A new compositional variety of zirconolite characterized by high Mg, Al, Y2O3 and REE, and low Fe is described from a sapphirine granulite xenolith entrained in an intrusive norite body which was emplaced into the late Archaean (2520–2480 Ma) Vestfold Hills high-grade terrain during the early Proterozoic. The zirconolite, and similarly Mg-Al rich perrierite-(Ce), formed as a result of sanidinite facies partial melting of the particularly magnesian and aluminous sapphirine granulite xenolith during its incorporation into the c. 1170°C basic magma at c. 2240 Ma. The high REE compared to Al cations require that a previously unrecognized coupled substitution:

occurs in this zirconolite. Full chemical analyses are presented for zirconolite and perrierite from this unique occurrence.

We present a relative sea-level (RSL) history, constrained by AMS radiocarbon-dated marine–freshwater transitions in isolation basins from a site adjacent to the Lambert Glacier, East Antarctica. The RSL data suggest an initial ice retreat between c. 15,370 and 12,660 cal yr B.P Within this period, meltwater pulse IA (mwp IA, between c. 14,600–14,200 and 14,100–13,700 cal yr B.P.) occurred; an exceptionally large ice melting event, inferred from far-field sea-level records. The RSL curve shows a pronounced highstand of approximately 8 m between c. 7570–7270 and 7250–6950 cal yr B.P. that is consistent with the timing of the RSL highstand in the nearby Vestfold Hills. This is followed by a fall in RSL to the present. In contrast to previous findings, the isolation of the lakes in the Larsemann Hills postdates the isolation of lakes with similar sill heights in the Vestfold Hills. An increase in RSL fall during the late Holocene may record a decline in the rate of isostatic uplift in the Larsemann Hills between c. 7250–6950 and 2847–2509 cal yr B.P., that occurred in response to a documented mid-Holocene glacier readvance followed by a late-Holocene retreat.

Evidence is provided from a sediment core from saline Abraxas Lake, Vestfold Hills, that indicates that the lake existed through the Last Glacial Maximum. It can therefore be concluded that at least part of the Vestfold Hills also remained ice-free through the Last Glacial Maximum, or at most was covered by a thin, non-erosive cold-based ice sheet. The evidence for the continued existence of Abraxas Lake includes a 14C date that significantly predates the Last Glacial Maximum (though this cannot be considered direct proof of the existence of the lake prior to the Last Glacial Maximum); the presence of saline porewater throughout the core, including in compacted sediments deposited during the glacial period, which implies that the lake obtained its salt prior to any Holocene marine highstand; and the occurrence of marine-derived fauna from the onset of significant biological activity late in the Pleistocene. The occurrence of ice-free land in the Vestfold Hills and similar oases suggests that the margin of the polar ice cap did not reach far beyond its current position at the Last Glacial Maximum, at least in regions now occupied by these oases.

A varied suite of sapphirine-bearing and quartz-undersaturated granulites, the Taynaya Paragneiss, occur as boudins and enclaves within the c. 2500 Ma old felsic orthogneisses of northern Vestfold Hills. Highly magnesian varieties with XMg (=100x(Mg/(Mg+Fe)) near 95 preserve the assemblage sapphirine + enstatite + spinel, whereas sapphirine + cordierite + sillimanite + corundum occurs in aluminous and feldspathic types with XMg near 90. Phase equilibria and relative thermometry based on Al2O3 solubility in enstatite indicate equilibration of these assemblages at c. 830–880°C and 0.35–0.85 GPa. There is no evidence for the extreme temperatures (1000–1100°C) previously proposed for early metamorphism in the Vestfold Hills, and no indication in the metamorphic assemblages of isobaric cooling prior to 2500 Ma. Two types of metasomatism have altered the bulk rock compositions near boudin and enclave margins. Cordierite rinds locally formed on corundum-sillimanite granulites reflect interaction with magmatic precursors to the enclosing felsic gneisses, as supported by the isotopic and chemical compositions of cordierite channel volatiles. More extensive metasomatism producing schistose phlogopite + sapphirine rinds on all boudins involved infiltration of a LILE-enriched fluid which introduced K2O, H2O, Fe, Rb, Ba and minor Sr along the boudin margins. Whole rock geochemistry of Taynaya Paragneiss unaffected by this metasomatism is consistent with their derivation from evaporitic mudstones, and implies the existence of a basement older than the dominant 2500 Ma orthogneisses.

An ice dam with a former impoundment volume of 1.1 × 106 m3 is reported from the Vestfold Hills, East Antarctica. The ice of the dam was derived from wind-drifted snow subsequently changed into ice by normal summer melt and freeze processes. The reformation (after 1979 and 1987) and failure of this ice dam (during 1987 and 1990) indicates the potential for the release of geomorphologically significant flows in a polar climate. The origin of a nearby fluvially eroded channel is attributed to the release of an ice-dammed impoundment. The potential of such flows for reworking glacial debris may be important when considering the sedimentology of former proglacial areas.

Freshwater drainage systems, fed by melting of nearby inland ice and perennial snowdrifts, exist in the south-eastern part of arid, ice-free, coastal Vestfold Hills. Most important is the complex Druzhby system. Intriguing questions arise about the conditions controlling its seasonal development and about the consequences of possible changes of those conditions. A water-balance was calculated for 1990–91. The system went through four seasonal phases of which only one displayed a fully developed external drainage. Evidently, the relative duration of those phases can vary considerably from one year to another. The system depends critically on the water supply from ice-dammed Chelnok Lake, which could readily be drained by a minor retreat of Sørsdal Glacier. Exposed to excessive evaporation, the large Crooked Lake would then become internally drained and reach a new equilibrium in ∼830 years. A Crooked Lake sediment core can be interpreted as suggesting this occurred during the Holocene. The idea, inferred from striae, of a late Holocene Chelnok Glaciation reaching the northern shores of Crooked Lake is questioned. Instead, it is suggested that the Chelnok striae originate from local basal melting of the ice sheet draining southward into a deglaciated Sørsdal trough. At present, runoff is determined by opposing short and long-term climatic influences.

Studies of glacier margins have suggested that form and structure can be used to infer mass balance condition and stability. This paper examines this idea by investigating the form and structure of the Antarctic ice sheet at two coastal oases in East Anarctica. Two principal forms of the margin of the ice sheet in the Vestfold and Bunger hills that are discussed are ice cliffs and gently-sloping ice margins with an inner moraine. The form of the ice margins in both areas is primarily related to the accumulation of drift snow and superimposed ice and not to mass balance condition. It is concluded that the form and structure of ice margins are ambiguous indicators of mass balance condition and stability and that a change in mass budget is probably neither a sufficient nor a necessary condition for a change in the morphology of ice margins. Although we argue that the form and structure of the ice margins tells us little about stability, interpretation of the Holocene history and geomorphology of the oases suggests that the ice margins have been stable at least throughout the Holocene and that this condition of overall stability continues today.

A regional chemical boundary termed the ‘salt line’, in the Vestfold Hills of East Antarctica, has been investigated using X-ray diffraction and electron probe analyses of surficial salts, and conductivity of surficial sediments. West of the salt line, halite and thenardite are abundant. These salts are derived from dispersal of marine aerosols, saturation of sediment by seawater during postglacial marine transgression, and glacial dispersal of salt-saturated fjord bottom sediments. East of the salt line, subglacial calcium carbonates and salts formed by chemical weathering of their substrates occur. Chemically and morphologically diverse minerals form the weathering products. They include two minerals not found previously in Antarctica, dypingite and hydromagnesite, and the first confirmed occurrence of brushite.

Archaean gneisses in the Rauer Group of islands, East Antarctica, record a prolonged history of high-grade deformational episodes, many of which predate that identified in mid-Proterozoic gneisses. Eleven generations of mafic dykes, belonging to discrete chemical suites, have been used as relative time markers to constrain this deformational history. Based on the timing of intrusion with respect to structures, dykes in the Rauer Group have been correlated with largely undeformed and dated dyke suites in the adjacent Vestfold Hills. This has allowed absolute ages to be inferred for the early- to mid-Proterozoic mafic dyke suites in the Rauer Group, and a correlation of the interspersed structural events. Most structures in the Rauer Group, however, developed in response to high-grade progressive deformation at approximately 1000 Ma. During this deformational episode, strains were repeatedly partitioned into sub-vertical, noncoaxial, high-strain zones recording NW-directed sinistral transpression, that separated zones of lower strain dominated by coaxial folding with axes parallel to the shear direction. Three additional mafic dyke suites intruded during this deformation which was followed by three stages of brittle-ductile deformation and a final suite of lamprophyre dykes. Due to the numerous intrusive time markers, the Rauer Group serves as an excellent illustration of how complicated gneiss terrains may be.

Fossil marine diatom assemblages from the Sørsdal Formation, a deposit of diatomaceous sand from Marine Plain in the Vestfold Hills, provide age and palaeoenvironmental information from a Pliocene coastal setting in East Antarctica. Benthic and meroplanktic diatom taxa suggest deposition in a shallow coastal embayment with water depths of 20–25 m. Diatom biostratigraphy indicates that the Sørsdal Formation belongs to the Fragilariopsis barronii Zone (4.5 to 4.1 Ma), through correlation to reference sections in the Ross Sea and Southern Ocean. Features of the other biota suggest higher sea-surface temperatures and reduced sea-ice cover, consistent with global records of higher sea level.

Mixing in Ellis Fjord, Vestfold Hills, East Antarctica, is controlled by processes which are influenced by the extent of ice formation. A study of water temperature and salinity at a site near the middle of the fjord was undertaken from May 1994 to February 1995 after a summer (1993–94) in which the ice cover of the fjord was largely retained. Vertical mixing resulting from the exclusion of salt during the limited winter formation of ice was insufficient to mix completely the non-meromictic basins of the fjord. In contrast, a previous study during a winter with far more ice production recorded much stronger vertical mixing throughout the fjord. Warming and freshening of the fjord during the 1994–95 summer, when the ice again did not melt significantly, was attributable to the flow of warmer, less saline water along the fjord. This process was probably related to the formation of tidal jets at the narrow and shallow entrance to the fjord, and was thus influenced by the ice conditions around the entrance. These jets would also have introduced significant amounts of extra-fjord water (along with any resident biota) into the fjord.

Thirty-four permanently stratified water bodies were identified in a survey of the Vestfold Hills. Of these, 21 were lakes, six were seasonally isolated marine basins (SIMBs), and seven were marine basins with year round connection to the open ocean. The basins varied markedly in salinity (4 g l−1 to 235 g l−1), temperature (−14°C to 24°C), depth (5 m to 110 m), area (3.6 ha to 146 ha) and surface level (−30 m to 29 m above sea level). The stratification in all the basins was maintained by increases in salinity. During winter, a thermohaline convection cell was present in all lakes and SIMBs directly beneath the ice cover. These cells were the result of brine exclusion from the forming ice, and increased in density throughout winter, penetrating progressively deeper into the lake. Minimum stability, and therefore the maximum likelihood of turnover, occurred at the time of maximum ice formation in spring. At the end of the period of ice formation, the convection cell broke down, and stratification of the surface water occurred. When the ice melted completely, lenses of relatively fresh water capped the lakes, which reduced the effect of wind mixing. Net meltwater input increased the stability of the meromictic basins, while periods of lower water level resulted in deeper penetration of the thermohaline convection cell, increasing the possibility of turnover and destratification.