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Pre-existing basement structure and its influence on continental rifting and fracture zone development along Australia's southern rifted margin




Gibson, George M
Totterdell, J M
White, Lloyd
Mitchell, C
Stacey, A R
Morse, Michael
Whitaker, A

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Geological Society of London


Palaeogeographical reconstructions of the Australian and Antarctic margins based on matching basement structures are commonly difficult to reconcile with those derived from ocean-floor magnetic anomalies and plate vectors. Following identification of a previously unmapped crustal-scale structure in the southern part of the early Palaeozoic Delamerian orogen (Coorong Shear Zone), a more tightly constrained plate reconstruction for these margins is proposed. This reconstruction places the Coorong Shear Zone opposite the Mertz Shear Zone in Antarctica and lends itself to a revised interpretation of continental rifting along Australia's southern margin in which rift basin architecture, margin segmentation and the formation of ocean-floor fracture zones are all linked to pre-existing basement structure and the reactivation of a few deep-rooted crustal structures inherited from the Delamerian orogeny in particular. Reactivation of the Coorong Shear Zone and other basement structures (Avoca-Sorell Fault Zone) during the earlier stages of rifting was accompanied by the partitioning of extensional strain and formation of late Jurassic-Early Cretaceous normal faults and half-graben in the Bight and otway basins with opposing NE-SW and NW-SE structural trends. Previously, the Mertz Shear Zone has been correlated with the Proterozoic Kalinjala Mylonite Zone in the Gawler Craton but this positions Australia 300-400 km too far east relative to Antarctica prior to breakup and fails to secure an equally satisfactory match in both basement geology and the superimposed extension-related structures.



Keywords: Basement structures; Continental rifting; Crustal structure; Crustal-scale structure; Extensional strain; Magnetic anomalies; Plate reconstruction; Structural trends; Buildings; Floors; Tectonics; Plates (structural components); basement rock; continental



Journal of the Geological Society


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