Mineraalikemiallisia todisteita erittäin magneisum-rikkaista kivisulista Karoon magmaprovinssissa

Peer reviewe

Faecal microorganisms in run-off from cattle farming

Numbers of faecal microbes (faecal coliforms, enterococci, sulphite-reducing clostridia and coliphages) were determined in run-off waters from cattle farms in 1998-2005. Water samples were collected from drain wells and open ditches adjacent to exercise yards and forested feedlots for cattle, a grass field with slurry applications and a pasture with buffer strips. The indicator numbers were the highest in run-off waters from asphalt exercise yards while the figures were even 100-fold smaller in waters from a bark covered yard. In the forested feedlots, where cattle were fed for the winter months or all the year round, the indicator numbers were as high as the ones in a grass field with slurry applications or a pasture. There was a severe risk of transporting pathogens to the environment, especially if run-off water from exercise yards and feedlots are only poor purifed and allowed to flow into ditches and watercourses. The existence of buffer strips between fields and watercourses may reduce the numbers of faecal microbes in surface run-off

18O-rikastuminen Karoon suuren magmaprovinssin antarktisen osan vaippalähteissä

Karoo continental flood basalt (CFB) province is known for its highly variable trace element and isotopic composition, often attributed to the involvement of continental lithospheric sources. Here, we report oxygen isotopic compositions measured with secondary ion mass spectrometry for hand-picked olivine phenocrysts from similar to 190 to 180 Ma CFBs and intrusive rocks from Vestfjella, western Dronning Maud Land, that form an Antarctic extension of the Karoo province. The Vestfjella lavas exhibit heterogeneous trace element and radiogenic isotope compositions (e.g., epsilon(Nd) from -16 to +2 at 180 Ma) and the involvement of continental lithospheric mantle and/or crust in their petrogenesis has previously been suggested. Importantly, our sample set also includes rare primitive dikes that have been derived from depleted asthenospheric mantle sources (epsilon(Nd) up to + 8 at 180 Ma). The majority of the oxygen isotopic compositions of the olivines from these dike rocks (delta O-18 = 4.4-5.2%; Fo = 78-92 mol%) are also compatible with such sources. The olivine phenocrysts in the lavas, however, are characterized by notably higher delta O-18 (6.2-7.5%; Fo = 70-88 mol%); and one of the dike samples gives intermediate compositions (5.2-6.1%, Fo = 83-87 mol%) between the other dikes and the CFBs. The oxygen isotopic compositions do not correlate with radiogenic isotope compositions susceptible to crustal assimilation (Sr, Nd, and Pb) or with geochemical indicators of pyroxene-rich mantle sources. Instead, delta O-18 correlates positively with enrichments in large-ion lithophile elements (especially K) and Os-187. We suggest that the oxygen isotopic compositions of the Vestfjella CFB olivines primarily record large-scale subduction-related metasomatism of the sub-Gondwanan mantle (base of the lithosphere or deeper) prior to Karoo magmatism. The overall influence of such sources to Karoo magmatism is not known, but, in addition to continental lithosphere, they may be responsible for some of the geochemical heterogeneity observed in the CFBs.Peer reviewe

Korkeakoulujen keskityttävä tieteellisyyteen

Artikkelin lähtökohtana on valmistunut Avoimen korkeakoulun toimikunnan mietintö. Kirjoittajat näkevät, että mietinnössä ei ole riittävästi selvitetty avoimen korkeakouluopetuksen tarvetta eikä se anna riittävää pohjaa tasa-arvopyrkimysten toteutumiselle. Korkeakouluopetus voi tapahtua vain tieteellisessä ilmapiirissä, tiedeyhteisössä, joka rakentuu tutkimukselle. Artikkelissa on myös kuvattu laajemmin korkeakoulujen asemaa aikuiskoulutuksessa

Jurassic dikes of Vestfjella, western Dronning Maud Land, Antarctica : geochemical tracing of ferropicrite sources

"Ferropicrites and their differentiates make up a geochemically distinctive group of dikes that crosscut Jurassic continental flood basalts of the Karoo large igneous province at Vestfjella, western Dronning Maud Land. Antarctica. The Vestfjella ferropicrites can be divided into two geochemical types: The depleted ferropicrites have (La/Sm)(N) of 1.2-1.3, (Sm/Yb)(N) of 4.5, initial epsilon(Nd) from +7 to +8, initial epsilon(Sr) from -18 to -19, and show relative depletion of highly incompatible elements, but pronounced enrichment of V; The enriched ferropicrites have (La/Sm)(N) of 1.7, (Sm/Yb)(N) of 5.1-5.4, initial epsilon(Nd) from +3 to +4, initial epsilon(Sr) from 0 to + 1, and show general enrichment of incompatible trace elements. The immobile incompatible element signatures of the ferropicrites have not been significantly affected by alteration, fractional crystallization, or contamination. Based on primitive olivine phenocrysts (Fo(79-88)) and high epsilon(Nd) values, the depleted ferropicrites represent near-primary melts derived from anomalous hot mantle sources. Overall, geochemical compositions favor a pyroxenite source for the ferropicrites. Unusually high (V/Lu)(N) values of the depleted ferropicrites indicate an affinity to oceanic Fe-Ti gabbros and geochemical modeling favors such a recycled mantle source component in them. The enriched ferropicrites probably represent near-primary melts, but this cannot be confirmed. They may also record an exceptionally Fe-rich source component, but their high Fe contents stem at least partly from relatively low-degree melting at high pressures, as indicated by the high (La/Sm)(N) and (Sm/Yb)(N) rados. Examination of a global ferropicrite dataset reveals that the recycled Fe-Ti gabbro component is detectable in many ferropicrites. (C) 2008 Elsevier B.V. All rights reserved.""Ferropicrites and their differentiates make up a geochemically distinctive group of dikes that crosscut Jurassic continental flood basalts of the Karoo large igneous province at Vestfjella, western Dronning Maud Land. Antarctica. The Vestfjella ferropicrites can be divided into two geochemical types: The depleted ferropicrites have (La/Sm)(N) of 1.2-1.3, (Sm/Yb)(N) of 4.5, initial epsilon(Nd) from +7 to +8, initial epsilon(Sr) from -18 to -19, and show relative depletion of highly incompatible elements, but pronounced enrichment of V; The enriched ferropicrites have (La/Sm)(N) of 1.7, (Sm/Yb)(N) of 5.1-5.4, initial epsilon(Nd) from +3 to +4, initial epsilon(Sr) from 0 to + 1, and show general enrichment of incompatible trace elements. The immobile incompatible element signatures of the ferropicrites have not been significantly affected by alteration, fractional crystallization, or contamination. Based on primitive olivine phenocrysts (Fo(79-88)) and high epsilon(Nd) values, the depleted ferropicrites represent near-primary melts derived from anomalous hot mantle sources. Overall, geochemical compositions favor a pyroxenite source for the ferropicrites. Unusually high (V/Lu)(N) values of the depleted ferropicrites indicate an affinity to oceanic Fe-Ti gabbros and geochemical modeling favors such a recycled mantle source component in them. The enriched ferropicrites probably represent near-primary melts, but this cannot be confirmed. They may also record an exceptionally Fe-rich source component, but their high Fe contents stem at least partly from relatively low-degree melting at high pressures, as indicated by the high (La/Sm)(N) and (Sm/Yb)(N) rados. Examination of a global ferropicrite dataset reveals that the recycled Fe-Ti gabbro component is detectable in many ferropicrites. (C) 2008 Elsevier B.V. All rights reserved.""Ferropicrites and their differentiates make up a geochemically distinctive group of dikes that crosscut Jurassic continental flood basalts of the Karoo large igneous province at Vestfjella, western Dronning Maud Land. Antarctica. The Vestfjella ferropicrites can be divided into two geochemical types: The depleted ferropicrites have (La/Sm)(N) of 1.2-1.3, (Sm/Yb)(N) of 4.5, initial epsilon(Nd) from +7 to +8, initial epsilon(Sr) from -18 to -19, and show relative depletion of highly incompatible elements, but pronounced enrichment of V; The enriched ferropicrites have (La/Sm)(N) of 1.7, (Sm/Yb)(N) of 5.1-5.4, initial epsilon(Nd) from +3 to +4, initial epsilon(Sr) from 0 to + 1, and show general enrichment of incompatible trace elements. The immobile incompatible element signatures of the ferropicrites have not been significantly affected by alteration, fractional crystallization, or contamination. Based on primitive olivine phenocrysts (Fo(79-88)) and high epsilon(Nd) values, the depleted ferropicrites represent near-primary melts derived from anomalous hot mantle sources. Overall, geochemical compositions favor a pyroxenite source for the ferropicrites. Unusually high (V/Lu)(N) values of the depleted ferropicrites indicate an affinity to oceanic Fe-Ti gabbros and geochemical modeling favors such a recycled mantle source component in them. The enriched ferropicrites probably represent near-primary melts, but this cannot be confirmed. They may also record an exceptionally Fe-rich source component, but their high Fe contents stem at least partly from relatively low-degree melting at high pressures, as indicated by the high (La/Sm)(N) and (Sm/Yb)(N) rados. Examination of a global ferropicrite dataset reveals that the recycled Fe-Ti gabbro component is detectable in many ferropicrites. (C) 2008 Elsevier B.V. All rights reserved."Peer reviewe

Hunting basalts in the savannah : The expedition of the Geological museum to Mozambique 20.8.-9.9.2012

Englanninkielinen abstraktiOur two-person “flood basalt task force” (authors Arto Luttinen and Jussi Heinonen) of the Finnish Museum of Natural History (LUOMUS) spent three weeks in Mozambican countryside collecting samples of the little-studied flood basalt formations of the Jurassic ~180 Ma Karoo large igneous province. The expedition was related to the recently launched MARZ (Magmatism in the Africa- Antarctica Rift Zone) project that is funded by the Academy of Finland. Fieldwork was carried out within three provinces, Tete, Sofala, and Manica in cooperation with Professor Daud Jamal, Dr. Estêvão Sumburane, Mr. Teofilo Gove (all from the Eduardo Mondlane University in Maputo), and Dr. António Alface (Direcção Nacional de Geologia, Tete). During the field campaign, we took lodging in towns and villages and also camped on the forest savannah, and were greatly impressed by the friendliness and helpfulness of the local people. Despite the tropical conditions, the quality of the bedrock outcrops was surprisingly good and we were able to collect ~150 rock samples, well above our initial expectations. The samples will be analysed for major and trace elements, Sr and Nd isotopes, and selected samples will be used for Ar- Ar plagioclase and U-Pb zircon dating. Our samples are from areas that have not been previously studied in detail and the results hopefully will shed light on the mysteries related to the origin of Karoo and other flood basalt provinces. More information about the MARZ project: www.luomus.fi/english/geology/research/ marzENG.ht

Syvä avoin varasto ja matala suljettu kuljetussysteemi laakiobasalttisekvenssille paljastui Magmakammiosimulaattorin avulla

Karoo continental flood basalt (CFB) province is known for its highly variable trace element and isotopic composition, often attributed to the involvement of continental lithospheric sources. Here, we report oxygen isotopic compositions measured with secondary ion mass spectrometry for hand-picked olivine phenocrysts from similar to 190 to 180 Ma CFBs and intrusive rocks from Vestfjella, western Dronning Maud Land, that form an Antarctic extension of the Karoo province. The Vestfjella lavas exhibit heterogeneous trace element and radiogenic isotope compositions (e.g., epsilon(Nd) from -16 to +2 at 180 Ma) and the involvement of continental lithospheric mantle and/or crust in their petrogenesis has previously been suggested. Importantly, our sample set also includes rare primitive dikes that have been derived from depleted asthenospheric mantle sources (epsilon(Nd) up to + 8 at 180 Ma). The majority of the oxygen isotopic compositions of the olivines from these dike rocks (delta O-18 = 4.4-5.2%; Fo = 78-92 mol%) are also compatible with such sources. The olivine phenocrysts in the lavas, however, are characterized by notably higher delta O-18 (6.2-7.5%; Fo = 70-88 mol%); and one of the dike samples gives intermediate compositions (5.2-6.1%, Fo = 83-87 mol%) between the other dikes and the CFBs. The oxygen isotopic compositions do not correlate with radiogenic isotope compositions susceptible to crustal assimilation (Sr, Nd, and Pb) or with geochemical indicators of pyroxene-rich mantle sources. Instead, delta O-18 correlates positively with enrichments in large-ion lithophile elements (especially K) and Os-187. We suggest that the oxygen isotopic compositions of the Vestfjella CFB olivines primarily record large-scale subduction-related metasomatism of the sub-Gondwanan mantle (base of the lithosphere or deeper) prior to Karoo magmatism. The overall influence of such sources to Karoo magmatism is not known, but, in addition to continental lithosphere, they may be responsible for some of the geochemical heterogeneity observed in the CFBs.Peer reviewe

Raskaat harvinaiset maa-alkuaineet ja laakiobasalttien lähteet

Editor's ChoiceHeavy rare earth elements (HREEs) in mafic and ultramafic volcanic rocks are useful recorders of mantle source processes because their ratios are not easily modified by differentiation. Here we utilize REEBOX PRO, a simulator of adiabatic decompression melting of the mantle, to study the behavior of HREEs in the formation of continental flood basalt (CFB) parental magmas in the mantle. We simulate partial melting of depleted peridotite, pyrolitic peridotite, pyroxenite, and peridotite-pyroxenite mixtures at mantle potential temperatures of 1350-1650 degrees C and lithospheric thicknesses of 50-150 km, and compare the results to natural data. Many large igneous provinces are typified by low-Ti and high-Ti CFBs with contrasting HREE patterns. Our results show that low-Ti CFBs originate mainly from peridotitic sources. Flat mid-ocean ridge basalt-like HREE patterns typical of low-Ti CFBs can be generated beneath thick lithosphere (similar to 100 km), given that mantle potential temperatures are high (>1500 degrees C) and garnet is completely consumed from the source. We thus challenge the common interpretation that flat HREE patterns always indicate shallow sources for CFB parental magmas. High-Ti CFBs require pyroxenite-bearing sources (>= 10%). Contrary to a common view, their steep oceanic island basalt-like HREE patterns can be generated beneath quite a thin lithosphere (similar to 50 km), which is due to increased garnet stability in pyroxenite sources. When applied to CFBs of the Karoo large igneous province, the results are compatible with a model where a mantle plume penetrates a progressively thinning Gondwana lithosphere.Peer reviewe