This study uses field, petrographic and geochemical methods to estimate how much granitic melt was formed and extracted from a granulite facies terrane, and to determine what the grain-and outcrop-scale melt-flow paths were during the melt segregation process. The Ashuanipi subprovince, located in the north-eastern Superior Province of Quebec, is a large (90 000 km 2 ) metasedimentary terrane, in which > 85% of the metasediments are of metagreywacke composition, that was metamorphosed at midcrustal conditions (820-900°C and 6-7 kbar) in a late Archean dextral, transpressive orogen. Decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase, together with preserved former melt textures indicate that anatexis was by the biotite dehydration reaction: biotite + quartz + plagioclase ¼ melt + orthopyroxene + oxides. Using melt ⁄ orthopyroxene ratios for this reaction derived from experimental studies, the modal orthopyroxene contents indicate that the metagreywacke rocks underwent an average of 31 vol% partial melting.The metagreywackes are enriched in MgO, CaO and FeO t and depleted in SiO 2 , K 2 O, Rb, Cs, and U, have lower Rb ⁄ Sr, higher Rb ⁄ Cs and Th ⁄ U ratios and positive Eu anomalies compared to their likely protolith. These compositions are modelled by the extraction of between 20 and 40 wt %, granitic melt from typical Archean low-grade metagreywackes. A simple mass balance indicates that about 640 000 km 3 of granitic melt was extracted from the depleted granulites.The distribution of relict melt at thin section-and outcrop-scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary (porous) flow from the site of melting, across the layers and into bedding planes between adjacent layers. In other rocks pervasive grain boundary flow of melt occurred along the layers for a few, to tens of centimetres followed by channelled flow of melt in a network of short interconnected and structurally controlled conduits, visible as the net-like array of leucosomes in some outcrops. The leucosomes contain very little residual material (< 5% biotite + orthopyroxene) indicating that the melt fraction was well separated from the residuum left in situ as melt-depleted granulite. Only 1-3 vol percentage melt remained in the melt-depleted granulites, hence, the extraction of melt generated by biotite dehydration melting in these granulites, was virtually complete under conditions of natural melting and strain rates in a contractional orogen.

Many magmas in the continental crust are believed to have formed by partial melting in the lower to middle crust, and the transfer of that melt to the upper crust. However, it is poorly known how the compositions of these magmas evolve. In general, the principal processes involved are redistribution and contamination of the melt fraction with some of the host-rock it passes through and once magma ascends out of the anatectic zone and traverses cooler crust and begins to crystallize. The nature of the protolithrnigmatite-granite transition and the process that creates a granitic magma during anatexis, as well as the processes that control the magma composition outside the source region are of a particular interest as they enable us to constrain the morphological, mineralogical and geochemical variations of anatectic melts produced during anatexis of greywacke metasedimentary rocks.The Ashuanipi subprovince and contiguous metasedimentary subprovinces in the Superior province contains reworked Archaean crust that displays a continuous section from mid-crustal anatectic rocks to shallow level granite plutons. In other words, the superior province represents a crustal section which is continuous from partially melted source to upper crustal magma sink and the Ashaunipi portion of it is an example of a source region for granulitic magma. There, the transition from palaesome to granite was an open system process through intermediate stages of metatexite and diatexite.Field, pétrographie and geochemical methods have been used to estimate how much granitic melt was formed and extracted from granulite facies terrane, and to determine what the grain and outcrop-scale melt-flow paths were during the melt segregation process. More than 85 % of the metasediments in the Ashuanipi subprovince are of metagreywacke composition that was metamorphosed at mid-crustal conditions (820-900 °C and 6-7 kbar). Decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase, together with preserved former melt microstructures indicate that anatexis was by the biotite dehydration reaction: biotite + quartz + plagioclase = melt + orthopyroxene + oxides. Using melt/orthopyroxene ratios for this reaction derived from experimental studies, the modal orthopyroxene contents present in the Ashuanipi rocks indicate that the metagreywacke rocks underwent an average of 31 vol% partial melting.The metagreywackes are enriched in MgO, CaO and FeO and depleted in SÍO2, K2O, Rb, Cs and U, have lower Rb/SR, higher Rb/Cs and Th/U ratios and positive Eu anomalies compared to their likely protolith. These compositions are modelled by the extraction of between 20 and 40 wt % granitic melt from typical Achaean low-grade metagreywackes.The distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary (porous) flow from the site of melting, across the layers and into bedding planes between adjacent layers. In other rocks, pervasive g...