STUDY OF STRAIN AND PARTIAL-MELT TRANSFER IN A BANDED MIGMATITE

An attempt is made to analyse in detail the strain and area change aro und the tip of a foliation-parallel leucosome. Strain is determined in the mesosomes above and below the leucosome and the melanosome, in bo th the XZ (foliation and lineation parallel) and YZ(foliation parallel , lineation perpendicular) planes, using the following methods: March analysis of biotite orientation fabric; Fry method of zircon position fabric; and R-f/phi' method using cordierite grain outlines. In additi on, March analysis of the orientation of sillimanite inclusions within the cordierite grains helps confirm the last method. Area change is m easured by determining the population density of zircon around the leu cosome in the XZ plane. The amount of material lost can account for th e area gain in the leucosome and we suggest the sample, at the observe d scale, was 'closed' in terms of melt movement. The results are used to construct tentative strain paths for the various components of the migmatite. Evidence suggests the leucosome was filled by true melt. Fl uid deformation of the leucosome melt is demonstrated by the orientati ons of zircons. (C) 1997 Elsevier Science Ltd.