This proposal seeks to measure noble gases in odp drill core gabbros, diorites and diabases from holes 735B and 1256D. The gases will be extracted by in vacuo and heating methods. He, Ne, and Ar will be measured and ratios used to separate atmospheric, radiogenic and non-radiogenic components of the gas. 3He, in particular, is of interest because the only possible source for this isotope is the Earth's mantle. Preliminary measurements reveal that He is surprisingly high in oceanic intrusive rocks, especially deformed rocks. The hypothesis that deformation adds noble gas to the crust will be tested by a depth study of granoblastic dikes from hole1256D. Preliminary results also reveal surprising small scale variability in noble gas concentration within samples, possibly related to amphibole concentration and hydrous melting. This hypothesis will be tested by a detailed transect in an amphibole diorite with special attention paid to mineralogy and fluid inclusions.
This will be the first comprehensive study of noble gas concentration in oceanic gabbroic rocks and the first ever in amphibole. The results will be of interest to a broad range of earth scientists. The work will have implications for the origins and abundance of volatiles in ocean crust and, ultimately, subduction-related volcanos. The project has an international component, will provide funds for a Ph.D. student and will involve undergraduates through WHOI fellowships and collaboration with a local state college.
