Volcanic earthquake swarms at Mt. Erebus, Antarctica

Mount Erebus is an active volcano in Antarctica located on Ross Island. A convecting lava lake occupies the summit crater of Mt. Erebus. Since December 1980 the seismic activity of Mt. Erebus has been continuously monitored using a radio-telemetered network of six seismic stations. The seismic activity observed by the Ross Island network during the 1982–1983 field season shows that: (1)Strombolian eruptions occur frequently at the Erebus summit lava lake at rates of 2–5 per day; (2)centrally located earthquakes map out a nearly vertical, narrow conduit system beneath the lava lake; (3)there are other source regions of seismicity on Ross Island, well removed from Mt. Erebus proper. An intense earthquake swarm recorded in October 1982 near Abbott Peak, 10 km northwest of the summit of Mt. Erebus, and volcanic tremor accompanying the swarm, may have been associated with new dike emplacement at depth.     

Melt inclusions in basalts of Ross Island area,Antarctica

There are many melt and fluid inclusions (mainly CO₂-rich) in olivine and pyroxene phenocrysts in basalts from the Ross Island area. The melt inclusions can be classified as follows: (1) crystalline melt inclusions (type I), (2) fluid-melt inclusions (type II) and (3) glass inclusions (type III). The daughter minerals in type I include olivine, plagioclase, ilmenite, etc. Fluid-melt inclusions are a new type which represent the immiscibility of magma and fluid at a particular stage of evolution. Three types of fluid-melt inclusions were examined in this study: a) crystal + liquid + gas, b) inclusions coexisting with glass inclusions and fluid inclusions, and c) crystal + daughter mineral (dissolved salt) + gas. Both primary and secondary melt inclusions are recognizable in the samples. The secondary melt inclusions were formed during healing of fractures in the host minerals in the process of magma rise. The homogenization temperatures (both Leitz 1350 stage and quench method were used) of melt inclusions in basalts range from 1190 to 135°C at high pressure (about 7 kbars), indicating that the basalts may have come from the upper mantle. Melt-fluid immiscibility in basaltic magma shows that the CO₂-rich fluids may be the main fluid phase in the upper mantle, which are of significance in understanding the evolution of magma and various processes in the deep levels of the earth. The homogenization temperatures of melt and aqueous fluid inclusions in granites and metamorphic rocks in this area vary from 980 to 1100°C and 279 to 350°C, respectively.     

Lithostratigraphy of the Cretaceous Strata of West James Ross Island,Antarctica

As a result of recent field work, a new lithostratigraphic group is defined on the west coast of James Ross Island, Antarctica. Characterised by comparatively coarse-grained sediments, the Gustav Group is 2300 m thick and has an approximate age range of Barremian-Santonian. Four formations are recognised within the group (the Lagrelius Point, Kotick Point, Whisky Bay and Hidden Lake Formations), and of these, the Whisky Bay Formation is further subdivided into six local members. Type sections are erected for each of these stratigraphic units and representative lithologies and faunas described.     

Rare earth element evidence for differentiation of McMurdo volcanics,Ross Island,Antarctica

Eighteen samples of the McMurdo volcanics on Ross Island, Antarctica consisting of basanitoid, trachybasalt and phonolite have been analyzed for rare earth elements (REE) in order to determine the details of differentiation using quantitative trace element modeling. The basanitoids have REE patterns similar to those for alkali basalts or nephelinites from ocean islands. Since there is no correlation between REE and silica contents among five basanitoids, some of the variability in the REE contents must be related to the extent of partial melting, variation in the residual mineralogies of the mantle during melting, or to inhomogeneities in the REE composition of the mantle.In order to explain the data, more than one differentiation sequence is necessary. In each case a basanitoid melt is the parent which differentiates to trachybasalt upon separation of olivine, clinopyroxene, spinel, ±kaersutite±plagioclase±apatite. If clinopyroxene, kaersutite, anorthoclase, plagioclase and apatite separate from a trachybasalt melt, a mafic phonolite results.If, however, no kaersutite is involved, an anorthoclase phonolite results. A distinct type of mafic phonolite results if kaersutite is one of the minerals that separates from the anorthoclase phonolite. If the anorthoclase phonolite precipitates plagioclase and anorthoclase and if the melt reacts with plagioclase-rich continental rocks, a trachyte results.Formerly spelled: Shine Soon Sun     

Palynoassemblages associated with a theropod dinosaur from the Snow Hill Island Formation (lower Maastrichtian) at the Naze,James Ross Island,Antarctica

The Cape Lamb Member of the Snow Hill Island Formation at The Naze on the northern margin of James Ross Island, east of the Antarctic Peninsula, yielded a theropod dinosaur recovered near the middle of a 90 m thick section that begins at sea level, ends below a basalt sill, and is composed of interbedded green–gray massive and laminated fine-grained sandstones and mudstones. Sixteen palynoassemblages were recovered from this section, which yielded moderately diverse assemblages with a total of 100 relatively well-preserved species. The principal terrestrial groups (32%) are represented by lycophytes (8 species), pteridophytes (15 species), gymnosperms (13 species), angiosperms (21 species) and freshwater chlorococcaleans (3 species). Marine palynomorphs (68%) belong to dinoflagellates (61 species), chlorococcaleans (6 species), and one acritarch. The vertical distribution of selected species allows the distinction of two informal assemblages, the lower Odontochitina porifera assemblage from the base to its disappearance in the lower part of the section, and the remaining section characterized by the Batiacasphaera grandis assemblage. The global stratigraphic ranges of selected palynomorphs suggest an early Maastrichtian age for this section and the entombed dinosaur that is also supported by the presence of the ammonoid Kitchinites darwinii. These assemblages share many species with latest Campanian–early Maastrichtian palynofloras from Vega and Humps Islands, New Zealand, and elsewhere in the Southern Ocean, establishing a good correlation among them. The dominance or frequent presence of dinoflagellates throughout the section supports the general interpretation of a shelf marine depocenter. The consistent presence of terrestrial palynomorphs suggests contributions from littoral/inland environments.     

Geochemistry, Mineralogy and Magmatic Evolution of the Basaltic and Trachytic Lavas from Gough Island, South Atlantic

The Gough Island lavas range from picrite basalt through tosodalite-bearing aegirine-augite trachyte. The basaltic lavasare predominantly nepheline normative alkali basalts, althougha group of hypersthene normative tholeiitic basalts does occur.The oldest lavas on the island, represented by the Lower Basaltseries, are approximately 1?0 m.y. old and the youngest arethe Upper Basalts with an age of {small tilde} 0?13 m.y. Relatively coherent variations are described by the basalticand trachytic lavas with respect to both bulk rock major andtrace element geochemistry and mineral chemistry, and quantitativepetrogenetic modelling suggests that most of the variation canbe attributed to crystal fractionation/accumulation processesacting on a number of geochemically distinct parental magmas.The Upper Basalts and Lower Basalts have (within the limitsof sampling) a relatively restricted composition compared tothe Middle Basalt series lavas, with the latter ranging frompicrite basalt through to trachyandesite. The picrite basaltsand coarsely pyroxene-olivine phyric basalts represent partialcumulates with varying proportions (up to 40 wt. per cent) ofaccumulated olivine and clinopyroxene. In contrast, the moderatelyphyric and aphyric/finely porphyritic lavas represent the productsof crystal fractionation with the most evolved lavas havingexperienced at least 40 per cent fractional crystallizationof clinopyroxene, olivine, plagioclase and minor Fe-Ti oxidesand apatite. The detailed abundance variations in these lavasindicate that a number of parental magma compositions have fractionatedto produce the overall variations in basalt geochemistry, andsome of the magmas have interacted through mixing processes. The trachytic lavas show a large range in trace element abundance,but have only a limited major element variation. Most of thisvariation can be attributed to extensive (up to 70 per cent)fractional crystallization of predominantly alkali feldsparwith minor clinopyroxene, olivine, biotite, titano-magnetiteand apatite. A number of genetically distinct trachytes canbe recognized which are probably not related to each other byany simple fractional crystallization process. The compositionof the least evolved trachytes can be adequately accounted forby relatively extensive (up to 60 per cent) fractionation ofthe more evolved Middle Basalt series lavas. The trace element and isotopic characteristics of primitiveGough Island basalts support the concept that the source region(s)giving rise to these lavas is extremely enriched in highly incompatibleelements relative to primordial or ‘undepleted’mantle of bulk earth composition. It is unlikely that the lavashave sampled undepleted mantle as might be suggested by thesimilarity of the Sr and Nd isotopic ratios to ‘bulk earth’values. Rather, a model is favoured whereby the lavas are derivedfrom previously enriched sub-oceanic mantle which was subsequentlyinvaded and further enriched, at some time prior to partialmelting, by melts or fluids highly enriched in incompatibleelements. The enrichment could have occurred as veining by smalldegree partial melts or by infiltration of metasomatic fluids.     

南极长城站区寒冻风化特征

通过对南极长城站区寒冻风化速率的观测和分析，结合气温等因素的变化，讨论了该区寒冻风化与影响因素之间的关系。研究表明，该区夏季风化速率为冬季的36－7．5倍；海拔较高的地方风化速率比海拔低的高1．28－3．35倍；壁朝向东、东南的风化强度比朝向北、北西的大2．6－16倍。低温年份的风化速度仅有高温年份的7．2％－16．6％，与世界其它冰缘区的风化速率对比，本区寒冻风化速率属中等水平。     

Conifer fossil woods from the Santa Marta Formation (Upper Cretaceous), Brandy Bay,James Ross Island,Antarctica

Conifer fossil woods from the Santonian to lower Campanian Santa Marta Formation are anatomically studied in detail. The wood flora is dominated by conifers, mainly Araucariaceae. Conifer fossil woods represent 84% of the samples (26 of 31) of the assemblage. The remaining samples are dicotyledon woods which are not included in this study. Woods are mostly calcified and preservation is often excellent. Fossil woods include three species of Agathoxylon, Phyllocladoxylon antarcticum, Cupressinoxylon hallei and a new species of Cupressinoxylon, C. rotundum Pujana sp. nov. The conifer-dominated forests are consistent with the pollen and macrofloras previously described from sediments of the same stratigraphic unit. This fossil wood assemblage contributes to understand the floristic changes that took place in the Cretaceous forests.     

Strontium isotopic geochemistry of the volcanic rocks and associated megacrysts and inclusions from Ross Island and vicinity,Antarctica

Twelve whole-rock samples of volcanic rocks and a composite of 11 basanitoid samples from Ross Island and vicinity, Antarctica show a narrow range of ⁸⁷Sr/⁸⁶Sr ratios from 0.7030₅ to 0.7033₉. This range is consistent with a model of differentiation from a single parent magma, but the data allow a 30% variation in the ⁸⁷Rb/⁸⁶Sr ratio in the source region if the average ratio is less than 0.057 and if the source region has existed as a closed system for 1.5 b.y. Megacrysts of titaniferous augite, kaersutite, and anorthoclase are isotopically indistinguishable from the host volcanic rocks and therefore are probably cogenetic with the volcanic sequence. A single trachyte sample is isotopically distinct from the rest of the volcanic rocks and probably was contaminated with crustal strontium.Ultramafic and mafic nodules found in association with basanitoids and trachybasalts have ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7027₅ to 0.7057₅. Several of these nodules exhibit evidence of reaction with the melt and are isotopically indistinguishable from their hosts, but data for seven granulite-facies nodules show an apparent isochronal relationship. Although this isochron may be fortuitous, the resulting age of 158±22 m.y. is similar to ages reported for the voluminous Ferrar Dolerites, and suggests isotopic re-equilibration within the lower crust and upper mantle. These nodules are not genetically related to the Ferrar Dolerites, as evidenced by their lower initial ⁸⁷Sr/⁸⁶Sr ratios.Three ultramafic nodules are texturally and isotopically distinct from the rest of the analyzed nodules. These are friable, have larger ⁸⁷Sr/⁸⁶Sr ratios, and may represent a deeper sampling of mantle rock than the granulite-facies nodules. They were, however, derived at a shallower depth than the alkalic magma. Thus they are not genetically related to either the magma or the granulite-facies nodules.     

Late Cretaceous flora of the Hidden Lake Formation,James Ross Island (Antarctica), its biostratigraphy and palaeoecological implications

Plant fossils from the volcano-clastic marine deposits of the Coniacian Hidden Lake Formation of James Ross Island in Antarctica are described based on their macromorphology. Stratigraphic positions of fossiliferous horizons and details of the lithostratigraphic situation of the middle part of the Hidden Lake Formation are published for the first time. The flora consists primarily of leaf impressions and petrified wood. There are also small amounts of mesofossils, dispersed cuticles and charcoalified wood. The megafossils typically occur fragmented, underpinning their allochtonous origin. The plants are described in systematical order. This contribution in contrast to earlier observations reports a high diversity of pteridophytes (11 taxa) and conifers (6 taxa). Angiosperms representing families Nothofagaceae, Atherospermataceae, probably Lauraceae and Sterculiaceae are the most abundant and common plant groups of the flora (12 taxa). The presence of the tropical fern family Marattiaceae and rarity of the genus Nothofagus are of interest, arguing for the prevalence of a warm temperate to tropical humid climate during the Coniacian in this part of Antarctica.     

The Albian fern flora of Alexander Island,Antarctica

The Albian Alexander Island macrofossil flora from the Antarctic Peninsula preserves a diverse community of liverworts (Marchantiophyta), ferns (Polypodiopsida), Lycopodiales, Equisetales, Cycadales, Ginkgoales, seed-ferns (Bennettitales and Pentoxylales), Coniferales, and the first representatives of angiospermous leaves in Antarctica. Despite the presence of angiosperms in this assemblage, ferns are the most diverse element of the flora and are also ecologically dominant, while angiosperms contribute a smaller component to floristic diversity and have low abundance. Here we describe 11 fern taxa from this assemblage. The fossils are assigned to Cladophlebis, Sphenopteris and two newly created genera. The new genera and species are described under Adiantitophyllum serratum gen. et. sp. nov. and Nunatakia alexanderensis gen. et. sp. nov., and the new species are recognized as Cladophlebis dissecta sp. nov., Cladophlebis drinnanii sp. nov., Cladophlebis macloughlinii sp. nov. and Sphenopteris sinuosa sp. nov. In total, there are 24 fern species known from Alexander Island. In comparison to older floras (Jurassic) there is a greater diversity of ferns, while latest Cretaceous floras preserve significantly fewer fern species and more angiosperms. Possible factors that might account for such high fern diversity are high rainfall or generally humid conditions, regular disturbances by flooding and occasionally fire, and the preservation of a diverse range of fern communities that represent several palaeoenvironments.     

Geomorphology of the Ablation Point massif, Alexander Island, Antarctica

A coloured geomorphological map at the approximate scale of 1:50,000 is presented for the Ablation Point massif area. The main gcomorphological features have been described, such as ice and snow cover, glacial landforms and deposits (and chronology), ice marginal lakes, melt pools, gelifluction landforms and patterned ground and valley-slope landforms. The area is thought to be a good analogue for glacial-age maritime northwest Europe.     

Transect across the West Antarctic rift system in the Ross Sea,Antarctica

In 1994, the ACRUP (Antarctic Crustal Profile) project recorded a 670-km-long geophysical transect across the southern Ross Sea to study the velocity and density structure of the crust and uppermost mantle of the West Antarctic rift system. Ray-trace modeling of P- and S-waves recorded on 47 ocean bottom seismograph (OBS) records, with strong seismic arrivals from airgun shots to distances of up to 120 km, show that crustal velocities and geometries vary significantly along the transect. The three major sedimentary basins (early-rift grabens), the Victoria Land Basin, the Central Trough and the Eastern Basin are underlain by highly extended crust and shallow mantle (minimum depth of about 16 km). Beneath the adjacent basement highs, Coulman High and Central High, Moho deepens, and lies at a depth of 21 and 24 km, respectively. Crustal layers have P-wave velocities that range from 5.8 to 7.0 km/s and S-wave velocities from 3.6 to 4.2 km/s. A distinct reflection (PiP) is observed on numerous OBS from an intra-crustal boundary between the upper and lower crust at a depth of about 10 to 12 km. Local zones of high velocities and inferred high densities are observed and modeled in the crust under the axes of the three major sedimentary basins. These zones, which are also marked by positive gravity anomalies, may be places where mafic dikes and sills pervade the crust. We postulate that there has been differential crustal extension across the West Antarctic rift system, with greatest extension beneath the early-rift grabens. The large amount of crustal stretching below the major rift basins may reflect the existence of deep crustal suture zones which initiated in an early stage of the rifting, defined areas of crustal weakness and thereby enhanced stress focussing followed by intense crustal thinning in these areas. The ACRUP data are consistent with the prior concept that most extension and basin down-faulting occurred in the Ross Sea during late Mesozoic time, with relatively small extension, concentrated in the western half of the Ross Sea, during Cenozoic time.     

Mineralogy and Geochemistry of a Basanite to Phonolite Sequence at Hut Point Peninsula, Antarctica, based on Core from Dry Valley Drilling Project Drillholes 1, 2 and 3

The Dry Valley Drilling Project (DVDP) cored three holes (DVDP1, 2 and 3) at Hut Point Peninsula (HPP) on Ross Island, Antarctica.DVDP 1 reached 201 m and penetrated 40 stratigraphic units,mainly basanite and Ne-hawaiite lava flows and associated pyroclasticrocks. DVDP 2 and 3 are nearly identical. DVDP 3 reached 381m and penetrated 15 stratigraphic units. The lower unit is a214 m thick basanite hyaloclastite, this is overlain by flowsand pyroclastic rocks of basanite, Ne-hawaiite, and then alternatingNe-mugearite and Ne-benmoreite flows. Phonolite stratigraphicallyoverlies the drill site. Primary olivine (Fo₈₈-Fo₇₄) is confined to the basanites, althoughxenocrysts occur in other rock types. Calcium-rich clinopyroxeneis ubiquitous but shows little variation in terms of Ca, Mg,Fe²⁺. Kaersutite is common in all lavas except the basanitesand shows very little compositional variation. It is believedto have crystallized at temperatures below 1100 °C and atpressures between 1·5 and 10 kb. Rhönite, a titanosilicateis a common groundmass phase in some basanite lavas. Oxide mineralsshow a wide range of compositions; spinel and chromian spineloccur as inclusions in olivine in the basanites. Titano-magnetiteoccurs in most samples examined. Labradorite is the predominantfeldspar in the basanite, with andesine and oligoclase importantin all other rock types. DVDP and HPP samples show a well-defined sequence of basanite-Ne-hawaiite-Ne-mugearite-Ne-benmoreite-phonolite,termed the DVDP lava lineage. Differentiation of the lineagehas been modeled using major element least squares mass balancemodels. Over 75 per cent of the evolution from basanite to phonoliteoccurs in the initial step from basanite to Ne-hawaiite, whichrepresents a 43 per cent residual. The phonolite is only a 25per cent residual from a basanite parent; thus even though Ne-mugeariteand Ne-benmoreite are common, they represent only minor stepsin the differentiation sequence. The mass balance models indicatethat olivine, clinopyroxene, kaersutite, opaque oxides and feldsparare the dominant fractionated phases. Trace element (includingrare earth element) contents calculated using the Rayleigh equationconfirm all models. ^* Present address: Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801.     

Stratigraphy and structure of Deception Island, South Shetland Islands, Antarctica

Deception Island is an active volcano with a large structural collapse caldera that has been interpreted by several investigators as having been generated by different processes. The general stratigraphy and structural study of the volcano is presented, with special emphasis on the distribution and structural disposition of the different stratigraphic units. The rocks of Deception Island have traditionally been divided into pre- and post-caldera products. A subdivision of the pre-caldera deposits, called ‘pre- and syn-caldera deposits,’ has been observed in two main units. Bulk magnetic susceptibility analyses are used to support the field stratigraphy presented. The localization and distribution of dikes is used to assign the central collapse of the volcano to rifting induced by tensional tectonics occurring in the Bransfield Strait and the presence of transcurrent faults around the island.     

The age and origin of the Balleny and Scott volcanic provinces,Ross Sea,Antarctica

The Balleny and Scott volcanic provinces are two isolated and remote volcanic occurrences located along the rifted margin of Western Antarctica in the Ross Sea. They include oceanic plateaus, seamounts, and volcanic islands. Although volcanic activity has been documented through remote sensing, there is no geochronological data based on radio-isotope methods constraining the duration of the volcanic activity in this region. As a consequence, hypotheses, based on the interpretation of chemical characteristics of the lavas, that suggested the volcanism to be either the result a deep mantle plume or a large-scale shallow melting anomaly have not yet been tested decisively.In order to tackle this issue, we have now dated lavas dredged from seamounts from both Balleny and Scott provinces using the ⁴⁰Ar/³⁹Ar technique. Our new age dates suggest that the Balleny and Scott volcanic provinces were active since at least 2.8 Ma and 2.4 Ma respectively. This suggests that these volcanic provinces were active simultaneously to the magmatism of the McMurdo volcanic group in the Western Antarctica Rift System that comprises Mount Erebus and Mount Melbourne stratovolcanoes. Our new dates suggest that there is no obvious age trend across the Balleny and Scott provinces. Combined with plate reconstructions since the end of Mesozoic, these data suggest that the Scott province does not coincide with any potential hot-spot track, thus negating a deep mantle plume origin for this volcanism. The case of the Balleny province is more ambiguous. The hypothesis of this province representing the end of the Tasman seamounts chain formed by a hot-spot track with decreasing-age trend is not confirmed by the new geochronological data, since available dates for the region are rather scarce and unreliable for the Tasman seamounts.Therefore, we suggest that the Balleny and Scott provinces originated from shallow mantle melting processes, a hypothesis that seems to be consistent with our re-interpretation of the SrNdPb isotope data of the lavas from the Balleny and Scott provinces. We argue that these provinces were derived from a heterogeneous subcontinental lithospheric mantle metasomatized during ancient subductions and which is now scattered in the shallow mantle of the southwest Pacific realm. This scattered mantle source component has been melting since the beginning of Cenozoic, and was then progressively depleted in the most fusible components. This new working model can explain the presence of several magmatic provinces in the southwest Pacific-Antarctica realm which show similar chemical signatures.     

Tectonometamorphic Evolution of Jutulsessen,Gjelsvikfjella, cDML,East Antarctica

The Jutulsessen area, can provide a vital clue to the supercontinent assembly of Gondwana Land as it is situated within the Circum East Antarctic Mobile Belt just east of the Penksockett rift marking the divide between the central Dronning Maud Land from the Western Dronning Maud Land. This landmass is dominated by migmatitic quartzo-feldspathic rocks intruded by syn to post-tectonic granites. The work highlights the data from western part cDML area with a view to arrive at a more comprehensive model for the cDML and subsequently to the super continent assembly. Granitic and migmatitic gneisses comprising of amphibolitic and biotite rich enclaves. The gneisses show variations from quartzo-felspathic gneiss to amphibolitic gneiss. The area has witnessed complex geological history involving at different deformational episodes with concomitant metamorphism. The pervasive dominant foliation trends NW-SE with shallow to medium dips towards SW. In the Stabben area, a nonfoliated intrusive syenite-gabbro pluton limits the gneissic exposures. Compositionally, the orthogneisses plot in the monzogranitegranodiorite field where as the mafic dykes/enclaves plot in the basalt-andesite-rhyodacite field. The bulk geochemical characteristics suggest significant crustal contamination. Garnet-biotite Fe-Mg exchange thermometry gives peak metamorphic temperature of 483° C for the gneisses and 628° C for the dioritic enclave within gneisses. A peak metamorphic grade of upper amphibolite to granulite facies is deduced from the mineral assemblages. Widespread anatexis has led to extensive occurrence of migmatites in the area. Recent geochronological studies assign an age of 1170 Ma to 970 Ma for the migmatites/gneisses and an emplacement age of 501 Ma for the Stabben gabbro and syenite. The discriminant plots of the Jutulsessen rocks indicate diverse origin ranging from pre-plate collision to post-collision orogenic tectonic setting. The mafic enclaves/dykes show ocean island arc to MORB affinities. Voluminous addition of juvenile crust during the Pan-African orogeny strongly overprints earlier structures.     

Localized ductile thrusting north of the Variscan Front,Ross Island,southwest Ireland

Two thrusts occur on Ross Island: the Head of Ross Thrust and the more southerly Ross Island Thrust. These lie to the north of the Killarney–Mallow Fault (KMF), the boundary frequently interpreted as the Variscan Front. The Ross Island Thrust, exposed in outcrop and in seven borehole cores, has emplaced dark blue–grey limestones of the Courceyan Ballysteen Formation over pale grey–brown Rockfield Limestone Formation of Chadian–Holkerian age. These lithologies at Ross Island exhibit a continuum of deformation at both the micro‐ and macro‐scale, beginning with the generation of a spaced cleavage, formed during layer parallel shortening, that was subsequently rotated into parallelism with fold axial planes. Extensional microstructures are predominant in thin section and are associated with attenuation of the fold limb. Calcite veins are also attenuated and lie parallel to a mylonitic fabric close to the thrust plane. Lithological boundaries, the prominent pressure solution cleavage and the southerly dipping limb of an asymmetrical antiform are all parallel and form a composite planar anisotropy. This has controlled the location of the ductile Ross Island Thrust, which formed during the attenuation and shearing of a common fold limb. Ductile thrusts within the limestones at Ross Island contrast with the reactivation of basin‐margin extensional faults further to the south along the major KMF. The Ross Island Thrust is considered to result from deformation ahead of the major northerly propagating Variscan décollement thrust and does not necessitate a continuous décollement structure north of the KMF. Mineralization at Ross Island exhibits remobilization associated with the formation of a pressure‐solution cleavage and probably pre‐dates thrusting. Copyright © 2003 John Wiley & Sons, Ltd.     

Provenance of LGM glacial till (sand fraction) across the Ross embayment,Antarctica

The provenance of Late Quaternary Ross Embayment till was investigated by comparing the coarse sand composition of East and West Antarctic source area tills with till samples from across the Ross Sea. The West Antarctic samples from beneath the Whillans (B) and Kamb (C) ice streams are petrologically distinct from samples of lateral moraines flanking several East Antarctic outlet glaciers. The characteristic assemblage of four West Antarctic samples includes felsic intrusive and detrital sedimentary lithic fragments, plagioclase and abundant quartz. In contrast, most of the ten East Antarctic till samples contains abundant mafic intrusive and detrital sedimentary lithic fragments as well as less abundant quartz. The distinctive composition of these source areas can be linked to 33 samples from 20 cores of Last Glacial Maximum (LGM) age till distributed across the Ross Sea. Western Ross Sea till samples exhibit mineralogic and lithological similarities to East Antarctic till samples, although these western Ross Sea tills contain higher percentages of felsic intrusive and extrusive lithic fragments. Eastern Ross Sea till samples are compositionally similar to West Antarctic till, particularly in their abundance of quartz and dearth of mafic and extrusive lithic components. Central Ross Sea till exhibits compositional similarities to both East and West Antarctic source terranes including a mafic lithic component, and marks the confluence of ice draining from East and West Antarctica during the LGM, thus West Antarctic-derived ice streams did not advance into the western Ross Sea. This indicates that even if pre-LGM equivalents of the present Siple Coast ice streams existed, they did not simply expand allowing West Antarctic-derived ice to dominate the LGM Ross Ice Sheet.     

Lithostratigraphy of Upper Jurassic-Lower Cretaceous strata of eastern Alexander Island,Antarctica

As a result of recent field work, the 4000m thick Kimmeridgian-Albian Fossil Bluff Formation of eastern Alexander Island is elevated to Group status (Fossil Bluff Group). Four formations are recognised within the group (which in ascending order are the Ablation Point, Himalia Ridge, Spartan Glacier and Pluto Glacier Formations), characterised by slumped strata, conglomerates, mudstones and sandstones, respectively. Type sections are selected, and representative lithologies and faunas described for each of these stratigraphic units. This succession constitutes probably the best exposed sequence through the Jurassic-Cretaceous boundary at a southern high palaeolatitude.