Granulite facies metamorphism in the Mallee Bore area, northern Harts Range: implications for the thermal evolution of the eastern Arunta Inlier, central Australia

Abstract

ABSTRACT The Mallee Bore area in the northern Harts Range of central Australia underwent high‐temperature, medium‐to high‐pressure granulite facies metamorphism. Individual geothermometers and geobarometers and average P‐T calculations using the program Thermocalc suggest that peak metamorphic conditions were 705–810C and 8–12 kbar. Partial melting of both metasedimentary and meta‐igneous rocks, forming garnet‐bearing restites, occurred under peak metamorphic conditions. Comparison with partial melting experiments suggests that vapour‐absent melting in metabasic and metapelitic rocks with compositions close to those of rocks in the Mallee Bore area occurs at 800–875C and >9–10 kbar. The lower temperatures obtained from geothermometry imply that mineral compositions were reset during cooling. Following the metamorphic peak, the rocks underwent local mylonitization at 680–730C and 5.8–7.7 kbar. After mylonitization ceased, garnet retrogressed locally to biotite, which was probably caused by fluids exsolving from crystallizing melts. These three events are interpreted as different stages of a single, continuous, clockwise P‐T path. The metamorphism at Mallee Bore probably occurred during the 1745–1730 Ma Late Strangways Orogeny, and the area escaped significant crustal reworking during the Anmatjira and Alice Springs events that locally reached amphibolite facies conditions elsewhere in the Harts Ranges.