Feldspar and oxide thermometry of granulites in the Adirondack Highlands

Autor: S. R. Bohlen, Eric J. Essene
Rok vydání: 1977
Předmět:
Zdroj: Contributions to Mineralogy and Petrology. 62:153-169
ISSN: 1432-0967
0010-7999
Popis: Thermometry of regionally metamorphosed granulites of the Adi- rondack Highlands has been undertaken using feldspar and iron-titanium- oxide equilibria. Electron microprobe analyses of 20 coexisting oligoclase (An18 3o) and microcline perthite (Ors7 87) pairs from charnockites and granitic gneisses give KD(Na/(Na + Ca + K)plag/(Na/(Na + Ca + K))or = 2-3 yielding temperatures of 650 ~ to 750~ in comparison to Seck's (1971) experimental and Stormer's (1975) calculated temperatures for inferred pres- sures of 8 kilobars. Microprobe analyses of 10 coexisting titaniferous magne- tite (ulv6spinels~ 1645) and ilmenite (hematitess 4.7-6.5) pairs from the Marcy massif anorthosite and related gabbros give temperatures of 620 ~ to 800 ~ C in comparison to Buddington and Lindsley's (1964) experimental data. Oxygen fugacities buffered by this assemblage range between 10-2~ and 10 16 and always lie within 10 +1 of thefo2 buffered by fayalite-magne- tite-quartz. Exsolved albite in alkali feldspar and ilmenite (oxidized ulv6spinel lamellae) must be reintegrated to infer metamorphic temperatures. Both thermometers give internally consistent, reproducible and geologically rea- sonable results. The inferred 750 ~ and 700~ isotherms wrap around the anorthosite massif in roughly concentric circles. Maximum metamorphic temperatures (790_+ 50 ~ C) occur between Saranac Lake and Tupper Lake, New York.
Databáze: OpenAIRE
Externí odkaz: