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 ≥ 350-400°C to < 100°C), talc + tremolite ± serpentine ± olivine, serpentine + magnetite, and finally plagioclase alteration phases formed. To test the hypothesis of a supra-subduction zone origin for the Dramala mantle, we measured Li, B and Be contents of minerals by secondary ion mass spectrometry. Whole-rock contents were measured using inductively coupled plasma-mass spectrometry and prompt gamma neutron activation analysis. We observe low Li and B contents of primary minerals (olivine, orthopyroxene, clinopyroxene) consistent with values for unmetasomatized mantle minerals; only Li contents of clinopyroxene (up to 3·7 μg/g) are slightly elevated. The bulk Li contents (0·5-1·1 μg/g) are in the upper range of values for unmetasomatized mantle, whereas B contents (<0·04-1·1 μg/g) are variable and slightly elevated compared with the unmetasomatized mantle as a result of serpentinization. Beryllium abundances in all minerals are very low (<0·005 μg/g), except for pargasite, where a maximum Be content of 0·012 μg/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 (0·1-28 μg/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 fluid-rock ratios, decreasing T during serpentinization and lack of equilibrium as a result of fast obduction-exhumation. 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 settin

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 (10.57–10.1 Ma) in the southern Tokaj Mts, where they post-date hydrothermal activity. The boron content (10.1–52.12 µg/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 1000 µg g−1 and 30 µg g−1, respectively. All other trace elements showing relative enrichments are generally present in low concentrations (µg g−1 level), except Sr in carbonate-bearing serpentinites (thousands of µg g−1). 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

Tectonic significance of changes in post-subduction Pliocene-Quaternary magmatism in the south east part of the Carpathian-Pannonian Region

The south-eastern part of the Carpathian–Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza–Dacia microplate. Plio-Quaternary magmatic activity in this area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3 Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3–3.9 Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani–Gurghiu–Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (< 0.03 Ma) interrupted at 1.6–1.2 Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6–1.3 Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6 Ma) and South Harghita area at a distance of ca. 200 km imply a regional connection with the inversion tectonics

Tudomány az innováció szolgálatában: neutronos anyagvizsgálati módszerek ipari alkalmazásai a Budapesti Neutron Centrumban

2019. március 28-án az MTA dísztermében ünnepelhettük a Budapesti Kutatóreaktor fennállásának 60. évfordulóját, hiszen az akkor még csak 2 MW-os reaktor 1959. március 25-én lépett először működésbe. Jelenleg a Budapesti Neutron Centrum (BNC), az MTA EK és az MTA Wigner FK konzorciuma, koordinálja a Budapesti Kutatóreaktor körül folyó tudományos és ipari K+F tevékenységeket. A Kutatóreaktor a köré települt mérőhelyekkel, tágabb értelemben pedig az MTA csillebérci kampusza az egyik legjelentősebb technikai és tudásközpontnak számít hazánkban. A neutronközpont a hazai és nemzetközi tudományos közösség, valamint az ipari szereplők számára is elérhető nyílt kutatási infrastruktúra, azaz a mérőhelyek kiválóság-alapú felhasználói programok, ill. kétoldalú megállapodások révén az érdekeltek számára hozzáférhetők

Age evaluation and causation of rock-slope failures along the western margin of the Antrim Lava Group (ALG), Northern Ireland, based on cosmogenic isotope (36Cl) surface exposure dating.

The temporal pattern of postglacial rock-slope failure in a glaciated upland area of Ireland (the western margin of the Antrim Lava Group) was evaluated using both 36Cl exposure dating of surface boulders on run-out debris and 14C dating of basal organic soils from depressions on the debris. The majority of the 36Cl ages (~ 21–15 ka) indicate that major failures occurred during or immediately following local deglaciation (~ 18–17 ka). Other ages (~ 14–9 ka) suggest some later, smaller-scale failures during the Lateglacial and/or early Holocene. The 14C ages (2.36–0.15 cal ka BP) indicate the very late onset of organic accumulation and do not provide close limiting age constraints. Rock-slope failure during or immediately following local deglaciation was probably in response to some combination of glacial debuttressing, slope steepening and paraglacial stress release. Later failures may have been triggered by seismic activity associated with glacio-isostatic crustal uplift and/or permafrost degradation consequent upon climate change. The 36Cl ages support the findings of previous studies that show the deglacial - Lateglacial period in northwest Ireland and Scotland to have been one of enhanced rock-slope failure