Structural setting and magmatic evolution of Montefiascone volcanic complex, vulsini district, central Italy

Abstract

Abstract A comparative study concerning volcanological, petrographic and geochemical aspects of Montefiascone Volcanic Complex has been carried out. This complex, together with those of Paleo-Bolsena, Bolsena and Latera, forms the Vulsini Volcanic District, located in the northernmost part of Roman Comagmatic Province. Four groups of lavas, belonging to Montefiascone Volcanic Complex, have been recognized on petrographic and geochemical grounds: Tephritic Leucitites (TEL), Leucite-Bearing Basanites (LBSN), Evolved Tephritic Leucitites (ETEL) and Leucititic Tephrites (LT). Lavas clearly show Ti and Nb anomalies, further supporting the genesis of these magmas from a subduction-related metasomatized mantle source. The majority of the lava erupted, comparable in volume with the pyroclastic products, appears to be of leucititic affinity, having suffered only a slight amount of differentiation. Major- and trace-element compositions very similar to those of ETEL and LT have been obtained from TEL and LBSN by means of simple mass balance and Rayleigh fractional crystallization model. According to petrographic observations, main liquidus phases are clinopyroxene, leucite, olivine and magnetite, and magmatic differentiation acts essentially by fractional crystallization. Eruptive activity is spread over a large area and the volcanic centres are aligned following NNW-SSE, WNW-ESE and E-W directions. Explosive activity, on the other hand, was mainly located at Montefiascone Caldera. The great abundance of nearly primary magmas in the area leads us to think that the structural setting was not suitable for developing a great, unique magma reservoir, but rather a series of small, elongated bodies.