Loss of 40Ar(rad) from leucite-bearing basanite at low temperature: implications on K/Ar dating.

AbstractThe Bakony-Balaton Highland Volcanic Field (BBHVF) is located in the central part of Transdanubia, Pannonian Basin, with over 50 alkali basaltic volcanoes. The basanite plug of Hegyestu erupted in the first phase of volcanic activity. K/Ar and Ar/Ar ages were published for the BBHVF. K/Ar and Ar/Ar ages of the leucite-bearing basanite of Hegyestás were conflicting. This is caused by the special Ar retention feature of leucite in this basanite.K/Ar ages measured in the usual way were 25–45% younger, but after HCl treatment of the rock, or after reducing the baking temperature of the argon extraction line from 250°C to 150°C, they became similar to theAr/Ar ages. All Ar/Ar determinations were performed after HF treatment. HCl treatment dissolved olivine, nepheline, leucite, magnetite and from 1-1 sample analcime or calcite. K dissolution studies from different locations of Hegyestü have shown that K content is mostly ≈2%, but it may decrease to ≈0.3%. HCl treatment dissolved 28.0–63.5% of the K content. The calculated K concentration for the dissolved part of samples with ~2%K was 4.02-6.42%: showing that leucite is responsible for the low temperature loss of 40Ar(rad). Ar may release at low temperature from very finegrained mineral, or when the Ar release mechanism changes. A 40Ar(rad) degassing spectrum has been recorded in the 55–295°C range of baking temperature and the data were plotted in the Arrhenius diagram. The diagram shows that a change of the structure in the 145–295°C range caused the loss of 40Ar(rad). On fractions of HCl treated rock 7.56±0.17 Ma isochron K/Ar age has been determined. This is regarded as minimum age of eruption and it is similar to the Ar/Ar isochron age (7.78±0.07 Ma).

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Volcanic architecture, eruption mechanism and landform evolution of a Plio/Pleistocene intracontinental basaltic polycyclic monogenetic volcano from the Bakony-Balaton Highland Volcanic Field, Hungary

Open Geosciences ◽

10.2478/v10085-010-0019-2 ◽

2010 ◽

Vol 2 (3) ◽

Cited By ~ 12

Author(s):

Gábor Kereszturi ◽

Gábor Csillag ◽

Károly Németh ◽

Krisztina Sebe ◽

Kadosa Balogh ◽

...

Keyword(s):

Volcanic Activity ◽

Pannonian Basin ◽

Scoria Cone ◽

Volcanic Field ◽

Volcanic Complex ◽

Monogenetic Volcano ◽

Eruption Centre ◽

Volcanic Facies ◽

Eruption Volume ◽

Core Descriptions

AbstractBondoró Volcanic Complex (shortly Bondoró) is one of the most complex eruption centre of Bakony-Balaton Highland Volcanic Field, which made up from basaltic pyroclastics sequences, a capping confined lava field (~4 km2) and an additional scoria cone. Here we document and describe the main evolutional phases of the Bondoró on the basis of facies analysis, drill core descriptions and geomorphic studies and provide a general model for this complex monogenetic volcano. Based on the distinguished 13 individual volcanic facies, we infer that the eruption history of Bondoró contained several stages including initial phreatomagmatic eruptions, Strombolian-type scoria cones forming as well as effusive phases. The existing and newly obtained K-Ar radiometric data have confirmed that the entire formation of the Bondoró volcano finished at about 2.3 Ma ago, and the time of its onset cannot be older than 3.8 Ma. Still K-Ar ages on neighbouring formations (e.g. Kab-hegy, Agár-teto) do not exclude a long-lasting eruptive period with multiple eruptions and potential rejuvenation of volcanic activity in the same place indicating stable melt production beneath this location. The prolonged volcanic activity and the complex volcanic facies architecture of Bondoró suggest that this volcano is a polycyclic volcano, composed of at least two monogenetic volcanoes formed more or less in the same place, each erupted through distinct, but short lived eruption episodes. The total estimated eruption volume, the volcanic facies characteristics and geomorphology also suggests that Bondoró is rather a small-volume polycyclic basaltic volcano than a polygenetic one and can be interpreted as a nested monogenetic volcanic complex with multiple eruption episodes. It seems that Bondoró is rather a “rule” than an “exception” in regard of its polycyclic nature not only among the volcanoes of the Bakony-Balaton Highland Volcanic Field but also in the Neogene basaltic volcanoes of the Pannonian Basin.

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In Vitro Drug Release, Permeability, and Structural Test of Ciprofloxacin-Loaded Nanofibers

Pharmaceutics ◽

10.3390/pharmaceutics13040556 ◽

2021 ◽

Vol 13 (4) ◽

pp. 556

Author(s):

Luca Éva Uhljar ◽

Sheng Yuan Kan ◽

Norbert Radacsi ◽

Vasileios Koutsos ◽

Piroska Szabó-Révész ◽

...

Keyword(s):

Amorphous State ◽

Physical Mixture ◽

Water Soluble ◽

Vinyl Pyrrolidone ◽

Amorphous Solid Dispersion ◽

Release Mechanism ◽

Dissolution Studies ◽

In Vitro Diffusion ◽

Poly Vinyl Pyrrolidone

Nanofibers of the poorly water-soluble antibiotic ciprofloxacin (CIP) were fabricated in the form of an amorphous solid dispersion by using poly(vinyl pyrrolidone) as a polymer matrix, by the low-cost electrospinning method. The solubility of the nanofibers as well as their in vitro diffusion were remarkably higher than those of the CIP powder or the physical mixture of the two components. The fiber size and morphology were optimized, and it was found that the addition of the CIP to the electrospinning solution decreased the nanofiber diameter, leading to an increased specific surface area. Structural characterization confirmed the interactions between the drug and the polymer and the amorphous state of CIP inside the nanofibers. Since the solubility of CIP is pH-dependent, the in vitro solubility and dissolution studies were executed at different pH levels. The nanofiber sample with the finest morphology demonstrated a significant increase in solubility both in water and pH 7.4 buffer. Single medium and two-stage biorelevant dissolution studies were performed, and the release mechanism was described by mathematical models. Besides, in vitro diffusion from pH 6.8 to pH 7.4 notably increased when compared with the pure drug and physical mixture. Ciprofloxacin-loaded poly(vinyl pyrrolidone) (PVP) nanofibers can be considered as fast-dissolving formulations with improved physicochemical properties.

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Jarosite in Antarctic deep ice supports the ice-weathering model for jarosite formation on Mars

10.5194/egusphere-egu21-6279 ◽

2021 ◽

Author(s):

Giovanni Baccolo ◽

Barbara Delmonte ◽

Paul Niles ◽

Giannantonio Cibin ◽

Elena Di Stefano ◽

...

Keyword(s):

Low Temperature ◽

Volcanic Activity ◽

Liquid Water ◽

Chemical Weathering ◽

Ice Core ◽

Hydrothermal Processes ◽

Meridiani Planum ◽

History Of ◽

Alternative Proposal ◽

Iron Bearing

On Earth, jarosite is a weathering product forming in acidic-oxidative environments from the alteration of iron-bearing minerals in presence of liquid water. Typical settings where this iron-potassium hydrated sulphate is found, are weathering zones of pyrite-rich deposits, evaporative basins and fumaroles. Jarosite is not only known on Earth, it also occurs on Mars, where it was firstly identified by the Opportunity rover. The mineral was in fact recognized in the finely layered formations outcropping at Meridiani Planum and that were accurately investigated by the rover (Klingelh&#246;fer et al. 2004). Since jarosite requires liquid water to form, its occurrence on Mars has been regarded as an evidence for the presence of liquid water in the geologic past of Mars (Elwood-Madden et al., 2004). Since then, many models have been proposed to describe the environments where the precipitation of Martian jarosite took place. The most accepted ones deal with evaporative basins similar to Earth&#8217;s playas, others concern volcanic activity and hydrothermal processes. An alternative proposal predicted that jarosite may have formed as a consequence of weathering of mineral dust trapped in massive ice deposits, i.e. the ice-weathering model (Niles & Michalsky, 2009). The hypothesis that jarosite formed on Mars because of low-temperature, acidic and water limited weathering, is not new (Burns, 1987), but until now no direct evidences were available to support it.A potential Earth analogue to investigate such processes is deep Antarctic ice. We present a first investigation of deep ice samples from the Talos Dome ice core (East Antarctica) aimed at the identification of englacial jarosite, so as to support the ice-weathering model. Evidences gathered through independent techniques showed that jarosite is actually present in deep Antarctic ice and results from the weathering of dust trapped into ice. The process is controlled by the re-crystallization of ice grains and the concurrent re-location of impurities at grain-junctions, which both depend on ice depth. This study demonstrates that the deep englacial environment is suitable for jarosite precipitation. Our findings support the hypothesis that, as originally predicted by the ice-weathering model, paleo ice-related processes have been important in the geologic and geochemical history of Mars.&#160;ReferencesBurns, R. Ferric sulfates on Mars. J. Geophys. Res. 92, E570-E574 (1987).Elwood-Madden et al., 2004. Jarosite as an indicator of water-limited chemical weathering on Mars. Nature 431, 821-823 (2004).Klingelh&#246;fer, G. et al. Jarosite and Hematite at Meridiani Planum from Opportunity's M&#246;ssbauer Spectrometer. Science 306, 1740-1745 (2004).Niles, P. B. & Michalski, J. M. Meridiani Planum sediments on Mars formed through weathering in massive ice deposits. Nat. Geosci. 2, 215-220 (2009).

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The main pulse of the Siberian Traps expanded in size and composition

Scientific Reports ◽

10.1038/s41598-019-54023-2 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 6

Author(s):

L. E. Augland ◽

V. V. Ryabov ◽

V. A. Vernikovsky ◽

S. Planke ◽

A. G. Polozov ◽

...

Keyword(s):

Volcanic Activity ◽

Volcanic Rocks ◽

West Siberia ◽

Main Pulse ◽

Environmental Consequences ◽

Siberian Traps ◽

Minimum Age ◽

Area North ◽

Permian Mass Extinction ◽

Compositional Diversity

AbstractEmplacement of large volumes of (sub)volcanic rocks during the main pulse of the Siberian Traps occurred within <1 m.y., coinciding with the end-Permian mass extinction. Volcanics from outside the main Siberian Traps, e.g. Taimyr and West Siberia, have since long been correlated, but existing geochronological data cannot resolve at a precision better than ~5 m.y. whether (sub)volcanic activity in these areas actually occurred during the main pulse or later. We report the first high precision U-Pb zircon geochronology from two alkaline ultramafic-felsic layered intrusive complexes from Taimyr, showing synchronicity between these and the main Siberian Traps (sub)volcanic pulse, and the presence of a second Dinerian-Smithian pulse. This is the first documentation of felsic intrusive magmatism occurring during the main pulse, testifying to the Siberian Trap’s compositional diversity. Furthermore, the intrusions cut basal basalts of the Taimyr lava stratigraphy hence providing a minimum age of these basalts of 251.64 ± 0.11 Ma. Synchronicity of (sub)volcanic activity between Taimyr and the Siberian Traps imply that the total area of the Siberian Traps main pulse should include a ~300 000 km2 area north of Norilsk. The vast aerial extent of the (sub)volcanic activity during the Siberian Traps main pulse may explain the severe environmental consequences.

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Ion Transport in Hydrodictyon africanum

The Journal of General Physiology ◽

10.1085/jgp.50.6.1607 ◽

1967 ◽

Vol 50 (6) ◽

pp. 1607-1625 ◽

Cited By ~ 57

Author(s):

J. A. Raven

Keyword(s):

Free Energy ◽

Low Temperature ◽

Electrical Potential ◽

Bathing Solution ◽

Electrical Potential Difference ◽

Energy Gradient ◽

Na Efflux ◽

K Concentration ◽

Net Fluxes ◽

External K

The concentrations of K, Na, and Cl in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and Cl and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and Cl and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low temperature indicate that most of the tracer K and Cl influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efflux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.

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Effects of High Potassium and Low Temperature on the Growth and Magnesium Nutrition of Different Tomato Cultivars

HortScience ◽

10.21273/hortsci12983-18 ◽

2018 ◽

Vol 53 (5) ◽

pp. 710-714 ◽

Cited By ~ 1

Author(s):

Huixia Li ◽

Zhujun Chen ◽

Ting Zhou ◽

Yan Liu ◽

Sajjad Raza ◽

...

Keyword(s):

Low Temperature ◽

Shoot Biomass ◽

Total Biomass ◽

High Potassium ◽

Hydroponic Experiment ◽

Root Shoot Ratio ◽

High K ◽

Significant Difference ◽

Tomato Cultivars ◽

K Concentration

The interaction between potassium (K) and magnesium (Mg) in plants has been intensively studied. However, the responses of different tomato (Solanum lycopersicum L.) cultivars to high K levels at low temperatures remained unclear. Herein, a complete randomized hydroponic experiment was conducted to evaluate the effects of temperature (25 °C day/18 °C night vs. 15 °C day/8 °C night) and K concentrations (156 mg·L−1 vs. 468 mg·L−1) on the growth and Mg nutrition of tomato cultivars Gailiangmaofen (MF) and Jinpeng No. 1 (JP). Compared with the control temperature (25 °C day/18 °C night), the low temperature decreased total biomass, shoot biomass, and Mg uptake in shoot by 17.3%, 24.1%, and 11.8%, respectively; however, the root/shoot ratio was increased. High K had no significant effect on plant growth or biomass compared with the control K concentration (156 mg·L−1); however, Mg concentrations and uptake in shoot were significantly lower under high-K treatment. Significant difference was observed for K uptake, but not for Mg uptake, between the two cultivars. There was no significant interaction between temperature and high K on Mg uptake of tomato, so a combined stress of low temperature and high K further inhibited Mg uptake and transport. Low temperature and high K increased the risk of Mg deficiency in tomato.

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