The geological interpretation of seismic cross sections across the Ninetyea
st Ridge allowed the oceanic crust to be recognized within its limits; subs
equently, from the top to the bottom, it is composed of basalts, dolerites,
gabbros, and serpentinized peridotites. Seismic and gravity data suggest t
hat the ridge represents a fault-related structure, whose uplifting is caus
ed by the serpentinization of peridotites. Two major stages are distinguish
ed in the tectonic and magmatic evolution of the ridge.