Differentiation in the early Earth: An experimental investigation.

Persistent Link:
http://hdl.handle.net/10150/186611
Title:
Differentiation in the early Earth: An experimental investigation.
Author:
McFarlane, Elisabeth Ann.
Issue Date:
1994
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The Earth may have been covered with a terrestrial magma ocean. Is there evidence for resulting extensive mineral fractionation? Agee and Walker, 1988, proposed that significant flotation and addition of olivine into the upper mantle can explain the elevated Mg/Si ratio of this region. A number of element ratios were present in the primitive mantle of the Earth in approximately chondritic ratios (e.g., Jagoutz et al., 1979) providing constraints on amounts of mineral fractionation if appropriate partition coefficient values are known (e.g., Kato et al., 1988a). In addition, the V, Cr and Mn abundance pattern in the mantles of the Earth and moon are similar to one another, which could imply a related origin for these bodies (e.g., Ringwood, 1990). Previous attempts to explain the origin of this abundance pattern have been unsuccessful (e.g., Drake et al., 1989). High pressure and temperature mantle mineral/silicate melt partition coefficient values are experimentally determined in this work. These values are used via equilibrium crystallization to examine the effect of mineral fractionation on the primitive mantle. The effect of mineral fractionation on the abundance pattern of V, Cr and Mn in the upper mantle of the Earth is examined. Fractionation of majorite garnet, magnesiowustite and Mg-perovskite yields a V, Cr and Mn abundance pattern that is different than inferred. Thus, the pattern of V, Cr and Mn was not established by high pressure mantle mineral/silicate melt fractionation. Other mineral fractionation effects are also examined. Significant addition of olivine to the upper mantle is disallowed based on the Ni/Co ratio. Significant fractionation of majorite garnet, magnesiowustite and Mg-perovskite is precluded based on several element ratios (e.g., Mg/Al, Ca/Al for majorite garnet; e.g., Mg/Al, Ca/Al, Mg/Si, Mg/Ca for magnesiowustite; e.g., Ca/Al, Sc/Sm, Mg/Ca for Mg-perovskite). Thus, the primitive mantle does not show evidence of significant fractionation of volumetrically important liquidus phases. The implication is that the Earth's Mg/Si ratio unique, and that compositionally distinct reservoirs of material were largely preserved in the accretionary environment.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Dissertations, Academic.; Geology.; Geochemistry.; Mineralogy.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Planetary Sciences; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Drake, Michael J.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleDifferentiation in the early Earth: An experimental investigation.en_US
dc.creatorMcFarlane, Elisabeth Ann.en_US
dc.contributor.authorMcFarlane, Elisabeth Ann.en_US
dc.date.issued1994en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe Earth may have been covered with a terrestrial magma ocean. Is there evidence for resulting extensive mineral fractionation? Agee and Walker, 1988, proposed that significant flotation and addition of olivine into the upper mantle can explain the elevated Mg/Si ratio of this region. A number of element ratios were present in the primitive mantle of the Earth in approximately chondritic ratios (e.g., Jagoutz et al., 1979) providing constraints on amounts of mineral fractionation if appropriate partition coefficient values are known (e.g., Kato et al., 1988a). In addition, the V, Cr and Mn abundance pattern in the mantles of the Earth and moon are similar to one another, which could imply a related origin for these bodies (e.g., Ringwood, 1990). Previous attempts to explain the origin of this abundance pattern have been unsuccessful (e.g., Drake et al., 1989). High pressure and temperature mantle mineral/silicate melt partition coefficient values are experimentally determined in this work. These values are used via equilibrium crystallization to examine the effect of mineral fractionation on the primitive mantle. The effect of mineral fractionation on the abundance pattern of V, Cr and Mn in the upper mantle of the Earth is examined. Fractionation of majorite garnet, magnesiowustite and Mg-perovskite yields a V, Cr and Mn abundance pattern that is different than inferred. Thus, the pattern of V, Cr and Mn was not established by high pressure mantle mineral/silicate melt fractionation. Other mineral fractionation effects are also examined. Significant addition of olivine to the upper mantle is disallowed based on the Ni/Co ratio. Significant fractionation of majorite garnet, magnesiowustite and Mg-perovskite is precluded based on several element ratios (e.g., Mg/Al, Ca/Al for majorite garnet; e.g., Mg/Al, Ca/Al, Mg/Si, Mg/Ca for magnesiowustite; e.g., Ca/Al, Sc/Sm, Mg/Ca for Mg-perovskite). Thus, the primitive mantle does not show evidence of significant fractionation of volumetrically important liquidus phases. The implication is that the Earth's Mg/Si ratio unique, and that compositionally distinct reservoirs of material were largely preserved in the accretionary environment.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectDissertations, Academic.en_US
dc.subjectGeology.en_US
dc.subjectGeochemistry.en_US
dc.subjectMineralogy.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePlanetary Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairDrake, Michael J.en_US
dc.contributor.committeememberBoynton, Williamen_US
dc.contributor.committeememberSwindle, Timothyen_US
dc.contributor.committeememberPatchett, Jonathanen_US
dc.contributor.committeememberRuiz, Joaquinen_US
dc.identifier.proquest9424944en_US
dc.identifier.oclc722419758en_US
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