Granulite Xenoliths from the Sumikawa Granite Body, Niigata Prefecture, Japan: Finding of Spinel+Quartz Assemblage from the japanese Islands.

Shimura, Toshiaki; Kawai, Teizi; Kagashima, Shin-ichi

doi:10.5575/geosoc.108.347

Cited by 7 publications

(2 citation statements)

References 23 publications

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“…These equations mean that the product minerals are spinel and quartz. As a result, the spinel must be in contact with quartz directly (e.g., Vielzeuf, 1983;Shimura et al, 2002;Kawakami and Motoyoshi, 2004; Kawasaki et al, 2011). Generally, almost all pelitic metamorphic rocks contain quartz.…”

Section: Geobarometer Geobarometers For Spinel-bearing Rocksmentioning

confidence: 99%

“…Spinel coexisting with quartz is commonly regarded as an ultrahigh-temperature (UHT) metamorphic mineral assemblage (e.g., Hensen and Green, 1971;Vielzeuf, 1983;Waters, 1991;Harley, 1998;Shimura et al, 2002;Ganguly et al, 2017) although additional minor chemical components such as Zn can extend the spinel + quartz stability to below 900 °C (Shimura et al, 2002;Harley, 2008;Clark et al, 2011). In spinel + quartz stable cases, spinel occurs in direct contact with quartz.…”

Section: Introductionmentioning

confidence: 99%

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Decompressional spinel + plagioclase symplectite from Tenmondai Rock, Lützow-Holm Complex, East Antarctica: Implications for the garnet-aluminosilicate-spinel-plagioclase geobarometer

Shimura

Harada

Fraser

et al. 2023

Journal of Mineralogical and Petrological Sciences

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Spinel + plagioclase symplectites in pelitic metamorphic rocks have been reported from many localities. We report in detail an occurrence of this texture from Tenmondai Rock, Lützow-Holm Complex, East Antarctica. This texture is produced by the following metamorphic reaction; garnet + sillimanite = spinel + plagioclase. This can be described as the following two net-transfer reactions; 5Grs + Alm + 12Als = 3Hc + 15An, and 5Grs + Prp + 12Als = 3Spl + 15An. We propose new geobarometers (GASpP) based on these equations. For example, one of these is P = (−155790 + 587.4T + RT lnK Fe ) / 29.378, for garnet + sillimanite + spinel + plagioclase assemblage in the CFASZn-system. Where P is pressure in bar, T is temperature in K, and R represents gas constant. The equilibrium constant is, K Fe = (a Grs 5 a Alm )/(a Hc 3 a An 15 ). Our proposed new geobarometers are free from quartz, corundum, orthopyroxene, and cordierite within these equations. These barometers are useful to estimate pressure conditions for spinel-bearing pelitic metamorphic rocks within a wide pressure-temperature range (andalusite, kyanite, and sillimanite fields). We estimate the metamorphic pressure-temperature (P-T ) conditions at Tenmondai Rock by applying the GASP, GRIPS, GRAIL, GASpP geobarometers, and the Zr-in-Rt geothermometer. The metamorphic evolution of the rocks at Tenmondai Rock is characterized by a clockwise P-T-t path. The peak P-T condition is about 820 MPa and 850 °C. Spinel + plagioclase symplectite was produced during the decompressional stage of this metamorphic evolution, at about 450 MPa and 700 °C.

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