Eclogite dehydration and melt-induced embrittlement at high-pressure conditions

Abstract

We document the complex interaction between metamorphic reactions and deformation behaviour at high-pressure conditions by combining (micro-) structural, petrographical and geochemical data from an eclogite body. The well-equilibrated eclogite fabric is crosscut by mineral veins. Precipitated veins host the eclogitic high-pressure assemblage with variation in modal composition, indicating that fracturing occurred at eclogite facies conditions. Deflection of the eclogite fabric adjacent to the veins implies ductile reactivation of the veins as flanking structures and strain localization under continuous aseismic shearing. In consequence, the reactivated veins are characterized by undulatory extinction and subgrain formation in quartz indicating crystal plasticity. We show that prograde post-eclogitization metamorphism resulted in progressive dehydration and melting of the eclogite. Subsequent increase in pore-pressure-induced rock failure. The mesoscopic to microscopic characteristics of eclogite-facies veins indicate a cyclic behaviour of fracturing, vein formation and crystal-plasticity which demonstrates the strong interaction of chemical and mechanical processes operating at depth.