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13 results on '"Bjerga, Anders"'

1. Extreme Mantle Heterogeneity Revealed by Geochemical Investigation of In Situ Lavas at the Central Mohns Ridge, Arctic Mid‐Ocean Ridges.

Author

Stubseid, Håvard Hallås, Bjerga, Anders, Rydland Pedersen, Leif‐Erik, and Pedersen, Rolf Birger

Subjects
LAVA flows, ISOTOPE geology, GEOCHEMISTRY, BASALT, LAVA, DIAPIRS
Abstract

Mid‐ocean ridge basalts reflect the mantle's composition and reveal processes from melting to eruption. The Mohns and Knipovich Ridges have ultraslow spreading rates, low magma budgets and erupted lavas indicating various mantle domains. Here, we use geochemistry and isotope systematics of in situ samples from two axial volcanic ridges (AVRs) to study mantle heterogeneity and melt production. By linking chemical variations to high‐resolution bathymetry and age data, we document systematic changes over time in the mantle source of the volcanic sequence. At Mohns Ridge AVR‐M10 (72.3°N), we observed significant variations in chemistry (e.g., (La/Sm)N from 0.7 to 2.9) and isotope systematics in basaltic samples from a small area (∼1 km2), suggesting the emplacement of multiple small‐volume lava flows. Pb isotope variations, for example, 206Pb/204Pb (17.91–18.76), are comparable with the observed range along the entire Mohns and Knipovich Ridges. Temporal constraints document that erupted basalts have changed from highly radiogenic Pb compositions to a more depleted signature within 30 ka. To explain the extreme variations in the erupted lavas at the Mohns Ridge, the mantle would need to be highly heterogeneous in composition with effective melt extraction and limited mixing prior to eruption. We use the highly heterogenous mantle underneath the Mohns Ridge to understand the melt extraction processes and mixing of melts and propose a two‐stage melting model: continuous generation of enriched melts from a deep and fertile source in the first stage, while depleted melts from a shallower and more refractory mantle occur sporadically and simultaneously with the intermittent ascent of diapirs. Key Points: Significant variations in chemistry within a small area suggest the emplacement of multiple small‐volume lava flowsTemporal constraints document that erupted basalts have changed from highly radiogenic Pb compositions to a depleted signature within 30 kaExtreme mantle heterogeneity is recorded in on‐axis lavas when melt extraction is efficient and homogenization in magma chambers is limited [ABSTRACT FROM AUTHOR]

Published
2024
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4. Fagutredning mineralressurser i norskehavet landskapstrekk, naturtyper og bentiske økosystemer

Author

Pedersen, Rolf B., Rydland Olsen, Bernt, Barreyre, Thibaut, Bjerga, Anders, Denny, Alden, Heggernes Eilertsen, Mari, Fer, Ilker, Haflidson, Haflidi, Thomassen Hestetun, Jon, Jørgensen, Steffen, Ribeiro, Pedro A., Steen, Ida Helene, Stubseid, Håvard, Tandberg, Anne Helene S., Thorseth, Ingunn, Pedersen, Rolf B., Rydland Olsen, Bernt, Barreyre, Thibaut, Bjerga, Anders, Denny, Alden, Heggernes Eilertsen, Mari, Fer, Ilker, Haflidson, Haflidi, Thomassen Hestetun, Jon, Jørgensen, Steffen, Ribeiro, Pedro A., Steen, Ida Helene, Stubseid, Håvard, Tandberg, Anne Helene S., and Thorseth, Ingunn

Published
2022

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

Author

Helsengreen, Maria, Rosén, Alexander, Bjerga, Anders, Täkte, Cecilia, Linder, Lars, Dalen, Dag Morten, Berg Roksvaag, Kristian, Hanna, Pohjonen, Helsengreen, Maria, Rosén, Alexander, Bjerga, Anders, Täkte, Cecilia, Linder, Lars, Dalen, Dag Morten, Berg Roksvaag, Kristian, and Hanna, Pohjonen

Abstract

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.

Published
2022

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

Author

Bjerga, Anders

Subjects
Serpentinization, Talc-carbonate, Leka Ophiolite Complex, Ultramafic rocks, Central Norway, Thermodynamic modeling
Abstract

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 &LT; 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. MAMN-GEOV GEOV399

Published
2014

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