THERMOBAROMETRY OF ECLOGITES FROM THE EASTERN BLUE RIDGE, NORTH CAROLINA

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 (Na_0.20Ca_0.75Mg_0.63 Fe²⁺_0.15Fe³⁺_0.10Al_0.25Si_1.91) has, in some cases, reacted to form diopsidic pyroxene (Na_0.08Ca_0.84Mg_0.72 Fe²⁺_0.23Fe³⁺_0.04Al_0.12Si_1.95) -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.