Metamorphic evolution of calcsilicate granulites near Battye Glacier, northern Prince Charles Mountains, East Antarctica

Calcsilicate granulites of probable Middle Proterozoic age (c.1000-1100 Ma) in the vicinity of Battye Glacier, northern Prince Charles Mountains, East Antarctica, contain prograde metamorphic assemblages comprising various combinations of wollastonite, scapolite, clinopyroxene, An-rich plagioclase, calcite, quartz, titanite and, rarely, orthoclase, ilmenite, phlogopite and graphite. Comparison of the prograde assemblages with calculated and experimentally determined phase relations in the simple CaO-Al2O3-SiO2-CO2-H2O system suggests peak metamorphism at greater than or equal to 835 degrees C in the presence (in wollastonite-bearing assemblages at least) of a CO2-bearing fluid (X-CO2 greater than or equal to 0.3) at a probable pressure of 6-7 kbar. Well-preserved retrograde reaction textures represent: (1) breakdown of scapolite to anorthite + calcite +/- quartz; (2) formation of grossular-andradite garnet and, locally, (3) epidote, both principally by reactions involving scapolite breakdown products and clinopyroxene; (4) local coupled replacement of clinopyroxene and ilmenite by hornblende and titanite, respectively; and finally (5) local sericitization of prograde and retrograde plagioclase. These retrograde reactions are interpreted to be the result of cooling and variable infiltration by H2O-rich fluids, possibly derived from crystallizing pegmatitic intrusions and segregations that may be partial melts, which are common throughout the area.