Sedimentary basins of eastern Australia: paleomagnetic constraints on geodynamic evolution in a global context

Abstract

Changes in plate movements cause intraplate deformation and lead to basin development, fluid flow and mineralisation phases. Movement changes are detailed by seafloor-spreading data, back to the Oxfordian, and by paleomagnetic data before that time. Paleomagnetism records and interprets plate movement changes as pole path features—loops, bends, overprints—and these are applicable as tectonic and stratigraphic baselines at continental and global scales. Australian pole path features, from Late Paleozoic to Holocene, are interpreted in terms of regional evolution of eastern Australian basins and in relation to global plate movements. Emphasis is on the Late Paleozoic pole path of Australia. Two opposing views, the SLP path and the KG path, are discussed. Discussed also is an emerging pole path for the New England Orogen (NEO path), representing a potentially more detailed version of the KG path. The Mesozoic pole path of Australia is understudied and poorly defined. The Cenozoic path is better defined, but disputed in detail. The Late Paleozoic to Holocene pole path shows four major loops, L2 to L5, and several bends and lesser features. The L2 loop (mid-Carboniferous apex) relates to formation of the Westralian Superbasin; the L3 loop (Late Carboniferous–Early Permian) relates to formation of the Bowen–Gunnedah–Sydney basin system and oroclinal deformation of the Southern New England Orogen; the poorly defined L4 loop (Late Triassic–Early Jurassic) relates to formation of basins in eastern Queensland and rifting along the New Guinean margin of the Australian Plate; the poorly defined L5 loop (Late Jurassic–Early Cretaceous) relates to rifting along the western, northeastern and southern margins of the Australian Plate. Other features—minor Early Permian and Late Permian loops, bends of mid–Late Triassic, Early–Late Cretaceous and latest Cretaceous–earliest Tertiary age, and a Mio-Pliocene excursion—likewise are interpreted in terms of tectonostratigraphic and basin-forming phases. The L2 and L3 loops in particular are interpreted also within a global context. The L2 loop indicates a Late Devonian to mid-Carboniferous northward excursion of northeastern Gondwanaland, interpreted as leading to contact with the central Asian Altaids. This identifies the Central Asian Orogenic Belt and the Kanimblan and Alice Springs Orogenies as Pangea-forming, Variscan orogens on conjugate, northeastern Gondwanaland and southeastern Laurasian, margins of the Paleoasian Ocean. Alice Springs Orogeny-related deformation may have led to eastward extrusion of the Thomson Orogen, a Variscan equivalent to Cenozoic India–Asia deformation. The succeeding early-Late Carboniferous southward movement of northeastern Gondwanaland was extremely fast and created an extensional environment, initiating the Westralian Superbasin. The L3 loop reflects a fundamental change in rotation of Gondwanaland from counterclockwise (Late Carboniferous) to clockwise (Early Permian), leading to Stephanian initiation of the Bowen–Gunnedah–Sydney basin system and Early Permian oroclinal deformation of the Southern New England Orogen. The Texas, Coffs Harbour and Manning Oroclines are interpreted as telescoped mega dragfolds related to a major dextral shear system along the Protopacific margin of Gondwanaland and Alice Springs Orogeny-related dextral shear along the Darling River and Cobar–Inglewood Lineaments. A relationship between magnetic overprint phases and the younger limb and/or apex of pole path loops is emerging. Practical application in identifying and dating fluid flow and mineralisation phases has been demonstrated for the Paleoproterozoic–Mesoproterozoic pole path of Australia, but not yet so for the Phanerozoic pole path.