Lavas or ignimbrites? Permian felsic volcanic rocks of the Tisza Mega-unit (SE Hungary) revisited: A petrographic study.

Permian felsic volcanic rocks were encountered in petroleum exploration boreholes in SE Hungary (eastern Pannonian Basin, Tisza Mega-unit, Békés-Codru Unit) during the second half of the 20th century. They were considered to be predominantly lavas (the so-called "Battonya quartz-porphyry") and were genetically connected to the underlying "Battonya granite." New petrographic observations, however, showed that the presumed lavas are crystal-poor (8-20 vol%) rhyolitic ignimbrites near Battonya and resedimented pyroclastic or volcanogenic sedimentary rocks in the Tótkomlós and the Biharugra areas, respectively. The studied ignimbrites are usually massive, matrix-supported, fiamme-bearing lapilli tuffs with eutaxitic texture as a result of welding processes. Some samples lack vitroclastic matrix and show low crystal breakage, but consist of oriented, devitrified fiammes as well. Textural features suggest that the latter are high-grade rheomorphic ignimbrites.Felsic volcanic rocks in SE Hungary belong to the Permian volcanic system of the Tisza Mega-unit; however, they show remarkable petrographic differences as compared to the other Permian felsic volcanic rocks of the mega-unit. In contrast to the crystal-poor rhyolitic ignimbrites of SE Hungary with rare biotite, the predominantly rhyodacitic-dacitic pyroclastic rocks of the Tisza Mega-unit are crystal-rich (40-45 vol%) and often contain biotite, pyroxene, and garnet. Additionally, some geochemical and geochronological differences between them were also observed by previous studies. Therefore, the Permian felsic volcanic rocks in SE Hungary might represent the most evolved, crystal-poor rhyolitic melt of a large-volume felsic (rhyodacitic-dacitic) volcanic system.The Permian volcanic rocks of the studied area do not show any evident correlations with either the Permian felsic ignimbrites in the Finis Nappe (Apuseni Mts, Romania), as was supposed so far, or the similar rocks in any nappe of the Codru Nappe System. Moreover, no relevant plutonic-volcanic connection was found between the studied samples and the underlying "Battonya granite."

Microbially Mediated Ore-Forming Processes and Cell Mineralization.

Sedimentary black shale-hosted manganese carbonate and oxide ores were studied by high-resolution in situ detailed optical and cathodoluminescence microscopy, Raman spectroscopy, and FTIR spectroscopy to determine microbial contribution in metallogenesis. This study of the Urucum Mn deposit in Brazil is included as a case study for microbially mediated ore-forming processes. The results were compared and interpreted in a comparative way, and the data were elaborated by a complex, structural hierarchical method. The first syngenetic products of microbial enzymatic oxidation were ferrihydrite and lepidocrocite on the Fe side, and vernadite, todorokite, birnessite, and manganite on the Mn side, formed under obligatory oxic (Mn) and suboxic (Fe) conditions and close to neutral pH. Fe- and Mn-oxidizing bacteria played a basic role in metallogenesis based on microtextural features, bioindicator minerals, and embedded variable organic matter. Trace element content is determined by source of elements and microbial activity. The present Urucum (Brazil), Datangpo (China), and Úrkút (Hungary) deposits are the result of complex diagenetic processes, which include the decomposition and mineralization of cell and extracellular polymeric substance (EPS) of Fe and Mn bacteria and cyanobacteria. Heterotrophic cell colonies activated randomly in the microbialite sediment after burial in suboxic neutral/alkaline conditions, forming Mn carbonates and variable cation-bearing oxides side by side with lithification and stabilization of minerals. Deposits of variable geological ages and geographical occurrences show strong similarities and indicate two-step microbial metallogenesis: a primary chemolithoautotrophic, and a diagenetic heterotrophic microbial cycle, influenced strongly by mineralization of cells and EPSs. These processes perform a basic role in controlling major and trace element distribution in sedimentary environments on a global level and place biogeochemical constraints on the element content of natural waters, precipitation of minerals, and water contaminants.

Evidence for oxygen isotopic exchange in chondrules from Kaba (CV3.1) carbonaceous chondrite during aqueous fluid-rock interaction on the CV parent asteroid.

We report on the mineralogy, petrography, and oxygen isotopic compositions of primary olivine and plagioclase/feldspathic mesostases in chondrules and of secondary magnetite and fayalite in chondrules and matrix of an oxidized Bali-like CV3.1 carbonaceous chondrite, Kaba. In this meteorite, compositionally nearly pure fayalite (Fa98-100) associates with hedenbergite (Fs~50Wo~50), magnetite, and Fe,Ni-sulfides. There are several textural occurrences of this mineral paragenesis: (i) coarse-grained intergrowths in interchondrule matrix, (ii) veins starting at the opaque nodules in the peripheries of type I chondrules and crosscutting fine-grained rims around them, and (iii) rims overgrowing olivine of type I and type II chondrule fragments. Oxygen isotopic compositions of fayalite and magnetite are in disequilibrium with chondrule olivines. On a three-isotope oxygen diagram, δ17O vs. δ18O, compositions of olivine plot along primitive chondrule minerals (PCM) line having a slope of ~1.0; deviations from the terrestrial fractionation line, Δ17O = δ17O - 0.52 × Î´18O, range from ~-8‰ to ~-5‰. In contrast, fayalite and magnetite plot along mass-dependent fractionation line with a slope of ~0.5; their δ18O values range from -1 to ~+9‰; Δ17O is nearly constant (average ± 2SE = -1.5±1‰). Oxygen isotopic compositions of chondrule plagioclase and feldspathic mesostases are in disequilibrium with chondrule olivines: they deviate to the right from the PCM line by ~12‰ and plot close to the mass-dependent fractionation line defined by fayalite and magnetite. Based on the mineralogy, petrography, oxygen isotopic compositions of fayalite and magnetite, and the previously published thermodynamic analysis of the fayalite-bearing assemblages in ordinary and carbonaceous chondrites, we conclude that Kaba fayalite and magnetite formed during aqueous fluid-rock interaction at low water/rock ratio (0.1-0.2) and elevated temperatures (~200-300°C) on the CV chondrite parent asteroid. The Δ17O values of Kaba fayalite and magnetite (-1.5±1‰) correspond to Δ17O of aqueous fluid that operated on the CV chondrite parent asteroid and resulted in its alteration. Plagioclase and feldspathic mesostases in Kaba chondrules experienced postcrystallization oxygen isotopic exchange with this 16O-depleted fluid; olivine grains retained their original compositions acquired during chondrule melts crystallization. The inferred oxygen isotopic exchange in Kaba chondrules appear to have not affected their Al-Mg isotope systematics.

A new approach used to explore associations of current Ambrosia pollen levels with current and past meteorological elements.

The paper examines the sensitivity of daily airborne Ambrosia (ragweed) pollen levels of a current pollen season not only on daily values of meteorological variables during this season but also on the past meteorological conditions. The results obtained from a 19-year data set including daily ragweed pollen counts and ten daily meteorological variables are evaluated with special focus on the interactions between the phyto-physiological processes and the meteorological elements. Instead of a Pearson correlation measuring the strength of the linear relationship between two random variables, a generalised correlation that measures every kind of relationship between random vectors was used. These latter correlations between arrays of daily values of the ten meteorological elements and the array of daily ragweed pollen concentrations during the current pollen season were calculated. For the current pollen season, the six most important variables are two temperature variables (mean and minimum temperatures), two humidity variables (dew point depression and rainfall) and two variables characterising the mixing of the air (wind speed and the height of the planetary boundary layer). The six most important meteorological variables before the current pollen season contain four temperature variables (mean, maximum, minimum temperatures and soil temperature) and two variables that characterise large-scale weather patterns (sea level pressure and the height of the planetary boundary layer). Key periods of the past meteorological variables before the current pollen season have been identified. The importance of this kind of analysis is that a knowledge of the past meteorological conditions may contribute to a better prediction of the upcoming pollen season.