Presentation Information
[R8-06]Various retrograde metamorphism of calc-silicate granulites from Skallevikhalsen, East Antarctica - Revisit
*Yoshikuni Hiroi1, Tomokazu Hokada, Tatsuro Adachi, Daniel Joseph Dunkley, Madhusoodhan Satish-Kumar, Yoichi Motoyoshi (1. Non)
Keywords:
Zircon,Graphite with growth spirals,Rutile,Retrograde pressure-temperature path
The dolomitic calc-silicate granulite in the said area contains various nodular blocks with different petrographic features. Here, we describe two nearby specimens, YH05011501B and YH05011501C, and present their metamorphic ages and retrograde pressure-temperature (P-T) paths. Specimen B consists primarily of Ca-amphibole, scapolite, and calcite, with minor amounts of clinopyroxene and olivine. It is completely surrounded by a rind of phlogopite that contains calcite. Scapolite is partially replaced by fine-grained muscovite. Specimen B contains many large, oscillatory-zoned zircons that have undergone dissolution, regrowth, and recrystallization. Two distinct ages, 608 Ma and 534 Ma, were obtained from different parts of the same zircon grain. Specimen C consists primarily of rutile, sapphirine, spinel, cordierite, anorthite, Ca-amphibole, phlogopite, talc, magnesite, and dolomite. It contains characteristic graphite with growth spirals. The graphite is in direct contact with cordierite, anorthite, talc, and dolomite, suggesting that it formed from a fluid with low carbon oversaturation during the retrograde stage. Spinel is commonly partially replaced by corundum + magnesite aggregates, while anorthite is replaced by fine-grained muscovite. Intergrowths of talc and magnesite, with or without graphite, may be pseudomorphs after enstatite and/or forsterite. The presence of coarse-grained magnesite and rutile restricts the peak and retrograde P-T path.
