OS23C-2028
Noble Gas geochemistry of the newly discovered hydrothermal fields in the Gulf of California: preliminary He-isotope ratios from the Alarcon Rise and Pescadero basin vent sites

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Ronald Michael Spelz1, John E Lupton2, Leigh J Evans3, Robert A Zierenberg4, David A Clague5, Florian Neumann6 and Jennifer Brophy Paduan5, (1)Organization Not Listed, Washington, DC, United States, (2)NOAA Camp Springs, Camp Springs, MD, United States, (3)NOAA/PMEL, Newport, OR, United States, (4)University of California Davis, Earth and Planetary Sciences, Davis, CA, United States, (5)Monterey Bay Aquarium Research Institute, Watsonville, CA, United States, (6)CICESE National Center for Scientific Research and Higher Education of Mexico, Geology, Ensenada, Mexico
Abstract:
Numerous submarine deep-sea hydrothermal vents related to volcanic activity of the East Pacific Rise (EPR) are situated along the Pacific margins of Mexico. Until recently, active hydrothermal venting was unknown between the Guaymas Basin and 21°N on the EPR. MBARI's recent oceanographic surveys have added 7 new active vent sites. In this study, we aimed to sample the high-temperature hydrothermal fluids emanating from two distinct vent sites, named Meyibo and Auka, located in the Alarcon Rise and Pescadero Basin, respectively.

Mantle-derived He have long been identified in hydrothermal fluid releases. The presence of He in aqueous fluids with 3He/4He ratios greater than in-situ production values (~0.05 RA, where RA = air He or 1.4 x 10-6) indicates the presence of mantle-derived melts. Preliminary analyses of He-isotope ratios derived from the newly discovered Meyibo and Auka hydrothermal fields show high 3He/4He ratios (~8RA), typical of MORB’s. Auka vent field, characterized by chimneys composed of light carbonate minerals and oil-like hydrocarbons, and temperatures between 250-290oC, show average values of ~7.87RA. In contrast, the black-smokers at the Meyibo field, composed of dark sulfide minerals and temperatures over 350oC, yielded a higher He ratio of ~8.24RA.

Recently, it has become clear that regional maximum mantle He values correlate with the velocity structure in the mantle, therefore, He has the potential to map regions of the underlying mantle that are undergoing partial melting. Seismic records could then be compared with the geochemical He ratio signal and supply information regarding tectonics and other processes involved in the generation of these gases. The data presented here will be completing a totally new inventory of He results from hydrothermal vents in the EPR and fault-termination basins distributed along the P-NA plate boundary in the Gulf of California. The results will be further coupled with the analysis of other geochemical indicators of mantle degassing to assess the relationship between He-isotopes and mantle velocity structure in the region.

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