Northern Victoria Land Research Articles

Chemical characterisation of a volcanic event (about AD 1500) at Styx Glacier plateau, northern Victoria Land, Antarctica

AbstractA dark layer (∼1 cm thick, 93.41 m deep) was identified in an ice core (116 m deep, covering the period -1350-1995) drilled at Styx Glacier plateau, northern Victoria Land, Antarctica. The ice-core section was dated around AD 1500 ± 20 by a firn-densification model. A chemical characterisation was performed on ten subsamples (resolution 3 cm) located around the dark layer by ion chromatography. The concentration/depth profiles of anions (Cl-, Br-, NC3-, H2PO4-, SO42-), cations (Na+, NH4+, K+, Mg*+, Ga2^) and some organic anions (acetate, formate, propionate and methanesulphonate (MSA)) indicate very high concentration peaks for all the components. However, non-sea-salt sulphate (nssSo/-) and F- show the greatest increase with respect to background values (370 and 860 times, respectively). A crustal contribution is attributed to Ga2+ and MSA. The profiles of gas-phase emitted substances (HF, HBr, HNOs and carboxylic acid) suggest gas emission just before the volcanic eruption. Chloride depletion is evident in the dark layer with respect to Na+/Cl- sea-water ratio. At present, it is not possible to attribute an unambiguous source to the volcanic event, but several pieces of evidence lead us to believe that this may be a time-limited local event.

Cenozoic climatic change in Antarctica recorded by volcanic activity and landscape evolution

A long-lasting Cenozoic record (∼50 m.y.) of alkaline igneous rocks characterizes northern Victoria Land, Antarctica. Landscape analysis allows distinction between older volcanic and intrusive rocks with well-developed alpine topography sculptured by wet-based glaciers, and younger volcanic cones lacking these features. Many K-Ar and Rb-Sr dates testify that the erosion that formed the alpine landscape ceased between ca. 8.2 and 7.5 Ma. Since ca. 8 Ma, morphological evolution has been driven by cold-based glaciers; warm-based glaciers were no longer active. That this change affected a 300-km-long coastal area suggests a persistent cause of global significance. Glacier dynamics control landscape shaping as a function of ice thickness and temperature, which are driven by climatic conditions. In this view, a significant climatic change occurred in northern Victoria Land between 8.2 and 7.5 Ma. The perfectly preserved serrated alpine ridges, with their delicate spires, testify that no warm-based ice sheets overrode the region after 7.5 Ma and that polar conditions held sway in the Pliocene and Pleistocene Epochs.

Permafrost as a climatic indicator in northern Victoria Land, Antarctica

AbstractKnowledge of permafrost characteristics and distribution in Antarctica and their relationships with present and past climates is still poor. This paper reports investigations on permafrost in an area located between Nansen Ice Sheet to the south and Mount Melbourne (2732 m a.s.l.) to the north. Investigation methods included geomorphological surveys and geoelectrical soundings as well as crystallography, chemical and isotopic analyses of the ground ice. Geomorphological surveys helped to explain the relationships between periglacial landforms (e.g. rock glaciers and patterned ground) and the glacial history of the area. Geoelectrical soundings allowed us to define different ground-ice units in the ice-free areas. Each unit was characterised by a different type of permafrost (dry or ice-poor permafrost, marine or continental massive buried ice and sub-sea permafrost). To identify the nature of ground ice, trenches were dug and some shallow boreholes were drilled to a maximum depth of-3.6 m in massive buried ice. Samples of both ice-poor permafrost and massive ice were collected and analyzed. Chemical, isotopic δ18O and crystal analyses were also carried out. The relationships between climate and thermal regimes of the active layer and the upper part of permafrost were determined using a monitoring station for ground temperatures at Boulder Clay Glacier, near the Italian Antarctic station. During winter, there were several significant thermal-inversion events in the ground, which cannot be explained only by air-temperature changes, suggesting a possible influence of winter snowfall, even if these events are usually considered very rare.

A model of the glacial retreat of upper Rennick Glacier, Victoria Land, Antarctica

AbstractThe morphology of the Lichen Hills in the upper section of Rennick Glacier, Victoria Land, Antarctica, is summarised as follows: (a) a top surface on the volcanic rocks with scattered erratic blocks; (b) an exhumed Kukri Peneplain, sculptured with roches moutonnees with striae and crescentic gouges on which lie moraines and patches of drift of mainly volcanic rocks; (c) a granitic bedrock eroded by glaciers into sharp peaks and cirques on top of which there is a glacial drift attributable to ancient blue-ice areas higher than those observed at present and which may be correlated with the Terra Nova drift (Late Wisconsin); (d) various Holocene ice-cored moraines that are pushed to the lee side of the nunataks arid are often banded in strips of different lithology. The bands of the Holocene moraines are related to the rock complexes that became exposed from the ice during the lowering of the surface of the glacier Analysis of the lithology and pattern of the supraglacial debris, as well as of the blue-ice areas, allows us to construct a depositional model for the moraines, and to relate the glacial drift to blue-ice areas existing since the Last Glacial Maximum (LGM).The proposed model shows the different stages of recession of upper Rennick Glacier that are also valid for similar situations observed in northern Victoria Land. A surface lowering of upper Rennick Glacier of several hundred metres shows that significant changes have occurred at the Pacific edge of the East Antarctic ice sheet since the LGM.

Sea-spray and marine biogenic seasonal contribution to snow composition at Terra Nova Bay, Antarctica

AbstractPrimary and secondary marine aerosol contributions to snow composition in Terra Nova Bay Antarctica, were evaluated by chemical analysis of surface and snow-pit samples. A seasonal pattern of marine inputs, very clear for secondary aerosol (mainly constituted by nssSO4- and methanesulphonic acid (MSA) coming from phytoplanktonic activity) and less evident for sea spray (Na+, CF, Mg2+) was shown by snow-pit samples. Altitude and distance from the coast were found to be the main parameters affecting seasonal change in the composition of snow collected within about a 200 km radius of the Terra Nova Bay Italian base. Using Na+ as a sea-spray indicator and MSA as a biogenic marker, fractionating aerosol effects (which are altitude-induced) as well as source contributions for Cl- and nssSO42- were found. A nssSO42- /MSA ratio of 2.7 (w/w), indicating their distribution from the common source dimethylsulphide, was calculated from Analysis of fresh summer snow collected in horizontal and vertical transects in northern Victoria Land.

Geochemical and isotopic structure of the early Palaeozoic active margin of Gondwana in northern Victoria Land, Antarctica : Rocchi S., Tonarini S., Armienti P., Innocenti F. & Manetti P., Tectonophysics, 1998, 284/3–4 (261–281)

Geochemical and isotopic structure of the early Palaeozoic active margin of Gondwana in northern Victoria Land, Antarctica : Rocchi S., Tonarini S., Armienti P., Innocenti F. & Manetti P., Tectonophysics, 1998, 284/3–4 (261–281)

Mercury, cadmium and lead accumulation in Antarctic mosses growing along nutrient and moisture gradients

Accumulation of Hg, Cd and Pb by moss was studied in a coastal ice-free area (Edmonson Point, northern Victoria Land) in relation to the water and nutrient availability and substratum characteristics. Although metal concentrations in surface soils were among the lowest ever reported from remote areas, those of Hg and Cd in mosses were higher, being in the same range as those usually reported in regional surveys in the northern hemisphere. By contrast, Antarctic mosses showed very low Pb concentrations, and no impact from local human activities was detected. Marine aerosols, seabird guano and volcanic emissions appeared to be the more probable sources of Cd and Hg. Besides atmospheric deposition, the main pathway of metals to mosses was probably through evapo-transpiration at their surface which determines an upward migration of ions and their bioaccumulation.

Geochronology and geochemistry of pre‐Jurassic superterranes in Marie Byrd Land, Antarctica

Marie Byrd Land, Antarctica, is a major part of the proto‐Pacific supercontinental margin. On the basis of new geochronological and geochemical data relating to its pre‐Jurassic evolution, Marie Byrd Land is subdivided into western or interior (“Ross”) and eastern or exterior (“Amundsen”) provinces, equivalent to two superterranes in New Zealand. The Ross province is characterized by Cambrian? metagraywackes and I‐type orthogneiss dated at 505±5 Ma by U‐Pb SHRIMP (Sensitive High Resolution Ion Microprobe). Its magmatic record consists of Devonian‐Carboniferous (375±5 Ma and circa 339±6 Ma), predominantly I‐type granitoids, and further minor granitic magmatism in Permo‐Triassic times. This Paleozoic history is comparable to that of the Gondwana margin in northern Victoria Land, western New Zealand, and SE Australia. The Amundsen province has no observed Paleozoic graywacke succession; evidence from Rb‐Sr and U‐Pb SHRIMP dating supports calc‐alkaline granitoid events in Ordovician/Silurian (450–420 Ma) and Permian (276±2 Ma) times. The latter may be the previously unknown source of Permian volcanic detritus in the Ellsworth and Transantarctic mountains. The Amundsen province is considered to be the equivalent of the Median Tectonic Zone of New Zealand, and arc magmatism of comparable ages is found in the Antarctic Peninsula and Thurston Island. The underlying lithosphere of the two provinces may be distinguished by Nd isotope data; granitoids and metasedimentary rocks of the Ross province have Meso‐Proterozoic Nd model ages, generally 1300–1500 Ma, compared to 1000–1300 Ma for the Amundsen province. On the basis of published palaeomagnetic data, the two provinces amalgamated to form Marie Byrd Land in mid‐Cretaceous times, only shortly before rifting of the New Zealand continental block away from Antarctica.

Spatial distribution and seasonal pattern of biogenic sulphur compounds in snow from northern Victoria Land, Antarctica

A study of the spatial and temporal distribution of methane sulphonic aeid (MSA) and nssSO42-concentrations in snow-pit samples was performed to determine the main and secondary sources, transport effects and seasonal pattern of biogenic sulphur compounds. Four snow pits, about 3 m deep, excavated at the same time at different altitudes (870-2960 m a.s.1.) in northern Victoria Land, Antarctica, gave coherent information about the effect of altitude and seasonality on the snow chemical composition. A progressive, well-defined decreasing concentration trend is shown as altitude increases, with the biggest effect in the first 1000 m a.s.1. At higher altitudes, biogenic sources make the most important contribution to the tola! sulphate balance with respect to sea-mray input. Particular attention was paid to the relationship between MSA and nssSO42-by using MSA as a univoca] biogenic marker. The nssSO42-/MSA ratio was evaluated with respect to altitude and seasonality to determine the effect of transport mechanisms (such as long-range transport and fractionation) or non-dimethyl sulphide sources on nssSO42-snow content.

Geochemical and isotopic structure of the early Palaeozoic active margin of Gondwana in northern Victoria Land, Antarctica

The regional distribution of geochemical and isotopic compositions of granitoid rocks from a Gondwana continental margin is studied to highlight its structure and geodynamic evolution. The intrusive rocks emplaced during the early Palaeozoic Ross Orogeny in northern Victoria Land (Antarctica) constitute a high-K calc-alkaline association. The geographic patterns of isotope and geochemical data on granitoid rocks allow the distinction of two portions of the continental margin, separated by a sharp discontinuity. The portion towards the palaeo-Pacific Ocean (Oceanward Side) displays strongly regular inland increase of Sr- and decrease of Nd-isotope ratios, coupled with analogous variations in major and trace elements; on this basis we infer a NW-SE-trending margin affected by SW-directed subduction. The portion towards the East Antarctic Craton (Continentward Side) shows a similar regular variation only for Nd isotope compositions, consistent with a hypothesis of a N-S-striking margin with west-ward subduction. In the Oceanward Side, isotope and trace-element characteristics suggest that the granites were generated by extensive interaction of mantle-derived magmas with high-level crustal melts. The origin of Continentward Side intrusives is compatible with a process of interaction between mantle-derived melts and a mafic granulite lower crust. The granitoids of the two crustal sectors share the same Proterozoic Sm-Nd model ages, suggesting that they both belong to the same crustal province. We interpret this arrangement of crustal segments as due to the shift and rotation of a forearc sliver of the Gondwana margin. This movement was likely enhanced by oblique subduction under an irregular margin weakened by the presence of a magmatic arc.

Atmospheric dust concentration record from the Hercules Névé firn core, northern Victoria Land, Antarctica

During the ninth Italian Antarctic Expedition, a 22 m deep firn core was drilled on the Hercules Névé (ΗΝ) in the Transantarctic Mountains, northern Victoria Land, Antarctica, The continuous dust record from HN, spanning 70 years from 1927 to 1994, displays sharp differences between the upper 15.5 m and the bottom part. The background of dust concentration in the upper part is quite homogeneous, with values around 6.5 x 103 particles g −1 of water, and some peaks reaching maximum values of 1.0-1.5 x 104 particles g−1 of water. in this part the volume-size distribution of particles shows a relative maximum around 0.9 μm while a second maximum occurs for particles larger than 12 μm . The larger particles are likely to have a local origin, while the small-size component may be representative of long-range transport dust. Below 15.5 m the record shows higher values in both background and peak concentration, with mean values of 1.6 x 104 particles g−1. The volume-size distribution changes from 0.9 to 1.5μm in parallel with the increase of dust concentration. The dust record suggests significant increases in concentration for the periods 1932-42 and 1951-64. It suggests some correlations with precipitation anomalies over South America and indirectly supports the hypothesis that small-sized dust at HN may originate from South America.

Chemical and isotopic profiles from snow pits and shallow firn cores on Campbell Glacier, northern Victoria Land, Antarctica

The chemical (Na+, K+, Mg2+, Ca2+, CH3SO3 − (MSA), Cl− , NO3 − , SO4 2-) and isotopic (δl8O) composition of snow and firn samples from Campbell Glacier, northern Victoria Land, Antarctica, was studied to evaluate the accumulation rate of snow and to investigate the chemical contribution from some emission sources (marine biogenic activity, sea and crust). During the 1994-95 Italian Antarctic Expedition, snow and firn were collected from snow pits and from cores obtained from drilling at three sites (A: 74°41'S, 164°30' E; B: 74°15' S, 164° '04' E; C: 73°45' S, 163°20' E), located ai 50 m (on the floating glacier tongue), 800 m and 1580 m a.s.l., respectively. The mean concentration of sea salt decreased with increasing distance from the coast and with altitude. Generally, the Na+/K+ and Na+/Ca2+ ratios were much lower than the bulk sea-water ratios at sites B and C. The MSA showed mean concentrations (0.27 and 0.17 ¿teq 1 at sites B and C, respectively) consistent with data obtained from other Antarctic sites. The mean concentrations of NO3 ranged from 2.1 μeq 1−1 (site A) to 0.97 μeq1 1 (site C).The mean nss (non-sea-salt) SO4 2-/SO4 2- ratio was -0.055,0.54 and 0.42 at sites A, B and C, respectively. Moreover, the relationship between a2+, nssCa2+, SO4 2- and nssSO4 was quite different at sites B and C. in order to expla in the relationships between the elements and compounds studied at these sites, chemical fractionation and/or reactions inside air masses and différent origin of the air masses at the two sites should be considered. A comparison of the isotopic and chemical profiles was carried out in order to provide a more reliable chronological scale. The chemical and δ18O seasonal variations recorded along the firn cores from the upper site of Campbell Glacier seem to be fairly homogeneous. This made it possible to identify many annual cycles (14-18 years for the 7 m firn core). Using the measured density values, the accumulation rale was also calculated for lower and upper Campbell Glacier. It did not appear to differ between the two sites (150-170 kg m −2a−1 at site B and 140-180 kg m−2a−1at site C) and is in keeping with rates calculated previously for the same area.

70 years of northern Victoria Land (Antarctica) accumulation rate

Measurements of oxygen isotope ratio , major anions and cations, insoluble dust and tritium were performed every 4-6 cm along the Hercules Névé (northern Victoria Land, Antarctica) 22 m firn core. Concentration/depth profiles for H2O2, methane sulphonic acid and non-sea-salt sulphate (nssSO4 2-) were used to obtain a dating for the core by a multiparametric method involving a normalisation procedure and a linear combination of original profiles. This dating was compared with the and dust records to obtain a reliable identification of successive annual snow layers. The time-scale obtained from the seasonally varying signals was confirmed by an absolute date obtained from the 1965 thermonuclear atmospheric bomb test tritium peak. Around 70 years (1926-94) of annual accumulation rate data were obtained from the core. variations recorded along the core may be ascribed to seasonal variations of this parameter related to temperature variations.

Preliminary evidence of a biomass-burning event from a 60 year-old firn core from Antarctica by ion chromatographic determination of carboxylic acids

An ion chromatographic method for the determination of fluoride and some organic anions (lactate, acetate, glycolate, propionate, formate, methane sulphonate and pyruvate) at sub-μgl−1 concentration levels is applied to a 22 m (63 years) firn core drilled at Hercules Névé, northern Victoria Land, Antarctica. The first effective distribution data of acetate, propionate and formate for this region are reponed here. Mean values of 9.9,7.7 and 2.4 μgl−1 were calculated for acetate, Formate and propionate, respectively, in the absence of particular events (background values). The temporal (1928-82) concentration/depth profiles of these components showed a probable long-term biomass-burning event in the 1930s that can be related back to processes in the Southern Hemisphere. Such burning events may be demonstrated from the simultaneous concentration increase of carboxylic acid, potassium, ammonium and fluoride and from a very high dust content. Similar increasing trends in the same time period are not shown by other snow components usually considered as source indicators (methane sulphonic acid: biogenic marker; nssSO4 2- : biogenic and volcanic indicator; Na+ and Cl−: sea-spray contribution; Ca2+ : crustal input), so it was possible to exclude such alternative explanations.

P-T paths and migmatite formation: An example from Deep Freeze Range, northern Victoria Land, Antarctica

Migmatites exposed in the Deep Freeze Range, northern Victoria Land, Antarctica contain the mineral assemblage biotite + quartz + plagioclase + K-feldspar ± garnet ± cordierite ± sillimanite in mesosomes, with concordant and discordant leucosomes. Partial melting is considered the main migmatite-forming process at approximately 700–750 °C and 4–5 kbar. In mesosomes, garnet displays contrasting microstructural and compositional features. In some samples, spessartine-rich almandines record growth zoning in core regions. These garnets, together with cordierite and K-feldspar, grew along the main foliation at the expense of biotite and sillimanite. This textural evidence suggests a PT heating path due to regional low P-high T metamorphism linked to the Ross Orogeny. In other samples, spessartine-poor almandines are resorbed and overgrown with coronas consisting mainly of cordierite aligned along the main foliation. In these rocks, the matrix is defined by the association biotite + cordierite; relics of sillimanite are present in cordierite. These textural features are indicative of an early higher pressure assemblage (garnet + sillimanite) that was overprinted by a lower pressure assemblage containing cordierite as a stable phase. These samples follow an isothermal decompression path in P-T space. Data suggest two contrasting P-T paths which are interpreted as P-T trajectories of different crustal levels in the same tectonic setting that developed during the Cambro-Ordovician Ross Orogeny.

Cenozoic geodynamics of the Ross Sea region, Antarctica: Crustal extension, intraplate strike‐slip faulting, and tectonic inheritance

An integrated study of onshore and offshore geology of the Ross Sea region (namely, Victoria Land, north of Ross Island, and the Ross Sea, Antarctica) has revealed a complex, post‐Eocene tectonic framework. Regional NW‐SE right‐lateral, strike‐slip faults are the outstanding feature of this framework and overprint an older Mesozoic extensional event, responsible for formation of N‐S basins in the Ross Sea. The Cenozoic framework includes kinematic deformation and reactivation along the NW‐SE faults, including formation of pull‐apart basins, both positive and negative flower structures, and push‐up ridges. N‐S extensional faults are well developed between NW‐SE faults and indicate E‐W extension during the Cenozoic, produced by the NW‐SE right‐lateral strike‐slip motion together with regional crustal extension. NNW‐SSE compression, induced by the right‐lateral, strike‐slip kinematics, is indicated by locally inverted NE‐SW faults and basins. The evolution, geometry, and location of the Rennick Graben and the Lanterman Range fit well into this model. Variations in the deformational style across the region can be linked to corresponding variations in the bulk crustal rheology, from brittle behavior in the west, to ductile deformation (at subseismic‐scale resolution) near the Eastern Basin. A semibrittle region that favors N‐S clustering of Cenozoic magmatic activity lies in between. In this region, Cenozoic volcanoes develop at the intersections of the NW‐SE and the major N‐S faults. The NW‐SE faults cut almost continually from the Ross Sea to East Antarctica through lithospheric sectors with different rheology and thickness. At least two of the NW‐SE faults correspond to older Paleozoic terrane boundaries in northern Victoria Land. The NW‐SE faults link in the Southern Ocean with major transform faults related to the plate motions of Australia, New Zealand, and Antarctica.

Mutinaite, a new zeolite from Antarctica: The natural counterpart of ZSM-5

Mutinaite is the third new zeolite from Ferrar dolerites at Mt. Adamson (Northern Victoria Land, Antarctica). The mineral occurs as subspherical aggregates of tiny radiating lath-like fibres or as aggregates of transparent, colourless to pale-milky, tiny tabular crystals; it has vitreous luster, white streak and good 100 cleavage. Mutinaite is brittle with dmeas = 2.14(3) and dcalc = 2.17 g/cm3. Optically, it is biaxial negative with α = 1.485(2), β = 1.487(2) and γ = 1.488(2). The orientation is X = b, Y = a, Z = c. Mutinaite is orthorhombic with a = 20.223(7), b = 20.052(8), c = 13.491 (5)Å, space group Pnma. The strongest powder X-ray diffraction lines are (d(Å), I, hkl): 11.20, 84, 101, 011; 9.98, 35, 200,020; 3.85, 100, 501, 051; 3.75, 98, 303; 3.67, 27, 133; 3.00, 32, 503. The framework topology is that of the synthetic zeolite ZSM-5. The chemical formula is: (Na2.76K0.11Mg0.21Ca3.78)Σ = 6.86(Al11.20Si84.91)Σ=96.11O192 · 60H2O. The Si/Al ratio, equal to 7.6, is the highest found in a natural zeolite. Thermal stability and rehydration capacity are very high. The name is from Mutina, the ancient Latin name of the city of Modena.

Crystal structure of the zeolite mutinaite, the natural analog of ZSM-5

We describe the crystal structure of the high-silica zeolite mutinaite, recently found at Mt. Adamson (Northern Victoria Land, Antarctica). Mutinaite is the natural counterpart of the synthetic zeolite ZSM-5. The new mineral, (Na 2.76 K 0.11 Mg 0.21 Ca 3.78 ) (Al 11.20 Si 84.91 ) · 6O H 2 O H 2 O, is orthorhombic, space group Pnma, with a = 20.201(2), b = 19.991(2), and c = 13.469(2) A. A single-crystal X-ray diffraction experiment was performed at the synchrotron radiation source ESRF (Grenoble). No Si-Al order in the framework has been detected. Large distances between ions in the channels and framework oxygens suggest weak interactions between the framework and extraframework species.

Petrology and Geochronology of Eclogites from the Lanterman Range, Antarctica

The mafic eclogites of the Lanterman Range are the first record of a well-preserved high-pressure assemblage from the Pacific end of the Transantarctic Mountains. They occur among pods and lenses (from <1 to 30 m in size) of mafic and ultramafic metamorphic rocks that constitute a narrow zone intercalated with amphibolite-facies metasediments. This zone extends along the faulted contact between the Wilson Terrane and the Bowers Terrane, in northern Victoria Land. Most of the amphibolites and retrogressed eclogites analysed have geochemical compositions that resemble transitional to E-type mid-ocean ridge basalt (MORB) and Nd isotope data indicative of differentiation from a depleted mantle source. The age of the igneous precursors is not well determined, but Sm–Nd whole-rock data indicate a Neoproterozoic age, most probably around 700–750 Ma. For this group of metabasites a tectonic setting of an incipient ocean basin is proposed on geological and geochemical grounds. In contrast, the well-preserved eclogites are characterized by strong enrichment in more incompatible elements and pronounced negative Ta and Nb anomalies in MORB-normalized element patterns. Geochemical and Nd isotope data suggest that they are derived from a different mantle source with an enriched signature. The age of the protolith of the well-preserved eclogites, however, remains unconstrained. In the well-preserved eclogite samples the reaction textures testify to three main metamorphic states: (1) an eclogite facies stage, (2) a medium-pressure amphibolite facies stage, and (3) a low-pressure amphibolite facies stage. The high-pressure event occurred at temperatures of up to 850°C based on garnet and omphacite thermometry and at a minimum pressure of 15 kbar based on the jadeitic content of omphacites. Internal Sm–Nd isochrons from two well-preserved eclogites are 500±5 Ma (rutile, clinopyroxene, amphibole, whole rock and garnet) and 492±3 Ma (rutile, clinopyroxene, whole rock and garnet). Rutile–whole-rock 238U-206Pb ages ( 500 Ma) overlap the range of the Sm–Nd mineral ages. The inferred P–T path, the microtextural features and the overlap of the Sm–Nd garnet ages with the range of the 238U-206Pb rutile–whole-rock ages indicate fast cooling and suggest that the time of the high-pressure event was 500 Ma. These data place both the formation and exhumation of eclogite within a convergent plate margin setting, thus documenting the subduction–accretional nature of the early Palaeozoic Ross Orogen in northern Victoria Land.

Petrology and Geochronology of Eclogites from the Lanterman Range, Antarctica

The mafic eclogites of the Lanterman Range are the first record of mineral ages. The inferred P–T path, the microtextural features a well-preserved high-pressure assemblage from the Pacific end of and the overlap of the Sm–Nd garnet ages with the range of the the Transantarctic Mountains. They occur among pods and lenses U–Pb rutile–whole-rock ages indicate fast cooling and suggest (from <1 to ~30 m in size) of mafic and ultramafic metamorphic that the time of the high-pressure event was ~500 Ma. These data rocks that constitute a narrow zone intercalated with amphiboliteplace both the formation and exhumation of eclogite within a facies metasediments. This zone extends along the faulted contact convergent plate margin setting, thus documenting the subduction– between the Wilson Terrane and the Bowers Terrane, in northern accretional nature of the early Palaeozoic Ross Orogen in northern Victoria Land. Most of the amphibolites and retrogressed eclogites Victoria Land. analysed have geochemical compositions that resemble transitional to E-type mid-ocean ridge basalt (MORB) and Nd isotope data indicative of differentiation from a depleted mantle source. The age of the igneous precursors is not well determined, but Sm–Nd whole