Abstract

A succession of nine major hawaiite lava field s erupted on Mount Etna during the period 1910-1983 have been extensively sampled. Whole-rock chemical and petrographic data reveal a significant spatial variation within each of the lava fields studied and a uniform temporal variation in the succession of lavas. Spatial variations in lava composition within individual flow fields are related to high-level magma mixing and crystal fractionation processes. The effects of mixing are demonstrated by incompatible trace element chemistry, phenocryst compositions and petrographic textures. Mixing involves several end-member magma compositions, some of which can be related to earlier eruptions using geochemical and volcanological evidence. The effects of post-mixing crystal fractionation overprint variation caused by mixing, particularly for the 1910-1923 lava fields; some pre-mixing fractionation also occurs. Strong time-integrated trace element variations for the period 1910-1983 take the form of changing incompatible element ratios caused by a significant enrichment of K and Rb and a depletion in Ba, Nb, and Zr with time. The temporal variation is controlled by sequential melting of a heterogeneous, enriched mantle source and is particularly noticeable in post-1964 lavas coinciding with an increase in eruptive volumes and lava basicity. Magma generated in the enriched mantle source collects in a deep crustal storage region (c. 20km deep) where it fractionates to hawaiite before ascending in a series of intermittent, rapid pulses to the high-level plumbing system. The high-level central conduit and radial dyke systems are charged with older, residual magmas of contrasting trace element chemistry. Ascending new magma entering this region mixes with the older magma in the central conduit and/or in the dykes and subsequently undergoes crystal fractionation to variable degrees before eruption.

Document Type

Thesis

Publication Date

1988

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