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Oxygen, carbon and hydrogen isotope studies of contact metamorphism

Citation

Shieh, Yuch-Ning (1969) Oxygen, carbon and hydrogen isotope studies of contact metamorphism. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JJY7-J871. https://resolver.caltech.edu/CaltechTHESIS:02202014-142721576

Abstract

The O18/O16, C13/C12, and D/H ratios have been determined for rocks and coexisting minerals from several granitic plutons and their contact metamorphic aureoles in northern Nevada, eastern California, central Colorado, and Texas, with emphasis on oxygen isotopes. A consistent order of O18/O16, C13/C12, and D/H enrichment in coexisting minerals, and a correlation between isotopic fractionations among coexisting mineral pairs are in general observed, suggesting that mineral assemblages tend to approach isotopic equilibrium during contact metamorphism. In certain cases, a correlation is observed between oxygen isotopic fractionations of a mineral pair and sample distance from intrusive contacts. Isotopic temperatures generally show good agreement with heat flow considerations. Based on the experimentally determined quartz-muscovite O18/O16 fractionation calibration curve, temperatures are estimated to be 525 to 625°C at the contacts of the granitic stocks studied.

Small-scale oxygen isotope exchange effects between intrusive and country rock are observed over distances of 0.5 to 3 feet on both sides of the contacts; the isotopic gradients are typically 2 to 3 per mil per foot. The degree of oxygen isotopic exchange is essentially identical for different coexisting minerals. This presumably occurred through a diffusion-controlled recrystallization process. The size of the oxygen isotope equilibrium systems in the small-scale exchanged zones vary from about 1.5 cm to 30 cm. A xenolith and a re-entrant of country rock projecting into on intrusive hove both undergone much more extensive isotopic exchange (to hundreds of feet); they also show abnormally high isotopic temperatures. The marginal portions of most plutons have unusually high O18/O16 ratios compared to "normal" igneous rocks, presumably due to large-scale isotopic exchange with meta-sedimentary country rocks when the igneous rocks were essentially in a molten state. The isotopic data suggest that outward horizontal movement of H2O into the contact metamorphic aureoles is almost negligible, but upward movement of H2O may be important. Also, direct influx and absorption of water from the country rock may be significant in certain intrusive stocks.

Except in the exchanged zones, the O18/O16 ratios of pelitic rocks do not change appreciably during contact metamorphism, even in the cordierite and sillimanite grades; this is in contrast to regional metamorphic rocks which commonly decrease in O18 with increasing grade. Low O18/O16 and C13/C12 ratios of the contact metamorphic marbles generally correlate well with the presence of calc-silicate minerals, indicating that the CO2 liberated during metamorphic decarbonation reactions is enriched in both O18 and C13 relative to the carbonates.

The D/H ratios of biotites in the contact metamorphic rocks and their associated intrusions show a geographic correlation that is similar to that shown by the D/H ratios of meteoric surface waters, perhaps indicating that meteoric waters were present in the rocks during crystallization of the biotites.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Oxygen isotope geothermometers, Isotopic exchange during contact metamorphism
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Taylor, Hugh P.
Thesis Committee:
  • Taylor, Hugh P. (chair)
  • Epstein, Samuel
  • Silver, Leon T.
  • Albee, Arden Leroy
  • Burnett, Donald S.
Defense Date:15 July 1968
Non-Caltech Author Email:ynshieh (AT) purdue.edu
Funders:
Funding AgencyGrant Number
NSFGA 992
Atomic Energy CommissionAT(04-3)-427
Record Number:CaltechTHESIS:02202014-142721576
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:02202014-142721576
DOI:10.7907/JJY7-J871
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8092
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:20 Feb 2014 23:52
Last Modified:21 Dec 2019 03:03

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