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  • Several petrographically and geochemically distinct suites of mafic dykes crop out in the Mesoproterozoic Musgrave Block. Intergranular dolerites (group A), as well as the voluminous Giles Complex layered mafic-ultramafic intrusions and Tollu Group basaltic volcanics, were formed by large-scale melting of heterogeneous enriched subcontinental lithospheric mantle about 1080 Ma ago, more than 100 m.y. after the 1200-Ma regional high-grade metamorphism of the Musgrave Block country rocks. The coeval Kulgera (eastern Musgrave Block) and Stuart (Arunta Block) dyke swarms are chemically and isotopically similar. Slightly younger (-1000 Ma), particularly heterogeneous olivine dolerites (group C) were also derived from a similarly enriched source. Mantle heterogeneity was apparently both lateral (as group C dolerites show significant geographical variations) and vertical (because chemically distinct dyke suites of similar age crop out in the same area). Microgabbro dykes and sills associated with troctolitic intrusions of the Giles Complex are compositionally similar to both gabbronorite intrusions of the Giles Complex and to group A dolerite dykes therein. The least fractionated microgabbros are probably representative of an evolved magma that was parental to the major gabbroic intrusions of the Giles Complex, and underwent some degree of high-pressure pyroxene ± olivine fractionation. They cannot be directly parental to the leucotroctolite cumulates. which reflect much more extensive high-pressure fractionation before they were emplaced. Quartz dolerites emplaced 800 Ma ago (group B) were derived by higher-pressure partial melting of a much less enriched (-Nd +2.8 to +3.8), homogeneous asthenospheric mantle source, probably related to mantle-plume activity. They are virtually identical chemically and isotopically with dykes, including the Amata (eastern Musgrave Block) and Gairdner (Gawler Craton) dyke swarms, that crop out over a distance of more than 1000 km.

  • Upper Permian silicified gymnospenn woods from the Bainmedart Coal Measures (Amery Group) near Beaver Lake, East Antarctica, are described as two new species, Australoxylon bainii and A. mondii, on the basis of morphometric and qualitative characters - including ray anatomy, tracheid shape, and cross-field pit structure. Australoxylon mondii has two forms, one of which is characterised by a distinctive ray architecture comprising semidetached rows of ray cells with intervening gaps bridged by sporadic joins. Wood of Vertebraria could not be distinguished from Australoxylon mondii on microanatomical characters, which suggests that these two organ taxa may represent different parts of the same glossopterid plant. Many characters used traditionally in wood taxonomy could not be applied owing to substantial variation or preservational differences both within and between specimens. Three types of presumed biogenic cavities occur in the woods. Coprolite-containing cavities distributed in seasonal bands represent rare evidence for Permian wood-boring arthropods. Other, irregularly distributed cavities and appositions were probably fonned by pathogenic fungi. Growth-ring analysis indicates a markedly seasonal climate with low to moderate interseasonal variation in wood production. Significant intraseasonal influences on growth are also evidenced by numerous false rings.

  • The trilobite and brachiopod fauna of the Gap Creek Formation is revised. Recorded are the trilobites: Geragnostus aff. splendens, Opipeuter angularis, O. ?inconnivus, Carolinites ?genacinaca, Caningella hardmani, Encrinurella ?reedi, and several indeterminate forms. Brachiopods include ?Pseudomimella sp., ?Oligorthis sp., Tritoechia sp., Spanodonta hoskingiae, and Tinopena shergoldi gen. et sp. nov. Also recorded are the gastropods Teiichispira sp. and Helicotoma sp., and calcareous plates of uncertain affinities. Correlations based largely on the telephinid trilobites indicate this fauna is of late Bendigonian (Be3-Be4) age.

  • Samples from eight dredge hauls collected during BMR cruise 107 from several seamounts in the Vening Meinesz chain, south of Christmas Island, yielded calcareous nannofossils, foraminiferids, and fragmentary macrofossils with ages ranging from Late Cretaceous to Holocene. Many samples are mixtures, suggestive of debris flows, and some contain lithologies of various ages. The Late Cretaceous assemblages suggest shallow-water to upper bathyal depths. The seamounts were built up rapidly by volcanism, probably commencing during the Albian or Santonian, continuing through the Campanian, by which time they had shoaled, and ceasing during the Maastrichtian. Atolls comprising mounds of shelly algal biostromes dominated by rudists and Inoceramus had formed by the Maastrichtian. The sea was warm at this time, when the area was at latitudes far south of those of today. The Palaeogene assemblages suggest increasingly deeper depositional environments. The Paleocene is indirectly indicated by the presence of nannofloras of this age reworked into younger assemblages, but Eocene calcareous microfossils are well represented. Shallow-water assemblages (including large neritic benthic foraminifetids) are wide-spread in the late Early to early Middle Eocene samples, suggesting subtropical or tropical water temperatures. The fresh volcanic content in some samples hints at the possibility of renewed volcanism during the Eocene. The Oligocene is marked by pelagites containing nannofossils. Most of the Neogene assemblages are Late Miocene or younger, although some Middle Miocene nannofloras were recovered. Depositional depths appear to have been bathyal during this time, an accompaniment to seamount sinking and crustal and subcrustal cooling. Volcanism had ceased. Debris flows, however, continued to transport shallow-water sediments downslope. Holocene and present-day oozes mantle all previous deposits.

  • Rapid changes in the operating environment for national geological surveys are forcing an almost constant re-evaluation of their role and the Australian Geological Survey Organisation is no exception. The diversification of the Australian Geological Survey Organisations client base to include national resource managers and policy makers, the changing demands of an increasingly competitive minerals and petroleum industry, and changes in government policy relating to program delivery have created the need for a sharp client focus on the organisations work and output. This paper explores the present needs for geoscience information and draws some implications for the future direction of Australias national geological survey.

  • From 3.5 Ga the overall uniformity of the composition and character of sedimentary and mantle- and crustal-derived igneous rocks, and the persistence of ore types related to convergent continental margins (e.g. volcanic-hosted massive sulphide, porphyry Cu-Mo, Sn-W and lode Au), indicates continuity of tectonic processes broadly similar to the present. Secular variations in abundance of these ores reflect tectonic cycles having periods of perhaps several hundred million years, but other ores reflect long-term changes in tectonic style and the composition of the ocean and atmosphere. Thus the development of extensive continental margins and depositional basins from about 3.0 Ga heralded development of giant Au-U conglomerate and banded iron formation deposits, with at least the former suppressed in the Palaeoproterozoic as a result of increased atmospheric PO2. Aggregation of large continents and the development of extensive basins allowed formation of giant Cu-Co, Pb-Zn and U-platinum group elements-Au ores from about 2.0 Ga. There is no firm evidence that mantle heterogeneity has contributed to ore distribution, nor that Archaean crust or mantle was anomalously enriched in Au or platinum group elements. Mineralogical and isotopic data from volcanic-hosted massive sulphide deposits support the hypothesis that there was abundant sulphate in deep oceans from 3.5 Ga, and the lack of Pb and barite in Late Archaean ores may be related to the mafic-rich composition of the local shallow crust, steep thermal gradients, anoxic, sulphate basin waters or the compositions of particular magma types. Both the ocean margin (Holland 1973) and the hydrothermal plume/gravity current models for the origin of banded iron formations are broadly compatible with their composition, secular distribution and timing with respect to glaciation, ocean anoxia and tectonic activity. In the gravity current model the possible impact of the hydrothermal activity on climate warrants further investigation.

  • The present upper crustal composition of the Earth is attributed largely to intracrustal differentiation, resulting in the production of K-rich granites. The crust grows episodically and it is concluded that at least 60 per cent of it was emplaced by the late Archaean (ca 2.7 Ae). Archaean tonalites and trondhjemites resulted from slab melting of young hot oceanic crust. In contrast, most subduction-related rocks, now the main contributors to crustal growth, are derived from the mantle wedge above subduction zones. The contrast between the processes responsible for Archaean and post-Archaean crustal growth is attributed to faster subduction of younger (hotter) oceanic crust in the Archaean (ultimately due to higher heat flow) compared with subduction of older cooler oceanic crust in more recent times. The terrestrial continental crust appears to be unique compared to crusts on other planets and satellites in the solar system, ultimately, a consequence of the presence of water on Earth.

  • Subset of Rockchem whole-rock database release 3. Contains 2093 whole-rock analyses of rocks from the Lachlan Fold Belt, Rocky Cape Block and Dundas Trough.