| Paper No. 105-0 | ||
| THERMOBAROMETRY OF ECLOGITES FROM THE EASTERN BLUE RIDGE, NORTH CAROLINA | ||
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PAGE, F. Z., ESSENE, E. J., and MUKASA, S. B., Department of Geological Sciences, Univ of Michigan, 2534 C.C. Little, Ann Arbor, MI 48109-1063, fpage@umich.edu Eclogites from the Eastern Blue Ridge of North Carolina contain a more highly varied mineralogy than
previously recognized. Garnets are
found to contain inclusions of omphacitic and diopsidic pyroxene, hornblende,
epidote, sphene, rutile, quartz, apatite, and minor Cu-Fe sulfides. These
eclogites are located at the base of the Ash Metamorphic Suite, and are
thought to have been emplaced along the Taconic Suture. Eclogites
from near Bakersville, NC are primarily composed of garnet-omphacitic or
diopsidic clinopyroxene-hornblende-epidote-rutile-quartz, and are variably
overprinted with hornblende and plagioclase. Matrix
omphacitic clinopyroxene (Na0.20Ca0.75Mg0.63
Fe2+0.15Fe3+0.10Al0.25Si1.91)
has, in some cases, reacted to form diopsidic pyroxene (Na0.08Ca0.84Mg0.72
Fe2+0.23Fe3+0.04Al0.12Si1.95)
-plagioclase, and is variably replaced with secondary hornblende. A
new find of orthopyroxene is associated with matrix diopside-plagioclase
in some samples. The jadeite content of unreacted clinopyroxene cores (Jd
0.30) indicates pressures greater than 13 kbar at 700°C.Garnets
are zoned (cores: Alm 47.7 Pyp 30.3 Grs 21.0 Sps 1.0), with Mg2+-poor,
Fe2+, Mn2+ -rich retrograde rims (Alm 52.6 Pyp 25.4
Grs 20.5 Sps 1.5). Secondary amphibole-plagioclase
preferentially form along garnet-clinopyroxene boundaries.Hornblende
inclusions are different in composition from those in the matrix, the former
containing more K+ and Ti4+ and less Fe3+. The
reaction clinozoisite+sphene=grossular+rutile+quartz+H2O
indicates pressure of 7 kbar at 650°C, suggesting that these inclusions
are probably entrapped during prograde metamorphism. Inclusions
of clinopyroxene in garnet yield temperatures of 520-600°C for pressures
of 13 kbar. However, due to rapid Fe2+/Mg2+
exchange, these T may be reset during cooling. The
overprinted hypersthene-diopside-plagioclase-quartz assemblage suggests
a late granulite facies event.
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GSA Annual Meeting, November 5-8, 2001
General Information for this Meeting | ||
| Session No. 105 Metamorphic Petrology II Hynes Convention Center: Ballroom A 8:00 AM-12:00 PM, Wednesday, November 7, 2001 | ||
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