Spatial and temporal distribution of a C ‐like asthenospheric component in the Rano Rahi Seamount Field, East Pacific Rise, 15°–19°S
2006; Wiley; Volume: 7; Issue: 3 Linguagem: Inglês
10.1029/2005gc000994
ISSN1525-2027
AutoresL. Standish Hall, John J. Mahoney, John M. Sinton, Robert A. Duncan,
Tópico(s)earthquake and tectonic studies
ResumoLavas of the Rano Rahi seamount field define a Nd‐Pb‐Sr isotopic array that connects, and substantially overlaps, the arrays of the nearby East Pacific Rise axis and 5.6–28 Ma lavas of the Pukapuka ridge system, situated between the seamount field and French Polynesia. Dating of Rano Rahi samples by 40 Ar‐ 39 Ar incremental heating methods yields ages between 0.23 and 4.67 Ma. Most of the dated lavas were erupted within 60 km of the axis, and no systematic isotopic variation with age is observed. The isotopic and incompatible element data indicate a persistent two‐component mantle source comprising variable proportions of normal Pacific ocean‐ridge‐type mantle and a “ C ”‐like Pukapuka end‐member with lower ɛ Nd , higher 87 Sr/ 86 Sr and 206 Pb/ 204 Pb, and relative enrichment in the highly incompatible elements. The Rano Rahi data reveal peaks of low ɛ Nd , high 87 Sr/ 86 Sr, and high 206 Pb/ 204 Pb at about 16°–17°S and 18.5°–19°S that appear to correspond to two concentrations of C ‐rich mantle, probably streaming eastward from French Polynesia. The northern stream may have reached the axis more recently and/or be less continuous than the southern stream.
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