The NERC-funded joint geophysical and oceanographic OSCAR project aims to develop understanding of the interactions between relatively young oceanic crust and the overlying abyssal ocean through heat transfer and fluid flow. The movement of hydrothermal fluids through the oceanic crust causes changes in its structure and composition: circulating heat, precipitating minerals in open cracks and fractures, and forming alteration fronts which influence permeability and seismic properties, though little is known about the rate and extent of these processes.
Seismic refraction and reflection data from the Costa Rica Rift acquired from the spreading ridge to ~6 Ma crust at DSDP/ODP Hole 504B will be used to investigate this problem, in conjunction with real geology observed in the borehole. The construction of two and three dimensional P- and S‑wave velocity models over the ridge, borehole, and flow lines connecting the two sites, will aim to better understand the structure of oceanic crust, particularly the nature of the boundaries within seismic layer 2, and how this structure changes as the crust ages. Particle motion and anisotropy analyses will aim to constrain estimates of fracturing, permeability and porosity in the upper crust, and the changes that occur as aligned fractures formed at the ridge are sealed through hydrothermal mineralisation.
When combined with other research streams within OSCAR focussing on heat flow and geothermal heating of the deep ocean, this will integrate geophysical and oceanographic understanding of heat transfer and fluid flow at active mid-ocean ridges, and the potential effects on global ocean circulation and long-term oceanic crustal composition.
