This report describes the operation of the Mawson geophysical observatory for 1990. The observatory continuously records the geomagnetic field and global seismic activity at Mawson, and was part of the Bureau of Mineral Resources (BMR) contribution to the Australian National Antarctic Research Expeditions (ANARE). The period covered by this report is from 1 January 1990 to 30 November 1990.

The Natural Variability Sub-program of the Co-operative Research Centre for Antarctic and Southern Ocean Environments aims to study past environmental change by examining ice core and sedimentary records in Antarctica and the Southern Ocean. As the first stage in marine sedimentological studies, Voyage 7 of the Australian National Antarctic Research Expeditions (ANARE) 1992/1993 shipping season included a geoscience program comprising echo sounder traverses, gravity coring and grab sampling of the Antarctic continental shelf and slope on the Mac. Robertson Shelf and in Prydz Bay. This record describes the preliminary results of the voyage and presents location information for core and grab samples and preliminary descriptions of grab samples and lists of subsamples taken by associated research programs.

Legacy product - no abstract available

The Cenozoic glacial history of East Antarctica is recorded in part by the stratigraphy of the Prydz Bay-Lambert Graben region. The glacigene strata and associated erosion surfaces record at least 10 intervals of glacial advance (with accompanying erosion and sediment compaction), and more than 17 intervals of glacial retreat (enabling open marine deposition in Prydz Bay and the Lambert Graben). The number of glacial advances and retreats is considerably less than would be expected from Milankovitch frequencies due to the incomplete stratigraphic record. Large advances of the Lambert Glacier caused progradation of the continental shelf edge. At times of extreme glacial retreat, marine conditions reached > 450 km inland from the modern ice shelf edge. This review presents a partial reconstruction of Cenozoic glacial extent within Prydz Bay and the Lambert Graben that can be compared to eustatic sea-level records from the southern Australian continental margin.

A late Quaternay, current-lain sediment drift deposit over 30 metres in thickness has been discovered on the continental shelf of East Antarctica in an 850 metre deep glacial trough off George Vth Land. Radiocarbon dating indicates that a period of rapid deposition on the drift occurred in the mid-Holocene, between about 3 000 and 5 000 years before present.

A geological investigation was carried out by the writer. The aim was to check the previous mapping of the geology, and if necessary, to assist the Magnetician in locating a suitable site for magnetic observations. Some aspects of geomorphology, and the reconnaissance survey work carried out are discussed in this report.

No abstract available

Measurements of water turbidity, currents, seafloor sediment samples and geophysical data document the sedimentary processes and the Late Quaternary sedimentary history of a continental shelf valley system on the East Antarctic continental margin.

No abstract available

The Bunger Hills area, which forms part of the East Antarctic Shield, consists predominantly of granulite facies orthogneiss (pyroxene-quartz-feldspar gneiss), with subordinate maficgranulite and garnet, sillimanite, and cordierite-bearing paragneiss. The igneous precursors of granodioritic orthogneiss crystallised about 1500 - 1700 Ma ago, whereas late Archaean (2640 Ma) tonalitic orthogneiss occurs in the Obruchev Hills, in the southwest of the area. Metamorphism reached a peak of about 750 - 800 ° C and 5 - 6 kb (Mj) 1190±15 Ma ago (U-Pb zircon age) and was accompanied by the first of three ductile deformation events (Dj). Voluminous, mainly mantle-derived plutonic rocks were emplaced between 1170 (during D 3 ) and 1150 Ma. They range in composition from gabbro, through quartz gabbro, quartz monzogabbro, and quartz monzodiorite, to granite. Abundant dolerite dykes, of at least four chemically distinct groups, were intruded at about 1140 Ma. Their intrusion was associated with the formation of shear zones, indicating at least limited uplift; all subsequent deformation was of brittle-ductile or brittle type. Alkaline mafic dykes were emplaced 500 Ma ago. Marked geochronological similarities with the Albany Mobile Belt of Western Australia suggest that high-grade metamorphism in both areas was the result of continental collision between the Archaean Yilgarn Craton of Australia and the East Antarctic Shield. However, Gondwana reconstructions and the composition of the plutonic rocks suggest that the Bunger Hills metamorphics may have formed in an Andean-type continental arc, with the actual collision zone having been to the east of the present Bunger Hills. Exposures west of the Denman Glacier are also mainly granulite-facies gneiss, intruded by a variety of mafic to felsic plutonic rocks. They differ from the Bunger Hills in being partly derived from Archaean protoliths (- 3000 Ma), in lacking isotopic evidence for a Mesoproterozoic high-grade event, and in not being intruded by dolerite dyke swarms. They also show evidence of much more extensive 500 - 600 M a (Pan-African) metamorphism and plutonism (syenite to granite), and in this regard they are comparable with the Leeuwin Block metamorphics of southwestern Australia, although these were derived from significantly younger protoliths (T^D model ages: 1100 - 1500 Ma). If this early Palaeozoic activity was also a consequence of continental collision, it would explain the markedly different geological history of the terranes on either side of the Denman Glacier and could account for the final uplift of the Bunger Hills. However, the compressional tectonic regime implicit in the collision hypothesis was followed by an extensional regime, which, in southwestern Australia, eventually resulted in the formation of the Perth Basin rift zone. This structure is aligned with the Denman Glacier trough on our preferred Gondwana reconstruction, suggesting that it may have extended well to the south before the breakup of Gondwana.