For more than 30 years, deep seismic reflection profiles have been acquired routinely across Australia to better understand the crustal architecture and geodynamic evolution of key geological provinces and basins. Major crustal-scale breaks have been interpreted in some of the profiles, and are often inferred to be relict sutures between different crustal blocks, as well as sometimes being important conduits for mineralising fluids to reach the upper crust. The widespread coverage of the seismic profiles now provides the opportunity to construct a map of major crustal boundaries across Australia, which will allow a better understanding of how the Australian continent was constructed from the Mesoarchean through to the Phanerozoic, and how this evolution and these boundaries have controlled metallogenesis. Starting with the locations of the crustal breaks identified in the seismic profiles, geological (e.g. outcrop mapping, drill hole, geochronology, isotope) and geophysical (e.g. gravity, aeromagnetic, magnetotelluric) data are used to map the crustal boundaries, in plan view, away from the seismic profiles. For some of these boundaries, a high level of confidence can be placed on the location, whereas the location of other boundaries can only be considered to have medium or low confidence. In other areas, especially in regions covered by thick sedimentary successions, the locations of some crustal boundaries are essentially unconstrained. From the Mesoarchean to the Phanerozoic, the continent formed by the amalgamation of many smaller crustal blocks over a period of nearly 3 billion years. The development of the map of crustal boundaries of Australia will help to constrain tectonic models and plate reconstructions for the geological evolution of Australia, will provide constraints on the three dimensional architecture of Australia, and will suggest regions of higher potential for future mineral exploration.

No abstract available

The 42 element, 1190 sample Mobile Metal Ion subset of the National Geochemical Survey of Australia database was used to develop and illustrate the concept of Degree of Geochemical Similarity of soil samples. Element concentrations were unified to parts per million units and log(10)-transformed. The degree of similarity of pairs of samples of known provenance in the Yilgarn Craton were obtained using least squares linear regression analysis and demonstrated that the method successfully assessed the degree of similarity of soils related to granitoid and greenstone lithologies. Exploratory Data Analysis symbol maps of all remaining samples in the database against various reference samples were used to obtain correlation maps for not only granitoid- and greenstone-related soil types, but also to distinguish between for example samples derived from marine vs regolith carbonate. Likewise, the distribution of soil samples having a geochemical fingerprint similar to mineralised provinces (e.g., Mt Isa) can be mapped and this can be used as a first order prospection tool. Sensitivity analysis confirmed the method to produce robust results without undue influence from either single elements with anomalous concentrations or elements with a high proportion of censored values.

The Arunta Region of central Australia exposes the southern margin of the North Australian Craton and contains a record of multiple Proterozoic craton margin processes over a 1500 million year period. The place of mafic magmatism in this evolution is constrained by SHRIMP U-Pb dating of zircon, which is a primary igneous phase in the evolved sectors of mafic-ultramafic plutons across the region. The earliest mafic magmatism was in the 1800-1810 Ma Stafford Event, which is the first thermal system recognised in the region. Mafic plutons from this event may correlate with other expressions of mafic magmatism northwards within the craton. A second episode of mafic magmatism is recognised at 1770-1790 Ma (Yambah Event) and lacks correlatives elsewhere in the craton, as do all subsequent Arunta Region mafic magmatic events. Zircon overgrowths in Stafford- and Yambah-age plutons record conversion of these early intrusions into granulite grade metamorphic complexes during the Strangways Event, a regionally pervasive metamorphic system whose termination at ca. 1690 Ma coincided with local intrusion of dolerite dykes. Gabbro intrusion at ca. 1640 Ma in the Liebig Event is restricted within the Warumpi Province which is recognised as a separate terrane in the south of the region. There is no record of a mafic magmatic component to the ca. 1590 Ma Chewings event and most of the earlier intrusions do not record metamorphism at this time. Later mafic magmatic systems include pyroxenite intruded as part of the Mordor Complex at ca 1130 Ma (Teapot Event); and both erupted and intruded basaltic magma are components of the fault-bound Irindina Province which experienced high grade metamorphism during the Ordovician (Larapinta Event). The dating establishes that each of these craton margin event systems includes a mafic magmatic component, which suggests that repeated extensional systems are an important component of the tectonic evolution.

The Lambert-Amery System is the largest glacier-ice shelf system in East Antarctica, draining a significant portion of the ice sheet. Variation in ice sheet discharge from Antarctica or Greenland has an impact on the rate of change in global mean sea level; which is a manifestation of climate change. In conjunction with a measure of ice thickness change, ice sheet discharge can be monitored by determining the absolute velocities of these glaciers. In order to demonstrate the capability of the DORIS system to determine glacier velocities, Geoscience Australia undertook a Pilot Project under the auspices of the International DORIS Service. A DORIS beacon was deployed on the Sorsdal (November 2001 - January 2002 and November 2003 - January 2004) and Mellor (December 2002 - January 2003) glaciers. The DORIS data, transmitted from the autonomously operating ground beacon for each satellite pass, were stored in the receiver on-board the satellite and later downlinked to the DORIS control centres for processing. This paper describes the campaigns that were conducted at the Sorsdal and Mellor glaciers, the data processing standards for modelling the Doppler measurements, precise orbit determination of the satellites using the data from the globally distributed DORIS network, tracking station position and reference frame modelling, the point positioning mode employed for determining the position and velocities of the transmitting beacon antennas located on the glaciers and provides the velocity estimates that have been determined from the analysis of these tracking data. For the Sorsdal 2001/2002 campaign, using SPOT-4 data only, the measured effective horizontal ice motion was estimated to be 30 ± 0.4 cm/day (azimuth of N246°E.± 1º). The inferred velocities for the Sorsdal 2003/2004 campaign, using SPOT-4 and SPOT-5 data, was 5.7 ± 0.8 cm/day (azimuth of N264°E ± 7.5°) for the first eight days and 11.4 ± 1.4 cm/day (azimuth of N241°E ± 1.5°) for the subsequent 21 days. There was a noted decrease in the inferred velocities between the beginning and the end of the observing period. A sub-division of the latter 21 day observing period into three segments showed a decrease in 2-D velocity from 18.3 ± 0.7 cm/day to 11.2 ± 0.7 cm/day and then to 7.4 ± 0.9 cm/day for the first, second and third segments respectively. In comparison, a GPS derived velocity over the time-span of the 2001/2002 Sorsdal campaign gave a mean ice flow rate of 31 cm/day. The GPS velocity was derived from two daily position estimates 65 days apart. The DORIS determination from 26 days of continuous SPOT-4 and SPOT-5 data compared well with the GPS derived velocity. For the 2002/2003 Mellor glacier campaign, using SPOT-4 and SPOT-5 data, the estimated average ice velocity was 104 ± 25 cm/day (azimuth of N33°E ± 0.1º); which compared well with an InSAR derived velocity of between 110 and 137 cm/day. The point positioning technique as implemented in this study was further validated and assessed by replicating the computational process to determine the position and velocity of the permanent International DORIS Service site at Terre Adélie, Antarctica. Through these experiments, it has been successfully demonstrated that the DORIS system is capable of determining the velocities of glaciers with an accuracy of a few cm/day over a period of several weeks; operating in remote regions in an autonomous mode. With an increasing number of DORIS-equipped satellites and multiple daily passes, it has the potential to measure glacial velocities at a high temporal resolution (sub-daily).

The Wallareenya extensional jog developed between c. 2955 and 2940 Ma at a releasing bend in the northeast-trending Tabba Tabba Shear Zone, in the Archaean Pilbara Craton of northwestern Australia. The extensional jog, or pull-apart, formed during transtensional movement along the shear zone, and was simultaneously filled by a sequence of magmas that range in composition from gabbro to monzogranite. Magmas were emplaced through fractures which conform to Riedal R1 and R2 and P fracture directions and that segment the area into diamond-shaped blocks. Some of these conduits were utilised by up to five magma generations. Space for emplacement was created primarily through active extension within the evolving jog, and the emplacement age of the magmas decreases systematically westwards, tracking a paralleled migration in the main focus of extension. Away from fractures and magma conduits, horizontal sheeting shows that the magmas spread out laterally at suitable horizons such as the contact with overlying metasedimentary country rocks.

No abstract available - Retired at request of Fellows, M. Incomplete record

A key component of marine bioregional planning is to map the spatial patterns of marine biodiversity, often measured as species richness, total abundance or abundance/presence of key taxa. In this study, predictive modelling approaches were used to map soft bottom benthic biodiversity on the Carnarvon Shelf, Western Australia, using a range of physical surrogates. This surrogacy approach could also explicitly link physical environmental attributes to the marine biodiversity patterns. The statistical results show that between 20% and 37% of variances on the two biodiversity measures (Species Richness and Total Abundance) were explained by the Random Forest Decision Tree models. The best statistical validation performance was found at the Point Cloates area. This was followed by the Gnaraloo area, then by the Mandu Creek area. The models identified different individual physical surrogates for the three study areas and the two biodiversity measures. However, it was found that the infaunal biodiversity at the three study areas of the Carnarvon Shelf were driven by similar ecological process. Sediment properties were the most important physical surrogates for the infaunal biodiversity. Coarser and heterogeneous sediments favour higher infaunal species richness and total abundance. The prediction maps indicate the highest infaunal biodiversity at deeper water of the Point Cloates area. In contrast, the majority of the Mandu creek area has low infaunal biodiversity. This may be due to the much narrower shelf width (e.g., ~6 km) in this part of Carnarvon Shelf than the Point Cloates and Gnaraloo areas. The narrow shelf would limit the space for oceanographic processes to work on the sediment and develop heterogeneous sediment properties that support diverse and productive infaunal species.

Introduction to a thematic issue of AJES on the Tasmanides. Most papers were originally presented at the 15th Australian geological Convention in Sydney, 3-7 july 2000.

The benthic silicate and oxygen fluxes from Moreton Bay sediments were positively correlated (R2 =0.99) and the silicate to organic carbon flux ratio of 0.14 was similar to that for marine diatoms (0.13). The majority (about 75%) of the benthic silicate flux was attributed to the degradation of fresh diatomaceous detritus and the remainder could be contributed from clay (smectite) dissolution in the warm waters (30oC) during these summer months. Biogenic silica in the upper 2 cm of Moreton Bay sediments was enriched (Si:C = 0.35 +/- 0.25) with respect to the Si:C ratio (0.13 +/- 0.04) of dominant diatom populations, and we suggest that this enrichment is the result of the deposition of Si-enriched faecal pellets and diatom aggregates to the sediments. Combined hydrodynamic and biogeochemical processes resulted in distributions of biogenic silica and total organic carbon in the surface sediments that were spatially coincident. A silicate budget for Moreton Bay indicated the following. 1. The benthic input of silicate was balanced approximately by the silicate load to the sediments from primary productivity. 2. Silicate was recycled through diatomaceous phytoplankton about 18 times before it was lost to the ocean. 3. The export of silicate to the Pacific Ocean was about the same as the terrestrial input.