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Geothermometry of exsolved augites from the Laramie Anorthosite Complex, Wyoming

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Abstract

Exsolved augite pyroxenes from the ferromonzonite border facies of the ferrosyenite in the Laramie Anorthosite Complex have been studied with the transmission electron microscope and the electron microprobe to determine their exsolution histories. The Lindsley and Andersen (1983) geothermometer gives initial crystallization temperatures of ≥1000° C for the bulk augite crystal (Wo32 En22 Fs46). Exsolved lamellae are predominantly pigeonites with very low calcium contents (Wo1–3 En23–24 Fs71–74) and have formation temperatures estimated to be in the range of 600 to 975° C. The uniform compositions of lamellae and hosts, despite the range in lamellar size and orientation, suggest that either 1) the ferromonzonite experienced an extended plateau in cooling or a reheating event at 600 to 650° C or 2) the pyroxenes recorded a blocking temperature. Two-feldspar geothermometry on exsolved feldspars also records 600° C and suggests that these low temperatures are not blocking temperatures.

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  1. Kenneth J. T. Livi

    Present address: Department of Earth and Planetary Sciences, The Johns Hopkins University, 21218, Baltimore, MD, USA

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  1. Department of Earth and Space Sciences, State University of New York at Stony Brook, 11794, Stony Brook, New York, USA

    Kenneth J. T. Livi

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Livi, K.J.T. Geothermometry of exsolved augites from the Laramie Anorthosite Complex, Wyoming. Contr. Mineral. and Petrol. 96, 371–380 (1987). https://doi.org/10.1007/BF00371255

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  • DOI: https://doi.org/10.1007/BF00371255

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