Tectonic evolution of the Reynolds-Anmatjira Ranges: a case study in terrain reworking from the Arunta Inlier, central Australia

Abstract

The Reynolds-Anmatjira Range region forms part of the Arunta Inlier in central Australia and has undergone four tectonothermal cycles that span an interval of c. 1450 Ma. The first two cycles were the Stafford Tectonic Event c. 1820 Ma, and the Strangways Orogeny c. 1770–1780 Ma, both of which were associated with regional low-pressure high-temperature metamorphism up to granulite grade that was coeval with the emplacement of voluminous sheet-like granites. The subsequent Chewings Orogeny occurred at around 1590–1570 Ma and was a long-lived event that produced regional low-pressure greenschist to granulite facies metamorphism without obvious associated magmatism. During the mid-Palaeozoic Alice Springs Orogeny (400–300 Ma), the terrain was dissected by a system of sub-greenschist to mid-amphibolite facies shear zones. In the Reynolds Range, the Proterozoic events produced a single regional foliation that is axial planar to simple large-scale folds. The composite regional Proterozoic foliation increases in grade smoothly from northwest to southeast, producing a pattern of isograds that is remarkably similar to those that formed during the mid-Palaeozoic Alice Springs Orogeny. Despite this simple pattern, the isograds reflect the superimposed metamorphic effects of four unrelated tectonothermal cycles. Without geochronological and stratigraphic information, the degree of terrain reworking in the Reynolds-Anmatjira Range region could have been largely obscured by the apparent simplicity of many of the structural and metamorphic relationships.