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Stable isotope systematics of coexisting biotite and muscovite in high-grade pelitic rocks of southwestern Maine

Conference · · Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5690227
 [1];  [2]; ;  [3];  [4]
  1. Southern Methodist Univ., Dallas, TX (United States). Stable Isotope Lab.
  2. Univ. of Oregon, Eugene, OR (United States). Dept. of Geological Science
  3. Southern Methodist Univ., Dallas, TX (United States). Dept. of Geological Science
  4. Univ. Maine, Orono, ME (United States). Dept. Geological Science
+ Show Author Affiliations

Oxygen isotope ratios were determined on mica mineral separates from 61 Siluro-Devonian pelitic schists from the Brimstone Mt. anticline and in the vicinity of the Songo pluton. These data complement previously reported hydrogen isotope ratios on garnet grade through K feldspar-sillimanite grade metamorphic rocks subjected to 450--650C, and 3--4Kb. The largest change in the delta O-18 values of biotite and muscovite occurs between the chlorite-bearing lowest grade rocks of the garnet zone and higher grade rocks from zones 4--8. At constant bulk delta O-18, the largest calculated change in biotite and muscovite delta O-18 values due to the disappearance of chlorite is on the order of 1 per mil. The Delta O-18 values of the muscovite-biotite pairs are remarkably constant and not dependent on the peak metamorphic temperature. Using the muscovite-biotite fractionation factor of Javoy (1977), the mineral pairs record an apparent equilibration temperature of 430 [+-] 70 C. The observed fractionations may have been obtained across the entire metamorphic complex during prolonged residence at ambient postmetamorphic crustal conditions, consistent with > 50 Ma at 380 C. The near constant Delta O-18 values were achieved without complete homogenization of the mineral delta O-18 values suggesting that the postmetamorphic history obscures the details of the isotopic exchange during the earlier polymetamorphism.

OSTI ID:
5690227
Report Number(s):
CONF-921058--
Journal Information:
Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
Country of Publication:
United States
Language:
English

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Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
BIOTITE
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
GEOLOGIC FORMATIONS
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MAINE
METAMORPHISM
MICA
MINERALS
MUSCOVITE
NORTH AMERICA
NUCLEI
OXYGEN 18
OXYGEN ISOTOPES
RESERVOIR TEMPERATURE
SILICATE MINERALS
STABLE ISOTOPES
USA