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Oxygen isotope ratios in coexisting minerals of regionally metamorphosed rocks

Citation

Garlick, George Donald (1965) Oxygen isotope ratios in coexisting minerals of regionally metamorphosed rocks. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/YC63-0F49. https://resolver.caltech.edu/CaltechTHESIS:03192015-140536982

Abstract

The O18/O16 ratios of coexisting minerals from a number of regionally metamorphosed rocks have been measured, using a bromine pentafluoride extraction-technique. Listed in order of their increasing tendency to concentrate O18, the minerals analyzed are magnetite, ilmenite, chlorite, biotite, garnet, hornblende, kyanite, muscovite, feldspar, and quartz. The only anomalous sequence detected occurs in a xenolith of schist, in which quartz, muscovite, biotite, and ilmenite, but not garnet, have undergone isotopic exchange with surrounding trondjemite.

With few exceptions, quartz-magnetite and quartz-ilmenite fractionations decrease with increasing metamorphic grade determined by mineral paragenesis and spatial distribution. This consistency does not apply to quartz-magnetite and quartz-ilmenite fractionations obtained from rocks in which petrographic evidence of retrogradation is present.

Whereas measured isotopic fractionations among quartz, garnet, ilmenite, and magnetite are approximately related to metamorphic grade, fractionations between these minerals and biotite or muscovite show poor correlation with grade. Variations in muscovite-biotite fractionations are relatively small. These observations are interpreted to mean that muscovite and biotite are affected by retrograde re-equilibration to a greater extent than the anhydrous minerals analyzed.

Measured quartz-ilmenite fractionations range from 12 permil in the biotite zone of central Vermont to 6.5 permil in the sillimanite-orthoclase zone of southeastern Connecticut. Analyses of natural assemblages from the kyanite and sillimanite zones suggest that equilibrium quartz-ilmenite fractionations are approximately 8 percent smaller than corresponding quartz-magnetite fractionations. Employing the quartz-magnetite geothermometer calibrated by O'Neil and Clayton (1964), a temperature of 560°C was obtained for kyanite-bearing schists from Addison County, Vermont. Extending the calibration to quartz-ilmenite fractionations, a temperature of 600°C was obtained for kyanite-schists from Shoshone County, Idaho. At these temperatures kyanite is stable only at pressures exceeding 11 kbars (Bell, 1963), corresponding to lithostatic loads of over 40 km.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Geology
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Epstein, Samuel
Thesis Committee:
  • Unknown, Unknown
Defense Date:2 June 1964
Funders:
Funding AgencyGrant Number
Kennecott Copper CorporationUNSPECIFIED
Harvey Mudd Summer FellowshipUNSPECIFIED
Penrose BequestUNSPECIFIED
Atomic Energy CommissionUNSPECIFIED
Record Number:CaltechTHESIS:03192015-140536982
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:03192015-140536982
DOI:10.7907/YC63-0F49
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8793
Collection:CaltechTHESIS
Deposited By: Bianca Rios
Deposited On:20 Mar 2015 14:56
Last Modified:21 Dec 2019 04:32

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