Numerical Modeling of Mantle Convection beneath the Aegir Ridge, a Shadow in the Iceland Hotspot

The Iceland Hotspot has produced extensive volcanism across much of the ocean basin between Greenland and Norway, forming one of the world's largest igneous provinces. An apparent igneous "shadow" in hotspot activity is observed at the Aegir Ridge, which facilitated seafloor spreading after continental breakup until magma supplies dwindled and spreading jumped west. Enigmatically, significantly less crust was produced at Aegir, despite its close proximity to the Iceland Hotspot, than at contemporary ridges not influenced by hotspots. Three-dimensional thermal convection models are used to simulate the interaction between a mantle plume and the rifting of continental lithosphere by a ridge system representative of the region. Two end-member hypotheses for Aegir's anomalously low production are investigated. First, that material emanating from the hotspot was diverted away from Aegir by the thick lithosphere of the Jan Mayen Microcontinent, as the opening Kolbeinsey Ridge rifted it from Greenland. Second, that volcanism more proximal to the hotspot partially melted plume material which did reach the Aegir ridge, but was then unable to contribute significant melt. Time-evolving, three-dimensional visualizations of the data show the plume head deforming at the onset of breakup, spreading furthest axially along the ridges, then briefly draw back and partially tear as the opening Kolbeinsey spreading center creates a new cavity for the material to occupy. The Aegir Ridge experiences reduced or no hotspot influence for low volumetric fluxes (<3 km^3 yr^-1) or low-viscosity, and hence thin (<80 km), plume layers; these values result in pronounced difficulty for the plume material to overcome the lithospheric protrusion at Jan Mayen and feed the Aegir Ridge. With partial melting further investigated, predictions of crustal thicknesses over the life of the Aegir Ridge will be compared to seismological measurements, constraining which hypothesis or combination thereof best reproduces the data.