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891.
Zdeněk Dolníček Kamil Kropáč Pavel Uher Martin Polách 《Chemie der Erde / Geochemistry》2010,70(3):267-282
Numerous mineral veins are hosted in a body of teschenite which is situated within the Lower Cretaceous flysch siliciclastics of the Silesian Unit at Tichá. Mineralogy, fluid inclusions, stable isotopes and trace elements have been studied in order to assess the origin of this mineralization. Three stages of vein cementation have been recognized, each of them being characterized by distinct mineral composition and genetic conditions. The first stage is composed of titanite, aegirine-augite to aegirine, annite, analcime and strontian apatite. These minerals originated from NaCl-rich, CaCl2-poor magmatic brine (total fluid salinities range between 47 and 57 wt%), leaving after crystallization of host teschenite in low-pressure (<1 kbar) environment. Crystallization temperatures reached ~390–510 °C for early phases, titanite and aegirine-augite. The second stage is formed by calcite, chlorite, dolomite, siderite, strontianite, quartz, pyrite and sphalerite. The parent fluids were low-salinity (0.5–4.5 wt% NaCl eq.) aqueous solutions with low content of strong REE-complexing ligands, that were progressively cooled during mineral precipitation (up to ~190 °C at the beginning, ~90 °C at the end of crystallization). These fluids are interpreted to be predominantly of external origin, derived from surrounding sedimentary sequences during diagenetic dewatering of clay minerals. The highly positive δ18O and near-zero δ13C values indicate an interaction of fluids with sedimentary carbonates. The third stage is formed by a dense net of calcite veinlets, which probably originated during tectonic deformations connected with orogenetic movements during the Tertiary. The source of strontium for first stage mineralization was probably related to the special conditions of magmatic evolution of the host teschenite, whereas strontium for second stage minerals could have been remobilized during hydrothermal alteration from earlier teschenite-hosted mineral phases and/or limestone. 相似文献
892.
Jaromír Ulrych Emil Jelínek Zdeněk Řanda Felicity E. Lloyd Kadosa Balogh Ernst Hegner Jiří K. Novák 《Chemie der Erde / Geochemistry》2010,70(4):319-333
High-Ti melanephelinite (3.8–5.9 wt% TiO2), medium-Ti (phono)tephrite (2.7–3.1 wt% TiO2), and low-Ti olivine melanephelinite/basanite (1.9–2.3 wt.% TiO2) are subordinate rock types in the central European Cenozoic Volcanic Province. A contrasting melanephelinite to (phono)tephrite series occurs in the Lou?ná–Oberwiesenthal Volcanic Centre (37–28 Ma) and also as satellite volcanic bodies (26–12 Ma) together with olivine melanephelinite/basanite (17–20 Ma) on the southwestern periphery of the Kru?né hory mountains (Erzgebirge). The volcanic rocks intrude the Variscan basement of the uplifted shoulder of the Oh?e/Eger Rift in the Kru?né hory mountains of the Bohemian Massif. Low Mg# (44–59) and Cr, Ni contents and enrichment of LILE, Zr, Hf, Nb, Ta, U, Th and LREE in the high-Ti melanephelinites contrast with the composition of primitive low-Ti olivine melanephelinites/basanites displaying high Mg# (63–74) and high contents of compatible elements. The high-Ti melanephelinites reveal a wide range in initial 87Sr/86Sr of ca. 0.7034–0.7038 and εNd of 2.4–4.9. The low-Ti melanephelinites show an overlapping range of initial 87Sr/86Sr of ca. 0.7035–0.7036 and εNd of 4.3–5.5. The large variation in initial 87Sr/86Sr ratios at similar εNd values in those rock types is interpreted as evidence for melting of metasomatized lithospheric mantle sources comprising K-bearing phases with radiogenic Sr. Modification of the olivine-free alkali basaltic magmas by differentiation or crustal contamination could give rise to the medium-Ti (phono) tephrites. The initial isotope ratios of all samples are consistent with HIMU-mantle sources and contributions from lithospheric mantle. The olivine-free melanephelinitic rocks often contain alkali pyroxenite–ijolite xenoliths with initial 87Sr/86Sr ratios of ca. 0.7036 and εNd of 3.0. We interpret these xenoliths as samples of an intra-crustal alkali complex derived from similar mantle sources as those for the basaltic volcanic rocks. 相似文献
893.
The central zone of the Miocene Štiavnica stratovolcano hosts several occurrences of Cu–Au skarn–porphyry mineralisation,
related to granodiorite/quartz–diorite porphyry dyke clusters and stocks. Vysoká–Zlatno is the largest deposit (13.4 Mt at
0.52% Cu), with mineralised Mg–Ca exo- and endoskarns, developed at the prevolcanic basement level. The alteration pattern
includes an internal K- and Na–Ca silicate zone, surrounded by phyllic and argillic zones, laterally grading into a propylitic
zone. Fluid inclusions in quartz veinlets in the internal zone contain mostly saline brines with 31–70 wt.% NaCl eq. and temperatures
of liquid–vapour homogenization (Th) of 186–575°C, indicating fluid heterogenisation. Garnet contains inclusions of variable
salinity with 1–31 wt.% NaCl eq. and Th of 320–360°C. Quartz–chalcopyrite veinlets host mostly low-salinity fluid inclusions
with 0–3 wt.% NaCl eq. and Th of 323–364°C. Data from sphalerite from the margin of the system indicate mixing with dilute
and cooler fluids. The isotopic composition of fluids in equilibrium with K-alteration and most skarn minerals (both prograde
and retrograde) indicates predominantly a magmatic origin (δ18Ofluid 2.5–12.3‰) with a minor meteoric component. Corresponding low δDfluid values are probably related to isotopic fractionation during exsolution of the fluid from crystallising magma in an open
system. The data suggest the general pattern of a distant source of magmatic fluids that ascended above a zone of hydraulic
fracturing below the temperature of ductile–brittle transition. The magma chamber at ∼5–6 km depth exsolved single-phase fluids,
whose properties were controlled by changing PT conditions along their fluid paths. During early stages, ascending fluids
display liquid–vapour immiscibility, followed by physical separation of both phases. Low-salinity liquid associated with ore
veinlets probably represents a single-phase magmatic fluid/magmatic vapour which contracted into liquid upon its ascent. 相似文献
894.
AbstractThe solar backscattered ultraviolet (SBUV/SBUV-2) merged ozone datasets, version 8.6, including column ozone and ozone profiles for the 1979–2012 period are examined for the 35°N–60°N zonal belt in the northern hemisphere mid-latitudes and four sub-regions: central Europe, continental Europe, North America, and East Asia. The residual long-term patterns for total ozone and ozone profiles are extracted by smoothing the time series of differences between the original and the modelled ozone time series. Modelled ozone is obtained using the standard trend model accounting for ozone variability due to changes in stratospheric halogens and various dynamical factors commonly used in previous ozone trend analyses. Since about 2005 spring and summer total ozone in the troposphere and lower stratosphere has decreased in some regions (central and continental Europe, North America, and the 35°N–60°N zonal belt) compared with modelled ozone. The negative departure from modelled ozone in 2010 is approximately 2–3% of the overall 1979–2012 monthly mean level. It seems that this decrease is a result of yet unknown dynamical processes rather than to chemical destruction because the differences have a longitudinal structure, and total ozone in the upper stratosphere still follows changes in stratospheric halogen loading. 相似文献
895.
To study impacts of climate variations on cropproduction, the growth models are used to simulateyields in present vs. changed climate conditions.Met&Roll is a four-variate (precipitation amount,solar radiation, minimum and maximum temperatures) stochasticweather generator used to supply synthetic dailyweather series for the crop growth model CERES-Maize.Three groups of experiments were conducted in thisstudy: (1) Validation of Met&Roll reveals some discrepanciesin the statistical structure of synthetic weatherseries, e.g., (i) the frequency of occurrence of longdry spells, extreme values of daily precipitationamount and variability of monthly means areunderestimated by the generator; (ii) correlations andlag-1 correlations among weather characteristicsexhibit a significant annual cycle not assumed by themodel. On the whole, the best fit of the observed andsynthetic weather series is experienced in summermonths. (2) The Wilcoxon test was employed to comparedistributions of maize yields simulated with use ofobserved vs. synthetic weather series. As nostatistically significant differences were detected,it is assumed that the generator imperfections inreproducing the statistical structure of weatherseries negligibly affect the model yields. (3) Thesensitivity of model yields to selectedcharacteristics of the daily weather series wasexamined. Emphasis was placed on the characteristicsnot addressed by typical GCM-based climate changescenarios: daily amplitude of temperature, persistenceof the weather series, shape of the distribution ofdaily precipitation amount, and frequency ofoccurrence of wet days. The results indicate that someof these characteristics may significantly affect cropyields and should therefore be considered in thedevelopment of climate change scenarios. 相似文献
896.
897.
The influence of Zn speciation on Zn transport by drainage from different soils to surface water is examined in a stream catchment
in an agricultural area. Drainage waters were collected from two types of soils, a mineral soil (MS) and a soil rich in organic
matter (OS) by means of artificial drainage pipes. The speciation of dissolved Zn in the stream and the drainage waters was
determined using ligand-exchange and voltammetry. About 50–95% of dissolved Zn is bound in strong complexes, and the free
Zn2+ ion concentration is in the range of 1–16% of dissolved Zn. A substantial part of Zn is present in weaker organic or inorganic
complexes. The simulated Zn speciation using the WHAM VI model is compared to the determined speciation. Free Zn2+ concentrations predicted by the WHAM VI model are generally higher than the analytically determined free Zn2+, but are mostly within the same order of magnitude. Effects of different soil organic matter content on Zn speciation and
transport are discussed. Zn speciation in the drainage at the OS site is influenced by the distribution of organic matter
between the solid and solution phase. The abundant organic Zn complexes in solution contribute to facilitate Zn transport
from soil into surface waters, through the drainage at the OS site. Drainage from the OS site contributes about twice as much
Zn input to the receiving water as the MS soil, as related to specific area. The mineral soil contains much lower organic
matter, and a part of Zn bound with inorganic phases can hardly be released by dissolved organic ligands, leading to much
higher Zn retention at the MS site. 相似文献