Garnets as hydrochronometers

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5770914

Chamberlain, C P ^[1]; Conrad, M E ^[2]

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1. Dartmouth Univ., Hanover, NH (United States). Dept. of Earth Sciences
2. Lawrence Berkeley Lab., Berkeley, CA (United States)

This study examines oxygen isotope zoning in garnets from a Barrovian metamorphic terrane in eastern Vermont. Previous Sr isotopic and structural studies of these garnets have shown that they grew over an approximately 10 myr interval during thrusting and nappe emplacement. These studies show that the garnets are strongly zoned in delta O-18. This zoning is the result of equilibration of garnet with water derived from dehydration of subjacent pelites during nappe stage deformation. The magnitude of delta O-18 zoning depends upon the garnet's location in the outcrop studied. The garnets come from an isotopically light delta O-18 felsic schist that is adjacent a relatively heavy delta O-18 schist. Garnets from the felsic schists within 10 meters of the contact with the isotopically heavier schists have nearly homogeneous dealt O-18 values around 9.5[per thousand]. Garnet in the felsic schists 85 meters from the contact are more strongly zoned, with delta O-18 ranging from a low of ca 6.0[per thousand] in the cores to a high of ca 9.0[per thousand] at the rims. These zoning patterns were produced by continuous infiltration of relatively heavy delta O-18 waters, derived from the subjacent schists into the felsic schists during garnet grade metamorphism. It is possible to determine the time integrated fluid fluxes by comparison of observed zoning profiles in garnet with those calculated from the equation describing combined advective-diffusive of a tracer. Using this method, the authors calculate time integrated fluid fluxes of 1.5 [times] 10[sup 4] cm[sup 3]/cm[sup 2]. Fluxes of this magnitude could have been produced by dewatering of 1.5 km of schist during garnet grade metamorphism.

• OSTI ID: 5770914
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
FLUIDS
GARNETS
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
METAMORPHIC ROCKS
METAMORPHISM
MINERALS
NORTH AMERICA
NUCLEI
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
RESERVOIR FLUIDS
ROCKS
SCHISTS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
USA
VERMONT