Compressional wave velocity and index properties of the gabbroic rocks drilled at Hole 1105A of the Atlantis Bank, Southwest Indian Ridge

Abstract

Compressional wave velocities (Vp) and index properties of 70 mini- gabbroic rock-core samples of 2.5 cm diameter × 2.1 cm long from 157.1 m below seafloor in Hole 1105A of the Atlantis Bank, Southwest Indian Ridge, were measured in the laboratory. Comparison of the Vps and onboard lithostratigraphy revealed that the Vps of the gabbros and olivine gabbros are very close and have the values 6.74±0.04 and 6.7±0.07 km/s, respectively. Oxides and oxide olivine gabbros have markedly lower Vps (6.53±0.076 and 6.59±0.077 km/s) respectively as abundance of Fe-Ti oxide minerals vary as a result of alteration processes. They are also consistent with well-log results of Hole 1105A and Hole 735 B from the bank. The mean bulk density of the rocks is 2.93±0.15 gm/c3. The other index properties - porosity, void ratio and grain density and their means are consistent with model populations of the rock minerals. © Geol. Soc. India.