Origin of widespread Cretaceous alkaline magmatism in the Central Atlantic: a single melting anomaly?

• Published in: Lithos
• Main Authors: Merle, Renaud E., Jourdan, Fred, Chiaradia, Massimo, Olierook, Hugo K.H., Manatschal, Gianreto
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: info:eu-repo/classification/ddc/550; Central Atlantic Ocean; New England Seamounts; Geochronology; Cretaceous alkaline magmatism; Tore–Madeira Rise; Mid-Atlantic Ridge; Nash; Nes; Nes’; North Atlantic
• Online Access: https://archive-ouverte.unige.ch/unige:120450

The age and origin of the Late Cretaceous magmatism on the North American and Iberian-African margins and the adjacent northern Central and Southern North Atlantic ocean are not well constrained due to the lack of ap- propriate data. To solve this issue, we used the 40Ar/39Ar geochronology and Sr-Nd-Pb isotopes geochemistry of basalts from the New England Seamounts (NES) and the J-Anomaly Ridge (JAR) as these localities on the North American margin are still poorly investigated. We obtained a reliable age of 82.39 ± 0.12 Ma (2σ) for the Nash- ville Seamount (NES) and an alteration age of ca. 76 Ma for the JAR. Our new dates from the New England Sea- mounts, combined with those available from the Tore–Madeira Rise and SW Portugal, on the Iberia–African margins, confirm an overlapping period of activity around 105-80 Ma on both the North American and Iberian-African margins and the adjacent oceanic basins. Plate kinematic reconstructions indicate that these mag- matic occurrences were located within a ~1000 km radius within the yet narrow Atlantic Ocean. The J-Anomaly Ridge samples were most likely formed at the mid-Atlantic ridge around ~120 Ma. The Sr-Nd-Pb initial isotopic ratios from the New England seamounts show similarities with the chemical signa- ture of the Tore–Madeira Rise and, to a lesser extent, SW Portugal. Moreover, New England Seamounts display a trend toward EMI isotopic end-member, similar to those documented in at the Late Cretaceous Godzilla sea- mount on the Tore–Madeira Rise and sills from ODP Site 1276. The shared chemical signature is distributed across a torus-shaped area of ~2000 × 2000 km at a near-fixed location on Earth and is not temporally-controlled, sug- gesting a large-scale chemical anomaly in the shallow mantle. Therefore, geochronological, geochemical and plate reconstructions imply a large-scale, anomalously fertile mantle source that generated widespread magmatism during the Late Cretaceous in the northern Central Atlantic.