Redox state and water content in the upper mantle: Linkages to the atmosphere, hydrosphere and continents

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dc.contributor.advisorLee, Cin-Ty A.en_US
dc.creatorLi, Zhengxueen_US
dc.date.accessioned2009-06-03T19:50:47Zen_US
dc.date.available2009-06-03T19:50:47Zen_US
dc.date.issued2008en_US
dc.description.abstractGeochemical and petrologic tools were deployed to investigate the redox state and water content of the earth's upper mantle. Study results are discussed in the context of their linkages to the atmospheric oxygen level, hydrospheric water budget and lithospheric evolution of continents. Because the partitioning of V is redox-sensitive and otherwise similar to that of Sc which is not redox sensitive, the V/Sc ratios of basalts of different ages act as a natural recorder of the redox states of the upper mantle. Through a comparison between global mid-ocean ridge basalts and Archean basalts, the fO2 of the upper mantle was inferred to have changed by no more than 0.3 log units since Archean. Combined with results from a thermodynamic model simulating the redox reactions of volcanic gases, this observation argues against the idea that the increase in oxygen in the atmosphere ∼2.3 billion years ago was caused by redox transition in the upper mantle. Through a geochemical and petrologic study at the Feather River Ophiolite (in northern California), global water recycling rates at subduction zones were estimated based on reconstructed serpentinization depths for the oceanic lithospheric mantle. Within uncertainties, the estimated water recycling rates roughly match global volcanic dewatering rates, which suggest the hydrospheric water storage is current at steady-state. Based on water contents measured in mantle xenoliths from the Colorado Plateau and vicinity, the idea that the lithospheric mantle beneath the western North America was rehydrated by the dewatering of the flat-subducting Farallon slab is confirmed. As predicted by an updated flow law for olivine aggregates, hydration might have weakened the basal lithosphere beneath the Colorado Plateau and thus induced lithospheric thinning by ∼15 km as a result of basal erosion. Extrapolation of the flow law to thick, cratonic lithosphere further suggests lithospheric thinning of much larger extents can occur if enough water was introduced during hydration. If so, subduction-induced hydration might have played an important role in regulating the lithospheric evolution of continents.en_US
dc.format.extent150 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoTHESIS GEOL. 2008 LIen_US
dc.identifier.citationLi, Zhengxue. "Redox state and water content in the upper mantle: Linkages to the atmosphere, hydrosphere and continents." (2008) Diss., Rice University. <a href="https://hdl.handle.net/1911/22144">https://hdl.handle.net/1911/22144</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/22144en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectGeophysicsen_US
dc.subjectGeochemistryen_US
dc.titleRedox state and water content in the upper mantle: Linkages to the atmosphere, hydrosphere and continentsen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentEarth Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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