The structure of Kangaroo Island (South Australia): Strain and kinematic partitioning during Delamerian basin and platform reactivation

Abstract

Kangaroo Island forms the southern part of the Fleurieu arc‐segment of the Adelaide Fold‐Thrust Belt. The Island consists of three structurally distinct lithotectonic domains. In the southern zone basinal and regionally metamorphosed Cambrian Kanmantoo Group strata are deformed by regional southwest‐trending folds and thrusts. The Kangaroo Island Shear Zone forms a broad east‐west‐trending strongly transposed zone, which consists of anastomosing mylonitic phyllonites. Along this shear zone the basinal strata are transpressionally displaced towards the northwest. Most of the exposed hangingwall of the shear zone is formed by a regional‐scale northerly overturned anticline, and parts of the footwall are also overturned. The northern zone forms a 15 km wide foreland thrust belt incorporating a veneer of Cambrian platformal sediments, that overlie the southernmost extension of the Gawler Craton in South Australia. These rock types, which are absent on the Fleurieu Peninsula mainland, are displaced along discrete north‐vergent thrusts and reverse faults. The lithotectonic domains of Kangaroo Island reflect a basin evolution which is geometrically and in part also sedimentologically distinct from the mainland. The original geometry of the east‐west oriented basin appears to be the principal factor that controlled the structural partitioning between the lithotectonic domains of Kangaroo Island during the Cambro‐Ordovician Delamerian Orogeny, which resulted in basin inversion and northwest‐directed contraction.