Crustal structure of the Eggvin Bank, west of Jan Mayen. Data processing, velocity modeling and interpretation of recordings from a marine wide-angle seismic survey

Abstract

The Eggvin Bank is a shallow area located on the northern segment of Kolbeinsey Ridge. Its crustal structure was investigated along a 301 km long transect from the Greenland Basin to the Iceland Plateau, crossing over the Jan Mayen Fracture Zone and the Eggvin Bank. P- and S-wave velocities were obtained from forward and inverse modeling of three-component ocean bottom seismometer data.

Optimal results of modeling were obtained with a four layered model (I: Sediments. II-A: Upper crust. II-B: Middle crust. III: Lower crust) over a half-space (IV: Upper mantle). In Iceland Plateau and Eggvin Bank the sediments were estimated zero to 0.5 km thick with Pwave velocities between 1.8 and 2.3 km/s. Poisson's ratio in the sediments was estimated to be 0.39. Average P-wave velocities of the upper and middle crust, Layer II-A and II-B, were estimated to 3.45 - 4.60 km/s and 5.50 - 6.55 km/s, respectively. Poisson's ratios was estimated to be 0.35 for both layers. Relatively low P-wave velocity and high Poisson's ratio are ascribed to high porosity in extrusive and intrusive igneous rocks. Serpentinization is another possible cause. P-wave velocities in the lower crust, layer III, were estimated to 6.80 - 7.20 km/s, with a Poisson's ratio of 0.29. These velocities are typical for gabbros. Average upper mantle P-wave velocities were modeled to 7.83 km/s under the Eggvin Bank. Poisson's ratio was estimated to be 0.25, indicating normal preidotitic composition.

Iceland Plateau crust resembles structures to the south. The Eggvin Bank has a velocity profile similar to oceanic crust, in particularly as found in the Iceland Plateau. The velocity profile differs form continental crust in Jan Mayen Micro Continent as well as mapped structures beneath the Jan Mayen island. Eggvin Bank crustal thickness (8 - 11 km) is greater than average oceanic crust (7 km), as well as crust in the Iceland Plateau (9 km). Thicker crust locally underneath the major seamounts was interpreted to be directly related to their presence. In the center of the bank crustal thickness (8 - 9 km) compare with Iceland Plateau. Layer II-A and II-B are thicker in the Eggvin Bank compared to Iceland Plateau. This is interpreted to derive from extensive volcanic activity on the bank.

Crystalline structures in the Greenland Basin were poorly constrained because recordings could not be recovered from the deployed OBS in this part of the survey line. However, a substantial change in crustal thickness could be identified across the Jan Mayen Fracture Zone. Depth conversion estimated sediments to be 0.2 - 2.0 km thick in the Greenland Basin, and the crystalline thickness was modeled 4.0 _1.2 km. Fracture zone related serpentinization in upper mantle was not indicated by average P-wave velocity (8.0 km/s) and Poisson's ratio (0.25).