Christopher L. Waters, University of California San Diego
Kenneth W. Sims, University of WyomingFollow
Samuel Adam Soule, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
Janne Blichert-Toft, Laboratoire de G eologie de Lyon, Ecole Normale Sup erieure de Lyon and Universit e Claude Bernard Lyon 1,Lyon, France
Nelia W. Dunbar, New Mexico Tech, Socorro, New Mexico
Terry A. Plank, Columbia University
Julie Prytulak, Imperial College, London, UK
Robert Sohn, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
Maurice A. Tivey, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
The ridge crest at 9°N-10°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 ∼2-4 km on either side of the axial summit trough. In this study, we employ 230Th- 226Ra 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 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, and 238U-230Th- 226Ra for lava glass samples collected from several flow units up to ∼2 km away from the axial summit trough on the ridge crest at 9°50′N EPR. Statistical analysis of the 238U- 230Th-226Ra 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 ∼2 ka, and this likely reflects variations in the relative mixing proportions of depleted and enriched melts derived from a heterogeneous mantle source. ©2013. American Geophysical Union. All Rights Reserved.
Geochemistry, Geophysics, Geosystems
Waters, Christopher L.; Sims, Kenneth W.; Soule, Samuel Adam; Blichert-Toft, Janne; Dunbar, Nelia W.; Plank, Terry A.; Prytulak, Julie; Sohn, Robert; and Tivey, Maurice A. (2013). "Recent Volcanic Accretion at 9°N-10°N East Pacific Rise as Resolved by Combined Geochemical and Geological Observations." Geochemistry, Geophysics, Geosystems 14.8, 2547-2574.