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

Spinel + plagioclase symplectites in pelitic metamorphic rocks have been reported from many localities. We report detail an occurrence of this texture Tenmondai Rock, Lützow-Holm Complex, East Antarctica. This is produced by the following reaction; garnet sillimanite = spinel plagioclase. can be described as two net-transfer reactions; 5Grs Alm 12Als 3Hc 15An, and Prp 3Spl 15An. propose new geobarometers (GASpP) based on these equations. For example, one P (−155790 587.4T RT lnKFe) / 29.378, for assemblage CFASZn-system. Where pressure bar, T temperature K, R represents gas constant. The equilibrium constant is, KFe (aGrs5 aAlm)/(aHc3 aAn15). Our proposed are free quartz, corundum, orthopyroxene, cordierite within These barometers useful to estimate conditions spinel-bearing a wide pressure-temperature range (andalusite, kyanite, fields). (P-T) at Rock applying GASP, GRIPS, GRAIL, GASpP geobarometers, Zr-in-Rt geothermometer. evolution characterized clockwise P-T-t path. peak P-T condition about 820 MPa 850 °C. symplectite was during decompressional stage evolution, 450 700