Thermal evolution of the Phlegraean magmatic system

Abstract

A series of 2-D conductive/convective numerical models show a rather limited range of possible magma chamber configurations that predict the present thermal regime at Campi Flegrei. These models are calculated by HEAT, which allows continuous adjustment of heterogeneous rock properties, magma injection/replenishment, and convective regimes. The basic test of each model is how well it reproduces the measured thermal gradients in boreholes at Licola, San Vito, and Mofete reported by AGIP in 1987. The initial and boundary conditions for each model consists of a general crustal structure determined by geology and geophysics and major magmatic events: (1) the 37 ka Campanian Ignimbrite; (2) smaller volume 37–16 ka eruptions; (3) the 12 ka Neapolitan Yellow Tuff; (4) recent magmatism (e.g., Minopoli at ∼10 ka and Monte Nuovo in 1538 AD). While magma chamber depth is well constrained, magma chamber diameter, shape, volume, and peripheral convective regimes are poorly known. Magma chamber volumes between 200 and 2000 km 3 have been investigated with cylindrical, conical (funnel-shaped), and spheroidal shapes. For all reasonable models, a convective zone, developed above the magma chambers after caldera collapse, is necessary to achieve the high gradients seen today. These models should help us understand recent bradyseismic events and future unrest.