Carbon and strontium isotope chemostratigraphy (52 delta C-13(carb) and delta O-18, and 50 Sr-87/Sr-86 analyses of carbonate components in whole-rock samples) was applied for constraining an apparent depositional age of the carbonate protolith to amphibolite-grade, calcite marbles occurring in siliciclastic sedimentary sequences hosting iron formations (the Dunderlandsdalen type iron ores) of previously unknown age in the Rodingsfjallet Nappe Complex of the Rana region, Nordland, Norway. The least altered Sr-87/Sr-86 (0.70676) and delta C-13 (+2.5 to +5.6%.) values of the marbles (Dunderland Marble 2a) in the hanging wall sequence of the Stensundtjern iron formation in the Rana region are consistent with seawater composition in the time interval 800-730 Ma, hence the Middle Cryogenian (pre-Sturtian). The least altered Sr- and C-isotopic values obtained from two other marbles units (Marble 3 and 4) of the Rodningsfjallet Nappe Complex are consistent with the Late Cryogenian (c. 660 and 670-700 Ma, respectively). The ages obtained provide the first insight into the depositional time of sediment-hosted iron formations of the Uppermost Allochthon in the North-Central Norwegian Caledonides. The Middle Cryogenian-age of marbles associated with iron formations in the Rana region and those located c. 250 km to the north (the Hafjellet iron ore horizon) share similar Sr-87/Sr-86 and delta C-13 ratios and hence similar chemostratigraphic ages. These iron formations were originally accumulated outside of Baltica, on a glacially influenced carbonate-siliciclastic shelf, apparently on a margin of an unknown microcontinent. The Scandinavian Dunderlandsdalen and the Hafjellet iron ores of Middle Cryogenian age (800-730 Ma) were accumulated in an open marine environment distant from volcanic centres, and hence represent an outstanding exception to other reported Neoproterozoic iron formations which were all accumulated in volcanically active continental rift settings. (C) 2015 Elsevier B.V. All rights reserved.

The Mofjell Group contains a number of sulfide zones and Zn-Pb-Cu deposits. New data show that the group comprises a largely bimodal volcanic-sedimentary assemblage formed in an island-arc to back-arc setting. Data on the lithologies and deposits show that the sulfide deposits belong to the bimodal-mafic or bimodal-felsic class of VMS deposits. The environment with a bimodal volcanic suite mixed with sediments is an environment which is regarded as favorable for both rich and large massive sulfide deposits.

The geology of northeastern Mozambique has been remapped at 1:250 000 scale. Proterozoic rocks, which make up the bulk of the area, form a number of gneiss complexes defined on the basis of their lithologies, metamorphic grade, structures, tectonic relationships and ages. The gneiss complexes, which contain both ortho- and paragneisses, range from Palaeo- to Neoproterozoic in age, and were juxtaposed along tectonic contacts during the late Neoproterozoic to Cambrian Pan-African Orogeny. In this paper we describe the geological evolution of the terranes north of the Ludo Belt, a major tectonic boundary which separates the complexes described in this paper from the Nampula Complex to the south. The Marrupa, Nairoto and Meluco Complexes are dominated by orthogneisses of felsic to intermediate compositions. Granulitic rocks, including charnockites, are present in the Unango, M'Sawize, Xixano and Ocua Complexes (the last forms the centre of the Lurio Belt). The Neoproterozoic Geci and Txitonga Groups are dominated by metasupracrustal rocks at low metamorphic grades and have been tectonically juxtaposed with the Unango Complex. Geochemical data integrate and support: a model of terrain assembly in northeast Mozambique, which is largely published and mainly derived from our new geochronological, lithostratigraphic and structural work. This model shows the contrast between the mainly felsic lower tectonostratigraphic levels (Unango, Marrupa, Nairoto and Meluco Complexes) and the significantly more juvenile overlying complexes (Xixano, Muaquia, M'Sawize, Lalamo and Montepuez Complexes), which were all assembled during the Cambrian Pan-African orogeny. The juxtaposed terranes were stitched by several suites of Cambrian late- to post-tectonic granitoids.

The Nampula Block covers over 100,000km2, making it the largest Mesoproterozoic crustal segment in northern Mozambique and an important component of the Neoproterozoic to Cambrian (Pan-African) East African Orogen. It is bounded in the north by the WSW–ENE trending Lúrio Belt. The oldest rocks (Mocuba Suite) are a polydeformed sequence of upper amphibolite-grade layered grey gneisses and migmatites associated with intrusive trondhjemite-tonalite-granodiorite and granitic orthogneisses. A banded gneiss, interpreted as a meta-volcanic rock, yielded a U-Pb SIMS zircon date of 1127±9Ma. Metamorphic rims, dated at ca. 1090Ma, probably grew during a later magmatic phase, represented by the tonalitic Rapale Gneiss, two samples of which were dated at 1095±19 and 1091±14Ma, respectively. The earliest (D1) deformation that took place at approximately this time, was associated with high grade metamorphism and migmatisation of the Mocuba Suite. The geochemistry of these rocks suggests that they were generated in a juvenile, island-arc setting. The Mocuba Suite is interlayered with extensive belts of meta-pelitic/psammitic, calc-silicate and felsic to mafic meta-volcanic paragneisses termed the Molócuè Group. U-Pb data from detrital zircons from a calc-silicate paragneiss gave a bimodal age distribution at ca. 1100 and 1800Ma, showing derivation from rocks of the same age as the Mocuba Suite and a Palaeoproterozoic source region. The age of the Molócuè Group has been directly determined by dates of 1092±13 and 1090±22Ma, obtained from two samples of the leucocratic Mamala Gneiss (meta-felsic volcanics?), one of its major constituent components. The final phase of Mesoproterozoic activity is represented by voluminous plutons and sheet-like bodies of foliated megacrystic granite, augen gneiss and granitic orthogneiss of the Culicui Suite, which have A-type granite geochemical characteristics and are interpreted to have been generated in a late tectonic, extensional setting. Three samples from the suite gave identical ages of ca. 1075Ma. The Nampula Block was extensively re-worked during the major (D2: Pan-African) collision orogen in Late Neoproterozoic to Cambrian times, when the major regional fabrics were imposed upon the Mesoproterozoic rocks under amphibolite-facies metamorphic conditions. In the dated samples, this orogenic event is represented by metamorphic zircon rim ages of ca. 550 to 500Ma. The new data indicate that the Mesoproterozoic rocks of the Nampula Block were originally accreted to a Palaeoproterozic crustal Block and the Nampula Block only reached its current position, separated from the other Mesoproterozoic blocks of NE Mozambique by the Lúrio Belt, during Neoproterozoic collision and plate movements. The geological history of the Nampula Block is comparable with that described from other parts of the Mesoproterozoic orogenic belts of the Kalahari craton and helps to constrain an integrated model of their evolution.

Marbles are minor but characteristic components of metasedimentary units within nappes in the Pan-African Mozambique Belt in NE Mozambique. Metasedimentary units remain largely undated, and carbon and strontium isotope stratigraphy of marbles has been used for indirect dating of the depositional history in this part of the Mozambique Belt. Sixty-nine samples from nine occurrences of dolomite, calcite and magnesite marbles in the Montepuez, Xixano, Lalamo, Ocua and Nampula metamorphic complexes were analysed for major and trace elements, and a subset of 39 samples for C, O and Sr isotopes. The least altered δ13C values range from −3.5 to +7.1‰ (V-PDB) and 87Sr/86Sr ratios from 0.70504 to 0.70671. These values are considered as the best proxy to seawater composition at the time of deposition. The apparent deposition ages, derived from available seawater evolution curves, range from c. 1250 to c. 660Ma. An age of 1250–910Ma is obtained from a tripartite marble unit in the Montepuez Complex which is exposed in the Montepuez quarries. Five other age-groups are represented by marble units with apparent depositional ages of 800–750Ma (Xixano North), 800–660Ma (Montepuez West), c. 750Ma (Nampula), c. 740Ma (Xixano South and Lalamo), and 740–670Ma (Montepuez East). The data suggest that: (i) Pan-African nappes in NE Mozambique include Neoproterozoic and probable Mesoproterozoic sediments; (ii) Neoproterozoic rocks of the Xixano and Nampula complexes might have different ancestry and were tectonically juxtaposed during the Neoproterozoic Pan-African orogeny.

A new regional compilation map and U-Pb ages on a suite of variably deformed, Ordovician, calc-alkaline intrusive igneous rocks requires a reinterpretation of the nature of continental collision and extensional exhumation of deep-seated rocks of the Western Gneiss Region west and northwest of Trondheim. A suite of calc-alkaline plutonic rocks, in the age range 482 to 438 Ma, previously known from the region of Smola-Hitra-Orlandet-Froan above the Hoybakken extensional detachment fault associated with the Devonian 'Old Red Sandstone' basins, is shown to extend over wide areas below the fault, commonly as strongly foliated and lineated gneisses that had been previously mistaken for parts of the Proterozoic Western Gneiss Region. At Follafoss, a member of this intrusive suite is unconformably overlain by weakly metamorphosed conglomerate and volcanogenic sedimentary rocks of probable Late Ordovician age, suggesting that both the sedimentary rocks and the underlying intrusions correlate with the Storen Nappe in the upper part of the local sequence of Caledonide nappes.U-Pb evidence of metamorphic ages from deep-seated rocks of the Western Gneiss Region include: 1) zircon reaction rims on Proterozoic igneous baddeleyite in the Selnes Gabbro at 401 +/- 2 Ma; 2) widespread development of zircon overgrowth and metamorphic zircon with omphacite and coesite inclusions from the Hareidlandet eclogite at 402 +/- 2 Ma; and 3) extreme Devonian thermal resetting and neocrystallization of titanite over a wide area of the Proterozoic basement gneisses ending at 395 to 3 Ma, here fully documented for the first time. At Kjorsvika, west of Trondheimsfjord, a ductilely deformed gneiss of the Ordovician intrusive suite contains igneous titanite dated at 455 Ma that shows little evidence for Devonian thermal resetting. This gneiss ties only 1 to 2 km northwest from a large area of Proterozoic gneisses with 100 percent Devonian reset titanite across a ductilely deformed contact that must represent a phase of extensional detachment (Agdenes detachment) much older than the more brittle detachments (compare Hoybakken detachment) associated with some of the present outcrops of the Devonian clastic basins.These and other relationships suggest the following broad sequence of Siluro-Devonian events in the region: A) Early Scandian (430 - 410 Ma) thrusting with emplacement of the composite Storen Nappe onto the relatively cool Baltoscandian margin of Baltica during contemporaneous subduction of its distal part, locally producing eclogites, possibly representing the earliest initiation of high-level 'post-orogenic' clastic basins. B) Early mid-Scandian (410 - 406 Ma) continued subduction and imbrication of a more proximal part of the Baltoscandian margin, with its heating and high-pressure metamorphism. Continued deep-level thickening by imbrication providing the gravitational potential for foreland- and hinterland-directed extension at high levels, while deposition in Devonian clastic basins probably continued. C) Late mid-Scandian (406 - 396 Ma) continued subduction of more proximal Baltican continental basement with common production of HP and UHP eclogites. Imbricate thrusting of a subducted and heated proximal continental slab provided the gravitational potential to initate hinterland backsliding and extensional emplacement of the cool high-level Storen Nappe against the cooling basement. Deposition in high-level Devonian clastic basins was active. D) Early late-Scandian (396 - 390 Ma). The extension and cooling initiated in C) brought an enormous volume of Proterozoic basement from high amphibolite facies to low amphibolite facies and through about 600degreesC, terminating Pb loss and neocrystallization of titanite at 395 +/- 3 Ma. During this phase, ductile extensional deformation progressed into a sinistral shear field, producing folds and subhorizontal stretching lineations within the previously thrust and extensionally juxtaposed, deep and high-level packages. E) Late Scandian (390 - 375 Ma) extension in a sinistral shear field bringing the ductilely deformed package into contact with brittle, highest-level rocks along detachments associated with outcrop areas of the Devonian clastic basins. In this sequence, the brittle detachments (E) played a relatively minor role, whereas the mid-Scandian deep-crustal imbrication and related high-level collapse (B, C and early D) were the main events that brought deep metamorphic rocks relatively close to the surface.

A first attempt to employ carbon and strontium isotope stratigraphy together with 1.20,000 scale mapping for chronstratigraphic Subdivision and geological correlation of non-fossiliferous sedimentary successions in the polydeformed, high-grade, marble-dominated terrane has been successful. The isotope stratigraphy was based on 315 analyses of major and trace elements, as well as on 231 delta(13)C(carb) and delta(18)O and 104 Sr-87/Sr-86 whole-rock analyses of calcite and dolomite marbles, representing all major marble units of the Narvik, Evenes and Niingen nappe complexes, and the Bogen Group in the north-central Norwegian Caledonides. A thick succession of calcite and dolomite marbles in the Ofoten Synform, previously considered to be stratigraphically homogeneous and of Late Ordovician-Early Silurian age, is shown to be a complex assemblage of Neoproterozoic, Cambrian and Early Silurian carbonate formations which were tectonically imbricated and emplaced in a non-chronostratigraphic order. The real breakthrough with the new geological mapping has been the establishment and use of the Cambrian and Early Silurian chemo/chronostratigraphic markers that reveal stratigraphic heterogeneity and tectonic repetition, provide a reliable stratigraphic subdivision, and facilitate the compilation of a chronologically-based geological map.

We have utilised potential field data in combination with seismic interpretation and bedrock mapping to improve the understanding of basement structures and rifting processes on the continental shelf offshore Nordland, northern Norway. Comparing the Bouguer gravity field to gravity responses from Airy roots at different depths for the northern Scandinavia mountains it is shown that the compensating masses are situated at a relatively shallow depth in the upper crust. The Tysfjord granite within the Transscandinavian Igneous Belt extends to a substantial depth (minimum 22 km) in the crust. These voluminous granites may be related to Proterozoic plate subduction along the western edge of the Baltic shield, analogous to the Sierra Nevada Batholith in California. The NW-SE trending late Devonian extensional structures (Kollstraumen detachment, and Nesna and Sagfjord shear zones) extend from the mainland north-westwards below the Helgeland, Vestfjorden and Ribban basins. The Bivrost Lineament most likely represents a detachment dipping 5-15degrees to the southwest and may constitute the offshore extension of the Nesna shear zone. The entire Nordland mainland and offshore area is to a great extent affected by the NE-SW trending late Caledonian gravity collapse. Later (Late-Palaeozoic-Mesozoic) offshore rifting events have resulted in a shallow Moho and rotated fault-blocks separated by transfer zones giving rise to intermediate wavelength gravity and aeromagnetic anomalies. Changes in Moho depths occur across the Surt, Bivrost and Vesteralen transfer zones indicating that these structures are continuous to great depths within the crust. The more local transfer zones separate structural domains characterised by different fault-polarities within the Ribban and Vestfjorden basins. The Myken intrusive complex (Palaeocene age?) to the northeast of the Utgard High gives rise to large gravity and magnetic anomalies comparable to the anomalies originating from the basement structuring.

Zircon fractions extracted from an oceanic, low-K rhyodacite and an arc-related trondhjemite body in the Bymarka ophiolite, close to Trondheim, Central Norwegian Caledonides, have yielded a precise U-Pb age of 482 +/- 5 and an interpreted age of c. 481 Ma, respectively. The dates are considered to represent the crystallisation ages of these felsic rocks. Geochemical data indicate that the rhyodacite is comparable to plagiogranites occurring in the nearby Lokken ophiolite, and is considered to be cogenetic with the metabasaltic greenstones of the ophiolite. The trondhjemite, on the other hand, transects the greenstones and shows a clear, subduction-related, geochemical signature. In common with neighbouring, dismembered and tectonically disrupted ophiolites, the Bymarka ophiolite is considered to have been obducted upon a microcontinental block represented by Gula Complex rocks, in Early Arenig time. Just prior to this development, seaward subduction of oceanic crust had provided appropriate conditions for the formation of blueschist-facies metamorphic parageneses, and led to the generation of late-stage arc products. A plausible palaeogeographic scenario in Late Cambrian to Early Ordovician time along and outboard of Baltica involved dual subduction systems, with seaward polarities, in the eastern part of Iapetus, or the Egir Sea. This involved an anticlockwise-rotating Baltican plate facing first Siberia, in Cambrian time, and then Laurentia in the Early Ordovician. Fairly rapid contraction of this oceanic tract occurred in a transpressive regime involving two, discretc, tectonothermal and obduction/accretion events in the time interval Late Cambrian to Early Arenig.

Late orogenic, Early to Middle Devonian extension in the Scandinavian Caledonides was unidirectional in western Norway. New data from two detachment zones (Hoybakken and Kollstraumen) north of the More-Trondelag Fault Complex show that bidirectional, opposed, orogen-parallel extension dominated in this region. At this time, the fault complex acted as a transfer zone for the Hoybakken detachment. Extension and uplift in central Norway triggered significant magmatic activity, in contrast to the lack of granite intrusions during exhumation of western Norway.