Compressional and shear-wave velocity structure of the continent-ocean transition zone at the eastern Grand Banks, Newfoundland

Abstract

[1] The seismic structure of the continent-ocean transition (COT) at magma-poor rifted margins can explain geological processes leading to continental breakup. At the Newfoundland-Iberia rift, compressional seismic velocity (Vp) is interpreted with multichannel seismic reflections and drilling results to document continental crustal stretching and thinning, exhumation of the mantle, and incipient seafloor-spreading. However, Vp cannot uniquely constrain COT geology. We present an updated 2-D model for Vp and a new shear-wave velocity model (Vs) for SCREECH Line 2 on the Newfoundland margin using multichannel seismic reflections and coincident ocean-bottom seismometer refraction data. In shallow COT basement we find Vp / Vs ratios average 1.77, which is normally too high for upper continental crust and too low for serpentinized mantle. This observation can be explained by stretching of a mafic middle and/or lower continental crust into the COT. We further support the presence of hydrated mantle peridotites at depth during rifting.