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Controversy over the plate tectonic affinity and evolution of the Saxon granulites in a two- or multi-plate setting during inter- or intracontinental collision makes the Saxon Granulite Massif a key area for the understanding of the Palaeozoic Variscan orogeny. The massif is a large dome structure in which tectonic slivers of metapelite and metaophiolite units occur along a shear zone separating a diapir-like body of high-Pgranulite below from low-Pmetasedimentary rocks above. Each of the upper structural units records a different metamorphic evolution until its assembly with the exhuming granulite body. New age and petrologic data suggest that the metaophiolites developed from early Cambrian protoliths during high-Pamphibolite facies metamorphism in the mid- to late-Devonian and thermal overprinting by the exhuming hot granulite body in the early Carboniferous. A correlation of new Ar-Ar biotite ages with publishedP-T-tdata for the granulites implies that exhumation and cooling of the granulite body occurred at average rates of similar to 8 mm/year and similar to 80 degrees C/Ma, with a drop in exhumation rate from similar to 20 to similar to 2.5 mm/year and a slight rise in cooling rate between early and late stages of exhumation. A time lag ofc. 2 Ma between cooling through the closure temperatures for argon diffusion in hornblende and biotite indicates a cooling rate of 90 degrees C/Ma when all units had assembled into the massif. A two-plate model of the Variscan orogeny in which the above evolution is related to a short-lived intra-Gondwana subduction zone conflicts with the oceanic affinity of the metaophiolites and the timescale ofc. 50 Ma for the metamorphism. Alternative models focusing on the internal Variscan belt assume distinctly different material paths through the lower or upper crust for strikingly similar granulite massifs. An earlier proposed model of bilateral subduction below the internal Variscan belt may solve this problem., Zweitver��ffentlichungen der Universit��t Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1227

Late Neoproterozoic-Early Cambrian calc-alkaline granitoids are ubiquitous in the continental basement of Iran and indicate formation within a Cadomian arc system at the northern margin of Gondwana. A basement complex comprising mainly mica schist, paragneisses, and metagranite along with metabasite and rare pegmatite is exposed in the Zayanderud region north of Shahrekord located in the hinterland of the Zagros mountain range. This complex is unique in the Neotethyan realm because it includes eclogites with Jurassic metamorphic ages implying involvement of continental crust at the onset of subduction. Ion microprobe U Pb zircon dating along with trace element and oxygen isotope analyses for metagranites define two zircon age clusters of ca. 552 and 565 Ma confirming connection with the other Ediacaran age basement arc plutons in the belt. Zircon geochronology for pegmatite, by contrast, yielded a concordant age population averaging 176.5 ± 3.3 (2σ) Ma. Zircon crystals from the pegmatite also have unusually low rare earth element (REE) abundances with sharp increases towards the heavy REE. Along with an absence of a negative Eu anomaly, this indicates a high-grade metamorphic origin of zircon crystallizing from a pegmatite which was formed by melting of mica schist and possibly amphibole eclogite during decompression where incipient garnet breakdown released Zr and HREE to form zircon, and LREE were retained in stable apatite and titanite. Corresponding 40Ar/39Ar phengite dates from the pegmatite and the mica schist country-rock are overlapping with or only slightly postdate the U Pb zircon ages, indicating rapid cooling after reaching maximum metamorphic pressure in the Early Jurassic. The Zayanderud basement complex is thus potentially a rare example of deep burial of continental crust and rapid exhumation due to buoyant escape during the incipient stages of subduction, well before the ultimate closing of the Neotethys ocean basin between Arabia and Eurasia in the mid-Tertiary.

The Alborz Mountains in N Iran underwent several tectono-metamorphic events that reflect the opening and closure of the Paleo- and Neotethys Oceans. Metamorphic rocks that recorded these are rare and discontinuously exposed. They range from the HP-LT Asalem-Shanderman Complex in the west, to the Gasht Metamorphic Complex (GMC, this study), to the Gorgan Schists, and Fariman Schists near Mashhad in the east. They are considered to have formed during the closure of the Paleotethys Ocean. The GMC comprises poorly exposed metasediments and amphibolite metamorphosed under greenschist- to amphibolite-facies conditions. In addition, smaller volumes of granite occur. As the evolution of the basement rocks of the Alborz Mountains is still poorly known and their radiometric ages are very limited, we applied different dating methods to selected samples of the GMC basement to better understand the geological evolution of this part of the Alborz Mountains.The granite yielded an Ediacaran 551 ± 2.5 Ma LA-ICP-MS U-Pb pooled zircon age. Monazites in two amphibolite-facies metapelites (Bt-Ms-St ± And schists) yielded Triassic 226 ± 24 and 229 ± 25 Ma CHIME U-Pb ages. Foliation-defining biotite and retrograde white mica replacing andalusite porphyroblasts in metapelites and peak-metamorphic amphibole from an amphibolite yielded much younger 175.1 ± 0.5 Ma to 177.0 ± 0.4 Ma 40Ar/39Ar plateau ages.The Ediacaran crystallization age of the granite agrees with the late Neoproterozoic to Cambrian zircon age of the Lahijan granite in the eastern GMC reported by Guest et al. (2006) and indicates that the Alborz basement was a part of the northern margin of Gondwana at that time. It rifted and drifted away from Gondwana due to the opening of the Neotethys, probably in the Permian, along with other Iranian blocks (the so-called Cimmerian terranes). The mid to late Triassic monazite ages date the Barrovian peak metamorphism of the GMC and mark collision and accretion of a Cimmerian terrane following closure of the Paleotethys. The monazite ages overlap with the early Late Triassic age of deposition of the lowest parts of the unconformably overlying Shemshak Group in the central and eastern Alborz Mountains (ca. 213 Ma, Horton et al. 2008). Younger and very similar Toarcian 40Ar/39Ar ages for both pro- and retrograde minerals with different nominal closure temperatures, reflect very rapid cooling of GMC basement below the Shemshak Group due to extension-triggered uplift. This late Toarcian to Aalenian extension event can be correlated with the regional Mid-Cimmerian unconformity of mid-Bajocian age (c. 170 Ma) that resulted from the tectonic movements causing rapid uplift and erosion (Fürsich et al. 2009). Extension probably started in the western Alborz Mountains in the Toarcian and culminated in the Aalenian in the eastern Alborz with the formation of a deep-marine basin and was triggered by the onset of the subduction of Neotethys oceanic crust beneath the Central Iranian Microcontinent (Wilmsen et al. 2009). Fürsich et al. 2009, Geol. Soc., London, Spec. Publ. 312, 189-203. Guest et al., 2006, GSA Bulletin 118, 1507-1521. Horton et al., 2008, Tectonophysics 451, 97–122. Wilmsen et al. 2009, Terra Nova 21, 211–218.

In the originally published version of this manuscript, the Supplementary Data was supplied with an incorrect hyperlink. The hyperlink has now been corrected to give the correct supplementary data for this article.

Metamorphic rocks in the Alborz Mountains are mainly known from the HP-LT Asalem-Shanderman Complex, the Gasht Complex, Gorgan Schists, and the Fariman Schists near Mashad. Recent argon ages are limited to eclogites and blueschists of the Asalem-Shanderman Complex, where phengites yielded c. 350 Ma step-heating ages that reflect cooling, following peak metamorphism related to subduction of the Palaeotethys Ocean (Rosetti et al. 2016).The Gasht Complex in the Gasht-Masuleh area comprises metasediments and metabasic rocks metamorphosed at amphibolite-facies peak metamorphic conditions (c. 630°C and 8.6 kbar, Razaghi et al., 2018). The metamorphism is most probably related to the accretion of Cimmerian terranes to the Turan Terrane in the late Triassic following closure of the Palaeotethys Ocean and resulting in the Cimmerian Orogeny.Micas from metapelites, amphibole from an amphibolite and magmatic white mica from deformed granite from the Gasht Complex yield very similar 40Ar/39Ar step-heating plateau ages between 175.1 ± 0.5 Ma and 177.0 ± 0.4 Ma (2 sigma) that are independent of grain size and nominal closure temperatures. In addition, clearly retrograde white mica replacing andalusite porphyroblasts in a metapelite yielded a similar plateau age of 176.1 ± 0.5 Ma.In the Gasht-Masuleh area the contact between basement and the cover rocks is largely tectonic due to later faulting, but the Gasht Complex must have formed the depositional basement to the late Triassic- Middle Jurassic Shemshak Group. Sedimentation started in the Carnian above the regionally developed Eo-Cimmerian unconformity in the central and eastern Alborz and continued until the mid-Bajocian.Notably, within the Shemshak Gp. a distinct, regional scale unconformity developed in the mid-Bajocian (c. 170 Ma) recognized by rapid coarsening in sediment grain size. Only locally, in the eastern Alborz Mountains, it developed as an angular unconformity related to block rotation. This Mid-Cimmerian unconformity formed as a result of tectonic movements causing rapid uplift and erosion.Our c. 175 – 177 Ma mica and amphibole plateau ages for the Gasht Complex are unlikely to reflect slow cooling following the (Carboniferous? Late Triassic?) metamorphism, as this would result in increasingly younger ages for amphibole, white mica and biotite. Instead, the indistinguishable ages for peak metamorphic and retrograde minerals must be due to very rapid cooling at the Toarcian-Aalian boundary (c. 174 Ma) that resulted from rapid basement uplift and at the surface caused the mid-Bajocian Mid-Cimmerian unconformity. Thus, the c. 175 – 177 Ma 40Ar/39Ar ages document the thermal response of the basement below the Shemshak Group to a mid-Jurassic extensional tectonic event.From a regional perspective, the Mid-Cimmerian unconformity may represent the break-up unconformity of back-arc rift basins that formed due to northward Neotethys subduction to the south of the Alborz Mountains (Wilmsen et al. 2009) and/or the onset of sea-floor spreading within the South Caspian Basin to the north (Fürsich et al. 2009).Fürsich et al. 2009, Geol. Soc., London, Spec. Publ. 312, 189-203. Razaghi et al., 2018, Geosciences 27, 269-280. Rosetti et al. 2016, J. Geol. Soc. London 174, 741-758. Wilmsen et al. 2009, Terra Nova 21, 211–218.

The orogenic development after the continental collision between Laurussia and Gondwana, led to two contrasting associations of mantle-derived magmatic rocks on the territory of the Bohemian Massif: (i) a 340–310 Ma lamprophyre-lamproite orogenic association; and (ii) a 300–275 Ma lamprophyre association of anorogenic affinity. Major types of potassic mantle-derived magmatic rocks recognized in the orogenic and anorogenic associations include: (i) calc-alkaline to alkaline lamprophyres; (ii) alkaline ‘orthopyroxene minettes’ and geochemically related rocks grouped here under the new term lampyrite; and (iii) peralkaline lamproites. These three types significantly differ with respect to mineral, whole-rock and Sr–Nd–Pb–Li isotope composition and spatial distribution. The calc-alkaline lamprophyres occur throughout the entire Saxo-Thuringian and Moldanubian zones, whereas the different types of malte-derived potassic rocks are spatially restricted to particular zones. Rocks of the Carboniferous lamprophyre-lamproite orogenic association are characterized by variable negative εNd(i) and variably radiogenic Sr(i), whereas the rocks of the Permian lamprophyre association of anorogenic affinity are characterized by positive εNd(i) and relatively young depleted-mantle Nd-model ages reflecting increasing input from upwelling asthenospheric mantle. The small variation in the Pb isotopic composition of post-collisional potassic mantle-derived magmatic rocks (of both the orogenic and anorogenic series) implies that the Pb budget of the mantle beneath the Bohemian Massif is dominated by the same crust-derived material, which itself may include material derived from several sources. The source rocks of ‘orthopyroxene minettes’ are characterized by isotopically light (‘eclogitic’) Li and strongly radiogenic (crustal) Sr and may have been metasomatized by high-pressure fluids along the edge of a subduction zone. In contrast, the strongly Al2O3 and CaO depleted mantle source of the lamproites is characterized by isotopically heavy Li and high SiO2 and extreme K2O contents. This mantle source may have been metasomatized predominantly by melts. The mantle source of the lamprophyres may have undergone metasomatism by both fluids and melts.

The Postmasburg Manganese Field (PMF), Northern Cape Province, South Africa, once represented one of the largest sources of manganese ore worldwide. Two belts of manganese ore deposits have been distinguished in the PMF, namely the Western Belt of ferruginous manganese ores and the Eastern Belt of siliceous manganese ores. Prevailing models of ore formation in these two belts invoke karstification of manganese-rich dolomites and residual accumulation of manganese wad which later underwent diagenetic and low-grade metamorphic processes. For the most part, the role of hydrothermal processes and metasomatic alteration towards ore formation has not been adequately discussed. Here we report an abundance of common and some rare Al-, Na-, K- and Ba-bearing minerals, particularly aegirine, albite, microcline, banalsite, sérandite-pectolite, paragonite and natrolite in Mn ores of the PMF, indicative of hydrothermal influence. Enrichments in Na, K and/or Ba in the ores are generally on a percentage level for most samples analysed through bulk-rock techniques. The presence of As-rich tokyoite also suggests the presence of As and V in the hydrothermal fluid. The fluid was likely oxidized and alkaline in nature, akin to a mature basinal brine. Various replacement textures, particularly of Na- and K- rich minerals by Ba-bearing phases, suggest sequential deposition of gangue as well as ore-minerals from the hydrothermal fluid, with Ba phases being deposited at a later stage. The stratigraphic variability of the studied ores and their deviation from the strict classification of ferruginous and siliceous ores in the literature, suggests that a re-evaluation of genetic models is warranted. New Ar-Ar ages for K-feldspars suggest a late Neoproterozoic timing for hydrothermal activity. This corroborates previous geochronological evidence for regional hydrothermal activity that affected Mn ores at the PMF but also, possibly, the high-grade Mn ores of the Kalahari Manganese Field to the north. A revised, all-encompassing model for the development of the manganese deposits of the PMF is then proposed, whereby the source of metals is attributed to underlying carbonate rocks beyond the Reivilo Formation of the Campbellrand Subgroup. The main process by which metals are primarily accumulated is attributed to karstification of the dolomitic substrate. The overlying Asbestos Hills Subgroup banded iron formation (BIF) is suggested as a potential source of alkali metals, which also provides a mechanism for leaching of these BIFs to form high-grade residual iron ore deposits., Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 966

The Upper Devonian Munster Basin of southern Ireland has traditionally been viewed as a post-orogenic molasse deposit that was sourced from the Caledonides of central Ireland and subsequently deformed by the end Carboniferous Variscan orogenic event. The basin fill is composed of super-mature quartz arenite sandstone that clearly represents a second cycle of deposition. The source of this detritus is now recognized as Lower Devonian Dingle Basin red bed sequences to the north. This genetic link is based on the degree of similarity in the detrital mica chemistry in both of these units; micas plot in identical fields and define the same trends. In addition, the two sequences show increased textural and chemical maturity up-sequence and define indistinguishable Ar-40/Ar-39 age ranges for the detrital mica grains. Partial resetting of the Ar ages can be attributed to elevated heat flow in the region caused by Munster Basin extension and subsequent Variscan deformation. The combined evidence from southwest Ireland therefore points to a Caledonian or possibly Taconian primary source area that initially shed detritus into the Lower Devonian Dingle Basin which was subsequently recycled into the Upper Devonian Munster Basin following mid-Devonian Acadian basin inversion. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Shear folding, which is also referred to as slip folding, involves shear along planes that are oriented approximately parallel to the axial plane of the fold structure. These planes, which are typically axial-planar cleavage planes, facilitate high-angle reverse slip leading to fold limb rotation and amplification. This study builds on recent advances in our understanding of the role of weak fault zones in facilitating slip on misoriented faults; i.e., faults at a high angle to the maximum principal tectonic stress (sigma(1)). Analysis of folded marine sedimentary rocks from the Variscan of southern Ireland provides unambiguous microstructural evidence for reverse shear on chemically weakened cleavage domains. Significant silica loss in these cleavage domains, and as a consequence marked mechanical weakening, is seen as the primary cause for the reverse slip associated with the shear folding of these sedimentary rocks.

Amonchquite dyke, in the vicinity of Loch Roag, Lewis, Outer Hebrides has an unusually enriched chemistry, and contains a unique assemblage of megacrysts and xenoliths from the lithosphere of the Hebridean craton. A Ar-40/Ar-39 plateau age of 45.2 +/- 0.2 Ma (2 sigma) of a phlogopite megacryst from the dyke overlaps an earlier reported K-Ar age, and confirms that the British Palaeogene Igneous Province extended into the Eocene. Similar late low-volume melts were erupted in the Eocene and Oligocene in West and East Greenland, suggesting that such late-stage magmatic rejuvenescence is a widespread feature across the North Atlantic Igneous Province.

The current view regarding the timing of regionally developed penetrative tectonic fabrics in sedimentary rocks is that their development postdates lithification of those rocks. In this case, fabric development is achieved by a number of deformation mechanisms, including grain rigid body rotation, crystal-plastic deformation, and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal structure of cleavage in low-grade metamorphic rocks. In this study we combine field observations with strain studies to characterize considerable (>50%) Acadian crustal shortening in a Devonian clastic sedimentary sequence from southwest Ireland. Despite these high levels of shortening there is a marked absence of the domainal cleavage structure and intraclast deformation that are expected with this level of deformation. Fabrics in these rocks are predominantly a product of rigid body rotation and repacking of extraformational clasts during deformation of a clastic sedimentary sequence before lithification was complete.

The Variscan orogeny, resulting from the collision of Laurussia with Gondwana to form the supercontinent of Pangaea, was followed by a period of crustal instability and re-equilibration throughout Western and Central Europe. An extensive and significant phase of Permo-Carboniferous magmatism led to the extrusion of thick volcanic successions across the region (e.g. NE German Basin, NW part of the Polish Basin, Oslo Rift, northern Spain). Coeval transtensional activity led to the formation of more than 70 rift basins across the region. The various basins differ in terms of their form and infill according to their position relative to the Variscan orogen (i.e. internide or externide location) and to the controls that acted on basin development (e.g. basement structure configuration). This paper provides an overview of a variety of basin types, to more fully explore the controls upon the tectonomagmatic-sedimentary evolution of these important basins.

A tectonic model is proposed for the Palaeoproterozoic Lapland-Kola orogen (LKO) in the northern Fennoscandian Shield. Although long regarded as an Archaean craton, integrated geological, geochemical and geophysical observations show that the Lapland-Kola orogen is a Palaeoproterozoic collisional belt containing both Archaean terranes and an important component of juvenile Palaeoproterozoic crust. Rifting, from 2.5 to 2.1 Ga, began under the influence of a mantle plume (> 1000 km diameter), related to the break-up of the Kenorland supercontinent. Two linear suture zones within the orogeriic core mark the sites of continental separation, ocean formation and closure. One of these is identified as a belt of 1.98-1.91 Ga juvenile crust of both arc magmatic and sedimentary origin, marked by the Lapland Granulite, Umba and Tersk terranes. Palaeomagnetic data and ancient sedimentary detritus within these terranes suggest limited oceanic separation. Collision of juvenile terranes with the surrounding Archaean took place mainly between 1.93 and 1.91 Ga, resulting in a Himalayan-scale mountain belt, manifest by a thick-skinned region of high- P granulite-facies metamorphism, including the classical Lapland Granulite Belt and a broad zone of compressional deformation extending southwards into the Belomorian Mobile Belt. Protracted cooling and exhumation, possibly related to the buttressing effect of surrounding lithosphere, culminated in the intrusion of 1.80-1.77 Ga post-tectonic granites.

The Black Ball Head diatreme on the Beara Peninsula (Co. Cork, south-west Ireland) intrudes Lower Carboniferous marine siliciclastic sediments, and comprises an inner and an outer zone of pyroclastic infill. The outer zone is dominated by lithoclasts of local sediments and igneous rocks, whereas the inner zone is characterised by an assemblage of kaersutite, phlogopite and Ti-magnetite megacrysts and ultramafic pyroxenite nodules. 40Ar/39Ar step-heating dating of two kaersutite megacrysts from the inner zone yielded a c. 318 ‘ 3Ma plateau age (2ao). This late Namurian age is interpreted to be the age of diatreme emplacement. The pyroclastic infill is foliated and the c. 318Ma age therefore provides an older age limit for the Variscan deformation in this part of the Rhenohercynian fold belt.

An extensive rift system developed within the northern foreland of the Variscan orogenic belt during Late Carboniferous-Early Permian times, post-dating the Devonian-Early Carboniferous accretion of various Neoproterozoic Gondwana-derived terranes on to the southern margin of Laurussia (Laurentia-Baltica; Fig. 1). Rifting was associated with widespread magmatism and with a fundamental change, at the Westphalian-Stephanian boundary, in the regional stress field affecting western and central Europe (Ziegler 1990; Ziegler & Cloetingh 2003). The change in regional stress patterns was coincident with the termination of orogenic activity in the Variscan fold belt, followed by major dextral translation between North Africa and Europe. Rifting propagated across a collage of basement terranes with different ages and thermal histories. Whilst most of the Carboniferous-Permian rift basins of NW Europe developed on relatively thin lithosphere, the highly magmatic Oslo Graben in southern Norway initiated within the thick, stable and, presumably, strong (cold) lithosphere of the Fennoscandian craton. The rift basins in the North Sea, in contrast, developed in younger Caledonian age lithosphere, which was both thinner and warmer than the lithosphere of the craton to the east.

The Permo-Carboniferous evolution of the central North Sea is characterized by three main geological events: (1) the development of the West European Carboniferous Basin; (2) a period of basaltic volcanism during the Lower Rotliegend (latest Carboniferous early Permian); and (3) the development of the Northern and Southern Permian Basins in late Permian times. The timing of the late Carboniferous Permian basaltic volcanism in the North Sea is poorly constrained, as is the timing of extensional tectonic activity following main inversion during the Westphalian due to the propagation of the Variscan deformation front. Results of high precision Ar-Ar dating on basalt samples taken from a core from exploration well 39/2-4 (Amerada Hess) in the UK sector of the central North Sea, suggests that basaltic volcanism was active in the late Carboniferous, at c. 299 Ma. The presence of volcanics below the dated horizon, suggests that the onset of Permo-Carboniferous volcanism in the central North Sea commenced earlier, probably at c. 310 Ma (Westphalian C). This is contemporaneous with other observations of tholeiitic volcanism in other parts of NW Europe, including the Oslo Graben, the north-east German Basin, southern Sweden and Scotland. Interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity, but the exact age of the fault activity is difficult to constrain with the data available.

The Kolvitsa Belt in the south-western Kola Peninsula formed coeval with the earliest Palaeoproterozoic rift-belts in the Fennoscandian Shield. The Palaeoproterozoic history of this belt comprises the deposition of the 2.47 Ga Kandalaksha amphibolite (metabasalt) sequence onto 2.7 Ga granitoid gneisses, the intrusion of the 2.45–2.46 Ga Kolvitsa Massif of gabbro-anorthosite and the subsequent multiple injection of mafic dykes and magmatic brecciation, followed by the intrusion of 2.44 Ga dioritic dykes, and extensive shearing at 2.43–2.42 Ga. The gabbro-anorthosite and dykes contain high-pressure garnet-bearing assemblages that have previously been considered as evidence for metamorphism in a compressional setting of the Kolvitsa Belt at 2.45–2.42 Ga, i.e. coeval with the formation of the Imandra–Varzuga rift-belt and layered mafic intrusions in an extensional setting. The Kochinny Cape study area on the White Sea coast presents an unique remnant of a 2.44 Ga mafic dyke swarm that endured ca. 1.9 Ga collision but preserved its primary structural pattern well. All these dykes were intruded along numerous NW-trending shear zones within the Kolvitsa Massif and contain angular xenoliths of sheared gabbro-anorthosite. Every new batch of mafic melt underwent shearing during or immediately after solidification, and later dykes intruded into already sheared dykes. Thus, rocks of the Kolvitsa Massif and its dyke complex were successively injected into a large-scale shear zone which was active from ca. 2.46 to 2.42 Ga. Multiple injection of mafic melts, the presence of mutually intruding, composite, sheared mafic dykes, of magmatic breccias with gabbroic groundmass, and of host rocks fragments (showing no evidence of tectonic stacking at the time of brecciation), all indicate an extensional setting. Shearing was also extensional as it occurred simultaneously with the multistage magmatism. The asymmetric morphology of deformed dykes, and asymmetric flexures within weakly deformed lenses show that all these extensional shear zones, apart from a few exceptions, are dextral, were formed in a transtensional setting and are attributed to general W–E to WSW–ENE extension. Structural data available for 2.4–2.5 Ga magmatic rocks elsewhere in the Kola region suggest that the same kinematics operated on a regional scale. The presence of the garnet-bearing assemblages in gabbro-anorthosite and dykes may be explained by crystallisation and shearing of the magmatic rocks at deep crustal levels. Alternatively, corona development might have occurred much later as a result of tectonic loading due to the juxtaposition and overthrusting of the Umba Granulite Terrane onto the Kolvitsa Belt at ca. 1.9 Ga. In view of the field evidence and published ages, an overall extensional setting rather than a combination of compressional and extensional zones is preferable for Palaeoproterozoic tectonics in the north-eastern Fennoscandian Shield at 2.5–2.4 Ga.

The Lapland–Kola Orogen (LKO; former Kola craton) in the northern Fennoscandian Shield comprises a collage of partially reworked late Archaean terranes with intervening belts of Palaeoproterozoic juvenile crust including the classic Lapland Granulite Terrane. Rifting of Archaean crust began at c 2.5–2.4 Ga as attested by layered mafic and anorthositic intrusions developed throughout the northernmost Fennoscandian Shield at this time. Oceanic separation was centred on the Lapland Granulite, Umba Granulite (UGT) and Tersk terranes within the core zone of the orogen. Importantly, SmNd data show that Palaeoproterozoic metasedimentary and metaigneous rocks within these terranes contain an important, generally dominant, juvenile component over a strike length of at least 600 km. Evidently, adjacent Archaean terranes, with negative eNd signatures, contributed relatively little detritus, suggesting a basin of considerable extent. Subduction of the resulting Lapland–Kola ocean led to arc magmatism dated by the NORDSIM ion probe at c 1.96 Ga in the Tersk Terrane in the southern Kola Peninsula. Accretion of the Tersk arc took place before c 1.91 Ga as shown by ion probe UPb zircon dating of post-D1, pre-D2 pegmatites cutting the Tersk arc rocks, juvenile metasediments as well as Archaean gneisses in the footwall of the orogen. Deep burial during collision under high-pressure granulite-facies conditions was followed by exhumation and cooling between 1.90 and 1.87 Ga based on SmNd, UPb and ArAr data. Lateral variations in deep crustal velocity and Vp/Vs ratio, together with reflections traversing the entire crust observed in reprocessed seismic data from the Polar Profile, may be interpreted to image a trans-crustal structure — possibly a fossilised subduction zone — supporting an arc origin for the protoliths of the Lapland Granulite, UGT and Tersk terranes and the location of a major lithospheric suture — the Lapland–Kola suture.

Combined K–Ar and Ar–Ar dating of a xenolith-bearing alkaline dyke, previously considered to be of late Palaeozoic age, suggest a mid-Eocene age of c. 43 Ma, indicating that it is part of extensive rift-related Tertiary intrusive activity. High 3 He/ 4 He ratios of 11–16 R a , potentially up to 23 R a ( R a =atmospheric ratio of 1.39×10 −6 ) have been measured from mantle xenoliths in the dyke and are consistent with previous determinations of the helium isotope composition of Tertiary lavas in Greenland and Scotland linking the magmatism with the proto-Iceland mantle plume.

A SmNd model age traverse across the Kola Peninsula has been undertaken to gain insight into the major episodes of crustal growth and to test the possible presence of early Archaean “Saamian” crust in the region. Granitoid gneisses and subordinate metasediments have been sampled from the main Archaean geological units, i.e. from northeast to southwest: the Murmansk domain (model ages of 2.68–2.96 Ga); Central Kola domain including samples from the Superdeep Borehole (2.74–2.92 Ga); Belomorian domain, including the eastern part of the Tersk area (2.70–2.93 Ga). The narrow range of depleted mantle model ages from 2.68 to 2.96 Ga for Archaean granitoid orthogneisses, close to the oldest crystallization ages from the region, indicate a major episode of late Archaean crustal growth and reveal no indication of ancient “Saamian” material in keeping with other geochronological evidence. Similar results (2.86 to 2.93 Ga) for Archaean metasediments support this conclusion. Proterozoic model ages for supracrustals from the western part of the Tersk area (2.16 to 2.23 Ga) indicate that the crust in this area is much younger than previously recognized. Initial ϵ Nd values for late Archaean samples with reasonable age constraints fall within a range of +2.3 to −2.5. Two well-dated samples from the Belomorian domain have the highest initial ϵ Nd values [ ϵ Nd (2.81 Ga) = + 2.0 and ϵ Nd (2.78 Ga) = + 2.3] and suggest that a depleted mantle source was present in the Kola region in late Archaean times. Dated samples from the Central Kola domain have lower initial ϵ Nd (between − 2.5 and + 1.2) suggesting a possible regional difference in mantle character. In contrast to the depleted signature of the Archaean orthogneisses between 2.7 Ga and ∼ 2.8 Ga, previous studies of earliest Palaeoproterozoic rift-related majic intrusives in the Kola and Karelia regions report negative ϵ Nd values at 2.4–2.5 Ga. Possibly these data reflect a change to more enriched-mantle values.

[EN] A multiple basic to intermediate sill is reported for the fi rst time in the south-eastern Iberian Ranges. It is composed of several tabular to irregular levels intercalated within the fl uvial sediments of the Alcotas Formation (Middle-Upper Permian). The sill could represent the youngest Paleozoic subvolcanic intrusion in the Iberian Ranges. The igneous rocks are classifi ed as basaltic andesites. They show a subophitic microstructure constituted by plagioclase (An62 – An6), augite (En48Wo44Fs7 –En46Wo39Fs15), pseudomorphosed olivine, minor amounts of oxides (magnetite and ilmenite) and accessory F-apatite. According to the mineralogy and whole-rock composition, their geochemical affi nity is transitional from subalkaline to alkaline. Radiometric dating of the sill is not feasible due to its signifi cant alteration. Field criteria, however, suggest an emplacement coeval to the deposition of the Alcotas Formation (Middle-Upper Permian). This hypothesis is supported by the transitional affi nity of these rocks, similar to other Middle-Upper Permian magmatisms in the western Tethys, e.g., from the Pyrenees. Taking into account their isotopic signature (εSr: -6.8 to -9.2; εNd: +1.7 to +8.3), an enriched mantle source with the involvement of a HIMU component has been identifi ed. This interpretation is supported by the trace element contents. Some of these HIMU characteristics have been recognised in the Middle-Upper Permian magmatisms of the Central Pyrenees (Anayet Basin) and the High Atlas (Argana Basin). However, none of these source features are shared with other Middle-Upper Permian magmatisms of the western Tethys (Catalonian Coastal Ranges, Corsica-Sardinia and southern France), nor with the Lower Permian magmatism of the Iberian Ranges. These differences support the presence of a heterogeneous mantle in the western Tethys during the Permian., [ES] Se describe por primera vez en el sudeste de la Cordillera Ibérica un sill múltiple de carácter básico a intermedio. Está compuesto por varios cuerpos tabulares a irregulares intercalados entre los sedimentos de origen fl uvial de la Formación Alcotas (Pérmico Medio-Superior). El sill podría representar la intrusión subvolcánica paleozoica más reciente en la Cordillera Ibérica. Estas rocas subvolcánicas se clasifi can como andesitas basálticas. Muestran una textura subofítica constituida por plagioclasa (An62 – An6), augita (En48Wo44Fs7 –En46Wo39Fs15), pseudomorfos de olivino, minerales opacos (magnetita e ilmenita) y F-apatito accesorio. De acuerdo con su composición mineral y de roca total, su afi nidad geoquímica es transicional entre subalcalina y alcalina. La datación radiométrica del sill no es posible debido a su elevado grado de alteración. No obstante, los criterios de campo sugieren un emplazamiento contemporáneo con el depósito de la Formación Alcotas (Pérmico Medio-Superior). Esta hipótesis está apoyada por la afi nidad transicional de estas rocas, similar a otros episodios magmáticos del Pérmico Medio-Superior en el Tethys occidental, como los que afl oran en los Pirineos. Teniendo en cuenta su signatura isotópica (εSr: -6.8 a -9.2; εNd: +1.7 a +8.3), se propone un origen a partir de un manto enriquecido, con la participación de un componente de tipo HIMU. Esta interpretación está apoyada por sus contenidos en elementos traza. Algunas de estas características del protolito han sido reconocidas en los magmatismos del Pérmico Medio-Superior del Pirineo (cuenca del Anayet) y del Alto Atlas (cuenca de Argana), pero no son habituales en otros magmatismos de edad Pérmico Medio-Superior del Tethys occidental (Cadenas Costero Catalanas, Córcega-Cerdeña y Sur de Francia), ni en el magmatismo Pérmico Inferior de la Cordillera Ibérica. Estas diferencias apoyan la presencia de un manto heterogéneo en el Tethys occidental durante el Pérmico.

Amphibole and mica Ar-40/Ar-39 ages as well as zircon, rutile and titanite U-Pb geochronology of eclogites and associated host rocks from the Higher Himalayan Crystalline Nappes (Indian Plate) in the Upper Kaghan Valley, Pakistan allow distinction of a multistage exhumation history. An Eocene age for peak-pressure metamorphism has been obtained by phengite Ar-40/Ar-39 (47.3 +/- 0.3 Ma) and zircon U-Pb (47.3 +/- 0.4 and 47.4 +/- 0.3 Ma) ages from cover and basement gneisses. A very short-lived metamorphic peak and rapid cooling is documented by an amphibole Ar-40/Ar-39 age of 46.6 +/- 0.5 Ma and a rutile U-Pb age of 44.1 +/- 1.3 Ma from eclogites. Phengite and biotite ages from cover and basement sequences metamorphosed during the Himalayan orogeny are 34.5 +/- 0.2 to 28.1 +/- 0.2 Ma whereas youngest biotites, yielding 23.6 +/- 0.1 and 21.7 +/- 0.2 Ma, probably reflect argon partial resetting. The amphibole age, together with those derived from phengite and zircon demonstrate a rate of initial exhumation of 86-143 mm/a i.e. an extremely rapid transport of the Indian Plate continental crust from ultra-high pressure (UHP) conditions back to crustal levels (47-46 Ma for transport from 140 to 40 km depth). Subsequent exhumation (46-41 Ma, 40-35 km) slowed to about 1 mm/a at the base of the continental crust but increased again later towards slightly higher exhumation rates of ca. 2 mm/a (41-34 Ma, 35- 20 km). This indicates a change from buoyancy-driven exhumation at mantle depths to compression forces related to continent-continent collision and accompanied crustal folding, thrusting and stacking that finally exposed the former deeply-buried rocks.

207Pb/206Pb ages are presented for detrital zircons (Laser Ablation Microprobe ICP-MS) and whole-rock Nd isotopic determinations (TIMS) from samples of Neoarchean and Palaeoproterozoic metasedimentary rocks from the Umba granulite terrane and the Keivy domain of the Central Kola composite terrane, Kola Peninsula, north-western Russia. Three are samples of rocks from the Umba granulite terrane that were deposited ≈ 2.20–1.90 Ga; they contain Archaean detritus, much of it older than 3.0 Gyr, as well as abundant 2.20–1.95-Gyr-old material. Deposition may have occurred on the margin of an Archaean craton with an exposed Palaeoproterozoic magmatic arc source, possibly during orogenesis. Two samples from the Keivy domain have remarkably similar, dominantly Archaean detrital zircon age spectra. One was deposited pre-2.4 Ga, whereas the other was probably deposited post-2.01 Ga. Both had similar sources, compatible with the proximal country rocks, and possible shallow-water (?) cratonic margin depositional settings.