Abstract
Lower Calcsilicate Unit metasediments and Napperby Gneiss metagranites at Conical Hill in the Reynolds Range, central Australia, underwent at least two periods of fluid flow. The ingress of surface-derived fluids (δ 18O < 6‰; δ 2H < −80‰) during 1780 Ma contact metamorphism produced wholesale lowering of δ 18O values in both the Lower Calcsilicate Unit and the Napperby Gneiss. Fluid flow during cooling from the peak of 1600 Ma regional metamorphism formed quartz + garnet veins and caused epidotisation of the Lower Calcsilicate Unit. The fluids in this later event were water-rich ( X CO 2 < 0.1), saline, and were probably exsolved from crystallising partial melts within the Napperby Gneiss. Quartz-epidote oxygen isotope fractionations suggest that epidotisation occurred at 575–625°C. The scale of fluid flow during epidotisation was probably smaller than that during contact metamorphism and represents a local redistribution of mass. The Reynolds Range as a whole shows a long history of fluid-rock interaction and the final isotopic and petrological character of the terrain is the product of several fluid-flow events.
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