NSF Forms - Ridge 2000 Program

lies on the far side of a ridge that separates it from the axis. If this sample proves to be young (~ 1 gram) visibly unaltered, fresh glass are indicated by
special symbols in the data figures. As with all U-series disequilibrium studies ( 234 U/ 238 U) will be
measured on each glass to ensure the absence of post-eruptive alteration or assimilation of altered
crust. We plan to analyze six samples from the ABE bulls-eye region, two from each of the other
hydrothermal sites, and thirty additional samples from the length of the ELSC and VFR,
encompassing the entire range of chemical variation. That makes a total of 44 samples. All of these
samples will be analyzed for 226 Ra, 230 Th, 232 Th, 238 U and 234 U. A subset of samples from the
hydrothermal sites will also be analyzed for 210 Pb directly by gamma measurements and by alpha
spectrometry using 210 Po as a proxy. These measurements are important as disequilibria will
indicate that the samples are less than 100 years. We have several samples appropriate for such
measurements. In addition, new samples from the Fisher cruise (see letter in Appendix) could
contribute to our U-series studies. The Scripps resident technicians are experts in rock sampling,
and will be providing the necessary on board assistance. We emphasize that we do not require these
samples for the success of our proposed program, but we will certainly make use of them if they are
obtained as planned.
Our scientific aims require high precision measurements that are possible at only a handful of
laboratories in the world. Dissolution and spiking of samples will follow the methods of [Sims et
al., 2002; Standish, 2005], which together with chemical separation techniques [Goldstein et al.,
1989; Layne and Sims, 2000] will be completed at Harvard in Langmuir’s clean lab. Standish
carried out U-series measurements as part of his thesis, and he will use the same methods and Sims’
spikes to do the chemistry at Harvard. If we hear that the proposal will be funded, Standish will
immediately begin the chemistry, and we anticipate the lab to be fully operational before the start
date of the project.
Because concentrations of U-series isotopes in volcanic rocks are very low, these measurements
also require high sensitivity and high–abundance sensitivity mass spectrometers, capable of
measuring as few as 10 8 atoms and isotopic ratios as small as 10 -6 . WHOI owns two mass
spectrometers ideally suited for the measurement of U-series nuclides, as detailed in the facilities
section, and such data from WHOI are already included in more than a dozen publications.
7. RESPONSIBILITIES OF PERSONNEL AND WORK PLAN
This work involves a multi-disciplinary approach, where diverse geochemical tools will be
combined with geological constraints and interaction with those investigating hydrothermal systems
and the biota. Our team for this proposal has the necessary background and expertise to efficiently
carry out the proposed work. Langmuir was chief scientist on the sample collection cruise, and
supervises the major element, trace element and isotope work on the samples, as well as their
interpretation within the tectonic context based on the bathymetric and sidescan data [Martinez et al.
2006)]. Sims has been responsible for the application of U-series data to problems of melt
formation, volcanology and geology in the 9°N region. Standish completed U-series work with
Sims at Woods Hole as part of his thesis, and is currently a post-doc in Langmuir’s lab at Harvard.
Bezos, who has a minor role in this project, is the Research Associate scientist working on major
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