Structures and Melt Fractions as Indicators of Rheology in Cordierite-Bearing Migmatites of the Bayerische Wald(Variscan Belt, Germany)

Abstract

a melt, but the degree of their shape-preferred orientation increases The relation between melt volume fraction, melt segregation and with increasing melt segregation and differential stress. The mideformation mechanisms of minerals in migmatites, and the concrostructures suggest that deformation mechanisms and hence the trolling effects of all these factors on the bulk mechanical behaviour, bulk mechanical behaviour of migmatites change in space and time were investigated using rocks from the Bayerische Wald (Bohemian during partial melting. The observed complex interplay of melt Massif, Variscan belt, Germany). Biotite dehydration melting at volume fraction, melt segregation, bulk strength contrasts, mechanical 800–850°C and 0·5–0·7 GPa was the migmatite-forming process properties of different minerals and time cannot be described by a in this area. Four migmatite types were distinguished that alternate single flow law. Detailed mapping of migmatite areas, along with on the scale of several decimetres to several tens of metres. Type microstructural observations, deformation experiments considering MIG1 is massive and undeformed. Types MIG2 and MIG3 are heterogeneous melt distribution and numerical models that integrate both stromatic (leucosome–mesosome interlayering), but differ in the different flow laws for various stages of partial melting, may serve degree of deformation. Type MIG4 has an interlayering of meto derive quantitative models for the bulk mechanical behaviour of lanosome and leucosome and is strongly deformed. Melt volume crustal sections in the future. fractions found by volume estimation of pure-melt leucosomes on outcrop, hand-specimen and thin-section scales are 20–40 vol. % and coincide fairly well with melt volume fractions produced in dehydration melting experiments with similar bulk compositions at the relevant pressure and temperature conditions (20–30 vol. %). The degree of melt removal from mesosomes and melanosomes (melt