Along-strike Refraction Tomography Results from the ENAM Community Seismic Experiment within the East Coast Magnetic Anomaly
Abstract
The Eastern North American Margin (ENAM) and other rifted continental margins are most commonly studied with offshore margin-perpendicular seismic profiles to better understand the development of rifting and the interplay between extension and magmatism during the breakup of Pangea. The prominent along-shore East Coast Magnetic Anomaly (ECMA) correlates with seismically mapped extrusive volcanic material and elevated lower crust velocities (Vp >7.0 km/s) interpreted as evidence for mafic synrift magmatic intrusions. However, this relationship is based on widely spaced datasets, leaving the details of along-strike changes in crustal architecture related to this magmatism unconstrained. Imaging the margin's along-strike structure provides important constraints on differential magmatism and/or margin segmentation.
We present crustal-scale active-source seismic data from the ENAM Community Seismic Experiment collected offshore the margin in 2014. We analyzed seismic gathers from 21 ocean bottom seismometers along two shore-parallel lines that follow the ECMA for 500 km centered near Cape Hatteras, North Carolina. There are several anomalous regions across both lines of early, faster than sediment (Vp ≈ 5 km/s) arrivals within short (< 30 km) source-receiver offsets and abrupt discontinuities in the arrival time of some longer (> 70 km) offsets. We used first arrival travel times to create an initial velocity model of sedimentary and crustal structure. We then used first and secondary arrival travel times in an iterative process of raytracing and tomographic inversion to add interfaces and improve the model. Our first arrival model shows variations in the thickness and velocity of shallow sediments. The short offset, high velocity arrivals and the discontinuities in far offset arrivals could be the result of salt diapirism or seaward dipping reflectors (SDRs) near the OBS, both of which have been imaged using multi-channel seismic reflection data. Initial layered models further demonstrate variations in sedimentary cover and basement topography. In both first arrival and layered models, the Moho's depth varies significantly (between 23 and 28 km). We will further investigate these anomalies to determine if they are the consequence of near surface structures or are representative of the true Moho.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T13F0274B
- Keywords:
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- 8105 Continental margins: divergent;
- TECTONOPHYSICSDE: 8109 Continental tectonics: extensional;
- TECTONOPHYSICSDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8159 Rheology: crust and lithosphere;
- TECTONOPHYSICS