STRAIN LOCALIZATION AND MELT SEGREGATION IN METAPELITES

Crustal rocks commonly experience partial melting in deep parts of orogenic belts. Present concepts predict that the generation of partial melt is directly related to shear localization, which allows paths for the melt to migrate. Existing experimental studies, however, are insufficient to directly relate melt generation to deformation. We present the results of a series of laboratory experiments on synthetic rocks of pelitic composition to demonstrate how and when partial melt generates in association with strain localization during non-coaxial deformation at intermediate pressure (300 MPa) and high temperature (750^oC) with a constant strain rate ( 3x10^-4). The results reveal that shear localization and partial melting are initially independent. Low angle Riedel shears occur in a brittle manner when the differential stress is at its peak. The generation of melt, which introduces ductility in the system, is associated with strong weakening of the material. The amplification of melt production (~ 22%) is restricted in the window of this strong weakening phase; it decreases asymptotically with larger strain. Comparison with static experiments suggests that partial melt generates with a factor of 1.7 times more for the dynamic experiments.