Constraining formation of the Eggvin Bank (West of Jan Mayen, N. Atlantic) from OBS data

Abstract:

The anomalously high magma flux in the Eggvin Bank area has triggered new research efforts to better understand the crustal development in this area. The Eggvin Bank is located between the Jan Mayen Island and the west coast of Greenland. Some proposed origins of the Eggvin Bank are: a distinct plume located beneath Jan Mayen; an extension of the Iceland plume; minor spreading or leakage along West Jan Mayen Fracture Zone (WJMFZ); intruded continental crust extending from Jan Mayen Microcontinent (JMMC); and rifted Greenland sub-continental lithospheric mantle. In this first modern refraction seismic study of the Eggvin Bank, we present a 2D velocity model based on OBS data. The OBSs were deployed approx. N-S over the Eggvin Bank with good data quality constrained by 4 OBSs. The air-gun array used during OBS shooting produced good quality reflection data. Three distinct seamounts are observed along the profile: the northern seamount (water depth 730m), has a flat top with a thin sedimentary veneer on top, which indicates it has been eroded at sea surface; while the southern two seamounts, one (water depth 550m) is less flat with around 100m thick sedimentary units on top, another one is rounded with tiny sedimentary veneer on top having the shallowest water depth (460m). This could suggest that the southern seamounts are younger, since they are shallower but without obvious signs that they were subaerially exposed. However, increased cooling of the lithosphere across the WJMFZ in the north may also contribute to depth differences. A normal fault offsetting sedimentary strata (~300 m) in the Greenland Basin indicates recent tectonic activity north of the Eggvin Bank. The velocity modeling shows crustal thickness with large variations, ranging from 8 km to 14 km, where crustal thickness changes of 4-5 km are associated with 20-30 km wide segments with thick crust under the seamounts. The crust consists of three oceanic crustal layers: upper crust (2.8km/s-4.8km/s); middle crust (5.5 km/s -6.5 km/s); lower crust (6.7 km/s - 7.35 km/s). The high crustal thickness and crustal morphology differ from the more uniform Kolbeinsey Ridge crust to the south, and it may represent oceanic crust with multiphase off-axis volcanic activity.