Fluid geochemistry in the Ivigtut cryolite deposit, South Greenland     

Jasmin Khler  Jens Konnerup-Madsen  Gregor Markl 《Lithos》2008,103(3-4):369-392

The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na₃AlF₆] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO₂, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO₂ and H₂O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ¹³C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ¹⁸O of CO₂ (+ 21 to + 42‰ VSMOW) and δ¹⁸O of H₂O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H₂O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.  相似文献   

Podnebí Ĉeskoslovenské socialistické republiky. Tabulky. Das Klima der Tschechoslowakischen sozialistischen Republik. Tabellen     

Alois Gregor 《Studia Geophysica et Geodaetica》1962,6(3):314-314

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Advances in Vent, Seep, Whale- and Wood-Fall Biology     

Lisa A. Levin  James P. Barry  Horst Felbeck  Craig R. Smith  & Craig M. Young 《Marine Ecology》2007,28(1):1-2

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Colonization, succession, and nutrition of macrobenthic assemblages in a restored wetland at Tijuana Estuary, California     

Serena M. Moseman  Lisa A. Levin  Carolyn Currin  Charlotte Forder   《Estuarine, Coastal and Shelf Science》2004,60(4):755-770

Modes of colonization, the successional trajectory, and trophic recovery of a macrofaunal community were analyzed over 19 months in the Friendship marsh, a 20-acre restored wetland in Tijuana Estuary, California. Traditional techniques for quantifying macrofaunal communities were combined with emerging stable isotopic approaches for evaluation of trophic recovery, making comparisons with a nearby natural Spartina foliosa habitat. Life history-based predictions successfully identified major colonization modes, although most taxa employed a variety of tactics for colonizing the restored marsh. The presence of S. foliosa did not seem to affect macrofaunal colonization or succession at the scale of this study. However, soil organic matter content in the restored marsh was positively correlated with insect densities, and high initial salinities may have limited the success of early colonists. Total macrofaunal densities recovered to natural marsh levels after 14 months and diversity, measured as species richness and the Shannon index (H′), was comparable to the natural marsh by 19 months. Some compositional disparities between the natural and created communities persisted after 19 months, including lower percentages of surface-feeding polychaetes (Polydora spp.) and higher percentages of dipteran insects and turbellarians in the Friendship marsh. As surficial structural similarity of infaunal communities between the Friendship and natural habitat was achieved, isotopic analyses revealed a simultaneous trajectory towards recovery of trophic structure. Enriched δ¹³C signatures of benthic microalgae and infauna, observed in the restored marsh shortly after establishment compared to natural Spartina habitat, recovered after 19 months. However, the depletion in δ¹⁵N signatures of macrofauna in the Friendship marsh indicated consumption of microalgae, particularly nitrogen-fixing cyanobacteria, while macroalgae and Spartina made a larger contribution to macrofaunal diets in the natural habitat. Future successional studies must continue to develop and employ novel combinations of techniques for evaluating structural and functional recovery of disturbed and created habitats.  相似文献   

Third international conference on “Current Problems in Optics of Natural Waters” (ONW’2005)     

I. M. Levin  O. V. Kopelevich  V. Yu. Osadchii 《Oceanology》2007,47(1):141-143

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A quasi-one-dimensional velocity regime of super-thermal electron stream propagation through the solar corona     

B. N. Levin 《Solar physics》1984,92(1-2):317-328

The propagation of an inhomogeneous-stream of fast electrons through the corona-the type III radio burst source - is considered. It is shown, that the angular spectrum width of plasma waves excited by the stream is defined both by Landau damping by particles of the diffuse component and by damping (in the region of large phase velocities) by particles of the stream itself having large pitch angles. The regime of quasi-one-dimensional diffusion in the velocity space is realized only in the presence of a sufficiently dense diffuse component of super-thermal particles and only for a sufficiently large inhomogeneity scale of the stream. A large scale of the stream space profile is formed, evidently, close to the region of injection of super-thermal particles. It is the result of stripping of part of the electrons from the stream front to its slower part due to essential non-one-dimensionality of the particle diffusion in velocity space.Results obtained may explain, in particular, the evolution of a stream particle angular spectrum in the generation region of type III radio bursts observed by spacecrafts (Lin et al., 1981). For the relatively low energetic part of the stream, the oblique plasma wave stabilization by a diffuse component results in a quasi-one-dimensional regime of diffusion. The latter conserves the beam-like structure of this part of the stream.  相似文献   

Seismic hazard monitoring in Kamchatka and its applications to the M = 6.6 earthquake of 6 October 1987     

V. M. Zobin  E. I. Gordeev  V. F. Bakhtiarov  E. I. Ivanova  Yu. M. Khatkevich  V. N. Khodenko  V. E. Levin  V. P. Mityakin 《Natural Hazards》1992,6(1):51-70

The earthquake of 6 October 1987 (M = 6.6), which occurred near the Shipunsky Cape, Kamchatka, was the largest crustal event in the vicinity of the main city of Kamchatka — Petropavlovsk-Kamchatsky — during the last three decades. It was followed by numerous aftershocks. This earthquake allowed us to test the effectiveness of the seismic hazard monitoring in Kamchatka, including the seismological, geodetic and hydrogeochemical surveys. The seismic survey provided the location and source nature of the main shock and aftershocks and the seismic environment of the main shock. The geodetic and hydrogeochemical surveys have yielded data on the response to earthquakes of the Earth's surface deformations, water level, and chemical elements concentration in the underground water. As a result, the following data were obtained:

u

The earthquake of 6 October had a seismic moment 4–10 E18 Nm, thrust type of faulting and the source volume of 20 × 20 × 10 km³. The maximum intensity was VI–VII (MSK-64 scale) and maximum acceleration 88 cm/s².

Before this event, a relative increase in the number of the upper mantle (depth more than 100 km) moderate magnitude earthquakes during 5 years and a one-year period of seismic quiescence for small shallow earthquakes, were recognized. Significant anomalies in HCO₃ and H₃BO₃ concentrations in the underground waters were observed in the wells a week before the main shock.

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Quantification of mixing processes in ore-forming hydrothermal systems by combination of stable isotope and fluid inclusion analyses     

Gregor Schwinn  Baldorj Baatartsogt  Gregor Markl 《Geochimica et cosmochimica acta》2006,70(4):965-982

In the Schwarzwald area, southwest Germany, more than 400 hydrothermal veins hosting different gangue and ore mineral assemblages cross-cut the crystalline basement rocks. Many of the post-Variscan fluorite-barite-quartz veins are considered to have precipitated through mixing of a deep saline brine with meteoric, low salinity waters. This hypothesis was tested using carbon, sulfur, and oxygen isotope data of sulfides, sulfates and calcite, coupled with fluid inclusion studies. Primary hydrothermal calcites from the deposits show a positive correlation of their δ¹³C (V-PDB) and δ¹⁸O (V-SMOW) values, which range from −12 to −3‰ and from 12 to 18.5‰, respectively. Carbon and oxygen isotope compositions of paragenetically young, remobilized calcite types are shifted towards higher values and range from −12 to −1‰ and from 20 to 25‰, respectively. We developed an improved calculation procedure for modeling the covariation of carbon and oxygen isotopes in calcite resulting from mixing of two fluids with different isotopic compositions and total carbon concentrations. In our model, the carbon speciation in the two model fluid end-members and the fluid mixtures are calculated using a speciation and reaction path code. The carbon and oxygen isotope covariation of primary Schwarzwald calcites can effectively be modeled by a mixing trend of a deep saline brine and a meteoric, low salinity water. Sulfur isotope data of barites from 44 hydrothermal fluorite-barite-quartz veins vary from 9 to 18‰ (CDT), sulfide ore minerals show δ³⁴S values between −14.4 and 2.9‰. Calculated sulfide-sulfate equilibrium temperatures are in the range between 300 and 350 °C. These temperatures differ significantly from the formation temperatures of 150 to 200 °C of most of the deposits as estimated from fluid inclusions, and are interpreted as preserved paleotemperatures of the deep aquifer. This assumption has been carefully checked against possible contamination of an equilibrated sulfide-sulfate system from the deep aquifer with sulfate from surface-derived sources, considering also the kinetics of the sulfide-sulfate isotope exchange. A combination of the S isotopic results with microthermometric fluid inclusion data and constraints on the temperature of the meteoric water was used to calculate mixing ratios of the two fluid end-members. The results indicate that mass fractions of the deep saline brine in the mixed fluid were between 0.5 and 0.75. Considering all geologic, geochemical and isotopic information, we propose that the majority of the post-Variscan hydrothermal veins in the Schwarzwald area were precipitated by district-scale mixing of a homogeneous deep saline brine with meteoric waters.  相似文献   

A new astrobleme in the Pacific Ocean     

B. W. Levin  E. V. Gretskaya  G. S. Nemchenko 《Doklady Earth Sciences》2006,411(1):1336-1338

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Influence of oxygen fugacity on mineral compositions in peralkaline melts: The Katzenbuckel volcano, Southwest Germany     

Ute Mann  Michael Marks  Gregor Markl   《Lithos》2006,91(1-4):262-285

The igneous rocks of the Katzenbuckel, Southwest Germany, represent a unique and unusual alkaline to peralkaline association within the European Volcanic Province. The magmatic activity can be subdivided into two main phases. Phase I comprises the main rock bodies of phonolite and nepheline syenite, which were later intruded by different peralkaline dyke rocks (tinguaites and alkali feldspar syenite dykes) of phase II. The dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late-stage pneumatolytic activity causing autometasomatic alterations.

As is typical for alkaline to peralkaline igneous rocks, early mafic minerals of phase I rocks comprise olivine, augite and Fe–Ti oxides, which are substituted in the course of fractionation by Na-amphibole and Na-pyroxene. For the early magmatic stage, calculated temperatures range between 880 and 780 °C with low silica activities (0.4 to 0.6) but high relative oxygen fugacities between 0.5 and 1.9 log units above the FMQ buffer. Even higher oxygen fugacities (above the HM buffer) are indicated for the autometasomatic alteration, which occurred at temperatures between 585 and 780 °C and resulted in the formation of pseudobrookite and hematite.

The unusually high oxygen fugacities (even during the early magmatic stage) are recorded by the major element compositions of the mafic minerals (forsterite content in olivine between 68 and 78 mol%, up to 6.2 wt.% ZrO₂ and 8.5 wt.% TiO₂ in clinopyroxene), the unusual mineral assemblages (pseudobrookite, freudenbergite) and by the enrichment of Fe³⁺ in the felsic minerals (up to 2.8 wt.% Fe₂O₃ in alkali feldspar and up to 2.6 wt.% Fe₂O₃ in nepheline). These observations point to a metasomatically enriched and highly oxidized lithospheric mantle as a major source for the Katzenbuckel melts.  相似文献