Abstract
Ferropseudobrookite exsolution rods with about Fe2+0.8Fe3+0.4Ti1.8O5 are first observed in quartz from a garnet-orthopyroxene-bearing quartzo-feldspathic gneiss, Napier Complex, East Antarctica. The elongated direction of ferropseudobrookite rods is the c-axis and parallel to either the <101> or <111> of low-quartz. The formation of the exsolution must result from the cooling of the gneiss. The chemical composition of ferropseudobrookite suggests that the formation temperature is over 1000 C and the oxygen fugacity in quartz is log fO2 = -6.0 to 7.0. The present exsolution phenomenon suggests that quartz has the solubility not only Ti ion but also Fe2+ and Fe3+ and that the gneiss contains Fe3+ ion under the peak metamorphic condition.
