Retrograde fluids in granulites: Stable isotope evidence of fluid migration

Journal Article · Mon Jul 01 00:00:00 EDT 1991 · Journal of Geology; (United States)

DOI:https://doi.org/10.1086/629517· OSTI ID:5616807

Morrison, J ^[1]; Valley, J W ^[2]

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1. Univ. of Southern California, Los Angeles (United States)
2. Univ. of Wisconsin, Madison (United States)

Widespread retrograde alteration assemblages document the migration of mixed H{sub 2}O-CO{sub 2} fluids into granulite facies rocks in the Adirondack Mountains. Fluid migration is manifest by (1) veins and patchy intergrowths of chlorite {plus minus} sericite {plus minus} calcite, (2) small veins of calcite, many only identifiable by cathodoluminescence, and (3) high-density, CO{sub 2}-rich or mixed H{sub 2}O-CO{sub 2} fluid inclusions. The distinct and varied textural occurrences of the alteration minerals indicate that fluid-rock ratios were low and variable on a local scale. Stable isotope ratios of C, O, and S have been determined in retrograde minerals from samples of the Marcy anorthosite massif and adjacent granitic gneisses (charnockites). Retrograde calcite in the anorthosite has a relatively small range in both {delta}{sup 18}O{sub SMOW} and {delta}{sup 13}C{sub PDB} (8.6 to 14.9% and {minus}4.1 to 0.4%, respectively), probably indicating that the hydrothermal fluids that precipitated the calcite had exchanged with a variety of crustal lithologies including marbles and orthogneisses, and that calcite was precipitated over a relatively narrow temperature interval. Values of {delta}{sup 34}S{sub CDT} that range from 2.8 to 8.3% within the anorthosite can also be interpreted to reflect exchange between orthogneisses and metasediments. The recognition of retrograde fluid migration is particularly significant in granulite facies terranes because the controversy surrounding the origin of granulites arises in part from differing interpretations of fluid inclusion data, specifically, the timing of entrapment of high-density, CO{sub 2}-rich inclusions. Results indicate that retrograde fluid migration, which in some samples may leave only cryptic petrographic evidence, is a process capable of producing high-density, CO{sub 2}-rich fluid inclusions.

• OSTI ID: 5616807
• Journal Information: Journal of Geology; (United States), Vol. 99:4; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ADIRONDACK MOUNTAINS
RESERVOIR FLUIDS
GEOCHEMISTRY
ANORTHOSITES
CALCITE
CARBON 13
CARBON DIOXIDE
CATHODOLUMINESCENCE
CHLORITE MINERALS
ENVIRONMENTAL TRANSPORT
GRANULITES
INCLUSIONS
ORIGIN
OXYGEN 18
ROCK-FLUID INTERACTIONS
SULFUR 34
TEXTURE
WATER
APPALACHIAN MOUNTAINS
CARBON COMPOUNDS
CARBON ISOTOPES
CARBON OXIDES
CARBONATE MINERALS
CHALCOGENIDES
CHEMISTRY
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FLUIDS
GABBROS
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
ISOTOPES
LIGHT NUCLEI
LUMINESCENCE
MASS TRANSFER
METAMORPHIC ROCKS
MINERALS
MOUNTAINS
NUCLEI
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
STABLE ISOTOPES
SULFUR ISOTOPES
580000* - Geosciences