Physical properties and minerals of Leg 65 Holes basalts

Velocities and densities of submarine basalts obtained during Leg 65 are distinguished by their relatively high values (about 6.3 km/s and 2.9 g/cm/**3, respectively). This is consistent with their low degree of alteration. The range of velocities covered by these samples correlates well with porosity, and a comparison with in situ velocities from refraction data suggests maximum porosities ih the upper 100 meters of the crust of about 10%.

Geochemistry of basalts fropm DSDP Leg 65 basalts

Samples of basalt collected on Leg 65 near 22°N on the East Pacific Rise all display the depleted light rare-earth pattern of "normal" oceanic crust. Consequently the La/Ta ratio is close to 18, as opposed to the value of 9 associated with the flat or enriched patterns found along parts of the Mid-Atlantic Ridge and the Emperor Seamount chain. The Leg 65 samples are chemically similar to those from the CYAMEX area at 21 °N and to the Leg 54 samples from 9°N, suggesting homogeneity of the upper mantle under the northern part of the East Pacific Rise over a minimum distance of about 1500 km. The geochemistry of the rocks and their field relationships with respect to depth and distance from the axis of the Rise show no pattern of distribution linked to the degree of fractional crystallization and thus cast doubt on any possible model involving large, long-lived magma chambers at the axis of the Rise.