Faial is one of the most volcanically active islands of the Azores Archipelago. Historical eruptions occurred on the Capelo Peninsula (westernmost sector of the island) during A.D. 1672–1673 and more recently in A.D. 1957–1958. The other exposed volcanic products of the peninsula are so far loosely dated within the Holocene. Here, we present a successful attempt to correlate scoria cones and lava flows yielded by the same eruption on the Capelo Peninsula using paleomagnetic data from 31 sites (10 basaltic scoriae, 21 basaltic lava flows). In the investigated products, we recognize at least six prehistoric clusters of volcanic activity, whereas 11 lava sites are correlated with four scoria cones. Dating was conducted by comparing our paleomagnetic directions with relocated Holocene reference curves of the paleosecular variation of the geomagnetic field from France and the UK. We find that the studied volcanic rocks exposed on the Capelo Peninsula are younger than previously believed, being entirely formed in the last 8 k.y., and that the activity intensified over the last 3 k.y. Our study confirms that paleomagnetism is a powerful tool for unraveling the chronology and characteristics of Holocene activity at volcanoes where geochronological age constraints are still lacking

Furnas is one of three active central volcanoes on São Miguel Island, Azores, and is considered to be one of the most hazardous in the archipelago. In this study, the pre-eruptive magma plumbing system of the 10 young (<5 ka), intra-caldera, sub-Plinian, trachytic eruptions of the Upper Furnas Group (UFG) is investigated via whole rock major and trace element geochemistry, mineral chemistry, thermobarometry, and petrogenetic modelling. The main aim of this work is to elucidate the petrogenesis of the Furnas trachytes, constrain the P–T–fO₂ conditions under which they evolve, and investigate the temporal evolution of the magma plumbing system. Results indicate that the trachytes are derived predominantly from extended fractional crystallisation of alkali basalt parental magmas, at depths between ~3 and 4 km. This is considered to take place in a density-stratified reservoir, with alkali basalt magmas at the base and hydrous trachytes forming an upper cap or cupola. The presence of this reservoir at shallow crustal depths beneath the caldera likely inhibits the ascent and subsequent eruption of mafic magmas, generating a compositional Daly Gap. Rare syenitic ejecta represent in situ crystallisation of trachytic magmas in the thermal boundary zone at the top of the reservoir. Trachytic enclaves within these syenites, in addition to banded pumices and ubiquitous clinopyroxene antecrysts in the UFG pumice falls, provide evidence for mingling/mixing processes within the magmatic system. Despite relatively uniform major element compositions, systematic trace element variations within individual eruptions highlight the importance of fractional crystallisation during late-stage evolution of the trachytes. This is facilitated by the accumulation of water and the development of mild peralkalinity, which contribute to low pre-eruptive melt viscosities and efficient crystal settling. Compositional zoning patterns between individual eruptions cannot be accounted for by periodic tapping of a single magma batch undergoing fractional crystallisation. Instead, up to four individual cycles are recognised, in which a zoned cap of eruptible trachytic magma, formed at the top of the reservoir, was erupted in one or more eruptions and was re-established via intermittent replenishment and subsequent fractional crystallisation.

The mafic magmatism of the last 50 ka on Terceira Island, Azores archipelago, occurred along three segments of the fissure zone that crosses the island. The two subaerial segments developed with different trends over pre-existing, quiescent or extinct, central volcanoes. The Serreta submarine ridge is the offshore segment of the fissure zone that erupted recently in 1998–2001. The combined study of CO₂+H₂O fluid inclusions hosted in mafic minerals and rock geochemistry of the magmas, reveals different storage and ascent conditions among the fissure zone segments. The maximum pressure of fluid trapping for all the fissure systems occurred at the Moho Transition Zone, between 498 and 575 MPa (20.3–21 km deep). At this depth interval all magmas stagnated for some time, before ascending toward the surface, experiencing fractional crystallization and degassing. Magmas of the southeastern and Serreta segments of the fissure zone ascended rapidly through the crust without further stops. Those of the central segment experienced a multi-step ascent, with fluid trapping at 406 and 209 MPa (16.5–8.5 km deep) and associated geochemical evolution toward trachybasalt. The magma ascent below the different segments of the fissure zone varies from almost isochoric at the submarine segment, associated with minimum re-equilibration of the inclusions, to polybaric slow ascent at the central segment, associated to almost complete re-equilibration of the inclusions. Variable degrees of re-equilibration and multi-step ascent may be linked to both the presence of pre-existing intracrustal crystallized bodies of more evolved composition and the stress field acting on this area. The latter responds to the local and shallow conditions related to the presence of older central volcanoes and to the main regional spreading direction of the Terceira Rift, which at regional scale, is approximately orthogonal to the fissure zone axis.