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dc.contributor.authorMagde, Laura S.  Concept link
dc.coverage.spatialEast Pacific Rise
dc.coverage.spatialReykjanes Ridge
dc.date.accessioned2013-01-17T19:13:08Z
dc.date.available2013-01-17T19:13:08Z
dc.date.issued1997-03
dc.identifier.urihttps://hdl.handle.net/1912/5722
dc.descriptionSubmitted 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 March 1997en_US
dc.description.abstractThe formation of new oceanic crust is the result of a complex geodynamic system in which mantle rises beneath spreading centers and undergoes decompression melting. The melt segregates from the matrix and is focused to the rise axis, where it is eventually intruded and/or erupted to form the oceanic crust. This thesis combines surface observations with laboratory studies and geodynamic modeling to study this crustal-production system. Quantitative modeling of the crustal and mantle contributions to the axial gravity and topography observed at the East Pacific Rise shows that the retained melt fraction in the mantle is small (<3%) and is focused into a narrow column extending up to 70 km beneath the ridge axis. Consistent with geochemical constraints, the extraction of melt from the mantle therefore appears to be efficiently focus melt toward the ridge axis. A combination of laboratory and numerical studies are used to constrain the pattern of mantle flow beneath highly-segmented ridges. Even when the buoyant component of mantle flow is constrained to be two-dimensional, laboratory studies show that a segmented ridge will drive three-dimensional mantle upwelling. However, using reasonable mantle parameters in numerical models, it is difficult to induce large-amplitude three-dimensional mantle upwelling at the relatively short wavelengths of individual segments (~50 km). Instead, a simple model of three-dimensional melt migration shows that the observed segment-scale variations in crustal thickness can be explained by focusing of melt as it upwells through a more two-dimensional mantle flow field. At the Reykjanes Ridge, the melt appears to accumulate in small crustal magma chambers, before erupting in small batches to form numerous overlapping hummocky lava flows and small volcanoes. This suggests that crustal accretion, particularly at slow-spreading centers, may be a highly discontinuous process. Long-wavelength variations in crustal accretion may be dominated by variations in mantle upwelling while short-wavelength, segment-scale variations are more likely controlled by a complex three-dimensional processes of melt extraction and magma eruption.en_US
dc.description.sponsorshipDuring my first three years in the Joint Program, I was supported by an National Science Foundation Graduate Student Fellowship. Other support has been derived from National Science Foundation grants OCE-9296017, OCE-9224738, OCE-9215544, and EAR grant 93-07400.en_US
dc.format.mimetypeapplication/pdf
dc.language.isoen_USen_US
dc.publisherMassachusetts Institute of Technology and Woods Hole Oceanographic Institutionen_US
dc.relation.ispartofseriesWHOI Thesesen_US
dc.subjectMid-ocean ridgesen_US
dc.subjectPlumesen_US
dc.subjectStructural geologyen_US
dc.subjectPlate tectonicsen_US
dc.subjectSubmarine geologyen_US
dc.subjectMantleen_US
dc.titleMantle upwelling, melt generation, and magma transport beneath mid-ocean ridgesen_US
dc.typeThesisen_US
dc.identifier.doi10.1575/1912/5722


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