The Tasmanian region's geological history bears on the history of the entire southern margin of Australia. The southern margin is already a major producer of petroleum from the Upper Cretaceous and Paleocene sequences in the Gippsland Basin, and has given encouraging exploration results in several other basins. The Otway Basin, in particular, is the scene of major recent offshore gas discoveries in the Cretaceous sequence. Both the west Tasmanian margin and the South Tasman Rise have petroleum potential. The targets on the forthcoming Rig Seismic sampling cruise of 31 days (AGSO Cruise 147) are on the west Tasmanian margin, the South Tasman Rise, the East Tasman Rise, and the adjacent oceanic areas. The general bathymetry of the region is shown in Figure 1. The targets were defined by the early 1994 Tasmante cruise (Exon et al., 1994), which used the French research vessel l' Atalante on an exchange basis to swath-map the sea bed. About two-thirds of both the South Tasman Rise (STR) and the west Tasmanian margin were mapped, an areal coverage exceeding 200 000 km 2. The very accurate 1:250 000 scale bathymetric maps and sonar images arising from the Tasmante survey provide an unequalled source of structural information. A simplified bathymetric map of the region, based largely on the Tasmante swath-mapping, is shown in Figure 2. The aim of the present sampling cruise is to ground truth the maps and ideas arising from the Tasmante cruise. It is designed to sample basement and Phanerozoic sedimentary rocks in all three continental blocks, Cainozoic volcanics in continental and oceanic terrains, and Cainozoic sediments on the continental blocks, by dredging and coring. This will help elucidate the Phanerozoic history of the area with emphasis on petroleum geology and plate tectonic hisory, and also the Cainozoic and especially Quaternary history with emphasis on plate tectonic history, and changes in climate and sedimentation patterns. Water column sampling is designed to provide more information about oceanographic controls on sedimentation. An additional aim is to sample manganese nodules in deep water to assess them as a potential resource, by the use of free-fall grabs. As a result of interest in the volcanic cones about 100 km of Hobart, mapped during the Tasmante cruise, which define major fishing grounds, two photographic profiles and one dredge are planned for there. The main sampling areas are discussed briefly below.

Legacy product - no abstract available

The history of Mid-Proterozoic metasedimentary gneisses, felsic and mafic orthogneisses of the Tomkinson Ranges, western Musgrave Block, involved multiple low- to high-P metamorphic events and polyphase deformation. Isoclinal, gently inclined to recumbent D1/2 folding accompanied the intrusion of pre-S1 mafic and felsic orthogneisses and post-S1 , pre-S2 felsic orthogneisses under peak conditions of P=5±1 kbar and T-750 °C at ~1200 Ma. K-feldspar megacrystic granitoid stocks formed at ~1188 Ma. Post-S2 mafic to ultramafic magmatism resulted in the large layered intrusions of the Giles Complex at ~1080 Ma, whilst the terrane was at conditions of P=6±1 kb. At ~1080-1060 Ma, microgranitoid dykes and veins intruded Giles Complex sills in the Tomkinson Ranges, while comagmatic volcanics of the Tollu Group unconformably overlie other parts of the Musgrave Block further west. Type A mafic dykes, which may represent feeder veins to the Tollu Group, intruded rocks of the Tomkinson Ranges before a third deformation event, D3, resulted in a system of steep, southeast-trending mylonites with a granulite facies S3 foliation and a well-developed down-dip L3 stretching lineation. Type A mafic dykes and their host felsic granite gneiss show marginal to complete recrystallisation to granulite facies mylonitic S3 assemblages at conditions of P-11 kb and T-700°C. Near-isothermal decompression returned such parts of the Musgrave Block to conditions of P-4-5 kb late in D3. Parts of the Musgrave Block that are unconformably overlain by the Tollu Group probably remained closer to the earths surface during D3. Coarse-grained, ~800 Ma Type B mafic dykes and aphanitic, ~1000 Ma Type C mafic dykes cut S3, and are cut by a system of mylonite and retrograde shear zones, D4-7. East-trending ~550 Ma D6 ultramylonite pseudotachylite zones represent the effects of the Late Proterozoic to Cambrian Petermann Orogeny, which resulted in significant dislocation of parts of the Musgrave Block and the partial to complete recrystallisation of post-S3 dykes near the Woodroffe thrust zone at sub-eclogite facies conditions of P=14±1 kb and T=700-750°C. These late high-pressure assemblages suggest that the structural grain in rocks of south-central Australia resulted, to a major extent, from Late Proterozoic to Cambrian compression.

At the invitation of Newercrest Mines Limited I visited the Telfer Gold Mine from Tuesday July 12, returning on Thursday morning July 13th. Whilst at the site, I visited the open pit accompanied by Don Thompson, and with Don, Nick Langsford and Campbell Mackey visited sites of the Mount Crofton Granite at Mount Crofton, Minyari Granite at Minyari Hills, and the Wilkie Granite some 15 kms east of the Telfer mine. I also examined granite core in holes ORC 1-6. These notes describe my thoughts on the sites that I visited, and also give some recommendations for some potential future work. I have prepared these notes at the request of Nick Langsford and they contain information that is essentially off the top of my head. Please note that they are not meant to be comprehensive and that I have not had time to validate anything that is within them. I prepared these at the Newcrest Office in Perth on Thursday afternoon of July l3th and that I did some minor refinements to them back at AGSO on July 17th.

Altered basalt, dolerite and gabbro have been dredged from a previously unsampled portion of the Macquarie Ridge (47o-48° S), using the commercial fishing vessel Amaltal Explorer. These rocks are petrographically and geochemically similar to mafic-ultramafic volcanic and plutonic suites of MORB-like petrological affinity, collected along the ridge between 49° and 58° S by previous investigators. The northernmost part of the Macquarie Ridge (Puysegur Bank) is thus geologically related to the rest of the ridge, even though it is bathymetrically part of the New Zealand continental shelf. Sedimentary rocks dredged from 47o-48° S were derived from both oceanic Macquarie Ridge and continental New Zealand sources. There is no evidence of subduction-related magmatism along any part of the Macquarie Ridge.

An introduction to this special issue of the Journal.

No abstract available

Product Specifications Coverage: Partial coverage, predominantly in northern Australia, along major transport routes, and other selected areas. About 1000 maps have been published to date. Currency: Ranges from 1968 to 2006. Coordinates: Geographical and UTM. Datum: AGD66, new edition WGS84; AHD. Projection: Universal Transverse Mercator UTM. Medium: Paper, flat copies only.

During 1.3-1.0 Ga, multiple magmatic/tectonic events, causally linked to extensive mantle melting, markedly affected the Musgrave Block, the Albany-Fraser belt and parts of the east Antarctic shield. It is possible that southern parts of the central Australian Arunta Block were also affected by this event. Equivalent terranes can be juxtaposed in conventional Gondwana reconstructions of southwestern Australia and Antarctica. Effects of a ~1060 Ma Gondwana-wide magmatism include areally extensive dyke swarms and volcanics of the central Australian Bentley Supergroup. It is unclear to what extent the effects of a ~550 Ma convergent event that resulted in significant crustal overthickening and high-P recrystallisation in Musgrave Block rocks can be extrapolated to neighbouring terranes. Nonetheless, this event may be indicative of plate margin processes of latest Neoproterozoic age that controlled the assembly of central Australia.

Layered mafic-ultramafic intrusions of the Giles Complex, western Musgrave Block are confined to a southern granulite facies block thrust northward over an amphibolite facies block and southward over sediments of the Officer Basin. The Tomkinson Ranges to Jameson Range region, at the westernmost end of the southern granulite facies terrane, consists of 17 medium to large-scale faulted segments or intact layered mafic-ultramafic sills and lopoliths emplaced into felsic to intermediate or mafic granulite facies orthogneiss. Protoliths of these gneisses, giving ages of -1.55 and 1.3 Ga, were metamorphosed at -1.2 Ga. Emplacement of the mafic-ultramafic bodies into multiply deformed felsic granulites (D1 and D2-pure shear; T>750°C, P=5±1 kb), previously believed to have occurred at about 1200-1188 Ma, is now thought more likely to be of 1.08--1.06 Ga--coeval with the Tollu Group volcanics. The western Musgrave Block displays crustal zonation of near-contemporaneous units, from deep crustal ultramafic-dominated intrusions in the north (south of the Woodroffe Thrust), to gabbro-pyroxenite intrusions in the Tomkinson Ranges, to troctolite intrusions in the southwest, to upper crustal volcanics of the Tollu Group-i.e. a southward rise in crustal level. The layered intrusions include: (1) large olivine-clinopyroxene-plagioclase troctolite to troctolite-anorthosite bodies, with Fe-rich olivine and plagioclase as liquidus phases, crystallised from highly evolved silica-undersaturated liquids and representing high-pressure orthopyroxene fractionation prior to intrusion. These bodies are commonly magnetite-rich, representing high oxygen fugacities, and include little or no ultramafic component, e.g. Jameson, Blackstone, Cavenagh, and Bell Rock intrusions; (2) large orthopyroxene-clinopyroxene-plagioclase gabbronorite to norite intrusions, including a significant (up to about 30%) ultramafic component, e.g. Michael Hills, Mount Davies, Kalka; (3) small to medium-sized layered pyroxenite-peridotite-gabbro intrusions, e.g. Murray Range, Claude Hills, The Wart, Gosse Pile, Ewarara, and (4) stratiform anorthosites forming lenses and recrystallised tongues interlayered with felsic granulites, mainly around Teizi bore. Ultramafic increments crystallised from little-fractionated primitive basaltic magmas saturated with olivinespinel form late magmatic pulses injected into above-solidus resident gabbroic bodies. Intrusion was followed by isobaric cooling (Wingellina Hills: P=6±1 kb; Blackstone: ~4 kb). Near-coeval relations between the Giles Complex and the Tollu Group volcanics imply rapid uplift and erosion of deep crustal zones followed by volcanic activity. Feeders for the volcanics are represented by type-A dykes correlated with the ~1.05-1.07 Ga Kulgera swarm of the eastern Musgrave Block, and by extensive granite veining and related granulite facies recrystallisation of large sectors of the Giles Complex (D3-simple shear; early stage T=650-700°C, P=11 kb; late stage P=4.5±1.1 kb). Northward thrusting of the granulite facies block over amphibolite facies gneisses along the western extension of the Woodroffe Thrust -550 Ma was associated with elevated pressures along the fault zone (P=14.0±1.1 kb; T=750°C), contemporaneous with the Petermann Ranges deformation.