Quantitative field methods for estimating melt production and melt loss

Melt extraction in migmatites occurs via melt channels of increasing width from source areas (often recognizable by the location of incongruent phases ) via concordant leucosomes to discordant melt conduits. To test the contri bution of migmatites to granite genesis, melt production and melt loss need to be quantified at specimen and outcrop scale. Melt production during dehydration melting can be modelled by calculating t he volume ratio of melt and incongruent phases from balanced melting reacti ons. Melt loss can be quantified by (i) comparing these predicted volume ra tios with ratios derived in outcrop; and (ii) modelling strain patterns nea r melt loss structures. A field test in SW Finland shows a reasonable corre spondence between melt loss estimates from leucosome/garnet volume ratios a nd from melt loss structures, if the original shape of the melt patch is as sumed to have been linear. (C) 2001 Elsevier Science Ltd. Ali rights reserv ed.