The south-east Reynolds Range, central Australia, is cut by steep north-west-trending Alice Springs age (c. 334 Ma) shear zones that are up to hundreds of metres wide and several kilometres long with reverse senses of movement. Amphibolite facies (550-600°C, 500-600 MPa) shear zones cut metapelites, while greenschist facies shear zones (420-535°C, 400-650 MPa) cut metagranites. The sheared rocks commonly underwent metasomatism implying that the shear zones were the pathways of significant fluid flow. Altered granites within greenschist facies shear zones have gained Si and K but lost Ca and Na relative to their unsheared counterparts, suggesting that the fluid flowed down-temperature (and hence probably upward) through the shear zones. Time-integrated fluid fluxes calculated from silica addition are up to 2.1×1010 mol m−2 (c. 4.2×105 m3 m−2). Similar time-integrated fluid fluxes are also estimated from changes in K and Na. The sheared granitic rocks locally have d18O values as low as 0‰ which is much lower than the d18O values of the adjacent unsheared granites (7 to 9‰), implying that the fluid which flowed through these shear zones was derived from the surface. For the estimated time-integrated fluid fluxes, the fluids would be able to retain their isotopic signature for many tens to hundreds of kilometres. The flow of surface-derived fluids into the ductile middle crust, with subsequent expulsion upwards through the shear zones, may have been driven by seismic activity accompanying the Alice Springs deformation.

A correlation between the style of partial melting and synmeta‐morphic fluid flow exists in metapelites from the Mount Lofty Ranges, Reynolds Range, and Omeo Zone (Australia). Mount Lofty Ranges migmatites comprise granitic leucosomes in rocks that are still biotite rich, with no indications of other mafic minerals being formed along with the melts. By contrast, in the Reynolds and Omeo migmatites, garnet, cordierite, and/or spinel formed along with the melts. Oxygen isotope data are most consistent with the Mount Lofty Ranges undergoing significant fluid–rock interaction during regional metamorphism, which may have fluxed fluid‐present partial melting. By contrast regional metamorphic fluid flow in the Reynolds Range and Omeo Zone was limited, leading to partial melting via fluid‐absent reactions. The style of melting reactions may help to constrain the timing of isotopic resetting and fluid flow in metamorphic terrains, which is currently a contentious issue.