Metamorphism and deformation on western Mt Chapple, Arunta Region, central Australia: A record of multiple high-grade tectonic events

Abstract

Extensive exposures of deep crustal rocks in the south-central Arunta Region record a complex tectonic history from Proterozoic terrane assembly to Paleozoic exhumation. Western Mt Chapple was previously inferred to include evidence of much of this history. Detailed mapping and structural and metamorphic analysis, however, demonstrate three structurally distinct, high-grade deformational events, but no indication of the youngest, lowermost amphibolite to greenschist facies, Alice Springs exhumational overprint. Evidence of the oldest deformation is confined to local exposures of NE-striking gneissosity; neither metamorphic grade nor kinematics are constrained. The second event produced a steeply dipping, WNW-striking, NNE-dipping foliation, steeply E-plunging mineral lineation, and kinematic indicators recording dextral transpression in present-day geographic coordinates. Mineral assemblages preserved in blocks between D3 shear zones record D2 metamorphic conditions of 691–746 ± 50°C and 550–900 MPa. Northwest-striking D3 shear zones are characterised by an exceptionally well developed, NW-striking, steeply NE-dipping foliation and steeply SE-plunging mineral lineation with kinematic indicators that demonstrate sinistral-reverse, triclinic shear. Shear zone mineral assemblages record metamorphism at 702 ± 50°C. These data demonstrate a history of high-temperature deformation, including significant strike-parallel movement, which predates the Alice Springs orogeny.