| dc.description.abstract | There now exist sufficient numbers of recovered marine and ophiolitic samples to correlate their measured velocities and densities with marine seismic survey data in order to determine the mean density of the oceanic crust. Two methods are proposed: 1) assigning general lithologies to the various seismic layers of the crust based upon the ophiolite model, and 2) determining a velocity-density relationship for oceanic crustal rocks and subsequently converting the seismic velocity structure to density structure.
The mean densities and velocities of unaltered basalts, dolerites, and gabbros have the following values: 2.82±0.09 g/cm³, 5.88±0.38 km/s; 2.84±0.08 g/cm³, 6.38±0.44 km/s; and 2.92±0.09 g/cm³, 7.05±0.32 km/s, respectively. Applying these mean densities to eight different layered models yields a density of the igneous oceanic crust of 2.90 g/cm³. This is essentially a first order approximation and does not include formation porosity.
In determining a velocity-density relationship for crustal rocks, it was necessary to use two velocity ranges. For velocities less than 6.65 km/s (the grain velocity of basalt), velocity and density were calculated parametrically as functions of porosity. And, for velocities greater than 6.65 km/s, a linear regression of the type ρ = A + B/Vᵨ was fit to all samples in order to reflect changes in lithology and grain size. Applying these equations to the layer velocities of the aforementioned models yields a mean crustal density of 2.89 g/cm³. | en |
