The bedrock of Jutulsessen in Gjelsvikfjella, Dronning Maud Land (Antarctica), experienced highgrade metamorphism during the Ediacaran-Cambrian orogeny associated with the assembly of Gondwana. This event caused partial melting of granodioritic gneiss and the formation of metatexite migmatites. This study investigates in situ melting, melt mobilisation, and extraction, with emphasis on how deformation structures influence melt generation and transport. Petrographic evidence for incipient melting includes quartz films along plagioclase grain boundaries, cuspate outlines of quartz and K-feldspar, and "string of beads" textures. Neosomes contain poikilitic hornblende formed by fluid-present, incongruent melting of biotite. Field observations document progressive melt evolution, as evidenced by several sets of neosomes and leucocratic veins. In situ N1 neosomes form first, followed by axial-plane-parallel N2 neosomes, which later coalesce into a network of cross-cutting leucocratic veins (V3). Melt migration is closely linked to deformation-related dilation sites, which localise melt segregation and facilitate transport, indicating that folding, partial melting, and melt movement occurred simultaneously at the outcrop scale. Aplite and pegmatite dykes, observed elsewhere in the Jutulsessen area, cut the regional foliation and record post-kinematic emplacement. Their field relations and geochronological constraints suggest mid-crustal crystallisation. These observations fit within the established tectonic framework for Dronning Maud Land, which involves continental collision followed by post-collisional extension and orogenic collapse. Within this context, the Jutulsessen metatexites provide a well-constrained example of crustal anatexis in an orogenic environment and provide insight into the generation and transport of granitic magmas in the continental crust.

The tectonic status, the mode of Caledonian deformation and the transport distance of the Precambrian units on the Fennoscandian Shield that constitute the so-called tectonic windows within the realm of the Scandinavian Caledonian nappe pile have long been a subject of dispute. It has been argued for several hundred kilometres of eastward transport for some of these tectonic units, whereas parautochthonous to autochthonous positions have also been suggested. In this contribution, geophysical data have been studied to shed light on this controversy. A dominant regional NNW–SSE to north–south structural grain of Precambrian origin extends beneath the Caledonian nappes. Indeed, similar structural patterns appear in several of the tectonic windows within the orogen. However, magnetic anomalies in southern Norway and the Nordland area show an apparent c. 90° counterclockwise rotation into the Caledonian trend along a line from Nordfjord in western Norway to Senja in northern Norway, whereas the anomalies in Finnmark (northernmost Norway), seem to be rotated clockwise along a line from Kvænangen to Porsangerfjorden. We suggest that this pattern extending through the Caledonides likely represents a boundary between two crustal domains with different Caledonian reworking. The eastern domain demonstrates less extensive modification during the Caledonian continent–continent collision. Some thrusts within basement windows in the eastern domain accommodated transport of a few tens of kilometres, revealing a parautochthonous status for most of these windows. Interpretations of aeromagnetic and gravity data have shown that the Caledonian nappes occurring along detachments extend to a maximum depth of c. 9 km below sea-level. The thickest nappe piles occur along the late Caledonian detachments. The eastern basement domain with minor Caledonian deformation has a thinner nappe stack (up to 4–5 km below). Our combined interpretations also show the need to modify the tectonostratigraphy of the northern Scandinavian Caledonides. The Lower Laksefjord Nappe in Finnmark, for instance, is interpreted as a parautochthonous window into the Precambrian basement and is not part of the Laksefjord Nappe Complex that has been transported hundreds of kilometres.

Sillimanite-bearing gneisses in the Romsdal region of the Western Gneiss Region (south Norway) have been investigated to document the presence, formation, composition and petrological evolution of the sillimanite-bearing assemblages. Sillimanite is found in augen gneiss, as nodular gneiss, and in well-foliated sillimanite–mica gneiss. Lenses and layers of eclogite occur within the gneiss units. The sillimanite-bearing gneisses are heterogranular and dominated by quartz, plagioclase (An29–41), K-feldspar and biotite (Mg# = 0.48–0.58; Ti = 0.16–0.36 a.p.f.u.), with variable amounts of white mica (Si = 6.1–6.3). K-feldspar occurs as porphyroclasts in augen gneiss, and garnet constitutes resorbed porphyroblasts. Garnet (Alm46–56Sps24–36Prp10−20Grs4–6; Mg# = 0.22–0.29) shows rimward-decreasing Mg#, together with a smaller grossular decrease and a marked spessartine increase up to Sps36. The foliation is defined by crystal-preferred-orientation micas, elongation of shape-preferred-orientation coarse K-feldspar phenocrysts and a modal banding of phases. Sillimanite occurs as coarse orientation-parallel matrix porphyroblasts, as finer grains and as fibrolitic aggregates. Quartz constitutes coarser elongated grains and monomineralic rods. Pseudosection modelling suggests that the peak-metamorphic mineral assemblage of garnet–sillimanite–feldspar–biotite–quartz–ilmenite–liquid equilibrated at temperatures up to 750 °C and pressures of 0.6 GPa. Subsequent retrogression consumed garnet. Mineral replacement and melt crystallization involved sillimanite, white mica, K-feldspar and quartz. The results document a metamorphic retrogression of the sillimanite gneisses in accordance with the presence of remnants of eclogites and high-pressure granulites in this northwestern part of the Western Gneiss Region.

Fluid infiltration into Proterozoic and Early Palaeozoic dry, orthopyroxene-bearing granitoids and gneisses in Dronning Maud Land, Antarctica, has caused changes to rock appearance, mineralogy, and rock chemistry. The main mineralogical changes are the replacement of orthopyroxene by hornblende and biotite, ilmenite by titanite, and various changes in feldspar structure and composition. Geochemically, these processes resulted in general gains of Si, mostly of Al, and marginally of K and Na but losses of Fe, Mg, Ti, Ca, and P. The isotopic oxygen composition (δ18OSMOW = 6.0‰–9.9‰) is in accordance with that of the magmatic precursor, both for the host rock and infiltrating fluid. U-Pb isotopes in zircon of the altered and unaltered syenite to quartz-monzonite indicate a primary crystallization age of 520.2 ± 1.0 Ma, while titanite defines alteration at 485.5 ± 1.4 Ma. Two sets of gneiss samples yield a Rb-Sr age of 517 ± 6 Ma and a Sm-Nd age of 536 ± 23 Ma. The initial Sr and Nd isotopic ratios suggest derivation of the gneisses from a relatively juvenile source but with a very strong metasomatic effect that introduced radiogenic Sr into the system. The granitoid data indicate instead a derivation from Mid-Proterozoic crust, probably with additions of mantle components.

In this study, we have investigated rock weathering phenomena in the central part of Dronning Maud Land, Antarctica. The area is characterized by low mean annual temperatures (-18 degrees C), strong katabatic winds, and minimal liquid water at the surface. Weathering features, including ventifacts, tafoni, and grus accumulations, are characterized through field observations, rock surface temperature measurements, and microscopic analysis. Abrasion by sand and ice particles transported by strong winds has locally resulted in ridge-shaped ventifacts and rock surfaces with elongated pits, furrows, and grooves. The abrasion-caused features, such as polished facets, keels, and grooves, indicate a northeast-facing wind direction, aligning with the present-day wind regime. The dominant weathering processes in coarse-grained intrusive rocks are oxidation and granular disintegration. Feoxidation induces cracking, increasing the porosity and enhancing susceptibility to further weathering. Additionally, temperature fluctuations on rock surfaces caused by solar radiation create thermal stress, which can lead to the formation of microcracks. These microcracks, formed due to thermal expansion, are likely to propagate through subcritical cracking, which is a slow, long-term process. Together, Fe-oxidation, thermal expansion, and subcritical cracking are important mechanisms contributing to long-term weathering and rock decay. Salt weathering, facilitated by snow and ice meltwater, particularly within tafoni, leads to flaking and disintegration of the parent rock. These findings shed light on the complex interactions shaping the geomorphology of central Dronning Maud Land and provide insights into long-term weathering processes operating in Antarctica's extreme environment.

Graphite formation in the deep crust during granulite facies metamorphism is documented in the Proterozoic gneisses of the Lofoten–Vesterålen Complex, northern Norway. Graphite schist is hosted in banded gneisses dominated by orthopyroxene-bearing quartzofeldspathic gneiss, including marble, calcsilicate rocks and amphibolite. The schist has major graphite (<modality 39%), quartz, plagioclase, pyroxenes, biotite (Mg# = 0.67–0.91; Ti < 0.66 a.p.f.u.) and K-feldspar/perthite. Pyroxene is orthopyroxene (En69–74) and/or clinopyroxene (En33–53Fs1–14Wo44–53); graphite occurs in assemblage with metamorphic orthopyroxene. Phase diagram modelling (plagioclase + orthopyroxene (Mg#-ratio = 0.74) + biotite + quartz + rutile + ilmenite + graphite-assemblage) constrains pressure-temperature conditions of 810–835 °C and 0.73–0.77 GPa; Zr-in-rutile thermometry 726–854 °C. COH fluids stabilise graphite and orthopyroxene; the high Mg#-ratio of biotite and pyroxenes, and apatite Cl < 2 a.p.f.u., indicate the importance of fluids during metamorphism. Stable isotopic δ13Cgraphite in the graphite schist is −38 to −17‰; δ13Ccalcite of marbles +3‰ to +10‰. Samples with both graphite and calcite present give lighter values for δ13Ccalcite = −8.7‰ to −9.5‰ and heavier values for δ13Cgraphite = −11.5‰ to −8.9‰. δ18Ocalcite for marble shows lighter values, ranging from −15.4‰ to −7.5‰. We interpret the graphite origin as organic carbon accumulated in sediments, while isotopic exchange between graphite and calcite reflects metamorphic and hydrothermal re-equilibration.

Central Dronning Maud Land (cDML) is part of the late Mesoproterozoic Maud Belt in East Antarctica, which was metamorphosed and deformed during the Ediacaran–Cambrian Gondwana assembly. Here we study high-pressure (HP) mafic rocks in Gjelsvikfjella, cDML, which occur as lenses and pods transposed in highly strained, upper amphibolite-facies gneisses. We present a P–T–t history for the HP rocks based on mineral assemblages, reaction textures and new U–Pb zircon data. Relics that indicate an early HP granulite-facies stage have been identified in anhydrous garnet–clinopyroxene rocks. The peak-pressure assemblage was plagioclase-free and contained garnet, titanite, clinopyroxene and quartz. The HP assemblage has been extensively overprinted by lower-pressure phases and exhibits a variety of symplectite and corona textures that record the post-peak-pressure evolution of the rocks. Decompression and heating in the granulite-facies field resulted in the replacement of titanite by ilmenite–clinopyroxene symplectite, formation of clinopyroxene–plagioclase intergrowths and resorption of garnet by plagioclase–clinopyroxene kelyphite. Formation of late orthopyroxene in symplectites and kelyphites demonstrates that the P–T evolution entered the medium-pressure granulite-facies field. The peak metamorphic stage was followed by retrograde cooling into the amphibolite facies. In situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating of zircons indicate Mesoproterozoic protolith ages (1150–1000 Ma) and Ediacaran–Cambrian metamorphic reworking at ca. 568 and ca. 514 Ma. The HP granulites were formed and exhumed during a clockwise P–T evolution related to continental collision during Gondwana amalgamation, followed by post-collisional extension and orogenic collapse.

Proterozoic foliated and nodular sillimanite gneisses from the Bamble lithotectonic domain, South Norway, are analysed to unravel their microfabric evolution with mineral reactions during metasomatism and associated deformation. The nodules form cm-scaled spherical to ellipsoidal sillimanite-quartz aggregates that locally grade into foliated sillimanite gneisses. Independent on their fabric, they record incomplete breakdown reactions of biotite and K-feldspar recorded by muscovite lamellae and associated Fe-oxide needles in biotite and by muscovite-quartz aggregates after K-feldspar. Muscovite is partly replaced by sillimanite. Based on immobile Al, the nodular gneiss forming reactions give excess K, Mg and H2O that may leave the nodular gneiss to form a metasomatic agent and caused regional metasomatism (scapolitisation) in the surrounding rocks. Quartz in the foliated gneisses shows a pronounced shape but no marked crystallographic preferred orientation. There is no indication of major strain accumulation by quartz dislocation creep. Muscovite shows lobate phase boundaries to quartz, which is interpreted as reaction fabric, from the breakdown reactions of K-feldspar and biotite. The nodular and sillimanite gneisses formed during metasomatic mineral reactions, where major elements K, Mg and H2O leave the rock and an Al-rich metasomatic restite remains. We suggest that the metasomatism involved a molar volume loss, where reactions forming muscovite, quartz and sillimanite occurred by incongruent dissolution-precipitation creep at low stresses forming the nodular and foliated gneisses. Our study demonstrates that metasomatism with chemical rock changes and mass transfer associated with incongruent dissolution-precipitation contributed to the observed reaction and deformation microfabric.

Tafoni are a type of cavernous weathering that is found in a variety of rock types and locations around the world. Tafoni have been documented in a number of climatic zones ranging from hot and cold deserts to moist coastal environments. Despite the widespread distribution of tafoni, the major processes controlling tafoni weathering are not well understood and are still a matter of discussion. This study addresses the frequent distribution of well-developed tafoni in the cold, arid environment of the inland mountain range of central Dronning Maud Land, Antarctica. The aim is to document and characterize the nature of tafoni present in Gjelsvikfjella (2°E) eastward to Filchnerfjella (8°E) and to discuss formation processes. The cavities occur in groups and are typically spherical to oval shaped. They range in diameter and depth from 1 dm up to 1.5 m. The cold, arid environment of this region favors mechanical weathering mechanisms such as freeze-thaw actions and wind abrasion. Furthermore, the structural, textural, and mineralogical properties of the parent rock can potentially have a strong control on weathering and cavity development. Observed tafoni are typically formed in massive granitoid intrusives and granitic gneisses and migmatites. Chemical dissolution of pyroxene to iddingsite and radiation from rare earth element–bearing accessory minerals cause microfracturing, which facilitates freeze-thaw actions and accordingly enhances the weathering.

In a combined geological, petrological and isotopic study from the Lofoten-Vesterålen Complex, Norway, graphite is documented formed in the deep Proterozoic crust. Graphite schist is hosted in sequences of banded gneisses dominated by orthopyroxene-bearing quartzofeldspatic gneiss, interlayered with horizons of marble, calcsilicates and amphibolite. The schist displays a strong foliation and has a major content of graphite up to a modality of 39%. Quartz and plagioclase (Ab47-93An5-52), pyroxenes, biotite (Mg# = 0.67-0.91; Ti < 0.66 a.p.f.u.), and K-feldspar (Ab1-8Kfs92-99) or perthite (Ab35-64An3Kfs50-62) are additional major phases. Pyroxene is present either as orthopyroxene (En69-74Fs26-29; Mg#=0.70-0.74), as clinopyroxene (En33-53Fs1-14Wo44-53; Mg#=0.70-0.97), or both. Pseudosection modeling of the plagioclase + orthopyroxene (Mg#-ratio = 0.74) + biotite + quartz + rutile + ilmenite + graphite-assemblage constrains its stability field to pressure-temperature conditions of 810-835 °C and 0.73-0.77 GPa. Zr-in-rutile also supports a temperature of formation of 740-870°C. Stable isotopic δ13C in graphite schist shows values from -38 to -17‰ while δ13C values of marbles range from +3‰ to +10‰. Mixed graphitic and calcite carbon samples give lighter values for the calcite (δ13Ccalcite = -8.65‰ to -9.52‰) and heavier values for graphite (δ13Cgrapite = -11.50‰ to -8.88‰) compared to the “pure” samples. δ18O for marble shows relatively light values for calcite ranging from -15.44‰ to -7.53‰ reflecting metamorphic and hydrothermal processes. From the stable C-isotopes we interpret the graphite origin as organic carbon accumulated in sediments contemporaneous with the Early Proterozoic global Lomagundi-Jatuli isotopic excursion. From petrography and mineral composition, we deduce the reaction equations producing and consuming H2O- and CO2-fluids leading to the stabilisation of graphite and orthopyroxene. The high Mg#-ratio of biotite and pyroxenes is an indication of metasomatism, and together with a high Cl-content of apatite up to 2 a.p.f.u. show the importance of fluids during the high-grade formation of graphite. The enrichment of graphite resulted in zones with strong schistosity and a sharp strain gradient towards host massive granulite gneiss; High-ordered graphite occurs as euhedral “flakes” (i.e., flake graphite) of fine- to medium grain size, with a strong preferred crystal orientation forming the well-developed foliation together with the crystal preferred orientation of biotite. The presence of graphite reduces crustal strength and causes strain localisation in the granulite facies crust.

The Kongsberg and Bamble lithotectonic domains of SE-Norway are known as classical Precambrian high-grade metamorphic terrains. The area has undergone extensive metasomatism with formation of albitites and scapolite-rich rocks and numbers of previously economically important deposits including the Kongsberg Silver and the Modum Cobalt mines. We demonstrate here that the central part of the Bamble lithotectonic domain (Kragero area) has locally developed low-grade metamorphic minerals (prehnite, pumpellyite, analcime, stilpnomelane and thomsonite) belonging to the prehnite-pumpellyite and zeolite facies. Structurally, the low-grade minerals occur as fracture fills, in the alteration selvages around fractures where the rock is albitized, and along shear zones and cataclastic zones. The fracture fill and the alteration selvages vary from millimetres scale to 1 m in thickness. The fractures with low-grade minerals are part of larger fracture systems. The low-grade minerals typically formed by both displacive (swelling) and replacive reactions and in a combination of these. Prehnite together with albite, K-feldspar, quartz, epidote and hydrogarnet form lenses along (001) faces in biotite and chlorite leading to bending of the sheet silicates through a displacive reaction mechanism. Numerous replacement reactions including the earlier minerals as well as the low-grade minerals occur. As albite, K-feldspar, talc, quartz, actinolite, titanite, calcite and hydrogrossular form in the same veins and in the same biotite grain as the classical low-grade minerals, they probably belong to the low-grade assemblage and some of the albitization in the region presumably occurred at low-grade conditions. Alteration of olivine (Fo69) at low-grade conditions results in the formation of clay minerals including ferroan saponite. Reconnaissance studies at the east (Idefjord lithotectonic domain) and the northwest (Kongsberg lithotectonic domain) sides of the Oslo rift together with reports of low-grade assemblages in south-western Sweden along the continuation of the rift into Skagerrak suggest that the low grade assembles occur in rocks adjacent to the Oslo rift along its full extent. Ar-Ar dating of K-feldspar from the low-grade assemblages gave an age of 265.2 +/- 0.4 Ma (MSWD = 0.514 and P = 0.766), suggesting that the low-grade metamorphism and some of the metasomatism is induced by fluids and heat from the magmatic activity of the Permian Oslo rift, which requires transport of fluid over distances of several kilometres. The metamorphic conditions are constrained by stability fields of prehnite, pumpellyite and analcime to be less than 250 degrees C and at a pressure less than 5 kbars. The displacive reactions created micro-fractures and porosity in the adjacent minerals that enhance fluid flow and low-grade mineral formation on a local scale. On a thin section scale, the displacive growth of albite in biotite results in a local volume increase of several 100%. Whether the opening of the larger, horizontally oriented fracture systems needed to transport the fluid over a distance of several kilometres was also the results of displacive reactions remains unknown. The low-grade metamorphism and metasomatism formed in the shoulder of the Oslo rift and may have contributed to its uplift.

The Proterozoic gneisses of the Bamble lithotectonic domain (south Norway) underwent intense scapolitisation caused by K- and Mg-rich fluids and extensive albitisation with formation of numerous ore deposits. By detailed studies of mineral reaction fabrics we document release of the chemical active Mg, K and Fe-components forming the metasomatic fluid: Breakdown of biotite to muscovite releases K, Mg, Fe, Si and H2O. As reaction products tiny Fe-oxide needles are present in the transforming rock. H2O is reacting with K-feldspar to produce additional amounts of white mica and quartz. During a subsequent reaction muscovite is replaced to sillimanite again releasing quartz and a K-rich fluid. The reactions form the peculiar sillimanite-nodular quartzite, but also well-foliated sillimanite-mica gneiss. Optical and EBSD microfabric studies reveal a shape preferred orientation for quartz, but despite of a pronounced foliation, quartz does not show a crystallographic preferred orientation. A crystallographic preferred orientation is present for mica and sillimanite. Coarse micas show sutured boundaries to quartz, implying low nucleation rates, no crystallographic or surface-energy control during growth and no obvious crystallographic relationship to quartz. Our study illustrates the transformation of a quartzofeldspatic lithology into sillimanite-bearing quartzite. The mineral replacement and deformation show ongoing metamorphic reactions during deformation. The microfabric data indicates reaction at non-isostatic stress condition. The deduced mineral replacement reactions document a source of K-, Mg- and Fe-rich metasomatic fluids necessary to cause the pervasive scapolitisation and Fe-deposition in the area. The mineral reactions and deformation produce rocks with a new mineralogy and structure; an increased understanding of these processes is important for the modelling of crustal building and geological history.

Our study of a banded charnockite complex of the Mühlig-Hofmannfjella in Dronning Maud Land, Antarctica, illustrates how the combination of high-temperature (re-)crystallization processes, melts, and volatile fluids leads to complex intrusive, metasomatic, and structural relationships. The igneous complex consists of gently dipping sets of charnockite interlayered with dolerite and leucogranite. The banded complex formed primarily by magmatic processes, but with superimposed modifications by metasomatism. The charnockite has a ferroan composition and contains both orthopyroxene (Fs80–84) and olivine (Fa94–96). Zircon U-Pb dates the emplacement of charnockite at 515 Ma, and inherited zircon cores and negative εNd values of −3 to −5 indicate that the age of the source of the magma was about 1100 Ma. Neodymium isotopes were not homogenized during the Cambrian magmatic event, which suggests that the generation and emplacement of the magma took place in separate batches during construction of the banded complex. By contrast, the Rb-Sr system in the charnockite was extensively homogenized, likely because of the superimposed late-magmatic fluid activity, which also produced the bands and networks of leucogranites. These events occurred during the late stages of the assembly of Gondwana, with postcollisional extension and mantle upwelling maintaining a high heat flow.

The eclogites from Vårdalneset, Western Gneiss Region, Norway, show an exceptional large variety of reaction and deformation microfabrics that document the processes and conditions during burial and exhumation. Coarse grained eclogites comprise about 35% omphacite, 25% garnet and 20% amphibole with various amounts of white mica, zoisite, kyanite, rutile, zircon and pyrite. Their fabric is characterized by few mm long and several hundred µm wide amphibole and omphacite grains aligned in the foliation plane with zoned garnet porphyroblasts up to several mm in diameter. In contrast, finer-grained mylonitic eclogites with grain diameters of few hundred µm comprise systematically higher amounts of garnet (45%) and omphacite (35%) and generally less amphibole (< 5%) but similar amounts of zoisite, white mica, rutile and quartz. In the coarse-grained eclogite, amphibole shows evidence of dislocation creep as indicated by undulatory extinction, subgrains and recrystallized grains in necks of boudinaged coarse amphibole layers as well as in contact to garnet. The large garnet porphyroblasts generally show a complex zonation with an inclusion-rich Fe-poor and Mg-rich inner core surrounded by a zone with Fe- and Ca-rich patches and a broad Mg-rich, Ca- and Fe-poor rim. Only at contact to coarse amphibole an additional, a few tens of µm thin serrated rim further enriched in Mg can occur. At the direct contact to such serrated Mg-rich rims, amphibole is partly replaced by a fine-grained quartz-kyanite ± rutile aggregate, indicating dehydration reactions of amphibole. Quartz - kyanite ± rutile aggregates are surrounding garnet also in contact to omphacite, zoisite and to other garnet crystals. The microstructures suggest that deformation and dehydration of amphibole are coupled and played an important role during deformation of the eclogites finally leading to the mylonitic eclogites with higher amounts of garnet and omphacite. Deformation is suggested to have triggered the dehydration reaction by a slight and local increase in temperature. Furthermore, deformation provided additional pathways for the escaping fluids along the increased grain and phase boundary area, as indicated by commonly present quartz within interstitials between recrystallized amphibole grains. In all samples, few µm wide amphibole rims replacing garnets document restricted rehydration-reactions at a later stage. The large variety of the deformation and reaction microfabrics exemplarily show that both deformation and metamorphic reactions did not proceed at long-term continuous conditions, but that both are coupled and occurred episodically.

Graphite impacts crustal rheology and electric conductivity in the lower crust. In a combined geophysical and geological study from the Proterozoic Lofoten‐Vesterålen Complex, Norway, we show the enrichment of graphite resulted in zones with strong schistosity and a sharp strain gradient towards host massive granulite gneiss. Increased graphite content resulted in high‐conductivity zones with true resistivity values <10 Ωm compared with a resistivity of >3,000 Ωm in the low‐conductive crust. The regionally distributed graphite zones contain up to 39% graphite with variable amounts of quartz, feldspars, biotite and pyroxenes and where graphite is present in stable assemblage to orthopyroxene. High‐ordered graphite and biotite with a strong‐preferred orientation define the well‐developed foliation. Our results demonstrate that graphite accounts for the high electric conductivity of this former Proterozoic lower‐crustal segment. The presence of graphite causes strain localisation in the granulite facies crust, reducing crustal strength and may thereby influence continental architecture and evolution of collision zones.

There are three provinces in Northern Norway in which occurrences of graphite are abundant; the Island of Senja, the Vesterålen archipelago, and the Holandsfjorden area. From these provinces, we report graphite resources from 28 occurrences. We use a combination of airborne and ground geophysics to estimate the dimensions of the mineralized areas, and, combined with sampling and analysis of the graphite contents, this gives us inferred resources for almost all the occurrences. The average TC (total carbon) content is 11.6%, and the average size is 9.3 Mt or 0.8 Mt of contained graphite. We demonstrate that the Norwegian graphite occurrences have grades and tonnages of the same order of magnitude as reported elsewhere. The graphite-bearing rocks occur in a sequence that encompasses carbonates, meta-arenites, acid to intermediate pyroxene gneisses, and banded iron formations metamorphosed into the granulite facies. Available radiometric dating shows that the graphite-bearing rocks are predated by Archean gneisses and postdated by Proterozoic intrusions of granitic to intermediate compositions.

Microfabrics of mylonitic orthopyroxene-bearing quartzofeldspatic granulites from central Dronning Maud Land, Antarctica, have been investigated to evaluate the deformation behaviour at lower crustal conditions. The microfabric is characterized by a fine-grained matrix of dispersed feldspar, quartz and orthopyroxene, which contains monophase elongate quartz and feldspar aggregates, so-called ribbons, and elongate monocrystalline orthopyroxene ribbon grains. The observed crystallographic preferred orientation (CPO) of orthopyroxene ribbon grains that contain clinopyroxene exsolution lamellae in (100) and kink bands in equidimensional porphyroclasts indicate (100)[001] dislocation glide. Fine-grained matrix orthopyroxene formed by deformation of porphyroclasts and growth in strain shadows during diffusional creep, indicating a separate stage of deformation and reaction. Although dislocation creep of coarse ribbon quartz is indicated by sutured grain boundaries at high angle to the ribbon boundary and few subgrains, the weak CPO is rather unspecific. Fine-grained matrix quartz shows no indication of dislocation creep. We suggest that epitactic growth during quartz-producing mineral reactions played a major role for ribbon formation during diffusional creep. Our study demonstrates the importance of episodic deformation and metamorphic reactions in lower continental crust with transient high stresses allowing for dislocation glide of orthopyroxene enclosed in a fine-grained polyphase matrix undergoing diffusional creep on long term.

The bedrock of Muhlig-Hofmannfiella, 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 degrees 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.

Northeastern Mozambique exposes a deeply eroded high-grade segment of the East African Orogen, situated at the critical intersection of the Pan-African orogenic belts, showing widespread granulite facies lithologies. This study documents and characterizes metamorphism attributed to the multistage Neoproterozoic and Early Palaeozoic events, relating to a polyphase Pan-African history of outboard nappe stacking, nappe emplacement onto Mesoproterozoic crust, and compressional and extensional deformation along the Lurio belt: 1) A Neoproterozoic nappe stack (Cabo Delgado Nappe Complex) records high-pressure granulite facies: The highest peak conditions reach P = 1.45 GPa and T > 800 degrees C are in Grt-Cpx-Pl-bearing mafic granulites of the Xixano Complex. A post-peak isothermal decompressional P-T evolution is supported by garnet chemical zoning pattern, pseudsection modelling and garnet corona textures. 2) The underlying Mesoproterozoic gneiss complexes record amphibolite facies to intermediate-pressure granulite fades, the high-grade metamorphism is documented by Grt-Opx-Cpx-Pl-bearing mafic granulites and chamockitic gneisses in the southern part of the Unango and Marrupa complexes. This metamorphism is attributed to crustal thickening related to overriding of the nappe complex and shortening along the Lurio belt during the early Palaeozoic Kuunga orogeny. 3) The Ocua Complex coring the Lurio belt is a locus of Early Palaeozoic high-pressure metamorphism. A minimum of P = 0.79 +/- 0.13 GPa at T = 760 +/- 98 degrees C is constrained by Grt-Opx-Cpx-Pl-Qz assemblage in mafic granulite from the western limb while high-pressure granulite metamorphism was reached in the eastern part of the complex. The high-pressure granulite facies conditions is followed by isothermal decompression.

Garnet–clinopyroxene mafic rocks have been investigated in the outer coastal area of the northwestern‐most part of the Western Gneiss Region (WGR), South Norway. The garnet–clinopyroxene rocks occur as lenses with amphibolitized and deformed margins ranging in size from 1 m2 up to 2–3 km2. They are regionally widespread and included in migmatitic gneisses, mica schists and amphibolites. The mafic lenses vary from fine‐ to coarse‐grained with a strain variation from massive to coaxial S > L tectonite fabric. Garnet is Alm42‐53Prp17‐35Grs20‐33Sps0‐3. Clinopyroxene is a Na–Al diopside (En34‐43Fs8‐17Wo48‐52) with Al up to 0.50 a.p.f.u. and Na content up to Jd24. Garnet and clinopyroxene occur in an assemblage with edenitic‐pargasitic amphibole (Ti < 0.32 a.p.f.u.), plagioclase (An16‐43Ab57‐71), quartz, locally biotite (Mg# = 0.0.46–0.56; Ti = 0.51–0.59 a.p.f.u.), calcite, epidote and accessory rutile, ilmenite, zircon and apatite. Garnet porphyroblasts occur commonly as euhedral crystals, and locally with corroded rims surrounded by a corona of plagioclase or amphibole–plagioclase. Growth of secondary garnet is locally observed in S > L tectonite rock. Clinopyroxene occurs as elongated subhedral crystals forming a strong fabric, or as a coarse symplectite with plagioclase. Amphibole is present as matrix grains in the garnet–clinopyroxene assemblage, but occurs also in coronas on garnet as symplectite with plagioclase, or as replacement textures on clinopyroxene. Secondary titanite is produced on rutile, and spinel+plagioclase on ilmenite. The P–T evolution is modelled by P–T pseudosections (TheriakDomino software), thermobarometry and by mapping of garnet chemistry. Garnet porphyroblasts show a decrease in CaO and MnO, an increase in MgO and variable FeO with resulting increasing Mg# from core to rim, indicating growth under increasing temperatures and decompression. Calculation of garnet+clinopyroxene+plagioclase+quartz+rutile stability combined with garnet and clinopyroxene isopleths of grossular and Mg# composition yields a maximum temperature metamorphism of 1.4–1.8 GPa and >900°C. The P–T modelling supports high‐P granulite facies conditions for the equilibration of the garnet–clinopyroxene‐dominated mafic lenses. The maximum temperature metamorphism is associated with partial melting. In addition, an outermost small Mn increase, and local reversal of the Mg# ratio and CaO‐flattening in garnet of the mafic lenses are interpreted as retrogression into amphibolite facies. This is in accordance of mineral replacement of clinopyroxene to amphibole and titanite growth on rutile. The data support an evolution where the eclogite facies crust in the northwestern‐most coastal part of WGR underwent decompression during heating into high‐P granulite facies conditions, followed by cooling and amphibolitization. Our investigation gives a regional petrological documentation and illustrates an extensive high‐T equilibration in the Caledonian root zone subsequent to the deep crustal burial.