Constraints from mantle xenoliths on the geodynamic evolution of Earth’s upper mantle

dc.contributor.advisorLassiter, John C.
dc.contributor.committeeMemberGardner, James E
dc.contributor.committeeMemberGrand, Stephen P
dc.contributor.committeeMemberRowe, Michael C
dc.contributor.committeeMemberZhao, Donggao
dc.creatorByerly, Benjamin Lee
dc.date.accessioned2017-03-02T16:31:40Z
dc.date.available2017-03-02T16:31:40Z
dc.date.issued2014-05
dc.date.submittedMay 2014
dc.date.updated2017-03-02T16:31:40Z
dc.description.abstractGeophysical studies identify a region of slow seismic velocity mantle beneath the central Rio Grande rift that potentially represents a region of hot asthenospheric mantle that has replaced destabilized lithosphere. We determine that the majority of mantle xenoliths from Elephant Butte on the central Rio Grande rift axis are, based on their geochemical affinity to depleted mantle, derived from asthenospheric mantle that has accreted to the base of the Proterozoic lithosphere. Using mantle heat flow models, we estimate the boundary between residual lithosphere and accreted asthenosphere to be at ~45km depth. The amount of lithosphere thinning that has occurred cannot be accounted for by rift-related extension and we therefore suggest that convective removal of a large portion of Proterozoic lithosphere has occurred. Convecting upper mantle-derived peridotites display extreme isotopic depletions that are not observed in mid-ocean ridge basalts (MORB). Previous studies suggest that these isotopically ultradepleted domains represent rare refractory mantle domains that do not participate in MORB petrogenesis. We demonstrate the isotopically ultradepleted domains are not only a ubiquitous feature of convecting upper mantle, but are also capable of melting if advected beneath mid-ocean ridges. To explain the lack of MORB with ultradepleted isotopes, we suggest that MORB compositions are biased towards fertile enriched source components. Estimates of upper mantle composition based on MORB therefore overestimate the fertility of the upper mantle. The Lu-Hf system is commonly used to estimate the timing of melt depletion events in the lithospheric mantle. This is typically done with pseudoisochrons from genetically related mantle xenoliths. Most studies, however, misinterpret Lu/Hf – Hf isotopes correlations by using Cpx Lu/Hf ratios when whole rock Lu/Hf ratios are appropriate due to equilibration above the Lu-Hf closure temperature. Hafnium isotopes do not typically correlate with indicators of melt depletion, which suggests that Hf isotopes do not record ancient melting events. This is likely due to overprinting of Hf isotopes by later metasomatic events.
dc.description.departmentEarth and Planetary Sciences
dc.format.mimetypeapplication/pdf
dc.identifierdoi:10.15781/T2XD0R320
dc.identifier.urihttp://hdl.handle.net/2152/45854
dc.language.isoen
dc.subjectMantle xenoliths
dc.subjectEarth
dc.subjectUpper mantle
dc.subjectGeodynamic evolution
dc.subjectMid-ocean ridge basalts
dc.subjectGeochemistry
dc.subjectIsotope geochemistry
dc.subjectMantle geochemistry
dc.subjectGeodynamics
dc.titleConstraints from mantle xenoliths on the geodynamic evolution of Earth’s upper mantle
dc.typeThesis
dc.type.materialtext
thesis.degree.departmentGeological Sciences
thesis.degree.disciplineGeological Sciences
thesis.degree.grantorThe University of Texas at Austin
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy

Access full-text files

Original bundle

Now showing 1 - 1 of 1
Loading...
Thumbnail Image
Name:
BYERLY-DISSERTATION-2014.pdf
Size:
3.45 MB
Format:
Adobe Portable Document Format

License bundle

Now showing 1 - 1 of 1
No Thumbnail Available
Name:
LICENSE.txt
Size:
1.84 KB
Format:
Plain Text
Description: