The Arthur Lineament of northwestern Tasmania is a Cambrian (510 Ϯ 10 Ma) high-strain metamorphic belt. In the south it is composed of metasedimentary and mafic meta-igneous lithologies of the 'eastern' Ahrberg Group, Bowry Formation and a high-strain part of the Oonah Formation. Regionally, the lineament separates the Rocky Cape Group correlates and 'western' Ahrberg Group to its west from the relatively low-strain parts of the Oonah Formation, and the correlated Burnie Formation, to its east. Early folding and thrusting caused emplacement of the allochthonous Bowry Formation, which is interpreted to occur as a fault-bound slice, towards the eastern margin of the parautochthonous 'eastern' Ahrberg Group metasediments. The early stages of formation of the Arthur Lineament involved two folding events. The first deformation (CaD1) produced a schistose axial-planar fabric and isoclinal folds synchronous with thrusting. The second deformation (CaD2) produced a coarser schistosity and tight to isoclinal folds. South-plunging, north-south stretching lineations, top to the south shear sense indicators, and south-verging, downward-facing folds in the Arthur Lineament suggest south-directed transport. CaF1 and CaF2 were rotated to a north-south trend in zones of high strain during the CaD2 event. CaD3, later in the Cambrian, folded the earlier foliations in the Arthur Lineament and produced west-dipping steep thrusts, creating the linear expression of the structure.KEY WORDS: Arthur Lineament, Cambrian, strain, structure, Tasmania, Tyennan Orogeny.*Corresponding author and present address: Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia (Oliver.Holm@ga.gov.au).Formation amphibolites, which the granitoid intrudes, have been correlated with the Kanunnah Subgroup, which has a preferred age of 650-580 Ma (Crawford 1992). We conclude that the Bowry Formation cannot be a lithostratigraphic correlative of the Kanunnah Subgroup or any part of the Ahrberg Group. Turner and Bottrill (2001) discussed the problems associated with large differences in metamorphic history between the Bowry Formation and other parts of the 'Timbs Group' and concluded that the Bowry Formation had a faulted margin against the remainder of the 'Timbs Group', with a metamorphic grade difference across the fault. The western section of the 'Timbs Group' is interpreted here as a parautochthonous slice of the Ahrberg Group, and is referred to in this paper as the 'eastern' Ahrberg Group. The autochthonous Ahrberg Group is referred to as the 'western' Ahrberg Group. The Bowry Formation is referred to here as a separate unit with no specific correlates. The Bowry Formation is fault bounded in the southern Arthur Lineament, has internal evidence of a different metamorphic history (Turner & Bottrill 2001) and is probably much older. There are other fault-bounded units within the Arthur Lineament, in particular, east of the Bowry Formation and faulted against the high-strain Oonah Formation is a block of material that is similar in appearance to t...

The Arthur Lineament is a Cambrian age high-strain metamorphic belt that transects northwestern Tasmania and forms the eastern margin of the Mesoproterozoic and Neoproterozoic Rocky Cape Block. It formed as a result of Middle Cambrian arc-continent collision, and is composed of both allochthonous slices (Bowry Formation and Reece amphibolite), the para-autochthonous 'eastern' Ahrberg Group and the autochthonous 'western' Ahrberg Group. Amphibolites and mafic schists of the 'eastern' Ahrberg Group rocks show a temporal change in composition from transitional alkaline basalt to dominant E-MORB-type rift tholeiites, whereas the 'western' Ahrberg Group metabasic rocks are typical E-MORB rift tholeiites. The lithostratigraphy of the Ahrberg Group matches very well that of the Upper Neoproterozoic (650-580 Ma) Togari Group of the Smithton Trough and King Island. In contrast, amphibolites of the allochthonous Bowry Formation, which also show E-MORB-type patterns typical of rift-type tholeiites, are intruded by granitoid sheets dated at 777 ± 7 Ma, similar to the Precambrian granites exposed on King Island (760 ± 12 Ma). The Bowry Formation granitoids have distinctive high Ti, Zr, Nb compositions best matched by granites produced by extended fractionation of rift basalts with significant crustal assimilation. This suggests that the Bowry Formation metabasic rocks may correlate with the Willouran flood basalts in South Australia, and together record the ca 780 Ma breakup event hypothesised to mark the breakup of the Rodinian supercontinent.

The Proterozoic stratigraphy of Tasmania has some common aspects with South Australia but the Wickham Orogeny (760 Ma) has been a major contrasting feature.We have used chemical U-Th-Pb monazite dating to clarify the age relationships Monazites are typically concordant, with the measured common Pb component much less than the analytical error in electron probe micro -analysis (EPMA) (Cocherie et al. 1998, Scherrer et al. 2000. In-situ analysis and the high spatial resolution of EPMA allows the correlation of monazite age with the structural environment of the monazite grains and this is a major advantage in dating of metamorphic events (Williams & Jercinovic 2002). Finally, monazite has a high closure temperature so that in medium grade metamorphic rocks the grains close as they grow and resetting is controlled by recrystallisation: driven by strain, partial melting or hydrothermal activity (Cocherie et al. 1998, Seydoux-Guillame et al. 2002. For these reasons in -situ chemical dating of monazite by EPMA is revolutionising the dating of low to medium grade, regional metamorphic rocks. The major disadvantage of EPMA chemical age dating is that the high detection limits on Pb (~100 ppm) restrict the application to older events and/or high-Th monazite grains. Quantitative analyses of monazite grains were obtained using a Cameca SX50 electron probe microanalyser operat ed at 20kV and 100nA. The errors quoted in this work were estimated from counting statistics. The counting errors have been propagated through the age calculation using the rules for normally distributed er rors (e.g. Barford 1985). They do not include any systematic errors associated with calibration, or the errors in decay constants. The EPMA calibration was checked regularly using a monazite from the Wilson Lake Terrane, Canada (Thermal ionisation mass spectrometry (TIMS) age of 1000 2 (95% confidence) Ma; G. A. Jenner, pers. comm.) and reproduces the TIMS age to within error. Based on this result, we estimate that the systematic error is less than 1%. Weighted means and probability plots were calculated using ISOPLOT v2.49 (Ludwig 2001). For individual spot analyses, the 1 error is quoted in the tables. All other ages are given with errors shown at the 95% confidence level.King Island, located to the northwest of Tasmania, is composed of several different (meta-) sedimentary and igneous sequences (Fig. 2 ). The western half of the island is

Surface mining of coal can involve extensive footwall slopes parallel to shallow to moderately dipping coal measures strata. Footwall failure mechanisms typically invoke bedding-parallel defects but also require either the existence of flatter structures, which cross-cut bedding, or require break-out through the rock mass to allow failure surfaces to emerge.Permian-aged Baralaba Coal Measures of the Bowen Basin, Queensland, are prospective for coal with extraction by open-pit methods. The Baralaba Coal Measures contains multiple seams within an interburden sequence comprising sandstone, siltstone, mudstone and carbonaceous variations. The coal measures sequence has been deformed into a complex pattern of NW-striking folds which has resulted in bedding dip ranging from 15° to 60°. Bedding has been classified as shallow (10–30°) to moderate (30–60°).Geotechnical investigations conducted to support coal extraction up to depths of 200 m suggest that structural controls strongly influence footwall slope design. For the purpose of footwall slope design, a distinction can be made between deposit areas of relatively simple structure (uniformly dipping bedding on fold limbs) and structurally complex areas (where layer-parallel shortening close to fold hinges has resulted in a system of low-angle thrusts and asymmetrical minor folds).