Serpentinized ultramafic slivers associated with mafic subduction zone rocks in the hinterland of central Vermont preserve talc-carbonate, chlorite-tremolite, and chlorite-talc zones that formed via a series of H2O- and CO2-bearing net-transfer reactions. Reactions took place within both MgO–SiO2–H2O–CO2 (MSHC) and CaO–MgO–Al2O3–SiO2–H2O–CO2 (CMASHC), with MSHC reactions preceding CMASHC reactions. Three linearly independent basis net-transfer reactions were derived for each system. Each set of basis reactions includes one closed system reaction, one reaction open to H2O, and one reaction open to CO2. The basis reactions derived for MSHC are: 9Enstatite + Serpentine = 3Forsterite + 2Talc; 6Enstatite + 3H2O = Talc + Serpentine; 6Enstatite + Serpentine + 3CO2 = 3Magnesite + 2Talc. The basis reactions derived for CMASHC are: 2Serpentine + VIAl IVAlMg–1Si–1 (TK) = Chlorite; 2Serpentine + 5Talc + 6CaMg–1 (CM) = 3Tremolite + 6H2O; 7Talc + 3Dolomite + 3CM = 3Tremolite + 2Serpentine + 6CO2. Modal spaces show that carbonatization of serpentinite occurred in MSHC after serpentinization of peridotite, and that MSHC evolved into CMASHC due to metasomatic addition of Al3+ and Ca2+ during serpentinite carbonatization. The reaction pathway interpreted for CMASHC is dependent primarily on carbonatization and decarbonatization reactions, with chlorite-tremolite and chlorite-talc zones forming via decarbonatization and talc-carbonate zones forming via carbonatization of serpentinite. The modal spaces herein can be utilized for any ultramafic body with comparable zonation. Applying these spaces to ultramafic rocks at Belvidere Mountain in northern Vermont suggests that the mineralogical diversity seen there may result from multiple independent reaction paths within MSHC, NCMASH, CMASH, and CMASHC.

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