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.

ABSTRACT The 100-mile-long Mesabi Iron Range contains the Biwabik Iron Formation, the largest of the Lake Superior–type iron-formations in the United States, deposited on the northern edge of the Paleoproterozoic Animikie Basin. This basin has been interpreted as a foreland basin that developed north of the Penokean Fold-and-Thrust Belt (ca. 1850 Ma), or alternatively, as a backarc basin north of the Wisconsin magmatic terrane. The basal unit in the basin, the siliciclastic Pokegama Formation, was deposited upon the ca. 2700 Ma granitic-volcanic basement. It is conformably overlain by the Biwabik Iron Formation, 200–750 ft thick, which consists of four members: lower cherty, lower slaty, upper cherty, and upper slaty. There are two prominent stromatolite zones. Both of the above formations contain attributes of deposition in a tidally influenced environment. The Biwabik is conformably overlain by the Virginia Formation, a thick turbiditic sequence of interbedded black shale, graywacke, and ash beds. All three formations dip southeastward at 10°–20°. The iron-formation (taconite) generally consists of 20%–30% Fe present in carbonates, silicates, and oxides, and 70%–80% SiO 2 . Direct shipping ores, also called natural ores, were originally mined on the Mesabi Iron Range and were instrumental in making the United States an industrial giant and in the winning of WWI and WWII. These ores originated along fault zones in the iron-formation where silica was removed leaving high-grade oxidized hematite-goethite natural ore bodies of 50%–55% Fe. Processing of low-grade magnetic taconite began in 1952, passed the natural ores in tonnage in 1967, and is now totally dominant. Field trip stops will include all three formations, with emphasis on the iron-formation. The final stop is in the folded Thomson Formation, the southerly equivalent of the Virginia Formation.

Deformation in accretionary orogens, such as the eastern Australian Tasmanides, is clearly partitioned either as thin-skinned thrusting or thick-skinned faulting, with structural style dependent on the nature and stratal thicknesses of the sequences involved. The thin-skinned thrust systems consist of either detachment-related folds and thrust sheets within attenuated passive margin sequences or thrust sheets of chevron-folded turbidites with leading imbricate-fan geometry that are developed within former submarine fans overlying back-arc basin oceanic lithosphere. Thick-skinned belts consist of major thrust faults that root into the seismic reflection Moho with no apparent common décollement and cause crustal-scale imbrication of former arc, forearc, submarine fan, and accretionary complex elements. The Tasmanides are a composite orogenic system made up of three distinct orogenic belts whose character and structural style have resulted from the deformation of different tectonic components; the former rifted passive margin to make the Delamerian Orogen, a turbidite fan system(s) in a back-arc setting to make the Lachlan Orogen, and an arc-subduction complex that includes some older accreted components to make the New England Orogen. The inboard Delamerian Orogen consists of an external, craton-vergent thrust belt with foreland-style, detachment-related folds and thrusts linked to a high-T/low-P metamorphic complex. The centrally located Lachlan Orogen is made up of three separate thrust systems largely developed in submarine turbidite fans and incorporates a shear-zone-bounded high-T/low-P metamorphic belt. The outermost New England Orogen is constructed from craton-vergent, fore-arc and magmatic arc sequences, subduction complexes, and ophiolite fragments.