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Tectonic models for development of the Svalbard Caledonides depend on reliable assessment of the metamorphic evolution of the various basement provinces involved. The Mosselhalvøya Group (MG) and the Atomfjella Complex (AC) have previously been assigned to the Nordaustlandet and West Ny-Friesland terranes, respectively. New analytical data and petrographic observations indicate that both units experienced two-stage metamorphism under similar pressure–temperature (P–T) conditions. Two stages of amphibolite facies metamorphism (M1 and M2) are clearly recorded by garnet and staurolite porphyroblast textures. The results of thermodynamic phase equilibrium modeling indicate that peak M2 metamorphism occurred at ∼7–7.5 kbar and 590–600 °C in both units. Zirconium-in-rutile trace element thermometry confirms the temperature estimates for M1 and M2 stages of metamorphism. Monazite chemical Th-U-Pb dates from the MG resolve a two-stage garnet growth at 444 ± 7 Ma (M1) and 423 ± 6 Ma (M2). In contrast, monazite dated in the AC defines a single age of 420 ± 4 Ma interpreted as M2 growth. We suggest M2 was coeval with early strike-slip motion along the Billefjorden Fault Zone, whereas M1 reflects initial tectonic burial of the studied units. The similarity in metamorphic history between the both units suggests that the boundary between them is a subordinate thrust fault within the Atomfjella thrust stack rather than a major boundary separating the Nordaustlandet and West Ny-Friesland terranes. The MG should be included within the West Ny-Friesland terrane and the tectonic boundary with the Nordaustlandet terrane is likely the Eolussletta Shear Zone.

Our study of a banded charnockite complex of the Muhlig-Hofmannfjella in Dronning Maud Land, Antarctica, illustrates how the combination of high-temperature (re-)crystallization processes, ...

This study focusses on the Grenville-age Maud Belt in Dronning Maud Land (DML), East Antarctica, which was located at the margin of the Proto-Kalahari Craton during the assembly of Rodinia. We present new U–Pb zircon ages and Hf–O isotope analyses of mafic and granitic gneisses exposed in the Orvin-Wohlthat Mountains and Gjelsvikfjella, central DML (cDML). The geochronological data indicate continuous magmatic activity from 1160 to 1070 Ma which culminated at 1110–1090 Ma, followed by high-grade metamorphism between 1080 and 1030 Ma. The majority of zircons from the Orvin-Wohlthat Mountains exhibit radiogenic Hf isotopic compositions corresponding to suprachondritic εHf (t) values and Mesoproterozoic model ages, indicating crystallization from predominantly juvenile magmas. However, the involvement of ancient sedimentary material, which were most likely derived from the adjacent Proto-Kalahari Craton, is revealed by a few samples with negative to neutral εHf (t) and significantly elevated δ18O values (8–10‰). Samples from further west, in Gjelsvikfjella have more mantle-like zircon O isotopic compositions and late Paleoproterozoic Hf model ages, indicating the incorporation of ancient, previously mantle-derived continental crust. The rocks in cDML, thus define part of an extensive Mesoproterozoic magmatic arc with subduction under the Proto-Kalahari margin. This involved significant growth of new continental crust, possibly related to slab retreat, accompanied by subordinate recycling of older crustal components. The Maud Belt has previously been correlated with the 1250–1030 Ma Natal Belt in southern Africa, which lay to the west in the context of Gondwana, although this assertion has recently been questioned. Our study supports the latter view in demonstrating that the continental arc magmatism in the Maud Belt appears to be temporally and tectonically unconnected to the accretion of (slightly older) juvenile oceanic islands in the Natal Belt, which, in contrast to the Maud Belt, show subduction polarity away from the craton. We thus speculate that the Namaqua-Natal to Maud Belt contact (exposed in the Heimefront Shear Zone) may represent a changed tectonic environment from arc/continent-continent collision to slightly younger continental margin orogenesis at the westernmost termination of this part of the global Grenville Orogen. The Maud Belt marks the beginning of a major, long-lived accretionary Andean-type tectonic regime on the eastern margin of Proto-Kalahari in the Meso-Neoproterozoic during Rodinia assembly and break-up until the formation of Gondwana. acceptedVersion

Despite the exclusion of the Southern Ocean from assessments of progress towards achieving the Convention on Biological Diversity (CBD) Strategic Plan, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has taken on the mantle of progressing efforts to achieve it. Within the CBD, Aichi Target 11 represents an agreed commitment to protect 10% of the global coastal and marine environment. Adopting an ethos of presenting the best available scientific evidence to support policy makers, CCAMLR has progressed this by designating two Marine Protected Areas in the Southern Ocean, with three others under consideration. The region of Antarctica known as Dronning Maud Land (DML; 20°W to 40°E) and the Atlantic sector of the Southern Ocean that abuts it conveniently spans one region under consideration for spatial protection. To facilitate both an open and transparent process to provide the vest available scientific evidence for policy makers to formulate management options, we review the body of physical, geochemical and biological knowledge of the marine environment of this region. The level of scientific knowledge throughout the seascape abutting DML is polarized, with a clear lack of data in its eastern part which is presumably related to differing levels of research effort dedicated by national Antarctic programmes in the region. The lack of basic data on fundamental aspects of the physical, geological and biological nature of eastern DML make predictions of future trends difficult to impossible, with implications for the provision of management advice including spatial management. Finally, by highlighting key knowledge gaps across the scientific disciplines our review also serves to provide guidance to future research across this important region.

SIMS U-Pb zircon dating of metaigneous rocks of the Nordbreen Nappe from the West Ny-Friesland terrane (Eastern Basement Province of Svalbard) yields crystallization ages of 1,761 +/- 4 Ma for a fe ...

Geological mapping and investigation of the mountain chain in Dronning Maud Land (DML) has been carried out by a number of geologists from South Africa, Japan, India, Germany, Russia and Norway over the last 40-50 years. The produced geological maps of these teams are, for a large part, based on fairly old data which makes these maps inhomogeneous. The maps are at different scales, contain different levels of details, and the standards for classification of the rock units may also differ between the maps. This limits the ability to use these maps to draw an overview tectonic model of the evolution of Dronning Maud Land.In this contribution, we present a newly compiled geological map and GIS database of the Dronning Maud Land. The map will be available soon as an open-access database, but the readers can test a test version of it at: https://geokart.npolar.no/Html5Viewer/index.html?viewer=Geology_DML. The geological importance of the Dronning Maud Land to understanding the evolution of the southern parts of the Gondwana supercontinent was the main motivation factor as the DML is considered as the missing link between the geology of South Africa, Australia and Indian subcontinent.The new database covers the area between 20o W and 45o E and was compiled at a scale level of 1:250 000. However, the database provides another scale level of 1:5 000 000 to put the DML in the regional framework of the Gondwana. The geological map is descriptive based on the new topographic dataset of the Landsat 8. The project was based at the Norwegian Polar Institute from 2014 to 2018 and supported by a research grant from the Ministry of Foreign Affairs, Norway.

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. acceptedVersion

Accepted manuscript version, licensed CC BY-NC-ND 4.0. The bedrock of Mühlig-Hofmannfjella, central Dronning Maud Land in eastern Antarctica, is part of the high-grade Maud Belt and comprises a deep-seated metamorphic-plutonic complex. The P-T-t evolution of anatectic supracrustal gneisses has been recovered through a study of mineral assemblages, textural relationships and U-Pb ID TIMS geochronology on zircon and monazite followed by pseudosection modelling. Peak conditions reached granulite facies conditions (T ≥ 810–820 °C) at moderate crustal depths (P = ca. 8 kbar) and resulted in partial melting. Peak-pressure conditions were followed by isothermal decompression at elevated temperatures. After exhumation to crustal levels of about 4–5 kbar, the area underwent a final near-isobaric cooling, which is documented by a secondary growth of garnet. Zircons indicate a period of growth at 570–566 Ma, whereas monazite ages range from 610 to 525 Ma. A likely heat source for the granulite facies metamorphism is decay of radioactive heat-producing elements in the core of the orogen. The combined geochronology and metamorphic data indicate a prolonged, clockwise P-T path, which reflects collision and formation of a long-lived orogenic plateau.

A high-grade metamorphic complex is exposed in Filchnerfjella (6–8°E), central Dronning Maud Land. The metamorphic evolution of the complex has been recovered through a study of textural relationships, conventional geothermobarometry and pseudosection modelling. Relicts of an early, high-P assemblage are preserved within low-strain mafic pods. Subsequent granulite facies metamorphism resulted in formation of orthopyroxene in rocks of mafic, intermediate to felsic compositions, whereas spinel + quartz were part of the peak assemblage in pelitic gneisses. Peak conditions were attained at temperatures between 850–885 °C and 0.55–0.70 GPa. Reaction textures, including the replacement of amphibole and garnet by symplectites of orthopyroxene + plagioclase and partial replacement of garnet + sillimanite + spinel bearing assemblages by cordierite, indicate that the granulite facies metamorphism was accompanied and followed by decompression. The observed assemblages define a clock-wise P-T path including near-isothermal decompression. During decompression, localized melting led to formation of post-kinematic cordierite-melt assemblages, whereas mafic rocks contain melt patches with euhedral orthopyroxene. The granulite facies metamorphism, decompression and partial crustal melting occurred during the Cambrian Pan-African tectonothermal event.

40Ar/39Ar geochronological data on hornblende, biotite and K-feldspar provide constraints on the cooling path experienced by a high-grade metamorphic complex from the Muhlig–Hofmannfjella and Filchnerfjella (6–8°E), central Dronning Maud Land, Antarctica, during the late Neoproterozoic-early Palaeozoic Pan–African orogeny. Hornblende ages yield c. 481 Ma, biotite ages range from c. 466 Ma to c. 435 Ma, whereas K-feldspar ages of the gneisses are c. 437 Ma. The 40Ar/39Ar data suggest initial cooling at a rate of ~10 °C/Myr between 481 and 465 Ma, followed by a lower cooling rate of ~6 °C/Myr during the subsequent c. 30 million years. The K-feldspar 40Ar/39Ar ages place a lower time limit on the duration of the exhumation, by the time of thermal relaxation to a stable continental geotherm. The 40Ar/39Ar data reflecting cooling indicate tectonic exhumation related to orogenic collapse during a later phase of the Pan–African orogeny.

A high-P granulite facies gneiss complex occurs in north-west Payer Land (74°28′−74°47′N) in the central part of the East Greenland Caledonian (Ordovician–Devonian) orogen. High-P metamorphism of the Payer Land gneiss complex resulted in formation of the assemblages Grt + Cpx + Amp + Qtz + Ru ± Pl in mafic rocks, and Grt + Ol + Cpx + Opx + Spl in rare ultramafic pods. Associated metapelites experienced anatexis in the kyanite stability field. Peak metamorphic assemblages formed around 800–850 °C at pressures of c. 1.4–1.7 GPa, corresponding to crustal depths of c. 50 km. Mafic granulites contain abundant reaction textures, including the replacement of garnet by symplectites of Opx + Spl + Pl, indicating that the high-P event was followed by decompression while the granulites remained at elevated temperatures. Charnockitic gneisses from Payer Land show evidence of late Archean (c. 2.8–2.4 Ga) crustal growth and subsequent Palaeoproterozoic (c. 1.85 Ga) metamorphism. The gneiss complex experienced intense reworking during the Caledonian continental collision. On the basis of Caledonian monazite ages recorded from the high-P anatectic metapelites, the clockwise P–T evolution and formation of the high-P granulite facies assemblages is related to Caledonian crustal thickening, which resulted in formation of eclogites approximately 300 km north of Payer Land. The Payer Land granulites comprise a metamorphic core complex, which is separated from the overlying low-grade supracrustal rocks (the Neoproterozoic Eleonore Bay Supergroup) by a late Caledonian extensional fault zone, the Payer Land Detachment. The steep, nearly isothermal, unloading P–T path recorded by the granulites can be explained by erosional and tectonic unroofing along the Payer Land Detachment.

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Caledonian eclogites and associated high-pressure rocks are present in a 400×100-km long belt along the coast of North–East Greenland. Kyanite and clinozoisite eclogites on Weinschenk Island (77°54′N, 21°17′W) occur as lenses within amphibolite facies, quartzofeldspathic gneisses. The eclogites have been extensively overprinted by lower pressure assemblages and exhibit a variety of coronitic and symplectitic reaction textures that record the exhumation path of the rocks. Textural relationships and mineral composition data indicate that the initial high-pressure, plagioclase-free assemblage was garnet+omphacite±kyanite±clinozoisite+rutile. Compositional growth zoning in garnet, together with distribution of mineral inclusions within it, record a prograde evolution from epidote–amphibolite facies progressing into the eclogite facies. Post-peak pressure reaction textures include clinopyroxene–plagioclase intergrowths after omphacite; the replacement of kyanite by sapphirine–plagioclase, spinel–plagioclase and corundum–plagioclase symplectites; and resorption of garnet by amphibole–plagioclase kelyphites. The replacement textures indicate that post-eclogite facies decompression took place while the rocks remained at elevated temperatures (upper amphibolite/granulite facies conditions). The metamorphic evolution of the eclogites is in agreement with eclogite formation by thick-skinned crustal imbrication and subhorizontal shortening of the Laurentian margin during Caledonian collision, exhumation to amphibolite facies by emplacement of the eclogite-bearing thrust sheet on the Laurentian margin and accompanying erosion, and final exhumation to the surface by post-Caledonian crustal thinning.

High-pressure metamorphic rocks (eclogites and high-pressure granulites) occur along the entire length of the Norwegian Caledonides, and have formed from a variety of protoliths. In some cases, the relationship between protoliths, high-pressure rocks and their later retrogression products have been preserved in-situ. Fluid-inclusion data suggest a simple correlation between metamorphic grade and metamorphic fluid composition: (1) Eclogites and high-pressure granulites contain N 2 -bearing fluids (pure N 2 , or mixtures with CO 2 or H 2 O, with X N 2 > 5%). In some eclogite-facies rocks, CO 2 /1bN 2 inclusions are associated with aqueous brine inclusions (ca. 30 wt% NaCl), the two compositions representing immiscible fluids at peak metamorphic conditions. (2) Granulite -facies protoliths and eclogites reworked in the granulite-facies contain pure CO 2 or CO 2 -dominated fluids with less than 2.5% N 2 . (3) Rocks retrograded in the amphibolite facies contain H 2 O/1bNaCl fluids. Immiscibility between brine and anhydrous N 2 /1bCO 2 fluid, and between anhydrous fluid and waterbearing aluminosilicate-melt have taken place in some eclogites. During high-grade metamorphism, nitrogen may be incorporated in minerals, as NH 4 substituting for K, or it may occur as N 2 in the free fluid phase. The partitioning of nitrogen between minerals and fluids depends upon the water activity and oxygen fugacity during metamorphism, low a H 2 O and/or high f O 2 partitioning nitrogen to the fluid phase. A rock interacting with a carbonic fluid at granulite-facies PT conditions will be depleted in mineralogically bound nitrogen. In cases where the protoliths of high-pressure rocks have been through a previous, granulite-facies event, a local source for the nitrogen contained in high-pressure fluid is therefore unlikely.

[1] The basement of Svalbard comprises several terranes that were assembled along NS-trending faults during the Caledonian orogeny. The NW and NE parts of Svalbard are considered to be derived from east Greenland, while SW Svalbard has affinities with Pearya, Ellesmere Island. High-pressure (HP) metamorphic rocks, such as eclogites and blueschists occur in west Svalbard and provide constraints on the history of the Caledonian convergence. The Motalafjella HP rocks display a geometry which is compatible with an initial dome structure sealed by Ordovician deposits. Retrogressed eclogites in Biscayarhalvoya appear in the uppermost unit of a nappe stack that formed in a constrictional deformation regime. The syncollisional exhumation of the eclogites was achieved before the deposition of Late Silurian conglomerates. The two field occurrences of HP rocks are interpreted with a detailed age review for the Svalbard terranes and a restoration of Svalbard paleogeography in the Devonian. We propose that the different tectonic events are part of a continuous Ordovician-Silurian orogenic sequence, predating the Scandian collision between Laurentia and Baltica. The closure of an ocean between Laurentia and a microplate was responsible for the formation and exhumation of the HP rocks of Motalafjella in the Ordovician, and later followed by the collision of the microplate with Laurentia in the Silurian. This orogenic phase can be considered as an equivalent of the Taconic orogeny in the Appalachians. The relative position of the Svalbard terranes and Greenland during this orogenic episode is constrained by strain directions measured in the field.

Excellent outcrops in Dronning Maud Land, Antarctica, provide unique insight into the mode and extent of fluid infiltration into metamorphic and plutonic rocks in the middle crust. The fluids are liberated from pegmatitic veins and give rise to alteration halos. In the alteration halos, the conspicuous change in colour is correlated with (1) hydration mineral reactions, and (2) high density of microcracks in quartz and feldspar exceeding that observed in the unaltered host rock by an order of magnitude. The field relations indicate that the veins originated as melt-driven hydraulic fractures, sealed by pegmatite and aplite crystallising from volatile-rich melts, with the alteration halo being the wake of the process zone formed at the tip of the propagating fractures. It is proposed that (1) the size of the alteration zone and the width of the vein are correlated, resulting in higher values of both these quantities for cracks propagating at higher velocities and consequently higher crack propagation toughnesses; (2) the damage zone is characterised by a transient state of high permeability which was short-lived due to rapid healing and sealing of microcracks; (3) the infiltration and retrogression of the high-grade rocks can be considered as a quasi-instantaneous process on geologic time scales with a duration of hours to weeks.

Paleozoic blueschist facies rocks are relatively scarce on Earth due to warmer geother- mal gradients at that time and/or later reequilibration. Ferro-magnesiocarpholite (Fe-Mg carpholite), the typical low-temperature blueschist facies index mineral in metapelites, was discovered 30 yr ago and is known only in Tethyan belts metamorphosed ,80 m.y. ago. Herein we report the discovery of Paleozoic Fe-Mg carpholite in the ca. 470 Ma blueschists of Motalafjella, Svalbard Caledonides, the oldest known occurrence on Earth. The car- pholite-bearing rocks reached pressure-temperature (P-T) conditions of 15-16 kbar and 380-400 8C and followed a nearly isothermal exhumation path. In the cooling Earth per- spective, these P-T estimates for Motalafjella blueschists demonstrate the existence of cold subduction-zone gradients (;7 8C/km) from the middle Paleozoic onward.

The nunataks of Muhlig-Hofmannfjella and Filchnerfjella in central Dronning Maud Land, East Antarctica, comprise a deep-seated metamorphic-plutonic rock complex, dominated by a dark colour due to dark feldspar and containing granulite facies minerals including perthite, plagioclase, orthopyroxene and garnet. The area was affected by a late Pan-African fluid infiltration outcropping as conspicuous light alteration zones restricted to halos around thin granitoid veins. The veins were formed during infiltration of volatile-rich melts, probably originating from underlying magma-chambers. The alteration halos were formed by CO2-H2O-volatiles emanating from the veins into the host rock causing hydration of the granulite facies assemblages. The alteration involves a breakdown of orthopyroxene to biotite and sericitisation of plagioclase at crustal conditions around 350–400°C and 2 kbar. The marked colour change is caused by transformation of feldspars, spread of dusty micas, opaques and fluid inclusions in addition to replacement of coarse to finer grains. The process is locally penetrative indicating that fluid infiltration can affect large rock volumes. The frequent distribution of alteration zones throughout the mountain range independent of lithological variations shows that the fluid infiltration is regionally extensive.

The Mühlig-Hofmann- and Filchnerfjella in central Dronning Maud Land, Antarctica, consist of series of granitoid igneous rocks emplaced in granulite and upper amphibolite facies metamorphic rocks. The area has experienced high-temperature metamorphism followed by near-isothermal decompression, partial crustal melting, voluminous magmatism and extensional exhumation during the later phase of the late Neoproterozoic to Cambrian Pan-African event. Remnants of kyanite–garnet–ferritschermakite–rutile assemblages indicate an early higher-pressure metamorphism and crustal overthickening. The gneisses experienced peak granulite facies temperatures of 800–900 °C at intermediate pressures. Breakdown of garnet + sillimanite + spinel-bearing assemblages to cordierite shows subsequent re-equilibration to lower pressures. An E–W foliation dominating the gneisses illustrates transposition of migmatites and leucocratic melts which evolved during the near-isothermal decompression. Occurrence of extensional shear bands and shear zones evolving from the ductile partial melting stage through semiductile towards brittle conditions, shows that the uplift persisted towards brittle crustal conditions under tectonic W/SW-vergent extension. Late-orogenic Pan-African quartz syenites intruded after formation of the main gneiss fabric contain narrow semiductile to brittle shear zones, illustrating that the extensional exhumation continued also after their emplacement. The latest record of the Pan-African event is late-magmatic fluid infiltration around 350–400 °C and 2 kbar. At this stage the Pan-African crust had undergone 15–20 km exhumation from the peak granulite facies conditions. We conclude that the later phase of the Pan-African event in central Dronning Maud Land is characterized by a near-isothermal decompression P–T path and extensional structures indicating tectonic exhumation, which is most likely related to a late-orogenic collapsing phase of the Pan-African orogen.

A translation of the Danish book Gronlands geologiske udvikling, published in 2005, Geological history of Greenland summarizes the results of more than 60 years of geological mapping and investigations in Greenland by the Geological Survey of Denmark and Greenland. This is a beautifully illustrated, large-format volume. The 270 pages provide a stunning visual presentation, with as many as 850 colour illustrations, photographs and maps accompanied by comprehensive captions. Even if the reader has only a very limited knowledge or interest in geology, the many high-quality scenic pictures of Greenlandic landscapes are impressive. Sixty fact boxes explain basic geological concepts and processes. A full glossary of geological terms, as well as suggestions for further reading, is also provided.