Abstract
The EDGE experiment offshore the U.S. east coast obtained near vertical incidence seismic reflection data, as well as wide angle seismic reflection and seismic refraction data. These results are combined with magnetic total intensity data in order to establish the origin for the East Coast Magnetic Anomaly (ECMA) and to hypothesize about geological events taking place at the time that opening was initiated in the North Atlantic.
Prominent seaward dipping reflectors (SDR’s) which reach a depth of almost 25 km represent layers of volcanics which give rise to the ECMA. Because these reflectors extend below the depth where the Curie temperature is reached, and because the volcanic layers lie directly over material believed to be derived from asthenospheric melt. it is believed that no continental crust lies below the seaward dipping reflectors (except at their feather edge). The seaward dipping reflectors alone are responsible for the ECMA. The crustal section here represents the Initial Oceanic Crust which is thicker and possesses higher seismic velocities than normal oceanic crust. It should not be called “transitional crust,” “modified continental crust,” or “rift stage crus!.” The 7.2 - 7.5 kmfsec layer is the lower part of the Initial Oceanic Crust rather than an underplating to a thinned continental crust. For the sub-horizontal volcanic layers (which give ri se to the SDR’s) to produce the ECMA it is necessary that they largely possess a single magnetic polarity . This can only take place if the subaerial sea floor spreading which produced these volcanic layers was initiated at a very high rate. As the spreading subsequently slows down, normal and reversely magnetized volcanic layers are presumably juxtaposed below each other, resulting in an effective cancellation of their magnetic effects and giving rise to a magnetic quiet zone. As the axis of sea floor spreading subsides to submarine depths the flow length of volcanic layers becomes small and typical sea floor spreading type magnetic anomalies can be produced. This model is also used to explain the coincidence of salt diapirs with the ECMA and also with the disappearance cf typically hyperbolic echoes from oceanic basement as the margin IS approached from the seaward side.
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Talwani, M., Ewing, J., Sheridan, R.E., Holbrook, W.S., Glover, L. (1995). The Edge Experiment and the U.S. East Coast Magnetic Anomaly. In: Banda, E., Torné, M., Talwani, M. (eds) Rifted Ocean-Continent Boundaries. NATO ASI Series, vol 463. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-0043-4_9
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DOI: https://doi.org/10.1007/978-94-011-0043-4_9
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