Tectonic history related to the southern section of the Kalinjala Shear Zone, Eyre Peninsula, South Australia: And correlations with Terre Adélie Craton, Antarctica

Abstract

The southern edge of the Eyre Peninsula, experienced a separation from proto-Antarctica in the Cretaceous and has been projected to extend into Terre Adélie Craton, Antarctica. The Archaean and Palaeoproterozoic rocks of the southern Eyre Peninsula, have been modified by the Kimban Orogeny (~1730–1690 Ma) with the development of the regionally extensive Kalinjala Shear Zone, which has been correlated with the Mertz Shear Zone in Antarctica. In this contribution, new structural observations associated with the granulite facies Kalinjala Shear Zone, together with other shear zones, all showing similar kinematics of dextral top-to-the-north transport will be described. The Kimban Orogeny overprints and reworks a major lithospheric boundary between the Gawler Craton and a sequence of preceding events related to the ~ 1850 Ma Cornian Orogeny. Shear zones were initiated during the early stage of the Kimban Orogeny (KD1) in a dextral simple-shear regime, transitioning into a pure-shear (KD2) dominated regime. With shortenings of > 90% in the Kalinjala Shear Zone localized into regions containing pre-existing Tourneford Metdolerite Dykes emplaced at ~ 1810 Ma into the granites of the Donington Suite (1850–1843 Ma) and a basement of 2000–1859 Ma paragneisses. Geometrical relationships reveal the operation of oblique extrusion during the Kimban Orogeny, where a coaxial component acted sub-horizontal and orthogonal to the trend of the Kalinjala Shear Zone. Regions of low-strain and a ‘pinched-in’ and inverted sequence of Mesoproterozoic metasedimentary cover, the Hutchison Supergroup, are bounded by major km-scale shear zones with steep west-dipping tectonic contacts. Post-Kimban subvertical east–west-trending joints and faults record a rifting event which can be related to a Gondwana breakup. With post-rift Neogene fault activity recording additional tectonic episodes where pre-existing basement structures exert significant control on their orientation and distribution. Palaeogeographical reconstructions between the Eyre Peninsula and the Terre Adélie Craton, based on matching basement geology and structural style, are compared and reconciled with this new information.