Formation and reactivation of the Cambrian Kanmantoo Trough, SE Australia: implications for early Palaeozoic tectonics at eastern Gondwana’s plate margin

Abstract

The Kanmantoo Group is a thick and largely metamorphosed sedimentary succession that filled an isolated arcuate Cambrian basin (Kanmantoo Trough) which formed within continental Gondwana, and now lies on the southern margin of the present Australian continent. Kanmantoo Group sediments unconformably overlie Neoproterozoic and older Cambrian rocks. We consider that the geometry of the southern part of this trough was influenced by strike-slip movement along an intra-continental tear fault. To the north, the basin changes to a style dominated by orthogonal extension and eventually tapers and dies out normal to the tear fault. Balanced sections show that the kinematic style and strain distribution developed during early Palaeozoic inversion was controlled by the specific architecture of the Kanmantoo Trough. Early Palaeozoic tear faulting could have linked contrasting subduction polarities along the then contiguous palaeo-Pacific margin of Gondwana. The Kanmantoo Trough is considered to have formed at a passive margin related to east-directed subduction in what is now the Australian continent. In contrast, west-directed subduction formed an active margin at contiguous parts of current Antarctica. Kanmantoo Group sediments were derived from the south by erosion of a Grenvillean province mixed with sediments eroded from the emergent active margin of Gondwana. The inception, localization and sedimentation in the Kanmantoo Trough reflects a complex interaction of tectonic processes along the encroaching Ross–Delamerian Orogen.

The Ross orogeny of the transantarctic mountains: a northern Victoria Land perspective

“…In the majority of the so far proposed models for this event (e.g. Kleinschmidt and Tessensohn 1987;Flo¨ttmann et al 1998;Weaver et al 1984), the BT has been interpreted as an oceanic island arc driven to collision with the continental margin by W-directed subduction. Some authors (Finn et al 1999;Ferraccioli et al 2002), on the contrary, interpret the WT, BT and RBT as three originally adjacent zones in the framework of W-dipping subduction.…”

“…(1) W-dipping subduction (under the craton) (Kleinschmidt and Tessensohn 1987;Flo¨ttmann et al 1998), (2) E-dipping subduction followed by W-dipping subduction (Findlay et al 1991), (3) E-dipping subduction and continent-arc collision (Wodzicki and Robert 1986;Meffre et al 2000), (4) W-dipping subduction followed by strike-slip faulting (Weaver et al 1984). …”

The balloon Melange, northwest Nelson: Origin, structure, and emplacement

“…Gibson & Ireland (1996) have identified in Fiordland, magmatic rocks with ages of 481 ± 8 and 501 ± 8 Ma, which they attribute to an extension of the Late Cambrian to Early Ordovician Ross-Delamerian orogen into New Zealand. Large-scale shortening and thrusting has been identified in all other segments of the Ross-Delamerian orogen (Berry & Crawford 1988;Flöttmann & Kleinschmidt 1991;Jenkins & Sandiford 1992;Flöttmann et al 1998;Münker & Crawford 2000) and similar large-scale shortening in New Zealand would be consistent with events elsewhere. In both Tasmania and northern Victoria Land (Antarctica), the Ross-Delamerian orogeny is marked by an abrupt change from active to passive margin tectonics similar to the change seen in the Takaka Terrane.…”

Accretion of juvenile crust at the Early Palaeozoic Antarctic margin of Gondwana: geochemical and geochronological evidence from granulite xenoliths

“…A comparable change in the nature of the basement, from continental (west) to oceanic (east), is documented in the Tasmanides of SE Australia (Grey and Foster, 2004). The inferred oceanic subduction on the Ross Sea side of the Robertson Bay terrane could have had an opposite dip with respect to subduction below the Wilson margin, as inferred for coeval south‐eastern Australia‐Tasmania (Gibson, 1987; Flöttmann et al. , 1998; Münker and Crawford, 2000).…”