Radiation damage allows identification of truly inherited zircon

Many studies have reported U-Pb dates of zircon that are older than the igneous rocks that contain them, and they are therefore thought to be inherited from older rock complexes. Their presence has profound geodynamic implications and has been used to hypothesize about concealed micro-continents, continental crust beneath ocean islands, and recycling of continental material in the mantle beneath mid-ocean ridges. Here, we combine single zircon U-Pb dates and structural radiation damage determined by Raman spectroscopy from a Pliocene mid-ocean ridge gabbro and from Cenozoic igneous rocks to test whether radiation damage allows distinction between contamination and truly inherited zircon. We find that Precambrian zircon found in the Pliocene sample has accumulated substantially more radiation damage than could be explained if they had truly been inherited. In the Cenozoic samples, however, we find that the radiation damage of old grains corresponds with that of young magmatic zircon, suggesting they are genuinely inherited.publishedVersio

Volcanic evolution of an ultraslow-spreading ridge

Nearly 30% of ocean crust forms at mid-ocean ridges where the spreading rate is less than 20 mm per year. According to the seafloor spreading paradigm, oceanic crust forms along a narrow axial zone and is transported away from the rift valley. However, because quantitative age data of volcanic eruptions are lacking, constructing geological models for the evolution of ultraslow-spreading crust remains a challenge. In this contribution, we use sediment thicknesses acquired from ~4000 km of sub-bottom profiler data combined with 14C ages from sediment cores to determine the age of the ocean floor of the oblique ultraslow-spreading Mohns Ridge to reveal a systematic pattern of young volcanism outside axial volcanic ridges. Here, we present an age map of the upper lava flows within the rift valley of a mid-ocean ridge and find that nearly half of the rift valley floor has been rejuvenated by volcanic activity during the last 25 Kyr.publishedVersio

A Highly Depleted and Subduction-Modified Mantle Beneath the Slow-Spreading Mohns Ridge

The Mohns Ridge is a very slow-spreading ridge that, together with the Knipovich Ridge, marks the boundary between the North American and Eurasian plates in the Norwegian-Greenland Sea. In this study, we report the major and trace element composition of spatially associated basalts and peridotites from a gabbro-peridotite complex ∼20 km west of the Mohns Ridge rift flank. Formation of the ∼4–5 Myr crustal section involved accretion of normal mid-ocean ridge basalts with Na-content suggesting derivation from a depleted mantle source. This is consistent with the degree of partial melting estimated for clinopyroxene poor harzburgites using the Cr-number of spinel (14%–18%) and rare earth element modeling of orthopyroxene (16%–24%) and reconstructed whole-rock composition (14%–20%). If all the melting took place beneath the paleo-Mohns Ridge, a crustal thickness of ∼7–8 km is expected, which is nearly double the observed thickness. Orthopyroxene trace elements are not consistent with typical fractional melting expected for mid-ocean ridges but rather resemble that seen in supra-subduction zone peridotites. The geochemistry of both the basalts and the peridotites suggests that a water-rich slab flux in the past has influenced the mantle source. In turn, this caused hydrous melting which increased the depletion of the pyroxene components, leading to a highly depleted mantle that is now underlying much of the Arctic Mid-Ocean Ridges and represents the source for the spreading related magmatism.publishedVersio

Evolution of talc- and carbonate-bearing alterations in ultramafic rocks on Leka (central Norway)

The thesis focuses on several low-angle fracture zones within the ultramafic section of the Leka Ophiolite Complex, central Norway, along which the original lithology has been completely serpentinized and carbonated. The alteration zones have a core made up of talc-carbonate bearing rocks surrounded by serpentine-carbonate bearing rocks with a sharp contact towards the country rock peridotites. Mineral assemblages of the alterations are controlled by the temperature, pressure, XCO2 and the chemical composition of the protolith. The study is based on petrographic and geochemical analysis of samples from three different alteration zones. To assess the metamorphic evolution of the study area, forward modeling has been carried out using the thermodynamic software Perple_X. Modeling of mineral equilibrium in the SiO2 - MgO - FeO - Fe2O3 - CaO - H2O - CO2 system is used to constrain the conditions during complete serpentinization and carbonation of partly altered peridotites. Conditions during alteration of the country rock peridotites was constrained in the SiO2 - MgO - FeO - Fe2O3 - CaO - H2O system. The partly altered peridotites consist of the mineral assemblage olivine - clinopyroxene - serpentine - magnetite - brucite and formed at temperatures < 400°C by infiltration of pure H2O fluids. Completely serpentinized rocks with the mineral assemblage serpentine - magnesite - magnetite - dolomite formed at temperatures < 510°C and low XCO2 ( 0.05) by the breakdown of the minerals in the partly altered peridotites. Talc-carbonate rocks formed at static conditions by the breakdown of the serpentine in the previously formed serpentinite rock to form the assemblage talc - magnesite - magnetite - dolomite at temperatures < 550°C and higher concentrations of XCO2 . Carbon isotope values determined for dolomite from carbonate lenses within the talc-carbonate rock yield d13C values of ~5, indicative of a mantle source for the carbon required for the carbonation. Oxygen isotope values dSMOW 18O of ~10.8 - 11.3% together with initial 87Sr/86Sr values between 0.7029 - 0.7063, suggest dehydration of rocks with mantle affinity as a source for the fluids. The combination of radiogenic- and stable isotopes leads to the interpretation that the source of fluids for the hydration and carbonation of the peridotites is the dehydration of partly hydrated ultramafic rocks. The dehydration most likely occurred during the post-Caledonian extension in the Devonian. Assuming that the temperature conditions estimated for the formation of the talc-carbonate rocks represent minimum temperatures of the fluids at their origin, it is shown that the temperatures are high enough to trigger dehydration reactions of hydrous peridotites occurring in deeper parts of the ophiolite complex. The buoyant fluids could have moved up through the fracture network and reacted with the rocks at shallower depths. High pressure gradients during fluid flow may have resulted in enhanced permeability through hydrofracturing

Timing of strain partitioning and magmatism in the Scottish Scandian collision, evidence from the high Ba–Sr Orkney granite complex

The Orkney granite complex dominates the outcropping basement on Orkney, Scotland. It comprises a grey and a pink variably foliated granite, and structurally younger pegmatites and aplites. Based on geochemical characteristics the granites are assigned to the Scottish high Ba–Sr granites. The granites are deformed by synmagmatic extensional east–west-trending mylonite zones. These are locally overprinted by similarly oriented extensional phyllonites and, in one case, by similarly oriented extensional faults. The grey and the pink granites are dated by zircon U–Pb CA-ID-TIMS to 431.93 ± 0.46 and 430.26 ± 0.92 Ma, respectively. An aplite cutting mylonitic granite and cut by phyllonite is dated to 428.50 ± 0.31 Ma. We interpret the shear zones to record north–south extension during emplacement and cooling of the granites, likely at a shallow crustal depth (4–12 km). The extension is best explained by a subsidiary pull-apart structure related to displacement on the Great Glen Fault. In this case, the Orkney granite complex dates transcurrent faulting to 432–429 Ma, coeval with the 431–429 Ma Moine Thrust. This indicates that strain partitioning and high Ba–Sr magmatism across the Scottish Highlands was an immediate response to attempted subduction of Avalonia beneath Laurentia during the Scandian collision

Radiation damage allows identification of truly inherited zircon

Many studies have reported U-Pb dates of zircon that are older than the igneous rocks that contain them, and they are therefore thought to be inherited from older rock complexes. Their presence has profound geodynamic implications and has been used to hypothesize about concealed micro-continents, continental crust beneath ocean islands, and recycling of continental material in the mantle beneath mid-ocean ridges. Here, we combine single zircon U-Pb dates and structural radiation damage determined by Raman spectroscopy from a Pliocene mid-ocean ridge gabbro and from Cenozoic igneous rocks to test whether radiation damage allows distinction between contamination and truly inherited zircon. We find that Precambrian zircon found in the Pliocene sample has accumulated substantially more radiation damage than could be explained if they had truly been inherited. In the Cenozoic samples, however, we find that the radiation damage of old grains corresponds with that of young magmatic zircon, suggesting they are genuinely inherited

Business Case for sharing of Nordic health data : Assessing the economic effects of a realized program vision

Today, the Nordic region comprises over 27 million people and is the 10th largesteconomy in the world by GDP. The individual countries are ranked high ondigitalization and characterized by high productivity. A common trend across Nordiccountries is rising healthcare expenditure linked with an aging population andincreasing amounts of chronic illnesses and mental health issues. Besides the largeannual toll and productivity loss because of diseases, the Nordic region spent over4160 billion EUR on healthcare in 2020. To accommodate the radical changes indemography, Nordic Innovation has set a vision that the Nordic region will be “themost sustainable and integrated health region in the world, providing the bestpossible personalized health care for all its citizens” by 2030. In this report, weexamine the opportunities for the Nordic region to leverage health data to realizethis vision and attempt to evaluate the potential economic effects of the realizedvision. Even if we achieve the vision by 2030, we do not foresee the immediaterealization of the full value potential of health data. Rather, our analysis andmodeling show we can expect a time lag of a few years before the value realizationwill have a significant effect on the Nordic economies. Because of this, the estimatedeconomic benefits in this report present the values for the year 2040, but it is worthstressing that to see these effects as outlined in this report, there is a need toimplement changes as soon as possible, before 2030. Some effects will materializeearlier than 2040, assuming that the implementation is done by 2030