Magma dynamics of ancient Mt. Etna inferred from clinopyroxene isotopic and trace element systematics

Abstract

Dynamic magmatic processes driving volcanic eruptions, including melting, fractionation, and assimilation, provide critical insights into plumbing systems supporting long-lived magmatism. Here we describe an approach combining in situ elemental analyses in clinopyroxene phenocrysts, integrated thermobarometry models, and bulk crystalline Hf, Nd, and Pb isotopic studies to reconstruct a key period of ancient eruptions of Mount Etna (Sicily), Europe's largest, most active volcano. Trace element signatures recorded in clinopyroxene from 220 to 100 ka are consistent with derivation from a heterogeneous mantle of hydrated peridotite and ~10 % pyroxenite, also consistent with sources feeding recent Etna eruptions. Isotopic data from Mount Etna alkaline lava clinopyroxene, crystallised between 0.5 and 0.2 GPa, insignificantly vary from whole rock values, ruling out substantive assimilation of material during magma ascent from the onset of clinopyroxene fractionation through the mid-crust, storage, and eruption. Together, our results suggest that varying contributions of well-mixed hydrated peridotite and pyroxenite melts have been consistent features of magma assembly beneath Mt. Etna since the development of ancient alkaline centres.

Sector-zoned clinopyroxene as a recorder of magma history, eruption triggers, and ascent rates

“…Overall, P-T results are in agreement with previous thermobarometric constraints on Etnean clinopyroxene (Armienti et al, 2007(Armienti et al, , 2013Mollo et al, 2015;Miller et al, 2017;Ubide and Kamber, 2018). Pressure estimates from sector compositions suggest crystallisation in the intermediate level plumbing system of Mt.…”

“…We explored the effect of sector zoning on P-T estimates by solving iteratively the pressure-independent, melt-dependent thermometer T1 (±27°C uncertainty; Putirka et al, 1996) and the temperature-and water-dependent, melt-independent barometer 32b (±200 MPa uncertainty; Putirka, 2008). Clinopyroxene-only barometers have provided reliable results at Etna and other alkaline systems, and are particularly useful when studying recycled parageneses (Ubide et al, 2014;Mollo et al, 2015;Hammer et al, 2016;Miller et al, 2017;Ubide and Kamber, 2018;Crossingham et al, 2018). Barometer 32b requires an esti-mate of the water content of the melt, which was set at 2 wt.% to account for the hydrous nature of Etnean magmas (Armienti et al, 2007(Armienti et al, , 2013Ubide and Kamber, 2018).…”

Volcanic crystals as time capsules of eruption history

“…With regard to pressure estimates, the application of melt-dependent barometers is hindered here by the fact that most clinopyroxene compositions are antecrystic and out of equilibrium with whole rock or groundmass compositions. Melt-independent barometers, by contrast, have recently been used to explore storage depths of magmas feeding ancient (220–100 ka) 77 and recent (2001–2012) 32 Etnean eruptions. To account for the hydrous nature of Etna magmas, we used Equation 32b of ref.…”

“…Solved iteratively using the temperature returned by the thermometer of ref. 76 , this barometer has been assessed to provide most accurate results in Etna and other volatile-rich alkaline systems 74 , 75 , 77 .…”

Isotopic evolution of prehistoric magma sources of Mt. Etna, Sicily: Insights from the Valle Del Bove

“…Nevertheless, some basal tholeiites (here termed "ancient Etna") and prehistoric (i.e., < ~ 250 ka) alkaline lavas from the eastern flank (Carter and Civetta 1977;Marty et al 1994;D'Orazio et al 1997;Tanguy et al 1997;Tonarini et al 2001;Corsaro et al 2002) have been previously analysed, as have some of the older Plio-Pleistocene-age Iblean Plateau lavas (Fig. 1; Carter and Civetta 1977;Tonarini et al 1996;Trua et al 1998;Miller et al 2017).…”