Experimental deformation of partially molten Westerly granite under fluid-absent conditions, with implications for the extraction of granitic magmas

The mechanical behavior of partially molten Westerly granite was investigated in the temperature range 800°-1100°C, 250 MPa confining pressure, by means of constant strain rate, creep, and stress relaxation tests. The comparative viscosity of the melt alone was estimated at 950° and 1000°C from the distance it could be made to penetrate into a porous sand under a known pressure gradient. Under all conditions, deformation of the matrix of solid grains was by brittle fracture only. Samples containing up to 10 vol.% melt failed with the formation of a shear fault zone. At higher melt fractions, melt-filled "pores' collapsed by shear-enhanced compaction, squeezing the melt into axial cracks. Above 40 vol.% melt, unfractured solid grains were carried about passively in the flowing liquid. By analogy with the uniaxial compaction of water-saturated soils, a simple model is erected to describe a two-stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress. -from Authors