Partial-melt topology in statically and dynamically recrystallized granite

Microstructures of the Murray granite pluton (central Ontario, Canada) show evidence of both static and dynamic crystallization subsequent to partial melting. Backscattered electron analyses reveal interstitial K-feldspar and plagioclase at triple junctions of strain-free, isometric quartz grains. T he geometry of the quartz-feldspar boundaries mimics the original topology of the quartz-melt contacts during crystallization. This conclusion is sugg ested by the occurrence of both rounded and planar faces of quartz grains, and by low (27 degrees) dihedral angles of quartz-quartz-feldspar boundarie s, similar to dihedral angles in experimentally crystallized quartz-quartz- silicic melt systems. In contrast, feldspar seams in deformed granites have high axial ratios, are usually elongated perpendicular to the foliation pl ane, and are located preferentially along individual grain boundaries. Quar tz grains are dynamically recrystallized and occasionally transected by fel dspar seams, indicating that fracturing occurred in the presence of melt du ring crystal-plastic deformation of quartz, The subparallel orientation in quartz grains of intragranular, feldspar-bearing fractures and interstitial feldspar seams suggests that these features originated as intragranular an d intergranular fractures, respectively Partial-melt topology was therefore controlled by intergranular and, occasionally, by intragranular fracturing .