New chemical analyses of relatively low-grade metabasalt from the Eastern Creek Volcanics, 120-150 km north of Mount Isa, Queensland, show them to be continental tholeiites. A 2-stage model of fractional crystallisation is proposed to explain the major and trace element variation in the suite. The uncommonly high Cu content of the metabasalt (about 200 ppm) is attributed to concentration of an immiscible sulphide phase during fractionation. Examination of all available chemical data has led to the recognition of 5 types of alteration. The Cu content is depleted in metabasalts that are anomalously enriched in K2O, MgO, or CO2, but is not affected in metabasalt enriched in CaO or Na2O. This Cu depletion supports earlier models that attribute Cu mineralisation at Mount Isa to leaching of Cu from the Eastern Creek Volcanics and its redeposition in favourable pyritic, dolomitic sediments of the Mount Isa Group. The ore localisation has been associated with brecciation and appears to depend on the juxtaposition of the Mount Isa Group and the Eastern Creek Volcanics largely by faulting.

A reworking episode is indicated by occurrences of upper Cretaceous coccoliths among middle Eocene assemblages in four basins (Carnarvon, Perth, Eucla, and Otway Basins) along the Australian western and southern margins. The episode falls within the coccolith biostratigraphic interval from the lowest occurrence of Cyclicargolithus reticulatus to the highest occurrence of Daktylethra punctulata, which correlates with the foraminiferal zonal interval P.12-P,13. At the time of the episode (about 45-44 Ma) the sea advanced along the southern margin from the west, causing a transgression in the Eucla Basin and an ingression in the Otway Basin. Coincident with this sea-level rise, and probably the cause of it, was a major acceleration in the spreading rate south of Australia. In the absence of known in-situ occurrences of upper Cretaceous coccoliths on the southern margin or offshore to the south, the Naturaliste Plateau is thought to have been the most likely provenance for the reworked taxa in the Eocene of the Eucla and Otway Basins - short-lived strong currents stripped off coccolith-rich upper Cretaceous sediments on the plateau and transported them eastward. In the Perth Basin a local source, the upper Cretaceous coccolith-rich Gingin Chalk/ Lancelin Beds, is suggested for the reworked taxa, whereas in the Carnarvon Basin a distant source is more likely.

Geological hazards significantly affect communities in the tectonically active parts of the southwest Pacific and southeast Asian region. Geological hazards include intensive hazards, such as earthquakes, volcanoes, tsunamis, and landslides, and slow-onset hazards, such as subsidence, coastal erosion, and coastal progradation. The ways in which these hazards are perceived differs from one community to the next, and coping strategies can be either traditional or, more often, western in approach. Geological hazards have tended to be treated individually and at the national level, rather than as components of hazard mixtures and at a regional level. Furthermore, information on hazards in the region is widely dispersed; much of it is not readily accessible. A regional data base should be established for the collection, use, and dissemination of data on geological hazards, a comprehensive set of geological-hazard maps should be prepared, and a training scheme in geological-hazard assessment, mitigation, and preparedness should be established.

Seismic data recorded in deep water have several features that make them very well suited to migration by the use of a simple, constant velocity algorithm. A case is made for such migrations to be applied routinely to deep·water data .

A solution is presented for the practical determination of the direction of magnetism in core samples from drill holes.

The application of geology to waste disposal problems is important with respect to site selection, design, and management. The initial site selection should take into account soils, and geomorphological and hydrological considerations, and site investigations should be based on detailed geological mapping. The seismic refraction technique is a powerful tool for the assessment of excavation conditions for feasibility study and design, and electrical resistivity techniques are potentially useful for monitoring changes in groundwater composition as a result of pollution. Increased awareness of the need for pollution control means that hydro-geological investigations and the establishment of groundwater monitoring systems are mandatory. These factors are illustrated by three case studies in the Australian Capital Territory.

Thelodont scales recovered from the basal (calcareous) unit of the Cravens Peak Beds in the Georgina Basin, are referable to Turinia australiensis Gross, 1971, T. cf. pagei (Powrie, 1870), and Gampsolepis ? sp. undet. The thelodonts probably lived in a marginal marine environment (as evidenced from the associated ostracods and eridostracans) at about the same time as the placoderm Wuttagoonaspis sp. lived in the freshwater bodies, now represented by the sandstone and conglomerate facies of the Cravens Peak Beds. Scales of Turinia australiensis Gross, 1971, associated with Wuttagoonaspis plates, from the lower part of the Mulga Downs Group in the Cobar/Wilcannia area of New South Wales, are at least as young as late Early Devonian (Emsian), because they post-date the Pragian age of the underlying Amphitheatre Group. By correlation, those parts of the Cravens Peak Beds (Georgina Basin) and the Tandalgoo Red Beds (Canning Basin) that also contain Turinia australiensis are approximately coeval. After reaching Australia in Early Devonian time, the Turinia fauna began an adaptive radiation to give apparently younger (Middle Devonian) stocks that have survived longer in the Australian region than elsewhere, as the youngest known scales come from the Gneudna Formation (Iatest Givetian-earliest Frasnian) in the Carnarvon Basin, Western Australia.

The reports whose titles and abstracts appear below have recently been issued as microfiche.

The Sunda and Banda Arcs are contiguous surface features associated with the convergent boundary between the Southeast Asian and Australian-Indian Ocean plates, and where these two arcs meet, the tectonic environment changes from oceanic subduction to continent-island arc collision. This area has been investigated in an attempt to recognise and understand some of the effects of the introduction of continental crust into a subduction zone. Depositional environments encountered in Deep Sea Drilling Project (DSDP) hole 262 have been correlated with present environments to determine past horizontal distances between the leading edge of the subduction zone and the DSDP location on the Australian crustal margin. These data have been combined with the apparent plate motion at this margin to derive an estimate of the surface width of the subduction zone through time. The similarity between past width variations and present lateral variations has been used as the basis for proposing a collision model. Before the collision, the Indonesian subduction zone extended eastwards into the region that is now the southern Banda Arc. The continental edge of Australia first entered this subduction zone about 3 m.y. ago, in the mid-Pliocene. Initially, a wedge of deformed continental margin sediments began to develop at the leading edge of the subduction zone. The tectonic front that separated deformed from undeformed sediments and an associated bathymetric low migrated up the continental slope leaving in their wake a large wedge of deformed continental margin sediments, which produced a southerly bulge in the subduction zone. Ultimately, the deformation wedge began to absorb the near-surface stresses, and relative motion between the front and the southern plate slowed to near zero. Continuing relative plate motion carried the deformation front back towards the volcanic arc. Compression from this has been almost entirely taken up in the subduction zone, and has led to thickening and uplift of the deformation wedge and crust associated with the pre-collision outer-arc ridge. The proposed collision model explains many of the morphological, geological, and geophysical irregularities in the Timor region. On a broader regional scale, the evidence that the Southeast Asian plate at Timor is moving eastward at about 60 km / m.y. relative to the Eurasian plate, supports the interpretation that the India/China continental collision is pushing the Southeast Asian plate to the southeast.

Not surprisingly, Derrick and Wilson find much to disagree with in the interpretation of the geological history of the Mount Isa Inlier proposed in my paper (Blake, 1980). Most of the disagreement comes down to differences in opinion of how best to interpret the available evidence, and I hope to show in this reply to their discussion that there still is scope for alternatives to their interpretation.