| 1. |
- Jochum, K. P., et al.
(author)
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MPI-DING reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios
- 2006
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In: Geochemistry Geophysics Geosystems. - 1525-2027. ; 7:15 Febr
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Journal article (peer-reviewed)abstract
- [1] We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties ( at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive ( isotope dilution) and comparative bulk ( e. g., INAA, ICPMS, SSMS) and microanalytical ( e. g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.
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| 2. |
- de Hoog, Cees-Jan, 1969, et al.
(author)
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Cretaceous continental subduction and exhumation in the HP/UHP terrane of the eastern Alps, Pohorje Mts., Slovenia: petrological and age constraints.
- 2008
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In: MSG research in progress meeting, Cambridge UK, March 2008. ; Abstracts
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Conference paper (other academic/artistic)abstract
- The metamorphic grade of Cretaceous, so-called “Eo-Alpine” metamorphism in the Eastern Alps reached the highest metamorphic conditions in its southeastern parts, in the Pohorje Mts in Slovenia. The area belongs to the Austroalpine nappe system consisting mostly of medium to high-grade metamorphic rocks of the continental crust. An ultramafic complex comprising serpentinized harzburgites and locally garnet peridotites/pyroxenites occupies the southeastern part of the Pohorje. Eclogites are embedded as lenses in both the continental crust and ultramafic (mantle) rocks. Evidence for UHP metamorphism comes from kyanite-bearing eclogites and garnet peridotites (Janák et al., 2004, 2006). Eclogites can be devided into three groups, namely quartz eclogites, zoisite eclogites and kyanite eclogites. Quartz eclogites contain Grt + Omp + Qz + Rut + Zo, and are interpreted to be metabasalts, having a typical N-MORB composition. Zoisite eclogites contain Omp + Grt + Zo + Phn + Rut + Qz + Ky, whereas kyanite eclogites contain the peak metamorphic assemblage Omp + Grt + Ky + Rut + Zo + Qz. Omphacite commonly contains rods of quartz + amphibole as exsolutions. The content of the Ca-Eskola component is up to 7-8 mol %. Polycrystalline quartz possibly represents former coesite. Geothermobarometry on the peak metamorphic assemblage yields 3.0-3.1 GPa and 760-820 °C, within the stability field of coesite. Relict minerals from a prograde metamorphic stage, with exception of minor amphibole as inclusions in garnet, are not preserved. Retrograde phases involving amphibole, plagioclase, sapphirine, corundum and spinel formed during exhumation. Estimated P-T conditions for sapphirine formation are 0.11-0.12 GPa and 740-780oC, indicative of nearly isothermal exhumation. The protoliths of zoisite and kyanite eclogites were gabbros with compositions similar to those found at mid-oceanic ridges. Kyanite eclogites are found within or in the near vicinity of the ultramafic complex only, and are strongly depleted in LREE (LaN < 0.5, LaN/LuN between 0.05 and 0.3). Possibly they suffered small amounts of partial melting during decompression, following the reaction zo + qz = ky + gt + melt, or alternatively they represent strongly depleted cumulate dikes formed within depleted mantle. Serpentinized peridotites occur within an ultramafic body of 5x1 km in the southeast corner of Pohorje. The body is dominantly composed of cr-spinel-bearing harzburgites, but due to intense serpentinization only few remnants of olivine, orthopyroxene and Cr-spinel are preserved. Large orthopyroxene grains often display oriented clinopyroxene exsolutions and are variably replaced by pargasitic amphibole. From the presence of large (up to 1 cm) bastites we infer that the rocks were coarse-grained. The majority of the rock mass is replaced by serpentine minerals, chlorite, tremolite, magnesite and talc. Rare earth element patterns and high Cr# of spinels (up to 52) are indicative of large degrees of melting similar to those of peridotites found near spreading ridges. Garnet peridotites including garnet lherzolite, garnet websterite and garnetite are found within the ultramafic body and as a small single body further east. They show a polystage evolution. Stage I as spinel peridotite stage is inferred from the presence of Cr- spinel and aluminous pyroxenes. Stage II is a UHPM stage defined by the assemblage Grt + Ol + low-Al Opx + Cpx + Cr-Spi. Garnet formed as exsolutions from high-Al Cpx, coronas around Crspinel, and porphyroblasts. Stage III is a decompression stage with formation of kelyphitic assemblage of high-Al Opx, Al- Spi, Cpx and pargasite. Tremolitie, chlorite, serpentine and talc have been formed during stage IV. Geothermobarometry on stage II assemblage yields PT conditions of around 900 oC and 4 GPa. Continental crustal rocks, which host the above (ultra)mafic rocks, consist of amphibolites, ortho- and paragneisses and schists. They were strongly retrogressed during late-stage fluid introduction at low pressure and high temperature (ca. 700-600 °C and 0.5-1.2 GPa), which led to consumption of phengite and garnet, and the development of a secondary matrix consisting of muscovite, biotite, plagioclase, K-feldspar and occasionally sillimanite and staurolite. Cathodoluminescence images as well as zircon chemistry reveal cores rimmed by newly-formed metamorphic zircon. U-Pb dating (Cameca 1270, Nordsim facilities, Sweden) of zircon cores yielded Permian (286±10, 258±7 Ma) to Triassic (238±7 Ma) concordia ages, which are interpreted to be detrital. Rims of the zircon gave Cretaceous concordant ages between 90 and 94 Ma, with the weighted mean of 91.9±0.5 Ma. A few spots have slightly lower ages averaging to 86.6±1.0 Ma. The zircon rims all exhibit very low Th/U ratio (<0.02) typical of a metamorphic origin. The zircon rims are believed to record the Cretaceous (92-91 Ma) HP/UHP metamorphism, as they have nearly flat HREE patterns (LuN/GdN=1-4) and only small negative Eu anomalies, which indicate growth in the presence of garnet and absence of plagioclase, and is corroborated by the presence of garnet inclusions in the zircon rims. In contrast, older core domains have much steeper REE patterns and variable negative Eu anomalies, consistent with growth at low-pressure conditions. According to pseudosection modelling, the main growth of zircon occurred during the prograde path close to the P-T peak and continued during nearly isothermal decompression down to ca. 15 kbars, as indicated by pyrope-rich garnet overgrown by the zircon and instability of plagioclase above 15 kbars. Younger ages, down to 77 Ma, probably resulted from lead loss. The 91.9±0.5 Ma zircon age obtained in this study is nearly identical with that of peak metamorphism determined in the Pohorje eclogites using U/Pb ID-TIMS zircon (90.7±1.0 Ma) and Sm-Nd garnet-whole rock (90.7±3.9 and 90.1±2.0 Ma) dating (Miller et al. 2005). Hence, the eclogites with their country rocks were subducted and exhumed together as a coherent piece of continental crust, together with the Lower Austroalpine units from the Koralpe and Saualpe in the Austrian Eastern Alps of similar composition and age (Thöni and Miller, 1996). There is no evidence for a mélange-like rock assemblage that followed different P-T-t paths or several subduction/exhumation cycles as proposed for some other HP/UHP terranes. Sinking of the mantle and lower crustal wedge initially overlying the UHP rocks into the
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| 3. |
- de Hoog, Cees-Jan, 1969, et al.
(author)
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Oxidized sulfur-rich mafic magma at Mount Pinatubo, Philippines
- 2004
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In: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 146:6, s. 750-761
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Journal article (peer-reviewed)abstract
- Basaltic fragments enclosed in andesitic dome lavas and pyroclastic flows erupted during the early stages of the 1991 eruption of Mount Pinatubo, Philippines, contain amphiboles that crystallized during the injection of mafic magma into a dacitic magma body. The amphiboles contain abundant melt inclusions, which recorded the mixing of andesitic melt in the mafic magma and rhyolitic melt in the dacitic magma. The least evolved melt inclusions have high sulfur contents (up to 1,700 ppm) mostly as SO4 2?, which suggests an oxidized state of the magma (NNO+1.4). The intrinsically oxidized nature of the mafic magma is confirmed by spinel?olivine oxygen barometry. The value is comparable to that of the dacitic magma (NNO+1.6). Hence, models invoking mixing as a means of releasing sulfur from the melt are not applicable to Pinatubo. Instead, the oxidized state of the dacitic magma likely reflects that of parental mafic magma and the source region in the sub-arc mantle. Our results fit a model in which long-lived SO2 discharge from underplated mafic magma accumulated in the overlying dacitic magma and immiscible aqueous fluids. The fluids were the most likely source of sulfur that was released into the atmosphere during the cataclysmic eruption. The concurrence of highly oxidized basaltic magma and disproportionate sulfur output during the 1991 Mt. Pinatubo eruption suggests that oxidized mafic melt is an efficient medium for transferring sulfur from the mantle to shallow crustal levels and the atmosphere. As it can carry large amounts of sulfur, effectively scavenge sulfides from the source mantle and discharge SO2 during ascent, oxidized mafic magma forms arc volcanoes with high sulfur fluxes, and potentially contributes to the formation of metallic sulfide deposits.
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| 5. |
- de Hoog, Cees-Jan, 1969, et al.
(author)
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Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry.
- 2010
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In: Chemical Geology. - 0009-2541. ; 270:1-4, s. 196-215
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Journal article (peer-reviewed)abstract
- Trace-element compositions of olivine from 75 mantle rocks of diverse origin, including xenoliths from kimberlites, basaltic lavas and orogenic peridotites,were determined by laser ablation ICP-MS to study systematic variations between mantle lithologies, partitioning mechanisms in olivine and their potential for geothermobarometry and unravelling mantle processes. Samples were selected to cover a wide range of forsterite contents (89.1–93.4), equilibration temperatures and pressures (750–1450 °C; 15–80 kbar). Trace elements in olivine can be divided into three groups. Group I elements (Ni,Mn, Co, Cu, Zn and Li) showsmall concentration ranges and olivine is the major host mineral. These are mostly divalent elements and have ionic radii close to that of Mg. Group II elements (Cr, Al, V, Sc, Ca and Na) show large concentration ranges, which are mainly controlled by the equilibration temperature of the host rock. The elements are strongly concentrated in co-existing mantle minerals (garnet, clinopyroxene and spinel) and show a narrow range of bulk rock concentrations. They fit less comfortably in the olivine lattice than Group I elements because of their charge or size. Differences between garnet and spinel-facies rocks are apparent for Al, Ca and Sc. Group III elements (Ti, Zr, Nb and Y) show large ranges of concentration in olivine as well as in co-existing minerals, and are strongly dependent on bulk rock contents. Concentration differences between olivine from garnet and spinel-facies rocks are apparent for all these elements. They are strongly incompatible in olivine and other rock-forming mantle minerals because of their charge or size. Various mantle lithologies can be discriminated using olivine composition. Spinel, garnet and garnet–spinel peridotites can be distinguished in olivine Sc–Zr and MnO–Al2O3 diagrams, whereas volcanic olivine is distinguished by high Ca and Al contents (picritic olivine) or high Nb contents (kimberlitic olivine). Since concentrations of Group III elements in olivine are diagnostic ofwhole-rock contents they can be used to trace the petrogenetic history of the rock. For instance, Ti contents and Cr# (Cr/(Cr+Al)) of olivine correlate with the amount of melt extracted from a mantle residue, although refertilisation may subsequently have increased Ti contents in high-T peridotites from the base of the lithosphere. The olivine dataset can be used to examine substitution reactions. Uptake of Al and Cr appears to be largely charge-balanced by Na in garnet-facies olivine, and olivine Cr# strongly correlates with that of co-existing minerals, in particular clinopyroxene and spinel. In spinel-facies olivine a large excess of trivalent cations is present in olivine, which can be fully attributed to excess Al. This suggests a Tschermak-style substitution, in which replacement of Mg by Al in the octahedral site is charge-balanced by replacement of Si by Al in the tetrahedral site. Partition coefficients of Group II elements are highly temperature sensitive with most of the element variability being shownby olivine. This allows the definition of simple geothermometers based solely on the concentrations of these elements in olivine. The mostwidely applicable of these is Al-in-olivine for garnet peridotites, following the expression with P in kbar, Alol the Al concentration of olivine in ppm, and Cr#ol is Cr/(Cr+Al) in olivine. This thermometer predicts the temperature with a residual of 15 °C based on calibration with two-pyroxene and Al-in-opx geothermobarometers (Brey and Köhler, 1990). Although calibrated using lherzolite, it performs well for clinopyroxene-free harzburgites and also spinel peridotites. An alternative thermometer is presented for the case where the presence of Cr2+ is expected, e.g., for olivine inclusions in diamonds. The geochemical and thermobarometric information recorded by olivine can be a useful tool in studies of the petrogenesis of lithospheric mantle, olivine xenocrysts in mantle-derived magmas, the formation of diamonds and diamond exploration using detrital olivine.s only, the thermometer
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| 7. |
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| 8. |
- de Hoog, Cees-Jan, 1969, et al.
(author)
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Vapour-phase crystallisation of silica from SiF4-bearing volcanic gases
- 2005
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In: Geophysics. ; 48:(4-5), s. 775-785
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Journal article (peer-reviewed)abstract
- Thermodynamic modelling of magmatic gases shows that SiF4 may be an important F-bearing species at the high pressures typical of magma reservoirs. Upon decompression during degassing, SiF4 will react with water vapour to form HF and silica. Common magmatic gases of high-T fumaroles seem to contain too little SiF4 to be a significant source of silica, except if extremely large amounts of gas percolate through a small volume of rock, as is the case in lava domes. Only if fluorine contents of the gases exceed 1 mol% detectable amounts of silica may be formed, but such high fluorine contents have not yet been observed in natural gases. Alternatively, silica may be formed by heating of cool SiF4-rich gases circulating in cooling lava bodies. We suggest that these mechanisms may be responsible for the deposition of crystalline silica, most probably cristobalite, observed in vesicles in lavas from Lewotolo volcano (Eastern Sunda Arc, Indonesia). Silica occurs as vapour-crystallised patches in vesicles, and is sometimes associated with F-phlogopite, which further supports F-rich conditions during deposition. Because of the connection between F-rich conditions and high-K volcanism, we propose that late-stage gaseous transport and deposition of silica may be more widespread in K-rich volcanoes than elsewhere, and long-term exposure to ash from eruptions of such volcanoes could therefore carry an increased risk for respiratory diseases. The dependence of SiF4/HF on temperature reported here differs from the current calibration used for temperature measurements of fumarolic gases by remote sensing techniques, and we suggest an updated calibration.
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| 9. |
- Gilbert, M. Thomas P., et al.
(author)
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Paleo-Eskimo mtDNA genome reveals matrilineal discontinuity in Greenland
- 2008
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 320:5884, s. 1787-1789
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Journal article (peer-reviewed)abstract
- The Paleo- Eskimo Saqqaq and Independence I cultures, documented from archaeological remains in Northern Canada and Greenland, represent the earliest human expansion into the New World's northern extremes. However, their origin and genetic relationship to later cultures are unknown. We sequenced a mitochondrial genome from a Paleo- Eskimo human by using 3400- to 4500- year- old frozen hair excavated from an early Greenlandic Saqqaq settlement. The sample is distinct from modern Native Americans and Neo- Eskimos, falling within haplogroup D2a1, a group previously observed among modern Aleuts and Siberian Sireniki Yuit. This result suggests that the earliest migrants into the New World's northern extremes derived from populations in the Bering Sea area and were not directly related to Native Americans or the later Neo- Eskimos that replaced them.
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| 10. |
- Janak, M., et al.
(author)
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Eclogite-hosting metapelites from the Pohorje Mountains (Eastern Alps): P-T evolution, zircon geochronology and tectonic implications
- 2009
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In: European Journal of Mineralogy. - : Schweizerbart. - 0935-1221.
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Journal article (peer-reviewed)abstract
- Abstract: Phase-equilibrium modelling, geothermobarometry, ion-microprobe dating and mineral chemistry of zircon have been used to constrain the P–T–t evolution of metapelitic kyanite-bearing gneisses from the ultrahigh-pressure (UHP) metamorphic terrane of the Pohorje Mountains in the Eastern Alps. These eclogite-hosting rocks are part of the continental basement of the Austroalpine nappes. Based on calculated phase diagrams in the system Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O (NCKFMMnASH) and conventional geothermobarometry, the garnet-phengite-kyanite-quartz assemblages of gneisses record metamorphic conditions of 2.2–2.7 GPa at 700–800 C. These are considered as minima because of the potential for a diffusion-related modification and reequilibration of the garnet and phengite during early stages of decompression. It is therefore most likely that the gneisses experienced the same peak UHP metamorphism at 3 GPa as associated kyanite eclogites. Decompression and cooling to 0.5 GPa and 550 C led to the consumption of garnet and phengite, and the development of matrix consisting of biotite, plagioclase, K-feldspar sillimanite and staurolite. Textures and phase diagrams suggest a low extent of partial melting during decompression. Cathodoluminescence images as well as zircon chemistry reveal cores encompassed by two types of metamorphic zircon rims. Ion probe U-Pb dating of three zircon cores yielded Permian (286 10, 258 7 Ma) and Triassic (238 7 Ma) concordia ages. The zircon rims are Cretaceous with a mean concordia age of 92.0 0.5 Ma and some cores gave a similar age. The Cretaceous zircons all exhibit very low Th/U ratio (,0.02) typical of metamorphic origin. In these zircons, nearly flat HREE patterns, (Lu/Gd)N ¼ 1–4, and only small negative Eu anomalies indicate formation in the presence of garnet and absence of plagioclase, which is corroborated by occurrence of Mg- and Ca-rich garnet inclusions. Therefore, these zircons are interpreted to record the Cretaceous HP/UHP metamorphism. The 92.0 0.5 Ma age obtained in this study agrees with that (93–91 Ma) determined earlier in the Pohorje eclogites from U/Pb zircon, Sm-Nd and Lu-Hf garnet-whole-rock dating. This implies that the eclogites and their country rocks were subducted and exhumed together as a coherent piece of continental crust. There is no evidence for a me´lange-like assemblage of rocks, which followed different P–T–t paths, or several subduction and exhumation cycles as proposed for some other UHP metamorphic terranes.
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