THIN CRUST, ULTRAMAFIC EXPOSURES, AND RUGGED FAULTING PATTERNS AT MID-ATLANTIC RIDGE (22-DEGREES 24-DEGREES-N)

Off-axis rock sampling in the lat 22 degrees-24 degrees N region of th e Mid-Atlantic Ridge shows that the emplacement of mantle-derived rock s in the sea floor has been a common process there for the past few mi llion years. We find a good correlation between domains of positive re sidual gravity anomalies (inferred to have a thin crust) and the distr ibution of ultramafic samples. We also find that thin-crust domains ha ve a rugged topography, thought to reflect strong tectonic disruption. We propose that these thin-crust domains are made of tectonically upl ifted ultramafic rocks, with gabbroic intrusions and a thin basaltic c over. We also suggest that strong tectonic disruption may be a direct consequence of the lithological and rheological heterogeneity of these thin-crust domains.