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 Unpublished MSc.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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