This paper investigates the petrogenesis of the Seqi Ultramafic Complex, which covers a total are... more This paper investigates the petrogenesis of the Seqi Ultramafic Complex, which covers a total area of approximately 0.5 km 2. The ultramafic rocks are hosted by tonalitic orthogneiss of the ca. 3000 Ma Akia terrane with crosscutting granitoid sheets providing an absolute minimum age of 2978 ± 8 Ma for the Seqi Ultramafic Complex. The Seqi rocks represent a broad range of olivine-dominated plutonic rocks with varying modal amounts of chromite, orthopyroxene and amphibole, i.e. various
The origin of amphibolite-facies aluminous gneiss from the gold-hosting Neoarchean Storø Supracru... more The origin of amphibolite-facies aluminous gneiss from the gold-hosting Neoarchean Storø Supracrustal Belt in the Nuuk region of southern West Greenland is investigated in this study. An improved understanding of the formation of such aluminous gneiss has implications for genetic models (epithermal vs. orogenic style) for a local gold occurrence, which is hosted by sheeted quartz-veins within amphibolite in the hanging wall adjacent to the aluminous gneiss on the island of Storø. The aluminous gneiss mainly consists of garnet, plagioclase, sillimanite, quartz and biotite, which suggest a pelitic protolith. However, it has previously been postulated that the aluminous gneiss represents a hydrothermal alteration product, formed by leaching of a mafic precursor that was subsequently transformed to the current mineral assemblage during later regional metamorphism. In support of this hypothesis are decimeter-scale relicts of amphibolite, found within the decameter-wide aluminous gneiss, that share similar ratios of commonly fluid immobile elements, such as Al, Ti, Zr, Hf, Nb and Lu. likely of sedimentary origin and may provide a venue to further understand the exogenous environments of the Archean Earth, and thus further geochemical studies of such rocks are recommended in order to place constraints on the composition of the hydrosphere at that time.
Extensive subaerial exposures of a basalt-hosted petroleum reservoir around Marraat Killiit on Nu... more Extensive subaerial exposures of a basalt-hosted petroleum reservoir around Marraat Killiit on Nuussuaq, West Greenland, provide an unparalleled opportunity to investigate waterrockhydrocarbon interactions in an unconventional petroleum system. Exposed sections in this locality ...
There is ample geological evidence that Earth's climate resembled the present during the Arch... more There is ample geological evidence that Earth's climate resembled the present during the Archaean, despite a much lower solar luminosity. This was cast as a paradox by Sagan and Mullen in 1972. Several solutions to the paradox have been suggested, mostly focusing on adjustments of the radiative properties of Earth's atmosphere e.g. Kasting (1993), by increasing the mixing ratio of
... Jove, 1992). Gibbsite is not a common phase in most serpentine soils; however, limited isomor... more ... Jove, 1992). Gibbsite is not a common phase in most serpentine soils; however, limited isomorphic substitution of Al(III) in goethite and hematite was noted in New Cale-donia (Schwertmann and Latham, 1986). Manga-nese ...
Mariposite (Cr-rich muscovite) crystals formed the during metasomatic replacement of serpentinite... more Mariposite (Cr-rich muscovite) crystals formed the during metasomatic replacement of serpentinite yield Ar/Ar ages demonstrating that gold-quartz-carbonate mineralization in the Sierra Nevada Foothills Metamorphic Belt occurred as early as 152 Ma and continued until at least 122 Ma. The earliest gold mineralization is found in the Grass Valley District; mineralization subsequently migrated southward along the Melones fault zone, forming the
The macrodikes of the east Greenland Tertiary igneous province partially melted Precambrian basem... more The macrodikes of the east Greenland Tertiary igneous province partially melted Precambrian basement along their contacts. Field evidence suggests that silicic liquid produced by partial melting of the basement buoyantly migrated roofward in the intrusions, where it ponded, and kinetic and/or rheological barriers prevented the crustderived melt and mafic magma of the macrodikes from intimately mixing. However, extensive redistribution of mobile elements occurred locally between these reservoirs. Close agreement between element partitioning in the various lithologic units in the macrodikes and experimental observations involving liquid immiscibility and silicate liquid interdiffusion suggests that chemical equilibrium between the magma reservoirs was approached through diffusive element exchange.
Geological Society, London, Special Publications, 2002
The volcanic succession in the inland Prinsen af Wales Bjerge contains the oldest known onshore l... more The volcanic succession in the inland Prinsen af Wales Bjerge contains the oldest known onshore lava flows (61 Ma) of the Palaeogene East Greenland flood basalt province. These flows and interbedded sediments define the Urbjerget Formation and are found in the southernmost part of Prinsen af Wales Bjerge. Flows of the Urbjerget Formation are chemically similar to the coastal Vandfaldsdalen Formation flows and the two formations may be chronostratigraphical equivalents. The Urbjerget Formation is overlain by the < 57 Ma tholeiitic basalts of the Milne Land Formation. Four regional volcanic formations are found along the Blosseville Kyst, but the Milne Land Formation is the only one present in the southern Prinsen af Wales Bjerge. Flows of the absent formations (Geikie Plateau, Rømer Fjord and Skrænterne formations) may not have been able to enter the area due to local uplift, more distal located eruption sites or possibly topographic features. A high-Si (SiO2> 52 wt%) lave flow...
The gabbros of the Tertiary Kap Edvard Holm Layered Serieshave a stratigraphic thickness of more ... more The gabbros of the Tertiary Kap Edvard Holm Layered Serieshave a stratigraphic thickness of more than 5000 m. Earlier work has shown that the range in cumulus mineral compositions is restricted (plagioclase An81—An51; olivine Fo85—Fo66; pyroxenes Ca43Mg46Fe11 to Ca43Mg37Fe20). Field evidence of magma injections is common, which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma. A detailed study of a 600 m section (900–1500 m) in the Lower Layered Series reveals a period of crystallization when the magma chamber behaved as a closed system (900–1300 m). The rocks formed during this periodare well-laminated olivine–gabbros (900–110 m), which evolved to well-laminated oxide-gabbros (1100–1300 m). Compositional trends in the cumulusminerals are towards more evolved compositions (plagioclase An64—An58, pyroxene Mg# from 80 to 76) with stratigraphic height. From 1300 m to 1500 m, granular olivine-...
The Kruuse Fjord Gabbro Complex is a composite intrusion of layered gabbro and troctolite with su... more The Kruuse Fjord Gabbro Complex is a composite intrusion of layered gabbro and troctolite with subordinate ultramafic rocks and minor trondhjemitic bodies. It was emplaced into Archaean continental crust of East Greenland during early Tertiary rifting of Greenland from Eurasia. The work to date has identified an outer gabbro series and an inner troctolite series, and these are separated by a narrow zone of trondhjemitic intrusions. In the southeast, the partially crystallized cumulates of the gabbro series were intruded by a lenticular, ultramafic pluton 800 m in thickness. Volumetrically minor, syenite–trachyandesite net-veined dykes and later, diabase dykes cross-cut the plutonic rocks. Structural and topographic features suggest that the layered rocks were affected by synmagmatic subsidence and deformation but not by monoclinal coastal flexure.The gabbro series is composed of a marginal gabbro unit, about 20 m wide, bordering more than a 2 km thickness of layered olivine and magn...
Strontium concentrations of 253 natural water samples from Skagafjö rdur, a Tertiary tholeiitic f... more Strontium concentrations of 253 natural water samples from Skagafjö rdur, a Tertiary tholeiitic flood basalt region in northern Iceland range between 0.10 and 28 ppb. Surface environments (rivers, lakes, and peat soil waters) include the whole range of observed Sr concentrations whereas the Sr concentrations of ground waters are, in most cases, <3.5 ppb. Concentrations of Sr derived from basalt dissolution (i.e., rock-derived Sr) in waters of rivers and lakes exhibit a near linear correlation with the concentration of rock-derived Ca with a median molar Ca/Sr ratio of 1350. This systematic correlation suggests that Ca and Sr concentrations are controlled by weathering processes, i.e., the extent of dissolution of the basalt. The relative mobility of Sr during weathering in Skagafjö rdur is approximately half that of Ca, which is consistent with observed relative mobilities of these elements elsewhere in Iceland and in other basaltic regions. Peat soil waters commonly have lower concentrations of Sr and higher Ca concentrations than rivers and lakes, and molar ratios of rock-derived Ca to Sr in peat soil waters exhibit no systematic pattern. In several cases calculated concentrations of rock-derived Sr in peat soil waters yield negative values, suggesting a mineralogic sink for Sr in these waters. The low Sr concentrations in cold and thermal ground waters (<3.5 ppb) suggest mineralogic control over Sr in the ground water systems. Precipitation of secondary Sr minerals such as strontianite and celestite is ruled out as the ground waters are understaturated with respect to these minerals. Ground waters are characterized by high Ca/Sr molar ratios ($5000 compared to bedrock Ca/Sr ratio of 730) suggesting that Sr is being preferentially incorporated (relative to Ca) into secondary minerals. The secondary minerals present in the bedrock in Skagafjö rdur that can preferentially incorporate Sr include zeolites, such as heulandite, chabazite, and thomsonite, and smectite. Ion-exchange calculations demonstrate that activities of Sr 2+ and Ca 2+ in ground water solutions in Skagafjö rdur are consistent with ion-exchange equilibria between these waters and heulandite from other Tertiary basalts in Iceland suggesting that this mineral may play an important role in controlling the concentration of Sr in the Skagafjö rdur ground waters. Incorporation of Sr into calcite cannot explain the observed high Ca/Sr ratios of the Skagafjö rdur ground waters because calcite, when precipitating, only admits limited amounts of Sr. Aragonite is not considered a likely candidate either because it has only very slight preference for Sr over Ca and ground waters above 40°C are undersaturated with respect to this phase. However, predicted Sr content of calcite in equilibrium with the Skagafjö rdur ground waters (0.5-83 ppm Sr) is in good agreement with measured Sr content of this mineral in Tertiary basalts elsewhere in Iceland (<0.1-63 ppm), suggesting that the Skagafjö rdur ground waters can be used as analogues for Tertiary crustal solutions involved in the zeolite facies metamorphism of the Icelandic crust.
Magmatic augites reacted with high temperature aqueous solutions to form secondary calcic pyroxen... more Magmatic augites reacted with high temperature aqueous solutions to form secondary calcic pyroxenes during the subsolidus cooling of the Skaergaard intrusion. Secondary, hydrothermal clinopyroxenes replace wall rock igneous augites at the margins of veins filled with calcic amphibole. These veins are up to several millimeters wide and tens of meters in length. Hydrothermal clinopyroxenes are a ubiquitous and characteristic phase in the earliest veins throughout the Layered Series of the intrusion, and occur rarely in late veins that, in some places, crosscut the early veins. Associated secondary phases in early veins include amphiboles ranging in composition from actinolite to hornblende, together with biotite, Fe-Ti oxides and calcic plagioclase. Hydrothermal clinopyroxenes in late veins may be associated with actinolite, hornblende, biotite, magnetite and albite. Hydrothermal clinopyroxenes are depleted in Fe, Mg and minor elements, and enriched in Ca and Si relative to igneous augites in the Layered Series gabbros. Secondary vein pyroxenes are similar in composition to calcic pyroxenes from amphibolite facies metamorphic rocks. Clinopyroxene solvus thermometry suggests minimum temperatures of equilibration of between 500 ~ and 750 ~ C. These temperatures, combined with numerical transport models of the intrusion, suggest that vein clinopyroxenes could have formed during 20,000 to 60,000 year time intervals associated with a maximum in the fluid flux through fractures in the Layered Series.
... This central volcano activity and the volumetrically significant pyroclastic and effusive con... more ... This central volcano activity and the volumetrically significant pyroclastic and effusive continentalflood volcanism in the GreenlandFaeroes region could ABSTRACT Acknowledgements 1 10 100 1000 La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Ro ck /C ho nd rite s Lu ...
The average extensive air shower longitudinal development profile as a function of shower age in ... more The average extensive air shower longitudinal development profile as a function of shower age in the energy range from 10 17 to 10 18 eV is measured using data from the hybrid HiRes/MIA experiment. An angular bin signal based Cerenkov light component subtraction method and a shower maximum fitting method using a local parabolic function are used to correct and normalize the data. The Gaisser-Hillas and Greisen functions work equally well for describing the shower profile. The Gaussian function is a poor fit. A simple scale-free function is proposed and fits the data equally well. The best-fit parameters for the above functions are determined.
Annals of the Association of American Geographers, 2010
Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf ... more Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Weathering of basalts, tephras and related sediments produces clay and iron oxide/hydroxide miner... more Weathering of basalts, tephras and related sediments produces clay and iron oxide/hydroxide minerals in reddened layers referred to as interbasaltic paleosols, boles or laterites. We suggest that these &amp;amp;quot;redbeds&amp;amp;quot; present throughout the flood basalt stratigraphy of the North Atlantic Igneous Province preserve relatively continuous isotopic records of terrestrial climate change in the Cenozoic. The use of tephras in paleoclimate characterization
Low-grade alteration of basaltic lavas at Teigarhorn, eastern Iceland, resulted in three distinct... more Low-grade alteration of basaltic lavas at Teigarhorn, eastern Iceland, resulted in three distinct stages of mineral paragenesis that correlate to events in the burial and intrusive history of Icelandic crust. Metasomatism and brittle deformation during the paragenetic stages dramatically affected the paleohydrology of the lavas and formed temporally distinct mineral assemblages. The lavas initially contained up to 22 percent total porosity concentrated near the tops and bottoms of individual lava flows. Celadonite and silica (Stage I) precipitated along the walls of primary pores prior to deep burial of the lavas and occluded ϳ8 percent of the initial porosity. During burial (Stage II), hydrolysis of olivine and basaltic glass led to the formation of mixed-layer chlorite/smectite clays in the matrix of the lavas and as rims filling ϳ40 percent of the volume of primary pores. Chlorite contents in Stage II mixed-layer clay rims increased from ϳ20 to ϳ80 percent during the infilling of individual vesicles, reflecting increasing temperatures with time as the lavas were buried. The end of Stage II occurred after burial and is represented by filling of ϳ40 percent of total primary porosity by zeolites (scolecite or heulandite ؉ stilbite ؉ mordenite ؎ epistilbite) and replacement of plagioclase by zeolites and albite. The Stage II zeolite assemblages are indicative of two regional metamorphic mineral zones in eastern Iceland, the mesolite ؉ scolecite and heulandite ؉ stilbite zones. The presence of the boundary between the mesolite ؉ scolecite ؉ and heulandite ؉ stilbite zones indicates that the maximum temperature during burial metamorphism was 90°؎ 10°C. Localized areas of intense hydrothermal alteration associated with intrusion of basaltic dikes (Stage III) overprint Stages I and II. Extensive fracturing and hydrothermal brecciation during Stage III added 3 to 11 percent total porosity in which mm-to cm-scale museum-grade crystals of quartz, calcite (Iceland spar), stilbite, scolecite, heulandite, and laumontite precipitated. Estimates of the temperature during Stage III (based on fluid inclusion homogenization temperatures in calcite, chlorite geothermometry, and the zeolite assemblage) range from 120°t o 180°C. Although the thermobarometric conditions during Stages II and III led to similar mineral assemblages, careful attention to textural and geologic relations permits seemingly complex, multi-stage parageneses in metabasalts to be interpreted in a petrotectonic context.
Earth accreted 4567Myr ago from largely homogeneous material. From this initial capital of matter... more Earth accreted 4567Myr ago from largely homogeneous material. From this initial capital of matter, differentiation formed the chemical and physical compartments of core, mantle, continents, ocean and atmosphere, that characterize Earth today. Differentiation was, and still is, driven by energy from various sources including radioactive heat and relic heat from accretion. With evolution of photosynthesis, living organisms acquired the ability to harvest Solar energy and channel it into geochemical cycles. On our present Earth, the primary production from life contributes 3 times more energy to these cycles than Earth's internal heat engine. We hypothesize that the emergence of this energy resource modified Earth's geochemical cycles and ultimately stimulated the production of granite during the earliest Archaean, which led to the first stabilization of continents on Earth. Such biological forcing may explain the unique presence of granite on Earth, and why stable continents did not form during the first half billion years of Earth's history.
This paper investigates the petrogenesis of the Seqi Ultramafic Complex, which covers a total are... more This paper investigates the petrogenesis of the Seqi Ultramafic Complex, which covers a total area of approximately 0.5 km 2. The ultramafic rocks are hosted by tonalitic orthogneiss of the ca. 3000 Ma Akia terrane with crosscutting granitoid sheets providing an absolute minimum age of 2978 ± 8 Ma for the Seqi Ultramafic Complex. The Seqi rocks represent a broad range of olivine-dominated plutonic rocks with varying modal amounts of chromite, orthopyroxene and amphibole, i.e. various
The origin of amphibolite-facies aluminous gneiss from the gold-hosting Neoarchean Storø Supracru... more The origin of amphibolite-facies aluminous gneiss from the gold-hosting Neoarchean Storø Supracrustal Belt in the Nuuk region of southern West Greenland is investigated in this study. An improved understanding of the formation of such aluminous gneiss has implications for genetic models (epithermal vs. orogenic style) for a local gold occurrence, which is hosted by sheeted quartz-veins within amphibolite in the hanging wall adjacent to the aluminous gneiss on the island of Storø. The aluminous gneiss mainly consists of garnet, plagioclase, sillimanite, quartz and biotite, which suggest a pelitic protolith. However, it has previously been postulated that the aluminous gneiss represents a hydrothermal alteration product, formed by leaching of a mafic precursor that was subsequently transformed to the current mineral assemblage during later regional metamorphism. In support of this hypothesis are decimeter-scale relicts of amphibolite, found within the decameter-wide aluminous gneiss, that share similar ratios of commonly fluid immobile elements, such as Al, Ti, Zr, Hf, Nb and Lu. likely of sedimentary origin and may provide a venue to further understand the exogenous environments of the Archean Earth, and thus further geochemical studies of such rocks are recommended in order to place constraints on the composition of the hydrosphere at that time.
Extensive subaerial exposures of a basalt-hosted petroleum reservoir around Marraat Killiit on Nu... more Extensive subaerial exposures of a basalt-hosted petroleum reservoir around Marraat Killiit on Nuussuaq, West Greenland, provide an unparalleled opportunity to investigate waterrockhydrocarbon interactions in an unconventional petroleum system. Exposed sections in this locality ...
There is ample geological evidence that Earth's climate resembled the present during the Arch... more There is ample geological evidence that Earth's climate resembled the present during the Archaean, despite a much lower solar luminosity. This was cast as a paradox by Sagan and Mullen in 1972. Several solutions to the paradox have been suggested, mostly focusing on adjustments of the radiative properties of Earth's atmosphere e.g. Kasting (1993), by increasing the mixing ratio of
... Jove, 1992). Gibbsite is not a common phase in most serpentine soils; however, limited isomor... more ... Jove, 1992). Gibbsite is not a common phase in most serpentine soils; however, limited isomorphic substitution of Al(III) in goethite and hematite was noted in New Cale-donia (Schwertmann and Latham, 1986). Manga-nese ...
Mariposite (Cr-rich muscovite) crystals formed the during metasomatic replacement of serpentinite... more Mariposite (Cr-rich muscovite) crystals formed the during metasomatic replacement of serpentinite yield Ar/Ar ages demonstrating that gold-quartz-carbonate mineralization in the Sierra Nevada Foothills Metamorphic Belt occurred as early as 152 Ma and continued until at least 122 Ma. The earliest gold mineralization is found in the Grass Valley District; mineralization subsequently migrated southward along the Melones fault zone, forming the
The macrodikes of the east Greenland Tertiary igneous province partially melted Precambrian basem... more The macrodikes of the east Greenland Tertiary igneous province partially melted Precambrian basement along their contacts. Field evidence suggests that silicic liquid produced by partial melting of the basement buoyantly migrated roofward in the intrusions, where it ponded, and kinetic and/or rheological barriers prevented the crustderived melt and mafic magma of the macrodikes from intimately mixing. However, extensive redistribution of mobile elements occurred locally between these reservoirs. Close agreement between element partitioning in the various lithologic units in the macrodikes and experimental observations involving liquid immiscibility and silicate liquid interdiffusion suggests that chemical equilibrium between the magma reservoirs was approached through diffusive element exchange.
Geological Society, London, Special Publications, 2002
The volcanic succession in the inland Prinsen af Wales Bjerge contains the oldest known onshore l... more The volcanic succession in the inland Prinsen af Wales Bjerge contains the oldest known onshore lava flows (61 Ma) of the Palaeogene East Greenland flood basalt province. These flows and interbedded sediments define the Urbjerget Formation and are found in the southernmost part of Prinsen af Wales Bjerge. Flows of the Urbjerget Formation are chemically similar to the coastal Vandfaldsdalen Formation flows and the two formations may be chronostratigraphical equivalents. The Urbjerget Formation is overlain by the < 57 Ma tholeiitic basalts of the Milne Land Formation. Four regional volcanic formations are found along the Blosseville Kyst, but the Milne Land Formation is the only one present in the southern Prinsen af Wales Bjerge. Flows of the absent formations (Geikie Plateau, Rømer Fjord and Skrænterne formations) may not have been able to enter the area due to local uplift, more distal located eruption sites or possibly topographic features. A high-Si (SiO2> 52 wt%) lave flow...
The gabbros of the Tertiary Kap Edvard Holm Layered Serieshave a stratigraphic thickness of more ... more The gabbros of the Tertiary Kap Edvard Holm Layered Serieshave a stratigraphic thickness of more than 5000 m. Earlier work has shown that the range in cumulus mineral compositions is restricted (plagioclase An81—An51; olivine Fo85—Fo66; pyroxenes Ca43Mg46Fe11 to Ca43Mg37Fe20). Field evidence of magma injections is common, which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma. A detailed study of a 600 m section (900–1500 m) in the Lower Layered Series reveals a period of crystallization when the magma chamber behaved as a closed system (900–1300 m). The rocks formed during this periodare well-laminated olivine–gabbros (900–110 m), which evolved to well-laminated oxide-gabbros (1100–1300 m). Compositional trends in the cumulusminerals are towards more evolved compositions (plagioclase An64—An58, pyroxene Mg# from 80 to 76) with stratigraphic height. From 1300 m to 1500 m, granular olivine-...
The Kruuse Fjord Gabbro Complex is a composite intrusion of layered gabbro and troctolite with su... more The Kruuse Fjord Gabbro Complex is a composite intrusion of layered gabbro and troctolite with subordinate ultramafic rocks and minor trondhjemitic bodies. It was emplaced into Archaean continental crust of East Greenland during early Tertiary rifting of Greenland from Eurasia. The work to date has identified an outer gabbro series and an inner troctolite series, and these are separated by a narrow zone of trondhjemitic intrusions. In the southeast, the partially crystallized cumulates of the gabbro series were intruded by a lenticular, ultramafic pluton 800 m in thickness. Volumetrically minor, syenite–trachyandesite net-veined dykes and later, diabase dykes cross-cut the plutonic rocks. Structural and topographic features suggest that the layered rocks were affected by synmagmatic subsidence and deformation but not by monoclinal coastal flexure.The gabbro series is composed of a marginal gabbro unit, about 20 m wide, bordering more than a 2 km thickness of layered olivine and magn...
Strontium concentrations of 253 natural water samples from Skagafjö rdur, a Tertiary tholeiitic f... more Strontium concentrations of 253 natural water samples from Skagafjö rdur, a Tertiary tholeiitic flood basalt region in northern Iceland range between 0.10 and 28 ppb. Surface environments (rivers, lakes, and peat soil waters) include the whole range of observed Sr concentrations whereas the Sr concentrations of ground waters are, in most cases, <3.5 ppb. Concentrations of Sr derived from basalt dissolution (i.e., rock-derived Sr) in waters of rivers and lakes exhibit a near linear correlation with the concentration of rock-derived Ca with a median molar Ca/Sr ratio of 1350. This systematic correlation suggests that Ca and Sr concentrations are controlled by weathering processes, i.e., the extent of dissolution of the basalt. The relative mobility of Sr during weathering in Skagafjö rdur is approximately half that of Ca, which is consistent with observed relative mobilities of these elements elsewhere in Iceland and in other basaltic regions. Peat soil waters commonly have lower concentrations of Sr and higher Ca concentrations than rivers and lakes, and molar ratios of rock-derived Ca to Sr in peat soil waters exhibit no systematic pattern. In several cases calculated concentrations of rock-derived Sr in peat soil waters yield negative values, suggesting a mineralogic sink for Sr in these waters. The low Sr concentrations in cold and thermal ground waters (<3.5 ppb) suggest mineralogic control over Sr in the ground water systems. Precipitation of secondary Sr minerals such as strontianite and celestite is ruled out as the ground waters are understaturated with respect to these minerals. Ground waters are characterized by high Ca/Sr molar ratios ($5000 compared to bedrock Ca/Sr ratio of 730) suggesting that Sr is being preferentially incorporated (relative to Ca) into secondary minerals. The secondary minerals present in the bedrock in Skagafjö rdur that can preferentially incorporate Sr include zeolites, such as heulandite, chabazite, and thomsonite, and smectite. Ion-exchange calculations demonstrate that activities of Sr 2+ and Ca 2+ in ground water solutions in Skagafjö rdur are consistent with ion-exchange equilibria between these waters and heulandite from other Tertiary basalts in Iceland suggesting that this mineral may play an important role in controlling the concentration of Sr in the Skagafjö rdur ground waters. Incorporation of Sr into calcite cannot explain the observed high Ca/Sr ratios of the Skagafjö rdur ground waters because calcite, when precipitating, only admits limited amounts of Sr. Aragonite is not considered a likely candidate either because it has only very slight preference for Sr over Ca and ground waters above 40°C are undersaturated with respect to this phase. However, predicted Sr content of calcite in equilibrium with the Skagafjö rdur ground waters (0.5-83 ppm Sr) is in good agreement with measured Sr content of this mineral in Tertiary basalts elsewhere in Iceland (<0.1-63 ppm), suggesting that the Skagafjö rdur ground waters can be used as analogues for Tertiary crustal solutions involved in the zeolite facies metamorphism of the Icelandic crust.
Magmatic augites reacted with high temperature aqueous solutions to form secondary calcic pyroxen... more Magmatic augites reacted with high temperature aqueous solutions to form secondary calcic pyroxenes during the subsolidus cooling of the Skaergaard intrusion. Secondary, hydrothermal clinopyroxenes replace wall rock igneous augites at the margins of veins filled with calcic amphibole. These veins are up to several millimeters wide and tens of meters in length. Hydrothermal clinopyroxenes are a ubiquitous and characteristic phase in the earliest veins throughout the Layered Series of the intrusion, and occur rarely in late veins that, in some places, crosscut the early veins. Associated secondary phases in early veins include amphiboles ranging in composition from actinolite to hornblende, together with biotite, Fe-Ti oxides and calcic plagioclase. Hydrothermal clinopyroxenes in late veins may be associated with actinolite, hornblende, biotite, magnetite and albite. Hydrothermal clinopyroxenes are depleted in Fe, Mg and minor elements, and enriched in Ca and Si relative to igneous augites in the Layered Series gabbros. Secondary vein pyroxenes are similar in composition to calcic pyroxenes from amphibolite facies metamorphic rocks. Clinopyroxene solvus thermometry suggests minimum temperatures of equilibration of between 500 ~ and 750 ~ C. These temperatures, combined with numerical transport models of the intrusion, suggest that vein clinopyroxenes could have formed during 20,000 to 60,000 year time intervals associated with a maximum in the fluid flux through fractures in the Layered Series.
... This central volcano activity and the volumetrically significant pyroclastic and effusive con... more ... This central volcano activity and the volumetrically significant pyroclastic and effusive continentalflood volcanism in the GreenlandFaeroes region could ABSTRACT Acknowledgements 1 10 100 1000 La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Ro ck /C ho nd rite s Lu ...
The average extensive air shower longitudinal development profile as a function of shower age in ... more The average extensive air shower longitudinal development profile as a function of shower age in the energy range from 10 17 to 10 18 eV is measured using data from the hybrid HiRes/MIA experiment. An angular bin signal based Cerenkov light component subtraction method and a shower maximum fitting method using a local parabolic function are used to correct and normalize the data. The Gaisser-Hillas and Greisen functions work equally well for describing the shower profile. The Gaussian function is a poor fit. A simple scale-free function is proposed and fits the data equally well. The best-fit parameters for the above functions are determined.
Annals of the Association of American Geographers, 2010
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Weathering of basalts, tephras and related sediments produces clay and iron oxide/hydroxide miner... more Weathering of basalts, tephras and related sediments produces clay and iron oxide/hydroxide minerals in reddened layers referred to as interbasaltic paleosols, boles or laterites. We suggest that these &amp;amp;quot;redbeds&amp;amp;quot; present throughout the flood basalt stratigraphy of the North Atlantic Igneous Province preserve relatively continuous isotopic records of terrestrial climate change in the Cenozoic. The use of tephras in paleoclimate characterization
Low-grade alteration of basaltic lavas at Teigarhorn, eastern Iceland, resulted in three distinct... more Low-grade alteration of basaltic lavas at Teigarhorn, eastern Iceland, resulted in three distinct stages of mineral paragenesis that correlate to events in the burial and intrusive history of Icelandic crust. Metasomatism and brittle deformation during the paragenetic stages dramatically affected the paleohydrology of the lavas and formed temporally distinct mineral assemblages. The lavas initially contained up to 22 percent total porosity concentrated near the tops and bottoms of individual lava flows. Celadonite and silica (Stage I) precipitated along the walls of primary pores prior to deep burial of the lavas and occluded ϳ8 percent of the initial porosity. During burial (Stage II), hydrolysis of olivine and basaltic glass led to the formation of mixed-layer chlorite/smectite clays in the matrix of the lavas and as rims filling ϳ40 percent of the volume of primary pores. Chlorite contents in Stage II mixed-layer clay rims increased from ϳ20 to ϳ80 percent during the infilling of individual vesicles, reflecting increasing temperatures with time as the lavas were buried. The end of Stage II occurred after burial and is represented by filling of ϳ40 percent of total primary porosity by zeolites (scolecite or heulandite ؉ stilbite ؉ mordenite ؎ epistilbite) and replacement of plagioclase by zeolites and albite. The Stage II zeolite assemblages are indicative of two regional metamorphic mineral zones in eastern Iceland, the mesolite ؉ scolecite and heulandite ؉ stilbite zones. The presence of the boundary between the mesolite ؉ scolecite ؉ and heulandite ؉ stilbite zones indicates that the maximum temperature during burial metamorphism was 90°؎ 10°C. Localized areas of intense hydrothermal alteration associated with intrusion of basaltic dikes (Stage III) overprint Stages I and II. Extensive fracturing and hydrothermal brecciation during Stage III added 3 to 11 percent total porosity in which mm-to cm-scale museum-grade crystals of quartz, calcite (Iceland spar), stilbite, scolecite, heulandite, and laumontite precipitated. Estimates of the temperature during Stage III (based on fluid inclusion homogenization temperatures in calcite, chlorite geothermometry, and the zeolite assemblage) range from 120°t o 180°C. Although the thermobarometric conditions during Stages II and III led to similar mineral assemblages, careful attention to textural and geologic relations permits seemingly complex, multi-stage parageneses in metabasalts to be interpreted in a petrotectonic context.
Earth accreted 4567Myr ago from largely homogeneous material. From this initial capital of matter... more Earth accreted 4567Myr ago from largely homogeneous material. From this initial capital of matter, differentiation formed the chemical and physical compartments of core, mantle, continents, ocean and atmosphere, that characterize Earth today. Differentiation was, and still is, driven by energy from various sources including radioactive heat and relic heat from accretion. With evolution of photosynthesis, living organisms acquired the ability to harvest Solar energy and channel it into geochemical cycles. On our present Earth, the primary production from life contributes 3 times more energy to these cycles than Earth's internal heat engine. We hypothesize that the emergence of this energy resource modified Earth's geochemical cycles and ultimately stimulated the production of granite during the earliest Archaean, which led to the first stabilization of continents on Earth. Such biological forcing may explain the unique presence of granite on Earth, and why stable continents did not form during the first half billion years of Earth's history.
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