b'Ted Tynes best of Exploration geophysicsFeatureRadiometric and asthenosphere could be relevant, particularly if taken in conjunction with geothermal measurements.Radiometric surveying has been widely used in Australia, often being operated in conjunction with aeromagnetic surveying,Finlayson and Collins (1980, 299) described a portable and also in ground-based surveys. Obviously, the main objectiveseismograph designed and constructed in BMR for use in is direct detection of radioactive minerals, but many cases haverecording deep crustal events at unattended sites. Frequency been reported where small amounts of radioactivity have ledmodulated analogue tape recording was used; the playback to indirect discovery of other minerals, including petroleum.system could be used at up to 32 times recording speed, and In view of the wide-spread use of the method, it is surprisingenabled analogue-to-digital conversion. This system was that only a relatively few papers in the ASEG journals have beenused for many years in BMRs deep seismic investigations. The devoted specifically to this topic; in particular, there are very fewplayback system was described by Liu and Seers (1982, 419). A papers relating to developments in the technique. novel speed control system, combining frequency and phase control, ensured accurate tracking, rapid response, and a wide In an early paper, McSharry (1973, 456) showed that theacquisition dynamic range.corrections to airborne gamma-ray spectrometer measurements for the contribution of the air between ground and aircraftThe International Lithosphere program for the 1980s decade varied according to the system used; those systems with narrowwas described by McElhinny (1982, 441). A proposal for spectral windows were the most reliable. Australian participation was introduced, comprising transects in various parts of the continent, a study of intra-plate igneous Dickson (1979, 157) suggested that, as near-surface ore- activity in Australasia, and a study of recent plate movements bodies were progressively discovered, the search for deeperand deformation in the Australasian region.bodies would need changing techniques. These would includelngate and King (1982, 340) used long-period P waves recorded geochemical sampling for end products of the decay chainsat Charters Towers, Queensland, to estimate gross crustal such as He and Pb isotopes, and use of sniffers for detectingstructure. The spectrum of a seismic wave train was factored radon gas escaping to the surface. Webb (1980, 686) examinedinto contributions from various sources, one of which was the the use of total-count and spectrometer gamma detectors incrustal transfer function, which could then be isolated. The various situations. From a discussion of the various spectralthickness of the crust was estimated as 404 km, and the ratio peaks of the radioactive elements and their decay products, andof crustal to mantle velocities as 0.8.the properties of sodium iodide crystals used in the detectors, he concludes that a total-count detector with a low energyDenham and Lilley (1983, 150) reviewed current work in threshold should always be used; spectrometer channels maysolidearth geophysics, in the form of a list of workers in the give additional useful information depending on the area, butfield, together with the projects on which they were working.may not be of much use in some geological environments.Gravity and magnetic data in the Adelaide Geosyncline were Other papers include the establishment of calibration facilitiesidentified by Gunn (1984, 278) as representing an Atlantic for gamma-ray detectors (e.g. Kirton and Lyus, 1976, 378; Wenktype passive margin. Sinuous extensive coincident gravity and and Dickson, 1981, 699; Dickson and Lovberg, 1984, 156), andmagnetic anomalies from the west of South Australia appeared the radioactive properties of rocks, e.g. coal ash (Agostini, 1977,to represent an ancient Proterozoic rift system which did not 2), kimberlites (Kamara, 1981, 368), and granitic rocks (Webster,develop to crustal separation.1984, 693; Leys and Spencer, 1985, 411).Filloux et al. (1985, 228) described a MT survey in the Tasman Sea, using equipment designed at Scripps Institute Solid-Earth GeophysicsRegional and Deep Crustal of Oceanography. The survey indicated an unusually high This topic is of interest to thinking explorationists, in thatconductivity in the mantle, possibly due to thermal effects of its findings are relevant to understanding of the processesthe nearby chain of sea mounts.involved in basin formation and the development of mineralWake-Oyster et al. (1985, 679) reported on the progress of the provinces. Deep seismic sounding is the most useful andmajor lithospheric transect across southern Queensland, from accurate tool, but important contributions are made bythe Cheepie Shelf to Oakey, a distance of 670 km. Seismic regional gravity and magnetic surveys, and by magnetotelluricreflection and refraction, aeromagnetic, and gravity methods (MT) investigations. were used. Several records showing deep (sub-basement) Boyd and Thomas (1973, 62) reported a telluric investigation inreflections were displayed. Processing of the data was still in the Otway Basin of Victoria. Results were consistent with a veryprogress.low resistivity of the sediments to a depth of about 2400 m.Large intraplate mafic volcanoes in eastern Australia and Johnson (1973, 362) conducted a time-term analysis of the BassNew Zealand were found to be underlain by large intrusive Strait Upper Mantle Project (BUMP) seismic refraction results,complexes with positive gravity and magnetic anomalies and deduced a crustal thickness of 3035 km for Victoria and(Wellman, 1986, 697). They were thought to be associated with Tasmania, with thinning to 2025 km under Bass Strait. uplift of the country rock.Hall (1976, 286) pointed out the relevance of crustal studiesAt Perth, 1987 (Middleton and Pridmore, eds, 1987), the for exploration, and gave examplesmapping faultsstructure of the basement of the Clarence-Moreton Basin in the basement of the Dnyeper-Donetz Basin in USSR,was deduced from gravity and magnetic anomalies, and a which affect facies distribution and hence locations ofhypothesis was advanced for the formation and development petroleum accumulution in the sediments; and a revision ofof the Perth Basin. Preliminary results were given of a major regional geology in the Canadian Shield. He suggested thatdeep seismic survey in central Australia and of the 600 km investigations of even deeper features in the lithosphereprofile across southern Queensland. Seismic reflections from FEBRUARY 2020 PREVIEW 46'