Interactions between mantle plumes and mid-ocean ridges : constraints from geophysics, geochemistry, and geodynamical modeling Georgen, Jennifer E.
dc.coverage.spatial Southwest Indian Ridge 2010-06-25T12:40:11Z 2010-06-25T12:40:11Z 2001-09
dc.description 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 2001 en_US
dc.description.abstract This thesis studies interactions between mid-ocean ridges and mantle plumes using geophysics, geochemistry, and geodynamical modeling. Chapter 1 investigates the effects of the Marion and Bouvet hotspots on the ultra-slow spreading, highly-segmented Southwest Indian Ridge (SWIR). Gravity data indicate that both Marion and Bouvet impart high-amplitude mantle Bouguer anomaly lows to the ridge axis, and suggest that long-offset transforms may diminish along-axis plume flow. Building upon this observation, Chapter 2 presents a series of 3D numerical models designed to quantify the sensitivity of along-axis plume-driven mantle flow to transform offset length, spreading rate, and mantle viscosity structure. The calculations illustrate that long-offset transforms in ultra-slow spreading environments may significantly curtail plume dispersion. Chapter 3 investigates helium isotope systematics along the western SWIR as well as near a global array of hotspots. The first part of this study reports uniformly low 3HetHe ratios of 6.3-7.3 RlRa along the SWIR from 9°-24°E, compared to values of 8±1 Ra for normal mid-ocean ridge basalt. The favored explanation for these low values is addition of (U+ Th) into the mantle source by crustal and/or lithospheric recycling. Although high HetHe values have been observed along the SWIR near Bouvet Island to the west, there is no evidence for elevated 3HetHe ratios along this section of the SWIR. The second part of Chapter 3 investigates the relationship between 3HetHe ratios and geophysical indicators of plume robustness for nine hotspots. A close correlation between a plume's flux and maximum 3HetHe ratio suggests a link between plume upwelling strength and origination in the deep, relatively undegassed mantle. Chapter 4 studies 3D mantle flow and temperature patterns beneath oceanic ridge-ridge-ridge triple junctions (TJs). In non-hotspot- affected TJs with geometry similar to the Rodrigues TJ, temperature and upwelling velocity along the slowest-spreading of the three ridges are predicted to increase within a few hundred kilometers of the TJ, to approach those of the fastest-spreading ridge. Along the slowest-spreading branch in hotspot-affected TJs such as the Azores, a strong component of along-axis flow directed away from the TJ is predicted to advect a hotspot thermal anomaly away from its deep-seated source. en_US
dc.description.sponsorship Funding was provided by the National Science Foundation through grants OCE- 9811924 and OCE-9907630, and by a National Defense Science and Engineering Graduate Fellowship. en_US
dc.format.mimetype application/pdf
dc.identifier.citation Georgen, J. E. (2001). Interactions between mantle plumes and mid-ocean ridges : constraints from geophysics, geochemistry, and geodynamical modeling [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server.
dc.identifier.doi 10.1575/1912/3692
dc.language.iso en_US en_US
dc.publisher Massachusetts Institute of Technology and Woods Hole Oceanographic Institution en_US
dc.relation.ispartofseries WHOI Theses en_US
dc.subject Mantle plumes en_US
dc.subject Mid-ocean ridges en_US
dc.subject Knorr (Ship : 1970-) Cruise KN162 en_US
dc.subject Polarstern (Ship) Cruise PS86 en_US
dc.subject Agulhas (Ship) Cruise AG22 en_US
dc.title Interactions between mantle plumes and mid-ocean ridges : constraints from geophysics, geochemistry, and geodynamical modeling en_US
dc.type Thesis en_US
dspace.entity.type Publication
relation.isAuthorOfPublication daa4283c-9b77-4d0b-80cd-2f285bd677dc
relation.isAuthorOfPublication.latestForDiscovery daa4283c-9b77-4d0b-80cd-2f285bd677dc
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