Genetic concepts on the formation of the Austrian magnesite and siderite mineralizations in the Eastern Alps of Austria

A consanguineous origin of the sparry siderite and magnesite mineralizations of the Eastern Alps has been repeatedly discussed in the past, often without the back-up of sound scientificarguments. Here, it is shown that the characteristics of these mineralizations including structures, fluid parameters, timing etc. are amazingly similar suggesting in fact the genetic linkage of these deposits. The siderite as well as the magnesite mineralizations of the Eastern Alps exhibit metasomatic-epigenetic structures of lens-shaped orebodies with dolomitic alteration rims as dominant features. The basic chemical characteristics of the ore forming fluids in these mineralizations are those of highly fractionated hypersaline fluids exhibiting all the features of residual bittern brines. Fluid invasion and mineralization structures strictly depend on the original lithology of the host rocks, mainly carbonatic sedimentary rocks. In Late Triassic times, these buried evaporitic brines were mobilized either by magmatic/metamorphic processes in the underlying crystalline units or by the superimposed sedimentary upload of the Triassic platform carbonates thus leading to magnesite formation. Initially these residual, bittern brineswere completely free of Fe and rich in Mg suitable for the formation of magnesite. Deeperand more extensive circulation of these fluids and their interaction with the host-rock, resulted in the uptake of Fe and the formation of siderite.</p

Molecular hydrogen deficiency in HI-poor galaxies and its implications for star formation

We use a sample of 47 homogeneous and high sensitivity CO images taken from the Nobeyama and BIMA surveys to demonstrate that, contrary to common belief, a significant number (~40%) of HI-deficient nearby spiral galaxies are also depleted in molecular hydrogen. While HI-deficiency by itself is not a sufficient condition for molecular gas depletion, we find that H2 reduction is associated with the removal of HI inside the galaxy optical disk. Those HI-deficient galaxies with normal H2 content have lost HI mainly from outside their optical disks, where the H2 content is low in all galaxies. This finding is consistent with theoretical models in which the molecular fraction in a galaxy is determined primarily by its gas column density. Our result is supported by indirect evidence that molecular deficient galaxies form stars at a lower rate or have dimmer far infrared fluxes than gas rich galaxies, as expected if the star formation rate is determined by the molecular hydrogen content. Our result is consistent with a scenario in which, when the atomic gas column density is lowered inside the optical disk below the critical value required to form molecular hydrogen and stars, spirals become quiescent and passive evolving systems. We speculate that this process would act on the time-scale set by the gas depletion rate and might be a first step for the transition between the blue and red sequence observed in the color-magnitude diagram.Comment: 12 pages, 9 figures, accepted for publication in Ap

Vývoj povariských fluid v lomech u Nejdku, Jakubčovic a Bohučovic v Nízkém Jeseníku

Two different types of fluid were described in studied post-Variscan vein mineralization from Nejdek, Jakubčovice and Bohučovice quarries. First high salinity (between 18 and 28 wt. % NaCl eq.) and low temperature (ranging from 50 to 140 °C) fluids of H2O-NaCl-CaCl2 (±MgCl2) type, present in dolomite, sphalerite and calcite I, II, was originated from the highly evaporated seawater. Second low salinity (between 0 and 9 wt. % NaCl eq.) and low temperature (ranging from 40 to 80 °C) fluids of H2O-NaCl (±KCl) type, present in calcite III, was originated from the less evaporated seawater. Fluids represent moderate mixing with the sea or meteoric water and they also indicate slight to progressive interaction with the rocks (mainly illitization, dissolution of K-feldspar and albitization)

A metal-poor damped Ly-alpha system at redshift 6.4

We identify a strong Ly-alpha damping wing profile in the spectrum of the quasar P183+05 at z=6.4386. Given the detection of several narrow metal absorption lines at z=6.40392, the most likely explanation for the absorption profile is that it is due to a damped Ly-alpha system. However, in order to match the data a contribution of an intergalactic medium 5-38% neutral or additional weaker absorbers near the quasar is also required. The absorption system presented here is the most distant damped Ly-alpha system currently known. We estimate an HI column density ($10^{20.68\pm0.25}\,$cm$^{-2}$), metallicity ([O/H]$=-2.92\pm 0.32$), and relative chemical abundances of a system consistent with a low-mass galaxy during the first Gyr of the universe. This object is among the most metal-poor damped Ly-alpha systems known and, even though it is observed only ~850 Myr after the big bang, its relative abundances do not show signatures of chemical enrichment by Population III stars.Comment: Updated to match published versio

Directly imaging damped Lyman-alpha galaxies at z>2. I: Methodology and First Results

We present the methodology for, and the first results from, a new imaging program aimed at identifying and characterizing the host galaxies of damped Lyman-alpha absorbers (DLAs) at z>2. We target quasar sightlines with multiple optically-thick HI absorbers and use the higher-redshift system as a "blocking filter" (via its Lyman-limit absorption) to eliminate all far-ultraviolet (FUV) emission from the quasar. This allows us to directly image the rest-frame FUV continuum emission of the lower-redshift DLA, without any quasar contamination and with no bias towards large impact parameters. We introduce a formalism based on galaxy number counts and Bayesian statistics with which we quantify the probability that a candidate is the DLA host galaxy. This method will allow the identification of a bona fide sample of DLAs that are too faint to be spectroscopically confirmed. The same formalism can be adopted to the study of other quasar absorption line systems (e.g. MgII absorbers). We have applied this imaging technique to two QSO sightlines. For the z~2.69 DLA towards J073149+285449, a galaxy with impact parameter b=1.54"=11.89 kpc and implied star formation rate (SFR) of ~5 M/yr is identified as the most reliable candidate. In the case of the z~2.92 DLA towards J211444-005533, no likely host is found down to a 3-sigma SFR limit of 1.4 M/yr. Studying the HI column density as a function of the impact parameter, including 6 DLAs with known hosts from the literature, we find evidence that the observed HI distribution is more extended than what is generally predicted from numerical simulation.Comment: 22 pages, 13 figures. Accepted for publication in MNRAS. Typos correcte

Permian–polysulphide-siderite–barite–haematite deposit Rude in Samoborska Gora Mts., Zagorje–Transdanubian zone of the Inner Dinarides

Samoborska Gora Mts. is situated within westernmost part of the Zagorje&ndash;Mid&ndash;Transdanubian zone of the Inner Dinarides. The Samoborska Gora Mts. consists dominantly of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralization is hosted by Permian siliciclastic sediments, beneath gypsum and anhydrite strata. Central part of the deposit consists of 1.5 km long stratabound mineralization, grading laterally into ferruginous sandstone and protruding vertically into a gypsum&ndash;anhydrite layer. Siderite&ndash;polysulfide&ndash;barite&ndash;quartz veins are located underneath the stratabound mineralization. Late stage galena&ndash;barite veins overprints the formerly formed mineralization types. The Rude ore deposit was generated by NaCl&plusmn;CaCl2&ndash;H2O solutions. Stratabound mineralization was precipitated from solutions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150&deg;C to 230&deg;C. Vein type mineralization derived from solutions with salinities between 4 and 20 wt. % NaCl equ., homogenizing between 80&deg;C and 160&deg;C, while late stage galena&ndash;barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100&deg;C to 140&deg;C. Fluid inclusions bulk leachate chemistry recorded Na+&gt;Mg2+&gt;K+&gt;Ca2+&gt;Li+ and Cl&ndash;&gt;SO42&ndash; ions. Sulfur isotope composition of barites and overlying gypsum steams from the Permian seawater sulfate, supported by increased Br&ndash; content, which follows successively the seawater evaporation line. The sulfur isotopic composition of sulfides varies between &ndash;0.2 and +12.5 &permil;, as a result of thermal reduction of Permian marine sulfate. Ore&ndash;forming fluids were produced by hydrothermal convective cells (reflux brine model) and derived primarily from Permian seawater,- modified by evaporation and interaction with the Permian sedimentary rocks. Rude deposits in Samoborska Gora Mts. may be declared as a prototype of the Permian siderite&ndash;polysulfide&ndash;barite deposits, products of the rifting along the passive Gondwana margin, in the Inner Dinarides, and their equivalents in extension northeastward into Zagorje&ndash;Transdanubian Zone and Gemerides, and southeastward to Hellenide&ndash;Albanides.Samoborska Gora Mts. is situated within the westernmost part of the Zagorje–Mid–Transdanubian zone of the Inner Dinarides. The Samoborska Gora Mts. predominantly consists of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralization is hosted by Permian siliciclastic sediments, below gypsum and anhydrite strata. The central part of the deposit consists of a 1.5 km long stratabound mineralization, grading laterally into ferruginous sandstone and protruding vertically into a gypsum–anhydrite layer. Siderite–polysulphide–barite–quartz veins are located below the stratabound mineralization. The stratiform part of the deposit is situated above the stratabound and consists of haematite lajer with barite concretions and veinlets. Late stage galena–barite veins overprint earlier types of mineralization. The Rude ore deposit was generated by predominantly NaCl ±} CaCl2–H2O solutions. Detrital quartz from stratiform mineralization was precipitated from solutions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150 °C to 230 °C. Stratabound/siderite–polysulphide–barite–quartz vein type mineralization was derived from solutions with salinities between 5 and 19 wt. % NaCl equ., homogenizing between 80 °C and 160 °C, while late stage galena–barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100 °C to 140 °C. Fluid inclusion bulk leachate chemistry recorded Na+>Mg2+>K+>Ca2+>Li+ and Cl–>SO4 2–ions. Sulphur isotope composition of barites and overlying gypsum stems from Permian seawater sulphate, supported by increased Br– content, which follows successively the seawater evaporation line. The sulphur isotopic composition of sulphides varies between –0.2 and +12.5 ‰, as a result of thermal reduction of Permian marine sulphate. Ore–forming fluids were produced by hydrothermal convective cells (reflux brine model), and were derived primarily from Permian seawater, modified by evaporation and interaction with Permian sedimentary rocks. Rude deposits in SamoborskaGora Mts. may be declared as a precursor? of the Permian siderite–polysulphide–barite deposits (products of rifting along the passive Gondwana margin), in the Inner Dinarides, and their equivalents extending northeastward into the Zagorje–Transdanubian Zone and the Gemerides, and southeastward to the Hellenide–Albanides

The evolution of the Čanište epidote-bearing pegmatite, Republic of Macedonia: evidence from mineralogical and geochemical features

The epidote-bearing Čanište pegmatite and adjacent Upper Carboniferous granodiorites cut Precambrian gneises, at the western slopes of the Selečka Mts., the Eastern Pelagonian zone, FYRO Macedonia. The pegmatite exhibits zonal internal structure with the following sub-units: the wall zone (amazonite microcline ± biotite, quartz), the first intermediate zone (epidote + hematite + grossular + muscovite + quartz + almandine ± zircon, beryl, microcline, quartz), the second intermediate zone (albite + quartz ± microcline) and the core (massive quartz). According to the microprobe data epidote belongs to clinozoisite subgroup with formula (Ca1.96-1.99Mn0.02-0.03Fe2+0.00-0.02)(Al2.17-2.46Fe3+0.51-0.82Ti0.00-0.01)(Si2O7)(Si0.99-1.00Al0.00-0.01O4)O(OH). The occurrences of almandine and zircon with low U, Th and REE content, are indicative to weakly evolved granitic/granodioritic rocks. The absence of aplites suggests steady pressure condition during the course of pegmatite crystallization. Microthermometric data combined by the two-feldspar geothermometer gained pressure from 4.8 to 5.6 kbar for the second intermediate zone. The wall zone, composed of amazonite microcline, crystallized at temperature between 650 and 760. Dropping of melt temperature below 550°C, under the oxygen fugacity between 10-22 and 10-19.5 bar, was the principal trigger for deposition of minerals in the first intermediate zone. The residual fluid, depleted in Ca, Fe and K, and enriched in water, Na and Si, caused deposition of the second intermediate zone (albite + quartz) at temperature between 445 and 465°C. The massive quartz core crystallized in the very last stage of the pegmatite evolution (T ≈ 400-480°C) from melt residue enriched in silica, water and CO2 content.</p

Compactness of Cold Gas in High-Redshift Galaxies

Galaxies in the early Universe were more compact and contained more molecular gas than today. In this paper, we revisit the relation between these empirical findings, and we quantitatively predict the cosmic evolution of the surface densities of atomic (HI) and molecular (H2) hydrogen in regular galaxies. Our method uses a pressure-based model for the H2/HI-ratio of the Interstellar Medium, applied to ~3*10^7 virtual galaxies in the Millennium Simulation. We predict that, on average, the HI-surface density of these galaxies saturates at Sigma_HI<10 Msun/pc^2 at all redshifts (z), while H2-surface densities evolve dramatically as Sigma_H2(1+z)^2.4. This scaling is dominated by a (1+z)^2 surface brightness scaling originating from the (1+z)^-1 size scaling of galaxies at high z. Current measurements of Sigma_H2 at high z, derived from CO-observations, tend to have even higher values, which can be quantitatively explained by a selection bias towards merging systems. However, despite the consistency between our high-z predictions and the sparse empirical data, we emphasize that the empirical data potentially suffer from serious selection biases and that the semi-analytic models remain in many regards uncertain. As a case study, we investigate the cosmic evolution of simulated galaxies, which resemble the Milky Way at z=0. We explicitly predict their HI- and H2-distribution at z=1.5, corresponding to the CO-detected galaxy BzK-21000, and at z=3, corresponding to the primary science goal of the Atacama Large Millimeter/submillimeter Array (ALMA).Comment: 5 pages, 3 figures, 2 table