Low temperature creep of garnet: Insights from blueschist-facies skarn of the Preveli nappe (Crete, Greece)

We present a comprehensive record of deformation, metamorphism, and the state of stress during interaction between garnet-rich skarn and infiltrating fluids in an Eo-Hellenic subduction zone (Preveli nappe, Crete). The structural data and deformation microfabrics of quartz, coupled with petrological constraints, suggest that subduction of the Preveli rocks occurred under epidote-blueschist-facies conditions (T = 360 +/- 40(degrees)C, P > 1.0 GPa) and differential stresses >70 MPa. Localized deformation of fine-grained monomineralic grandite of the skarn led to mode I fractures and discrete shear zones along which synkinematic ferri-winchite developed. Brittle-viscous deformation of grandite in high-strain domains was accommodated by cataclasis, incongruent dissolution precipitation creep (IDPC), and incipient dislocation creep (DC). Cataclasis led to strong grain-size reduction and increased permeability resulting in fluid infiltration and enhanced IDPC as is documented by serrated reaction seams along which actinolite and ferri-winchite grew in sequence while replacing grandite. Incipient DC of grandite is indicated by lattice distortion and possible subgrains. Brittle-viscous deformation of grandite occurred at high differential stress (>250 MPa) and was significantly controlled by externally derived fluids, which contributed to hydraulic fracturing and the redistribution and addition of mobile elements.