Active volcanoes emit significant amounts of mercury (Hg) into the atmosphere, thus playing a key role in its cycling on the Earth. Being highly toxic, Hg enrichment in sedimentary rocks is often used to link major ancient bio-climatic crises to massive volcanic eruptions. Therefore, the Hg cycle from its degassing upon accumulation in marine and terrestrial environments is widely studied. Critically, it remains uncertain what is the concentration of Hg in magmas prior to degassing. Degassing and/or partitioning of Hg into the Earth’s core could explain its low concentrations in basalts. Conversely, differentiation and/or crustal assimilation could increase Hg concentrations in igneous and volcanic rocks (Deng et al., 2022). However, these observations remain ambiguous for the following reasons: i) the analyzed rocks are not from the same magmatic system, and, more importantly, ii) the results could be biased by unintentional under- or overestimation of Hg caused by analytical challenges related to its high volatility and extremely low concentration (< 100 ng/g) in crystalline rocks. The STECALMY project investigates the source and mobility of Hg in the Earth’s crust using as a study case the Sesia Magmatic System (SMS; Western Southern Alps, Italy), an exposed continental magmatic system that can be traced from its deepest roots to its volcanic products (Tavazzani et al., 2020 and references therein). Here, we first developed a rigorous sample preparation and analytical procedure to optimize Hg analyses in crystalline rocks. Different igneous rocks were pulverized with agate mortar and a planetary mill equipped with agate and tungsten carbide jars. Powders obtained with these three approaches were analyzed with Direct Mercury Analyzer (DMA-80) and, after total acid dissolution, with Cold-Vapour-Atomic-Fluorescence-Spectroscopy. The first results show that up to 80% of Hg can be lost during powdering with tungsten carbide jars. With this new rigorous protocol, we aim to analyze the Hg concentration in granites from the Valle Mosso pluton of the SMS, since it exposes to surface pre- to syn-eruptive features and forms the uppermost part of a magmatic plumbing system of a large Permian caldera-forming volcanic eruption (Tavazzani et al., 2020 and references therein).
Source and mobility of mercury in continental magmatic systems: the STECALMY Project
Narduzzi F.
;Petranich E.;Pavoni E.;Covelli S.;Crosera M.;Venier M.;Černok A.;Ziberna L.
2023-01-01
Abstract
Active volcanoes emit significant amounts of mercury (Hg) into the atmosphere, thus playing a key role in its cycling on the Earth. Being highly toxic, Hg enrichment in sedimentary rocks is often used to link major ancient bio-climatic crises to massive volcanic eruptions. Therefore, the Hg cycle from its degassing upon accumulation in marine and terrestrial environments is widely studied. Critically, it remains uncertain what is the concentration of Hg in magmas prior to degassing. Degassing and/or partitioning of Hg into the Earth’s core could explain its low concentrations in basalts. Conversely, differentiation and/or crustal assimilation could increase Hg concentrations in igneous and volcanic rocks (Deng et al., 2022). However, these observations remain ambiguous for the following reasons: i) the analyzed rocks are not from the same magmatic system, and, more importantly, ii) the results could be biased by unintentional under- or overestimation of Hg caused by analytical challenges related to its high volatility and extremely low concentration (< 100 ng/g) in crystalline rocks. The STECALMY project investigates the source and mobility of Hg in the Earth’s crust using as a study case the Sesia Magmatic System (SMS; Western Southern Alps, Italy), an exposed continental magmatic system that can be traced from its deepest roots to its volcanic products (Tavazzani et al., 2020 and references therein). Here, we first developed a rigorous sample preparation and analytical procedure to optimize Hg analyses in crystalline rocks. Different igneous rocks were pulverized with agate mortar and a planetary mill equipped with agate and tungsten carbide jars. Powders obtained with these three approaches were analyzed with Direct Mercury Analyzer (DMA-80) and, after total acid dissolution, with Cold-Vapour-Atomic-Fluorescence-Spectroscopy. The first results show that up to 80% of Hg can be lost during powdering with tungsten carbide jars. With this new rigorous protocol, we aim to analyze the Hg concentration in granites from the Valle Mosso pluton of the SMS, since it exposes to surface pre- to syn-eruptive features and forms the uppermost part of a magmatic plumbing system of a large Permian caldera-forming volcanic eruption (Tavazzani et al., 2020 and references therein).Pubblicazioni consigliate
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