OCEANIC CORE COMPLEX DEVELOPMENT AT ATLANTIS BANK, SOUTHWEST INDIAN RIDGE
The Atlantis Bank core complex exposes gabbro, oxide gabbro and rare serpentinized peridotite. It exhibits a dome-shaped corrugated detachment surface that has been subsequently cut by moderately-dipping transform-parallel normal faults, enabling Shinkai 6500 manned submersible sampling of the footwall, hanging wall, and detachment fault surface, providing details of the extensional fault system exposed over 39 km normal to the ridge axis. Ocean Drilling Program Hole 735B samples preserve a continuous vertical section through the interior of the detachment fault system. Together, the sample collections enable a 3-D understanding of the development of the detachment fault system.
Thermometry and microstructures of the granulite-grade footwall rocks and those of the detachment fault surface breccias suggest that deformation initiated at high temperatures (850º C) in the ductile regime, and continued to lower temperatures (600º C) and finally through the semi-brittle and brittle regimes as fault rocks were denuded along the detachment fault system. Preliminary analysis suggests that strain localization in gabbroic rocks was achieved through a variety of processes including: grain size reduction, grain boundary migration-recrystallization, development of lattice-preferred orientation, and fluid infiltration.