Wollastonite and scapolite in Precambrian calc‐silicate granulites from Australia and Antarctica

Abstract

Scapolite, wollastonite, calcite, diopside, grossular-andradite garnet and sphene occur in calc-silicate rocks in the granulite terrain of the Arunta Block, central Australia. This assemblage buffers the COz activity at a low value, so that any coexisting fluid phase must be HzO rich and COz poor (Xco, = 0.2-0.3). In contrast, the H20 activity in the surrounding felsic and mafic granulites was low. Thus fluid activities during granulite facies metamorphism were locally buffered in various rock units and fluid flow appears to have been restricted or fluid may have been absent. Late retrograde rims of garnet and garnet-quartz separate phases formed in the high-grade stage. Formation of these rims would have required either an influx of waterrich fluid or a decrease in pressure. Evidence from the surrounding granulites shows that in one locality, the calc-silicate rocks had undergone late isobaric hydration; in another locality, minor uplift had occurred soon after peak P-T conditions. In both, scapolite had partly broken down to plagioclase-calite. A calc silicate rock from the granulite terrain of Enderby Land, Antarctica, contains scapolite, wollastonite, calcite, diopside, quartz and sphene; this assemblage also indicates low COz activities. In this rock, wollastonite has broken down to calcite-quartz, to indicate isobaric cooling without influx of hydrous fluid. List of abbreviations used in text and figuresAb = albite An = anorthite And = andradite CaTs = Ca-Tschermak's molecule Cc = calcite Di = diopside Ga = garnet Ge = gehlenite Gr = grossular Me = meionite PI = plagioclase Q = quartz Sc = scapolite V = vapour Wo = wollastonite Zo = zoisite

The origins of granulites: a metamorphic perspective

“…11, 14A), where both P and T increase on the prograde segment and IBC ensues from P max , have been described or inferred from several terranes (e.g. Bohlen, 1987;Waters, 1986;Phillips & Wall, 1981;Warren, Hensen & Ryburn, 1987). Evidence used to deduce such paths includes:…”

“…1987Ellis, 1983Harley, 1988Harley, 1988Johannson & Moller, 1986Karsef al. 1980Dahl, 1980Dahl, 1980Sills & Rollinson, 1987Schenk, 1984Schenk, 1984Sandiford et al 1988Sandiford et al 1988Warren, Hensen & Ryburn, 1987Rollinson, Windley & Ramakrishnan, 1981Newton & Perkins, 1982Groenewald & Hunter, 1987Harley, unpubl. Schreurs, 1984Harley, unpubl.…”

Contrasting mineral parageneses in high‐temperature calc‐silicate granulites: examples from the Eastern Ghats, India

“…-polite-bearing calc-silicate rocks have been reported from scveral granulite facies terranes ( Table 1 in Warren et al, 1987;Harley, 1987;Harley & Buick, 1992) including the Eastern Ghats belt of India (Bhattacharya, 1972;Sivaprakash, 1981). The petrology of calc-silicate granulites has been the focus of several recent studies because they permit a,, in the accompanying fluid to be calculated (cf.…”

Solubility of grossular, Ca3Al2Si3O12, in H2O–NaCl solutions at 800°C and 10kbar, and the stability of garnet in the system CaSiO3–Al2O3–H2O–NaCl

“…In particular, Ca-rich garnets of the grossular-andradite (Ca 3 Al 2 Si 3 O 12 -Ca 3 Fe 2 Si 3 O 12 ) solid-solution series form during fluid-rock interaction in many metamorphic environments, including rodingite alteration of ultramafic rocks (e.g., Evans et al, 1979;Rice, 1983), contact metamorphism of carbonate lithologies (e.g., Einaudi et al, 1981), and regional metamorphism of calc-silicates. These garnets have been used to monitor CO 2 activity (e.g., Warren et al, 1987;Moecher and Essene, 1991) and fO 2 (e.g., Liou, 1974). Replacement of Si 4+ by a vacancy plus 4H + is a potential monitor of silica activity in 0016-7037/$ -see front matter Ó 2007 Elsevier Ltd. All rights reserved.…”