Gravity of Pito Deep: A Propagating Rift Tip on the Easter Microplate

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Detailed surveys of a propagating spreading center along the East Pacific Rise (EPR) at 95.5W show that plate boundary configurations, rather than being static, can undergo complex geometric changes. Models based on either dynamic, kinematic or mechanical processes within the crust and mantle have been developed to explain these intricacies. However, the applicability of these models to other propagating systems has yet to be established, and Dr. Martinez will conduct an evaluation of the various models by examining previously acquired data from the Pito Deep area at 23S on the EPR. This area contrasts with the 95.5 propagator in severval ways: the Pito Deep propagator is advancing along a broad "front", not a "tip" as at 95.5N; local topography varies enormously from a regional mean of 3500m to a local depression of 5980m; and complex topography north of the rift mimics the fabric and trend of the rift zone, suggesting an unusually strong coupling across this region. Any or all of these constrasts may be explained by the fact that Pito Deep is offset along a long (300 km vs 30 km for the feature at 95.5N) transform and intrudes into unusually old lithosphere (3 my vs 1 my). Dr. Martinez will grid existing SeaMARCII bathymetry and construct a terrain-corrected Bouger anomaly map of the Pito Deep region. With this and with assumptions of the nature of isostatic compensation he will calculate residual gravity anomalies to identify anomalies due to Moho topography. Anomalies that remain after this procedure will form the basis for testing among the competing models that require either: 1) viscous flow in the asthenosphere, 2) thermal effects due to dike intrusion, or 3) mechanical implications of a lithosphere of finite strength.