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

• Published in: Precambrian research 2016-08, Vol.281, p.537-565
• Main Authors: Waters-Tormey, Cheryl, Ashley, Kyle T., Jones, Daniel, Tracy, Robert
• Format: Article
• Language: English
• Subjects: Australia; Chewings; Extension; Fluid; Mount Hay; Strangways
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2016.03.006

•New geochronologic and thermobarometric data placed into a synthesis of the literature.•Well-constrained tectonic strain directions valuable for Mesoproterozoic paleogeographic reconstructions.•At least 7–14km of crustal thinning in central Australia, ca. 1552Ma.•Two causes of strain localization in the deep crust for the same deformation event. 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