplating but has only been previously observed offshore the margin. The origin of this magmatic underplating could be related to syn-rift magmatism observed along the ENAM, or as part of the Central Atlantic Magmatic Provence (CAMP). Refining the velocity structure of these models will aid in determining the location, thickness, and timing of intrusive magmatic events, and will aid in the investigation of the relation of magmatism, crustal thickness, and underplating along the margin. The inclusion of onshore-offshore data from the ENAM CSE will extend the velocity models offshore, and will aid in determining the lateral extent of underplating along each profile. Because of the complex tectonic history of the margin, characterized by two cycles of super-continent breakup, these results will aid in understanding how mechanical deformation and mantle melts interact during continental rifting, and can help constrain how these interactions lead to continental breakup.