664 NEO '9j ·Conference Procee dings Evolution of the eastern margin of Australian plate: possible correlatives in Australia, New Caledonia and New Zealand J.C Aitchison Department of Geology and Geophysics, University of Sydney ABSTRACT Studies of the terranes of eastern Australia, New Caledonia and New Zealand can be used to develop palinspastic reconstructions of areas which were adjacent to eastern Gondwana during the Late Paleozoic to Mesozoic. Some of the terranes which developed along, or were accreted to, this margin have subsequently underg one significant dispersal. Much of this dis- persal involved strike- slip faulting possibly during highly oblique subduction. More recent (Cretaceous-Paleocene) terrane dispersal was the result of crusta! attenuation and rifting between Australia and New Zealand and subsequent spreading in the Tasman Sea. All of these processes have contributed to the ongoing crusta) growth of the . eastern margin of the Australian Plate. INTRODUCTION Exposed rocks within the tectonic col1ages of the New England orogen, New Caledonia and New Zealand provide dues as to the geological evolution of the eastern margin of the Australian Plate. These areas contain rocks which developed along the easternmost portion of Gondwana during the Late Paleozoic to Early Mesozoic and seve r al workers , have suggested correlations (Harrington, 1983; Cawood, 1984; Waterhouse and Sivell, 1987). Recent terrane analysis studies have led to a greater appreciate of subtle differences in tectonic settings for many of the elements which comprise this plate margin. This work indicates that these terranes not only contain evidence of accretion along the Australian Plate margin but also later terrane dispersal. Most of the terranes in question developed in convergent plate margin settings such as calc-alkaline volcanic arcs , fore-arc basin s and accretionary complexes. Each area ha s unique geology, however , detailed pa l eontological, paleomagnetic , lithostratigraphic and geochemical studies NEO '93 Conference Proceedings I prov ide further evidence for common ancestry of some portions of these now widely separated areas. GYMPIE, EASTERN AUSTRALIA The Gympie province of the New England orogen in eastern Australia is char _ acterised by a Permian volcanic arc basement overlain by a mildly deformed, dominantly volcanidastic Permo-Triassic sedimentary assemblage (M urph y et al., 1976; Harrington, 1983). It comprises several poorly exposed and incompletely mapped lithotectonic units and is best regarded as a superterrane. The distinctive geochemistry and age of the basement rocks in the Gympie district shows strong similarity with volcanic rocks in the Brook Street terrane of New Zealand. Some workers consider the Gympie terrane to merely represent a "stepping-out" of arc volcanism along the margin of Gondwana (eg. Dirks et al., 1992). However, rocks of the Highbury Volcanics in clude distinctive clinopyroxene-phyric anka ramite lavas and other igneous lithologies characteristic of intra-oceanic island arcs (Sivell and Waterhouse, 1988) and are clearly exotic to eastern Australia. These rocks are succeeded by a sedimentary sequence which includes Atomodesmatinid-bearing limestones . Previous workers have commented on ove.rall similarities with New Zealand geology and have also suggested correlations be tween Permo- Triassic sedimentary rocks of the overlying Gympie Group and the New Zealand Dun Mountain Ophiolite Belt-Maitai terrane (Harrington, 1983). However, significant differences exist an d the two sequences are probably not co. rr e lativ e. The Dun Mountain Ophiolite Belt (Coombs et al., 1976; Kimbrough et al., -1992) is absent in Gympie as is much of its distinctive overlying cover (Landis, 1974; Aitchison and Landis , 1990). Many earlier correlations were made prior to more detailed studies of rocks in Gympie and 665