An ⁴⁰Ar‐³⁹Ar study of the Cape Verde hot spot: Temporal evolution in a semistationary plate environment

Abstract

The 40Ar‐39Ar analyses of 28 groundmass separates from volcanic rocks from the islands of Santiago, Sal, and São Vicente, Cape Verde archipelago, are presented. The new age data record the volcanic evolution for Santiago from 4.6 to 0.7 Ma, for Sal from around 15 to 1.1 Ma, and for São Vicente from 6.6 to 0.3 Ma. The major submarine constructional phase of Santiago was erupted within a few hundred thousand years interval around 4.6 Ma. Most of the subaerial Santiago volcanic rocks were erupted in a second episode from 3.3 to 2.2 Ma and late volcanism occurred at 1.1–0.7 Ma. Volcanism on Sal evolved in five stages: (1) poorly constrained early Miocene activity, (2) 16–14 Ma, (3) 12–8 Ma, (4) around 5.4 Ma, and (5) 1.1–0.6 Ma. São Vicente was constructed during three active periods: (1) >6.6–5.9 Ma, (2) 4.7–4.5 Ma, and (3) ∼0.3 Ma. Sr isotope analyses of carbonates from Maio confirm an Early Cretaceous age for limestones deposited on the seafloor and later uplifted. The Cape Verde Rise is indicated to have fully formed in the early Miocene around 22 Ma, accompanied by the initial alkaline volcanism. Considerable volcanism on Sal, Boa Vista, and Maio took place in the Miocene and Pliocene and extended over much larger areas than the present islands, whereas volcanism of the southwestern and northwestern island groups developed mainly during the Pliocene and Pleistocene and was mostly confined to the present island areas. The periods of volcanic activity may be broadly correlated between the northwestern and southwestern groups of islands. Young volcanism (0.3–0.1 Ma) throughout the northwestern group extends along a 150 km long NW‐SE trending lineament. A relatively moderate average melting rate for the hot spot over the 22 Ma period is estimated at ∼0.026 km3/a, corresponding to a total volume of 570 × 103 km3 of magma emplaced in the crust and a mantle volume flux of 28 m3/s, much lower than Iceland or Hawaii. The archipelago is situated to the south and SW of the center of the mantle plume anomaly and ahead of its relative movement. The timing and location of volcanism suggest that mantle melting takes place in three channels, an eastern one that has been active for 22 Ma and in southwestern and northwestern channels since late Miocene.

Tracers of Uplift and Subsidence in the Cape Verde Archipelago

“…However, it is more likely that the Principal Eruptive Formation and the Ponta do Altar-Baleia Complex were extruded during the same event, in a wider period between 16 and 9 Ma. This possibility is suggested by the island's volcanic structure and the apparently synchronous available geochronological data (Torres et al 2002a;Holm et al 2008), a possibility already admitted by Torres et al (2002a).…”

“…It is possible in places to observe the passage zone between subaerial and submarine morphologies, suggesting a contemporaneous water level at ∼ 50 m asl. The precise age of these lavas is still unknown because the geochronological data published so far (Torres et al 2002a;Holm et al 2008) was determined in the subaerial lavas found several kilometers to the south. The fact that the upper sequence of the Principal Eruptive Formation is presently found as low as the modern sea-level suggests that the relative sea-level height during the age range of its products was below the present level.…”

“…The sequence comprise NW dipping foresets of hyaloclastite breccia, with clusters of pillow-lavas, covered by flat-lying subaerial lavas not exceeding a total thickness of 10 to 15 m. The passage zone is clearly visible and regularly crop out at ∼ 90 m asl, constituting a solid indication of contemporaneous sea-level height. The subaerial lavas seem to have been extruded around 5.5 Ma (Torres et al 2002a;Holm et al 2008), so we assume the submarine lavas to be contemporaneous. The Serra Negra Formation lies conformably over the Ribeira de Fragata Formation.…”

“…Holm et al (2008) proposed an age range of 16 to 14 Ma for the lower series, considering the upper series to be part of the Ponta do Altar-Baleia Complex. However, it is more likely that the Principal Eruptive Formation and the Ponta do Altar-Baleia Complex were extruded during the same event, in a wider period between 16 and 9 Ma.…”

Multi-storey calcrete profiles developed during the initial stages of the configuration of the Ebro Basin's exorrheic fluvial network

“…As in the near island of Maio (Bemard-Griffiths et al, 1975;Grunau et al, 1975;Mitchell et al, 1983;Holm et al, 2008), no evi dence of volcanic activity after 4 Ma existed in Boa Vista. By contrast, in Sal also a nearby island there was activity in Pleistocene times (Torre5 et aI., 2002).…”