| 1. |
- Ranta, E., et al.
(author)
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Fluid-rock reactions in the 1.3Ga siderite carbonatite of the GrOnnedal-ika alkaline complex, Southwest Greenland
- 2018
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In: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 173:10
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Journal article (peer-reviewed)abstract
- Petrogenetic studies of carbonatites are challenging, because carbonatite mineral assemblages and mineral chemistry typically reflect both variable pressure-temperature conditions during crystallization and fluid-rock interaction caused by magmatic-hydrothermal fluids. However, this complexity results in recognizable alteration textures and trace-element signatures in the mineral archive that can be used to reconstruct the magmatic evolution and fluid-rock interaction history of carbonatites. We present new LA-ICP-MS trace-element data for magnetite, calcite, siderite, and ankerite-dolomite-kutnohorite from the iron-rich carbonatites of the 1.3Ga GrOnnedal-ika alkaline complex, Southwest Greenland. We use these data, in combination with detailed cathodoluminescence imaging, to identify magmatic and secondary geochemical fingerprints preserved in these minerals. The chemical and textural gradients show that a 55m-thick basaltic dike that crosscuts the carbonatite intrusion has acted as the pathway for hydrothermal fluids enriched in F and CO2, which have caused mobilization of the LREEs, Nb, Ta, Ba, Sr, Mn, and P. These fluids reacted with and altered the composition of the surrounding carbonatites up to a distance of 40m from the dike contact and caused formation of magnetite through oxidation of siderite. Our results can be used for discrimination between primary magmatic minerals and later alteration-related assemblages in carbonatites in general, which can lead to a better understanding of how these rare rocks are formed. Our data provide evidence that siderite-bearing ferrocarbonatites can form during late stages of calciocarbonatitic magma evolution.
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| 2. |
- Skelton, Alasdair, et al.
(author)
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Dimmuborgir: a rootless shield complex in northern Iceland
- 2016
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In: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 78:5
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Journal article (peer-reviewed)abstract
- The origin of Dimmuborgir, a shield-like volcanic structure within the Younger Laxa lava flow field near Lake Myvatn, in northern Iceland, has long been questioned. New airborne laser mapping (light detection and ranging (LiDAR)), combined with ground-penetrating radar results and a detailed field study, suggests that Dimmuborgir is a complex of at least two overlapping rootless shields fed by lava erupting from the nearby Ludentarborgir crater row. This model builds upon previous explanations for the formation of Dimmuborgir and is consistent with observations of rootless shield development at Kilauea Volcano, Hawaii. The larger rootless shields at Dimmuborgir, 1-1.5 km in diameter, elliptical in plan view, similar to 30 m in height, and each with a 500-m-wide summit depression, were capable of storing as much as 2-3x10(6) m(3) of lava. They were fed by lava which descended 30-60 min lava tubes along a distance of 3 km from the crater row. The height difference generated pressure sufficient to build rootless shields at Dimmuborgir in a timescale of weeks. The main summit depressions, inferred to be drained lava ponds, could have emptied via a 30-m-wide x 5-m-deep channel, with estimated effusion rates of 0.7-7 m(3) s(-1) and minimum flow durations of 5-50 days. We argue that the pillars for which Dimmuborgir is famed are remnants of lava pond rims, at various stages of disintegration that formed during pond drainage.
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| 3. |
- Skelton, Alasdair, et al.
(author)
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Hydrochemical Changes Before and After Earthquakes Based on Long-Term Measurements of Multiple Parameters at Two Sites in Northern IcelandA Review
- 2019
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In: Journal of Geophysical Research - Solid Earth. - 2169-9313 .- 2169-9356. ; 124:3, s. 2702-2720
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Research review (peer-reviewed)abstract
- Hydrochemical changes before and after earthquakes have been reported for over 50years. However, few reports provide sufficient data for an association to be verified statistically. Also, no mechanism has been proposed to explain why hydrochemical changes are observed far from earthquake foci where associated strains are small (<10(-8)). Here we address these challenges based on time series of multiple hydrochemical parameters from two sites in northern Iceland. We report hydrochemical changes before and after M >5 earthquakes in 2002, 2012, and 2013. The longevity of the time series (10 and 16years) permits statistical verification of coupling between hydrochemical changes and earthquakes. We used a Student t test to find significant hydrochemical changes and a binomial test to confirm association with earthquakes. Probable association was confirmed for preseismic changes based on five parameters (Na, Si, K, O-18, and H-2) and postseismic changes based on eight parameters (Ca, Na, Si, Cl, F, SO4, O-18, and H-2). Using concentration ratios and stable isotope values, we showed that (1) gradual preseismic changes were caused by source mixing, which resulted in a shift from equilibrium and triggered water-rock interaction; (2) postseismic changes were caused by rapid source mixing; and (3) longer-term hydrochemical changes were caused by source mixing and mineral growth. Because hydrochemical changes occur at small earthquake-related strains, we attribute source mixing and water-rock interaction to microscale fracturing. Because fracture density and size scale inversely, we infer that mixing of nearby sources and water-rock interaction are feasible responses to small earthquake-related strains. Plain Language Summary Changes in groundwater chemistry before and after earthquakes have been reported for over 50years. However, few studies have been able to prove that the earthquakes caused these changes. Also, no study has explained why these changes are often reported far from where the earthquake occurred. Here we address these challenges based on measurements of groundwater chemistry made at two sites in northern Iceland over time periods of 10 and 16years. We used statistical methods to prove that the earthquakes caused changes of ground water chemistry both before and after the earthquakes. We showed that changes of groundwater chemistry before earthquakes were caused by slow mixing between different groundwaters, which triggered reactions with the wall rock that changed groundwater chemistry, and that changes of groundwater chemistry after earthquakes were causes by rapid mixing between different groundwaters. That these changes were detected far from where the earthquakes occurred suggests that cracking of the wall rock at a very small scale was all that was needed for mixing of different groundwaters and reactions with the wall rock to occur.
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| 4. |
- Stockmann, Gabrielle, et al.
(author)
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Control of a calcite inhibitor (phosphate) and temperature on ikaite precipitation in Ikka Fjord, southwest Greenland
- 2018
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In: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 89, s. 11-22
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Journal article (peer-reviewed)abstract
- Ikaite (CaCO3 center dot 6H(2)O) forms submarine tufa columns in Ikka Fjord, SW Greenland. This unique occurrence is thought to relate to aqueous phosphate concentration and low water temperatures (< 6 degrees C). Phosphate ions are well-known inhibitors of calcite precipitation and Ikka Fjord has a naturally high-phosphate groundwater system that when mixing with seawater leads to the precipitation of ikaite. In the study presented here, experiments simulating conditions of Ikka Fjord show that a) the formation of ikaite is unrelated to the aqueous phosphate concentration (0-263 mu mol/ kg PO43-) in 0.1 M NaHCO3/0.1 M Na2CO3 solutions mixing with seawater at 5 degrees C and pH 9.6-10.6, and b) ikaite forms at temperatures up to 15 degrees C without phosphate and in open beakers exposed to air. Instead, supersaturation of ikaite and the seawater composition are the likely factors causing ikaite to precipitate in Ikka Fjord. This study shows that adding Mg2+ to a NaHCO3/Na2CO3 - CaCl2 mixed solution leads to the formation of ikaite along with hydrated Mg carbonates, which points to the high Mg2+ concentration of seawater, another known inhibitor of calcite, as a key factor promoting ikaite formation. In experiments at 10 and 15 degrees C, increasing amounts of either nesquehonite (Mg(HCO3)(OH)center dot 2H(2)O) or an amorphous phase co-precipitate with ikaite. At 20 degrees C, only the amorphous phase is formed. In warming Arctic seawater, this suggests Mg carbonate precipitation could become dominant over ikaite in the future.
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| 5. |
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| 6. |
- Tollefsen, Elin, et al.
(author)
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Adolescents with wheeze have increased risk of additional health problems. The Young-HUNT study, Norway
- 2007
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In: Preventive Medicine. - : Elsevier BV. - 1096-0260 .- 0091-7435. ; 44:2, s. 178-182
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Journal article (peer-reviewed)abstract
- OBJECTIVE: To explore the hypothesis of an association between current wheeze and other health problems in adolescence and to investigate any sex differences. METHODS: N=8817 adolescents aged 13-19 years completed a self-administered questionnaire including questions on health and lifestyle in Norway (1995-1997). RESULTS: All subjective health problems were significantly more prevalent in current wheezers compared to non-wheezers (frequent headache: girls 18% vs. 9%, boys 8% vs. 3%; frequent neck and shoulder pain: girls 10% vs. 5%, boys 6% vs. 2%; frequent joint and muscle pain: girls 6% vs. 2%, boys 6% vs. 2%; and frequent abdominal pain: girls 10% vs. 3%, boys 3% vs.1%). In both sexes, adjusted for covariates, current wheezers had statistically significant increased risk of reporting frequent headache (girls OR=2.0, boys OR=2.9), frequent neck and shoulder pain (girls OR=1.9, boys OR=3.3), frequent joint and muscle pain (girls OR=2.7, boys OR=3.5) and frequent abdominal pain (girls OR=2.7, boys OR=2.0). CONCLUSIONS: Current adolescent wheezers reported more additional health problems compared to non-wheezers. Even if girls reported more symptoms in general, the associations were stronger in boys. The findings are important for the clinical approach to teenage wheezers and should increase doctors' awareness of coexistence of other health complaints in these patients.
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| 7. |
- Tollefsen, Elin, et al.
(author)
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Allergy: a systemic disease? The HUNT and Young-HUNT study, Norway.
- 2008
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In: Pediatric Allergy and Immunology. - : Wiley. - 0905-6157 .- 1399-3038. ; 19:8, s. 730-736
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Journal article (peer-reviewed)abstract
- A systemic nature of allergic diseases has been hypothesized. As part of this discussion, we studied if adolescent allergic wheeze and increasing combinations of allergic organ involvements (lung, nose and skin) would also increase the reporting of other health problems (headache, muscle pain and abdominal pain). In addition, we studied if parental asthma was associated with adolescent clustering of allergic expressions and if parental asthma with additional health problems (headache or muscle pain) was associated with adolescent reporting allergy in combination with headache, muscle pain and abdominal pain. Adolescents 13-19 yr (n = 8817, 89%) participated in the Young-HUNT study, Norway, 1995-97. Parental data on asthma were eligible in n = 5620. Health and lifestyle were measured by questionnaires and interviews. Associations with additional health problems were significantly strengthened with combinations of wheeze and other allergic expressions. Odds Ratio for associations 'wheeze only', 'wheeze and rhinitis' and 'wheeze, rhinitis and eczema' were for headache 2.1, 3.4 and 3.7; for muscle pain 2.8, 3.2 and 4.9; for abdominal pain 3.6, 4.0 and 4.9. All p for trend were < 0.010. Similar results were obtained when studying allergic wheeze; p for trend < 0.001. Parental asthma was associated with clustering of adolescent allergic expressions, and parental asthma with headache or muscle pain was significantly associated with reported allergy combined with similar health problems in their offspring. The results indicate that allergy may be expressed beyond organs commonly viewed as part of an allergic disease, and hence may support a hypothesis of a systemic nature of allergic diseases.
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| 8. |
- Tollefsen, Elin, et al.
(author)
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Chemical controls on ikaite formation
- 2018
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In: Mineralogical Magazine. - : Mineralogical Society. - 0026-461X .- 1471-8022. ; 82:5, s. 1119-1129
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Journal article (peer-reviewed)abstract
- The hydrated carbonate mineral ikaite (CaCO3 center dot 6H(2)O) is thermodynamically unstable at all known conditions on Earth. Regardless, ikaite has been found in marine sediments, as tufa columns and in sea ice. The reason for these occurrences remains unknown. However, cold temperatures (<6 degrees C), high pH and the presence of Mg2+ and SO42 in these settings have been suggested as factors that promote ikaite formation. Here we show that Mg concentration and pH are primary controls of ikaite precipitation at 5 degrees C. In our experiments a sodium carbonate solution was mixed with seawater at a temperature of 5 degrees C and at a constant rate. To test the effect of Mg2+ and SO42 we used synthetic seawater which allowed us to remove these elements from the seawater. The pH was controlled by different ratios of Na2CO3 and NaHCO3 in the carbonate solution. We found that ikaite precipitated when both seawater and synthetic seawater from which SO4 had been removed were used in the experiments. However, ikaite did not precipitate in experiments conducted with synthetic seawater from which Mg had been removed. In these experiments, calcite precipitated instead of ikaite. By varying the Mg concentration of the synthetic seawater and the pH of the sodium carbonate solution, we constructed a kinetic stability diagram for ikaite and calcite as a function of Mg concentration and pH. One possible explanation of our finding is that Mg2+ inhibits calcite nucleation and thereby allows metastable ikaite to form instead.
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| 9. |
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| 10. |
- Tollefsen, Elin, 1960-
(author)
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Experimental, petrological and geochemical investigations of ikaite (CaCO3·6H2O) formation in marine environments
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Carbonates are a group of minerals that play an essential role in several processes on planet Earth, for example in the global carbon cycle and as a product of biomineralisation. Calcite (CaCO3) is by far the most common mineral in the carbonate group, and the stable form of carbonate at Earth surface conditions. However, calcite growth is often kinetically limited and polymorphs of calcite or hydrous calcium carbonates will form instead under certain circumstances. In this thesis, I investigate a hydrous form of calcium carbonate, ikaite (CaCO3 · 6H2O), which occasionally forms under conditions where normally calcite formation would be expected.Ikaite is metastable at surface conditions and has only been observed in nature at temperatures below 7°C. In Ikka Fjord, southwest Greenland, several hundred ikaite columns occur at the bottom of the fjord. Previous studies in Ikka Fjord have shown that ikaite columns are forming above submarine springs that are extremely sodium carbonate rich (pH ~10.5). An association with the surrounding igneous rocks, which comprise nepheline syenite and carbonatite, has been suggested. In the first part of this thesis, I investigate this association. A petrographic study of rocks samples from the igneous complex showed that the combined alteration of the minerals siderite and nepheline could explain the composition of the submarine spring water, and thereby the unique formation of ikaite columns at this site.It is from the mixture of sodium carbonate spring water and seawater that ikaite precipitates in Ikka Fjord, despite the fact that all other calcium carbonates are supersaturated in this mixture. Why ikaite precipitates and not the other forms of calcium carbonate was investigated by a series of experiments in the second and third parts of this thesis. Previous studies have suggested that ikaite was favoured by the low temperature in the fjord (<7°C) and the presence of phosphate (95- 263 μmol/kg) in the submarine spring water, which is known to inhibit calcite growth even at only trace concentrations. In the second part of this thesis, we simulated Ikka Fjord conditions in laboratory and showed that ikaite precipitation is not controlled by the presence of phosphate in the mixture. Instead, after a second series of experiments I found that it is the presence Mg in seawater that inhibits calcite growth and therefore favour ikaite precipitation.Ikaite is metastable and at temperatures above 7°C the mineral will transform or decompose to calcite and water. The transformation can occur pseudomorphically and pseudomorphs after ikaite have been found worldwide in the sediment record. Pseudomorphs after authigenic ikaite in sediments are named glendonite, and because of the narrow temperature range of ikaite observations in nature, glendonite has been used as a paleotemperature indicator. In the fourth part of this thesis, I explore the temperature range of ikaite nucleation by a series of experiments and found that ikaite nucleation can occur up to at least 35°C. This challenges the use of glendonite as a paleotemperature indicator.
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