The genetic link between the Azores Archipelago and the Southern Azores Seamount Chain (SASC): The elemental, isotopic and chronological evidences

Abstract

New geochemical, isotopic (Sr-Nd-Hf-Pb) and K-Ar data, are presented here on samples from the Southern Azores Seamount Chain (SASC) located south of the Azores Plateau. The SASC also includes the Great Meteor, Small Meteor and Closs seamounts, morphologically connected by a saddle at − 4100 m deep. We conclude that the SASC are characterized by a narrow isotopic variability that falls within the Azores isotopic field. Although each seamount has its own isotopic signature, their mantle source must comprise four local mantle end-members, three of which are common to the Azores, e.g. Plato isotopic signature results from the mixing between HIMU and N-MORB while Great Meteor signature results from this mix with the Azores Common Component (AzCC). A fourth end-member with high 208 Pb/ 204 Pb and decoupled Th/U ratios (Δ8/4 up to 59.2) is identified on Great Meteor northern flank. New K-Ar ages on Plato (33.4 ± 0.5 Ma) and Small Hyeres (31.6 ± 0.4 Ma) show nearly coeval volcanism, which is contemporaneous with the E-MORBs erupted at the MAR, drilled on oceanic crust with 30-34 Ma (DSDP82). This study endorses the genetic link between the Azores Archipelago and the SASC to the long-term activity of the Azores plume and the large-scale ridge-hotspot interaction, contributing to better constrain the temporal-spatial evolution of this region of the North Atlantic.

Northward drift of the Azores plume in the Earth’s mantle

“…The direct K–Ar 46 and indirect 47 dating of these complexes were traditionally used to affiliate them to the New-England hotspot track mainly located on the North-American plate 2 , despite major uncertainties on the age determination of these seamounts (ranging from 11 to 65 Ma for Great Meteor). However, recent tectonic 45 , geochronological and geochemical 48 studies bring complementary information for a genetic link with the Azores. A northward motion of the Azores plume at a rate of 1–2 cm/yr is consistent with such scenario of building a track from 85 to 20 Ma and the proposed migration of the plume away from the MAR at 10 ± 5 Ma 45 .…”

The Mechanical Nature of the Lithosphere Beneath the Eastern Central Atlantic Hotspots

“…New K-Ar age determinations show nearly coeval volcanism along the chain, with ages of ∼31-34 Ma (Ribeiro et al, 2017). A genetic link between the Azores Archipelago and the SASC has been proposed by Ribeiro et al (2017) on the basis of geophysical observations (Gente et al, 2003) and recent geochemical and isotopic (Sr-Nd-Pb-Hf) data. These authors suggest that the geochemical similarity between the SASC and the Azores mantle source resulted from the long-lived (∼85 Ma) Azores Plume.…”

“…The Great Meteor Seamount is rooted in a crust of 85 Ma age (Verhoef, 1984), and belongs to the Southern Azores Seamount Chain (SASC) located south of the Azores Plateau (Figure 1). The SASC is characterized by narrow isotopic variability that falls within the Azores isotopic field (Ribeiro et al., 2017). New K‐Ar age determinations show nearly coeval volcanism along the chain, with ages of ∼31–34 Ma (Ribeiro et al., 2017).…”

“…The SASC is characterized by narrow isotopic variability that falls within the Azores isotopic field (Ribeiro et al., 2017). New K‐Ar age determinations show nearly coeval volcanism along the chain, with ages of ∼31–34 Ma (Ribeiro et al., 2017). A genetic link between the Azores Archipelago and the SASC has been proposed by Ribeiro et al.…”

The dispersal capacity of Mollusca—a test on the South Azorean Seamount Chain

“…The other seamounts have a smaller plateau (Irving with about 750 km 2 , Atlantis and Hyères with about 350 km 2 ) or a summit deeper than 600 m like Plato. The SASC originated from the activity of the long-lived Azores mantle plume beneath the mid-Atlantic oceanic lithosphere (Ribeiro et al 2017). Great Meteor is not a piece of drifting continental plate, as had been once suggested (Fleischer et al 1970), and the flattened plateaus of the seamounts are believed to be abrasion surfaces formed near sea-level (Tucholke and Smoot 1990).…”