Geochemical heterogeneities in magma beneath Mount Etna recorded by 2001-2006 melt inclusions

Abstract

We present a geochemical study on olivine- and clinopyroxene-hosted melt inclusions (MIs) from 2001-2006 Etna basaltic lavas and pyroclastites. Three MI suites are distinguished on the basis of trace element fingerprinting. Type-1 MIs (from 2001 Upper South and 2002 Northeast vents) share their trace element signature with low-K lavas erupted before 1971. Critical trace element ratios (e.g.,K/La, Ba/Nb), along with Pb isotope data of Type-1 MIs provide evidence for a heterogeneous mantle source resulting from mixing of three end-members with geochemical and isotopic characteristics of EM2, DMM and HIMU components. Type-1 MIs composition does not support involvement of subduction-related components. Type-2 (from 2001 Lower and 2002 South vents) and Type-3 (2004 eruption) MIs reveal “ghost plagioclase signatures”, namely lower concentrations in strongly incompatible elements, and positiveSr, Ba and Eu anomalies. Both Type-1 and Type-2 MIs occur in 2006 olivines, which highlight the occurrence of mixing between Type-1 and Type-2 end-members. Type-2/Type-3 MIs testify to en-route processes(plagioclase assimilation and volatile fluxing) peculiar for “deep dike fed” eruptions. The latter are strongly controlled by tectonics or flank instability that occasionally promote upraise ofundegassed, more radiogenic primitive magma, which may interact with plagioclase-rich crystal mush/cumulates before erupting. Type-2/Type-3 MIs approach the less radiogenic Pb isotopic compositionof plagioclase from prehistoric lavas, thus suggesting geochemical overprinting of present-day melts by older products released from distinct mantle sources. Our study emphasizes that MIs microanalysis offers new insights on both source characteristics and en-route processes, allowing to a link between melt composition and magma dynamics.