| Summary: | Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1996 We analyze bathymetric and gravity anomalies at five plume-ridge systems to constrain crustal and mantle density structure at these prominent oceanic features. Numerical models are then used to explore the physical mechanisms controlling plume-ridge interaction and to place theoretical constraints on the temperature anomalies, dimensions, and fluxes of the Icelandic and Galapagos plumes. In Chapter 1 we analyze bathymetric and gravity anomalies along the hotspot-influenced Galapagos Spreading Center. We find that the Galapagos plume generates along-axis bathymetric and mantle-Bouguer gravity anomalies (MBA) that extend >500 km east and west of the Galapagos Islands. The along-axis MBA becomes increasingly negative towards the plume center, reaching a minimum of ~-90 mGal near 91°W, and axial topography shallows by ~1.1 km toward the plume. These variations in MBA and bathymetry are attributed to the combined effects of crustal thickening and anomalously low mantle densities, both of which are due to a mantle temperature anomaly imposed beneath the ridge by the Galapagos plume. Passive mantle flow models predict a temperature anomaly of 50±25°C is sufficient to produce the 2-4 km excess crust required to explain the along-axis anomalies. 70-75% of the along-axis bathymetric and MBA variations are estimated to arise from the crust with the remaining 25-30% generated by the anomalously hot, thus low-density mantle. Along Cocos-plate isochrons, bathymetric and MBA variations increase with increasing isochron age, suggesting the subaxial mantle temperature anomaly was greater in the past when the plume was closer, to the ridge axis. In addition to the Galapagos plume-ridge system, in Chapter 2 we examine alongisochron bathymetric and MBA variations at four other plume-ridge systems associated with the Iceland, Azores, ...
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