Induktív csatolású plazma tömegspektrometriai módszerek kidolgozása ólom izotóparányok geológiai mintákban történő meghatározásához = Development of inductively coupled mass spectrometric methods for determination of lead isotope ratios in geological samples

A kutatómunka során ólomizotópok arányainak klinopiroxénekben történő meghatározásához dolgoztunk ki analitikai kémiai módszereket induktív csatolású plazma ionforrással és egy detektorral működő kettős fókuszállású tömegspektrométer felhasználásával. Négy különböző mintabeviteli módszer került összehasonlításra. Az oldatos módszereknél a feltárás után az ólmot koronaéteres gyanta segítségével elválasztottuk a mátrixtól és a zavaró elemektől (Hg, Dy, Er, Yb), majd koncentrikus valamint nagynyomású folyadékporlasztóval történt az aeroszol előállítása és plazmába juttatása. Az izotóparányokra vonatkozó RSD értéke 0.3-0.4% volt. A szilárdmintás mintabevitelt elektrotermikus elpárologtatás (termikus frakcionálás) és lézerabláció útján valósítottuk meg. Az RSD értékek itt 0.6-0.7%, illetve 1.5-1.6% körül változtak. | In framework of our research project analytical methods were developed for determination of isotope ratios of lead in clinopyroxene matrices applying a single collector sector-field mass spectrometer with ion source of inductively coupled plasma. Four different sample introduction techniques were studied. In case of solution techniques the lead was separated from the matrix ant the disturbing elements (Hg, Dy, Er, Yb) applying a corona ether resin. For generation of aerosols Meinhard-type concentric as well as a hydraulic high pressure nebulizer were used. The relative standard deviations of isotope ratios amounted to 0.3-0.4%. For solid sampling electrothermal vaporization (thermal fractionation) and laser ablation were applied. The uncertainty of analytical measurements in these cases was about by factor 2 higher compared to the solution techniques

Signature of deep mantle melting in South Iceland olivine

We present new high-precision major and trace element data on olivine macrocrysts from various volcano-tectonic settings in Iceland and use these data as a proxy for mantle mode and melting conditions. Within individual sampling sites examined (seven lavas and one tephra) olivine-dominated fractional crystallization, magma mixing and diffusive re-equilibration control observed variability in olivine composition. High-pressure fractional crystallization of clinopyroxene may have lowered Ca and increased Fe/Mn in one olivine population and subsolidus diffusion of Ni and Fe-Mg affected the mantle-derived Ni/Fo ratio in some compositionally zoned olivine macrocrysts. Interestingly, magmas erupted at the southern tip of the Eastern Volcanic Zone (SEVZ), South Iceland, have olivines with elevated Ni and low Mn and Ca contents compared to olivines from elsewhere in Iceland, and some of the SEVZ olivines have relatively low Sc and V and high Cr, Ti, Zn, Cu and Li in comparison to depleted Iceland rift tholeiite. In these olivines, the high Ni and low Mn indicate relatively deep melting (P-final>1.4GPa,similar to 45km), Sc, Ti and V are compatible with low-degree melts of lherzolite mantle, and elevated Zn may suggest modal (low-olivine) or geochemical (high Zn) enrichment in the source. The SEVZ olivine macrocrysts probably crystallized from magmas derived from olivine-bearing but relatively deep, enriched and fertile parts of the sub-Icelandic mantle, and indicate swift ascent of magma through the SEVZ lithosphere.Peer reviewe

Mid-crustal storage and crystallization of Eyjafjallajokull ankaramites, South Iceland

Our understanding of the long-term intrusive and eruptive behaviour of volcanic systems is hampered by a relatively short period of direct observation. To probe the conditions of crustal magma storage below South Iceland, we have analysed compositions of minerals, mineral zoning patterns, and melt inclusions from two Eyjafjallajokull ankaramites located at Brattaskjol and Hvammsmuli. These two units are rich in compositionally diverse macrocrysts, including the most magnesian olivine (Fo(88)(-)(90)) and clinopyroxene (Mg#(cpx)( )89.8) known from Eyjafjallajokull. Olivine-hosted spinel inclusions have high Cr# (spl )(52-80) and TiO2 (1-3 wt%) and low Al2O3 (8-22 wt%) compared to typical Icelandic chromian spinel. The spinel-olivine oxybarometer implies a moderate oxygen fugacity of Delta logFMQ 0-0.5 at the time of crystallization, and clinopyroxene-liquid thermobarometry crystallization at mid-crustal pressures (1.7-4.2 kbar, 3.0+1.4 kbar on average) at 1120-1195 degrees C. Liquid-only thermometry for melt inclusions with Mg#(melt) 56.1-68.5 and olivine-liquid thermometry for olivine macrocrysts with Fo(80.7-88.9) yield crystallization temperatures of 1155-1222 degrees C and 1136-1213 degrees C, respectively. Diffusion modelling of compositional zonations in the Brattaskjol olivine grains imply that the Brattaskjol macrocusts were mobilized and transported to the surface from their mid-crustal storage within a few weeks (at most in 9-37 days). Trends in clinopyroxene macrocryst compositions and the scarcity of plagioclase indicate that the mid-crustal cotectic assemblage was olivine and clinopyroxene, with plagioclase joining the fractionating mineral assemblage later. In all, the crystal cargoes in the Brattaskjol and Hvammsmtili ankaramites are composed of agitated wehrlitic or plagioclase wehrlitic crystal mushes that crystallized over a large temperature interval at mid-crustal depths.Peer reviewe

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption.We usemultiparameter geophysical and geochemical data to show that the 110-squarekilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, nearexponential decline of both collapse rate and the intensity of the 180-day-long eruption.</p

Melt inclusion constraints on petrogenesis of the 2014-2015 Holuhraun eruption, Iceland

The 2014–2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine–plagioclase–augite–melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1 ± 0.7 kbar (7.5 ± 2.5 km), which is in agreement with the depths of earthquakes (6 ± 1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1–12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12–0.29 m s−1. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions

A Data Driven Approach to Investigate the Chemical Variability of Clinopyroxenes From the 2014–2015 Holuhraun–Bárdarbunga Eruption (Iceland)

Publisher's version (útgefin grein)The Holuhraun–Bárdarbunga (Iceland) eruption lasted approximately 6 months. Magma propagated laterally through a 40 km long dyke, while Bárdarbunga caldera was collapsing. This event was intensely monitored, providing an opportunity to investigate the relationships between eruption dynamics and erupted products. Whole rock and melt inclusion data do not show chemical variations of magma during the eruption. Nevertheless, zoning patterns in clinopyroxene suggest temporal variations of intensive parameters during crystallization. We investigated the chemical zoning of clinopyroxene using a data driven approach, on major and trace elements analyses from lava flow lobes emplaced during the eruption. We applied hierarchical clustering (HC) to identify compositional groups based on major and trace element chemistry. This analysis identifies five compositional groups, which can be associated with specific petrographic features. One cluster represents the chemistry of hourglass sectors, two constitute the oscillatory zoned mantle of the crystals, one cluster corresponds to a seldom present bright rim (in back scattered electron images) in the outer portions of the crystals, and a last one represents most of the outer rims. HC applied to trace elements also identifies five compositional clusters, which highlight progressively more evolved clinopyroxene compositions from the core to the rim of the crystals. Two of the clusters identified with trace elements corresponds to major element clusters. All together the data suggest that the chemical zoning in the inner portions of the clinopyroxene crystals was generated by crystallization in the magma reservoir and interaction between hot magma propagating through the dyke and unerupted magma cooling within the dyke. The fraction of zones produced by interaction with colder portion of the magma residing within the dyke dropped during the eruption, potentially signaling the thermal maturation of the dyke. Some of the analyses reveal that relatively close to the eruption time (i.e., the outer portions of the crystals) the dyke intercepted a lens of low temperature magma with a chemical composition that is distinguishable from the 2014 to 2015 Bárdarbunga eruption. Our approach can provide insights on the evolution of deep processes occurring during long-lasting eruptions by combining the analysis mineral chemistry of erupted products with multiparametric monitoring signals.LC, LP, and GS appreciated the support for fieldwork of the Faculty of Science of the University of Geneva and the access provided by the Vatnajökull National Park. LC and TS received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program (grant agreement no. 677493 – FEVER). LC and TS acknowledge the support of the Swiss National Science Foundation (grant no. 200021_184632). MP acknowledge the Università degli Studi di Perugia FRB2019 grant titled “ENGAGE – machinE learNinG Applications for Geological problEms.”Peer Reviewe