Eastern Dronning Maud Land Research Articles

Radar internal reflection horizons from multisystem data reflect ice dynamic and surface accumulation history along the Princess Ragnhild Coast, Dronning Maud Land, East Antarctica

Abstract Ice shelves, which regulate ice flow from the Antarctic ice sheet towards the ocean, are shaped by spatiotemporal patterns of surface accumulation, surface/basal melt and ice dynamics. Therefore, an ice dynamic and accumulation history are imprinted in the internal ice stratigraphy, which can be imaged by radar in the form of internal reflection horizons (IRHs). Here, IRHs were derived from radar data combined across radar platforms (airborne and ground-based) in coastal eastern Dronning Maud Land (East Antarctica), comprising three ice rises and adjacent two ice shelves. To facilitate interpretation of dominant spatiotemporal patterns of processes shaping the local IRH geometry, traced IRHs are classified into three different types (laterally continuous, discontinuous or absent/IRH-free). Near-surface laterally continuous IRHs reveal local accumulation patterns, reflecting the mean easterly wind direction, and correlate with surface slopes. Areas of current and past increased ice flow and internal deformation are marked by discontinuous or IRH-free zones, and can inform about paleo ice-stream dynamics. The established IRH datasets extend continent-wide mapping efforts of IRHs to an important and climatically sensitive ice marginal region of Antarctica and are ready for integration into ice-flow models to improve predictions of Antarctic ice drainage.

Metamorphic age and pressure-temperature conditions recorded in a sillimanite-garnet-bearing pelitic gneiss from Niban-nishi Rock of Niban Rock on the Prince Olav Coast, eastern Dronning Maud Land, East Antarctica: Evidence for Tonian metamorphism

Metamorphic age and pressure-temperature conditions recorded in a sillimanite-garnet-bearing pelitic gneiss from Niban-nishi Rock of Niban Rock on the Prince Olav Coast, eastern Dronning Maud Land, East Antarctica: Evidence for Tonian metamorphism

Spatial variations of 10Be in surface snow along the inland traverse route of Japanese Antarctic Research Expeditions

To contribute further to understanding of the nature of 10Be deposition in Antarctica, we determined 10Be concentrations in surface snow samples obtained along the inland traverse route of the 59th and 60th Japanese Antarctic Research Expeditions (JAREs) in eastern Dronning Maud Land. The 10Be concentrations ranged between 3.7 × 103 and 8.6 × 104 atoms/g. When plotted against latitude, they showed a clear trend of increasing concentration southward with an upward inflection point at around 75°S (elevation 3.5 km) for the 59th JARE. Comparison with both snow accumulation rate and δ18O data suggests that the inflection point divides the dominant deposition regime into two different groups: wet deposition (north of 75°S) and dry deposition with slight enhancement of 10Be fallout further inland (south of 75°S). Additional factors associated with 10Be transport from the stratosphere are also proposed.

Newly found Tonian metamorphism in Akebono Rock, eastern Dronning Maud Land, East Antarctica

In this paper, we report a new metamorphic age for kyanite-bearing garnet-biotite gneiss collected from Akebono Rock, which is located on Prince Olav Coast, in the Lützow-Holm Complex (LHC), East Antarctica. The metamorphic P–T path estimated from pseudosection modeling, together with garnet compositional zoning and experimentally calibrated geothermobarometry, suggests that the gneiss underwent a clockwise amphibolite-facies P–T history. Two populations of U–Pb zircon ages of 1121–1014 Ma and 972–904 Ma (n = 65) were identified, with the latter population having a weighted mean age of 937 ± 6 Ma. The younger population was dated from overgrowth rims and single zircon grains interpreted as metamorphic in origin. Ti-in-zircon thermometry supports crystallization of these zircon domains and grains at a temperature close to the metamorphic peak of 642 °C at 937 Ma. Monazite EMP dating from the other four samples show an age between 977 and 917 Ma. These lines of evidence indicate that prograde metamorphism of the Akebono Rock gneiss occurred during the Tonian, that is, substantially earlier than the LHC regional metamorphic age of late Neoproterozoic to Cambrian. Our results indicate that a fundamental revision of the sequence of metamorphic events in the Prince Olav Coast area of the LHC is required. We also identified three possible relationships between Akebono Rock and other geological units that record Tonian metamorphism, although we cannot determine which relationship is most likely. In particular, linear magnetic anomalies were identified near the boundary between the LHC and the Western Rayner Complex/inland nunataks of western Enderby Land, suggesting the presence of geological discontinuities.

Ice surface changes during recent glacial cycles along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica

Reconstructing past ice-sheet surface changes is key to testing and improving ice-sheet models. Data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past, present and future climate change. Here, we report the first cosmogenic multi-nuclide (10Be, 26Al, 36Cl) data from bedrock and erratics on nunataks along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica. Spanning elevations between 741 and 2394 m above sea level, the samples have apparent exposure ages between 2 ka and 5 Ma. The highest-elevation bedrock sample indicates (near-) continuous minimum exposure since the Pliocene, with a low apparent erosion rate of 0.15 ± 0.03 m Ma−1, which is similar to results from eastern Dronning Maud Land. In contrast to studies in eastern Dronning Maud Land, however, our data show clear indications of a thicker-than-present ice sheet within the last glacial cycle, with a thinning of ∼35–120 m during the Holocene (∼2–11 ka). Difficulties in separating suitable amounts of quartz from the often quartz-poor rock-types in the area, and cosmogenic nuclides inherited from exposure prior to the last deglaciation, prevented robust thinning estimates from elevational profiles. Nevertheless, the results clearly demonstrate ice-surface fluctuations of several hundred meters between the current grounding line and the edge of the polar plateau for the last glacial cycle, a constraint that should be considered in future ice-sheet model simulations.

Late Neoproterozoic–Cambrian magmatism in Dronning Maud Land (East Antarctica): U–Pb zircon geochronology, isotope geochemistry and implications for Gondwana assembly

Dronning Maud Land (DML) is a key area for the better understanding of the geotectonic history and amalgamation processes of the southern part of Gondwana. Here, we present comprehensive new zircon U–Pb–Hf–O, whole-rock Sm–Nd isotopic and geochemical data for late Neoproterozoic-Cambrian igneous rocks along a profile from central to eastern DML, which provides new insights into the crustal evolution and tectonics of the region. In central DML, magmatism dominantly occurred at 530–485 Ma, with 650–600 Ma charnockite and anorthosite locally distributed at its eastern periphery. In contrast, eastern DML experienced long-term and continuous granitic magmatism from ca. 650 Ma to 500 Ma. In central DML, the 650–600 Ma samples are characterized by highly elevated δ18O (7.5–9.5‰) associated with slightly negative to positive εHf(t) values (−1 to +3), indicating significant addition of high-δ18O crustal components, such as sedimentary material at the margin of the Kalahari Craton. Evolved Hf isotopic signatures (εHf(t) = −15 to −6) and moderately elevated O isotopic data (δ18O = 6–8‰) of the Cambrian granitic rocks from central DML indicate a significant incorporation of the pre-existing, old continental crust. In eastern DML, the suprachondritic Hf–Nd isotope signatures and moderate δ18O values of the late Neoproterozoic granites (650–550 Ma) from the Sør Rondane Mountains support the view that they mainly originated from crust of the Tonian Oceanic Arc Super Terrane (TOAST). The post-540 Ma granites, however, have more evolved Hf and Nd isotopic compositions, suggesting an increasing involvement of older continental components during Cambrian magmatism. Nd isotopes of the Cambrian granitic rocks in DML display an increasingly more radiogenic composition towards the east with model ages ranging from late Archean to Mesoproterozoic times, which is in line with the isotopic trend of the Precambrian basement in this region. The late Neoproterozoic (>600 Ma) igneous rocks in central and eastern DML were emplaced in two independent subduction systems, at the periphery of the eastern Kalahari Craton and somewhere within the Mozambique Ocean respectively. The accretion and assembly of the TOAST to the eastern margin of the Kalahari Craton and their collision with surrounding continental blocks was followed by extensive post-collisional magmatism due to delamination tectonics and orogenic collapse in the Cambrian. The late Neoproterozoic–Cambrian igneous rocks in DML thus record an orogenic cycle from subduction-accretion, continental collision to post-collisional process during and after the assembly of Gondwana.

Neoproterozoic geodynamic evolution of easternmost Kalahari: Constraints from U-Pb-Hf-O zircon, Sm-Nd isotope and geochemical data from the Schirmacher Oasis, East Antarctica

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 (εHft = +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.

Thermally induced icequakes detected on blue ice areas of the East Antarctic ice sheet

ABSTRACTOver a year of seismic observations, ~5000 short duration icequakes were detected by a permanent broadband station installed at the Princess Elisabeth base, located ~180 km inland in eastern Dronning Maud Land, East-Antarctica. Icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events, totalizing ~1500 icequakes. The corresponding icequake locations point towards two distinct zones of outcropping blue ice areas (BIAs) located respectively at 4 and 1 km from the seismic station, both on the leeward side of a nunatak protruding through the ice sheet. The temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled, in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes. Further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change. Besides providing information on the ice fracture mechanics and rheology, investigations of thermal icequakes may be regarded as a ground-based proxy for the monitoring of the thermal state of BIAs, and characterization of ice-sheet ablation zones.

Erosion at extended continental margins: Insights from new aerogeophysical data in eastern Dronning Maud Land

Modelling-, rock cooling-, sedimentation- and exposure-based interpretations of the mechanisms by which topography evolves at extended continental margins vary widely. Observations from the margin of Dronning Maud Land, Antarctica, have until now not strongly contributed to these interpretations. Here, we present new airborne gravity and radar data describing the eastern part of this margin. Inland of a tall (2.5 km) great escarpment, a plateau topped by a branching network of valleys suggests preservation of a fluvial landscape with SW-directed drainage beneath a cold-based ice sheet. The valley floor slopes show that this landscape was modified during a period of alpine-style glaciation prior to the onset of the current cold-based phase around 34 Ma. The volume of sediments in basins offshore in the Riiser-Larsen Sea balances with the volume of rock estimated to have been eroded and transported by north-directed drainage from between the escarpment and the continental shelf break. The stratigraphy of these basins shows that most of the erosion occurred during the ~40 Myr following late Jurassic continental breakup. This erosion is unlikely to have been dominated by backwearing because the required rate of escarpment retreat to its present location is faster than numerical models of landscape evolution suggest to be possible. We suggest an additional component of erosion by downwearing seawards of a pre-existing inland drainage divide. The eastern termination of the great escarpment and inland plateau is at the West Ragnhild trough, a 300 km long, 15–20 km wide and up to 1.6 km deep subglacial valley hosting the West Ragnhild glacier. Numerous overdeepened (by >300 m) segments of the valley floor testify to its experience of significant glacial erosion. Thick late Jurassic and early Cretaceous sediments fanning out from the trough's mouth into the eastern Riiser-Larsen Sea betray an earlier history as a river valley. The lack of late Jurassic relief-forming processes in this river's catchment in the interior of East Antarctica suggests this erosion was related to regional climatic change.

New geophysical data from a key region in East Antarctica: Estimates for the spatial extent of the Tonian Oceanic Arc Super Terrane (TOAST)

Within Antarctica, eastern Dronning Maud Land (DML) represents a key region for improving our understanding of crustal fragments that were involved in the amalgamation and breakup histories of Rodinia and Gondwana. An aerogeophysical survey was flown during the austral summers 2013/14 and 2014/15 to explore the largely ice-covered region south and east of Sør Rondane. Here, we present 40,000 new line kilometer of aeromagnetic data gathered across an area of ca. 295,000km2 with a 10km line spacing. Magnetic domains, major lineaments, locations, and depths of magnetic source bodies are detected from total field data, their tilt derivative, pseudo-gravity, and analytical signal transformations, and from Euler Deconvolution maps. These data are integrated with exposure information from the Sør Rondane, Belgica and the Yamato mountains in order to identify the eastern spatial extent of a major juvenile Early Neoproterozoic crustal province, the Tonian Oceanic Arc Super Terrane (TOAST). Magnetic data reveal a characteristic pattern with NW-SE trending elongated magnetic anomalies to the south of Sør Rondane. This area is interpreted as the eastward continuation of the distinct SE DML Province and therefore of the TOAST. Major curvilinear magnetic anomalies of several hundreds of kilometers length dissect the region south and southwest of Sør Rondane. These may represent boundaries of individual oceanic arc terrane or alternatively major Pan-African shear zones. A significant change of the magnetic anomaly pattern ca. 800km inland of Sør Rondane may indicate the southern minimum extent of the TOAST. Magnetic anomalies of varying size, amplitude, and orientation suggest a complex transitional area between the Belgica and Yamato Mts., which appears to separate the TOAST from an Indo-Antarctic craton to the east. The new data suggest that the TOAST is comparable in size with the Antarctic Peninsula and therefore represents a significant piece of Neoproterozoic crustal addition. It originated at the periphery or outboard of Rodinia and is a remnant of the Mozambique Ocean.

Spatial variation of isotopic compositions of snowpack nitrate related to post-depositional processes in eastern Dronning Maud Land, East Antarctica

Spatial variation of isotopic compositions of snowpack nitrate related to post-depositional processes in eastern Dronning Maud Land, East Antarctica

Sulfur isotopic composition of surface snow along a latitudinal transect in East Antarctica

AbstractThe sulfur stable isotopic values (δ34S) of sulfate aerosols can be used to assess oxidation pathways and contributions from various sources, such as marine biogenic sulfur, volcanoes, and sea salt. However, because of a lack of observations, the spatial distribution of δ34S values in Antarctic sulfate aerosols remains unclear. Here we present the first sulfur isotopic values from surface snow samples along a latitudinal transect in eastern Dronning Maud Land, East Antarctica. The δ34S values of sulfate showed remarkably uniform values, in the range of 14.8–16.9‰, and no significant decrease toward the inland part of the transect was noted. These results suggest that net isotopic fractionation during long‐range transport is insignificant. Thus, the δ34S values can be used to infer source contributions. The δ34S values suggest that marine biogenic sulfur is the dominant source of sulfate aerosols, with a fractional contribution of 84 ± 16%.

The Main Shear Zone in Sør Rondane, East Antarctica: Implications for the late-Pan-African tectonic evolution of Dronning Maud Land

Structural investigations in western Sor Rondane, eastern Dronning Maud Land (DML), provide new insights into the tectonic evolution of East Antarctica. One of the main structural features is the approximately 120 km long and several hundred meters wide WSW-ENE trending Main Shear Zone (MSZ). It is characterized by dextral high-strain ductile deformation under peak amphibolite-facies conditions. Crosscutting relationships with dated magmatic rocks bracket the activity of the MSZ between late Ediacaran to Cambrian times (circa 560 to 530 Ma). The MSZ separates Pan-African greenschist- to granulite-facies metamorphic rocks with “East African” affinities in the north from a Rayner-age early Neoproterozoic gabbro-tonalite-trondhjemite-granodiorite complex with “Indo-Antarctic” affinities in the south. It is interpreted to represent an important lithotectonic strike-slip boundary at a position close to the eastern margin of the East African-Antarctic Orogen (EAAO), which is assumed to be located farther south in the ice-covered region. Together with the possibly coeval left-lateral South Orvin Shear Zone in central DML, the MSZ may be related to NE directed lateral escape of the EAAO, whereas the Heimefront Shear Zone and South Kirwanveggen Shear Zone of western DML are part of the south directed branch of this bilateral system.

Mass balance of the Sør Rondane glacial system, East Antarctica

AbstractMass changes of polar ice sheets have an important societal impact, because they affect global sea level. Estimating the current mass budget of ice sheets is equivalent to determining the balance between surface mass gain through precipitation and outflow across the grounding line. For the Antarctic ice sheet, grounding line outflow is governed by oceanic processes and outlet glacier dynamics. In this study, we compute the mass budget of major outlet glaciers in the eastern Dronning Maud Land sector of the Antarctic ice sheet using the input/output method. Input is given by recent surface accumulation estimates (SMB) of the whole drainage basin. The outflow at the grounding line is determined from the radar data of a recent airborne survey and satellite-based velocities using a flow model of combined plug flow and simple shear. This approach is an improvement on previous studies, as the ice thickness is measured, rather than being estimated from hydrostatic equilibrium. In line with the general thickening of the ice sheet over this sector, we estimate the regional mass balance in this area at 3.15 ± 8.23 Gt a−1 according to the most recent SMB model results.

New detailed aeromagnetic and geological data of eastern Dronning Maud Land: Implications for refining the tectonic and structural framework of Sør Rondane, East Antarctica

The Sør Rondane Mountains (SRM) in eastern Dronning Maud Land (DML) are located in an area, where two apparent Pan-African (650–520Ma) orogenic mobile belts appear to intersect, the East African-Antarctic Orogen and the Kuunga Orogen. Hence, a better understanding of the tectonic structure of the Sør Rondane region is an important key for unravelling the complex geodynamic evolution of the eastern DML and adjacent regions of East Antarctica during the Late Neoproterozoic/Early Palaeozoic amalgamation of Gondwana. The SRM were recently (2011–2012) aerogeophysically investigated with a 5km flight line spacing, covering a total area of ∼140,000km2. The aeromagnetic data are correlated with ground-based magnetic susceptibility measurements and geological field data and allow to project tectonic terranes and individual structures into ice-covered areas. Magnetic anomalies and basement foliation trends are collinear in areas dominated by simple shear deformation, whereas an area of large-scale refolding correlates with a subdued small-scale broken magnetic anomaly pattern. The latter area can be regarded as a distinct tectonic domain, the central Sør Rondane corridor. It magnetically separates the SRM into an eastern, a central, and a western portion. This subdivision is presumably related to late Pan-African extensional tectonics and suggests that such a tectonic regime may play a larger role than previously assumed. Voluminous late Pan-African granitoids, which are mainly undeformed, correlate with positive magnetic anomalies between +30 and +80nT, while a strong magnetic high (+680nT) near the granitic intrusion at Dufekfjellet is caused by a highly magnetised enigmatic body. The recently discovered prominent magnetic anomaly province of southeastern DML continues into the southern part of the Sør Rondane region, where only a few outcrops are exposed. Findings at these westernmost nunataks of the SRM indicate that the subdued magnetic anomaly pattern of this southeastern DML province is most likely caused by the predominance of metasedimentary rocks of yet unknown age.

Shallow Reflection Surveys of the East Ongul Island, the Lützow-Holm Complex, East Antarctica

The shallow reflection surveys were carried out in 2007 and 2010 austral summers in East Ongul Island, the Lützow-Holm Complex (LHC), East Antarctica. LHC is identified by geologically as one of the Pan-African terrains of Eastern Dronning Maud Land. The multi-channel reflection surveys targeted to achieve the image of laminated layering of metamorphic rocks near the surface (the depths down to a few hundreds of meters) of the crystalline crust. Two surveys were conducted in total length of the profiles about 500 m along a main traffic load across the East Ongul Island. The multi-channel acquisition systems were utilized with combining the dense geophones along the profiles. Seismic sources were adopted by combining the boom of a power shovel, a weight drop and hammer shots with their intervals in a few tens of meters. The obtained data include clear first P-arrivals in far offset distance. The energy of P-S converted waves was enhanced because of the characteristics of the seismic sources. Pre-stacked images could be expected to the information on metamorphic layering for several lithological structure composed by hornblende gneiss, garnet gneiss and pyroxene gneiss appearing as the surface bedrocks. The conducted shallow reflection surveys would give rise to one step for understanding tectonic formation of LHC, as one of the Pan-African mobile belts in Gondwana super-continent.

Geologic evolution of the Sør Rondane Mountains, East Antarctica: Collision tectonics proposed based on metamorphic processes and magnetic anomalies

The Sør Rondane Mountains of eastern Dronning Maud Land, East Antarctica can be subdivided into two different crustal terranes: the NE-terrane and the SW-terrane. The former is underlain by basement rocks of amphibolite-facies (unit A) and granulite-facies (unit B), and the latter by granulite-facies (unit C) to greenschist-facies (units D and D′) rocks. The metamorphic evolution of the NE-terrane exhibits a clockwise pressure–temperature–time (P–T–t) path and the SW-terrane exhibits a counter-clockwise P–T–t path, and detrital zircon U–Pb ages are also different between the two terranes. The differences in the metamorphic evolution processes and detrital zircon provenance in these two regions can be explained by the collision of the NE-terrane and the SW-terrane which is constrained to have occurred at 600–650Ma. The collision is interpreted to reflect convergence between the East Maud-East African orogen terrane and the Maud-Nampula terrane of the Kalahari Craton, which are bounded by the Main Tectonic Boundary and passes through the Sør Rondane Mountains. The RTP magnetic anomalies suggest this suture is cut by the subsequent collision boundary between the Kalahari Craton and the Rayner Belt, which is exposed in the Lützow–Holm region. This collisional belt is considered to have formed at approximately 520–580Ma.

Sinistral transpressional and extensional tectonics in Dronning Maud Land, East Antarctica, including the Sør Rondane Mountains

In this paper we clarify the history of deformation in the Sør Rondane Mountains (SRMs), eastern Dronning Maud Land (DML), East Antarctica, and construct a form-line contour map of the metamorphic and plutonic rocks in order to comprehend their structural features and provide constraints on the collisional tectonics of East and West Gondwana. We divide the deformational history in the SRMs into 13 stages (D1–D13). The tectonic regime varied frequently from extension (D3–D4) to layer-normal compression and layer-parallel extension (D5), to compression (D6), extension (D7), sinistral transtension and sinistral strike-slip (D8), compression (D9–D11), and finally extension related to dextral shearing (D12–D13). D7 and D8 indicate major extensional tectonic activity in the southern part of the East African and Antarctic Orogen (EAAO) before the Pan-African compressional event, and after the c. 600Ma peak of metamorphism. The Pan-African compressional event resulted in the formation of upright folds with horizontal axes that curve along the coastline in central to eastern DML during the D9 deformation that took place between 600 and 560Ma. The coastline-parallel fold axes and subvertical axial-planes correspond to the X-axes and the XY-planes, respectively, of strain ellipsoids that were progressively rotated counterclockwise toward the central parts of a sinistral shear zone. Therefore, the curved fold axes and axial-planes suggest the EAAO acted as a zone of sinistral transpression during the collision of parts of East and West Gondwana. Around 560–550Ma, during D12, parallel dyke swarms of granitic pegmatite were intruded along normal faults under a regime of NNE–SSW horizontal extensional stress. The extensional paleo-stress and its related structures suggest dextral rather than sinistral shearing took place along the north-trending EAAO during this late Pan-African event. There is the possibility of a reversal of trans-orogen asymmetry from sinistral to dextral in the southern part of the EAAO. The dyke swarms are considered to have been the heralds of the voluminous 530–500Ma A-type granite intrusions in DML. At the same time, the Lützow–Holm Complex was under a non-extensional tectonic regime, and may have been situated in a different orogen from the EAAO.

Late Neoproterozoic extensional detachment in eastern Sør Rondane Mountains, East Antarctica: Implications for the collapse of the East African Antarctic Orogen

A geological study of the Balchenfjella area of the eastern Sør Rondane Mountains forms the basis of a revised tectonic history for eastern Dronning Maud Land in Antarctica. The Balchenfjella area can be structurally divided into two metamorphic units that are separated by a SE-dipping ductile extensional shear zone (the Balchen detachment fault). The mafic- and ultramafic-dominant part of the footwall side is exposed as a tectonic window adjacent to the detachment. Metamorphic and structural data indicate that the eastern Sør Rondane Mountains were affected by four phases of deformation (D1–D4). Phases D1 and D2 are developed in the footwall side of the shear zone, whereas D3 and D4 are recorded in both the footwall and hangingwall sides. Mineral assemblages in mafic lithologies are characteristic of granulite facies (D1 and D2) to amphibolite facies (D2 and D3) metamorphism. D1 is characterized by recumbent folds and this phase is interpreted as a compressional tectonic setting coincident with granulite facies metamorphism. D2 represents a transpressional deformation phase characterized by upright folds and a large-scale dextral shear zone. The Balchen detachment fault was formed during the extensional tectonic setting of D3. The timing of D3 extensional deformation is bracketed by the age of D2-related metamorphism (at c. 600Ma) and the timing of post-kinematic intrusion of granites (at c. 550Ma). The present results demonstrate that the eastern Sør Rondane Mountains underwent Late Neoproterozoic extensional collapse similar to that observed in other parts of the East African–Antarctic Orogen including the Arabian–Nubian Shield and Madagascar.

New aeromagnetic view of the geological fabric of southern Dronning Maud Land and Coats Land, East Antarctica

The ice shield of Antarctica, which measures several kilometers in thickness, presents a challenge when attempting to unravel the subglacial geology. Here, we report about systematic airborne magnetic surveys conducted over the last decade, which investigated a significant part of Dronning Maud Land (DML), imaging for the first time the crustal architecture of the interior of this sector of East Antarctica. High-resolution data reveal parallel, elongated magnetic anomalies in southeastern DML. These NW–SE trending anomalies can be traced farther east into sparser Russian magnetic data sets. Several high amplitude magnetic anomalies with values above 400nT have been observed in southwestern DML and Coats Land. They differ clearly in wavelength and amplitudes from the magnetic pattern found in the east and do not show any evidence of a Pan-African orogenic belt or suture zone connecting the Shackleton Range with eastern DML, as hypothesized in several studies. This leads to the assumption of the existence of a hitherto unrecognized large tectonic province in southeastern DML. Whereas an over 100km long magnetic lineament in the interior of the Dronning Maud Land may reflect a major shear zone akin to the Pan-African age Heimefrontfjella shear zone. Both findings bring new evidences to the still open question about the amalgation of East and West Gondwana. In addition, the magnetic data allow mapping the eastern extent of the presumable cratonic province of Coats Land, a region considered as a key piercing point for reconstructions of Rodinia. Furthermore, the Beattie Magnetic Anomaly in southern Africa is assumed to continue into East Antarctica. Two magnetic highs in western DML are identified as possible eastward continuation of this prominent anomaly.