Contrasting parageneses in mica schists of the Hohe Tauern, caused by manganese and zinc

Abstract

¶Two compositionally similar types of metapelites from the same outcrop in the eastern Hohe Tauern/Austria (Lieserkarscharte, Silbereck Series) have evolved two distinctly different AFM parageneses. While both contain quartz, muscovite, kyanite and hematite, one type contains additional chloritoid (chloritoid schist), the other one additional garnet, chlorite, staurolite and allanite (garnet schist). This behaviour is shown to be caused by higher contents of manganese and zinc in the garnet schists (MnO ≥ 0.25%, Zn ≥ 140 ppm), which triggered two FMASH isograd reactions that were never reached by the chemically purer chloritoid schists (MnO ≤ 0.03%, Zn ≤ 70 ppm). Garnet and staurolite appeared as new phases, buffering manganese and zinc, respectively. Both types of mica schist have evolved from a single, compositionally almost homogeneous pelite or chlorite pyrophyllite schist.