Abstract

Epidote blueschists on Ile de Groix, France, were selectively over-printed by chloritic greenschist assemblages on a millimetre to metre scale along foliation planes, in fold hinges, and along shear zones. Reactions balanced between the blueschist and greenschist assemblages show that overprinting of epidote blueschists can only be accomplished by the addition of H2O ± CO2 Conversion of epidote blueschists to chloritic greenschist assemblages thus depends on fluid-infiltration processes as the rocks pass through the greenschist facies, and does not necessarily reflect rapid rates of unroofing of a subduction complex. Epidote blueschists are therefore preferentially preserved in fluid-absent or impermeable rocks regardless of exhumation rates, in contrast to other blueschist types that require rapid unroofing to avoid a greenschist overprint.

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