Seismic reflection and gravity study of proposed Taconic suture under the New Jersey coastal plain; implications for continental growth

A vibroseis seismic reflection line near Buena, New Jersey, crosses the linear positive Salisbury Bouguer gravity and magnetic anomaly that follows the proposed Taconic suture. Two reflections at 1.4 and 1.7 sec under the positive gravity anomaly and beneath the Coastal Plain basement reflections at 1.1 sec are from interpreted Taconic suture rocks with ophiolitic crustal fragments (7.1-7.9 km/sec). A gently southeast-dipping reflection (2.0-2.7 sec) is interpreted as the detachment thrust below the allochthonous suture rocks. A stratified sequence (5.4-6.3 km/sec) is interpreted as remnants of parautochthonous lower Paleozoic drift-stage sedimentary rocks beneath the detachment thrust. Below 3.0 sec (8 km depth), the reflections are subhorizontal or gently dipping (11 degrees ) all the way to the Moho reflection at 11.0 sec. On the northwest end of the vibroseis line, a northwest-tilted Mesozoic rift-basin basement reflection is seen from 1.1 to 1.5 sec. These Mesozoic rocks (4.5-4.8 km/sec) are at least 1 km thick. The denser suture rocks with ophiolitic fragments and the less dense Mesozoic rocks explain almost all of the Salisbury Bouguer anomaly. No significant lateral density variations are needed below 8 km depth. These results are compatible with the Taconic suture under the New Jersey Coastal Plain being allochthonous and underlain by parautochthonous Grenville-age continental crust. A deep-seated Taconic suture at the edge of the Grenville North American basement may be southeast of the New Jersey Coastal Plain. This implies a greater amount of Taconic overthrusting and lesser amounts of accretion of the North American crust than previously proposed.