Abstract Lenses and boudins of eclogitized and non-metamorphic gabbroic and ultramafic rocks occurring in quartzofeldspathic gneisses and migmatites of the Marun-Keu Complex, Polar Urals, are of central interest for the study of fluid-controlled processes in the subducting continental lithosphere. Petrology and mineral chemistry, combined with multi-equilibrium geothermobarometry and phase-equilibrium modelling, applied to mafic eclogitic rocks show a prograde evolution from c. 685°C, 1.89 GPa and a H 2 O = 0.6 to c. 745°C, 2.13 GPa and a H 2 O = 1 followed by near-isothermal decompression down to c. 1.63 GPa. The absence of pre-eclogitic H 2 O-bearing mineral inclusions in garnet and omphacite suggests that the primary magmatic rocks have not been affected by prograde metamorphism during subduction due to the lack of fluid. We suggest that the Marun-Keu Complex represents a coherent crustal block that experienced the same P – T evolution but provides a metamorphic record of different P – T parameters because of an uneven introduction of aqueous-bearing fluids during subduction and exhumation. The tectonometamorphic history of the Marun-Keu Complex is best attributed to the relatively hot regime of the continental margin subduction beneath an island arc, whereas the blueschist-facies part of the complex towards the north could be related to the closure of the Uralian Ocean.

Abstract This paper considers the lithospheric structure and evolution of the wider Barents–Kara Sea region based on the compilation and integration of geophysical and geological data. Regional transects are constructed at both crustal and lithospheric scales based on the available data and a regional three-dimensional model. The transects, which extend onshore and into the deep oceanic basins, are used to link deep and shallow structures and processes, as well as to link offshore and onshore areas. The study area has been affected by numerous orogenic events in the Precambrian–Cambrian (Timanian), Silurian–Devonian (Caledonian), latest Devonian–earliest Carboniferous (Ellesmerian–svalbardian), Carboniferous–Permian (Uralian), Late Triassic (Taimyr, Pai Khoi and Novaya Zemlya) and Palaeogene (Spitsbergen–Eurekan). It has also been affected by at least three episodes of regional-scale magmatism, the so-called large igneous provinces: the Siberian Traps (Permian–Triassic transition), the High Arctic Large Igneous Province (Early Cretaceous) and the North Atlantic (Paleocene–Eocene transition). Additional magmatic events occurred in parts of the study area in Devonian and Late Cretaceous times. Within this geological framework, we integrate basin development with regional tectonic events and summarize the stages in basin evolution. We further discuss the timing, causes and implications of basin evolution. Fault activity is related to regional stress regimes and the reactivation of pre-existing basement structures. Regional uplift/subsidence events are discussed in a source-to-sink context and are related to their regional tectonic and palaeogeographical settings.

Abstract The NW–SE-trending Pai-Khoi fold–thrust belt links the Permian Uralian Orogen in the Polar Urals with the early Mesozoic fold belt on Novaya Zemlya. An interpretation of structural lineaments present in southern Novaya Zemlya suggests that the NW–SE-trending fold belt in southernmost Novaya Zemlya may have formed contemporaneously with parallel sinistral strike-slip faults. Analysis of regional-scale geological maps of the adjacent Pai-Khoi fold–thrust belt reveals large-scale structural relationships indicative of sinistral shear along the fold–thrust belt, including the presence of left-stepping en echelon folds within the Kara Shale Allochthon. This interpretation is corroborated by a field study of the allochthon-bounding Main Pai-Khoi Thrust, which reveals a consistently oblique tectonic stretching lineation, pitching 56° towards the east, suggesting tectonic displacement towards the west. It is therefore proposed that the Pai-Khoi fold–thrust belt is best described as a zone of sinistral inclined transpression. The interpretation of the Pai-Khoi fold–thrust belt as a zone of sinistral transpression has important implications for the interpretation of this tectonic boundary. This is reflected in a new structural cross-section through southernmost Novaya Zemlya, which is characterized by thick-skinned tectonics and steep strike-slip faults. These faults may link at depth with the Baidaratsky Fault.