STRUCTURAL AND TECTONIC SYNTHESIS FOR THE PERTH BASIN, WESTERN AUSTRALIA

Abstract

The Perth Basin is localised by reactivation of Neoproterozoic shear zones on the western margin of the Archaean Yilgarn Craton in Western Australia. While Ordovician to Silurian sandstones were deposited in the northern Perth Basin, the earliest sediments elsewhere are Middle Carboniferous to Permian in age. A sinistral transtensional regime, during which the main architecture of the basin was established, developed during NE‐SW extension between Greater India and Western Australia in the Permo‐Triassic. NW‐SE shortening with continued NE‐SW extension resulted in sinistral transpression in the late‐Early to Middle Triassic. Sag‐phase sedimentation in the LateTriassic followed this oblique rifting event.An analogy may be made between the Perth Basin and the Permo‐Carboniferous to Jurassic Karoo basins in southern and central Africa and Madagascar. Deposition of the Karoo sequence took place within pull‐apart and transtensional basins resulting from sinistral reactivation of basement shear zones. The Indian Gondwana Supergroup, and an equivalent sequence in Antarctica, were deposited within normal fault‐bounded graben. The Late Paleozoic to Early Mesozoic formation of the Perth Basin, the Karoo basins of Africa and Madagascar, and the Gondwana basins of India was due to intraplate stress resulting from convergence along the Panthalassa margin of Gondwanaland. Late‐Early to Middle Triassic compressional events in all basins mark terminal collision along the Panthalassa margin.The latest Triassic to Early Jurassic marks a new rifting event due to regional east‐west to WNW‐ESE extension, producing dextralplus normal displacements on many NW‐to NNW‐striking structures, and essentially normal displacements on north‐ to NNE‐striking faults. NW‐SE extension during the Upper Jurassic culminated in the NW separation of Greater India and the formation of oceanic crust in the Neocomian, and resulted in the superposition of structures developed in a dextral transtensional regime. Conjugate strike‐slip faults and minor thrust faults formed during the post‐Neocomian, with approximately north‐south compression and east‐west extension. Precambrian gneisses, granitoids and metasediments of SW Western Australia have been deformed during basin development, and dole rite dyke intrusion during the Carboniferous to Middle Triassic is restricted to these terranes.The sequence of events proposed herein for the Perth Basin is in agreement with the tectonic framework of a large portion of Gondwanaland. A better knowledge of the structural history of the Perth Basin may aid the interpretation of seismic and remote‐sensing data in the search for further hydrocarbon occurrences.