Magnetic Signature of a Volcanic to non-Volcanic Margin Transition off Atlantic Canada

Details Magnetic Signature of a Volcanic to non-Volcanic Margin Transition off Atlantic Canada Magnetic Signature of a Volcanic to non-Volcanic Margin Transition off Atlantic Canada

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.t52a0910d&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #T52A-0910

Physics

1219 Local Gravity Anomalies And Crustal Structure, 1517 Magnetic Anomaly Modeling, 3025 Marine Seismics (0935), 3040 Plate Tectonics (8150, 8155, 8157, 8158), 8105 Continental Margins And Sedimentary Basins

Scientific paper

The volcanic rifted margin along the Atlantic coast of Eastern North America is characterized by a strong, linear magnetic anomaly from the Blake Spur fracture zone to Nova Scotia. This anomaly, the East Coast Magnetic Anomaly (ECMA), has been shown to coincide at several locations with a thick layer of igneous material emplaced at the continent-ocean transition. Off Nova Scotia, the anomaly changes character, becoming disjointed and lower in amplitude until it fades to the northeast into the regional background level. This region may mark the transition from a volcanic to a non-volcanic style of rifted margin. Seismic reflection data across this transition region off Nova Scotia show that, in the southwest, the ECMA coincides with a zone of seaward dipping reflections in igneous basement. Further to the northeast, basement is obscured by an overlying complex zone of salt diapirs. Modelling of the magnetic anomaly indicates that the highest amplitude peak coincides with the seaward edge of an igneous body near the ocean-continent boundary. Just north of the New England Seamounts, the anomaly peak is 50 km wide and of moderate amplitude (+280 nT), consistent with a wide unit of volcanic material buried at 7 km depth beneath the sediments. Further to the northeast, the anomaly becomes narrower and more subdued, reflecting a source body that is smaller and deeper. The interpreted cessation of volcanism off Nova Scotia may be linked to a change in rifting style, mantle thermal conditions, or reduction in the lateral flow of magma from a distant hot spot. Seismic transects and magnetic data for different parts of the US Atlantic margin show that crustal thinning occurred across a much broader width of continental crust in the north than elsewhere along the margin. The calculated isostatic gravity anomaly for this part of the margin should help to determine the presence of anomalous crustal structure or uncompensated loading in this region. We will evaluate possible explanations for the observed variations in rifting style and volcanism using available seismic and potential field data.

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