built a complex sequence of interfingered deposits emitted byclosely spaced eruptive vents which are frequently associated withdome-building phases and pantelleritic lavas flows. Field relationshipsallowed us to recognize eight eruptive units, all lying above theMontagna Grande trachytes.As a whole, petrochemical characteristics of the erupted productsindicate an evolutionary trend in which Na-clinopyroxene wasthe liquidus phase, followed by alkali feldspar. Amphibole andquartz are late-crystallizing, whereas aenigmatite is both early- andlate-crystallizing as well. Aenigmatite and Na-clinopyroxene crystallizationbuffers efficiently the increase of agpaicity, induced byfeldspar crystallization, to values of agpaitic index <2.0.Some eruptions are characterized by distinctive mineral assemblages:the couple amphibole + aegirine occurs in the Fastucatephra, whilst the fayalite + ilmenite + quartz association characterizesthe Randazzo tephra. The Fastuca eruption, the most powerfulamong those studied, tapped a reservoir characterized by lower temperatureand highly reducing conditions in comparison with theother eruptions. The frequent coexistence of Na-rich and Na-poorpyroxenes, may result from syn-eruptive mixing among variablyevolved pantelleritic magmas. The occurrence of late-precipitatedhalite witnesses the exsolution of a Cl-rich brine during magmaascent.
|Numero di pagine||18|
|Rivista||BOLLETTINO DELLA SOCIETÀ GEOLOGICA ITALIANA|
|Stato di pubblicazione||Published - 2007|
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