Three generations of monazite in Austroalpine basement rocks to the south of the Tauern Window: evidence for Variscan, Permian and Eo-Alpine metamorphic events     

Erwin Krenn  Bernhard Schulz  Fritz Finger 《Swiss Journal of Geoscience》2012,105(3):343-360

Three monazite generations were observed in garnet-bearing micaschists from the Schobergruppe in the basement to the south of the Tauern Window, Eastern Alps. Low-Y monazite of Variscan age (321?±?14?Ma) and high-Y monazite of Permian age (261?±?18?Ma) are abundant in the mica-rich rock matrix and in the outer domains of large garnet crystals. Pre-Alpine monazite commonly occurs as polyphase grains with low-Y Variscan cores and high-Y Permian rims. Monazite of Eo-Alpine age (112?±?22?Ma) is rarer and was observed as small, partly Y-enriched grains (3?wt. %?Y₂O₃) in the rock matrix and within garnet. Based on monazite-xenotime thermometry, Y?+?HREE values in monazite indicate minimum crystallization conditions of 500?°C during the Variscan and 650?°C for the Permian and Alpine events, respectively. Garnet zoning and thermobarometric calculations with THERMOCALC 3.21 record an amphibolite facies, high-pressure stage of ~600?°C/13?C16?kbar, followed by a thermal maximum at 650?C700?°C and 6?C9?kbar. The Eo-Alpine age for these two events is supported by inclusions of Cretaceous monazite in the garnet domains used for thermobarometric constraints and through the high growth temperatures of Eo-Alpine monazite, which is consistent with that of the thermal maximum (~700?°C). The age and growth conditions of a few Mn-rich garnet cores, sporadically present within Eo-Alpine garnet, are unclear because inclusions of monazite, plagioclase and biotite necessary for thermobarometric- and age constraints are absent. However, based on monazite thermometry, Permian and Variscan metamorphic conditions were high enough for the growth of pre-Alpine garnet. The formation of Variscan garnet and its later resorption, plus Y-release, would also explain the high Y in Permian monazite, which cannot originate from preexisting Variscan monazite only. Monazite of Variscan, Permian and/or Eo-Alpine ages were also observed in other garnet-bearing micaschists from the Schobergruppe. This suggests that the basement of the Schobergruppe was overprinted by three discrete metamorphic events at conditions of at least lower amphibolite facies. While the Variscan event affected all parts of this basement, the younger events are more pronounced in its structurally lower units.  相似文献   

Macroscopically‐Zoned Grandite from the Garnetite Skarn of Meka Presedla (Kopaonik Mountain,Serbia)     

Pavle Tan?i?  Predrag Vuli?  Reinhard Kaindl  Bernhard Sartory  Radovan Dimitrijevi? 《《地质学报》英文版》2012,86(2):394-405

The macroscopically-zoned grandite from the garnetite skarn of Meka Presedla (Kopaonik Mountain, Serbia) was studied with optical microscopy, electron microprobe analysis (EMPA), Fourier transform infra-red (FT–IR), and Raman methods. The EMPA results indicate that the main core–rim compositional variations (Ca2.93–2.97Mn0.05–0.06Mg0.00–0.01Al1.14–1.26Fe3+0.72–0.83Ti0.00–0.02Si2.97–3.02O12) slightly differ along the zones, showing evidence for a quasi-cyclic alternation of the oscillatory zoning nature. Among this, considerable variation is observed only by the Al–Fe3+ substitutions in the octahedral site. The EMPA also indicate that the grandite zones compositionally vary, mostly within ±1 and ±2 mol% of the homogeneity level range, that is, Grs64±1Adr36±1Sps2 (A), Grs62±1Adr38±1Sps2 (B), Grs59±2Adr40±2Sps2 (C), Grs58±2Adr41±2Sps2 (D), and Grs58±1Adr41±1Sps2 (E). Therefore, the investigated garnet can be considered as relatively highly homogeneous. The majority of compositions lie within the narrow miscibility region of 0.58±2相似文献   

Submicromolar Oxygen Profiles at the Oxic–Anoxic Boundary of Temperate Lakes     

Mathias K. Kirf  Christian Dinkel  Carsten J. Schubert  Bernhard Wehrli 《Aquatic Geochemistry》2014,20(1):39-57

Elements involved in biogeochemical cycles undergo rapid turnover at the oxic–anoxic interface of stratified lakes. Here, the presence or absence of oxygen governs abiotic and biotic processes and rates. However, achieving a detailed sampling resolution to precisely locate the oxic–anoxic interface is difficult due to a lack of fast, drift-free sensors in the working range of 10 to a few 1,000 nmol O₂ L^?1. Here, we demonstrate that conventional amperometric and optical microsensors can be used to resolve submicromolar oxygen concentrations in a continuous profiling mode. The amperometric drift was drastically reduced by anoxic preconditioning. In situ offset correction in the anoxic layer and a high amplification scheme allowed for an excellent detection limit of < 10 nmol L^?1. The optical microsensors also showed a similar performance with a detection limit of < 20 nmol L^?1. Their drift stability allowed for a laboratory calibration in combination with a minor in situ anoxic offset correction. The two different sensor systems showed virtually identical profiles during parallel use in stratified lakes. Both sensors were able to resolve the fine-scale structure at the oxic–anoxic interface and revealed hitherto unnoticed extended zones of submicromolar oxygen concentrations even below a steep oxycline. The zones extended up to several meters and showed substantial vertical variability. These results underline the need of a precise localization of the oxic–anoxic interface on a submicromolar scale in order to constrain the relevant aerobic and anaerobic redox processes.  相似文献   

Polyphase tectonics and late Variscan extension in Austria (Moldanubian Zone,Strudengau area)     

Helga Zeitlhofer  David Schneider  Bernhard Grasemann  Konstantin Petrakakis  Martin Thöni 《International Journal of Earth Sciences》2014,103(1):83-102

New data suggest syn-convergent extrusion and polyphase tectonics followed by late Variscan extension in the Strudengau area of the southern Moldanubian zone in Austria. The tectonic history can be summarized as follows: (1) The oldest ductile event is observed in HT/LP metamorphic pelitic gneisses, which preserve E-dipping foliation planes (D₁-fabric) with NW–SE-trending lineations. (2) The overlying gneisses record HT/HP conditions with decompression-induced anatexis in the central part of the domain. These gneisses exhibit N–S trending, horizontal lineations along steep-dipping foliation planes (D₂-fabric) crosscutting the D₁-fabric of the pelitic gneisses. Along the margin, these rocks have been strongly mylonitized under amphibolite facies conditions (D₂). D₂ is interpreted as a significant vertical shear zone, which juxtaposes the HT/LP rocks against the orogenic lower crust. (3) Lastly, the whole area is overprinted by localized shear zones (D₃-fabric) with top-to-the-NW kinematics. This newly discovered Strudengau shearing event is associated with isoclinal folding that possesses axial planes parallel to the mylonitic foliation and fold axes parallel to the stretching lineations. Initial mylonitization occurred under greenschist facies, representing the latest ductile event of the Strudengau area. The new geochronological data presented here indicate a narrow time frame (c. 323–318 Ma) for the D₃ deformation. Therefore, this event is contemporaneous with the intrusion of the granites of the South Bohemian Batholith (330–310 Ma). The nearby South Bohemian Batholith and generally steep dyke swarms in the Strudengau area and to the north trend in a NE–SW preferred orientation, interpreted to be D₃-synkinematic magmatism. In a regional context, the NW–SE stretching during D₃ together with the synkinematic intrusion of dykes is associated with late orogenic extension in the Austrian Moldanubian Zone. Kinematic data of brittle normal faults and tension gashes are consistent with NW–SE-oriented extension under cooler conditions.  相似文献   

Geochemistry of highly acidic mine water following disposal into a natural lake with carbonate bedrock     

Christian Wisskirchen  Bernhard Dold  Kurt Friese  Jorge E. Spangenberg  Peter Morgenstern  Walter Glaesser 《Applied Geochemistry》2010

Acid mine drainage (AMD) from the Zn–Pb(–Ag–Bi–Cu) deposit of Cerro de Pasco (Central Peru) and waste water from a Cu-extraction plant has been discharged since 1981 into Lake Yanamate, a natural lake with carbonate bedrock. The lake has developed a highly acidic pH of ∼1. Mean lake water chemistry was characterized by 16,775 mg/L acidity as CaCO₃, 4330 mg/L Fe and 29,250 mg/L SO₄. Mean trace element concentrations were 86.8 mg/L Cu, 493 mg/L Zn, 2.9 mg/L Pb and 48 mg/L As, which did not differ greatly from the discharged AMD. Most elements showed increasing concentrations from the surface to the lake bottom at a maximal depth of 41 m (e.g. from 3581 to 5433 mg/L Fe and 25,609 to 35,959 mg/L SO₄). The variations in the H and O isotope compositions and the element concentrations within the upper 10 m of the water column suggest mixing with recently discharged AMD, shallow groundwater and precipitation waters. Below 15 m a stagnant zone had developed. Gypsum (saturation index, SI ∼ 0.25) and anglesite (SI ∼ 0.1) were in equilibrium with lake water. Jarosite was oversaturated (SI ∼ 1.7) in the upper part of the water column, resulting in downward settling and re-dissolution in the lower part of the water column (SI ∼ −0.7). Accordingly, jarosite was only found in sediments from less than 7 m water depth. At the lake bottom, a layer of gel-like material (∼90 wt.% water) of pH ∼1 with a total organic C content of up to 4.40 wet wt.% originated from the kerosene discharge of the Cu-extraction plant and had contaminant element concentrations similar to the lake water. Below the organic layer followed a layer of gypsum with pH 1.5, which overlaid the dissolving carbonate sediments of pH 5.3–7. In these two layers the contaminant elements were enriched compared to lake water in the sequence As < Pb ≈ Cu < Cd < Zn = Mn with increasing depth. This sequence of enrichment was explained by the following processes: (i) adsorption of As on Fe-hydroxides coating plant roots at low pH (up to 3326 mg/kg As), (ii) adsorption at increasing pH near the gypsum/calcite boundary (up to 1812 mg/kg Pb, 2531 mg/kg Cu, and 36 mg/kg Cd), and (iii) precipitation of carbonates (up to 5177 mg/kg Zn and 810 mg/kg Mn; all data corrected to a wet base). The infiltration rate was approximately equal to the discharge rate, thus gypsum and hydroxide precipitation had not resulted in complete clogging of the lake bedrocks.  相似文献   

Major ion and isotope geochemistry of fluids and gases from coalbed methane and shallow groundwater wells in Alberta,Canada     

Katrina Cheung  Patrick Klassen  Bernhard Mayer  Fariborz Goodarzi  Ramon Aravena 《Applied Geochemistry》2010

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The Valais units in Savoy (France): a key area for understanding the palaeogeography and the tectonic evolution of the Western Alps     

Andrea Loprieno  Romain Bousquet  Stefan Bucher  Stefano Ceriani  Florian H. Dalla Torre  Bernhard Fügenschuh  Stefan M. Schmid 《International Journal of Earth Sciences》2011,100(5):963-992

The Valais units in Savoy (Zone des Brèches de Tarentaise) have been re-mapped in great detail and are subject of combined stratigraphic, structural and petrological investigations summarized in this contribution. The sediments and rare relics of basement, together with Cretaceous age mafic and ultramafic rocks of the Valais palaeogeographical domain, represent the heavily deformed relics of the former distal European margin (External Valais units) and an ocean–continent transition (Internal Valais unit or Versoyen unit) that formed during rifting. This rifting led to the opening of the Valais ocean, a northern branch of the Alpine Tethys. Post-rift sediments referred to as “Valais trilogy” stratigraphically overlie both External and Internal Valais successions above an angular unconformity formed in Barremian to Aptian times, providing robust evidence for the timing of the opening of the Valais ocean. The Valais units in Savoy are part of a second and more external mid-Eocene high-pressure belt in the Alps that sutured the Briançonnais microcontinent to Europe. Top-N D1-deformation led to the formation of a nappe stack that emplaced the largely eclogite-facies Internal Valais unit (Versoyen) onto blueschist-facies External Valais units. The latter originally consisted of, from internal to external, the Petit St. Bernard unit, the Roc de l’Enfer unit, the Moûtiers unit and the Quermoz unit. Ongoing top-N D2-thrusting and folding substantially modified this nappe stack. Post 35 Ma D3 folding led to relatively minor modifications of the nappe stack within the Valais units but was associated with substantial top-WNW thrusting of the Valais units over the Dauphinois units along the Roselend thrust during W-directed indentation of the Adria block contributing to the formation of the arc of the Western Alps.  相似文献   

A catalogue of RR Lyrae stars from the Northern Sky Variability Survey     

Patrick Wils  Christopher Lloyd  Klaus Bernhard 《Monthly notices of the Royal Astronomical Society》2006,368(4):1757-1763

A search for RR Lyrae stars has been conducted in the publicly available data of the Northern Sky Variability Survey. Candidates have been selected by the statistical properties of their variation; the standard deviation, skewness and kurtosis with appropriate limits determined from a sample 314 known RRab and RRc stars listed in the General Catalogue of Variable Stars. From the period analysis and light-curve shape of over 3000 candidates 785 RR Lyrae have been identified of which 188 are previously unknown. The light curves were examined for the Blazhko effect and several new stars showing this were found. Six double-mode RR Lyrae stars were also found of which two are new discoveries. Some previously known variables have been reclassified as RR Lyrae stars and similarly some RR Lyrae stars have been found to be other types of variable, or not variable at all.  相似文献   

Lichenometry in the Cordillera Blanca, Peru: “Little Ice Age” moraine chronology   总被引：1，自引：1，他引：0  

Olga Solomina  Vincent Jomelli  Georg Kaser  Alcides Ames  Bernhard Berger  Bernard Pouyaud 《Global and Planetary Change》2007,59(1-4):225

This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 “Little Ice Age” moraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of “Little Ice Age” moraines. The time of deposition of the most prominent and numerous terminal and lateral moraines on the Pacific-facing side of the Cordillera Blanca (between AD 1590 and AD 1720) corresponds to the coldest and wettest phase in the tropical Andes as revealed by ice-core data. Less prominent advances occurred between AD 1780 and 1880.  相似文献   

Preface     

Bernhard M. Haisch  Marcello Rodonò 《Solar physics》1989,121(1-2):1-2

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