Alkali metasomatism in the major gneiss, northwest Adirondacks, New York: open system or closed?

Details Alkali metasomatism in the major gneiss, northwest Adirondacks, New York: open system or closed? Alkali metasomatism in the major gneiss, northwest Adirondacks, New York: open system or closed?

Sep 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981gecoa..45.1603c&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 45, Issue 9, pp.1603-1607

Physics

1

Scientific paper

The thickest clastic unit in the northwest Adirondacks. New York, undergoes gradual transition from amphibolite to granulite facies over a distance of 55 km from Emeryville to Colton. This Precambrian quartz-biotite-oligoclase-K-feldspar gneiss with migmatite characteristics has long been cited as having undergone progressive loss of K, Si, Fe 2+ , Ba and H 2 O toward Colton and granulite facies conditions ( and , 1958, 1960a. b). Chemical data obtained from new samples, however, cast doubt upon the interpretation of open system alkali metasomatism. Outcrop to outcrop chemical variation is shown to be of similar magnitude to the chemical variation recorded across the entire gneiss belt. Chemical differences between Emeryville and Colton are not those expected from progressive degranitization by loss of alkali-bearing fluid. Ratios of K/Rb and Ca-Na K suggest that metamorphism was isochemical on the scale of outcrop. These new data were obtained from mixtures of leucosome and fine-grained paragneiss at each of 7 outcrops. The sampling technique contrasts with that of A.E.J. and C. Engel who analyzed leucosome separately from fine grained (`least altered') gneiss.

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