Abstract
Many calderas show repeated unrest over centuries. Though probably induced by magma, this unique behaviour is not understood and its dynamics remains elusive. To better understand these restless calderas, we interpret deformation data and build thermal models of Campi Flegrei caldera, Italy. Campi Flegrei experienced at least 4 major unrest episodes in the last decades. Our results indicate that the inflation and deflation of magmatic sources at the same location explain most deformation, at least since the build-up of the last 1538 AD eruption. However, such a repeated magma emplacement requires a persistently hot crust. Our thermal models show that this repeated emplacement was assisted by the thermal anomaly created by magma that was intruded at shallow depth ~3 ka before the last eruption. This may explain the persistence of the magmatic sources promoting the restless behaviour of the Campi Flegrei caldera; moreover, it explains the crystallization, re-melting and mixing among compositionally distinct magmas recorded in young volcanic rocks. Our model of thermally-assisted unrest may have a wider applicability, possibly explaining also the dynamics of other restless calderas.
Highlights
To better understand restless calderas, we consider the recent history of Campi Flegrei, one of the best-known, yet most dangerous calderas, lying to the west of Naples and restless since the 1950s at least
An uplift of a fewmetres was observed in the peripheral areas of the caldera. In these same sites there has been no uplift during the unrest episodes of the last decades
Petrological data suggest that mafic magmas rise from the mantle up to a 8–10 km deep crustal level beneath Campi Flegrei, where they stagnate and differentiate; from there, silicic magmas rise towards 3–4 km deep crustal reservoirs[17]
Summary
To better understand restless calderas, we consider the recent history of Campi Flegrei, one of the best-known, yet most dangerous calderas, lying to the west of Naples and restless since the 1950s at least. Other studies underline the important role of magmatic gases on the deformation[14], heating the hydrothermal fluids and rocks[15] These and other petrological studies[16,17] concur in delineating the commonly accepted general architecture of the magmatic plumbing system below Campi Flegrei; this consists of an ~8 km deep main oblate reservoir, where mantle-derived primitive magmas reside undergoing differentiation and from which more differentiated magmas rise toward smaller oblate reservoirs, at 3–4 km depth. This magmatic model is consistent with the eruptions of more primitive magmas (mainly through regional fracture systems18) and the gas release from primitive magma in the deeper reservoir, feeding the shallower reservoirs[14]
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