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dc.contributor.authorElkins, Lynne J.
dc.coverage.spatialMohns Ridge
dc.coverage.spatialKnipovich Ridge
dc.coverage.spatialGakkel Ridge
dc.date.accessioned2009-06-30T18:30:46Z
dc.date.available2009-06-30T18:30:46Z
dc.date.issued2009-02
dc.identifier.urihttp://hdl.handle.net/1912/2855
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 February 2009en
dc.description.abstractTo explore the ability of melting mafic lithologies to produce alkaline ocean-island basalts (OIB), an experimental study was carried out measuring clinopyroxene (Cpx)- melt and garnet (Gt)-melt partition coefficients during silica-poor garnet pyroxenite melting for a suite of trace elements, including U and Th, at 2.5GPa and 1420-1450°C. Partition coefficients range from 0.0083±0.0006 to 0.020±0.002 for Th and 0.0094±0.0006 to 0.024±0.002 for U in Cpx, and are 0.0032±0.0004 for Th and 0.013±0.002 for U in Gt. Forward-melting calculations using these experimental results to model time-dependent uranium-series isotopes do not support the presence of a fixed quantity of garnet pyroxenite in the source of OIB. To use U-series isotopes to further constrain mantle heterogeneity and the timing and nature of melting and melt transport processes, U-Th-Pa-Ra disequilibria, radiogenic isotopes, and trace-element compositions were measured for the slow-spreading Arctic mid-ocean ridges (MOR). A focused case study of 33 young (<10ka) MOR basalts (MORB) from the shallow endmember of the global ridge system, the Kolbeinsey Ridge (67°05’-70°26’N) found that unaltered Kolbeinsey MORB have universally high (230Th/238U) (1.165-1.296) and relatively uniform (230Th/232Th) (1.196-1.324), εNd (8.43- 10.49), 87Sr/86Sr (0.70274-0.70301), εHf (16.59-19.56), and Pb isotopes (e.g. 208Pb/206Pb = 2.043-2.095). This suggests a homogeneous mantle source and a long peridotite melting column produces the thick Kolbeinsey crust. Trace element ratios suggest a young, depleted mantle source. Data from the slow- to ultraslow Mohns and Knipovich Ridges north of Kolbeinsey form a sloped array, and (230Th/232Th) correlates systematically with radiogenic isotopic variations. These data are readily reproduced by models for heterogeneous mantle melting. MORB from 85ºE on the global ultraslow-spreading endmember Gakkel Ridge are homogeneously depleted with low (230Th/238U) and high (226Ra/230Th) that lie along a global negative correlation. Arctic data support a global mantle temperature control on mean (230Th/238U).en
dc.description.sponsorshipThis work was made possible through funding support from the National Defense Science and Engineering Graduate Fellowship Program, from the Academic Programs Office, from the WHOI and MIT student travel assistance funds, and from National Science Foundation grant OCE-0422278 to K.W.W.S.en
dc.format.mimetypeapplication/pdf
dc.language.isoen_USen
dc.publisherMassachusetts Institute of Technology and Woods Hole Oceanographic Institutionen
dc.relation.ispartofseriesWHOI Thesesen
dc.subjectPetrogenesisen_US
dc.subjectBasalten_US
dc.subjectPolarstern (Ship) Cruise ARK V/Iben_US
dc.subjectPolarstern (Ship) Cruise ARK VII/1en_US
dc.subjectPoseidon (Ship) Cruise POS185en_US
dc.subjectPoseidon (Ship) Cruise POS210/1en_US
dc.subjectPoseidon (Ship) Cruise POD221en_US
dc.subjectPoseidon (Ship) Cruise POS229en_US
dc.subjectPoseidon (Ship) Cruise POS291en_US
dc.subjectPoseidon (Ship) Cruise POS326en_US
dc.subjectTrident (Ship) Cruise TR139en_US
dc.subjectEndeavor (Ship: 1976-) Cruise EN26en_US
dc.subjectProfessor Logatchev (Ship) Cruiseen_US
dc.subjectOden (Ship) Cruise 11en_US
dc.titleBasalt petrogenesis beneath slow- and ultraslow-spreading Arctic mid-ocean ridgesen
dc.typeThesisen
dc.identifier.doi10.1575/1912/2855


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