Helium and other noble gases sampling and analysing from Marmara sea seepages - PowerPoint PPT Presentation

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Helium and other noble gases sampling and analysing from Marmara sea seepages

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  1. Helium and other noble gases sampling and analysing from Marmara sea seepages Sylvain Bourlange Pete Burnard Bernard Marty CRPG – CNRS Vandoeuvre-lès-nancy

  2. Scientific Objectives • Fluid origin • Is the MOHO permeable across a plate boundary? • He and other gas fluxes at a major plate limit • Role of the gas fluxes on the seimogenic behavior of the fault

  3. Helium Isotopes: background • Background concentrations of He in seawater are extremely low • Concentrations and isotopic compositions of seawater in equilibrium with air are well constrained • Input of non-atmospheric He readily detected • sensitive tracer of ‘deep-seated’ fluids • Can be used to estimate total gas fluxes • Isotopic composition indicates gas source • Radiogenic (low 3He/4He) = crustal • Non-radiogenic (high 3He/4He) = mantle

  4. Helium isotope variations in Turkey • Helium isotope variations in Turkey: relationship to tectonics,volcanism and recent seismic activities (Gülec, Hilton and Mutlu, 2002) • Survey along NAFZ after 1999 earthquake

  5. (Gulec, Hilton and Mutlu, 2002)

  6. (Gulec, Hilton and Mutlu, 2002)

  7. Results • Presence of mantle-derived heliumalong the NAFZ • 27 % near Duzce (epicenter of 1999 7.2 magnitude earthquake) • Mantle derived He mostly occurs where the fault intersects volcanic activity • However, the relationships between mantle-derived helium and seismic activity are not understood very well. • For example, mantle-derived helium seems to decrease toward Marmara sea (4% near Yalova)

  8. Questions • What are the fluxes of noble gases output along the NAFZ (in the Marmara sea) ? • What is the amount of mantle-derived helium in the prolongation of the NAFZ in the Marmara sea ? • More representative analyses are possible in the marine environment

  9. fault-weaking fluid pressure • Coincidence between areas where helium of mantle origin emerges and areas of active tectonics (Oxburgh and O’Nions (1987)) • Release of mantle-derived helium and of CO2 compatible with a mantle origin in the NAFZ (Nagao et al., 1990) • Rice (1992): Fluids at sublithostatic pressures could be supplied by a high flux of deep crustal or mantle fluids to the seismogenic zone from the ductile lower crust

  10. Estimated vertical fluid flux in the fault zone

  11. What about such a process in NAFZ • « estimates of fluid flux based on helium isotopes suggest that they may thus contribute directly to fault weakening high fluid pressures at seismogenic zones » (Kennedy et al, 1997) • Much easier to determine fluxes in marine setting • Could we suspect such a process in the case of the NAFZ ?