Calculation of equilibration conditions for garnet granulite and garnet websterite nodules in African kimberlite pipes

D. A. Carswell; W. L. Griffin

doi:10.1007/BF01084630

Calculation of equilibration conditions for garnet granulite and garnet websterite nodules in African kimberlite pipes

D. A. Carswell^*, W. L. Griffin

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

11 Citations (Scopus)

Abstract

Pressure/temperature estimates based on different combinations of calibrated mineralogical thermometers and barometers and alternative assumptions concerning the Fe²⁺/(Fe²⁺+Fe³⁺) ratios in the mineral phases are compared for a suite of fourteen nodules. Preferred P/T values have been obtained by simultaneous solution of eq. (12) of Wood (1974) for garnet-orthopyroxene equilibria and the Ellis and Green (1979) equation defining the P,T,X dependence of the Fe²⁺-Mg²⁺ partition coefficient for coexisting garnet and clinopyroxene. However, to obtain realistic results it is first necessary to calculate the Fe³⁺ contents in the minerals-conveniently done on a charge balance basis. The favoured mean P/T estimates of 654±36°C and 10.8±3.1 kbs are compatible with a lower crustal origin for this nodule suite.

Original language	English
Pages (from-to)	229-244
Number of pages	16
Journal	TMPM Tschermaks Mineralogische und Petrographische Mitteilungen
Volume	28
Issue number	3
DOIs	https://doi.org/10.1007/BF01084630
Publication status	Published - Sept 1981
Externally published	Yes

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title = "Calculation of equilibration conditions for garnet granulite and garnet websterite nodules in African kimberlite pipes",

abstract = "Pressure/temperature estimates based on different combinations of calibrated mineralogical thermometers and barometers and alternative assumptions concerning the Fe2+/(Fe2++Fe3+) ratios in the mineral phases are compared for a suite of fourteen nodules. Preferred P/T values have been obtained by simultaneous solution of eq. (12) of Wood (1974) for garnet-orthopyroxene equilibria and the Ellis and Green (1979) equation defining the P,T,X dependence of the Fe2+-Mg2+ partition coefficient for coexisting garnet and clinopyroxene. However, to obtain realistic results it is first necessary to calculate the Fe3+ contents in the minerals-conveniently done on a charge balance basis. The favoured mean P/T estimates of 654±36°C and 10.8±3.1 kbs are compatible with a lower crustal origin for this nodule suite.",

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AU - Carswell, D. A.

AU - Griffin, W. L.

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N2 - Pressure/temperature estimates based on different combinations of calibrated mineralogical thermometers and barometers and alternative assumptions concerning the Fe2+/(Fe2++Fe3+) ratios in the mineral phases are compared for a suite of fourteen nodules. Preferred P/T values have been obtained by simultaneous solution of eq. (12) of Wood (1974) for garnet-orthopyroxene equilibria and the Ellis and Green (1979) equation defining the P,T,X dependence of the Fe2+-Mg2+ partition coefficient for coexisting garnet and clinopyroxene. However, to obtain realistic results it is first necessary to calculate the Fe3+ contents in the minerals-conveniently done on a charge balance basis. The favoured mean P/T estimates of 654±36°C and 10.8±3.1 kbs are compatible with a lower crustal origin for this nodule suite.

AB - Pressure/temperature estimates based on different combinations of calibrated mineralogical thermometers and barometers and alternative assumptions concerning the Fe2+/(Fe2++Fe3+) ratios in the mineral phases are compared for a suite of fourteen nodules. Preferred P/T values have been obtained by simultaneous solution of eq. (12) of Wood (1974) for garnet-orthopyroxene equilibria and the Ellis and Green (1979) equation defining the P,T,X dependence of the Fe2+-Mg2+ partition coefficient for coexisting garnet and clinopyroxene. However, to obtain realistic results it is first necessary to calculate the Fe3+ contents in the minerals-conveniently done on a charge balance basis. The favoured mean P/T estimates of 654±36°C and 10.8±3.1 kbs are compatible with a lower crustal origin for this nodule suite.

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Calculation of equilibration conditions for garnet granulite and garnet websterite nodules in African kimberlite pipes

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