Deep crustal structure and magmatic processes: the inception of seafloor spreading in the Norwegian-Greenland Sea

Summary An extensive investigation into the deep crustal structure of the conjugate Norwegian and E Greenland margins utilizing two-ship Expanded Spread and Wide Aperture CDP Profiling has led to the identification of a unique suite of crustal structures developed during the onset of seafloor spreading. On both margins, a region of low velocity crust was found proximal to marginal escarpments. Immediately seaward of the low velocity crustal block seaward-dipping reflectors occur within thick crust that is interpreted to be wholly igneous, a product of voluminous melt production enhanced by convective partial melting processes. This earliest formed oceanic crust is actually several kilometres thicker than the low velocity crust or the adjacent continental crust. Normal oceanic crustal thicknesses are not produced until about 5 My after the initiation of spreading when convective partial melting has abated and the magma budget has reduced. The extrusive unit reduces to normal thicknesses long before the intrusive and plutonic section, indicating that the thickening or thinning of oceanic crust is accomplished primarily by variations in the latter.

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