The amphibolite-eclogite transformation: an experimental study on basalt

Abstract

Phase relationships and phase compositions through the transformation from feldspar-amphibolite to eclogite have been experimentally investigated in a basaltic system, with specific attention given to amphibole crystal-chemistry as a monitor of P-T conditions. Modeling of amphibolite-eclogite transformation by mass-balance, including a reaction space calibration, and by a series of multivariant reactions shows a complex isopleth topology for amphibole cation substitutions in P-T projections. The notion of a dehydration front in the subducting slab is not viable if progressive dehydration occurs through continuous reactions involving chlorite, amphibole, paragonite, epidote, chloritoid. The beginning of eclogite hydration during the exhumation of a thickened crust may be monitored by aluminium behavior in amphibole at eclogite facies conditions. -from Author