Relative Gravity Along B96 Profile

Data taken from The Gravity Field of Northeastern Iceland ,Scheusener et al., J. Geophys. 42, 27-45, 1976

B96 shallow velocity profile. Full size version

Anticipated gravity anomaly over a "volcanic root." Note 100 km scale. Densities used for this calculation are based on the velocities from the 80 km shallow profile. Two first order methods were used to derive densities from velocities. Zero-porosity basalt has a velocity of 6.7 km/s. Surface extrusive processes introduce pore space which decrease this velocity. The method of Christensen and Shaw, [1970] was used to estimate the density assuming that velocitiy differences are due to pore space.

Another possible explaination for velocity differences, particularly at depth, is chemical composition. Domed structures may have a higher mantle component. High velocities can be considered a mix of granitic (velocity=2.7 km/s, density=2.7 g/cm³) and upper mantle material, 70% olivine, (velocity=8.2 km/s, density of 3.3 g/cm³).

The first method is more applicable near the surface where velocities are less than 6.7 km/s. The second method should be more applicable at depth where velocities exceed 6.7 km/s. Each method results in a different conversion of velocity to density. It should be noted however that there are numerous other factors to consider in such a comparison and this is very first order.

Anticipated gravity anomaly over a sediment basin modeled after the slow velocity zone seen on B96 shallow profile

B96 Regional velocity profile. Full size version

Anticipated gravity anomaly over a 6 km shallowing of the Moho modeled after that seen on B96 regional profile

Postscript plot of topography along the B96 array.