Recent volcanic accretion at 9 degrees N-10 degrees N East Pacific Rise as resolved by combined geochemical and geological observations

TitleRecent volcanic accretion at 9 degrees N-10 degrees N East Pacific Rise as resolved by combined geochemical and geological observations
Publication TypeJournal Article
Year of Publication2013
AuthorsWaters C.L, Sims K.WW, Soule S.A, Blichert-Toft J., Dunbar N.W, Plank T., Prytulak J., Sohn R.A, Tivey M.A
JournalGeochemistry Geophysics Geosystems
Volume14
Pagination2547-2574
Date Published2013/08
Type of ArticleArticle
ISBN Number1525-2027
Accession NumberWOS:000326242700001
Keywordscrustal emplacement processes; east pacific rise; geochemistry; Geochronology; heterogeneity; hf isotope; lava-flow morphology; mantle; mid-atlantic ridge; off-axis volcanism; ra-226 th-230 disequilibrium; seismic layer 2a; series disequilibria; spreading midocean ridges; U-series
Abstract

The ridge crest at 9 degrees N-10 degrees N East Pacific Rise (EPR) is dominated by overlapping lava flows that have overflowed the axial summit trough and flowed off-axis, forming a shingle-patterned terrain up to approximate to 2-4 km on either side of the axial summit trough. In this study, we employ Th-230-Ra-226 dating methods, in conjunction with geochemistry and seafloor geological observations, in an effort to discern the stratigraphic relationships between adjacent flows. We measured major and trace elements and Sr-87/Sr-86, Nd-143/Nd-144, Hf-176/Hf-177, and U-238-Th-230-Ra-226 for lava glass samples collected from several flow units up to approximate to 2 km away from the axial summit trough on the ridge crest at 9 degrees 50N EPR. Statistical analysis of the U-238-Th-230-Ra-226 data indicates that all but one measured sample from these flows cannot be resolved from the zero-age population; thus, we cannot confidently assign model ages to samples for discerning stratigraphic relationships among flows. However, because groups of samples can be distinguished based on similarities in geochemical compositions, particularly incompatible element abundances with high precision-normalized variability such as U and Th, and because the range of compositions is much greater than that represented by samples from the 1991-1992 and 2005-2006 eruptions, we suggest that the dive samples represent 6-10 eruptive units despite indistinguishable model ages. Geochemical variability between individual flows with similar ages requires relatively rapid changes in parental melt composition over the past approximate to 2 ka, and this likely reflects variations in the relative mixing proportions of depleted and enriched melts derived from a heterogeneous mantle source.

DOI10.1002/ggge.20134
Short TitleGeochem. Geophys. Geosyst.
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