The effect of B2O3 on the viscosity of haplogranitic liquids
The effect of B2O3 on the viscosity of a haplogranitic liquid (KrO-Na,O-AlrOr-SiO,) has\nbeen determined at I atm pressure in the temperature interval of 600-1600 \xb0C. Viscosity\nmeasurementso f a haplogranite, haplogranite + 4.35 wt% B2O3 and haplogranite + 8.92 wt% B2O3 have been performed using the concentric cylinder and micropenetration methods.\nThe viscosity of a B-enriched natural rhyolite obsidian, macusanite from Macusani,\nPeru, has also been determined.\nThe viscosity of haplogranite liquid decreases with the addition of B2O3 at all temperatures\ninvestigated. The viscosity decrease is nonlinear, with the strongestd ecreasee xhibited\nat low B2O3 concentration. The temperature dependence of the viscosity of all the\ninvestigated liquids is Arrhenian, in strong contrast to the case for B2O3 Iiquid. The Arrhenian\nactivation energy is much lower in the B2O3-bearing liquids than in the B2O3-free\nhaplogranite, with the result that the effect of B2O3 on viscosity is a strong function of\ntemperature. At temperatures corresponding to the crystallization of B-rich granitic and\npegmatitic systems the addition of I wt% of B2O3 decreases the viscosity 2 orders of\nmagnitude. The macusanite liquid exhibits a reduced viscosity compared with B-free rhyolite\nthat is consistent with the synthetic liquid systematics. B must be considered as a\nfluxing agent in B-rich granitic and pegmatitlc systems.