Eastern Australia

The Sydney-Gunnedah-Bowen Basin developed above the junction between (a) the western, early to mid-Paleozoic Lachlan and Thomson Fold Belts, terminally deformed and intruded in the mid-Carboniferous, and (b) the eastern, mid- to late Paleozoic New England Fold Belt (NEFB). Accordingly, the basement of the Sydney- Gunnedah-Bowen Basin varies along strike. In the south, the Sydney-Gunnedah Basin developed above the Late Devonian-Early Carboniferous Andean-type magmatic arc and fore arc, whereas in the north, the Bowen Basin developed behind the magmatic arc. The magmatic arc was displaced by crustal transtension during the latest Carboniferous-Early Permian. During transtension, the NEFB was intruded by S-type granitoids with co-magmatic ignimbrites and uplifted during right-lateral shearing to form the initial stage of an orocline. Thereafter to the end of the Triassic, eastern Australia developed through seven stages: Stage A (290-268 Ma), extension-volcanism of the collapsed Kanimblan-NEFB upland with thick volcanics and sediment, was a local manifestation of the first release of Pangean-induced heat and is comparable with the vast magmatic province of the same age that developed after the Variscan Orogeny in Europe. A glacio-eustatic marine transgression at 277 Ma crossed the NEFB to reach the newly formed Bowen and Sydney Basins. Stage B (268-258 Ma), a marine sag on the platform and embryonic magmatic arc/foreland basin, brought the sea to the western edge of the Bowen-Gunnedah- Sydney Basin and covered Tasmania. The first tuff attributable to the north-migrating convergent magmatic arc reached Tasmania 265 Ma, and the first convergent granitoid reached the NEFB also at 265 Ma and was followed by the deposition of coarse sediment in the embryonic foreland basin. Stage C (258-250 Ma), orogenic piedmont coal/tuff, initiated the foreland basin between the uplift of the mature NEFB and a foreswell that bounded the Galilee, Coorabin, and Tasmania Basins of the western craton. In Stage D (250-241 Ma), orogenic piedmont redbeds barren of coal and tuff, the sea was driven from the foreland basin by climactic outpouring of volcanolithic sediment from granitoids in the orogenic upland. Waning plutonic activity in the narrowing NEFB upland led to Stage E (241-235 Ma), a cratonic quartz-sand sheet that covered the entire foreland basin. Stage F (235-230 Ma), orogenic paralic sediment, saw a final pulse of sediment shed from the overthrusted NEFB. The terminal deformation and uplift of the NEFB represents the northern part of the Gondwanide event that involved the entire Panthalassan margin to South America in the final episode of the foreland basin/orogen. The final Stage G (230-200 Ma) involved rifting of the orogen by right-lateral transtension to form the Tarong and Ipswich coal and volcanic basins in a second release of Pangean heat. By the Early Jurassic, cratonic quartz sand breached the NEFB upland at the Queensland-New South Wales border. The modern New England upland dates from the mid-Cretaceous inception of the Eastern Highlands by the underplating of the lower-plate margin during the separation of the upper-plate Lord Howe Rise.