37 research outputs found
Geochemistry of Sarmatian volcanic rocks in the Tokaj Mts (NE Hungary) and their relationship to hydrothermal mineralization
Abstract
In the Tokaj Mts (NE Hungary), which is a part of the Inner Carpathian Volcanic Arc, large amounts of intermediate-acidic calc-alkaline volcanic rocks accumulated in a N-S oriented graben-like structure during the Badenian-Sarmatian-Pannonian period, in relation with the closure of the Alpine Tethys (Penninic) ocean. Although previous research on volcanism and related hydrothermal processes produced a huge number of K/Ar age data no systematic petrochemical database has been available up to now from the Tokaj Mts. In this study we publish new results of geochemical analyses completed on systematically collected basaltic, andesitic, dacitic and rhyolitic rocks, and of the spatialtemporal evaluation of petrochemical signatures, with special reference to origin of magmatism and relationships of rhyolite to hydrothermal mineralization. In the southern Tokaj Mts rhyolite contains K-feldspar phenocrysts, while this phenomenon is absent in the rhyolite from the northern areas of the mountains. In accordance with this, significant potassium enrichment occurs in the south (whole rock K2O content varies between 4.35 and 5.61 wt%), whereas rhyolite from the northern Tokaj Mts is less enriched in potassium (K2O content is from 3.28 to 5.1 wt%). The most significant difference between the northern and southern dacite is the age of their formation. They were formed at the same time as rhyolite and andesite (between 13.4 and 11 Ma) in the northern Tokaj Mts, while they are much younger (10.57â10.1 Ma) in the southern Tokaj Mts, where they post-date hydrothermal activity. The boron content (10.1â52.12 ”g/g) and the patterns of other trace elements of the volcanic rocks show typical subduction-related features; however, direct influx of subduction-related fluids during magma generation can be excluded. A more plausible explanation for the magma genesis is decompression melting of a previously metasomatized mantle, enriched with subduction-related components. Additionally, the unmineralized northern rhyolite samples contain much less Cl (usually below 0.2 wt%) than the high-K rhyolite in the southern part of the Tokaj Mts (usually more than 0.2 wt%), which correlates with the presence/absence of spatially and temporally related epithermal mineralization in these areas
Geochemistry of Ocean Floor and Fore-arc Serpentinites: Constraints on the Ultramafic Input to Subduction Zones
We provide new insights into the geochemistry of serpentinites from mid-ocean ridges (Mid-Atlantic Ridge and Hess Deep), passive margins (Iberia Abyssal Plain and Newfoundland) and fore-arcs (Mariana and Guatemala) based on bulk-rock and in situ mineral major and trace element compositional data collected on drill cores from the Deep Sea Drilling Project and Ocean Drilling Program. These data are important for constraining the serpentinite-hosted trace element inventory of subduction zones. Bulk serpentinites show up to several orders of magnitude enrichments in Cl, B, Sr, U, Sb, Pb, Rb, Cs and Li relative to elements of similar compatibility during mantle melting, which correspond to the highest primitive mantle-normalized B/Nb, B/Th, U/Th, Sb/Ce, Sr/Nd and Li/Y among subducted lithologies of the oceanic lithosphere (serpentinites, sediments and altered igneous oceanic crust). Among the elements showing relative enrichment, Cl and B are by far the most abundant with bulk concentrations mostly above 1000â”g gâ1 and 30â”g gâ1, respectively. All other trace elements showing relative enrichments are generally present in low concentrations (”g gâ1 level), except Sr in carbonate-bearing serpentinites (thousands of ”g gâ1). In situ data indicate that concentrations of Cl, B, Sr, U, Sb, Rb and Cs are, and that of Li can be, increased by serpentinization. These elements are largely hosted in serpentine (lizardite and chrysotile, but not antigorite). Aragonite precipitation leads to significant enrichments in Sr, U and B, whereas calcite is important only as an Sr host. Commonly observed brucite is trace element-poor. The overall enrichment patterns are comparable among serpentinites from mid-ocean ridges, passive margins and fore-arcs, whereas the extents of enrichments are often specific to the geodynamic setting. Variability in relative trace element enrichments within a specific setting (and locality) can be several orders of magnitude. Mid-ocean ridge serpentinites often show pronounced bulk-rock U enrichment in addition to ubiquitous Cl, B and Sr enrichment. They also exhibit positive Eu anomalies on chondrite-normalized rare earth element plots. Passive margin serpentinites tend to have higher overall incompatible trace element contents than mid-ocean ridge and fore-arc serpentinites and show the highest B enrichment among all the studied serpentinites. Fore-arc serpentinites are characterized by low overall trace element contents and show the lowest Cl, but the highest Rb, Cs and Sr enrichments. Based on our data, subducted dehydrating serpentinites are likely to release fluids with high B/Nb, B/Th, U/Th, Sb/Ce and Sr/Nd, rendering them one of the potential sources of some of the characteristic trace element fingerprints of arc magmas (e.g. high B/Nb, high Sr/Nd, high Sb/Ce). However, although serpentinites are a substantial part of global subduction zone chemical cycling, owing to their low overall trace element contents (except for B and Cl) their geochemical imprint on arc magma sources (apart from addition of H2O, B and Cl) can be masked considerably by the trace element signal from subducted crustal component
Optimization of cementitious composite for heavyweight concrete preparation using conduction calorimetry
The present work investigates the hydration heat of different cement composites by means of conduction calorimetry to optimize the composition of binder in the design of heavyweight concrete as biological shielding. For this purpose, Portland cement CEM I 42.5 R was replaced by a different portion of supplementary cementitious materials (blast furnace slag, metakaolin, silica fume/limestone) at 75%, 65%, 60%, 55%, and 50% levels to obtain low hydration heat lower than 250 j g(-1). All ingredients were analyzed by energy dispersive X-ray fluorescence (EDXRF) and nuclear activation analysis (NAA) to assess the content of major elements and isotopes. A mixture of two high-density aggregates (barite and magnetite) was used to prepare three heavyweights concretes with compressive strength exceeding 45 MPa and bulk density ranging between 3400 and 3500 kg m(-3). After a short period of volume expansion (up to 4 h), a slight shrinkage (max. 0.3 degrees/degrees degrees) has been observed. Also, thermophysical properties (thermal conductivity, volumetric specific heat, thermal diffusivity) and other properties were determined. The results showed that aggregate content and not binder is the main factor influencing the engineering properties of heavyweight concretes
TudomĂĄny az innovĂĄciĂł szolgĂĄlatĂĄban: neutronos anyagvizsgĂĄlati mĂłdszerek ipari alkalmazĂĄsai a Budapesti Neutron Centrumban
2019. mĂĄrcius 28-ĂĄn az MTA dĂsztermĂ©ben ĂŒnnepelhettĂŒk a Budapesti KutatĂłreaktor fennĂĄllĂĄsĂĄnak 60. Ă©vfordulĂłjĂĄt, hiszen az akkor mĂ©g csak 2 MW-os reaktor 1959. mĂĄrcius 25-Ă©n lĂ©pett elĆször mƱködĂ©sbe. Jelenleg a Budapesti Neutron Centrum (BNC), az MTA EK Ă©s az MTA Wigner FK konzorciuma, koordinĂĄlja a Budapesti KutatĂłreaktor körĂŒl folyĂł tudomĂĄnyos Ă©s ipari K+F tevĂ©kenysĂ©geket. A KutatĂłreaktor a körĂ© telepĂŒlt mĂ©rĆhelyekkel, tĂĄgabb Ă©rtelemben pedig az MTA csillebĂ©rci kampusza az egyik legjelentĆsebb technikai Ă©s tudĂĄsközpontnak szĂĄmĂt hazĂĄnkban. A neutronközpont a hazai Ă©s nemzetközi tudomĂĄnyos közössĂ©g, valamint az ipari szereplĆk szĂĄmĂĄra is elĂ©rhetĆ nyĂlt kutatĂĄsi infrastruktĂșra, azaz a mĂ©rĆhelyek kivĂĄlĂłsĂĄg-alapĂș felhasznĂĄlĂłi programok, ill. kĂ©toldalĂș megĂĄllapodĂĄsok rĂ©vĂ©n az Ă©rdekeltek szĂĄmĂĄra hozzĂĄfĂ©rhetĆk
Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks
Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks from the island of Syros (Greece) were studied, using secondary ion mass spectrometry, inductively coupled plasma optical emission spectrometry and prompt gamma neutron activation analysis. Partitioning between coexisting mineral phases was found to be rather constant and independent of element concentrations. For several mineral pairs, apparent partition coefficients vary in a narrow range, while concentrations vary by more than an order of magnitude. Hence, it was possible to establish sets of inter-mineral partition coefficients for Li, Be and B among 15 different high-pressure minerals. This data set provides important information on the behaviour of the light elements in different lithologies within subducting slabs from the onset of metamorphism to the eclogite stage. It is essential for modelling trace-element and isotope fractionation during subduction and dehydration of oceanic crust
Li, B and Be Contents of Harzburgites from the Dramala Complex (Pindos Ophiolite, Greece): Evidence for a MOR-type Mantle in a Supra-subduction Zone Environment
The Pindos ophiolite represents oceanic lithosphere obducted during the Jurassic. The Dramala mantle section mainly consists of highly depleted spinel harzburgite and minor plagioclase-bearing harzburgite. Textural observations and major element compositions of minerals indicate that the harzburgites experienced impregnation by a mafic, depleted melt and subsequent high-temperature (high-T) hydration and cooling (>750°C) forming pargasite and edenitic hornblende. During further cooling (from 350â400°C to ”g/g) are slightly elevated. The bulk Li contents (0âą5â1âą1 ”g/g) are in the upper range of values for unmetasomatized mantle, whereas B contents (”g/g) are variable and slightly elevated compared with the unmetasomatized mantle as a result of serpentinization. Beryllium abundances in all minerals are very low (”g/g), except for pargasite, where a maximum Be content of 0âą012 ”g/g was measured. The selective addition of Li to clinopyroxene can be related to the interaction with a depleted melt, and/or to partitioning of Li into clinopyroxene upon cooling. During high-T hydration and cooling, the fluid calculated to be in equilibrium with the pargasite or edenitic hornblende (based on Li, Be and B) could have been reaction-modified seawater. Low-T hydration may have led to a very minor increase in bulk B content of most samples and to the formation of serpentine with highly variable B contents (0âą1â28 ”g/g). Low-T hydration decreased the Li content of orthopyroxene, and Li was probably leached from some samples. The lack of correlation between degree of serpentinization and bulk B contents as well as the presence of high- and low-B serpentine can be explained by low fluidârock ratios, decreasing T during serpentinization and lack of equilibrium as a result of fast obductionâexhumation. The low light-element contents of primary minerals and whole-rock samples clearly argue against a supra-subduction zone (SSZ) origin of the Dramala mantle section, and against the previous hypothesis of hydrous melting of the Pindos mantle above a subduction zone. We therefore conclude that the Dramala harzburgites represent a mid-ocean ridge (MOR)-type mantle, and not an SSZ-type mantle, juxtaposed with MOR-type and SSZ-type oceanic crust, either in a back-arc or in an intra-oceanic subduction zone setting
Neutrons for concrete science
Neutron-based elemental analysis and imaging methods are well applicable to many fields of material science. In the framework of an international project (V4-Korea RADCON), a complex methodology developed at the Centre for Energy Research of Hungarian Academy of Sciences (the legal entity operating the Budapest Research Reactor and the Budapest Neutron Centre) is applied to fundamental research on concrete materials for radiation shielding purposes. Due to combined use of multiple analytical (instrumental neutron and prompt gamma activation analyses, INAA and PGAA) and imaging (neutron radiography and tomography, NR and NT) techniques, the investigation of many material characteristics (major, minor and trace element composition; macro-scale pore and grain structure, moisture movement behavior) became possible. These data provide a solid basis for the understanding, prediction or modelling of macroscopic properties (e.g. mechanical strength, durability). This paper presents case study achieved during the RADCON project by neutron-based methods