Limestone assimilation by basaltic magmas: an experimental re-assessment and application to Italian volcanoes

Abstract

International audienceThe results of an experimental study of limestone assimilation by hydrated basaltic magmas in the range 1050-1150°C, 0.1–500 MPa are reported. Alkali basalts doped with up to 19 wt% of Ca,Mg-carbonates were equilibrated in internally heated pressure vessels and the resulting phase relationships are described. The major effects of carbonate incorporation are: 1) generation of CO2-rich fluid phases; 2) change in liquidus phase equilibria; the crystallization of Ca-rich clinopyroxene is favored and the other phases (e.g. olivine, plagioclase), present in the absence of carbonate assimilation, are consumed. As a consequence of the massive clinopyroxene crystallization, the residual melt is strongly silica-depleted and becomes nepheline-normative. Compositional and mineralogical evolutions observed in Mt.Vesuvius eruptive products match those documented in our experiments with added carbonates, suggesting the possibility that carbonate assimilation increased during the last 25ka of activity. In Central-Southern Italy, carbonate assimilation at shallow levels probably superimposes on deeper source heterogeneities

The geochemical effects of olivine slurry replenishment and dolostone assimilation in the plumbing system of the Franklin Large Igneous Province, Victoria Island, Arctic Canada

“…The modeled effects of dolostone assimilation on the FCSC magma are very similar to those observed experimentally (Iacono Marziano et al 2008;Mollo and Vona 2014) and resemble products of volcanic systems where assimilation of host carbonates occurred (Chadwick et al 2007;Di Rocco et al 2012;Troll et al 2013). Dolostone assimilation in the FCSC magma could help explain the high-Fo compositions of olivine cores in the WUS OZ.…”

Calcium isotope constraints on the end-Permian mass extinction

“…Intrusion of Siberian Traps magmas through a thick sequence of carbonate sediments and coal (22) coeval with mass extinction (59) provides a mechanism for releasing sufficient quantities of CO 2 with the appropriate δ 13 C composition through the production of thermogenic methane during the heating of coal (22) and CO 2 -rich volatile phases during the incorporation of carbonate rocks into basaltic magma (60). Although previous studies have emphasized the release of carbon from methane clathrates or coal (51-53), δ 44∕40 Ca constraints instead suggest that carbon release associated with the end-Permian extinction may have included a substantial contribution from the incorporation of carbonate country rock into Siberian Traps magmas.…”

Carbon dioxide in silica-undersaturated melt. Part I: The effect of mixed alkalis (K and Na) on CO2 solubility and speciation

“…Reported P, T measurements are accurate to within ± 20 bars and ± 5ºC, respectively. All runs were ended by drop-quenching the sample holder into the cold part of the IHPV, which resulted in quench rates of 150°C/s for that kind of apparatus (Di Carlo et al, 2006;Iacono-Marziano et al, 2008;Morizet et al, 2010). In all cases, opening of the capsules produced a hissing sound suggesting that an excess fluid phase was present in the capsule during the experiment.…”