Mantle heterogeneity beneath the Nazca plate: San Felix and Juan Fernandez islands

• Published in: Nature (London) 1986-07, Vol.322 (6075), p.165-169
• Main Authors: Gerlach, D. C, Hart, S. R, Morales, V. W. J, Palacios, C
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Humanities and Social Sciences; Internal geophysics; Isotope geochemistry; Isotope geochemistry. Geochronology; letter; Marine; multidisciplinary; Science; Science (multidisciplinary); Solid-earth geophysics, tectonophysics, gravimetry
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/322165a0

The islands of San Felix, San Ambrosio and the Juan Fernandez group comprise one of the few subaerial occurrences of intraplate oceanic volcanism between the Mid-Atlantic Ridge and the East Pacific Rise south of 20° S, and are therefore valuable in the assessment of large-scale geochemical heterogeneities in the Earth's mantle 1–3 . We present here the results of a preliminary Sr, Nd and Pb iosotpic study of basic lavas from these islands. All samples show a moderate Dupal 3 signature (anomalous Sr, Nd and Pb isotopic compositions). Basalts from the Juan Fernandez group lie close to the mantle plane 4 , whereas basalts from San Felix display unusual isotopic characteristics which plot well below the Nd–Sr oceanic array. Based on this data, we propose the delineation of a new mantle array, linear in Nd–Sr–Pb isotopic space, with Tubuaii and Walvis Ridge as end members. The mixing relationships exhibited by this array suggest that both end members are geographically contiguous, and probably reside in delaminated sub-continental lithosphere.