Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: The Faial Island example (Azores)

Abstract

a b s t r a c t a r t i c l e i n f oThe morpho-structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass-wasting processes. We present here a multi-disciplinary study of the successive stages of development of Faial (Azores) during the last 1 Myr. Using high-resolution digital elevation model (DEM), and new K/Ar, tectonic, and magnetic data, we reconstruct the rapidly evolving topography at successive stages, in response to complex interactions between volcanic construction and mass wasting, including the development of a graben. We show that: (1) sub-aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca. 0.85 Ma, followed by its partial destruction over half a million years; (2) beginning about 360 ka a new small edifice grew on the NE of the island, and was subsequently cut by normal faults responsible for initiation of the graben; (3) after an apparent pause of ca. 250 kyr, the large Central Volcano (CV) developed on the western side of the island at ca 120 ka, accumulating a thick pile of lava flows in less than 20 kyr, which were partly channelized within the graben; (4) the period between 120 ka and 40 ka is marked by widespread deformation at the island scale, including westward propagation of faulting and associated erosion of the graben walls, which produced sedimentary deposits; subsequent growth of the CV at 40 ka was then constrained within the graben, with lava flowing onto the sediments up to the eastern shore; (5) the island evolution during the Holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano-tectonic depression. We conclude that the whole evolution of Faial Island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation. Each pulse has been separated by considerable periods of volcanic inactivity during which the Faial graben gradually developed. We propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement, as observed historically, when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the Capelinhos eruptive crises .

Constraints on the structure of the crust and lithosphere beneath the Azores Islands from teleseismic receiver functions

“…Setting of the Azores Islands with location of 10 seismic stations (names in brackets). The oldest radiometric age for each island are indicated (Chovelon 1982;Johnson et al 1998;Azevedo & Ferreira 2006;Calvert et al 2006;França et al 2006;Hildenbrand et al 2008;Hildenbrand et al 2012;Sibrant et al 2015a,b;Ramalho et al 2017). TR, Terceira Ridge; MAR, Middle Atlantic Ridge; PAR, Princess Alice Ridge; EAFZ, East Azores Fracture Zone; GF, Glória Fault; Eu, Eurasian Plate; Nu, Nubian Plate; NA, North American Plate.…”

Soil CO2 Degassing Path along Volcano-Tectonic Structures in the Pico-Faial-São Jorge Islands (Azores Archipelago, Portugal)

“…The CO 2 degassing maps here presented are thus important tools that characterize the CO 2 emission in quiescent periods of activity and are important to identify future periods of reactivation. Besides, several studies performed in these islands (e.g., Madeira and Brum da Silveira, 2003;Hildenbrand et al, 2012;Zanon and Frezzotti, 2013;Trippanera et al, 2014) have highlighted the importance of the tectonic control on the plumbing systems of the volcanoes, and most of the main degassing areas are also tectonically controlled, what reinforces the need to integrate different geological studies to better understand the volcanic systems. On another hand, the location of some of the identified DDS close to inhabited areas highlights the need to identify hazardous CO 2 zones both for the existing and for future constructions.…”

“…Faial Island is composed by four main volcanic systems: the Ribeirinha (848 to 358 ka) and Caldeira (>440 ka) central volcanoes and two basaltic fissure systems (Horta Platform and Capelo Peninsula fissure systems; Chovelon, 1982;Demande et al, 1982;Serralheiro et al, 1989;Pacheco, 2001Pacheco, , 2015Hildenbrand et al, 2012). Ribeirinha Volcano, located on the northeast sector of the island, is the oldest system and extensively dissected by the Pedro Miguel Graben (Pacheco, 2015).…”

“…Caldeira Volcano dominates the morphology of the island as the summit is truncated by a 2 km wide, 400 m deep caldera (Madeira and Brum da Silveira, 2003). Hildenbrand et al (2012) proposed a much younger age (about 120 ka ago) for the beginning of the subaerial shield-building phase of this volcanic system, when compared with the previous studies (Féraud et al, 1980). In what concerns the fissural systems, Horta Platform system should be active since at least 11 ka BP and its more recent activity is older than 6 ka BP (Serralheiro et al, 1989;Pacheco, 2015); Capelo Peninsula fissure system is the youngest volcanic system on the Island and the activity may have started between 8 and 6 ka BP (Madeira, 1998;Di Chiara et al, 2014).…”

A cirkon (U-Th)/He kormeghatározás módszertani alapjai és alkalmazása fiatal (<1 Ma) vulkánkitörések datálására

“…leucit vagy szanidin), hanem ezek hiányában teljeskőzet-mintán történik (vagy akár biotiton, amfibo lon), akkor az Ar-többlet hatása a ténylegesnél idősebb kort eredményezhet (pl. HORA et al 2007, HILDENBRAND et al 2012.…”