Deep Reflection Probes in Eastern Australia Reveal Differences in the Nature of the Crust

Since 1976 the Australian Bureau of Mineral Resources (BMR) has obtained good quality deep reflection data during sedimentary basin surveys using modern digital recording and processing techniques (Mathur 1983a). Most of these recordings, made on an experimental basis, showed that good reflections could be obtained from the deep crust without extra effort other than increased recording time, and that such data over long traverses are required to study the deep crust and upper mantle in detail (Mathur 1983b). The deep reflections discussed here were generally recorded over relatively short traverses and thus do not provide sufficient quantity of data to investigate the horizontal variation of the deep crustal structure. However, the strength, coherence, continuity and spatial distribution of the reflections from the deep crust provide valuable information on the nature of the crust in several areas of eastern Australia with a resolution higher than is possible from any other geophysical method. This paper presents some of these data to show the major differences in the character of the deep reflections between the Precambrian and Phanerozoic domains of eastern Australia and discusses what these characteristics might mean in terms of the fine structure of the deep crustal rocks with reference to the gross structure obtained from the refraction studies.