Mineralogical and geochemical evidence for multi-stage origin of mineral veins hosted by teschenites at Tichá, Outer Western Carpathians,Czech Republic

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.     

Phytoplankton in the south-western Kara Sea: composition and distribution

The taxonomic composition and spatial distribution of pelagic algae were studied in the south-western Kara Sea in August-September 1981. In the north-western and easternmost regions of the study area the phytoplankton community, dominated by neritic diatoms and autotrophic dinoflagellates, was at the late spring bloom stage of the seasonal succession. In the central deep-water zone of the sea, there was a predominance of heterotrophic dinoflagellates from the genera Protoperidinium and Dinophysis , and the autotrophic compartment of the algal community was clearly in a stage of decline. The distribution of the phytoplankton assemblages followed closely the major routes of receding marginal ice zones. Three stages of the seasonal succession were established for the area of interest: (1) early spring (ice edge) bloom of arcto-boreal neritic diatoms; (2) late spring bloom of neritic diatoms and autotrophic dinoflagellates, fuelled by continental run-off; and (3) summer minimum with a predominance of heterotrophic dinoflagellates, followed by autumnal decline of the phytoplankton community.     

埃达克岩：关于其成因的一些不同观点

埃达克岩的概念是十多年前提出来的,指由俯冲的年轻洋壳熔融形成的火成岩。自从最初在现代岛弧近十几个地方报道埃达克岩以来,新近又在几个地方发现有埃达克岩（如日本西南部,外墨西哥火山岩带,等等）。但是,过去十 多年的研究也表明,埃达克岩可以由俯冲期间的其它过程产生（例如,沿俯冲板片的撕裂边,留在上地幔中的板片残余等）。另外,埃达克岩似乎与一些岩石呈共生组合,这些岩石包括高镁安山岩、富Nb的弦玄武岩（NEAB）,还可能有玻安岩（几个研究者已在玻安岩中发现有埃达克岩的组分）。高镇安山岩不是来自埃达克与地幔的相互作用（Adak-type),就是来自此相互作用期间地幔的熔融（Piip-type);富Nb的弦玄武岩,据认为是来自一种被埃达我岩广泛交代的地幔的部分熔融。作为一个新的岩套,埃达克岩交代火山岩系列已被建议用来解释各种岩石组合。此外,大量的富Pb弧玄武岩也已被发现包含有超镁铁质的地幔包体,而这些包体有高亏损地幔与埃达克反应的明显证据。关于主要与下地壳熔而不是冲板片有关的埃达克岩的起源已提出几种假说,一个模型认为,下地壳熔融出现在玄武质岩浆底侵下地壳时。但是,有许多理由似乎可以排除这种模式。另一种模型认为,在大陆地壳很厚的区域,下地壳可能变成榴辉岩,从而拆离并下沉到地幔中（拆沉）。这个拆沉过程将导致下地壳下中拆沉的下地壳的上部与相对热的地幔接触,进而可引起下地壳熔融和埃达克岩的形成。这使我们认为,在中国东部发现的与俯冲作用无关的白垩纪埃达克可能是下地壳熔融与拆沉作用的产物。我们 还要强调,如果下地壳熔融与拆沉作用真能形成埃达克岩,那么埃达克岩这一术语不应该仅仅局限于与板片熔融有关的过程,而应包括那些与下地壳熔融有关的过程。太古宙的大陆地壳主要由奥长花岗岩、英云闪长岩和英安岩（TTD）组成。这种大陆地壳是来自板片熔融还是下地壳熔融仍是有争议的。然而,我们认为,太古宙期间地幔的较高温度会导致较多的洋中脊的形成,从而产生比今天“更多”的年轻洋壳的俯冲。据此,我们认为,太古宙TTD大陆地宙主要由板片熔融形成。我们也注意到,太古宙是广泛金矿化的时期。有些研究者还发现,金和铜的矿化与埃达克质交代火山岩系列有关。因此,该火山岩系列可能会寻找金属矿床的一个重要标志。     

Russian researchers reach subglacial Lake Vostok in Antarctica

Opening a new scientific frontier lying under the Antarctic ice, Russian researchers have drilled down and finally reached the surface of the gigantic freshwater lake, Lake Vostok. The mission chief likened the achievement to placing a man on the moon. Drilling in the area of the lake began 22 years ago in 1990, but progressed slowly as a result of funding shortages, equipment breakdowns, difficulties of drilling in the ＂warm＂ ice, and environmental concerns. In 1996, six years after drilling was started, a group of Russian and British scientists discovered the lake believed to be one of the largest fresh water reservoirs on the planet. This lake is among the last unexplored places on Earth. Sealed from the Earth＇s atmosphere for millions of years, it may provide vital information about microbial evolution, the past climate of the Earth, and the formation of the Antarctic ice sheet. Russian experts waited several years for international approval of their drilling technology before proceeding. As anticipated, lake water under pressure rushed up the borehole, pushing the drilling fluid up and away, then froze, forming a protective plug that prevented contamination of the lake. In December of the next Antarctic season, 2012--2013, researchers plan to re-drill the frozen sample of subglacial water for analysis.     

The second most disastrous windstorm of the nineteenth century in the Czech Lands, 26-27 October 1870

Theoretical and Applied Climatology - One of the most disastrous windstorms to take place over the Czech Lands occurred on the night of 26/27 October 1870. It is here analysed through the use of...     

Shelf-basin exchange in the Laptev Sea in the warming climate: a model study

GCM-based forecast simulations predict continuously increasing seasonality of the sea ice cover and an almost ice-free, summer-time, Arctic Ocean within several decades from the present. In this study we use a primitive equation ocean model: NEMO, coupled with the sea ice model LIM2, to test the hypothesis that under such an increased range in seasonal ice cover the intensity of shelf-basin water exchange will significantly increase. We use the simulated results for the Laptev Sea from a global model run 1958–2007 and compare results for two years with anomalously high and low summer sea ice extents: 1986–1987 and 2006–2007. The shelf–basin fluxes of volume, heat and salt during specific seasons are evaluated and attributed to plausible driving processes, with particular attention to dense water cascading. Analyses of the model temperature distribution at the depth of the intermediate maximum, associated with Atlantic Water, have shown a marked increase of the amount of the local origin cold water in late winter 2007 in the region, where dense water typically appears as a result of its formation on the shelf and subsequent downslope leakage. Calculation of the shelf-basin exchange during March-May in both years confirmed a substantial increase (a factor of two) of fluxes in “ice-free” 2007 compared to the “icy” 1987. According to several past model studies, dense water production on Arctic shelves in winter driven by ice freezing and brine rejection is not likely to cease in a warmer climate, but rather to increase. There is also observational evidence that cascading in the seasonally ice covered seas (e.g. the Barents Sea) is much more efficient than it is in the permanently ice covered Arctic Ocean, which supports these model results.