Emergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited

Abstract

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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.…”

“…The youngest and most active islands are Faial, Terceira and Pico of the Central Group, and São Miguel located in the eastern part of the plateau. The easternmost island, Santa Maria, shows no sign of recent activity and hosts the oldest rocks of the Archipelago, with a maximum radiometric age of 6 Ma (Sibrant et al 2015a;Ramalho et al 2017). Owing to slow gradual subsidence of aging oceanic crust (and volcanic loading in the case of the younger islands), one would expect the islands to subside (Sclater et al 1971) which is true for most islands on the plateau.…”

“…However, Santa Maria experienced recent significant uplift that started 3.5 Ma ago and which is most likely not related to flexural loading or erosion. Instead, magmatic intrusions/underplating below the oceanic crust is a more probable cause for the uplift (Ramalho et al 2017).…”

Intense hurricane transports sand onshore: Example from the Pliocene Malbusca section on Santa Maria Island (Azores, Portugal)

“…Santa Maria in the Azores (Fig. 1A) is one such island with extensive, lower Pliocene marine carbonates preserved by volcanic activity and exposed by subsequent uplift and erosion (Ávila et al, 2015;Rebelo et al, 2016;Ramalho et al, 2017). The south shore Malbusca section exhibits a 150-m, volcano-sedimentary sequence containing effusive products inter-bedded with bioclastic-rich sandstone, capped by subaerial lava flows (Fig.…”

“…A conceptual model (Fig. 3A, B) depicts physical relationships at Malbusca prior to development of the upper volcanic units (Ramalho et al, 2017) when the island was much like today's platform around the razed volcanic edifice of Lord Howe Island in the Tasman Sea (Kennedy et al, 2011).…”