Antarctica

At the end of the 19

th

century the South Pole region was still “terra incognita”. Thus a resolution to promote geographical exploration of the Antarctic Regions was passed by VI

th

International Geographical Congress in London in 1895. Besides political rivalry, a scientific collaboration was adopted during the VII

th

International Geographical Congress in Berlin in 1899. The field of work in Antarctica was divided into four quadrants assigning the Weddell and Enderby quadrants to Germany and the Ross and Victoria quadrants to England. Erich von Drygalski (1865–1949), who already had lead two expeditions to the west coast of Greenland (1891, 1892–1893), became leader of the “Deutsche Südpolarexpedition” (1901–1903). The expedition with the newly built first German polar research vessel “Gauss” was financed by the Imperial internal budget. Finally expeditions from Germany, England, Sweden, Scotland, and France took part in the international meteorological and magnetic co-operation. Unfortunately the “Gauss” was beset by ice close to the Antarctic Circle 85 km off the ice-covered coast of Kaiser Wilhelm II. Land, where a winter station was established on sea ice. After 50 weeks of captivity the ship came free and finally sailed home. Emperor Wilhelm II was very disappointed about Drygalski’s results, because Robert Falcon Scott (1868–1912) had reached 82° S at the same time. Geographical achievements seemed to be much more valuable than thoroughly measured scientific data, which were to be analyzed and published over three decades.

The characteristics of the metamorphosed banded iron formation (meta-BIF) in the Mt. Riiser-Larsen area, Amundsen Bay, Enderby Land, Antarctica were investigated in order to understand why a large magnetic anomaly appeared in this region. The study found many meta-BIF layers, consisting of one to nine layers within 30 m thickness in felsic gneiss. The thicknesses of individual layers were usually 0.5–2 m but sometimes varied from zero to 6 m. Almost all strong magnetic anomalies reported by Dolinsky et al. (2002) could be explained by the magnetization of the meta-BIF layers. To explain the source of the magnetic anomaly, the natural remanent magnetization of meta-BIF and its susceptibility are taken in to account. The largest layer including meta-BIF is estimated to be more than 7400 × 213 m. Magnetite in the layer was examined by thermomagnetic, magnetic hysteresis and microscopic analyses. The results indicated that almost pure magnetite with pseudosingle-domain (PSD) and multi-domain structure is the dominant composition of meta-BIF as well as quartz. The PSD magnetite grains were along the quartz crystal boundaries and formed a network structure. The electric conductivity of the meta-BIF is explained by this network structure rather than being due to the high magnetite concentration.

High-pressure experiments were carried out at pressures 7–15 kbar and temperatures 850–1150 °C using the piston cylinder apparatus. Experimental data give constraints on the

P-T

path of sillimanite-cordierite-sapphirine granulites from Rundvågshetta, Lützow-Holm Complex, East Antarctica. Combining the previous temperature estimates and the present data, we can infer that the Rundvågshetta granulites experienced the peak metamorphism at 925–1039 °C and 11.5–15 kbar within the stability field of garnet, orthopyroxene, sapphirine and sillimanite. Subsequent retrograde metamorphism took place at 824–1010 °C and 6.5–10.8 kbar accompanied by breakdown of garnet and consumption of orthopyroxene and sillimanite within the stability field of orthopyroxene, sapphirine, spinel and cordierite.

A third locality of sapphirine granulite was discovered in the Schirmacher Hills, central Dronning Maud Land, East Antarctica; one unique for the association with orthopyroxene and garnet. Sapphirine occurs as inclusions together with orthopyroxene within garnet and as discrete grains together with spinel, secondary orthopyroxene in cordierite coronas. Orthopyroxene porphyroblasts have the highest Al

2

O

3

contents (∼10 wt.-%) so far reported from Dronning Maud Land. The earlier of two metamorphic stages inferred for the sapphirine-bearing granulite is characterized by breakdown of sapphirine and orthopyroxene to form garnet at peak conditions approaching 950–1050°C and 9–10 kbar. The later stage is decompression when spinel-cordierite-orthopyroxene formed at about 950–980°C and 8 kbar. The age of the ultrahigh-temperature event could be ca. 1.15 Ga, somewhat older than the late Mesoproterozoic granulite-facies event elsewhere in central Dronning Maud Land. Metamorphic temperatures estimated to exceed 900°C imply that the tectonothermal regime in the Schirmacher Hills was distinct and could be critical in determining relationships between central Dronning Maud Land and metamorphic belts in southern Africa and in understanding the evolution of Rodinia and Gondwana.

Ferrosilite-fayalite bearing charnockite and biotite-hornblende bearing granite are exposed in Mühlig-Hofmannfjella, central Dronning Maud Land of East Antarctica. Both are interpreted as essentially parts of a single pluton in spite of their contrasting mineral assemblages. Based on petrologic and geochemical studies, it is proposed that H

2

O-undersaturated parent magma with igneous crustal component that fractionated under different oxygen fugacity conditions resulted in the Mühlig-Hofmannfjella granitoids.

The nunataks of Mühlig-Hofmannfjella and Filchnerfjella in central Dronning Maud Land, East Antarctica, comprise a deep-seated metamorphic-plutonic rock complex, dominated by a dark colour due to dark feldspar and containing granulite facies minerals including perthite, plagioclase, orthopyroxene and garnet. The area was affected by a late Pan-African fluid infiltration outcropping as conspicuous light alteration zones restricted to halos around thin granitoid veins. The veins were formed during infiltration of volatile-rich melts, probably originating from underlying magma-chambers. The alteration halos were formed by CO

2

-H

2

O-volatiles emanating from the veins into the host rock causing hydration of the granulite facies assemblages. The alteration involves a breakdown of orthopyroxene to biotite and sericitisation of plagioclase at crustal conditions around 350–400°C and 2 kbar. The marked colour change is caused by transformation of feldspars, spread of dusty micas, opaques and fluid inclusions in addition to replacement of coarse to finer grains. The process is locally penetrative indicating that fluid infiltration can affect large rock volumes. The frequent distribution of alteration zones throughout the mountain range independent of lithological variations shows that the fluid infiltration is regionally extensive.

Electron microprobe (EMP) dating on monazite in granulite-facies rocks from Forefinger Point, East Antarctica, yielded dominant ages of ∼500 Ma on matrix monazites. They are associated with secondary cordierite, biotite and sapphirine, formed during nearly isothermal decompression after the high

P-T

assemblages involving garnet, orthopyroxene and sillimanite. Older ages around 750–1000 Ma are detected in monazite cores and in monazite inclusions in garnet porphyroblast. Combining the available age data and the reaction textures, it becomes evident that the Forefinger Point granulites have been overprinted by a granulite-facies decompressional event of Pan-African age. Moreover, EMP monazite dating imply that the Forefinger Point granulites have experienced at least two stages of metamorphic evolution.

The Prince Charles Mountains have been subject to extensive geological and geophysical investigations by former Soviet, Russian and Australian scientists from the early 1970s. In this paper we summarise, and review available geological and isotopic data, and report results of new isotopic studies (Sm-Nd, Pb-Pb, and U-Pb SHRIMP analyses); field geological data obtained during the PCMEGA 2002/2003 are utilised. The structure of the region is described in terms of four tectonic terranes. Those include Archaean Ruker, Palaeoproterozoic Lambert, Mesoproterozoic Fisher, and Meso- to Neoproterozoic Beaver Terranes. Pan-African activities (granite emplacement and probably tectonics) in the Lambert Terrane are reported. We present a summary of the composition of these terranes, discuss their origin and relationships. We also outline the most striking geological features, and problems, and try to draw attention to those rocks and regional geological features which are important in understanding the composition and evolution of the PCM and might suggest targets for further investigations.

The aeromagnetic data of the Lambert Glacier — Prince Charles Mountains area provide a rather complex but surprisingly coherent image for studying the geology and tectonic history of this region. Several distinct structural units can be differentiated in the magnetic anomaly data. The aeromagnetic data from the Prince Charles Mountains and surrounding areas reveal the spatial boundaries of the Archaean cratons at the Prince Charles Mountains and Vestfold-Rauer areas and suggest the existence of a previously unknown craton in Princess Elizabeth Land. The magnetic data differentiate the inner structure of the Beaver-Rayner Proterozoic mobile belt and the complex marginal belt of the Archaean cratons reworked by Mesoproterozoic to Neoproterozoic tectonism. The aeromagnetic data clearly indicate no obvious link of the Pan-African mobile belt in Prydz Bay with Lützow-Holm Bay, and provide no evidence that it extends inland towards the Mawson Escarpment or Grove Mountains. Thus, East Gondwana probably was not divided into Indo-Antarctic and Australo-Antarctic sectors as suggested by a number of recent studies.

The geology of the Grove Mountains is poorly known. The magnetic anomalies of the Grove Mountains and surrounding areas are characterized by a prominent NE-SW to E-W fabric. Well defined magnetic anomalies along its periphery with the absence of intensive magnetic anomalies in the north are a distinctive feature of this region. The obliqueness of magnetic anomalies along the study area’s boundary with respect to its central part suggests that the northern Grove Mountains basement may be much older crust than the neighboring terranes of Meso- to early Neoproterozoic high-grade metamorphic rocks. The existence of two ancient cratonic blocks in the southern Prince Charles Mountains and Vestfold Hills suggests that this region may contain Archaean or Paleoproterozoic crust. The Grove Mountains crustal block is clearly discernible in the aeromagnetic data and can be considered as a region that underwent Grenvillian and/or Pan-African or both tectonism and reworking. The absence of any visible magnetic trends running towards the Prydz Bay coast or central part of the Mawson Escarpment precludes any direct tectonic correlation with these regions.

For a number of years the multi-national ADMAP working group has been compiling near surface and satellite magnetic data in the region south of 60° S. By the end of 2000, a 5 km grid of magnetic anomalies was produced for the entire region. The map readily portrays the first-order magnetic differences between oceanic and continental regions. The magnetic anomaly pattern over the continent reflects many phases of geological history whilst that over the abyssal plains of the surrounding oceans is dominated mostly by patterns of linear seafloor spreading anomalies and fracture zones. The Antarctic compilation reveals terranes of varying ages, including Proterozoic-Archaean cratons, Proterozoic-Palaeozoic mobile belts, Palaeozoic-Cenozoic magmatic arc systems and other important crustal features. The map delineates intra-continental rifts and major rifts along the Antarctic continental margin, the regional extent of plutons and volcanics, such as the Ferrar dolerites and Kirkpatrick basalts. The magnetic anomaly map of the Antarctic together with other geological and geophysical information provides new perspectives on the break-up of Gondwana and Rodinia evolution.

In the Ross Sea, large sedimentary basins reflect primarily the major extensional event associated with the Late Cretaceous breakup of Gondwana. Within the Interior Ross Embayment, no similar large basins have been identified to date. We have used aerogravity and Werner deconvolution methods applied to aeromagnetic data to map depth to magnetic basement, which helped delineate three major sedimentary basins, the Bentley Subglacial, Onset, and Trunk D Basins.

Ice penetrating radar (mostly airborne) and marine seismic surveys have revealed plateaus and terraces about 100–350 m below sea level beneath parts of the Ross Embayment including the West Antarctic ice sheet, the Ross Ice Shelf, and the eastern Ross Sea. These surfaces cover many thousands of square kilometers and are separated by bedrock troughs occupied by the West Antarctic ice streams. We interpret these surfaces as remnants of a level surface formed by wave erosion when the coastal regions of Antarctica were relatively free of ice. The flat and level nature of the surfaces that are near the same depth over large distances supports an origin by marine rather than glacial erosion. Marine seismic reflection profiles over one of the plateau remnants show thin, flat-lying glacial marine sediments draped with angular unconformity over gently dipping sediments of early Miocene age. Ice sheet and global sea level histories suggest that the shallower plateaus were last eroded in the middle Miocene, possibly within a warm interval from about 17 to 14 Ma, prior to formation of the modern West Antarctic ice sheet. The plateau surfaces cannot be directly correlated to Ross Sea unconformities but they may be extensions of ∼14-Ma unconformity RSU4. The plateaus along the Siple Coast, with depths around 350 m, do not rebound to close to sea level for models of removing past and present ice load. Another possible factor is that western Marie Byrd Land lithosphere was heated in Oligocene time due to substantial extension or intensified mantle plume activity. Subsequent cooling has caused a moderate amount of crustal subsidence since then. These plateaus are similar to the emergent wave cut platforms interrupted by deep fjords, termed “strand” flats that rim the coasts of Norway.

Airborne gravity data have been acquired over the two largest subglacial lakes in East Antarctica. 2D inversion of these data was performed for several fixed values of density contrast in order to estimate bathymetry and sediment thickness. For Lake Vostok the best agreement between profiles derived from gravity inversion and seismic soundings is achieved for densities 2.55 g cm

−3

for host rock and 1.85 g cm

−3

for sediment. The result shows a topographic rise of the lake bottom dividing the lake into two sub-basins. Our inversion results suggest that water thickness in Lake Concordia does not exceed 200 m for all possible density contrasts between ice/water and surrounding rock; the sediment layer cannot be resolved.

Since 1995, Polar Marine Geological Research Expedition has performed the geophysical investigations of Lake Vostok, Central East Antarctica. The study of this phenomenon is carried out by means of radio-echo sounding (RES) and reflection seismic. In total, 3250 km of RES profiles and 194 seismic measurements have been made. These scientific works resulted in mapping the ice thickness, bedrock and sub-ice topography and the Lake Vostok shoreline. We fixed 195 fragments of grounding line, according to RES data, with 169 of them (86%) being reliable while 26 (14%) are questionable. These results are the base for contouring the lake shore. The water table square estimates at some 17100 km2. We also detected 22 small-size subglacial water cavities around the Lake Vostok. Subice topography of the Lake Vostok bottom is divided into two main regions: the deep-water and shallow-water basins. The first one with depths from about −1700 to −800 m is located in the southern part of the lake. We assume its northern part to be shallow-water with the bottom depth of about −940 m.

During the austral summer field seasons of the 1995–2004 Polar Marine Geological Research Expedition (PMGRE) within the frame of the Russian Antarctic Expedition (RAE) carried out groundbased geophysical investigations in the sub-glacial Lake Vostok area in order to study the ice sheet and bed relief. Geomorphological analysis of the data allowed better understanding of sub-ice and sub-water structures. The most striking structure is the Vostok Basin which subdivides into five main substructures: lake plane, deepwater hollow, sub-water ridges, internal and external slopes. We detected six principal morphological substructures outside the Vostok Basin: lowlands, low hilly planes, high planes, ridged plane, Komsomolskiye Mountains and middle mountain land. A geomorphological chart has been produced.

A seismic exploration was conducted on the Mizuho Plateau, East Antarctica, during the 2001/2002 austral summer season as the “Structure and Evolution of the East Antarctic Lithosphere (SEAL)” project by the 43

rd

Japanese Antarctic Research Expedition (JARE-43). The survey line of this exploration (SEAL-2002 profile) was almost perpendicular to the Mizuho inland traverse routes (JARE-41 refraction survey line; SEAL-2000) and was almost parallel to the coastal line along the Lützow-Holm Bay. Several seismic shot records were obtained with clear arrivals of phases until a distance of 150 km in length. We have analyzed two shot data of both ends of the SEAL-2002 profile by using the conventional reflection method. Interval velocities were estimated by applying the normal-move-out (NMO) correction, then the obtained single-fold section obtained explicitly presents the horizontal reflectors originated from the middle crust, the lower crust and the Moho discontinuity. First, the reflector from the top of the middle crust was located at the depth of 23–24 km, which was corresponding to 8–9 s of two way travel time (TWT) in the single-fold section. Next, the reflector from the top of the lower crust was located at a depth of 31–34 km, corresponding to 11–12 s of TWT. The Moho reflector was observed in 13–14 s of TWT and the depth was estimated to be approximately 41–42 km.

Teleseismic data recorded by temporary and permanent stations located in the Northern Victoria Land region are analysed in order to identify the presence and location of seismic anisotropy. We work on data recorded by 24 temporary seismographic stations deployed between 1993 and 2000 in different zones of the Northern Victoria Land, and by the permanent very broad-band station TNV located near the Italian Base “M. Zucchelli”. The temporary networks monitored an area extending from Terra Nova Bay towards the South beyond the David Glacier and up to the Indian Ocean northward. To better constrain our study, we also provide an analysis of data recorded by TNV in the same period of time and we take into account also SKS shear wave splitting measurements performed by Barruol and Hoffman (1999) on data recorded by DRV. This study, to be considered as preliminary, reveals the presence of seismic anisotropy below the study region, with a mainly NW-SE fast velocity direction below the Terra Nova Bay area and rather large delay times, that mean a deep rooted anisotropic layer.

The geology of the ice-covered interior of the East Antarctic shield is completely unknown; inferences about its composition and history are based on extrapolating scant outcrops from the coast inland. Although the shield is clearly composite in nature, a large part of its interior has been represented by a single Precambrian block, termed the Mawson block, that includes the Archean-Mesoproterozoic Gawler and Curnamona cratons of Australia. In Australia, the Mawson block is bounded on the east by Neoproterozoic sedimentary rocks and the superimposed early Paleozoic Delamerian Orogen, marked by curvilinear belts of arc plutons, and on the west by the unexposed Coompana block and Mesoproterozoic Albany-Fraser mobile belt. In Antarctica, these crustal elements are inferred to extend across Wilkes Land and south to the Miller Range region. Aero- and satellite magnetic data provide a means to see through the ice, helping to elucidate the broad composition of the shield. Rocks of the Mawson block in Australia produce distinctive magnetic anomalies; Paleoproterozoic granites and Meso- to Neoproterozoic mafic igneous rocks are associated with high-amplitude, broad-wavelength positive aero- and satellite-magnetic anomalies. The same types of magnetic anomalies can be traced to ice-covered Wilkes Land, Antarctica, and are interpreted to signify similar rocks. However, the diagnostic satellite magnetic high ends ∼800 km south of the Antarctic coast, suggesting that the Mawson block is smaller than first proposed and that the remaining East Antarctic shield is composed of several Precambrian crustal blocks of largely undetermined composition and age. Nonetheless, the coincident eastern borders of these magnetic highs and high seismic-velocity anomalies characteristic of the Precambrian shield, together define the edge of thick cratonic lithosphere. East of this boundary, magnetic lows are explained by magnetite-poor upper Neoproterozoic and lower Paleozoic sedimentary rocks, and their metamorphic equivalents, which crop out discontinuously along the Ross margin of Antarctica and in eastern Australia. These rocks are inferred to overlie a Neoproterozoic rift margin, which transects older basement provinces. The coincidence of this cratonic rift boundary with the western limit of Paleozoic and Jurassic magmatism suggests that, although tectonically modified by younger events, the composite Antarctic-Australian shield comprised thick lithosphere that was not penetrated by Paleozoic and younger convergent-margin magmas.

The Matusevich Glacier trends 170° totally straight for more than 100 km. For this reason, a major fault was assumed along the glacier formerly. A westward directed ductile thrust system, trending 170°, was subsequently discovered in the upper Matusevich Glacier (“Exiles Thrust”). It formed under amphibolite facies conditions during the Ross Orogeny. Therefore, the course of the Matusevich Glacier was attributed to the Exiles Thrust instead of the postulated simple fault. During GANOVEX VIII/ITALANTARTIDE XV (1999/2000), the small-scale structures at the margins of the Matusevich Glacier were mapped. The most conspicuous and meaningful of these structures are cold, brittle, NW- to N-trending thrusts with slickensides, decorated with quartz fibres and uniformly SW-thrusting (−220°). They occur at the western side of the glacier (Lazarev Mts.). These structures are consistent with strike-slip tectonics along the Matusevich Glacier and could be interpreted as indicators of transpressional tectonics. Unfortunately, corresponding dextral strike-slip faults, which should strike about 170°, could not be observed directly. But 30 km to the west, 165° trending strike-slip structures are exposed at the eastern edge of Outrider Nunatak. Striations on steep fault planes indicate dextral displacement. This strike-slip tectonics produced a flower structure visible in one of the main granite-walls of Outrider Nunatak. Thus the neotectonics of westernmost Oates Land is characterized by brittle dextral strike-slip faulting, following the trend of much older Ross-age ductile thrust tectonics.

A comparable history as at this “Matusevich Fracture Zone” is known from the larger Rennick Glacier. Thus, two brittle dextral strike-slip fault zones are tracing older structures and cross at high angles the coastline of Antarctica. They are co-linear with off-shore fracture zones, the active parts of which are the transform faults between Antarctica and Australia. We discuss, whether the dextral faults on-shore could represent the continuations of the fracture zones off-shore. This idea is supported

(i)

by dextral offsets of the shelf where fracture zones reach Antarctica;

(ii)

possibly by magnetic anomalies along the Matusevich and Rennick Glaciers, which seem to continue off-shore;

(iii)

by several examples of oceanic fracture zones continuing into continental crust.

The Byrd Glacier discontinuity is a major tectonic boundary crossing the Ross Orogen, with crystalline rocks to the north and primarily sedimentary rocks to the south. Most models for the tectonic development of the Ross Orogen in the central Transantarctic Mountains consist of two-dimensional transects across the belt, but do not address the major longitudinal contrast at Byrd Glacier. This paper presents a tectonic model centering on the Byrd Glacier discontinuity. Rifting in the Neoproterozoic produced a crustal promontory in the craton margin to the north of Byrd Glacier. Oblique convergence of a terrane (Beardmore microcontinent) during the latest Neoproterozoic and Early Cambrian was accompanied by subduction along the craton margin of East Antarctica. New data presented herein in support of this hypothesis are U-Pb dates of 545.7 ±6.8 Ma and 531.0 ±7.5 Ma on plutonic rocks from the Britannia Range, directly north of Byrd Glacier. After docking of the terrane, subduction stepped out, and Byrd Group was deposited during the Atdabanian-Botomian across the inner margin of the terrane. Beginning in the upper Botomian, reactivation of the sutured boundaries of the terrane resulted in an outpouring of clastic sediment and folding and faulting of the Byrd Group.

The geology of the Byrd Group immediately south of Byrd Glacier records a major sequence of geologic events, beginning with the development of a carbonate platform (Shackleton Limestone) during the early Atdabanian (approximately 525 Ma), followed by a transitional interval of siliciclastic deposition and volcanism (Starshot Formation) during the late Botomian (approximately 512 Ma), and ending with a coarse cover of clastic molasse deposition (Douglas Conglomerate), no younger than plutonism at 492 ±2 Ma. Thus, the Byrd Group was deposited during a span of less than 33 myr, as a sequence of passive shelf-margin sedimentation through active uplift and erosion related to the Ross Orogeny. The newly subdivided Shackleton Limestone records at least two major depositional cycles, interrupted by a significant karst event. A layer of volcanic ash overlain by a thick layer of argillite in the uppermost Shackleton Limestone records the timing of a conformable carbonate to siliciclastic transition, accompanied by basalt volcanism of the Starshot Formation. Continued clastic deposition of the Starshot Formation coarsens upwards into the Douglas Conglomerate, where the primary sources of clastic detritus are derived from the Shackleton Limestone and possibly much of the Starshot Formation itself.

Kinematic data from the Rennick Glacier area indicate the presence of two intra-Wilson Terrane late-Ross opposite-directed high-strain reverse shear systems. High-grade rocks are W- and E-ward displaced over low-grade rocks and shallow-level intrusions. The shear zones are offset in a step-like pattern suggesting the presence of ENE trending right-lateral faults. The structural pattern accounts for a relationship between the Exiles and Wilson thrusts in Oates Land, which in our opinion can be traced from the Pacific coast to the Ross Sea. The western front of the Ross Orogen towards the East Antarctic Craton is best interpreted as a broad W-vergent fold-and-thrust belt, along which the intra-Wilson Terrane arc was detached and thrust onto the craton. The shear zones related to the Exiles Thrust system represent the internal, easternmost thrusts of this belt. Based on our data in combination with recent geophysical and geochronological results, the craton-orogen boundary must be located significantly further W than previously inferred. The boundary and hence the inferred termination of the proposed fold-and-trust belt may roughly lie in the area between Mertz and Ninnis Glaciers in George V Land, taking into account a considerable amount of likely post-Ross crustal extension possibly related to the Wilkes Subglacial Basin.

K-Ar ages of 82 slate and schist (white-mica-rich whole-rock) samples are reported for Late Precambrian-Early Ordovician metamorphic rocks of the Wilson, Bowers and Robertson Bay terranes of northern Victoria Land. These are amalgamated in two vertical sections along composite NE-SW horizontal profiles across (1) Oates Coast in the north, and (2) Terra Nova Bay area in the south. The ages are in the range 328–517 Ma. Both profiles show some age variation with altitude, but more importantly, they define an inverted wedge shaped pattern, reflecting a “pop-up” structure. This is oriented NW-SE at the eastern margin of the Wilson terrane, and the edges coincide with the Exiles and Wilson Thrusts which cross the region. Ages inside the “pop-up” structure are younger, ca. 460–480 Ma, than those along its eastern and western flanks, ca. 490–520 Ma. The K-Ar age patterns thus demonstrate a late Ross Orogenic age (ca. 460 Ma) for this structure, which may be associated with assembly of the Wilson and Bowers terranes.

The connections between the Antarctic Peninsula and Patagonia, here referred to as South America south of 44° S, are analysed in the light of new geological information and hypotheses. The previously supposed existence of a continuous belt of Late Paleozoic accretionary complexes in the western margin of both Patagonia and the Antarctic Peninsula has been repudiated in recent years, since these complexes are mainly Mesozoic in terms of deposition and metamorphism. This is consistent with paleogeographic models in which the Antarctic Peninsula lays west of Patagonia in prebreak-up times. This disposition is favoured by similarities in provenance between the late Early Permian to ?Late Triassic Duque de York Complex and Trinity Peninsula Group, which share sedimentological characteristics and U-Pb detrital zircon age patterns. After the Early Jurassic Chonide orogeny, the Antarctic Peninsula started to drift southwards, as indicated by paleomagnetic reconstructions of Weddell Sea ocean floor spreading, allowing the present-day margin of Patagonia to become progressively, from north to south, an actively subducting margin. In the Late Jurassic and Late Cretaceous, while the Antarctic Peninsula was drifting to its present position, turbiditic sedimentation took place at Hurd Peninsula, Livingston Island, previously considered to be Triassic in age, which has no equivalent in the Patagonian margin.

The new data presented here, combined with recent data and models from other authors, reveal two major geological problems to be resolved in the future: to identify a late Early Permian magmatic arc which shed detritus to both the Duque de York Complex and the Trinity Peninsula Group, and to resolve the apparent contradiction between left lateral post break-up movements in the Patagonian Andes, and right lateral displacements in the tectonic configuration of the Antarctic Peninsula.

Results of deep seismic soundings collected during four Polish Geodynamical Expeditions to West Antarctica between 1979 and 1991 were synthesised to produce a map of Moho depth beneath the NW coast of the Antarctic Peninsula. In this paper, we present a new interpretation of the deep landward projection of the Hero Fracture Zone based on two seismic transects. On each transect we found high velocity bodies with

Vp

>7.2 km s

−1

, similar to ones we detected previously in Bransfield Strait. However, these bodies are not continuous; they are separated by a zone of lower velocities located SW of Deception Island. In Bransfield Strait an asymmetric “mushroom”-shaped high velocity body was found at a depth interval from 13–18 km down to the Moho boundary at a depth of ca. 30 km. As a summary of results, we present a map of Moho depth along the coast of the Antarctic Peninsula, prepared using previous seismic 2D models. The map shows variations in crustal thickness from 38–42 km along the Antarctic Peninsula shelf in the southern part of the study area to 12–18 km beneath the South Shetland Trench.

Discovery Bank is located at the eastern end of the South Scotia Ridge. The new geophysical data point that this bank is continental in nature and may be a former fragment of the continental bridge that connected South America and the Antarctic Peninsula before the Oligocene and is located at the Scotia-Antarctic plate boundary along the South Scotia Ridge. In this region, continental fragments are bounded by the oceanic crust of the Scotia Sea to the north and of the Weddell Sea to the south. Seismicity indicates that at present active structures related to the plate boundary are located within the continental crust, whereas most of the continental- oceanic crust boundaries seem to be inactive.

The main crustal elements of the Scotia-Antarctic plate boundary at the region of Discovery Bank include, from north to south: the oceanic crust of the Scotia Plate, the Discovery Bank composed of continental crust, a tectonic domain with intermediate features, both in position and nature, between continental and oceanic crusts that includes the Southern Bank, and the oceanic crust of the northern Weddell Sea, which belongs to the Antarctic Plate.

The intermediate domain shows extreme crustal thinning and mantle uplift that are associated to the deep basins in all the MCS profiles, although we do not observe evidence of oceanic spreading. This domain was probably developed during the Late Cenozoic subduction of the Weddell Sea oceanic crust below the Discovery Bank and prior to the recent transcurrent tectonics. The complex bathymetry and structure of the plate boundary are a consequence of the presence of continental and intermediate crustal blocks. Deformation was preferently concentrated here, between the two stable oceanic domains.

Bransfield Basin is located at the Pacific margin of the Antarctic Peninsula and constitutes an incipient oceanic back-arc basin. This basin developed as a consequence of the separation of the South Shetland Block from the Antarctic Peninsula. Analysis of multichannel seismic profiles from Brazilian, Spanish, Japanese and Chinese cruises allows the shallow structure of the Bransfield Basin and its eastward prolongation through the South Scotia Ridge to be studied.

The Bransfield Basin is asymmetrical and taking into account the shallow structures, its opening may be interpreted as related to a low angle normal fault that dips NW, with the South Shetland Block constituting the hanging wall. The margin adjacent to the Antarctic Peninsula exhibits all the features associated with a lower plate passive margin, such as the development of landward tilted half-grabens, the presence of a break-up unconformity, and the deposition of an oceanward dipping “drift” sequence. However, the margin near the South Shetland Islands is typical of an upper-plate margin: poorly nourished, sharp and with high angle faults. Extension is more developed in the Central Bransfield Basin, where a volcanic axis is recognized as the expression of a young spreading center, and there is possibly incipient oceanic crust. In the Bransfield Basin extremities, present-day deposits represent the synrift sequence, and extension continues. The Bransfield Basin probably develops as a consequence of two interacting processes. The main one is rollback of the trench hinge related to the continued sinking of the subducted slab of the former Phoenix Plate. A second process is related to the westwards propagation of the deformations associated with the Scotia-Antarctic plate boundary along the South Scotia Ridge and up to the Bransfield Basin.

The age of the sedimentary sequences of Hurd Peninsula (here referred to the Miers Bluff Formation (MBF), has been considered so far as Triassic, coeval of the Trinity Group. Recently, a Tithonian ammonite species was found in a non-

in situ

block, coming from the lowermost unexposed part of the Formation. Our micropal-eontological study reveals the occurrence of calcareous nannofossils in six sections. The recorded nannofossil association comprises the following species:

Micula decussata, Calculites obscurus, Arkhangelskiella cymbiformis, Prediscosphaera cretacea, Lucianorhabdus cayeuxii, Cyclagelosphaera reinhardtii, Braarudosphaera bigelowii, Ceratolithoides aculeus, Broinsonia

cf.

parca, Thoracosphaera

sp. indet.,

Nephrolithus

sp. indet.,

Cretarhabdus

sp. indet.,

Watznaueria

sp. indet. It determines a Campanian-Maastrichtian age for the middle and upper part of MBF. Two calcareous nanofossil species,

Prediscosphaera cretacea

and ?

Fasciculithus

sp. indet., found in the Burdick Peak section suggest a Late Maastrichtian to (?) Paleocene age of the uppermost part of the MBF. The sediments of the MBF are possibly coeval of a part of Marambio Group (James Ross Island and Seymour Island) and Williams Point beds (Livingston Island).

Morphological and structural studies of the Fort Williams Point area (Greenwich and Dee Islands) reveal two regional trends, NE-SW and NW-SE. Detailed field observations show that the NWSE structural direction is associated with dykes and fractures resulting from a NW-SE shortening. This shortening is interpreted as related to active basaltic volcanism during the Mesozoic “Andean” history of the area. The NE-SW structural trend is associated with NE-SW trending sinistral faults post-dating the Cretaceous volcanic units. Kinematic analysis shows a roughly N-S trending shortening. This event is interpreted as related to the opening of the Bransfield Basin located to the south-east.

The Sejong Formation (100–200 m thick) represents a newly recognized Eocene volcaniclastic unit in Barton Peninsula, King George Island, West Antarctica. Detailed field mapping and lithofacies analysis indicate that the formation can be subdivided into three distinct facies associations (FA): (1) spatter/cinder-cone association (FA I), (2) volcaniclastic-apron association (FA II), and (3) distal-apron association (FA III). FA I, occurring at the base of the formation, comprises massive and jointed basalt lavas, which pass laterally into basaltic agglomerates and agglutinates through a transitional zone of fractured basalt lava flows. These field relations suggest fire-fountaining (Hawaiian) to Strombolian eruptions and subsequent emplacement of “ponded” lavas filling the vents of small-scale spatter/cinder cones at the precursory phase of arc volcanism in Barton Peninsula. FA II, unconformably overlying FA I, is represented by very thick, tabular beds of basaltic to andesitic, welded to non-welded, tuff breccias and lapilli tuffs, emplaced by pyroclastic flows (largely block-and-ash flows), with rare intervening andesite lava flows. FA II indicates onset of the main-phase of explosive and effusive eruptions (Vulcanian), probably associated with repetitive extrusions and collapses of lava domes at the summit crater of a stratovolcano, and thereby formation of large volcaniclastic aprons. The changes in eruption styles probably resulted from generation of more evolved (intermediate) magma, possibly due to compositional differentiation of the parental magma, and interaction of the magma with groundwater. FA III is intercalated with FA II as thin lenses and is characterized by fluvial red sandstone/siltstone couplets, locally alternating with channelized mass-flow conglomerates. FA III represents active hydrologic remobilizations during inter-eruptive periods and thereby development of ephemeral streams and floodplains in lowlands on and beyond the distal volcaniclastic aprons. These eruptive and depositional processes indicate a full emergence (subaerial setting) of the King George Island during the Eocene.

Elephant Island is an outcrop of the South Shetland Block, and is located at the southeastern prolongation of the Shackleton Fracture Zone. The South Shetland Block constitutes a continental fragment of the southern branch of the Scotia Arc and has been separated since the Pliocene from the Antarctic Peninsula by the opening of the Bransfield Strait and the transtensional fault zone that extends along the South Scotia Ridge. The northern boundary of the block is determined by subduction at the South Shetland Trench and its eastwards prolongation. The Shackleton Fracture Zone extends up to the South Shetland Block and constitutes the westernmost segment of the Scotia-Antarctic plate boundary. In this tectonic context, Elephant Island permits study of the rocks and the structures that resulted from deformation of the South Shetland Block near the triple junction with the Antarctic and Scotia Plates.

Several lines of evidence point to important and recent uplift of Elephant Island: presence of HP/LT metamorphic rocks, marine terraces, and high relief. This is the consequence of at least two processes: subduction of the thickened crust related to the Shackleton Fracture Zone that produced local crustal thickening and post glacial isostatic rebound.

This paper reports the results of a study of brittle structures in the western and southern cliffs of Elephant Island. It is shown that recent stresses were variable, in accordance with the tectonic setting. The northwestern sectors are dominated by compression with NE-SW and NW-SE trends respectively related to the Scotia-Antarctic sinistral transcurrence and to subduction of the oceanic lithosphere that was modified in the vicinity of the Shackleton Fracture Zone. In the southern sector, extension predominates with approximately WNW-ESE trend, related to Bransfield Strait opening and transtensional faults located along the South Scotia Ridge. In addition, radial extension has been identified in different sectors that may be related to the uplift of the island.

New tectonic and geomorphological data from Elephant Island have been obtained during a cooperative fieldwork campaign carried out in the 2002–2003 season by Brazilian and Spanish groups. The main phases of ductile deformation affecting the high-pressure metamorphic rocks of Elephant Island, D1, D2 and D3, were studied in more detail along a N-S profile in the western sector of the island. D2 was subdivided in two subphases, D2a and D2b. The brittle and brittle-ductile deformation postdating the three main phases was studied systematically for the first time in the island. The measurement of the orientation of more than 200 faults with their kinematics pointed out that normal faults indicating an extensional setting predominate in the southern sector of the island. By contrast, in the northern part of the studied profile, major faults are predominantly reverse, although normal faults are also present, indicating the overprinting of at least two deformation stages. A new 1:50000 topographic map of the island, with 20 m contour interval, was prepared being included in this paper a shadow map from a 3D digital model based on it. Geomorphological features of marine and glacial origin were identified and mapped. The most significant of these are the raised marine platforms up to 150 m a.s.l. at Cape Lindsey area and lower platforms, Holocene raised beaches and moraines at Stinker Point area.

Deception Island (63° S, 60° W) is situated in the South Shetland Islands, and it is the main active volcano in the Bransfield Strait, with recent eruptions in 1842, 1967, 1969 and 1970. Its volcanic and seismic activity has been monitored from 1986 to study the geodynamic activity on the island. In this paper we present the objectives and some results obtained in DECVOL project, a crossdisciplinary study which was planned to evaluate the volcanic status of the island after the crisis occurred during the 1998/1999 campaign, as well as the goals and activities which have been carried out in the framework of GEODEC project, a multidisciplinary project to continue with the studies on the island.

At Allan Hills, south Victoria Land, Antarctica, Mawson tuff breccias are intrusive into Permian and Triassic Beacon strata, contrary to previous reports of the relationship. North of Watters Peak, Mawson intrusive and extrusive rocks, a megaclast unit consisting principally of beds of Member C of the Triassic Lashly Formation, and

in situ

brecciated Permian and Triassic country rock, taken together, comprise an assemblage of Jurassic rocks interpreted as a magmatically-driven collapse structure. At adjacent Coombs Hills the contact at one locality is intrusive but at another the relationships are less clear. The intrusive, rather than stratigraphic, relationship between Mawson tuff breccias and Beacon strata leads to reinterpretation of the Prebble Formation field relations at Otway Massif as also intrusive. Previous interpretations, based on a major unconformity at Allan Hills, of an episode of Early Jurassic pre-Ferrar erosion that created significant topography can no longer be supported.

Volcanism in the Marie Byrd Land (MBL) volcanic province is related to the growth of an 1200 × 500 km structural dome that lies on the Amundsen Sea coast. Spatial and temporal patterns of volcanic activity suggest that dome uplift began around 29–25 Ma and has continued to the present. Uplift has been accompanied by sometimes voluminous basaltic and felsic volcanism and the development of horst and graben structure, with a maximum of ∼3 km of uplift. Estimates of crustal thickness, based on models of gravity data and surface wave dispersion studies, have not resolved questions about the origin of uplift. Mantle plume activity has been proposed; but more detailed tomographic imaging of the mantle, together with seismic determinations of crustal thickness, and the thickness and distribution of sub-ice volcanic rock, are needed to test this, and to answer other petrologic and tectonic questions discussed below.

The Victoria Land Basin is a deep rift margin basin that lies along the Ross Sea margin of the Transantarctic Mountains, Antarctica. Seismic data indicates that the 140 km wide basin contains some 14 km of sediments. Drilling results from the flank of the basin suggests that most of these sediments are late Eocene or younger in age. Four major sequences are defined on the seismic data by angular unconformities indicating several rift episodes. Constraints on the basin formation are derived using flexural cantilever models. The model reproduces the main features (shape, size, timing and broad stratigraphy) of the basin formation moderately well using four rift episodes on five main faults, but does not match the detailed geometry of the seismic stratigraphy.

The results of a stratigraphic study of the western Victoria Land Basin, Antarctica, are summarized. This analysis is based on all existing seismic reflection data integrated with lithological information from fully cored drillholes in the Cape Roberts area of western McMurdo Sound. A number of subsurface seismic reflectors were recognized in the Cape Roberts area and correlated to stratal interfaces previously recognized in the cores. These events were then traced regionally throughout the southern McMurdo Sound, and form the basis for a new seismic stratigraphic subdivision of the Cenozoic section. Key reflectors define boundaries of seismic stratigraphic units, each of which shows distinctive overall cross-sectional geometry and internal reflection character/facies. On this basis, we propose a new model for the evolution of the Victoria Land Basin, invoking five phases of tectonic activity and associated sediment accumulation patterns. Phase 1 (pre-latest Eocene) involved regional uplift and erosion of the Transantarctic Mountains to the immediate west of the basin. Phase 2 (latest Eocene to Early Oligocene) was an Early Rift stage characterized by sediment accumulation in laterally restricted grabens. Phase 3 (Early Oligocene to Early Miocene) was the Main Rift stage, in which sediment accumulation was no longer confined to grabens in the west of the basin, but rather formed an eastward-thickening wedge into the centre of the basin. Phase 4 (Early Miocene) was a consequence of passive thermal subsidence, producing a relatively even blanket of sediment across the entire basin. Phase 5 (post-Early Miocene) was associated with the “Terror Rift” and gave rise to a succession contain both young magmatic rocks and young faults and which thickens markedly into a central depocentre. The new framework allows recognition of thick, post-Early Miocene stratigraphic intervals as yet unsampled by stratigraphic drilling in McMurdo Sound.

Recent kinematic constraints for the region north of the western Ross Sea suggest that there was approximately 150 km of seafloor spreading in the Adare Basin, northeast of Cape Adare, between Chrons 20 and 8 (43 to 26 Ma). This kinematic history has important implications since the 150 km of extension in the Adare Basin occurred immediately north along strike from the Northern Basin of the Ross Sea, whose extensional history is not well known. This paper examines the transition from the structures in the Adare Basin to the structures of the Northern Basin and speculates on the manner in which the extension was accommodated in the Ross Sea. Magnetic anomaly data in the Adare Basin document a sequence of anomalies 18 to 12 formed during a period of very slow spreading. The easternmost part of this sequence, anomalies 16 to 18, coalesces into a single positive anomaly near 72° S, forming a distinct anomaly that can be traced southward from the Adare Basin across the continental margin and down the east side of the Northern Basin to a latitude of roughly 73° S. This observation has important implications for the tectonic history of the Ross Sea since it suggests that most of the extension in the Adare Basin continued into the Northern Basin. This, in turn, suggests that the Northern Basin was formed by a combination of crustal thinning and massive, narrowly focused intrusions.

In 2001 and 2002, the Australian Government acquired approximately 9 000 km of high-quality geophysical data over the margin of East Antarctica between 110–142° E that provide a sound framework for understanding the geology of the region. The data comprise 36-fold deep-seismic, gravity and magnetic data and non-reversed refraction/wide-angle reflection sonobuoys recorded along transects that extend from the lower continental slope out to oceanic crust at a spacing along the margin of approximately 90 km. The continental slope is underlain by a major rift basin beneath which the crust thins oceanwards through extensive faulting of the rift and pre-rift sedimentary section and by mainly ductile deformation of the crystalline crust. Outboard of the margin rift basin, the 90 to 180 km wide continent-ocean transition zone is interpreted to consist primarily of continental crust with magmatic components that can account for the lineated magnetic anomalies that have been interpreted in this zone. The thick sedimentary section in the COT zone is floored by dense lower crustal or mantle rocks indicating massive (>10 km) thinning of the lower and middle crust in this zone. The boundary between the margin rift basin and the COT is marked by a basement ridge which potential field modelling indicates is probably composed of altered/serpentinised peridotite. This ridge is similar in form and interpreted composition to a basement ridge located in a similar structural position at the inboard edge of the COT on the conjugate margin of the Great Australian Bight. On both margins, the ridge is probably the product of mantle up-welling and partial melting focussed at the point of maximum change/necking of crustal thickness. Integrated deep-seismic and potential field interpretations point very strongly to the boundary between unequivocal oceanic crust and largely continental crust of the continent-ocean transition as lying in very deep water, and considerably seaward of most previous interpretations (often based on inadequate seismic data or magnetic data only). We consider the continent-ocean boundary to be well-constrained from 124–131° E and unequivocal from 131–140° E, but open to debate in the sector from 110–124° E. There is a strong degree of pre-breakup symmetry between the conjugate margins of southern Australia and East Antarctica east of about 120° E. In addition to the crustal symmetry, there is also a strong correlation in seismic character between the margins, which allows us to date the major unconformities as probably of base Turonian, Maastrichtian and early Middle Eocene age.

The Australian Antarctic and Southern Ocean Profiling Project has acquired more than 20 000 km of north-south seismic reflection transects every 90 km along the East Antarctic continental margin between 38° E to 164° E. These data provide a unique overview of the broad scale depositional patterns around a large part of the Antarctic margin. Each line was examined and the post-rift section classified according to depositional environment.

The depositional environments recognised are:

1.

Submarine fans.

2.

Contourite drift and canyon complexes.

3.

Mixed contourite-turbidite drift sediments.

4.

Thin separated drifts.

5.

Non-deposition and erosion of older sediments.

6.

Prograding upper slope wedges.

7.

Distal abyssal plain deposits.

We have recognised nine sedimentary provinces on the continental slope and rise, based on the relative dominance of these environments. The distribution of contourite deposits is controlled by sediment input from the continent and by the shape of the margin. Prydz Bay has provided a large amount of sediment over a long period, producing the thickest post-rift sediment pile on the margin. It has been suggested that major sediment inputs have taken place via the Wilkes sub-glacial Basin, the Aurora Basin and Prydz Bay through the Lambert Graben. Our examination of the data implies that only Prydz Bay, western Enderby Land and the area at about Latitude 120° E have received large influxes of sediment, with western Enderby Land being relatively inactive during the Neogene. Sediment thicknesses are large when compared to the conjugate margin of Australia.

Seismic strain release on the Antarctic continent takes place at a much lower rate than in other continental, intraplate areas. Tectonic and glaciogenic forces controlling this observed distribution have previously been discussed in terms of the Antarctic continent only. Improved locations of large earthquakes in the surrounding, oceanic, Antarctic Plate show that a number of these events, including the great 25 March 1998 earthquake occurring between New Zealand and Antarctica, have intraplate settings. Such large episodes of strain-release suggest that it is more appropriate to address controls on Antarctic seismicity by considering the entire plate, including both the central region of continental crust and the surrounding oceanic crust. The catalogued seismicity for 20 years, between 1981 and 2000, is presented for the whole Antarctic Plate together with a discussion of the tectonic settings of the largest continental events and the oceanic events occurring during the same period. The forces acting on the oceanic and continental regions are discussed in the context of the unique tectonic setting of the Antarctic Plate, which is surrounded almost entirely by ocean-ridges. A correspondance exists between regions of low continental seismicity and the most extensive regions of surrounding oceanic Antarctic Plate. This suggests that the oceanic region, acting as a buffer in some places against plate boundary influences on the Antarctic continent, is an additional factor in controlling the distribution of seismicity.

During the last decade a variety of geodetic observations have been carried out in central Dronning Maud Land, East Antarctica, in order to investigate geodynamic and glaciologic phenomena. Of special interest is the interaction of recent and historic ice mass changes and the vertical crustal deformation, which is characterized by the rheological properties of the Earth, especially of the crust and the upper mantle. The geodetic information may help to constrain the recent isostatic uplift pattern, the recent and — using additional age information — past ice sheet configuration in central Dronning Maud Land. Coupling the geodetic data with these additional constraints on recent and past ice mass changes allows a self-consistent glacial load history to be investigated. A spectrum of viable load histories will be examined and the respective isostatic deformation signature will be computed, using a flat earth approach. First model computations will be presented and discussed, aiming to reconcile the modelled vertical uplift signature and the observations.

The Japanese Antarctic Station, Syowa (69° S, 39° E; SYO), is located on Lützow-Holm Bay of western Enderby Land, East Antarctica. Seismic observations at SYO started in 1959, and the arrivaltimes of the major phases for teleseismic events have been reported from the National Institute of Polar Research every year since 1968. Here, we summarize records from local earthquakes around SYO in the last three decades. In particular, the fifteen years since 1987 divided into three periods are examined in detail, with respect to the location of epicenters and estimation of magnitudes. A three-station seismic array was deployed around SYO in 1987–1989. By using these data, epicenters of local earthquakes were determined for the first time. Many different types of earthquakes, such as a mainshock-aftershock sequence, twin earthquake, and earthquake swarms were detected and clearly identified. The seismic activity during this period was higher than that of the following decade. Earthquake location was concentrated along the coast and central Lützow-Holm Bay.

In the next period between 1990–1996, nine local earthquakes were classified in many different types. The seismicity during this period was very low and magnitudes ranged from 0.1 to 1.4. Hypocenters of four earthquakes out of nine were localized in Lützow-Holm Bay and its northeastern coastal area by a single station method using SYO data. One local event was detected in 1997, two events in 1998 and one event in 2001 and 2003, respectively. The low seismic activity has continued to date (December 2003). The observed offshore location and low level off seismic activity is consistent with a glaciogenic component to the stress field causing the earthquakes.

This paper presents the Earth’s interior data of the Antarctic and surrounding regions obtained through the gravimetric tomography method developed by the authors and destined for reconstruction and displaying the structural geological inhomogeneities in different layers. Characteristics of the global geoid height model’s spherical harmonics are the input data for the method. They are both used for determination of the layers’ depths disturbing geopotential and for computing of harmonic dense anomalies. Vertical and lateral sections calculated show a distribution of masses in all range of depths up to 5300 km, geometry and sizes of density inhomogeneities, their displacement in depth under the impact of geodynamic processes, and also correlation of subsurface bodies with the known topographic features. A significant difference between geodynamic processes in geospheres of the core, mantle and crust is emphasized.

Some of the most interesting features of the Earth’s magnetic field and of its time variations are displayed in polar areas, where the geomagnetic field dipole poles are located. Space time models of the geomagnetic field give a mathematical description that allows generally to undertake a common epoch time reduction of magnetic surveys and to extract magnetic anomaly maps after removing the main part of the geomagnetic field; in addition in polar regions geomagnetic field models allow to follow the location of the geomagnetic dip poles in their time wandering. In this work the development of a dedicated regional magnetic reference model for Antarctica (Antarctic Reference Model, ARM) is presented and compared to the well known IGRF (International Geomagnetic Reference Field) model and it is shown that the first is more appropriate to better study the behaviour of secular variation and its unusual characteristics as observed in Antarctica.

Moreover single and multi-station analyses have been applied to the longest available time series of geomagnetic data for Antarctica in order to investigate the most interesting behaviour of secular variation: the geomagnetic jerks. It was found that geomagnetic jerks are also detectable in Antarctica and that they show a peculiar space time structure.

The region of the Ukrainian Antarctic geodetic and topographic surveys is the transition zone, which includes the Antarctic Peninsula with ice streams; large longitudinal fractures known as the Grandidier, Penola and Bransfield straits, separating the island part of the wide shelf from the Peninsula; small archipelagos appear as a result of the ancient ice shelf movement overlapping tectonic processes; and the open sea of the Pacific Ocean’s south-eastern margin. Such physiographic diversity of the region causes a necessity to use different geodetic research methods. The Ukrainian Vernadsky Station (former British Faraday Station) is located at the middle part of the region on the Galindez Island of the Argentine archipelago. Following investigations in this area were carried out under the auspices of the Ukrainian Antarctic Centre within the Ukrainian Antarctic Research State Program for the SCAR GIANT (Geodetic Infrastructure of Antarctic), ANTEC (Neotectonics of Antarctic) and IBCSO (International Bathymetric Chart of the Southern Ocean) Projects:

Several days duration seasonal GPS observations at the “SCAR GPS 2002” site on Galindez Island;

Repeated GPS observations on the British triangulation markers and extension of the geodetic network on the islands;

Large-scale mapping of islands’ topography and terrestrial photogrammetry survey of the island ice cliffs;

Echosounding of the Argentine archipelago’s seabed in unsurveyed shallow water;

Mapping of the Flask Glacier ice stream of the Antarctic Peninsula using ERS Synthetic Aperture Radar (SAR) interferometry data;

Geoid determination of the Bellingshausen Sea based on altimeter data for geological purposes.

As a result of the research different maps of the bottom topography by echosoundings, of the island relief by GPS observations, of topographic features of the moving glacier by the satellite data were created. The mass balance of the island’s ice cap by unconventional terrestrial photogrammetric technique was also studied.

Deception Island (62.93° S, 60.57°W) is one of the few active volcanoes in the Antarctica, whose most recent eruptions took place in 1842, 1967, 1969 and 1970. In the following paper geodetic investigations carried out in this area during the last years are described. During the continuous Spanish campaigns in Antarctica, several scientific groups have developed different projects in order to control deformation the island suffers as a result of its volcanic activity. With this purpose, a geodetic network has been designed and improved. Nowadays, the network consists of twelve stations around Port Foster which are provided with WGS-84 geodetic coordinates with respect to the ITRF2000, and another station at the Spanish Base Juan Carlos I on Livingston Island. Time analysis of these coordinates will lead us to get the horizontal deformation model. On the other hand, a levelling network has been designed to obtain the vertical deformation model. This network is denser in those areas where the volcanic activity is stronger, as at Fumarole Bay and the Hill of Obsidians. GPS, levelling and gravimetric measurements have also been collected in secondary points to obtain an experimental geoid model which makes possible an adequate reference frame for physical applications.

Spain has been taking part in Antarctic research through annual austral summer campaigns since 1987. The volcanic Deception Island in the South Shetland Islands is one of the main working areas. The information collected is numerous and diverse so in many cases is the same one. Also, this information is stored in several alphanumeric and graphic digital formats, and the maps are made in different geodetic and cartographic representation systems. The fundamental data are unified and integrated in SIMAC, a unique information system that can to be used as a “gate” through which the various scientific groups working on Deception Island may exchange data. SIMAC is an example of an Information System applied to Earth Sciences.

PANGAEA Publishing Network for Geoscientific and Environmental Data (http://www.pangaea.de) is an information system aimed at archiving, publishing, and distributing data related to climate variability, the marine environment, and the solid earth. The system is a public “data library” distributing any kind of data to the scientific community through the Internet. Data are stored in a relational database in a consistent format with related meta-information following international standards. Data are georeferenced in space and/or time, individually configured subsets may be extracted. Any type of information, data and documents may be served (profiles, maps, photos, graphics, text and numbers). Operation by Alfred Wegener Institute for Polar and Marine Research (AWI) and Center for Marine Environmental Sciences (MARUM) is assured in the long-term. Both institutions provide the technical infrastructure, system management and support for data management of projects as well as for individual scientists. Most important collections from Antarctic research archived in PANGAEA so far are the data of the Cape Roberts Project, geological maps and age determinations of rock outcrops, a complete set of JGOFS, WOCE, DSDP and ODP data including those from the Southern Ocean, any marine sediment cores, documentation and analytical data from German expeditions and an increasing inventory of data published by the running EPICA project.

Members of the naturally occurring decay series are found throughout the world’s oceans, though in activities that vary by several orders of magnitude within the same decay series. They can be distinguished on the basis of their overall reactivity — e.g., adsorption or incorporation — with particles. Physical and biogeochemical processes in the water column, and close to the sediment-water interface, lead to fractionation of mother and daughter nuclides and hence create disequilibria in the decay series. These disequilibria have become powerful tools in the study of marine processes. In order to illustrate their use in marine sciences, three examples are presented for the Atlantic sector of the Southern Ocean. For the group of particle-reactive radionuclides, the distribution of the short-lived isotope

234

Th (half-life 24.1 days) is used as a measure of export fluxes from the photic layer.

228

Ra and

227

Ac (half-lives 5.8 and 21.7 years, respectively), belong to the more soluble nuclides. In contrast to

234

Th, they are hardly found in the particulate fraction of a sea water sample but instead exist in the dissolved state.

228

Ra is indicative of shelf water input while

227

Ac is a tracer for upwelling deep water masses.

In order to investigate the long-term changes of the geomagnetic field intensity in the Antarctic region, paleomagnetic and rock-magnetic studies have been conducted on a deep-sea sediment core obtained from offshore Wilkes Land, East Antarctica. The core covers the last about 1.1 Ma. Stepwise alternating-field (AF) demagnetization of natural remanent magnetization (NRM) revealed that a great majority of samples are characterized by a single stable component of magnetization, sometimes associated with a secondary component completely demagnetized by a 30 mT AF field. Downcore changes of magnetic concentration represented by magnetic susceptibility (χ) and anhysteretic remanent magnetization (ARM) are a factor of five or less. Variations in magnetic grain size and coercivity are estimated to be small from ratio of ARM to χ and median destructive fields of ARM respectively. These results demonstrate that the core is rock-magnetically homogeneous, and thus could be considered to yield relative paleointensity record. The ratio of the NRM demagnetized at 30 mT (NRM

30mT

) versus the ARM demagnetized at 30 mT (ARM

30mT

), which is the reasonable parameter to eliminate the effects of the secondary remanence, is interpreted as our best approximation for paleointensity estimation. Absence of correlation between the normalized intensity (NRM

30mT

/ARM

30mT

) and the normalizer (ARM

30mT

) shows the appropriateness of the normalization. The obtained record is similar in general to other worldwide marine records. Such a global synchronicity might be attributed to dipole intensity changes.

Textural, mineralogical and geochemical investigations of three sedimentary sequences from the Ross Sea continental slope allow to give some important indications on climatic and environmental changes occurred during the Late Quaternary. The cores show cyclical changes in several proxies (grain size, mineralogical and geochemical parameters) which are in phase with glacial/interglacial changes (MIS 1–8). Such fluctuations are supposed to be driven by changes in transport mechanisms, reworking and provenance of the material, as well as by changes in direction and strength of marine currents induced by variations in the ice coverage.

The strength of interaction between tectonics, ocean circulation and climate is a major concern of palaeoclimate research. To evaluate the strength, we must assess the time of onset and development of the Antarctic Circumpolar Current (ACC) and its likely effects on climate, particularly Antarctic glaciation. Developments in numerical climate modelling, marine geology, tectonics and physical oceanography have cast doubt on widely held assumptions of a causal relationship between the ACC and glacial onset, in the Eocene-Oligocene boundary interval. Here we argue that our best chance to determine ACC onset and development is in the Scotia Sea region (“Drake Passage”), south of South America. There lies the greatest tectonic uncertainty, concerning when a complete deepwater circumpolar pathway was created, and (thus) when the ACC developed as we know it today. There also, the ACC is topographically constrained, and key factors (water mass and sediment distributions, sea-floor spreading history) are sufficiently well known. Determination of the time of onset would enable solution of other questions, such as the nature of Southern Ocean circulation and primary productivity in any period (possibly Oligocene and early Miocene) when Antarctica was glaciated but before a complete circumpolar deep-water pathway existed, and the extent to which ocean circulation changes affected palaeoclimate, particularly Antarctic glaciation. We assess the parameters that might be capable of determining ACC onset, and show that suitable sedimentary records are available in the Scotia Sea region.

Multichannel and high resolution seismic profiles from the central Scotia Sea and northern Weddell Sea show a sequence of seismic units interpreted to be the result of high-energy bottom currents. The seismic character of the units is indicative of active bottom flows, which developed extensive drifts under the influence of the Weddell Sea Bottom Water (WSBW) and the Antarctic Circumpolar Current (ACC). The opening of the connection between Jane Basin and the Scotia Sea is marked by a major regional unconformity that recorded a reorganization of bottom flows. The uppermost deposits are characterized by intensified bottom currents, which may reflect increased production of WSBW.

Radok Lake in Amery Oasis, East Antarctica, has a water depth of ca. 360 m, making it the deepest non-subglacial lake in Antarctica. Limnological analyses revealed that the lake had, despite a 3 m thick ice cover, a completely mixed water column during austral summer 2001/2002. High oxygen contents, low ion concentrations, and lack of planktonic diatoms throughout the water column indicate that Radok Lake is ultra-oligotrophic today. The late glacial and postglacial lake history is documented in a succession of glacial, glaciolimnic, and limnic sediments at different locations in the lake basin. The sediments record regional differences and past changes in allochthonous sediment supply and lake productivity. However, the lack of age control on these changes, due to extensive sediment redeposition and the lack of applicable dating methods, excluded Radok Lake sediments for advanced paleoenvironmental reconstructions.

A survey of some relict and active landforms in the Lachman and Rink Crags areas of NW James Ross Island on the Antarctic Peninsula has yielded new evidence that provides a better understanding of the Holocene morphoclimatic evolution of this currently deglaciated sector of James Ross Island. Six Holocene (mainly land-grounded) glacial advances were delimited by these morphological and stratigraphic studies, dated at 6700–6400, 4900–4400, and shortly after 3900

14

C yr

B.P.

, with three more recent advances, dated by regional correlations, that occurred between the Holocene regional climatic optimum (3900–3000

14

C yr

B.P.

) and the Little Ice Age (ca. 300

14

C yr

B.P.

). In some cases, ice-cored rock glacier formation followed the younger glacier advances. In recent decades, the significant climatic warming recorded in the NE region of James Ross Island has produced a number of changes in the periglacial and glacial landforms. Stone-banked terraces and lobes have developed in the Rink Crags, and protalus rampart formation has ceased in favor of protalus lobe development in the Cerro Triple area. Conical depressions filled with water have also increased in area over the surface of the Lachman II ice-cored rock glacier, threatening to destroy this landform.

Rink Crags Plateau is located on the northwestern part of James Ross Island, northeast of Antarctic Peninsula. Stone-banked lobes and terraces of various sizes are developed in a 1 km

2

area of average 4° slope upon the plateau. The largest lobes rise up to 5 m above the surrounding surface. Monitoring of painted markers upon the stone-banked lobes reveal that superficial movement of the tread surface was rapid on the central upper part of the lobes and terraces, whereas no movement was recorded near the risers. The solifluction velocity on the tread surface is up to 7.4 cmyr

−1

. The lobes and terraces have a distinct frontal ridge. Three lobes were excavated and their internal structures were described. Coarse material accumulates on the riser slope and bank raise. The risers contain two layers of gravels of contrasting fabric. Wedge structures occur at the boundary between the frontal ridge and the tread. We propose that the formation of high risers upon gentle slopes results from rapid gelifluction movement. Differences in the internals structures described in this and previous studies suggest the process of formation is different to those previously proposed.

This paper presents the results of a soil survey carried out in Byers Peninsula to characterize some of the main features of soils and processes involved in soil development in the largest ice-free area in the South Shetland Islands. Soils were sampled in four different sites at altitudes between 24 and 88 m a.s.l., along a transect of about 1.5 km in the southwestern sector of the peninsula. The sampling sites are located on different geomorphological units from the Holocene raised beaches to the pre-Holocene upper marine platforms. It was found that general soil properties and elemental composition differ among the distinctive edaphic environments that conform the soils on the platforms and on the raised beaches. From the platform to the beach, pH and electrical conductivity values decrease, as well as the clay and silt percentages. Increases in carbonate and sand contents were observed along the transect. The variability in some elements (K, Fe, Al, Ca, Sr) appears to be related to mineralogy and parent materials. In the studied soils, the main factors affecting soil development are related to cryogenic processes. Lixiviation and other weathering processes also play a role in soil evolution although their influence is restricted because water circulation is limited to the summer period.