The Mount Hay block, central Australia: Another puzzle piece for Paleo-Mesoproterozoic tectonic history

Abstract

The 100km2 Mount Hay block (Arunta Region, central Australia) is a >15km thick crustal cross-section comprised of granulite facies tectonites containing a tectonothermal record from ca. 1803 to ca. 1552Ma, as demonstrated by the combination of prior work and new monazite geochronology and thermobarometry. Igneous and sedimentary protoliths formed ca. 1803–1798Ma during 1810–1790Ma Stafford–Tanami time. Between ca. 1790 and 1740Ma, nearly continuous magmatism in the Aileron Province, and possibly ages of recrystallized zircon and monazite in the Mount Hay block, record subduction along the southern margin of the Proterozoic Australia-Mawson continent. Geologic mapping and zircon and monazite geochronology demonstrate that the Mount Hay block was penetratively deformed between ca. 1720Ma and 1700Ma during 1735–1690Ma Strangways time. This includes the >8km thick Mount Hay sheath fold, which records NE-SW subhorizontal shear, once Paleozoic tilting of the Mount Hay block is removed. While still in the deeper crust (>798±33°C; >7.6±0.7kbar), fabrics along the northern edge of the Mount Hay block were transposed by the cross-cutting >7km thick Capricorn ridge shear zone at ca. 1551.7±5.5Ma, during Chewings time. Once restored, the Capricorn ridge shear zone records NE-SW extension. A jump in strain rate while at high temperatures (∼725°C) initiated severe localization accommodated initially by pseudotachylite formation and cataclasis then mylonitization during Fe-rich fluid flux. Shearing may have continued to pressure–temperature conditions as low as <630±25°C and ∼3–5±1.2kbar indicating ∼7–14km uplift. Fluid flow in the Capricorn ridge shear zone corresponds well with growing evidence for regional Fe±K±Si metasomatism with similar timing. In published tectonic reconstructions, Chewings aged deformation, including the Capricorn Ridge shear zone, may be related to subduction to the south, or re-convergence between the Proterozoic Australia-Mawson continent and Laurentia. Robust links between the kinematics of deformation and geochronologic constraints, and the ability to restore major structures to their original orientations, makes the Mount Hay block a valuable additional puzzle piece for Proterozoic tectonic reconstructions for Australia, and possibly the supercontinent Nuna.