The Role of Deformation in Aiding Recrystallization: an Example from a High-pressure Shear Zone, Central Australia

Abstract A dolerite body in the western Musgrave Block was variably recrystallized in a 0.5–1 m wide, sharply defined, high-grade shear zone at P=12–14 kbar and T 750°C. All samples within and adjacent to the shear zone have a common protolith; they are divided into unfoliated group 1 samples outside the shear zone and foliated group 2 samples within the shear zone. Group 1 samples show a progressive increase in the degree of recrystallization as the shear zone is approached. Systematic changes in modal proportions and mineral composition reflect increased reaction rates as a result of increasing strain and variations in aH2O. Group 1 samples are dominated by garnet-bearing coronas that separate orthopyroxene, clinopyroxene and ilmenite from plagioclase. Low strain in the group 1 samples allowed the preservation of comparatively Al-rich Fe + Mg-poor compositional domains replacing igneous pyroxene. Group 2 samples are more thoroughly recrystallized, do not contain coronas and have more constant mineral compositions reflecting higher diffusion rates. The wide range in mineral composition and textures and their relationship to strain intensity within the gabbro body emphasize the important role that deformation and fluids on all scales play in the development of metamorphic textures.