Melting, differentiation and degassing at the Pantelleria volcano, Italy

Pantellerites are Fe- and volatile-rich, peralkaline rhyolites that erupt primarily in continental rift settings. As no eruptions of pantelleritic magma have been observed, interpreting the diversity of volcanic phenomena at pantelleritic volcanoes is challenging. Explosive eruptions range in scale from large ignimbrite-forming events like the ~45 ka Green Tuff eruption on Pantelleria to small cone-forming events. Effusive eruptions form structures as diverse as low-aspect-ratio lava domes and high-aspect-ratio lava shields. Although fewer in number than their calcalkaline counterparts, peralkaline rhyolite volcanoes nevertheless present a range of hazards.

The evolution of peralkaline magmas has been the subject of much recent debate, with some authors advocating for pantellerite genesis by melting alkali gabbros (e.g., Avanzinelli et al., 2004), and others favouring extensive fractional crystallisation (e.g., White et al., 2009). The volatile content of pantellerite melts had also been the subject of considerable uncertainty until a recent studied have confirmed the water-rich nature of pantelleritic melts.

In this paper, we presented major element, trace element and volatile compositions from glasses, crystals and melt inclusions from a number of post-Green Tuff eruptions from Pantelleria. The main outcomes were:

  1. A quantification of the degree of aluminous lherzolite melting required to generate the alkali basalts present around northwest coast of Pantelleria (~2%).
  2. A confirmation that pantellerites can be generated by extensive fractional crystallisation (~95%) of alkali basalts.
  3. High precision analyses of glass and melt inclusion volatile contents (H2O, CO2, Li, F, Cl, S) that confirm the H2O- and halogen-rich of pantellerite melts
  4. An evaluation that explosive peralkaline eruptions may emit much more sulphur than metauluminous eruptions of an equivalent size, up to ~100 Mt for a Green Tuff-sized eruption, becasue of the high sulphur solubilty in Fe- and alkali-rich melts.

Dammusi on Pantellieria
Dammusi on Pantellieria

Publication

Neave, D.A., Fabbro, G., Herd, R.A., Petrone, C.M. & Edmonds, M. 2012. Melting, Differentiation and Degassing at the Pantelleria Volcano, Italy. Journal of Petrology 53, 637–663.

 

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