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The Ekström Ice Shelf is one of numerous small ice shelves that fringe the coastline of western Dronning Maud Land, East Antarctica. Reconstructions of past ice-sheet extent in this area are poorly constrained, due to a lack of geomorphological evidence. Here, we present a compilation of geophysical surveys in front of and beneath the Ekström Ice Shelf, to identify and interpret evidence of past ice-sheet flow, extent and retreat. The sea floor beneath the Ekström Ice Shelf is dominated by an incised trough, which extends from the modern-day grounding line onto the continental shelf. Our surveys show that mega-scale glacial lineations cover most of the mouth of this trough, terminating 11 km away from the continental shelf break, indicating the most recent minimal extent of grounded ice in this region. Beneath the front ∼30 km of the ice shelf measured from the ice shelf edge towards the inland direction, the sea floor is characterised by an acoustically transparent sedimentary unit, up to 45 m thick. This is likely composed of subglacial till, further corroborating the presence of past grounded ice cover. Further inland, the sea floor becomes rougher, interpreted as a transition from subglacial tills to a crystalline bedrock, corresponding to the outcrop of the volcanic Explora Wedge at the sea floor. Ice retreat in this region appears to have happened rapidly in the centre of the incised trough, evidenced by a lack of overprinting of the lineations at the trough mouth. At the margins of the trough uniformly spaced recessional moraines suggest ice retreated more gradually. We estimate the palaeo-ice thickness at the calving front around the Last Glacial Maximum to have been at least 305 to 320 m, based on the depth of iceberg ploughmarks within the trough and sea level reconstructions. Given the similarity of the numerous small ice shelves along the Dronning Maud Land coast, these findings are likely representative for other ice shelves in this region and provide essential boundary conditions for palaeo ice-sheet models in this severely understudied region. [ABSTRACT FROM AUTHOR]

40Ar/39Ar and U–Pb data from five structural domains constrain the late Neoproterozoic – early Palaeozoic tectonothermal history of the eastern part of the East African–Antarctic Orogen in Sør Rondane. A total of 27 new Ar/Ar ages span 570–474 Ma, roughly corresponding to the age range of three generations of syn- to post-tectonic granitoids. The ages are distinct for the five structural domains. The oldest cooling ages come from the weakly deformed southern part of the SW Terrane of Sør Rondane (SW Terrane S), a sliver of a Tonian island arc, which escaped much of the late Neoproterozoic accretionary deformation. This terrane was intruded by the oldest and largest granitoid complex at c. 640–620 Ma. The oldest Ar/Ar amphibole and biotite ages of 570–524 Ma are from the Main Shear Zone, along the northern margin of the SW Terrane S sliver. It hosts granites of age c. 584–570 Ma strung out along the shear zone. Two younger granitoid phases are recorded in the adjacent four terranes to the west, north and east of the SW Terrane S, and correlate with the younger group of Ar/Ar biotite ages spanning 513–474 Ma. We interpret the magmatic and cooling history of duration > 150 Ma to reflect repeated phases of accretion, magmatism and reactivation, that is, collage-style tectonism, partly pre-dating the incorporation of Sør Rondane into Gondwana. The study area first accreted to the cryptic Valkyrie Craton in Tonian times, was then 'sandwiched' between the Kalahari and Indo-Antarctica cratons, and experienced extensional tectonics and elevated heat flux due to lithospheric delamination, which resulted in slow cooling during the Pan-African Orogeny. [ABSTRACT FROM AUTHOR]

The shape of ice shelf cavities are a major source of uncertainty in understanding ice‐ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland‐sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo‐ice streams. The trough does not cross‐cut the outer parts of the continental shelf. Conductivity‐temperature‐depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica. Plain Language Summary: Antarctica is surrounded by floating ice shelves, which play a crucial role in regulating the flow of ice from the continent into the oceans. The ice shelves are susceptible to melting from warm ocean waters beneath them. In order to better understand the melting, knowledge of the shape and depth of the ocean cavity beneath ice shelves is crucial. In this study, we present new measurements of the sea floor depth beneath Ekström Ice Shelf in East Antarctica. The measurements reveal a much deeper sea floor than previously known. We discuss the implications of this for access of warm ocean waters, which can melt the base of the ice shelf and discuss how the observed sea floor features were formed by historical ice flow regimes. Although Ekström Ice Shelf is relatively small, the geometry described here is thought to be representative of the topography beneath many ice shelves in this region, which together regulate the ice loss from a substantial area of East Antarctica. Key Points: Vibroseis seismic surveys used to map the ice shelf cavity beneath Ekström Ice Shelf in AntarcticaDeep trough with transverse sills and overdeepenings provide evidence of past ice streaming and retreatTwo ocean circulation regimes inferred in the shallow and deep parts of the cavity [ABSTRACT FROM AUTHOR]

Here, we report on a tetrapod footprint from the Transantarctic Basin in the far north of Victoria Land, which marks the first record of terrestrial vertebrates for this region. The single specimen derives from a previously unknown lithological unit of Middle or Late Triassic age of the Beacon Supergroup in the Helliwell Hills in the central Rennick Glacier area. It differs in both size and morphology clearly from Middle Triassic trackway types from the upper Fremouw Formation of the Queen Alexandra Range in southern Victoria Land, and likely represents a primitive amniote, procolophonid or therapsid. The footprint is the third evidence of fossil vertebrate trackways in Antarctica. [ABSTRACT FROM AUTHOR]

Abstract: Stress inversions of kinematic data measured from brittle deformation structures exposed in the southern Prince Charles Mountains have been carried out to elucidate the drivers of intracontinental deformation responsible for the development of the Lambert Graben, East Antarctica. Four palaeostress fields (D1–D4) were identified from these data, which when coupled with pre-existing geochronological and sedimentological evidence, provide a clear deformation framework. The architecture of the Lambert Graben is dominantly defined by north–south trending D2 and northeast–southwest trending D3 faults that formed respectively during: (1) Carboniferous–Permian intracontinental extrusion and (2) Cretaceous transtensional tectonics related to the dispersion of East Gondwana. Interestingly, sub-ice topography in the southern Prince Charles Mountains and further south towards the Gamburtsev Mountains is defined by bedrock lineaments that parallel the orientations of the main fault arrays. Previous work shows that the development of relief in the southern Prince Charles Mountains is Tertiary in age and probably not associated with Carboniferous–Permian or Cretaceous tectonic events. Based on a clear spatial link between the orientations of faults and bedrock lineaments, we suggest that inherited fault zones were integral in accommodating uplift driven by plate flexure as a response to crustal unloading during glacial incision. [Copyright &y& Elsevier]

In Antarctica, spectral mapping of altered minerals is very challenging due to the remoteness and inaccessibility of poorly exposed outcrops. This investigation evaluates the capability of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite remote sensing imagery for mapping and discrimination of phyllosilicate mineral groups in the Antarctic environment of northern Victoria Land. The Mixture-Tuned Matched-Filtering (MTMF) and Constrained Energy Minimization (CEM) algorithms were used to detect the sub-pixel abundance of Al-rich, Fe3+-rich, Fe2+-rich and Mg-rich phyllosilicates using the visible and near-infrared (VNIR), short-wave infrared (SWIR) and thermal-infrared (TIR) bands of ASTER. Results indicate that Al-rich phyllosilicates are strongly detected in the exposed outcrops of the Granite Harbour granitoids, Wilson Metamorphic Complex and the Beacon Supergroup. The presence of the smectite mineral group derived from the Jurassic basaltic rocks (Ferrar Dolerite and Kirkpatrick Basalts) by weathering and decomposition processes implicates Fe3+-rich and Fe2+-rich phyllosilicates. Biotite (Fe2+-rich phyllosilicate) is detected associated with the Granite Harbour granitoids, Wilson Metamorphic Complex and Melbourne Volcanics. Mg-rich phyllosilicates are mostly mapped in the scree, glacial drift, moraine and crevasse fields derived from weathering and decomposition of the Kirkpatrick Basalt and Ferrar Dolerite. Chlorite (Mg-rich phyllosilicate) was generally mapped in the exposures of Granite Harbour granodiorite and granite and partially identified in the Ferrar Dolerite, the Kirkpatrick Basalt, the Priestley Formation and Priestley Schist and the scree, glacial drift and moraine. Statistical results indicate that Al-rich phyllosilicates class pixels are strongly discriminated, while the pixels attributed to Fe3+-rich class, Fe2+-rich and Mg-rich phyllosilicates classes contain some spectral mixing due to their subtle spectral differences in the VNIR+SWIR bands of ASTER. Results derived from TIR bands of ASTER show that a high level of confusion is associated with mafic phyllosilicates pixels (Fe3+-rich, Fe2+-rich and Mg-rich classes), whereas felsic phyllosilicates (Al-rich class) pixels are well mapped. Ground truth with detailed geological data, petrographic study and X-ray diffraction (XRD) analysis verified the remote sensing results. Consequently, ASTER image-map of phyllosilicate minerals is generated for the Mesa Range, Campbell and Priestley Glaciers, northern Victoria Land of Antarctica. [ABSTRACT FROM AUTHOR]

Listvenites normally form during hydrothermal/metasomatic alteration of mafic and ultramafic rocks and represent a key indicator for the occurrence of ore mineralizations in orogenic systems. Hydrothermal/metasomatic alteration mineral assemblages are one of the significant indicators for ore mineralizations in the damage zones of major tectonic boundaries, which can be detected using multispectral satellite remote sensing data. In this research, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral remote sensing data were used to detect listvenite occurrences and alteration mineral assemblages in the poorly exposed damage zones of the boundaries between the Wilson, Bowers and Robertson Bay terranes in Northern Victoria Land (NVL), Antarctica. Spectral information for detecting alteration mineral assemblages and listvenites were extracted at pixel and sub-pixel levels using the Principal Component Analysis (PCA)/Independent Component Analysis (ICA) fusion technique, Linear Spectral Unmixing (LSU) and Constrained Energy Minimization (CEM) algorithms. Mineralogical assemblages containing Fe2+, Fe3+, Fe-OH, Al-OH, Mg-OH and CO3 spectral absorption features were detected in the damage zones of the study area by implementing PCA/ICA fusion to visible and near infrared (VNIR) and shortwave infrared (SWIR) bands of ASTER. Silicate lithological groups were mapped and discriminated using PCA/ICA fusion to thermal infrared (TIR) bands of ASTER. Fraction images of prospective alteration minerals, including goethite, hematite, jarosite, biotite, kaolinite, muscovite, antigorite, serpentine, talc, actinolite, chlorite, epidote, calcite, dolomite and siderite and possible zones encompassing listvenite occurrences were produced using LSU and CEM algorithms to ASTER VNIR+SWIR spectral bands. Several potential zones for listvenite occurrences were identified, typically in association with mafic metavolcanic rocks (Glasgow Volcanics) in the Bowers Mountains. Comparison of the remote sensing results with geological investigations in the study area demonstrate invaluable implications of the remote sensing approach for mapping poorly exposed lithological units, detecting possible zones of listvenite occurrences and discriminating subpixel abundance of alteration mineral assemblages in the damage zones of the Wilson-Bowers and Bowers-Robertson Bay terrane boundaries and in intra-Bowers and Wilson terranes fault zones with high fluid flow. The satellite remote sensing approach developed in this research is explicitly pertinent to detecting key alteration mineral indicators for prospecting hydrothermal/metasomatic ore minerals in remote and inaccessible zones situated in other orogenic systems around the world. [ABSTRACT FROM AUTHOR]

We report new strain analyses of mechanically twinned calcite in veins hosted by Neogene (13.6–4.3 Ma) sedimentary and volcanic rocks recovered from the Terror Rift system in the southern Ross Sea, Antarctica, by the ANDRILL (ANtarctic geological DRILLing) McMurdo Ice Shelf (MIS) Project. Strain analyses of the ANDRILL MIS AND-1B drill core samples yield prolate and oblate ellipsoids with principal shortening and extension strains ranging from –7% to 9%, respectively. The majority of samples show ≤25% negative expected values, indicating homogeneous coaxial strain characterized predominantly by subvertical shortening. We attribute the subvertical shortening strains to mechanical twinning at relatively shallow depths in an Andersonian normal faulting stress regime induced by sedimentary and ice sheet loading of the stratigraphic sequence and characterized by low stress magnitudes. Oriented samples yield a northwest-southeast average extension direction that is subparallel to other indicators of Neogene extension. This northwest-southeast extension is consistent with strain predicted by Neogene orthogonal rifting in a north-northeast–trending rift segment, as well as models of right-lateral transtensional rifting. The overall paucity of a noncoaxial layer-parallel shortening signal in the AND-1B twin populations favors orthogonal extension in the Neogene Terror Rift system, but could also be due to spatial partitioning of strain in a transtensional rift regime. [ABSTRACT FROM AUTHOR]

Highlights: [•] Magnetics and geology correlate quite well, revealing new structural insights. [•] The new central Sør Rondane corridor separates the region into E and W parts. [•] The prominent SE-DML province continues easterly into southern Sør Rondane. [•] The TTG-subterrane in the SW is divided into two distinct magnetic domains. [•] Strong high near Dufekfjellet is caused by a highly magnetised enigmatic body. [ABSTRACT FROM AUTHOR]

Exhumed faults in granitoids along the Lanterman Fault-Rennick Graben Fault system (northern Victoria Land, Antarctica) show superposed ductile to brittle deformation and pervasive hydrothermal fluid-rock interaction. These processes triggered multiple brittle slip events producing crosscutting epidote and prehnite-rich fault veins, ultracataclasites and pseudotachylytes of crushing origin. Combined microstructural and minerochemical investigations on fault damage zones show three types of alteration: (i) albitization of K-feldspar and Ca-plagioclase; (ii) crystallization of prehnite and calcite in veins; (iii) alteration of magmatic phases by secondary hydrous minerals (e.g. chlorite, white mica, epidote and prehnite). The fault experienced various episodes of strain weakening and hardening, due to alteration of minerals and precipitation of epidote and prehnite within ultracataclastic intervals, at decreasing temperature conditions (200 < T°C < 450) and varying CO 2 fugacity of the fluids. Cyclic crystallization of epidote/prehnite within the fault cores caused cementation and locking of faults, concentration of deformation at weaker horizons and a progressive broadening of the fault zone. Our results indicate that multiple co-seismic slip and syntectonic fluid flow very likely occurred prior to the Cenozoic brittle reactivation of inherited anisotropies in the northern Victoria Land crust along the Lanterman Fault-Rennick Graben Fault system and underlines its high potential for polyphasicity. • Exhumed faults in granitoids from Antarctica show multiple ductile to brittle shears. • Syntectonic hydrothermal fluid-rock interaction processes affect slip history. • Epidote and prehnite crystallization in fault rocks influence rheology. [ABSTRACT FROM AUTHOR]

• Geological architecture of eastern Kalahari in early Neoproterozoic times revealed. • First recognition of Tonian (ca. 770 Ma) continental arc in easternmost Kalahari. • Tectonic consequences of Rodinia turning inside out. • Back-arc extension results in ultra-high temperature metamorphism at ca. 650–600 Ma. • Study area escaped pervasive Gondwana continental collision tectonism. Late Tonian (ca. 785–760 Ma) granodioritic to granitic orthogneisses of the Schirmacher Oasis region in Dronning Maud Land (DML), East Antarctica, are interpreted as recording an active continental margin setting at the periphery of Kalahari and Rodinia. The rocks probably represent exposures of a significant tectonic province hidden beneath the ice, the erosional remnants of which are recorded as detrital zircons in late Tonian-Cryogenian metasedimentary rocks throughout central and eastern DML, as well as in ice-rafted debris from recent sediments offshore Dronning Maud Land. The orthogneisses have single-stage Sm-Nd model ages of ca. 1.3–1.5 Ga and zircon Hf-signatures (εHf t = +2 – +5), indistinguishable from the adjacent Grenville-age basement rocks of easternmost Kalahari. Their geochemistry suggests that they evolved in the late stages of a continental margin magmatic arc and possibly within a roll-back tectonic framework, suggestive of subduction of relatively old oceanic lithosphere. The eastern Kalahari continental arc is one of a number of continental arcs that characterize the western part of the fragmenting Rodinia and document the supercontinent "turning inside out" after its formation at ca. 1000 Ma and a period of relative tectonic quiescence between ca. 900 and 800 Ma. The rocks show an ultra-high temperature metamorphic overprint that was accompanied by syn-tectonic magmatism from ca. 650 to 600 Ma. The high temperature metamorphism is interpreted to relate to back-arc extension that also led to major anorthosite magmatism elsewhere, prior to continental collision in the region. The rocks lack the subsequent widespread high-grade metamorphic overprint at ca. 590–500 Ma which occurs in the adjacent regions due to Himalayan-style continental collision along the East African-Antarctic Orogen during Gondwana assembly. [ABSTRACT FROM AUTHOR]

Knowledge of sub-ice shelf sedimentary sequences, ice-ocean interactions, and biological activities is still relatively sparse, largely due to the challenges involved in accessing ice shelf cavities. The Sub-EIS-Obs project, funded by the Alfred-Wegener-Institute (AWI) and the Federal Institute for Geosciences and Natural Resources (BGR) in Germany, is a multidisciplinary study, which aims to recover and characterize sediment sequences beneath the Ekström Ice Shelf (EIS) in East Antarctica. The project addresses several research objectives, such as the crustal evolution during the breakup of Gondwana, the build-up and variability of the East Antarctic Ice Sheet (EAIS) throughout the Cenozoic, reconstruction of grounding-line dynamics, sedimentary and erosional processes beneath the ice stream and shelf, and multidisciplinary observations of climate induced changes in ice-ocean interactions.A pre-site seismic survey campaign was carried out on the Ekström Ice Shelf in 2016/2017 and 2017/2018, resulting in 615 km of multi-fold seismic data. Based on these data, four different units were defined, which, according to preliminary interpretation, document geologic history of the breakup of Gondwana in the Jurassic (Explora-Wedge volcanic deposits) and ongoing marine and glacio-marine sedimentation during the Meso- and Cenozoic. On top of all strata a glacio-marine surface cover deposited during the Last Glacial Maximum and Holocene sedimentation is indicated in the seismic profiles. In order to sample all units separately, coring locations were selected accordingly. A hot water drilling system was used to drill holes through the shelf ice (ice thicknesses range between ~210 and 330 m), enabling the deployment of a gravity corer, a Wippermann Grabber, a vibro- and a hammer coring system manufactured by Jilin University (Changchun, China), and a UWITEC percussion corer (BAS corer). Moreover, a camera installed in a pressure housing enabled recording of high-resolution video footage of the seafloor and associated benthic ecosystems as well as the base of the ice shelf. In addition, a Conductivity-Temperature-Depth probe was attached to all coring devices in order to record the oceanographic properties of the water column. Here, we present first results from the Sub-EIS-Obs sediment sampling campaigns 2017/2018 and 2018/2019. We present an overview of the long-term project aims, sampling strategy, performance of the hot water drilling operation, and recovered geological samples, and the video footages of the seafloor. [ABSTRACT FROM AUTHOR]