Dissolution and replacement creep: a significant deformation mechanism in mid-crustal rocks

摘要: Abstract Zoning patterns and zoning truncations in metamorphic minerals a granodioritic orthogneiss indicate that strain S–C fabrics these rocks were produced by dissolution, precipitation, replacement processes, even at epidote–amphibolite facies conditions. The fabric is defined alternating layers folia dominated quartz, feldspars, biotite+epidote. most plagioclase, orthoclase, epidote, sphene are truncated boundaries normal to the shortening direction, suggesting dissolution. Interfaces of relict igneous orthoclase phenocrysts face direction embayed replaced biotite, myrmekitic intergrowths plagioclase quartz. Metamorphic grains also epidote. We interpret microstructures reflect strain-enhanced cores many show asymmetric overgrowths with least two generations beards, all oriented on ends extension direction. textures precipitation components dissolved deformation-enhanced While biotite quartz probably deformed dislocation creep, overall deformation was accommodated dissolution perpendicular parallel it. These chemical processes must have been activated lower stresses than creep predicted from extrapolations data experiments dry rocks. Thus wet crust likely be weaker calculated experimental studies.