Abstract

Isotopic and petrologic studies of the Ivrea Zone, a segment of deep-crustal high-grade rocks, suggest that metamorphism did not involve the transfer of large quantities of CO2 from mantle to crust. High-grade Ivrea Zone calcites may retain high δ18O (up to 24‰ SMOW), indicating little interaction with externally derived fluid. Graphite isotopic compositions (δ13C = -10‰ to -25‰ PDB) that do not vary with grade are attributed to mixing between carbonate carbon and biogenic noncarbonate carbon. Calcites from high-grade, carbonate-poor amphibolites have δ13C of about 1‰ PDB and sedimentary, not infiltrative, origins. The general lack of carbon and oxygen isotopic homogenization suggests that fluid interactions may be explained in terms of fluid generated internally to the Ivrea Zone metasedimentary rocks.

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