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Referência Bibliográfica


ZANON, V. (2007 ) - Silicate inclusions into restitic xenoliths from lavas and pyroclasts of Aeolian Islands (southern Italy): properties of alkaline anatectic melts. IUGG XXIV General Assembly, Perugia, Itália, 02 - 13 de Julho (Poster).

Resumo


Aeolian magmas show different degree of crustal contamination. Among all possible contaminants there are several silica rich-melts produced by crustal melting of micaschists and gneisses of Calabro-Peloritano range. Evidences of this process can be found into restitic quartz-rich xenoliths that can be found mainly in poorly evolved compositions (both lavas and pyroclasts) and exceptionally also into evolved compositions in the Vulcano Island.

 

Mineralogy of these xenoliths is represented by 98% of quartz and 2% clinopyroxene, plagioclase, titanite, apatite and zircon. Quartzes sometimes trapped carbonic fluid and silicate melts both separately and as two immiscible components.

 

Mineral phases and REE pattern of coexisting silicate melts trapped into inclusions point to different episodes of melt production, in presence of CO2, during the ascent of xenoliths.

 

Simulations with MELTS code tracked the progressive chemical variations of these crustal melts and indicated a generalised immiscibility with the host magma due to the high difference in viscosity. Only evolved magmas (latites, ryholites) have comparable values of viscosity, and the scarce amount of xenoliths contained, points to a greater extent of assimilation.

 

A comparison with the textures of similar quartz-rich xenolith hosted into recent lavas erupted from Mt. Etna can tell something about the speed of dissolution/assimilation process with time, revealing a high ascent speed of these xenolith-bearing magmas.

 

In this framework, only fast-ascending magmas from the source zone and with short rests in storage areas (from few weeks to a few years) can preserve the most “primitive” and “fertile” xenoliths. The occurrence of crustal xenoliths is also linked to styles of eruptions: high output rate events (lava flooding and pyroclastic flow) show the greatest amount of xenoliths, while steady state activity, such as continuous strombolian eruptions with almost no drainage of lava doesn’t allow the survival of these xenoliths.

Observações


Anexos