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FRINATEK-Fri mat.,naturv.,tek

Hotspot Rift Interaction & Geochemistry of the North Atlantic Mantle: the Aegir Ridge 'Hole' in the Iceland Hotspot

Awarded: NOK 4.6 mill.

Modeling of the P-waves recorded during the Ocean Bottom Seismic (OBS) survey along the Aegir Ridge in 2010 demonstrates reliable imaging of the entire crust and uppermost mantle. The average crustal thickness is modeled at 4.5 km, which is less than normal for oceanic crust and suggests the presence of relatively cold underlying asthenosphere with minor influence from the nearby Iceland hot-spot. The S-wave recordings suggest that the crust consists of gabbroic rocks, which to some degree is cracked, leading to serpentinization of upper mantle rocks. Gravity modeling suggests the presence of lateral density variations in the upper mantle, which may indicate slight increase in temperature southwards, or alternatively, varying mantle composition. 3D numeric modeling shows that the thin crust along the Aegir Ridge partly can be explained by southward migration of magmatic material from the Iceland hot-spot along the Reykjanes Ridge. Furthermore, the magmatic material was probably partly blocked by the Jan Mayen micro-continent. Geochemical analysis of dredge samples acquired during the survey in 2010 suggests that the mantle source in the area resembles those of the basalts along the Kolbeinsey Ridge and on the Faroes, and that the Iceland hot-spot has no direct interaction with the Aegir Ridge.

We propose a combined seafloor dredging and wide-angle seismic study of hotspot-ridge interaction. Surrounded by extensive breakup volcanism on the margins, and the Iceland-Faeroes volcanic ridge, the magma-starved basin formed by the extinct Aegir Ridge is a major gap in the North Atlantic large igneous province, the latter created by the Iceland hotspot. Wide-angle seismic data show that the Aegir Ridge began creating moderately thick crust (8-11 km) the first 2-4 Myr spreading; but magma production qui ckly waned to form 3.5-6 km thick crust for the remaining spreading (51.4-25 Ma). This weak or non-existent hotspot influence despite extensive volcanism nearby provides a unique opportunity to learn about the dynamics of hotspot-rift interaction, the com position of plume-like mantle upwellings, and the geochemical evolution of ambient upper mantle MORB source. The lithospheric structure of the newly rifting Kolbeinsey Ridge and Jan Mayen micro-continent could divert mantle flow from the hotspot away fro m Aegir Ridge. If so, the Aegir Ridge lavas can reveal the uncontaminated composition of the ambient N-Atlantic mantle near the Iceland hotspot. Alternatively, the Aegir Ridge could be influenced by plume material, but generated only thin crust because th is material had undergone previous partial melting by hotspot volcanism elsewhere. If so, Aegir Ridge could reveal the most pure composition of any incompatible-element-depleted component(s) intrinsic to the Iceland mantle plume. The new data will address ongoing controversies over the cause of the background geochemical variability in the N-Atlantic ambient upper mantle and origin of the depleted components associated with the Iceland plume, the latter relevant to the composition and evolution of the dee per mantle. The refraction seismic data will constrain variations in the magma productivity of the seafloor generation along the Aegir Ridge, essential for the correct interpretation of the geochemical data.

Funding scheme:

FRINATEK-Fri mat.,naturv.,tek