Constraints on long-lived Mesoproterozoic and Palaeozoic deformational events and crustal architecture in the northern Mount Painter Province, Australia.

Abstract: Meta-sedimentary and igneous rocks preserved in the hanging wall of the Paralana Fault, northern Mount Painter Province, record a protracted (ca. 1600Myr) multi-staged metamorphic and poly-deformational evolution related to Mesoproterozoic and Palaeozoic orogenic events. The Mount Painter Province was located near the margin of both the South Australian Craton and the North Australian Craton, which allows comparisons of the tectonic evolution of these margins and provides context for the evolution of the eastern Proterozoic Australia for both the Columbia and Gondwana supercontinents. Within the Mount Painter Province meta-sedimentary rocks form part of a basin system developed adjacent to the margins of the Gawler Craton and Curnamona Province following the Olarian–Wartakan orogenic system. Sedimentation was followed by ca. 1590–1552Ma ductile deformation (D₁–D₃) at mid to upper crustal levels preserving a rapid (ca 6Myr) burial and exhumation cycle. Initial deformation is characterised by the development of a layer parallel fabric (S₁). S₁ is overprinted by recumbent north-verging folds (F₂) formed during mid to upper amphibolite facies peak metamorphism (M₂), which are overprinted by tight, upright shallow NE–SW plunging folds (F₃). D₃ folds developed contemporaneous with sinistral oblique shearing and the development of proto-mylonitic to ultra-mylonitic fabrics along the Paralana Fault Zone. The timing of D₃ deformation is constrained by the development of a penetrative steeply dipping foliation (S₃) in the ca. 1585–1569Ma shallowly emplaced Mount Neill Granite and relatively undeformed granites dated at ca. 1552Ma. Further constraint on the absolute timing of Mesoproterozoic tectonism is provided through the dating of zircon growth from samples of the meta-sedimentary Radium Creek Metamorphics. This dating reveals a 1555±16Ma metamorphic event, interpreted to be the consequence of M₃ amphibolite facies, regional metamorphism and accompanying metasomatism. The transition between D₂ and D₃ is interpreted to reflect a shift from ca. 1591–1585Ma N–S shortening to ca. 1585–1552Ma NW–SE shortening. This episode of orogenesis is correlated with the ca. 1585–1540Ma Kararan Orogeny in the northern Gawler Craton, which distinctly postdates the ca 1600–1590Ma Olarian Orogeny as previously interpreted. The Mesoproterozoic structural architecture was reactivated during Neoproterozoic extension (D₄) and the ca. 500Ma Delamerian Orogeny. Delamerian structures are formed in a predominantly brittle regime. Early thin-skinned thrusting was followed by thick-skinned deformation (D₅–D₆); during which open F₅ folds developed above oblique lateral ramps, and produced type 0 overprinting patterns with F₃ Mesoproterozoic folds. Steeply plunging F₆ buckle folds with SE-trending axial traces are the last phase of deformation recorded. Both Mesoproterozoic ductile deformation phases and the Palaeozoic ductile-brittle to brittle overprints were focussed along the Paralana Fault, emphasising the repeated long-lived evolution of this crustal scale fault system. [Copyright &y& Elsevier]