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Sökning: WFRF:(Skelton Alasdair)

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1.
  • Alasdair, Skelton, et al. (författare)
  • Spatial coupling between spilitization and carbonation ofbasaltic sills in SW Scottish Highlands: evidence of amineralogical control of metamorphic fluid flow
  • 2011
  • Ingår i: Geofluids. - : Wiley. - 1468-8115 .- 1468-8123. ; 11:3, s. 245-259
  • Tidskriftsartikel (refereegranskat)abstract
    • In a geochemical and petrological analysis of overprinting episodes of fluid–rock interaction in a well-studied metabasaltic sill in the SW Scottish Highlands, we show that syn-deformational access of metamorphic fluids and consequent fluid–rock interaction is at least in part controlled by preexisting mineralogical variations. Lithological and structural channelling of metamorphic fluids along the axis of the Ardrishaig Anticline, SW Scottish Highlands, caused carbonation of metabasaltic sills hosted by metasedimentary rocks of the Argyll Group in the Dalradian Supergroup. Analysis of chemical and mineralogical variability across a metabasaltic sill at Port Cill Maluaig shows that carbonation at greenschist to epidote–amphibolites facies conditions caused by infiltration of H2O-CO2 fluids was controlled by mineralogical variations, which were present before carbonation occurred. This variability probably reflects chemical and mineralogical changes imparted on the sill during premetamorphic spilitization. Calculation of precarbonation mineral modes reveals heterogeneous spatial distributions of epidote, amphibole, chlorite and epidote. This reflects both premetamorphic spilitization and prograde greenschist facies metamorphism prior to fluid flow. Spilitization caused albitization of primary plagioclase and spatially heterogeneous growth of epidote ± calcic amphibole ± chlorite ± quartz ± calcite. Greenschist facies metamorphism caused breakdown of primary pyroxene and continued, but spatially more homogeneous, growth of amphibole + chlorite ± quartz. These processes formed diffuse epidote-rich patches or semi-continuous layers. These might represent precursors of epidote segregations, which are better developed elsewhere in the SW Scottish Highlands. Chemical and field analyses of epidote reveal the evidence of local volume fluctuations associated with these concentrations of epidote. Transient permeability enhancement associated with these changes may have permitted higher fluid fluxes and therefore more extensive carbonation. This deflected metamorphic fluid such that its flow direction became more layer parallel, limiting propagation of the reaction front into the sill interior.
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2.
  • Andersson, Tommy, et al. (författare)
  • Bottom characterization of Lagoa das Furnas on Sao Miguel, Azores archipelago
  • 2016
  • Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 321, s. 196-207
  • Tidskriftsartikel (refereegranskat)abstract
    • Lagoa das Furnas is a crater lake located in an area exposed to geohazards from earthquakes and volcanic activity on the island of sao Miguel in the Azores Archipelago. Geophysical mapping of Lagoa das Furnas reveals a previously undiscovered volcanic dome. This dome is comprised largely of subaquatic pyroclastic debris of trachytic composition. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the dome link it to the historically documented Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the dome suggests that it is comprised of more evolved magma than that of the main Furnas 1630 dome located 1400 m away. This suggests that the dome was formed during a final phase of the 1630 eruption in the Lagoa das Furnas area.
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3.
  • Andersson, Thommy (författare)
  • Geology of Lagoa das Furnas, a crater lake on São Miguel, Azores archipelago
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. Lagoa das Furnas is a crater lake within the Furnas volcanic centre which is located on the island of São Miguel in the Azores archipelago. The Furnas volcanic centre has a long history of earthquakes and volcanic activity. The area is relatively well-studied, except for the lake floor. Therefore, a high resolution geophysical and geological mapping survey was conducted at Lagoa das Furnas. Sidescan sonar was used to map the surface of the lake floor and single beam sonar was used to acquire sub-bottom profiles. In addition to the geophysical mapping, sediment surface sampling and core drilling were carried out followed by geochemical analyses of the retrieved material. The mapped data permitted a characterisation of the floor of Lagoa das Furnas and revealed several volcanic features including fumarole activity and a volcanic cone in the southern part of the lake. In order to unravel the origin of this cone several methods were applied, including analyses of tephra and minerals collected from the cone itself and from nearby deposits of two known eruptions Furnas I and Furnas 1630. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the cone suggest a subaqueous eruption linked to the Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the cone suggests that it is composed of more evolved magma than that of the main Furnas 1630 implying that the lake cone is likely a product of the last eruptional phase. Historical documents reveal three lakes in Furnas valley before the 1630 eruption. Two of these lakes were lost due the eruption and the remaining lake is most likely Lagoa das Furnas and consequently did exist before the 1630 eruption.
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4.
  • Andrén, Margareta, et al. (författare)
  • Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland
  • 2016
  • Ingår i: Journal of Geophysical Research - Solid Earth. - 2169-9313 .- 2169-9356. ; 121:4, s. 2315-2337
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemical analysis of groundwater samples collected from a borehole at Hafralækur, northernIceland, from October 2008 to June 2015 revealed (1) a long-term decrease in concentration of Si and Naand (2) an abrupt increase in concentration of Na before each of two consecutive M > 5 earthquakes whichoccurred in 2012 and 2013, both 76 km from Hafralækur. Based on a geochemical (major elements and stableisotopes), petrological, and mineralogical study of drill cuttings taken from an adjacent borehole, we areable to show that (1) the long-term decrease in concentration of Si and Na was caused by constant volumereplacement of labradorite by analcime coupled with precipitation of zeolites in vesicles and along fracturesand (2) the abrupt increase of Na concentration before the first earthquake records a switchover tononstoichiometric dissolution of analcime with preferential release of Na into groundwater. We attributedecay of the Na peaks, which followed and coincided with each earthquake to uptake of Na along fracturedor porous boundaries between labradorite and analcime crystals. Possible causes of these Na peaks are anincrease of reactive surface area caused by fracturing or a shift from chemical equilibrium caused by mixingbetween groundwater components. Both could have been triggered by preseismic dilation, which was alsoinferred in a previous study by Skelton et al. (2014). The mechanism behind preseismic dilation so far from thefocus of an earthquake remains unknown.
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5.
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6.
  • Barbieri, Maurizio, et al. (författare)
  • Changes in groundwater trace element concentrations before seismic and volcanic activities in Iceland during 2010-2018
  • 2021
  • Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 793
  • Tidskriftsartikel (refereegranskat)abstract
    • We analysed temporal variations of trace element concentrations in groundwater from a 101 m-deep borehole (HA01) in northern Iceland during 2010–2018 and compared them with seismic and volcanic events that occurred in the same period to identify potential hydrogeochemical precursors. An increase of B, Al, V, Li and Mo concentrations started from eight months to one month before the 2014 Bárðarbunga eruption (~115 km from HA01), a major rifting event in central Iceland, while Ga and V concentrations began to increase one day and one month after the onset of the event, respectively. We also found that concentrations of some trace elements (Li, B, Ga, Mo, Sr, Rb and Fe) significantly increased before an Mw 5.0 earthquake that occurred ~80 km from the borehole in 2018. However, other notable hydrogeochemical changes were detected during the monitoring period without apparent correlation with the seismic and volcanic events in the region. This study shows that the systematic long-term hydrogeochemical monitoring in seismic and volcanic areas is critical to advance the science of seismic and eruptive precursors. Furthermore, the use of statistical tools, such as Principal Component Analysis (PCA) and Change Point (CP) detection can help identify the most useful chemical elements and validate the trend variability of those elements in the time series, reducing arbitrary choices of pre-seismic and pre-volcanic hydrogeochemical anomalies as potential precursors.
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7.
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8.
  • Batki, Aniko, et al. (författare)
  • Petrogenetic significance of ocellar camptonite dykes in the Ditrau Alkaline Massif, Romania
  • 2014
  • Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 200, s. 181-196
  • Tidskriftsartikel (refereegranskat)abstract
    • Camptonite dykes intrude the rift-related Mesozoic igneous body of the Ditrau Alkaline Massif, Eastern Carpathians, Romania. We present and discuss mineral chemical data, major and trace elements, and the Nd isotopic compositions of the dykes in order to define their nature and origin. The dykes are classified as the clinopyroxene-bearing (camptonite-I) and clinopyroxene-free (camptonite-II) varieties. Camptonite-I consists of aluminian-ferroan diopside phenocrysts accompanied by kaersutite, subordinate Ti-rich annite, albite to oligoclase and abundant calcite-albite ocelli. Camptonite-II comprises K-rich hastingsite to magnesiohastingsite, Ti-rich annite, albite to andesine, abundant accessory titanite and apatite, and silicate ocelli filled mainly with plagioclase (An(4-34)). Age-corrected Nd-143/Nd-144 ratios vary from 0.51258 to 0.51269. The high epsilon(Nd) values of +4.0 to +6.1 which are consistent with intra-plate composition, together with light rare earth element (LREE), large ion lithophile element (LIE) and high field strength element (HFSE) enrichment in the camptonites is ascribed to the formation of small melt batches of a metasomatised sub-lithospheric mantle source. The presence of an asthenospheric 'high mu' ocean island basalt (HIMU-OIB)-type mantle component in the source region has also been revealed. A 1-4% degree of partial melting of an enriched garnet Iherzolite mantle source containing pargasitic amphibole followed by fractionation is inferred to have been involved in the generation of the camptonites. They are deduced to be parental melts to the Ditrau Alkaline Massif.
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9.
  • Boschetti, Tiziano, et al. (författare)
  • Geothermometry and water-rock interaction modelling at Hafralækur : Possible implications of temperature and CO2 on hydrogeochemical changes previously linked to earthquakes in northern Iceland
  • 2022
  • Ingår i: Geothermics. - : Elsevier BV. - 0375-6505 .- 1879-3576. ; 105
  • Tidskriftsartikel (refereegranskat)abstract
    • The low enthalpy (T < 150 °C) groundwater in the HA01 borehole at Hafralækur has a long time series (2008–2018) of chemical and isotopic data. In the previous studies, the variations in chemical and isotope parameters were statistically related to seismic activity. However, the possible effect of temperature has not yet been evaluated. To fill this gap, the results obtained from the classical geothermometric equations (silica solid phases, Na/K, Na-K-Ca) were compared. However, considering that the use of classical geothermometry using the Na/K ratio or silica solid phases solubility is limited by the presence of clay minerals and alkaline conditions (i.e., the presence of pH-dependant silicate anions), new equilibria reactions between labradorite, zeolites (analcime, stilbite) and the activity of the dissolved species in the fluid are presented to overcome this problem. In addition, kinetic reaction path models are presented to trace the possible role of both temperature and CO2 during the most evident chemical variations during earthquakes.
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10.
  • Claesson, Lillemor, 1976- (författare)
  • Fluid-rock interaction in two seismically active areas : The Tjörnes Fracture Zone, northern Iceland and the Shillong Plateau, northeastern India
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Hydrogeochemical monitoring can improve our understanding of fluid-rock interaction, and may detect anomalies that are precursory to- or caused by- earthquakes. In this study, hydrogeochemical monitoring was carried out in two distinct tectonic settings, to study coupling between hydrogeochemical changes and seismic activity. The Tjörnes Fracture Zone, north Iceland (HU-01), and the Shillong Plateau, northeastern India (Silver Drop), are two seismically active areas with differing geology. Hydrogeochemical monitoring included regular groundwater sampling with subsequent major and trace element analysis and supporting stable isotope analysis at HU-01 only. Transition metal concentrations anomalies were detected at HU-01 prior to a MW 5.8 earthquake. Concentration increases of many major elements were detected after this earthquake. Hydrogeochemical recovery took place during the subsequent two years. The preseismic anomalies are interpreted as the result of increased fluid-rock interaction due to preseismic fracturing whereas the postseismic changes are attributed to source switching and/or mixing of fluids enabled by fault unsealing. The two-year recovery is probably related to the gradual sealing off of a fluid source. Pre- and post-seismic hydrogeochemical shifts (e.g. Na/Si, Ba/Sr) were detected at Silver Drop coinciding with two MW > 5 earthquakes. These shifts are likely due to changes in the type of feldspar weathering. A basalt dissolution experiment was carried out in order to understand the preseismic changes at HU-01. Rates and dissolution mechanisms interpreted from this experiment confirm that the metal anomalies at HU-01 could be induced by transient exposure of weakly altered basalt to groundwater interaction caused by microfracturing. Finally, from this study it can be concluded that a seismic event need not cause a hydrogeochemical shift, but a hydrogeochemical shift was always associated with a seismic event.
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11.
  • Claesson, Lillemor, et al. (författare)
  • The timescale and mechanisms of fault sealing and water-rock interaction after an earthquake
  • 2007
  • Ingår i: Geofluids. ; 7, s. 427-440
  • Tidskriftsartikel (populärvet., debatt m.m.)abstract
    • Hydrogeochemical monitoring of a basalt-hosted aquifer, which contains Ice Age meteoric water and is situatedat 1220 m below sea level in the Tjornes Fracture Zone, northern Iceland, has been ongoing since July 2002.Based on hydrogeochemical changes following an earthquake of magnitude (Mw) 5.8 on 16 September 2002, weconstrained the timescales of post-seismic fault sealing and water–rock interaction. We interpret that the earthquakeruptured a hydrological barrier, permitting a rapid influx of chemically and isotopically distinct Ice Agemeteoric water from a second aquifer. During the two subsequent years, we monitored a chemical and isotopicrecovery towards pre-earthquake aquifer compositions, which we interpret to have been mainly facilitated byfault-sealing processes. This recovery was interrupted in November 2004 by a second rupturing event, which wasprobably induced by two minor earthquakes and which reopened the pathway to the second aquifer. We concludethat the timescale of fault sealing was approximately 2 years and that the approach to isotopic equilibrium(from global meteoric water line) was approximately 18% after >10^4 years. Key words: earthquake, fault sealing, hydrogeochemistry, Iceland, Tjornes Fracture Zone, water–rock interaction
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12.
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13.
  • Eliaeson, Karin, et al. (författare)
  • Relationships of geochemistry and multiple sclerosis
  • 2009
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • The main aim of this study has been to investigate how registers and databases of geochemistry can be combined with registers of patient data in epidemiological studies. By testing the hypothesis that Multiple Sclerosis (MS) varies with geography and investigating if the variation can be explained by natural variability of zinc in different media, difficulties have been identified and recommendations for future epidemiological studies with similar scope are given. Multiple sclerosis (MS) is a chronic neurological illness that affects nerve cells in the central nervous system (CNS). It belongs to a group of illnesses called autoimmune diseases where the immune system attacks the body's own tissue. The onset of autoimmune reactions is not fully understood. Autoimmune diseases are believed to be multifactorial where both intrinsic factors (e.g. genetics, age, hormones) and environmental factors (e.g. infections, diet, drugs, chemicals etc.) may contribute to the induction, development and progression of the disease. There is a general believe that the epidemiological pattern of MS vary with geography, but even though the systematic study of MS started in 1929 the comparison of prevalence studies over the world still is very difficult and the results are not reliable. Iron, zinc, manganese, copper and molybdenum are examples of important building blocks for almost all living organisms and are thus termed essential elements. They originally derive from the Earth's crust and are taken up in organisms from soil, air and water. For some metals, no biological, nutritional or biochemical function has been established (yet) and they are thus termed non-essentials. The level of exposure to essential and non-essential elements is of crucial importance for the effect on living organisms. A too high dose can be toxic while a too low dose of essential elements will cause deficiency and consequent higher vulnerability for the exposure to toxic compounds or non-essential elements. In this study we have initially focused to check if the occurrence of MS could be correlated to background levels of zinc (Zn) since zinc is an element that participates in several important reactions in the body. We used the Swedish MS-register, which includes almost all MS-patients in Sweden. The best resolution on where the patients live is given on post code areas. Spatially distributed census data over postcode areas, valid for December 2005 and compiled by Official Statistics of Sweden, Statistics Sweden (SCB), were used in this study. Geochemical data from soil (till), stream-water and groundwater from the Swedish Geological Survey have been compiled into postcode areas. The analyzed data on the distribution of MS-patients indicate that a geographical pattern could be found with higher prevalence of MS in the county of Västerbotten and clusters around larges cities. No north -south or east-west gradient of the prevalence was found. However, visual interpretation of prevalence measures is strongly biased towards large post code areas, masking the variation of prevalence measures of small areas. This effect is striking in larger cities always having a large number of small post code areas. Combination of the patient registers and the geochemical registers was evaluated with multivariate analysis (MVA) and as a univariate study for zinc solely, but no correlation between the prevalence of MS and the occurrence of natural background levels of elements were found. Registers were analyzed both separately and together, but none of these models increased the degree to which variance was explained. This does not mean that no relationship between MS and geochemistry is possible but that correlations could not be found with the data, methods and models used in this project. The most important conclusion from this study is that to combine patient data with any kind of exposure data with a geographical variation, the administrative division (i.e. parishes, post code areas etc) are less appropriate. Divisions with respect to natural (geographical) borders such as catchment areas would be more useful for epidemiological purposes where a geographic component is of interest. To fulfil this, population data for catchment areas is needed. The density of the patient data and the exposure data is also of crucial importance. Moreover, there must be a variation in the exposure data large enough to result in a difference between areas. It is recommended that also the areas where no disease is found to be included in epidemiological studies. In these regions high or low levels of elements can also be present. The use of average values over districts is problematic. A high density of sampling in an area does not necessarily mean that the calculated mean value is representative for the whole area. How well an average value for a district describes the actual value depends both on the natural variability of substances in the media as well as the sampling density (i.e. high variance but many samples could give the same average value as low variance and few samples).
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14.
  • Engström, Anna, 1975- (författare)
  • Deformation and fluid-flow in magma-poor margins : A study of the Tasna Ocean-Continent transition, SE Switzerland
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • In this study, interaction between fluids and deformation during the final stages of magma-poor rifting was investigated. The Tasna Ocean-Continent transition, located in the Swiss Alps, was studied and a large data set was obtained from profiles oriented perpendicular to two detachment faults. One of these juxtaposed serpentinized mantle against continental crust and the other exhumed both mantle and continental crust to the seafloor. Deformation associated with detachment faulting showed many common features but also some phenomena which were unique to each fault, confirming their sequential activity and differing roles in the exhumation process. Oxygen isotopes indicated the presence of both pervasive and channeled fluid phases, either accompanying or post-dating serpentinization. Deformation in the fault zone occurred in previously serpentinized mantle indicating that serpentinization pre-dated final exhumation. Most strain localization and displacement occurred in fault cores which are narrow zones beneath the detachments. These are underlain by wide zones characterized by more distributed strain. Transitional fabrics as well as reactivated and/or overprinted deformation structures indicated that the final phase of rifting is complex. Fault cores acted as fluid conduits or barriers. Thus, the most deformed zones may become the least permeable. Hence the coupling between deformation and fluid flow is complex in a study area subjected to several phases of deformation and fluid flow. Finally the importance of serpentinization in the evolution of magma-poor rifting was investigated. It was found that serpentinization is the consequence rather than the reason for strain localization at magma-poor margins. However, serpentinization may be an important process which can accelerate exhumation rates in the very latest stages of magma-poor rifting. The pre-existing deformation history of the crust may also be of importance for the development and location of margins.
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15.
  • Engström, Anna, et al. (författare)
  • Isotopic and petrological evidence of fluid-rock interaction at a Tethyan ocean-continent transition in the Alps : implications for tectonic processes and carbon transferduring early ocean formation
  • 2007
  • Ingår i: Geofluids. - : Wiley. - 1468-8115 .- 1468-8123. ; 7:4, s. 401-414
  • Tidskriftsartikel (refereegranskat)abstract
    • We report overprinting stable isotope evidence of fluid–rock interaction below two detachment faults along which mantle rocks were exhumed to the seafloor, between the respective landward and seaward limits of oceanic and continental crust, at a Tethyan ocean–continent transition (OCT). This OCT, which is presently exposed in the Tasna nappe (south-eastern Switzerland) is considered an on-land analogue of the well-studied Iberian OCT. We compare our results with the fault architecture (fault core–damage zone–protolith) described by Caine et al. [Geology (1996) Vol. 24, pp. 1025–1028]. We confirm the existence of a sharp boundary between the fault core and damage zone based on isotopic data, but the boundary between the damage zone and protolith is gradational. We identify evidence for: (1) pervasive isotopic modification to 8.4 ± 0.1‰ which accompanied or post-dated serpentinization of these mantle rocks at an estimated temperature of 67–109°C, (2) either (i) partial isolation of some highly strained regions [fault core(s) and mylonite] from this pervasive isotopic modification, because of permeability reduction (Caine et al.) or (ii) subsequent isotopic modification caused by structurally channelled flow of warm fluids within these highly strained regions, because of permeability enhancement, and (3) isotopic modification, which is associated with extensive calcification at T = 54–100°C, primarily beneath the younger of the two detachment faults and post-dating initial serpentinization. By comparing the volumetric extent of calcification with an experimentally verified model for calcite precipitation in veins, we conclude that calcification could have occurred in response to seawater infiltration, with a calculated flux rate of 0.1–0.2 m year−1 and a minimum duration of 0.2–4.0 × 104 years. The associated time-averaged uptake flux of carbon during this period was 8–120 mol m−2 year−1. By comparison with the estimated area of exhumed mantle rocks at the Iberian OCT, we calculate a maximum annual uptake flux for carbon of 2–30 Tg year−1. This is an order of magnitude greater than that for carbon exchange at the mid-ocean ridges and 0.1–1.4% of the global oceanic uptake flux for carbon.
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16.
  • Fairchild, Ian J., et al. (författare)
  • Tonian-Cryogenian boundary sections of Argyll, Scotland
  • 2018
  • Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 319, s. 37-64
  • Tidskriftsartikel (refereegranskat)abstract
    • The Tonian-Cryogenian System boundary is to be defined at a GSSP (Global Boundary Stratigraphic Section and Point) beneath the first evidence of widespread glaciation. A candidate lies within the Dalradian Supergroup of Scotland and Ireland, which is least deformed and metamorphosed in Argyll, western Scotland. We present new stratigraphic profiles and interpretations from the Isle of Islay and the Garvellach Islands, update the chemostratigraphy of the Appin Group Tonian carbonates underlying the thick (ca. 1 km) glacigenic Port Askaig Formation (PAF) and demonstrate an environmental transition at the contact. The Appin Group forms a regionally extensive, > 4 km-thick, succession of limestones, shales and sandstones deposited on a marine shelf. On Islay, the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure, oolite, stromatolitic dolomite and intraclastic microbial mounds. Significantly deeper erosion at the unconformity at the base of the overlying PAF is demonstrated in the southern section. Carbonate facies show a gradual decline in delta C-13(VPDB) from +5 to + 2 parts per thousand upwards. In NE Garbh Eileach (Garvellach Islands), a continuously exposed section of Appin Group carbonates, 70 m thick, here designated the Garbh Eileach Formation (GEF), lies conformably beneath the PAF. The GEF and the GEF-PAF boundary relationships are re -described with new sedimentological logs, petrological and stable isotope data. Interstratified limestone and dolomicrosparite with delta C-13 of -4 to -7 parts per thousand (a feature named the Garvellach anomaly, replacing the term Islay anomaly) are overlain by dolomite in which the isotope signature becomes weakly positive (up to +1 parts per thousand) upwards. Shallow subtidal conditions become peritidal upwards, with evidence of wave and storm activity. Gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the GEF. The basal diamictite (D1) of the PAF is rich in carbonate clasts similar to slightly deeper water parts of the underlying succession. D1 is typically several metres thick with interstratified sandstone and conglomerate, but dies out laterally. Scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft -sediment deformation is interbedded with carbonate below and above D1. Dolomite beds with derived intraclasts and gypsum pseudomorphs are found above D1 (or equivalent position, where Dl is absent). Published and new Sr isotope studies, including successive leach data, demonstrate primary Tonian Sr-87/Sr-86 values of 0.7066-0.7069 on Islay, decreasing to 0.7064-0.7066 in the younger GEF limestones on the Garvellachs, with 1700-2700 ppm Sr. Other typically Tonian characteristics of the carbonates are the Sr-rich nature of limestones, molar tooth structure, and dolomitized peritidal facies with evidence of aridity. Seabed surveys suggesting uniformly-dipping strata and shallow borehole core material illustrate the potential for extending the Tonian record offshore of the Garvellachs. A candidate Tonian-Cryogenian GSSP is proposed on Garbh Eileach within the smooth delta C-13 profile at the cross-over to positive delta C-13 signatures, 4 m below the first occurrence of ice-rafted sediment and 9 m below the first diamictite. Although lacking radiometric constraints or stratigraphically significant biotas or biomarkers, the Scottish succession has a thick and relatively complete sedimentary record of glaciation, coherent carbon and strontium chemostratigraphy, lateral continuity of outcrops and 100% exposure at the proposed boundary interval.
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17.
  • Fritzon, Ruben, 1977-, et al. (författare)
  • Evaluating geochemical evidence of earthquake periodicity, Sparta Fault, Southern Greece
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Determining prehistoric earthquake periodicity and magnitudes is important for risk assessments in seismically active areas. We evaluate a geochemical method, which has previously been used to identify prehistoric slips on normal fault scarps through an analysis of variations in the concentration of rare earth elements and Y (REE-Y) along vertical transects. Our study object is the Sparta Fault, a normal fault in southern Greece, developed in limestone and previously documented, and dated using 36Cl, to have been last active 464 BC. From geochemical analyses of 39 fault rock samples, we conclude that REE-Y concentrations correlate strongly with the abundance of quartz and possibly other heterogeneities in the fault scarp. Because the sampled fault rock is a protocataclasite, formed at depth, variations in the abundance of quartz are not associated with prehistoric movements along the fault. We therefore conclude that geochemical evidence does not provide a reliable paleoseismic proxy for fault movement. We also present data indicating a co-variation between quartz and 36Cl concentrations, which we suggest requires a re-examination of this widely used application of the cosmogenic nuclide surface exposure dating method.
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18.
  • Fru, Ernest Chi, et al. (författare)
  • Transient fertilization of a post-Sturtian Snowball ocean margin with dissolved phosphate by clay minerals
  • 2023
  • Ingår i: Nature Communications. - 2041-1723. ; 14:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Marine sedimentary rocks deposited across the Neoproterozoic Cryogenian Snowball interval, similar to 720-635 million years ago, suggest that post-Snowball fertilization of shallow continental margin seawater with phosphorus accelerated marine primary productivity, ocean-atmosphere oxygenation, and ultimately the rise of animals. However, the mechanisms that sourced and delivered bioavailable phosphate from land to the ocean are not fully understood. Here we demonstrate a causal relationship between clay mineral production by the melting Sturtian Snowball ice sheets and a short-lived increase in seawater phosphate bioavailability by at least 20-fold and oxygenation of an immediate post-Sturtian Snowball ocean margin. Bulk primary sediment inputs and inferred dissolved seawater phosphate dynamics point to a relatively low marine phosphate inventory that limited marine primary productivity and seawater oxygenation before the Sturtian glaciation, and again in the later stages of the succeeding interglacial greenhouse interval.
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19.
  • Gerhardt, Karin, et al. (författare)
  • Nog nu, politiker – ta klimatkrisen på allvar : 1 944 svenska forskare och anställda i forskarvärlden: Vad är det ni inte förstår?
  • 2022
  • Ingår i: Aftonbladet. - 1103-9000. ; :2022-08-25
  • Tidskriftsartikel (populärvet., debatt m.m.)abstract
    • DEBATT. Som forskare och medborgare är vi arga och förtvivlade över den senaste tidens utveckling. Vi ser hur en majoritet av våra politiska partier överger klimatpolitiken och i stället föreslår eller genomför politik som går stick i stäv med Parisavtalet och Sveriges klimat- och miljömål.Våra politiker måste ta krisen på allvar och leda omställningen till ett framtida samhälle inom planetens gränser. Forskningen visar att en sådan framtid är möjlig. Det skriver 1 944 forskare och anställda från 45 svenska lärosäten och forskningsinstitut.
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20.
  • Goodfellow, Bradley W., et al. (författare)
  • Controls of tor formation, Cairngorm Mountains, Scotland
  • 2014
  • Ingår i: Journal Of Geophysical Research: Earth Surface. - 2169-9003. ; 119:2, s. 225-246
  • Tidskriftsartikel (refereegranskat)abstract
    • Tors occur in many granitic landscapes and provide opportunities to better understand differential weathering. We assess tor formation in the Cairngorm Mountains, Scotland, by examining correlation of tor location and size with grain size and the spacing of steeply dipping joints. We infer a control on these relationships and explore its potential broader significance for differential weathering and tor formation. We also assess the relationship between the formation of subhorizontal joints in many tors and local topographic shape by evaluating principle surface curvatures from a digital elevation model of the Cairngorms. We then explore the implications of these joints for tor formation. We conclude that the Cairngorm tors have formed in kernels of relatively coarse grained granite. Tor volumes increase with grain size and the spacing of steeply dipping joints. We infer that the steeply dipping joints largely formed during pluton cooling and are more widely spaced in tor kernels because of slower cooling rates. Preferential tor formation in coarser granite with a wider joint spacing that is more easily grusified indicates that joint spacing is a dominant control on differential weathering. Sheet jointing is well developed in tors located on relatively high convex surfaces. This jointing formed after the gross topography of the Cairngorms was established and before tor emergence. The presence of closely spaced (tens of centimeters), subhorizontal sheeting joints in tors indicates that these tors, and similarly sheeted tors elsewhere, formed either after subaerial exposure of bedrock or have progressively emerged from a regolith only a few meters thick. Key Points Tors form in kernels of coarse-grained granite among finer-grained granite Wide joint spacing in tors attributable to a slow cooling rate of the granite Sheet jointing discounts tor formation within a thick regolith
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21.
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24.
  • Hode Vuorinen, Jaana, 1974- (författare)
  • The Alnö alkaline and carbonatitic complex, east central Sweden - a petrogenetic study
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The Alnö complex on the central Swedish east coast is composed of a main composite intrusion (the main intrusion) and four smaller satellite intrusions (Söråker, Sälskär, Långharsholmen and Båräng) distributed around the main intrusion on Alnö Island and on the mainland north of the island. The major rock types exposed within the complex are melilitolite, pyroxenite, ijolite series (melteigite-ijolite-urtite), nepheline syenite, carbonatite and alnöite dykes. Melilitolite is only exposed within the Söråker intrusion. The intrusive sequence is melilitolite → pyroxenite → ijolite series → nepheline syenite → carbonatite → alnöite.Mineralogical, whole rock geochemical and radiogenic isotope (Nd-Sr-Pb) studies of exposed rocks from the Alnö alkaline complex, east central Sweden, were performed in order to investigate the genetic relationships between the diverse rock-types, and to evaluate the contributions from mantle and crustal components in the genesis of the complex. Most analysed samples fall within the depleted quadrant in a eNd-eSr diagram, similar to carbonatites and alkaline silicate rocks from other complexes, indicating derivation of parental magma(s) from a source that had experienced time-integrated depletion in LIL elements. Contamination by local crust is indicated by Sr and Pb isotope data, but is geographically restricted to samples collected from the outer parts of the main intrusion and from satellite intrusions. This localized contamination is attributed to selective hydrothermal element leaching of surrounding bedrock during fenitization. Nd- and Sr-isotope data separates the carbonatites into two groups (group I and II), each related to a specific set of silicate rock types. The overlap of group II carbonatites with ijolite and nepheline syenite could indicate a common origin through liquid immiscibility but this hypothesis cannot be confirmed by trace element data because initial concentrations are obscured by fractionation processes. Interestingly, results from AFC-modelling suggest that production of ijolite residual magma requires addition of a small volume (2.4 %) of carbonatite component to the parental magma, whereas formation of nepheline syenite residuals requires removal of an almost equal amount of carbonatite (1.5 %) to yield a statistically significant result. AFC-modelling further suggests that the various silicate rock types exposed within the complex are related to the same parental olivine-melilitite magma through crystal fractionation of olivine, melilite, clinopyroxene, nepheline, Ti-andradite and minor phases. These results agree with compositional trends exhibited by clinopyroxene and Ti-andradite from the silicate rocks of the main intrusion, which suggests co-genesis of pyroxenite, ijolite series rocks and nepheline syenite. Production of ijolite-like residual liquids can be achieved by <40% fractionation whereas production of nepheline syenite residuals requires >80% fractionation.An investigation of the origin of silicate minerals in carbonatites suggest that most silicate minerals observed in the carbonatites on Alnö Island are derived from surrounding wall-rock and/or produced through corrosive interaction between carbonatite liquid and assimilated phases. This leads to ambiguities when addressing the possible genetic link between carbonatites and associated silicate rocks as occurrences of identical “liquidus” phases in inferred immiscible liquids may not actually be such.
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25.
  • Jakobsson, Martin, et al. (författare)
  • Major earthquake at the Pleistocene-Holocene transition in Lake Vattern, southern Sweden
  • 2014
  • Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 42:5, s. 379-382
  • Tidskriftsartikel (refereegranskat)abstract
    • Lake Vattern, Sweden, is within a graben that formed through rifting along the boundary between two Precambrian terrains. Geophysical mapping and geological coring show that substantial tectonic movements along the Lake Vattern graben occurred at the very onset of the Holocene. This is evident from deformation structures in the soft sediment accumulated on the lake floor. Our interpretation of these structures suggests as much as 13 m of vertical tectonic displacements along sections of a >80-km-long fault system. If these large displacements are from one tectonic event, Lake Vattern must have had an earthquake with seismic moment magnitudes to 7.5. In addition, our geophysical mapping shows large landslides along sections of the steep lake shores. Pollen analysis of sediment infillings of some of the most prominent sediment deformation structures places this major seismic event at the Younger Dryas-Preboreal transition, ca. 11.5 ka. We suggest that this event is mainly related to the rapid release of ice-sheet load following the deglaciation. This paleoseismic event in Lake Vattern ranks among the larger known intraplate tectonic events in Scandinavia and attests to the significance of glacio-isostatic unloading.
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26.
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27.
  • Jonsson, Erik, et al. (författare)
  • Magmatic origin of giant 'Kiruna-type' apatite-iron-oxide ores in Central Sweden
  • 2013
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3, s. 1644-
  • Tidskriftsartikel (refereegranskat)abstract
    • Iron is the most important metal for modern industry and Sweden is by far the largest iron-producer in Europe, yet the genesis of Sweden's main iron-source, the 'Kiruna-type' apatite-iron-oxide ores, remains enigmatic. We show that magnetites from the largest central Swedish 'Kiruna-type' deposit at Grangesberg have delta O-18 values between -0.4 and +3.7%, while the 1.90-1.88 Ga meta-volcanic host rocks have d18O values between +4.9 and +9%. Over 90% of the magnetite data are consistent with direct precipitation from intermediate to felsic magmas or magmatic fluids at high-temperature (delta O-18(mgt). > +0.9 parts per thousand, i.e. ortho-magmatic). A smaller group of magnetites (delta O-18(mgt) <= +0.9 parts per thousand), in turn, equilibrated with high-delta O-18, likely meteoric, hydrothermal fluids at low temperatures. The central Swedish 'Kiruna-type' ores thus formed dominantly through magmatic iron-oxide precipitation within a larger volcanic superstructure, while local hydrothermal activity resulted from low-temperature fluid circulation in the shallower parts of this system.
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28.
  • Katrantsiotis, Christos, et al. (författare)
  • High-resolution environmental reconstruction in SW Peloponnese, Greece, covering the last c. 6000years : Evidence from Agios Floros fen, Messenian plain
  • 2016
  • Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 26:2, s. 188-204
  • Tidskriftsartikel (refereegranskat)abstract
    • A paleolimnological record from the central Messenian plain (southwestern Peloponnese, southern Greece) indicates rapid changes in the water level and chemistry of a transient lake on the flanks of the Taygetos Mountains during the last c. 6000years. The analyses are based on diatoms as well as carbon and nitrogen isotopes from bulk sediments in a 7.5-m-long sediment core retrieved from the drained fen of Agios Floros, at the northern banks of the ancient River Pamisos. The sequence consists of fen peat in the uppermost section underlain by lacustrine sediments, which are punctuated by two layers of clay with diatomaceous silt bands. High accumulation rate is recorded in the oldest part of the section (up to 23mm/yr), particularly during two decadal-long periods centered at c. 5700 and c. 5300 cal. BP. The diatom record reveals pronounced peaks in the planktonic taxon Cyclotella distinguenda, which correspond to the laminated sequences, reflecting the rapid development of a deep lake with an open water environment during these two time periods. Another two events with intermediate water levels are inferred at c. 5200 and c. 4600 cal. BP. These short-lived phases were probably, to a large extent, caused by local tectonic processes and the consequent hydrological anomalies of the nearby karst springs, although abrupt climatic changes with enhanced precipitation might have also played a role. At c. 4500 cal. BP, our data suggest the development of terrestrial conditions in this area, which can be attributed to the decreasing activity/dry up of springs, probably associated with more arid climate. After c. 2500 cal. BP, the diatom record infers a return to wetter conditions, probably as a response to more humid climate with marked seasonality and human activities, developing the present-day environment with cultivated and seasonally semi-flooded fields.
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29.
  • Kleine, Barbara (författare)
  • How do fluids move through rocks? : High fluxes of CO2 in the Earth's crust
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Metamorphic hydrous, CO2-bearing fluids play a critical role in the global carbon cycle. However, how big this influence is on the global carbon cycle and therefore on global climatic processes, is unknown. The actual amount of CO2 which is released into the atmosphere due to metamorphic processes is still debated. For this purpose, fluid-driven reactions in metamorphic rocks must be studied by tracking fluid-rock interactions along pathways of ancient fluids.In the study presented in this thesis, we study fluid-rock interaction in the southeastern part of the Greek island Syros in the Cycladic Archipelago (Aegean). On Syros fluid-rock interaction is recorded by the preservation of blueschist facies assemblages at greenschist facies conditions along a normal shear zone. Blueschist preservation is caused by a combination of metasomatic addition of SiO2 and Na2O and elevated XCO2 which is maintained by high fluxes of a CO2-bearing, hydrous fluid along the shear zone.This research aims to provide a better understanding of the role of mountain building in the carbon cycle. Flux estimates for climate-forcing fluid components (e.g. carbon) require that their concentration in the fluid, fluid volumes and velocities are known. This will be the focus of future work. Further, whole rock chemistry and the availability of specific minerals will be studied to achieve knowledge about which kind of parameters influence and enhance the propagation of fluids through rocks.
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30.
  • Kleine, Barbara I., 1987- (författare)
  • How do metamorphic fluids move through rocks? : An investigation of timescales, infiltration mechanisms and mineralogical controls
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis aims to provide a better understanding of the role of mountain building in the carbon cycle. The amount of CO2 released into the atmosphere due to metamorphic processes is largely unknown. To constrain the quantity of CO2 released, fluid-driven reactions in metamorphic rocks can be studied by tracking fluid-rock interactions along ancient fluid flow pathways. The thesis is divided into two parts: 1) modeling of fluid flow rates and durations within shear zones and fractures during greenschist- and blueschist-facies metamorphism and 2) the assessment of possible mechanisms of fluid infiltration into rocks during greenschist- to epidote-amphibolite-facies metamorphism and controlling chemical and mineralogical factors of reaction front propagation.On the island Syros, Greece, fluid-rock interaction was examined along a shear zone and within brittle fractures to calculate fluid flux rates, flow velocities and durations. Petrological, geochemical and thermodynamic evidence show that the flux of CO2-bearing fluids along the shear zone was 100-2000 times larger than the fluid flux in the surrounding rocks. The time-averaged fluid flow velocity and flow duration along brittle fractures was calculated by using a governing equation for one-dimensional transport (advection and diffusion) and field-based parameterization. This study shows that fluid flow along fractures on Syros was rapid and short lived.Mechanisms and controlling factors of fluid infiltration were studied in greenschist- to epidote-amphibolite-facies metabasalts in SW Scotland. Fluid infiltration into metabasaltic sills was unassisted by deformation and occurred along grain boundaries of hydrous minerals (e.g. amphibole) while other minerals (e.g. quartz) prevent fluid infiltration. Petrological, mineralogical and chemical studies of the sills show that the availability of reactant minerals and mechanical factors, e.g. volume change in epidote, are primary controls of reaction front propagation.
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31.
  • Kleine, Barbara I., et al. (författare)
  • Mineralogical controls on metamorphic fluid flow in metabasaltic sills from Islay, Scotland
  • 2016
  • Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 248, s. 22-39
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study we show that mineralogy was the primary control of metamorphic fluid flow in the well-studied metabasaltic sills in the SW Scottish Highlands. Here, basaltic sills have been partially carbonated by H2O-CO2 fluids at greenschist facies conditions. This has led to mineral zonation with carbonate-poor sill interiors separated from carbonate-rich sill margins by reaction fronts. Although deformation set the stage for metamorphic fluid flow in the SW Scottish Highlands by causing the preferred alignment of mineral grains, metamorphic fluid flow was not coupled with active deformation but occurred later utilizing the pre-existing mineral alignment as a means of accessing the sill interiors. The sills which were studied were partially carbonated with well-preserved reaction fronts. They were selected because (atypically for the SW Scottish Highlands) they are mineralogically heterogeneous making them ideal for a study of mineralogical controls of metamorphic fluid flow. Their mineralogical heterogeneity reflects chemical heterogeneity arising from magmatic flow differentiation and spilitization, which occurred before greenschist facies metamorphism. Magmatic flow differentiation resulted in parts of the sill containing large crystals with no preferred alignment. Large (up to 3 cm) plagioclase phenocrysts were concentrated in the sill interior whereas large (up to 1 cm) amphibole (after pyroxene) grains formed cumulate layers close to the sill margins. These large randomly oriented crystals were replaced by an interface-coupled dissolution-precipitation mechanism. Replacement is constant volume and with hydration and carbonation affecting the cores of these minerals while the rims are remained intact and unaltered. This finding points to intro-granular metamorphic fluid flow. In contrast inter-granular metamorphic fluid flow was facilitated by mineral alignment on different scales. Pre-metamorphic spilitization, produced layers of epidote called segregations, whereas regional deformation caused preferred alignment mainly of amphibole and chlorite. Epidote undergoes a series of volume changes during greenschist facies metamorphism. This created porosity which produced preferred pathways for metamorphic fluids affecting the advancement of fluid-driven reaction fronts. Preferred alignment of amphibole and chlorite also affected the advancement of reaction fronts. In this case, fluid flow was preferentially parallel to the foliation. In both cases, inter-granular metamorphic fluid flow utilized a pre-existing fabric albeit on different scales. These results show intra-granular metamorphic fluid flow in unfoliated rock and inter-granular metamorphic fluid flow in foliated rock. In both cases metamorphic fluid flow occurred after deformation controlled by pre-existing mineralogical heterogeneities, such as grain composition and shape anisotropy as well as preferred alignment of mineral grains.
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32.
  • Kleine, Barbara Irene, et al. (författare)
  • Pre-metamorphic controls on the propagation of fluid-driven reaction fronts at greenschist-facies metamorphic conditions
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • In this study we show that pre-metamorphic mineralogical and chemical heterogeneities control fluid flow and fluid-driven propagation of reaction fronts during regional metamorphism. The study was undertaken at Port Ellen, Islay, in SW Scottish Highlands. Here, basaltic sills have been partially carbonated by H2O-CO2 fluids at greenschist-facies conditions. This has led to mineral zonation with carbonate poor sill interiors separated from carbonate-rich sill margins by reaction fronts. The sills which were studied are partially carbonated and reaction fronts are well-preserved. These sills are unique for the Scottish Highlands in that they show excellent evidence of 1) extensive magmatic flow differentiation and 2) spilitization having occurred before greenschist-facies metamorphism. Magmatic flow differentiation concentrated large (up to 3 cm) phenocrysts of plagioclase in the sill interior and spilitic alteration produced layers of segregated epidote and caused albitization of these plagioclase phenocrysts resulting in their preservation throughout greenschist-facies metamorphism. Coupled with this pre-metamorphic mineralogical zonation, sill margins where enriched in Ti, Fe, P, HFSEs and REEs whereas the sill interiors were enriched in Al, Na and LILEs. In this study, we show spatial correlation of metamorphic reaction fronts with pre-metamorphic mineralogical zonation produced by magmatic flow differentiation (plagioclase phenocrysts size distributions) and epidote segregations produced by spilitization. We infer a pre-metamorphic mineralogical and chemical control on the positions of fluid-driven metamorphic reaction fronts. Based on mineralogical and chemical profiles across these sills and reaction textures preserved within them, we conclude that availability of reactant minerals and mechanical factors, such as volume change in epidote and foliation development due to chlorite formation are primary controls of fluid-driven reaction front propagation during metamorphism. We further suggest that elevated oxygen fugacity in the sill margins may have further promoted carbonation.
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33.
  • Kleine, Barbara I., et al. (författare)
  • Preservation of blueschist-facies minerals along a shear zone by coupled metasomatism and fast-flowing CO2-bearing fluids
  • 2014
  • Ingår i: Journal of Petrology. - : Oxford University Press (OUP). - 0022-3530 .- 1460-2415. ; 55:10, s. 1905-1939
  • Tidskriftsartikel (refereegranskat)abstract
    • Two types of blue halo (types I and II) composed of blueschist-facies minerals are centered around a brittle, normal shear zone in greenschist-facies rocks on the island of Syros, Aegean Sea, Greece. The shear zone is steeply dipping and cuts a near-horizontal layer of greenschist-facies rocks (albite + epidote + actinolite + chlorite + quartz). Type I and II blue haloes are 0.3 m and c. 1m wide respectively, and are seen on both sides of the shear zone. The inner type I haloes are composed of nearly pure glaucophane schist and were formed by metasomatic addition of Na2O and SiO2, and to a lesser extent of K2O and large ion lithophile elements (LILE), coupled with loss of CaO, Al2O3 and MnO. The outer type II haloes consist of a carbonated blueschist-facies assemblage (glaucophane + calcite + phengite + epidote + garnet + quartz).These experienced only slight metasomatic changes (i.e. addition of K2O and LILE), which cannot alone explain halo formation.We present  petrological, geochemical and thermodynamic evidence that this assemblage was preserved at greenschist-facies conditions because XCO2 was elevated by flow of a CO2-bearing fluid along the shear zone, which was approximately contemporaneous with greenschist-facies hydration in the surrounding rocks. We further note that the flux of CO2-bearing fluid along the shear zone was rapid with respect to the fluid flux in the surrounding rocks. Mass-balance calculations reveal that the fluid flux within the shear zone was at least 100-2000 times greater than the fluid flux within the surrounding rocks. Mineral textures show greenschist-facies minerals replacing blueschist minerals in the type II haloes, supporting our interpretation that the blueschist-facies minerals were preserved during greenschist-facies retrogression. A simplified P-T vs XCO2 pseudosection confirms that preservation of carbonated blueschist can occur at greenschist-facies conditions in the presence of a CO2-bearing fluid.
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34.
  • Kleine, Barbara I., et al. (författare)
  • RAPID FLUID FLOW ALONG FRACTURES AT GREENSCHIST FACIES CONDITIONS ON SYROS, GREECE
  • 2016
  • Ingår i: American Journal of Science. - : American Journal of Science (AJS). - 0002-9599 .- 1945-452X. ; 316:2, s. 169-201
  • Tidskriftsartikel (refereegranskat)abstract
    • Brittle fractures cut through greenschist facies metavolcanic rocks at Delfini on Syros, Greece. An equation for one-dimensional transport by advection along a single fracture and transverse diffusion outwards from this fracture was used to calculate time-averaged fluid velocities and the duration of fluid flow along the brittle fractures. These quartz and carbonate filled fractures are surrounded by symmetrical dark reaction halos. These reaction halos were formed by diffusion of CO2 outwards from the fracture in a hydrous fluid which caused carbonation of the country rock. Changes in concentration of relatively mobile elements (for example K, Na, Cs, Ba, Pb and Sr) occurred. However, little to no changes in most of the major elements and less mobile trace elements were observed. This implies that carbonation was largely isochemical with respect to most non-volatile components. The Sr/Ca ratio was used to model time-averaged fluid velocities and the duration of fluid flow along the fractures. Fluid flow along narrower fractures with discernibly tapering haloes was found to be rapid (10(-6) - 10(-5) ms(-1)) and short lived (0.1-400 years). These are time-averaged values and can therefore alternatively record a series of even shorter and faster pulses, perhaps associated with fracture propagation and associated seismicity. Within the widest fractures with constant halo widths (ca. 60 cm) fluid flow was slower (10(-8) to 10(-6) ms(-1)) and longer lived (100-15000 years). We suspect that the constant width of these haloes reflects a steady state having been reached at which halo width was controlled by the relative rates of fluid flow along the fracture and in the surrounding rock.
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35.
  • Kleine, Barbara Irene, et al. (författare)
  • Rapid fluid flow along fractures at greenschist-facies conditions on Syros, Greece
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Using an equation for one-dimensional transport by advection along a single fracture and transverse diffusion outwards from this fracture to model field, petrological and geochemical data we calculated time-averaged fluid velocities and constrain the duration of fluid flow along brittle fractures cutting through greenschist-facies metamorphosed quartz-mica schists at Delfini on Syros, Greece. These quartz and carbonate filled fractures are surrounded by symmetrical dark reaction halos. These reaction halos were formed by diffusion of CO2 outwards from the fracture in a hydrous fluid which caused carbonation of the country rock. Changes in concentration of relatively mobile elements (e.g. K, Na, Cs, Ba, Pb and Sr) occurred. However, little to no changes in most of the major elements and less mobile trace elements were observed. This implies that carbonation was largely isochemical with respect to most non-volatile components. The Sr/Ca ratio was used to model time-averaged fluid velocities and the duration of fluid flow along the fractures. Fluid flow along narrower fractures with discernibly tapering haloes was found to be rapid (10-6 to 10-5 ms-1) and short lived (0.1 to 400 years). These are time-averaged values and can therefore alternatively record a series of even shorter and faster pulses, perhaps associated with fracture propagation and associated seismicity. Within the widest fractures with constant halo widths (ca. 60 cm) fluid flow was slower (10-8 to 10-6 ms-1) and longer lived (100 to 15000 years). We suspect that the constant width of these haloes reflects a steady state having been reached at which halo width was controlled by the relative rates of fluid flow along the fracture and in the surrounding rock.
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36.
  • Kleine, Barbara I., et al. (författare)
  • The mechanism of infiltration of metamorphic fluids recorded by hydration and carbonation of epidote-amphibolite facies metabasaltic sills in the SW Scottish Highlands
  • 2015
  • Ingår i: American Mineralogist. - : Mineralogical Society of America. - 0003-004X .- 1945-3027. ; 100:11-12, s. 2702-2717
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study we investigate a group of metabasaltic sills from the SW Scottish Highlands metamorphosed at epidote-amphibolite facies conditions that provide useful insight into the mechanisms and characteristics of fluid infiltration during metamorphism. The sills are amphibole and garnet bearing and exhibit a strong foliation in the sill margins that developed pre- to syn- peak metamorphism. Fluid infiltration caused hydration and carbonation in the sills, expressed as 1) replacement of garnet and amphibole by chlorite and calcite and 2) replacement of amphibole and epidote to form chlorite and calcite. Using garnet-amphibole and garnet-chlorite geothermometers we show that these reactions occurred after peak metamorphism at T = 290 to 400°C. Reaction textures show that the fluid infiltration into the sill that caused hydration and carbonation occurred in the absence of deformation. The fluid infiltration was mineralogically controlled with greater fluid access in areas of abundant fine-grained elongate minerals such as amphibole and chlorite. The replacement of garnet by chlorite most likely occurred by an interface-coupled dissolution-precipitation mechanism as evidenced by perfect pseudomorphic textures of garnet, porosity generation behind the reactive interface and fracturing ahead of this interface. Porosity generated in the product chlorite enhanced fluid access to the replacement front. The study shows that deformation was not required for extensive fluid infiltration and alteration during metamorphism. Fluid flow uses a pre-existing foliation to gain access to the rock, taking advantage of the anisotropic shape of the aligned minerals.
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37.
  • Kleman, Johan, et al. (författare)
  • Landscape evolution and landform inheritance in tectonically active regions : The case of the Southwestern Peloponnese, Greece
  • 2016
  • Ingår i: Zeitschrift für Geomorphologie. - : Schweizerbart. - 0372-8854. ; 60:2, s. 171-193
  • Tidskriftsartikel (refereegranskat)abstract
    • The Peloponnese in southwestern Greece fronts the Hellenic Arc at the boundary between the European and African plates. The relief is developed across deeply eroded nappes and folds that represent the roots of Alpine mountains developed during Early Miocene collision. During the Plio-Pleistocene, the geomorphological development of the region was affected by both large-amplitude climatic swings and neotectonic uplift/subsidence of individual blocks. Combined tectonic and climatic forcing acting on existing mountain, piedmont and basin terrains developed across diverse low grade metamorphic and sedimentary rocks, including thick carbonate units, led to a geomorphological evolution that was both area-specific and highly variable over time. We here identify and analyse landforms of the southwestern Peloponnese and the climatic and tectonic events that have been driving the geomorphic evolution during the Plio-Pleistocene. The observational database consists of studies of river profiles, spatial landform distribution and genetic classification of landforms, some of them not previously described from the area. We observe that some important landforms and landscape elements can only be understood in the context of a long Plio-Pleistocene time perspective and reflect particular tectonic trends and events. We examine a partly dissected and southward-tilted pediment surface along the west side of the Mani Peninsula. The seaward truncation of this surface is interpreted to reflect Late Pliocene rifting and uplifting of the edge of Taygetos horst. Analysis of the spatial relations between landforms suggests that before the onset of rifting and the late-Pliocene-Pleistocene phase of uplift, a mature mountain-piedmont morphology already existed in the Taygetos-Mani block. The along-crest elevation differences were less pronounced than they are today, and the central part of the massif was fluvially dissected to a lesser depth than today. The pre-rifting elevation of the highest Taygetos summits is inferred to have been 1800-2000 m. Despite active neotectonics, the Peloponnese retains major landforms that have persisted through 1-3 Myr of slow erosion, due to partial exhumation, karstification and remoteness from drainage lines. A coherent inherited or relict surface comprising the highest summit of the Taygetos Mountains and a disjunct high-elevation, low-gradient valley is identified. We infer that this older morphology formed at considerably lower elevation and has since been uplifted to its present position. It is indicative of locally low summit erosion rates throughout Plio-Pleistocene uplift of the Taygetos horst. The impact of climate changes is most obvious at the lowest and highest elevations (<500 m and >2000 m). At the lowest elevations, eustatic sea level changes influenced the spatial location of erosion and sedimentation, and ravine systems developed in uplifted marine sediments. At the highest elevations, glaciation has during the last few glacial cycles left a diagnostic imprint. At intermediate elevations, the landscape can be described as a continuously evolving fluvial landscape in which climatic changes have left few or no diagnostic landforms. Our results have implications for interpretation of other mountainous carbonate areas, particularly in the climatically distinctive Mediterranean region. Tectonics appears to have been the first-order driver for geomorphic evolution, the effects of which must be clarified before study of climate impact on landform development can be possible or meaningful. The Taygetos Mountains and Mani Peninsula provide a case study that illuminates how a multiple age landscape can result from spatially extremely uneven erosional impacts, where tectonic isolation, remoteness from drainage lines, and karstification are important processes for creating inherited and only slowly changing landscape elements.
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38.
  • Kylander, Malin E., et al. (författare)
  • It's in your glass : a history of sea level and storminess from the Laphroaig bog, Islay (southwestern Scotland)
  • 2020
  • Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 49:1, s. 152-167
  • Tidskriftsartikel (refereegranskat)abstract
    • Severe winter windstorms have become an increasingly common occurrence over recent decades in northwestern Europe. Although there exists considerable uncertainty, storminess is projected to increase in the future. On centennial to millennial time scales in particular, the mechanisms forcing storminess remain unsettled. We contribute to available palaeostorm records by reconstructing changes over the last 6670 years using a coastal peat sequence retrieved from the ombrotrophic Laphroaig bog on Islay, southwestern Scotland. We use a combination of ash content, grain size and elemental chemistry to identify periods of greater storminess, which are dated to 6605, 6290-6225, 5315-5085, 4505, 3900-3635, 3310-3130, 2920-2380, 2275-2190, 2005-1860, 1305-1090, 805-435 and 275 cal. a BP. Storm signals in the first half of the record up to similar to 3000 cal. a BP are mainly apparent in the grain-size changes. Samples from this time period also have a different elemental signature than those later in the record. We speculate that this is due to receding sea levels and the consequent establishment of a new sand source in the form of dunes, which are still present today. The most significant events and strongest winds are found during the Iron Ages Cold Epoch (2645 cal. a BP), the transition into, and in the middle of, the Roman Ages Warm Period (2235 and 1965 cal. a BP) and early in the Little Ice Age (545 cal. a BP). The Laphroaig record generally agrees with regionally relevant peat palaeostorm records from Wales and the Outer Hebrides, although the relative importance of the different storm periods is not the same. In general, stormier periods are coeval with cold periods in the region as evidenced by parallels with increased ice-rafted debris in the North Atlantic, highlighting that sea-ice conditions could impact future storminess and storm track position.
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39.
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40.
  • Lewerentz, Alexander, et al. (författare)
  • Fluid and carbon flux estimation of regional metamorphic fluid flow in Glen Esk, SE Scottish Highlands : The role of hydrodynamic dispersion for broadening of an isotopic front
  • 2018
  • Ingår i: American Journal of Science. - : American Journal of Science (AJS). - 0002-9599 .- 1945-452X. ; 318:4, s. 435-457
  • Tidskriftsartikel (refereegranskat)abstract
    • During metamorphism, large quantities of fluids are mobilized and transported through the crust. Such fluids may interact with surrounding rock and serve as a medium for chemical transport. In this study, we use coupled carbonation and oxygen isotope fronts to estimate fluid and carbon fluxes for metamorphic fluid flow in vein pathways in the Dalradian metasediments that crop out in Glen Esk, SE Scottish Highlands. Comparison of wall rock and vein oxygen Isotope ratios indicate that the Barrovian sequence in Glen Esk was infiltrated by at least two separate fluid flow events, where fluid flow from the North Esk Fault overprints an earlier fluid flow event, for which the syn-metamorphic magmatic intrusions north of Glen Esk are a probable fluid source. Advection is the dominating mode of fluid transportation in veins. By advection-dispersion and advection-diffusion modeling, we estimate a time-averaged fluid flux of 0.0005 to 0.0135 m(3).m(-2).yr(-1) and a carbon flux of 0.04 to 0.71 mol C.m(-2).yr(-1) for fluid flow from the North Esk fault into the Dalradian metasediments. The duration of this fluid flow event is estimated to between 11 and 230 kyr. Our results also indicate that hydrodynamic dispersion was the main reason for broadening of the oxygen isotope front.
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41.
  • Lewerentz, Alexander, 1987- (författare)
  • Fluid-induced alteration of metasedimentary rocks in the Scottish Highlands
  • 2017
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Fluids, mainly H2O and CO2, are released from H- and C-bearing phases during prograde metamorphism. Because of the buoyancy of these fluids, they rise within the crust towards the surface of the Earth. Metamorphic fluids take advantage of permeable horizons, shear zones, fold hinges, fractures, and are channelled into high-flux zones. Fluid fluxes for channelized fluid flow may exceed background pervasive fluxes by several orders of magnitude. Metamorphic fluids react with the surrounding rock during fluid flow, and altered zones are commonly observed adjacent to high-flux conduits. Fluid-altered rock is texturally, mineralogically, chemically, and isotopically different from rock unaffected by fluid flow. In this thesis, fluid-rock interaction is studied at two localities in the Scottish Highlands: Glen Esk and the Isle of Islay.Glen Esk is one of the type localities used by George Barrow (1853-1932) to propose the concept of metamorphic zones and metamorphic index minerals as an approximate determination of metamorphic grade. In several of the metamorphic zones in Glen Esk, index mineral distribution is highly dependent on proximity to veins. The occurrence of index minerals is therefore not only controlled by pressure and temperature, but also by the availability of metamorphic fluids. Evidence of a retrograde fluid flow event from the North Esk Fault is observed in Glen Esk, for which a time-averaged fluid flux of 0.0003 – 0.0126 m3∙m-2∙yr-1 is calculated. The duration of the fluid event is estimated to between 16 and 334 kyr.On the Isle of Islay, kyanite is observed in rocks of chlorite or lower-biotite metamorphic grade, i.e. much lower temperatures than usually associated with kyanite formation. The favoured explanation for this is retrograde infiltration of extremely high-CO2 fluids, at least locally XCO2 > 0.7, at ~340°C, which altered these rocks and stabilised kyanite in a carbonate-bearing assemblage. Oxygen and carbon stable isotope profiles across the Islay Anticline reveals highly channelized fluid flow along the axial region of this fold, with fluid:rock ratios at least four times higher than in rock farther away from the fold. Although carbon and oxygen isotope ratios of metacarbonate rocks were altered along the Islay Anticline, negative anomalies observed below and above the Port Askaig Tillite Formation cannot solely be attributed to metamorphic fluid flow, which implies that these rocks to varying degree retain their primary paleoclimatological isotopic signatures.
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42.
  • Lewerentz, Alexander, 1987-, et al. (författare)
  • On the Association between Veining and Index Mineral Distributions in Barrow’s Metamorphic Zones, Glen Esk, Scotland
  • 2017
  • Ingår i: Journal of Petrology. - : Oxford University Press (OUP). - 0022-3530 .- 1460-2415. ; 58:5, s. 885-908
  • Tidskriftsartikel (refereegranskat)abstract
    • The concept of index mineral based metamorphic zones was first introduced by George Barrow in 1912 and the Barrovian metamorphic zones continue to be used as a framework for describing regional metamorphism. Pressure, temperature, and protolith composition are widely recognized as primary controls on index mineral distribution. Today, metamorphic fluid flow is also recognized as an important driver of metamorphic reactions. The aim of this study is to establish if and how metamorphic fluids control index mineral distribution during Barrovian metamorphism. We use samples from Barrow’s type locality in Glen Esk, SE Scottish Highlands, to study possible relationships between veining and index mineral distribution. In addition to petrographic and textural observations, we use whole-rock compositions, mineral compositions and oxygen isotope analyses. At low grade, in the chlorite zone and most of the biotite zone, no correlation between veining and index mineral distribution is seen. At higher grade, in the garnet and staurolite zones, index mineral abundance is shown to be higher adjacent to veins. These trends coincide with other mineralogical, chemical, and isotopic changes in the vein-proximal rock, indicative of fluid–rock interaction. Kyanite distribution is homogeneous in the kyanite zone. However, we show that this too relates to extensive fluid–rock interaction. Garnet-, staurolite-, and kyanite-bearing selvedges are common in the sillimanite zone. However, sillimanite distribution is unrelated to these selvedges, which supports models arguing that sillimanite formed during a separate metamorphic event. We infer fluid flow from high grade to low grade because the fluid was out of isotopic equilibrium with the lower grade rocks, but in equilibrium with the higher grade rocks. We conclude that fluid flow played a major role in the stabilization and distribution of Barrovian index minerals in Glen Esk, and that the importance of fluid flow was greater at higher metamorphic grades.
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43.
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44.
  • Lewerentz, Alexander, 1987- (författare)
  • Vein controlled crystal size distributions of Barrovian index minerals
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The concept of index mineral based metamorphic zones was first introduced by George Barrow in 1912, and Barrovian metamorphism is still applied by metamorphic petrologists. Today the importance of metamorphic fluids for driving metamorphic reactions is widely recognised. Even so, the general view is that Barrovian metamorphism is solely controlled by pressure, temperature, and protolith composition. This thesis aims to establish if and how fluids control index mineral formation and distribution during Barrovian metamorphism. To do so, samples from Barrow’s own type locality in Glen Esk, Southeast Scottish Highlands, are used to investigate possible relationships between veining and index mineral distribution. This was done using a combination of petrographic and textural observations and analyses, whole rock chemistry, mineral chemistry, as well as oxygen isotope analyses. These data show a grade dependant association of index mineral distribution and veining: in the chlorite zone and most of the biotite zone, no correlation between veining and index mineral distribution is seen. For the garnet and staurolite zones, index mineral abundance is shown to decrease away from veins. The kyanite zone shows a fairly homogenous kyanite distribution, but also indications of extensive fluid-rock interaction. Based on these observations and the analysis datasets, it is concluded that fluid played a major role in the stabilisation and distribution of the Barrovian index minerals in Glen Esk, and that the fluid control was larger at metamorphic grade.
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45.
  • Lupi, Matteo, et al. (författare)
  • Regional earthquakes followed by delayed ground uplifts at Campi Flegrei Caldera, Italy : Arguments for a causal link
  • 2017
  • Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 474, s. 436-446
  • Tidskriftsartikel (refereegranskat)abstract
    • Earthquake-triggered volcanic activity promoted by dynamic and static stresses are considered rare and difficult-to-capture geological processes. Calderas are ideal natural laboratories to investigate earthquake volcano interactions due to their sensitivity to incoming seismic energy. The Campi Flegrei caldera, Italy, is one of the most monitored volcanic systems worldwide. We compare ground elevation time series at Campi Flegrei with earthquake catalogues showing that uplift events at Campi Flegrei are associated with large regional earthquakes. Such association is supported by (yet non-definitive) binomial tests. Over a 70-year time window we identify 14 uplift events, 12 of them were preceded by an earthquake, and for 8 of them the earthquake-to-uplift timespan ranges from immediate responses to 1.2 yr. Such variability in the response delay may be due to the preparedness of the system with faster responses probably occurring in periods during which the Campi Flegrei system was already in a critical state. To investigate the process that may be responsible for the proposed association we simulate the propagation of elastic waves and show that passing body waves impose high dynamic strains at the roof of the magmatic reservoir of the Campi Flegrei at about 7 km depth. This may promote a short-lived embrittlement of the magma reservoir's carapace otherwise marked by a ductile behaviour. Such failure allows magma and exsolved volatiles to be released from the magmatic reservoir. The fluids, namely exsolved volatiles and/or melts, ascend through a nominally plastic zone above the magmatic reservoir. This mechanism and the associated inherent uncertainties require further investigations but the new concept already implies that geological processes triggered by passing seismic waves may become apparent several months after passage of the seismic waves. (C) 2017 Elsevier B.V. All rights reserved.
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46.
  • Mattsson, Hannes B., 1975- (författare)
  • Volcanism at the tip of a propagating rift : the Heimaey volcanic centre, south Iceland
  • 2004
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Primary magmas are generated by 4-6% partial melting near the garnet-spinel stability fields beneath Heimaey (i.e. 80-65 km depth). The magmas fractionate 31% olivine and clinopyroxene en-route to ponding at the base of the crust (and forming a parental Vestmannaeyjar magma). Abundant normally zoned phenocrysts of olivine and plagioclase, in combination with curvilinear trends in major element variation diagrams and heterogeneous isotope ratios (similar to MORB) suggests that the rock suite evolved by fractional crystallization and that crustal contamination and/or magma-mixing was insignificant. Although Heimaey rocks are devoid of clinopyroxene as a phenocryst phase, decreasing ratios of CaO/Al2O3 and Sc/Y with increasing degree of fractionation suggest that clinopyroxene was present as a fractionating phase. The most evolved lava on Heimaey (Eldfell) can be successfully related to the most primitive (Stórhöfði) through 73% fractional crystallization of an olivine + clinopyroxene + plagioclase + titanomagnetite assemblage. Individual magma batches were emplaced into different levels of the crust where they evolved separately from each other prior to eruption. The lack of equilibrium phenocryst assemblages in the Heimaey rocks suggests that the residence times in crustal magma chambers were short. Upon eruption, the pathways used by the rising magma are probably zones of weaknesses associated with extensional stress exerted by the propagating Eastern Volcanic Zone (as indicated by the preferentially aligned eruptive fissures). When magmas erupt in a shallow marine environment, tuff-cones are formed as a result of explosive interactions between magma and water/sediment mixtures. Tuffs comprise about 65% of total erupted volume on Heimaey. The tuff cones deposits consists of normally graded planar air-fall deposits and undulating cross-bedded base-surge deposits, with an increase in frequency of base-surge deposits closer to the vent regions. The distribution of crustal xenoliths in the Sæfell tuff-cone suggests that there is a downward migration of explosion foci in tuff cone forming eruptions, and that a diatreme (at least 820 meters deep) formed during the eruption. This is also supported by the steep dip (35-45°) measured for ring-fractures at the crater-rim of the tuff cone, which creates sharp unconformities between early and late stage tuff-deposits. A zone of graded tuff-breccias (5-20 m thick) marks the transition from phreatomagmatic to subaerial activity. The subaerial stage is characterized by effusive lava emplacement and the formation of scoria cones and lava ponds inside the tuff-cones. The most common type of lava flows found on Heimaey are inflated pahoehoe (e.g. the Helgafell lava field). Based on measurements of lava inflation features (i.e. the thickness of the upper-vesicular crust of flow-lobes) in the Helgafell lava field an eruption duration was estimated for that eruption (11-12 months). This estimate seems reasonable as it yields an averaged volumetric effusion rate of 0.05-0.06 km3/month, which is similar to the 1963-1967 Surtsey eruption (0.02 km3/month) and the 1973 Eldfell eruption (0.04 km3/month) considering that the estimate does not account for early spatter-fed flows. The oldest units on Heimaey (i.e. the six units comprising the Norðurklettar formation) formed over a short time span following the deglaciation of southern Iceland 10-9.3 ka ago. The Stórhöfði eruption occurred sometime between 9-6 ka, Sæfell and Helgafell to approximately 6 ka, and finally the Eldfell eruption, which occurred in 1973. Heimaey is believed to represent the early stage of forming a central volcano in the Vestmannaeyjar system, mainly because (1) the average erupted volumes for a single eruption are twice (0.33 km3 DRE) that previously reported as an average for Vestmannaeyjar, (2) there have been close to 1 eruption/km2 on Heimaey, compared to 0.1 eruption/km2 as average for the Vestmannaeyjar system, and (3) the occurrence of more evolved lavas, such as the hawaiites of Dalfjallshryggur and Eldfell, suggesting that a crustal magma chamber is developing under the island.
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47.
  • Mård Karlsson, Johanna, 1979-, et al. (författare)
  • Reconstructions of the coastal impact of the 2004 Indian Ocean tsunami in the Khao Lak area, Thailand
  • 2009
  • Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114, s. C10023-
  • Tidskriftsartikel (refereegranskat)abstract
    • Khao Lak, SW Thailand was severely affected by the tsunami on 26 December 2004. Here we present reconstructions of its coastal impact in this area. These are based on (1) eyewitness reports alone and (2) eyewitness reports supported by videos and photos of the tsunami and the damage it caused, field measurements, and satellite imagery. On the basis of eyewitness reports, we estimated that the sea began retreating at 1000 local time (LT) and, based also on photos, that the tsunami arrived at 1026-1029 LT. On the basis of videos of the tsunami, we estimated an offshore wave direction of 083 +/- 3 degrees and on the basis of the paths by which eyewitnesses were carried, we estimated an onshore direction of 088 +/- 6 degrees. On the basis of videos, we calculated that the velocity of the wavefront on its final approach was 33 +/- 4 km/h. We obtained tsunami heights of 7.3 +/- 0.8 m (relative to ground level) on the basis of eyewitness reports and 8.0 +/- 0.6 m (relative to mean sea level) on the basis of field and photographic data. On the basis of eyewitness reports and photos, we concluded that Khao Lak experienced at least two main waves with a period >40 min. From eyewitness reports and satellite imagery, we measured maximum inundation <= 0.5 km in the southern part of the area, which is confined by a steeply sloping hinterland, and <= 1.5 km in the more gently sloping northern part. Comparison between these reconstructions supports the reliability of eyewitness reports as a source of quantitative data, and comparison with the numerical simulation by Ioualalen et al. (2007) supports the validity of the simulation.
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48.
  • Nicholas, Kimberly, et al. (författare)
  • Analys av sju riksdagspartiers klimatpolitik utförd av klimat- och omställningsforskare : Sveriges klimatpolitik inför riksdagsvalet 2022 enligt Researchers’ Desk
  • 2022
  • Rapport (populärvet., debatt m.m.)abstract
    • ● Syftet med denna rapport är att ge forskares analys av riksdagspartiernas klimatpolitik inför valet 2022.● Alla som har bidragit till denna rapport är klimat- eller omställningsforskare och medlemmar i Researchers’ Desk1.● Researchers’ Desk är en oberoende, ideell organisation, med över 80 ledande forskare i Sverige, som arbetar med olika aspekter av klimatförändringarna.● Alla de åtta politiska partierna tillfrågades om att besvara en enkät med frågor om sina klimatmål och sin politik. Moderaterna avböjde att delta i undersökningen. De övriga sju partierna svarade med varierande grad av utförlighet.● Författarna av denna rapport har använt partiernas svar som underlag för sin kvalitativa analys och bedömning.● Vår granskning har fokuserat på förslagens ambitionsnivå, potential, realism och problem i relation till befintlig forskning.● Tidigare publicerat genom detta projekt:○ Mål för territoriella utsläpp, av Alasdair Skelton, Paul Glantz, och KimberlyNicholas○ Mål för LULUCF-sektorn, av Erik Pihl, Åsa Kasimir, och Peter Roberntz
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49.
  • Niemi, Maria, et al. (författare)
  • Lockdown Measures Which Reduced Greenhouse Gas Emissions With Little Negative Impact on Quality of Life
  • 2021
  • Ingår i: Earth's Future. - 2328-4277. ; 9:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Lockdown measures in response to the new Covid-19 virus have caused the largest ever fall of annual greenhouse gas emissions. A key question that we attempt to answer in this study is which, if any, of these measures can be productively encouraged post-lockdown in efforts to sustain at least part of this reduction in emissions. Sweden is uniquely suited for our study because the voluntary nature of lockdown in Sweden allowed us to assess the level of compliance to recommendations and its effects on greenhouse gas emissions. First, we assessed the change of perceived quality of life (QOL) among 746 individuals from Stockholm region due to adhering to lockdown measures. Second, we calculated the associated change of annual per capita greenhouse emissions. We found that avoiding travel for work, avoiding purchasing, and avoiding restaurants had the least negative effect on QOL, and at the same time the largest positive effect on carbon dioxide equivalent (CO(2)e) emission reductions. We conclude that these are potential leverage points for stimulating behavioral change that has a positive climatic impact.
  •  
50.
  • Nosenzo, Francesco, 1993- (författare)
  • Chemical and isotopic records of polycyclic histories in a subducted continental crust (Dora-Maira Massif, Western Alps)
  • 2023
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • At convergent plate margin, part of the continental crust can be subducted and exhumed. During continental subduction a pre-existing crust is reworked. Remnants of an older orogen are recycled and subjected to (ultra)-high-pressure metamorphism. During subduction, polycyclic rocks undertake a second metamorphic cycle, whereas monocyclic rocks are metamorphosed for the first time. In reworked rocks the pre-subduction record is overprinted and partially or completely lost. Despite this difficulty, reconstructing the pre-subduction history of the recycled crust is crucial, because pre-subduction characters (such as H2O content) can strongly influence how rocks respond to reworking during subduction.The Dora-Maira Massif is worldwide renowned as a (ultra)-high-pressure continental terrane. However, its northern part remained essentially unexplored in recent times. In this thesis work the northern Dora-Maira Massif is used as a case study to investigate recycling of continental crust. The aim is to constrain what type of crust is subducted and exhumed and to unravel the role of fluids during subduction of polycyclic material. Field work, petrology, thermodynamic modelling and geochronology are integrated.New field and geochronological evidence indicate that the northern Dora-Maira Massif displays an internal architecture more complex than what previously thought. It is subdivided in several tectonic units likewise the southern Dora-Maira Massif. Chemical and isotopic records of the reworked rocks reveal a pre-Alpine history spanning from the Lower Palaeozoic to the Mesozoic. A polycyclic basement preserves relicts of a pre-Alpine Barrovian metamorphism connected with the Variscan orogenesis. The absence of granulite-facies partially molten pre-Alpine rocks indicates that only the upper crust was reworked in the Dora-Maira Massif.Thermodynamic modelling indicates that polycyclic micaschists were rehydrated between the Variscan and the Alpine peak metamorphism. Polycyclic garnet texture and chemistry and metamorphic zircon record a main episode of fluid infiltration at the end of the Variscan cycle and not during the Alpine cycle. Pre-Alpine re-hydration of the upper crust allowed high-pressure re-equilibration during subduction.
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