The Limit of Volcanic Rifting: A Structural Model Across the Volcanic to Non-volcanic Transition off Nova Scotia

Details The Limit of Volcanic Rifting: A Structural Model Across the Volcanic to Non-volcanic Transition off Nova Scotia The Limit of Volcanic Rifting: A Structural Model Across the Volcanic to Non-volcanic Transition off Nova Scotia

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.t31d..04d&link_type=abstract

American Geophysical Union, Spring Meeting 2004, abstract #T31D-04

Physics

3025 Marine Seismics (0935), 8105 Continental Margins And Sedimentary Basins

Scientific paper

The rifted continental margin along much of the Atlantic coast of eastern North America is classified as volcanic, with thick sequences of igneous material emplaced at the continent-ocean transition during Late Triassic to Early Jurassic rifting. A strong, linear magnetic anomaly (ECMA) is observed along the margin from the Blake Spur fracture zone to the Scotian margin, coincident with seismic images of seaward dipping reflectors (SDRs). Along the SW Scotian Margin, the anomaly changes character, becoming lower in amplitude, disjointed and weaker as it fades to the east into the regional background level. The loss of magnetic signature and disappearance of SDRs have suggested that most of the Scotian margin is primarily non-volcanic, with the transition starting northeast of the New England seamounts. Three wide-angle seismic reflection / refraction lines were collected in 2001 across the continental margin and deep sedimentary basin offshore Nova Scotia to investigate the transition in rifting style. Line 3 crossed the ECMA at the SW end of the margin, where sediment thickness is less than 10 km. The velocity model shows a 120 km-wide transition zone separating thinned continental crust from oceanic crust. P-wave velocities in the upper and lower layers of the transition zone average 6.2 and 7.2 km/s, consistent with velocities for the transition zone off the US Atlantic margin where the volcanic nature has been well-established. The upper surface of the transitional crust is coincident with SDRs, and magnetic models also support an interpretation of volcanic origin. However, total thickness of the transitional crust is only 10 km, significantly thinner than the interpreted 15 to 20+ km of igneous material interpreted off the US. Oceanic crust adjacent to the transition zone is less than 6 km thick, suggesting a change to conditions that inhibited melting during the early stages of formation of oceanic crust. These observations allude to considerable complexity associated with the gradual reduction in volcanism, and eventual transition to a non-volcanic style of rifting, along the Scotian margin.

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