Northern Victoria Land Research Articles

Relationships between periglacial features and vegetation development in Victoria Land, continental Antarctica

AbstractThe relationships between vegetation patterns and periglacial features and their underlying ecology are still poorly understood and lack specific investigations in Antarctica. Here we present the results of vegetation colonization of different types of sorted patterned ground and gelifluction features (lobes and terracettes) at four sites in northern Victoria Land. This paper aims to understand the relationships between vegetation and the most widespread periglacial features in Victoria Land, discuss the role of periglacial features and vegetation in determining the ground surface temperature, and assess whether periglacial features provide ecological niches for vegetation colonization and development. Vegetation patterns are influenced by the feature type, mainly relating to patterned ground and debris island versus gelifluction features. The relations between vegetation and the periglacial features investigated in continental Antarctic are similar to those described for the Arctic, although in this part of the Antarctic vegetation is exclusively composed of cryptogams. Frost heave, ground texture and relief associated with different types of periglacial features provide a range of ecological niches sustaining vegetation biodiversity. Our data confirm the importance of periglacial features in shaping flora and vegetation biodiversity, as previously assessed only for the soil fauna in continental Antarctic.

Aeolian dust in the Talos Dome ice core (East Antarctica, Pacific/Ross Sea sector): Victoria Land versus remote sources over the last two climate cycles

AbstractA new ice core (TALDICE) drilled at Talos Dome (East Antarctica, Ross Sea sector) preserves a ca. 250 ka long record of palaeoclimate and atmospheric history. We investigate dust variability and provenance at the site during glacial periods and the Holocene through the Sr–Nd isotopic composition of ice core dust and potential source areas (PSA). We provide new isotopic data on dust sources from Victoria Land such as regoliths, glacial drifts, aeolian sands and beach deposits. Some of these sources are located at high altitude and are known to have been ice free throughout the Pleistocene. The major features of the TALDICE dust record are very similar to those from central East Antarctica. During glacial times, South America was the dominant dust supplier for Talos Dome as well as for the entire East Antarctic plateau. Conversely, during the Holocene the principal input of mineral dust at Talos Dome probably derives from proximal sources which are the ice‐free areas of northern Victoria Land, located at similar altitude with respect to the drilling site. Atmospheric mobilisation of dust from these neighbouring areas and transport inland to Talos Dome can be ultimately associated with advection of maritime air masses from the Pacific/Ross Sea region. Copyright © 2010 John Wiley & Sons, Ltd.

Late Miocene volcanic sequences in northern Victoria Land, Antarctica: products of glaciovolcanic eruptions under different thermal regimes

Late Miocene (c. 13–5 Ma) volcanic sequences of the Hallett Volcanic Province (HVP) crop out along >250 km of western Ross Sea coast in northern Victoria Land. Eight primary volcanic and six sedimentary lithofacies have been identified, and they are organised into at least five different sequence architectures as a consequence of different combinations of eruptive and/or depositional conditions. The volcanoes were erupted in association with a Miocene glacial cover and the sequences are overwhelmingly glaciovolcanic. The commonest and most representative are products of mafic aa lava-fed deltas, a type of glaciovolcanic sequence that has not been described before. It is distinguished by (1) a subaerially emplaced relatively thin caprock of aa lavas lying on and passing down-dip into (2) a thicker association of chaotic to crudely bedded hyaloclastite breccias, water-chilled lava sheets and irregular lava masses, collectively called lobe-hyaloclastite. A second distinctive sequence type present is characterised by water-cooled lavas and associated sedimentary lithofacies (diamictite (probably glacigenic) and fluvial sands and gravels) similar to some mafic glaciovolcanic sheet-like sequences (see Smellie, Earth-Science Reviews, 74, 241–268, 2008), but including (for the first time) examples of likely sheet-like sequences with felsic compositions. Other sequence types in the HVP are minor and include tuff cones, cinder cones and a single ice-marginal lacustrine sequence. The glacial thermal regime varied from polar, characterised by sequences lacking glacial erosion, glacigenic sediments or evidence for free water, to temperate or sub-polar for sequences in which all of these features are conspicuously developed.

Isotopic composition and thermal regime of ice wedges in northern Victoria Land, East Antarctica

AbstractIce wedges, with tops located 27 to 55 cm below the ground surface, were studied over several summers between 1998 and 2006 at three sites with differing elevations in northern Victoria Land, East Antarctica. The thermal regime, based on data‐logger measurements over five years, exhibits very low temperatures, an inferred absence of snow, and high temperature gradients between the ground surface and the top of the ice wedge that may trigger cracking. A co‐isotopic study of the wedge‐ice oxygen (δ18O) and hydrogen (δD) isotopic values shows extremely negative deuterium excess values and a strong divergence from the expected precipitation. These values and observations of hoarfrost crystals in ice‐wedge cracks during summer field surveys indicate that sublimation processes control the formation of ice in wedges, especially at high elevations within this region. Copyright © 2010 John Wiley & Sons, Ltd.

Arc accretion to the early Paleozoic Antarctic margin of Gondwana in Victoria Land

The Antarctic Ross Orogen was built up during the early Paleozoic in the framework of the convergence between the Paleo-Pacific oceanic plate and the Gondwana continental margin. Models for the Ross Orogen in northern Victoria Land are based on terranes having a variable provenance with respect to the margin. However, recent studies provide evidence for the occurrence of different pieces of the lithospheric puzzle: (i) the Wilson continental magmatic arc, representing the main part of the active Gondwana margin, (ii) the Bowers arc–backarc system, (iii) the Admiralty crustal ribbon including continental material of the Wilson forearc, and (iv) the newly discovered, Cambrian oceanic magmatic Tiger arc, along the Ross Sea coast. An updated model is presented in which, after the Early Cambrian magmatic activity of the Wilson arc, a retreat of the subduction zone in the Early–Middle Cambrian gave way to boudinage of the Wilson forearc, trenchward arc migration, opening of the Bowers backarc basin and inception of the outboard Tiger subduction zone. Renewed convergence resulted in the development of the Middle Cambrian Bowers arc, closure of the backarc and deep underthrusting of portions of it at the Middle–Late Cambrian. Finally, in the latest Cambrian to earliest Ordovician, fast exhumation was coupled in the north with erosion and sediment shed to the northeast, and with extension and potassic magmatism in central and southern Victoria Land.

Haplotype diversity in the Antarctic springtailGressittacantha terranovaat fine spatial scales - a Holocene twist to a Pliocene tale

AbstractThe mitochondrial COI gene of the Antarctic springtail,Gressittacantha terranova, was sequenced across a polar coastal landscape at Terra Nova Bay, northern Victoria Land. Samples from two altitudinal transects in the foothills directly south of Campbell Glacier were compared with samples from Springtail Valley (northern foothills) as an external reference population. We found that mtDNA haplotypes clustered into two lineages (clades) with a mean sequence divergence of 10% (uncorrected distance). However, there was no phylogeographic structure found at this spatial (landscape) scale with haplotypes from both divergent clades found sympatric across most populations. At the landscape scale, the considerable genetic divergence revealed withinG. terranovais around five times greater than any other continental Antarctic springtail examined to date. These data indicate a Pliocene divergence event inG. terranovaaround 4–5 million years ago. The unusual distributional profile of haplotypes - occurrence of multiple haplotypes at single sites and genetic contiguity between sites that are not physically contiguous - suggests a subsequent ‘reshuffling’ of haplotypes in the Holocene that has an ecological basis.

Notes on the lichen genusRhizoplacafrom continental Antarctica and on some other species from northern Victoria Land

AbstractFive taxa of the generaOmphalodinaandRhizoplacaknown from continental Antarctica are reassessed in order to identify a remarkable species collected from northern Victoria Land, for which the new combinationRhizoplaca macleanii(C.W. Dodge) Castello is proposed here. This poorly known species is known only from continental Antarctica. Two synonyms are discussed:Omphalodina exsulans(Th. Fr.) C. W. Dodge andO. siplei(C. W. Dodge & G. E. Baker) C. W. Dodge are synonyms ofRhizoplaca melanophthalma(DC.) Leuckert & Poelt. The correct name of another species isTephromela priestleyi(C. W. Dodge) Øvstedal. The nameO. johnstonii(C. W. Dodge) C. W. Dodge should be abandoned, type material being too scanty for a reliable identification. A contribution to the flora of the Terra Nova Bay area (northern Victoria Land) is provided, with two additional species, includingBuellia vilisTh. Fr. new to Antarctic regions, and two nomenclatural corrections.

The Dorn gold deposit in northern Victoria Land, Antarctica: Structure, hydrothermal alteration, and implications for the Gondwana Pacific margin

The Dorn gold deposit in northern Victoria Land, Antarctica is a fault related gold-only deposit and it represents the first described occurrence of gold mineralization in Paleozoic terranes of the Antarctic continent. The deposit is hosted in lower greenschist facies Middle Cambrian metavolcanic and metasedimentary rocks of the Bowers terrane. Gold-bearing veins are located in a brittle–ductile reverse high-strain zone, which was produced by transpressional deformation that overprints the structures of the Cambrian–Ordovician Ross Orogeny. The vein system is surrounded by a hydrothermal alteration zone that is as much as 300-m-wide, where the host rocks are partially to completely transformed into Fe–Mg carbonate-rich rocks with different degrees of replacement of the original mineralogy and texture. The type of host rock, the temperature estimates for mineralization from 290–320 °C, the quartz dominant vein system with sulfides and Fe-rich carbonates, and the controlling structures linked to a convergent margin tectonic setting together suggest that this mineralized vein system can be classified as an orogenic gold deposit. Close analogies are found with deposits of the Stawell zone in western Victoria, which is consistent with the correlation between units and hydrothermal events in northern Victoria Land and southeastern Australia.

Fault–slip analysis and transpressional tectonics: A study of Paleozoic structures in northern Victoria Land, Antarctica

The brittle structures of the Bowers Mountains (northern Victoria Land, Antarctica) have been studied in order to fully characterise the poorly described pre-Cenozoic brittle tectonics of this area. Field work revealed that the dominant structures are steeply-dipping reverse and strike-slip faults, locally associated with positive flower structures, diffuse veining and hydrothermal alteration. Field observations are combined with different methods of inversion of fault–slip data and with use of different open-source computer programs, that calculate resolved stress tensors and P– B– T axes in order to unravel the complex polyphase brittle architecture. The resolved regional stress field is characterized by E– W trending, horizontal σ 1 and local rotations into NE–SW directions in the Lanterman Range/Sledgers Glacier area, due to subsequent block rotation or to the interference between the far-field stress with pre-existing ductile discontinuities. The paleostress regime, unique overall structural framework and association with hydrothermal veining together with the strong similarities to deformation related to the Benambran Orogeny in the Lachlan fold belt in SE Australia supports the occurrence of a Late Ordovician–Silurian deformational event in northern Victoria Land (Antarctica).

Thermal state of permafrost and active‐layer monitoring in the antarctic: Advances during the international polar year 2007–2009

AbstractResults obtained during the International Polar Year (IPY) on the thermal state of permafrost and the active layer in the Antarctic are presented, forming part of ANTPAS (‘Antarctic Permafrost and Soils’), which was one of the key projects developed by the International Permafrost Association and the Scientific Committee for Antarctic Research for the IPY. The number of boreholes for permafrost and active‐layer monitoring was increased from 21 to 73 during the IPY, while CALM‐S sites to monitor the active layer were increased from 18 to 28. Permafrost temperatures during the IPY were slightly below 0°C in the South Shetlands near sea‐level, showing that this area is near the climatic boundary of permafrost and has the highest sensitivity to climate change in the region. Permafrost temperatures were much lower in continental Antarctica: from the coast to the interior and with increasing elevation they ranged between −13.3°C and −18.6°C in Northern Victoria Land, from −17.4°C to −22.5°C in the McMurdo Dry Valleys, and down to −23.6°C at high elevation on Mount Fleming (Ross Island). Other monitored regions in continental Antarctica also showed cold permafrost: Queen Maud Land exhibited values down to −17.8°C on nunataks, while in Novolazarevskaya (Schirmacher Oasis) at 80 m a.s.l. the permafrost temperature was −8.3°C. The coastal stations of Molodeznaya at Enderby Land showed permafrost temperatures of −9.8°C, Larsemann Hills – Progress Station in the Vestfold Hills region – recorded −8.5°C, and Russkaya in Marie Byrd Land, −10.4°C. This snapshot obtained during the IPY shows that the range of ground temperatures in the Antarctic is greater than in the Arctic. Copyright © 2010 John Wiley & Sons, Ltd.

A common volatilization trend in Transantarctic Mountain and Australasian microtektites: Implications for their formation model and parent crater location

We studied the variations of the volatile major elements Na and K in Transantarctic Mountain microtektites and Australasian microtektites with distance from the putative source crater location in Indochina. The dataset includes 169 normal-type Australasian microtektites (101 from this study and 68 from the literature) from 24 deep-sea sediment cores up to 8000 km from Indochina, and 54 Transantarctic Mountain microtektites from northern Victoria Land, 11 000 km due southeast of Indochina. Normal-type (MgO < 5.5 wt.% and SiO 2 = 60–78 wt.%) Transantarctic Mountain microtektites and Australasian microtektites share a common volatilization trend with Na and K contents decreasing with distance from Indochina. The average total alkali (Na 2O + K 2O) concentrations at distance ranges of 1000–2000 km, 2000–4000 km, 4000–8000 km and > 8000 km are 4.27 ± 0.67 wt.% ( n = 84), 3.20 ± 1.21 wt.% ( n = 50), 2.10 ± 0.25 wt.% ( n = 35) and 1.25 ± 0.25 wt.% ( n = 54), respectively. The trend highlights a relationship between increasing loss of volatiles in microtektites with longer trajectories and higher temperature-time regimes which should be taken into account in microtektite formation modeling. The trend is consistent with a previous hypothesis that Transantarctic Mountain microtektites belong to the Australasian strewn field and that Indochina is the target region for the parent catastrophic impact.

Cenozoic thermal evolution of lithospheric mantle in northern Victoria Land (Antarctica): Evidences from mantle xenoliths

Thermobarometry of spinel peridotites collected in northern Victoria Land in Cenozoic basalts of the Mt Melbourne Volcanic Province, reveals warming of local lithospheric mantle, marked by a shift of geothermal gradient from 0.5 °C/km to ∼ 3 °C/km during the development of Cenozoic magmatism related to the opening of the Ross Sea rift system. We suggest that a significant uplift fraction of the rift shoulder on the West Antarctic margin is due to the change in olivine molar volume induced by mantle heating. The heat source is provided by enhancement of asthenospheric convection induced by an “edge effect” in the mantle circulation, following the opening phase of the Ross Sea. Besides explaining the asymmetric uplift of the rift shoulder corresponding to the Transantarctic Mountains, this mechanism satisfactorily accounts for the time scale (∼ 10 Ma) and most of total uplift (∼ 3000 m) of the western border of the Ross Sea in northern Victoria Land.

Assessment of deep electrical conductivity features of Northern Victoria Land (Antarctica) under other geophysical constraints

The lithospheric and crustal structure of the Victoria Land continental block (Antarctica) has been studied by geological and geophysical surveys. Among them magnetovariational investigations (MV) have been addressed to highlight the deep electrical conductivity patterns which contribute to the understanding of continental rifting and tectonic setting of the region. The hypothetical event map for H linearly polarized perpendicular to the coast indicates a possible broad coast parallel conductivity anomaly zone. Despite the coast effect, this feature could be related to the deep upper mantle thermal anomaly leading to Cenozoic uplift of the Transantarctic Mountains rift flank. However, both the hypothetic event map polarized parallel to the coast and the induction arrows suggest that the area of enhanced conductivity may be confined to the Deep Freeze Range crustal block along the western flank of the Mesozoic Rennick Graben. We also discuss the possible association between increased conductivity over the Southern Cross block and extensive Cenozoic alkaline plutonism.

Pressure‐induced incipient amorphization of α‐quartz and transition to coesite in an eclogite from Antarctica: a first record and some consequences

AbstractMonocrystalline quartz inclusions in garnet and omphacite from various eclogite samples from the Lanterman Range (Northern Victoria Land, Antarctica) have been investigated by cathodoluminescence (CL), Raman spectroscopy and imaging, and in situ X‐ray (XR) microdiffraction using the synchrotron. A few inclusions, with a clear‐to‐opalescent lustre, show ‘anomalous’ Raman spectra characterized by weak α‐quartz modes, the broadening of the main α‐quartz peak at 465 cm−1, and additional vibrations at 480–485, 520–523 and 608 cm−1. CL and Raman imaging indicate that this ‘anomalous’α‐quartz occurs as relicts within ordinary α‐quartz, and that it was preserved in the internal parts of small quartz inclusions. XR diffraction circular patterns display irregular and broad α‐quartz spots, some of which show an anomalous d‐spacing tightening of ∼2%. They also show some very weak, hazy clouds that have d‐spacing compatible with coesite but not with α‐quartz. Raman spectrometry and XR microdiffraction characterize the anomalies with respect to α‐quartz as (i) a pressure‐induced disordering and incipient amorphization, mainly revealed by the 480–485 and 608‐cm−1 Raman bands, together with (ii) a lattice densification, evidenced by d‐spacing tightening; (iii) the cryptic development of coesite, 520–523 cm−1 being the main Raman peak of coesite and (iv) Brazil micro‐twinning. This ‘anomalous’α‐quartz represents the first example of pressure‐induced incipient amorphization of a metastable phase in a crustal rock. This issue is really surprising because pressure‐induced amorphization of metastable α‐quartz, observed in impactites and known to occur between 15 and 32 GPa during ultrahigh‐pressure (UHP) experiments at room temperature, is in principle irrelevant under normal geological P–T conditions. A shock (due to a seism?) or a local overpressure at the inclusion scale (due to expansion mismatch between quartz and its host mineral) seem the only geological mechanisms that can produce such incipient amorphization in crustal rocks. This discovery throws new light on the modality of the quartz‐coesite transition and on the pressure regimes (non‐lithostatic v. lithostatic) during high‐pressure/UHP metamorphism. In particular, incipient amorphization of quartz could favour the quartz‐coesite transition, or allow the growth of metastable coesite, as already experimentally observed.

Antarctic crustal thickness from satellite gravity: Implications for the Transantarctic and Gamburtsev Subglacial Mountains

Crustal thickness models are fundamental to understand the tectonic evolution of continents and constrain geodynamic models of their physiographic features. Of particular interest in Antarctica are the crustal thickness variations under the Transantarctic Mountains and Gamburtsev Subglacial Mountains, whose formation mechanisms are still debated. We have used a mean, global gravity field from the Gravity Recovery and Climate Experiment (GRACE) to estimate the depth to the Moho in East and West Antarctica through gravity inversion. We then combined the depth to Moho and known topography to estimate the total crustal thickness. Thick crust is resolved along the full length of the Transantarctic Mountains with a maximum crustal thickness of 46 km predicted near the pole and thinner (~ 40 km) crust in both northern Victoria Land and under the Pensacola Mountains. Within East Antarctica, the model predicts crust over 40 km thick below the Gamburtsev Subglacial Mountains, which may be the result of a Neoproterozoic suture zone underlying the ice sheet. In addition to addressing long-standing questions about the nature of East Antarctica's major mountain ranges, an improved estimate of crustal thickness variability may improve long-wavelength geodynamic and glaciological models of the continent.

Photosynthetic pigments in soils from northern Victoria Land (continental Antarctica) as proxies for soil algal community structure and function

Although soil algae are among the main primary producers in most terrestrial ecosystems of continental Antarctica, there are very few quantitative studies on their relative proportion in the main algal groups and on how their distribution is affected by biotic and abiotic factors. Such knowledge is essential for understanding the functioning of Antarctic terrestrial ecosystems. We therefore analyzed biological soil crusts from northern Victoria Land to determine their pH, electrical conductivity (EC), water content (W), total and organic C (TC and TOC) and total N (TN) contents, and the presence and abundance of photosynthetic pigments. In particular, the latter were tested as proxies for biomass and coarse-resolution community structure. Soil samples were collected from five sites with known soil algal communities and the distribution of pigments was shown to reflect differences in the relative proportions of Chlorophyta, Cyanophyta and Bacillariophyta in these sites. Multivariate and univariate models strongly indicated that almost all soil variables (EC, W, TOC and TN) were important environmental correlates of pigment distribution. However, a significant amount of variation is independent of these soil variables and may be ascribed to local variability such as changes in microclimate at varying spatial and temporal scales. There are at least five possible sources of local variation: pigment preservation, temporal variations in water availability, temporal and spatial interactions among environmental and biological components, the local-scale patchiness of organism distribution, and biotic interactions.

Water contents of pyroxenes in intraplate lithospheric mantle

Water contents of clinopyroxene and orthopyroxene in mantle peridotites from various xenolith occurrences in intraplate settings (both oceanic and continental) were determined by Fourier Transform Infrared Spectroscopy (FTIR). Samples from the following localities were studied: Sal Island (Cape Verde Archipelago); Baker Rocks and Greene Point (Northern Victoria Land, Antarctica); Panshishan and Lianshan (Subei Basin, Eastern China). They represent well-known localities where detailed petrographical and geochemical studies have already been carried out or areas which are currently under investigation. The water incorporated in these pyroxenes is low (cpx, 37–399 ppm; opx, 9–166 ppm) or very low (as in Greene Point, Antarctica; cpx, 5–16 ppm; opx, 9–16 ppm). Within each population there is no clear correlation with melting parameters such as MgO contents in any single mineral. Results are compared with the available literature data on water contents in mantle pyroxenes, which include peridotites from on-craton (hosted by kimberlitic-type magmas) and off-craton (hosted by alkaline basic magmas), as well as subarc mantle settings. The “relatively dry” (cpx, 140–528 ppm; opx, 38–280 ppm) sub-arc mantle xenoliths (Peslier et al. , 2002) are shown to be wetter than the intraplate (off-craton) xenoliths. Cratonic mantle pyroxenes are only represented by a few determinations on garnet peridotites and eclogite from Kaapvaal and Colorado Plateau. They record the highest water contents (cpx, 342–1012 ppm; opx, 180–491 ppm) so far measured in mantle pyroxenes from various tectonic settings. Despite the limited data set, the indication that the cratonic mantle is strongly hydrated is compelling. Rehydration of cratonic mantle may be related to plate subduction ( i.e. , Colorado Plateau) or alternatively to metasomatic enrichment ( i.e. , Kaapvaal Craton). However, assuming that the water content was initially very low, metasomatic events in intraplate settings, similar to those presented here, would not be able to produce a significant increase in pyroxenes water content. According to our own data and those reported in the literature, it appears that substantial rehydration may instead occur at convergent plate margins.

The Tiger Gabbro from northern Victoria Land, Antarctica: the roots of an island arc within the early Palaeozoic margin of Gondwana

Abstract: The Tiger Gabbro layered intrusion is one of the few mafic intrusive bodies found along the ancient Antarctic Gondwana margin. Major and trace element data and Sr–Nd isotope compositions for gabbronorites indicate an island arc signature for the Tiger Gabbro parental magma. This is the first evidence for an island arc from plutonic rocks in northern Victoria Land. The interpretation of the Tiger Gabbro as the roots of an Early Cambrian island arc (535 ± 21 Ma, Sm–Nd age), integrated with geochemical and geochronological data from the literature, matches the occurrence of the Glasgow volcanic rocks in the southern Bowers terrane, which possibly represents its effusive counterpart. A scenario for the early Palaeozoic Antarctic Gondwana margin is hence proposed in which the Tiger volcanic arc developed on the Robertson Bay microplate in response to subduction of the palaeo-Pacific plate. The Tiger arc igneous activity was coeval to the Wilson continental arc (represented by the Granite Harbour intrusive rocks), with the two subduction zones merging southwards into one. The migration of the Wilson arc towards the forearc region in turn generated the Middle Cambrian Bowers arc. Supplementary material: Major element, trace element, mineral and 40 Ar– 39 Ar data are available at http://www.geolsoc.org.uk/SUP18351 .

Lake‐ice blisters, terra nova bay area, northern victoria land, antarctica

.Ice blisters, typically 0.2–0.8 m high and 5–20 m long, develop annually on perennially frozen lakes in Northern Victoria Land. They are believed to be caused by hydrostatic pressures generated through progressive freezing of solute‐rich water beneath the lake‐ice cover during winter. Lake‐ice blisters in the study area differfrom icing blisters described from the northern hemisphere. The latter are caused by hydraulic pressures and are found at locations such as river beds or spring sites on sloping terrain. The Antarctic lake‐ice blisters reflect the occurrence of dry‐based perennially frozen lakes with high salt contents in an extremely cold and arid environment.

Cambrian intra-oceanic arc accretion to the austral Gondwana margin: constraints on the location of proto-New Zealand

Data from New Zealand and northern Victoria Land, Antarctica, indicate that the Cambrian Takaka Terrane intra-oceanic arc/backarc assemblage and the Bowers Terrane intra-oceanic arc/back-arc assemblage were accreted to the Gondwana margin by the Late Cambrian. Compelling similarities between the arc rocks and the immediate post-arc sediments firmly place the two regions in the same tectonic framework and imply close paleogeographic proximity. Currently, the Ross Orogen is thought to be the result of sinistral oblique convergence with west-directed subduction, and accretion of the arc assemblages is attributed to closure of backarc basins. Syntectonic fluvial conglomerates in both regions attest to the development of fluvial systems draining both the accreted arc and the contemporaneous continental margin arc. Trilobite faunas indicate that fluvial sedimentation commenced earlier in New Zealand than in northern Victoria Land. In the context of the widely accepted sinistral oblique convergence model, these data suggest an original position for New Zealand to the south of northern Victoria Land, probably in the region of the southern Ross Sea.