Reply to comment by J. Ganguly on Evaluation of thermobarometers for garnet peridotites'

Journal Article · Sat Feb 01 00:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90103-P· OSTI ID:5319338

Finnerty, A A ^[1]; Boyd, F R ^[2]

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1. Balance Hydrologics, Inc., Berkeley, CA (United States)
2. Carnegie Institution of Washington, DC (United States)

In the authors' 1984 and subsequent papers (Finnerty and Boyd, 1987; Finnerty, 1989) they evaluated more than 650 combinations of thermometers and barometers. Where possible they have used thermodynamic or mathematic formulations that authors have derived from their data. In cases where such formulations were either not provided or were incomplete, they have fitted data by the simplest possible procedures. Equation 9a of Lane and Ganguly (1980) requires calculation of the term X{sub Al{sub 2}O{sub 3}}{sup Opx} from analytical data in the form of weight-percent oxides. No procedure was given in their paper for calculation of this quantity. Different methods are required depending upon site occupancy models and upon whether the effects of components other than Mg, Al, and Si (MAS) are considered. Limiting their consideration to the MAS system, the authors tested alternate definitions of X{sub Al{sub 2}O{sub 3}}{sup Opx} by calculating P-T values for garnet peridotite xenoliths from northern Lesotho and comparing the estimates to those presented by Lane and Ganguly (1980, Fig. 5 LG80). When X{sub Al{sub 2}O{sub 3}}{sup Opx} was calculated as Al/(Al + 2Si), where the chemical symbols refer to the numbers of the respective cations calculated from the chemical analysis on a 6-oxygen basis, their estimates agreed with those in the Lane and Ganguly (1980) paper, insofar as could be determined by comparison with their Fig. 5. This formula was transferred into Program TEMPEST, and a plot generated with it was used as the basis for remarks in the text of the authors' paper. These remarks are correct, but an error was made in assembling the accompanying figures. A preliminary estimate calculated with the formula Al/(Al + Si) was inadvertently substituted for the correct figure and was included in their published paper (Fig. 4F). Pressure estimates in the invalid figure are low by about 10 kbar. The correct version of the original Fig. 4F is presented herein as Fig. 1.

• OSTI ID: 5319338
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 56:2; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
47 OTHER INSTRUMENTATION
GEOBAROMETRY
ACCURACY
CALIBRATION STANDARDS
GEOTHERMOMETRY
PERIDOTITES
CALIBRATION
DIAMONDS
GARNETS
GEOTHERMOMETERS
GRAPHITE
MATHEMATICAL MODELS
PRESSURE MEASUREMENT
SOLUBILITY
CARBON
ELEMENTAL MINERALS
ELEMENTS
IGNEOUS ROCKS
MEASURING INSTRUMENTS
MINERALS
NONMETALS
OXYGEN COMPOUNDS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STANDARDS
THERMOMETERS
580000* - Geosciences
440700 - Geophysical & Meteorological Instrumentation- (1990-)