ABSTRACT
The Lake George Area belongs to the southeastern part of the
Adirondack
Highlands. The rocks of this area show variations in mineral
assemblages
which are caused by differences in bulk chemical composition. This
makes
it unsuccessful to use a subdivision of the granulite facies which
is suggested
by de Waard (1965).
The CFM diagram (Abbott, 1982) is used to show the relationship
between
composition and paragenesis of the Lake George Area. In this
study, a different
result has been found in the order of partitioning of Fe between
coexisting
minerals, namely,
garnet>hornblende>biotite>orthopyroxene>clinopyroxene.
The hornblende granitic gneiss belongs to a different subfacies
from the
mafic granulite and charnockitic gneiss according to Abbott's
subdivision
of the facies. But, following the order of XFe of the minerals
from this
study, the typical mineral assemblage of this rock,
hornblende-garnet-biotite,
may belong to the same subfacies as the other rock types of this
area.
The study of biotites of metapelite in the Lake George Area
indicates different
substitution mechanisms in different regions of the granulite
facies.
From the garnet-orthopyroxene (clinopyroxene) thermometer,
710°C
was obtained for the highest estimate of the metamorphism. This
temperature
condition appears to be consistent with the observed mineral
assemblages
of a lower-grade part of the granulite facies and confirms the
isotherm
pattern of Bohlen et al. (1985).
Cooling ages of 971±17 Ma, 882±7 Ma and
656±17
Ma were obtained for hornblende, biotite and microcline,
respectively,
with 40Ar/39Ar dating method. With cooling ages of minerals and
reasonable
closure temperatures for each mineral, average cooling rates are
calculated:
2.7°C/Ma for the time interval of peak
metamorphism-hornblende, 2.2°C/Ma
for hornblende-biotite, and 0.7°C/Ma for biotite-microcline.
Ree, B., 1991. Mineral paragenesis of the granulite facies in the
Lake
George area, New York. Unpublished MSc. thesis, State University
of New
York at Albany. 68 pp., +x
University at Albany Science Library call number: SCIENCE
Oversize
(*) QE 40 Z899 1991 R65
thesis (scanned text) - 2.6MB pdf file
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