The Hercynian volcano-phitonic association of Ganna (Lake Lugano, Central Southern Alps, Italy)
Bakos, Francesco; Del Moro, Aldo; Visona, Dariο
European Journal of Mineralogy Volume 2 Number 3 (1990), p. 373 - 384
published: Jun 21, 1990
manuscript accepted: Jan 31, 1990
manuscript received: Jun 28, 1988
ArtNo. ESP147050203015, Price: 29.00 €
Abstract A late Permian caldera structure has been identified in the area immediately SSW of Lake Lugano. A lower thick sequence of andesites, dacites and rhyolites is intruded by the top of a leucogranitic pluton, also Permian in age. Magmatic activity ended with a short rhyolitic episode. Although the volcanic sequence is lithologically expanded and shows a marked calc-alkaline character, the pluton is composed mainly of leucogranitic differentiates linked by FC processes. A Rb/Sr whole-rock isochron dates the intrusion to 275 ± 8 Ma (MSWD = 0.11) ; the initial Sr isotope ratio (0.7089 ± 0.0034) and the occurrence of fayalite in some rock-types suggests that magma production involved mantle-derived materials.