| Summary: | Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001. Includes bibliographical references. Tectonically active for the past ~160 million years, the igneous basement of the Indian Ocean basin has formed due to complex interactions between mid-ocean ridges and mantle plumes. Plateaus, ridges and islands associated with the Kerguelen hotspot, the world's second largest, oceanic igneous province, dominate the bathymetry of the southeastern Indian Ocean. Lavas erupted by the Kerguelen plume range in age from the -119 million year old basalts of the southern Kerguelen Plateau to the recent eruptions at Kerguelen, Heard, and McDonald Islands. This dissertation presents: 1) the Pb geochronology of the oldest rocks recovered from the Kerguelen Plateau, 2) the geochronology and Sr-Nd-Pb-He isotopic characteristics of the olivinerich lavas of the Kerguelen Archipelago, and 3) Sr-Nd-Pb isotopic evidence for contamination of Southeast Indian Ridge basalts with melts from the Amsterdam-St. Paul and Kerguelen plumes. At Elan Bank of the Kerguelen Plateau, Leg 183 of the Ocean Drilling Program recovered basalt, trachyte, and garnet-biotite gneiss clasts from a 26 m thick fluvial conglomerate which is intercalated with Kerguelen Plateau basalts. Zircons and monazites obtained from the gneiss clasts yield a range of Proterozoic Pb-Pb dates when examined by conventional mass spectrometric and electron microprobe techniques. The deposition of the gneiss clasts, slow seismic velocities in the crust of Elan Bank, and anomalous isotopic compositions of basalts above and below the conglomerate suggest that some part of the crust of Elan Bank is a continental fragment formed during the rifting of East Gondwana. Cenozoic eruptions from the Kerguelen plume constructed the primarily basaltic Kerguelen Archipelago (6500 km 2) on the northern Kerguelen Plateau. "Ar/ 39Ar geochronology of 15 basalts from five stratigraphic sections yields isochron ages ranging from ...
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