Along-Strike Crustal Structure of the Eastern North American Margin within the East Coast Magnetic Anomaly

Session: Amphibious Seismic Studies of Plate Boundary Structure and Processes [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Crustal structure at passive margins provides insight into pre-, syn- and post-rift processes. The Eastern North American Margin (ENAM) extends along the US east coast and formed as Pangea separated ~190 Ma. The margin’s crustal architecture has been previously probed with long strike-perpendicular profiles showing extensive magmatic addition in the upper and lower crust at the rift-to-drift transition and along-strike structure has been interpolated between these profiles. This study uses data from the ENAM Community Seismic Experiment, with seismic profiles targeting crustal structure along the margin parallel East Coast Magnetic Anomaly (ECMA). Depth-velocity models of line 4A and 4B, created using ocean bottom seismometer (OBS) refraction tomography, show crustal structure for ~350 km along-strike to depths of ~30 km. The along-strike view created by these lines shows that sediment thickness is relatively uniform and there is more significant variation present in the lower crust than previously known. High velocity lower crust (HVLC) with a V_p> 7.2 km/s is interpreted as seismic evidence for magmatic addition and is present along a majority of lines 4A and 4B, except for a small region coincident to the Northern Fracture Zone. Patches of very fast HVLC (V_p> 7.5 km/s) reach a thickness of >4 km where present. Using these velocity models, we estimate between 106,000 km³and 201,000 km³of magmatic addition to the margin coincident to these lines, a 28 - 62% reduction from previous estimates based solely on previous strike-perpendicular profiles. We find minimal correlation between HVLC and the magnitude of ECMA, corroborating previous magnetic modeling along ENAM, which shows the magnetic source located predominantly in the upper crust. A region with no HVLC on line 4B directly correlates to a sharp decrease in the isostatic gravity anomaly. Calculations of mean crustal velocity vs. crustal thickness indicate that there may be variations in upwelling rates and/or mantle potential temperatures that coincide with the very fast HVLC.

Presenting Author: Collin C. Brandl

Authors