Pyroxene Geothermometry of Some Granulite Facies

Wood-and-Banno temperatures for the coexisting pyroxenes of equilibrated meta- morphic rocks in the hornblende granulite subfacies fall in the range 780-860~ Minimum temperature estimates for granulites include 760-790~ from the dehydration of hornblende to an orthopyroxene assemblage, and about 800~ from other evidence. The pyroxene temperatures are generally consistent with these temperature estimates, and are certainly not too low or more than 50 ~ too high. Pyroxene temperatures for the three subzones of Broken Hill granulites increase away from the orthopyroxene isograd and are sufficiently precise that the difference between the lowest and intermediate subzones is statistically significant. Temperatures for pyroxenes in pyroxene-granulite subfacies rocks are greater than 860~ The internal consistency, precision and apparent accuracy of the Wood-and- Banno pyroxene geothermometer in the metamorphic temperature range make it an important tool.