The >494 Ma Lillevik ophiolite fragment (Gratangseidet Igneous Complex) near Narvik, Scandinavian Caledonides

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Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

Recently it has been argued that the Sveconorwegian orogeny in southwest Fennoscandia comprised a series of accretionary events between 1140 and 920 Ma, behind a long-lived, active continental margin characterized by voluminous magmatism and high-grade metamorphism. Voluminous magnesian granitic magmatism is recorded between 1070 and 1010 Ma (Sirdal Magmatic Belt, SMB), with an apparent drop in activity ca. 1010-1000 Ma. Granitic magmatism resumed ca. 1000-990 Ma, but with more ferroan (A type) compositions (hornblende-biotite granites). This ferroan granitic magmatism was continuous until 920 Ma, and included emplacement of an AMCG (anorthosite-mangerite-charnockite-granite) complex (Rogaland Igneous Complex). Mafic rocks with ages corresponding to the spatially associated granites suggest that heat from underplated mafic magma was the main driving force for lower crustal melting and long-lived granitic magmatism. The change from magnesian to ferroan compositions may reflect an increasingly depleted and dehydrated lower crustal source. High-grade metamorphic rocks more than ~20 km away from the Rogaland Igneous Complex yield metamorphic ages of 1070-1015 Ma, corresponding to SMB magmatism, whereas similar rocks closer to the Rogaland Igneous Complex yield ages between 1100 and 920 Ma, with an apparent age peak ca. 1000 Ma. Ti-in-zircon temperatures from these rocks increase from ~760 to 820 °C ca. 970 Ma, well before the inferred emplacement age of the Rogaland Igneous Complex (930 Ma), suggesting that long-lived, high-grade metamorphism was not directly linked to the emplacement of the latter, but rather to the same mafic underplating that was driving lower crustal melting. Structural data suggest that the present-day regional distribution of high- and low-grade rocks reflects late-stage orogenic doming

Was Baltica part of Rodinia?

Late Ediacaran opening of the Iapetus Ocean is typically considered to reflect separation of Baltica and Laurentia during final breakup of the Rodinia supercontinent, with subsequent closure during the Caledonian Orogeny. However, evidence of the pre-opening juxtaposition of Baltica and Laurentia is limited to purportedly similar apparent polar wander paths and correlation of Rodinia-forming orogenic events. We show that a range of existing data do not unequivocally support correlation of these orogens, and that geologic and palaeomagnetic data instead favour separation of Baltica and Laurentia as early as 1.1–1.2 Ga. Furthermore, new detrital zircon U–Pb age and Ar–Ar thermochronological data from Norway point towards an active western Baltican margin throughout most of the Neoproterozoic and early Palaeozoic. These findings are inconsistent with the majority of palaeogeographic reconstructions that place Baltica near the core of the Rodinia supercontinent

The Paleoproterozoic Otish and Mistassini basins of Quebec, Canada: A record of Superia supercraton breakup and the end of the Lomagundi-Jatuli carbon isotope excursion

The Otish Supergroup and Mistassini Group of north-central Quebec are two weakly metamorphosed sedimentary successions deposited during the middle Paleoproterozoic along the modern-day eastern margin of the Archean Superior craton. This study presents new uranium-lead (U-Pb) detrital zircon and shale rhenium-osmium (Re-Os) geochronological data for these two successions, as well as δ13Ccarb data from sedimentary carbonate rocks, which comprise the first such data for the Otish Supergroup. New geochronological data presented here demonstrate that the Mistassini Group was deposited between 2121 Ma and 1825 Ma and postdates the Otish Supergroup by at least ∼20 m.y. The δ13Ccarb data from the Otish Supergroup are strongly enriched, typically +7‰ to +12‰, and therefore consistent with deposition during the Lomagundi-Jatuli carbon isotope excursion (LJE), which is generally considered to have occurred during ca. 2220−2060 Ma. Within the basal ∼200 m of the Mistassini Group, δ13Ccarb values reach almost +8‰, before shifting to near 0‰ in the overlying ∼1800 m of strata, which indicates that it records the termination of the LJE. The Re-Os depositional age of 1825 ± 9 Ma for mudstones of the Kallio Formation, the uppermost formation in the Mistassini Group, provides a minimum constraint for deposition in the basin. Cumulatively, the new radiometric ages and stable isotope ratio data provide a basis for a new tectonostratigraphic reconstruction that closely links the Mistassini and Otish basins to the evolution of the Labrador Trough and other basins along the eastern and southern margins of the Superior craton

Hydrocarbon generation and migration from Barremian – Aptian source rocks, Northern Orange Basin, offshore Western South Africa: A 3d numerical modelling study

A 3D numerical modelling workflow was applied to the Barremian—Aptian source rock interval in a shelfal to lower slope area of the northern Orange Basin, offshore western South Africa. The main objective was to investigate the timing of hydrocarbon generation and migration. Hydrocarbon migration has previously been investigated in the south of the basin by relating gas escape features with structural elements as seen on seismic sections, but migration pathways are still poorly understood. The modelling study was based on data from three exploration wells (AO-1, AE-1 and AF-1) together with 42 2D seismic sections totalling 3537 km in length, and a 3D seismic cube covering an area of 750 sq. km. Modelled formation temperatures increase from north to south in the study area and were consistent with downhole temperatures at well locations. However, there is variation between measured and modelled values of vitrinite reflectance (VR), especially in the Turonian and Cenomanian intervals. The measured VR is lower than the modelled VR within the Turonian section in the north of the study area, suggesting that erosion has affected the thermal maturity of the sediments. However, in the Cenomanian interval, the measured VR is higher than the modelled VR. Uplift, increased erosion in the hinterland and sediment transport to the coastal areas resulted in Cenomanian progradation of the Orange Basin fill

Temperature dependence of CO2-enhanced primary production in the European Arctic Ocean

The Arctic Ocean is warming at two to three times the global rate1 and is perceived to be a bellwether for ocean acidification2, 3. Increased CO2 concentrations are expected to have a fertilization effect on marine autotrophs4, and higher temperatures should lead to increased rates of planktonic primary production5. Yet, simultaneous assessment of warming and increased CO2 on primary production in the Arctic has not been conducted. Here we test the expectation that CO2-enhanced gross primary production (GPP) may be temperature dependent, using data from several oceanographic cruises and experiments from both spring and summer in the European sector of the Arctic Ocean. Results confirm that CO2 enhances GPP (by a factor of up to ten) over a range of 145–2,099 μatm; however, the greatest effects are observed only at lower temperatures and are constrained by nutrient and light availability to the spring period. The temperature dependence of CO2-enhanced primary production has significant implications for metabolic balance in a warmer, CO2-enriched Arctic Ocean in the future. In particular, it indicates that a twofold increase in primary production during the spring is likely in the Arctic

Crustal and basin evolution of the southwestern Barents Sea: from Caledonian orogeny to continental breakup

A new generation of aeromagnetic data documents the post-Caledonide rift evolution of the southwestern Barents Sea (SWBS) from the Norwegian mainland up to the continent-ocean transition. We propose a geological and tectonic scenario of the SWBS in which the Caledonian nappes and thrust sheets, well-constrained onshore, swing from a NE-SW trend onshore Norway to NW-SE/NNW-SSE across the SWBS platform area. On the Finnmark and Bjarmeland platforms, the dominant inherited magnetic basement pattern may also reflect the regional and post-Caledonian development of the late Paleozoic basins. Farther west, the pre-breakup rift system is characterized by the Loppa and Stappen Highs, which are interpreted as a series of rigid continental blocks (ribbons) poorly thinned as compared to the adjacent grabens and sag basins. As part of the complex western rift system, the Bjørnøya Basin is interpreted as a propagating system of highly thinned crust, which aborted in late Mesozoic time. This thick Cretaceous sag basin is underlain by a deep-seated high-density body, interpreted as exhumed high-grade metamorphic lower crust. The abortion of this propagating basin coincides with a migration and complete reorganization of the crustal extension toward a second necking zone defined at the level of the western volcanic sheared margin and proto-breakup axis. The abortion of the Bjørnøya Basin may be partly explained by its trend oblique to the regional, inherited, structural grain, revealed by the new aeromagnetic compilation, and by the onset of further weakening later sustained by the onset of magmatism to the west

Distribution of overwintering <i>Calanus</i> in the North Norwegian Sea

International audienceDuring winter 2003 and 2004, zooplankton and hydrographic data were collected in the northern parts of the Norwegian Sea (68?72° N, 8?17° E) west of the Norwegian shelf break at depths down to 1800 m. The results cover both inter and intra annual changes of hydrography and distribution of Calanus spp. For the whole survey area, average seawater temperature down to 1000 m was higher in 2004 than in the same period in 2003. For the upper 500 m the difference was ca. 1°C. Calanus finmarchicus dominated at ca. 75% of the total copepod abundance. Typical abundance of C. finmarchicus in the survey area was 30 000?40 000 m?2. C. hyperboreus was found deeper than C. finmarchicus while other copepods were found at the depth of C. finmarchicus or shallower. From January to February 2004, the peak of abundance of C. finmarchicus and C. hyperboreus shifted approximately 300 m upwards indicating that ascent from overwintering depth took place at a speed of 10 m d?1 during this period. In general, high abundance of copepods was found adjacent to the shelf slope while oceanic areas had low and intermediate abundance. In the southern part of the survey area, location of high and low copepod abundance shifted both between and within years. In the northern part of the survey area where the shelf slope is less steep, copepods was present at intermediate and high abundance during all surveys