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Journal of Petrology | Volume 45 | Number 1 | Pages 139-182 | 2004
© Oxford University Press 2004; all rights reserved
Evolution and Genesis of Magmas from Vico Volcano, Central Italy: Multiple Differentiation Pathways and Variable Parental Magmas
1 DIPARTIMENTO DI SCIENZE DELLA TERRA, UNIVERSITÀ DEGLI STUDI DI FIRENZE, VIA LA PIRA 4, I-50121, FIRENZE, ITALY
2 ISTITUTO DI GEOSCIENZE E GEORISORSE, C.N.R., SEZIONE DI FIRENZE, VIA G. LA PIRA, 4, I-50121, FIRENZE, ITALY
3 DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF DURHAM, SOUTH ROAD, DURHAM DHI 3LE, UK
* Corresponding author: Telephone: +390552756224. Fax: +39055218628. E-mail: gperini{at}steno.geo.unifi.it
Vico volcano has erupted potassic and ultrapotassic magmas, ranging from silica-saturated to silica-undersaturated types, in three distinct volcanic periods over the past 0·5 Myr. During Period I magma compositions changed from latite to trachyte and rhyolite, with minor phono-tephrite; during Periods II and III the erupted magmas were primarly phono-tephrite to tephri-phonolite and phonolite; however, magmatic episodes involving leucite-free eruptives with latitic, trachytic and olivine latitic compositions also occurred. In Period II, leucite-bearing magmas (87Sr/86Srinitial = 0·71037–0·71115) were derived from a primitive tephrite parental magma. Modelling of phonolites with different modal plagioclase and Sr contents indicates that low-Sr phonolitic lavas differentiated from tephri-phonolite by fractional crystallization of 7% olivine + 27% clinopyroxene + 54% plagioclase + 10% Fe–Ti oxides + 4% apatite at low pressure, whereas high-Sr phonolitic lavas were generated by fractional crystallization at higher pressure. More differentiated phonolites were generated from the parental magma of the high-Sr phonolitic tephra by fractional crystallization of 10–29% clinopyroxene + 12–15% plagioclase + 44–67% sanidine + 2–4% phlogopite + 1–3% apatite + 7–10% Fe–Ti oxides. In contrast, leucite-bearing rocks of Period III (87Sr/86Srinitial = 0·70812–0·70948) were derived from a potassic trachybasalt by assimilation–fractional crystallization with 20–40% of solid removed and r = 0·4–0·5 (where r is assimilation rate/crystallization rate) at different pressures. Silica-saturated magmas of Period II (87Sr/86Srinitial = 0·71044–0·71052) appear to have been generated from an olivine latite similar to some of the youngest erupted products. A primitive tephrite, a potassic trachybasalt and an olivine latite are inferred to be the parental magmas at Vico. These magmas were generated by partial melting of a veined lithospheric mantle sources with different vein–peridotite/wall-rock proportions, amount of residual apatite and distinct isolation times for the veins.
KEY WORDS: isotope and trace element geochemistry; polybaric differentiation; veined mantle; potassic and ultrapotassic rocks; Vico volcano; central Italy
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