Evolution of the East Gondwana convergent margin in Antarctica, southern Australia and New Zealand from the Neoproterozoic to latest Devonian

Abstract

Abstract New insights into the Late Precambrian-latest Devonian evolution of the Pacific margin of Gondwana are obtained by treating the margin in terms of three key tectonic elements: i) the in situ part of the Ross Orogen of Eastern Antarctica (Wilson Terrane) built on, and fringing, older crust; ii) the largely in situ southern Tasmanides of eastern Australia; and iii) offshore basement and island arc terranes now accreted either to the Ross Orogen, the Tuhua Orogen of southwestern New Zealand or, in one case, to the Australian Tasmanides. Detailed correlations between these elements suggest that the onset of convergence was essentially simultaneous along the margin over an original distance of ~1000\u202fkm. The first appearance of subduction-related igneous rocks occurred at ~540–530\u202fMa in the Tasmanides; ~535–530\u202fMa in the Tiger Arc of northern Victoria Land; and 550\u202fMa in southern Victoria Land of the Ross Orogen. New correlations of this paper suggest possible but unconstrained trajectories of offshore terranes. The Bowers Terrane was accreted to the East Gondwana margin at ~491\u202fMa, producing the main Ross Orogeny. The adjoining Takaka Terrane had docked briefly with that margin at ~497–494\u202fMa (Haupiri Disturbance in New Zealand) before crustal extension rifted it oceanward to drift away in the latest Cambrian to become subsequently amalgamated with the sedimentary Buller Terrane at ~390\u202fMa. The West Tasmania Terrane was accreted to the East Gondwana margin beginning at~500–499\u202fMa (generating phase 3 of the Tyennan Orogeny) and the connected Selwyn Block to the Tasmanides at ~500\u202fMa (main Delamerian Orogeny). Our new interpretations suggest that previous lithological correlations of subduction-related volcanics between the Ross Orogen and southern Tasmanides did not take into account major rollback in the Tasmanides from ~514 to ~503\u202fMa. Similarly, they suggest that the ~550–480\u202fMa Granite Harbour Intrusive roots of the continental margin Ross Arc are not correlatives of 514, 505 and\u202f~\u202f495–470\u202fMa granites intruding the Kanmantoo Group in the Delamerian Orogen of South Australia, either in time or in tectonic setting. We also recognize an early (~520–516\u202fMa) boninitic infant arc event in the outboard West Tasmania, Bowers, and Takaka terranes that predated ~500\u202fMa more mature arcs in the last two. Arc-related magmatism in the Ross Orogen reflects the interplay between two main subduction systems — that which generated the Ross Arc and an outboard one that generated intraoceanic arcs. Three major turbidite fan systems developed along the East Gondwana margin as responses to major deformations. Early Cambrian fan system 1 postdates the Beardmore Orogeny and includes the Kanmantoo Group in the Delamerian Orogen and the Berg and upper Priestley formations in the Wilson Terrane. Cambrian-Ordovician fan system 2 (the Robertson Bay Group, the Swanson Group in Marie Byrd Land, the Greenland Group in the Buller Terrane and the St Arnaud Group in the Delamerian Orogen) and Lower-Middle Ordovician fan system 3 (turbidites of the Eastern Lachlan Orogen, the Buller Terrane (New Zealand) and East Tasmania Terrane) both postdate different parts of the Ross Orogeny. Cessation of fan system at ~458\u202fMa correlates with ‘accretion’ of the Robertson Bay Terrane in northern Victoria Land.