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

Helium and other noble gases sampling and analysing from Marmara sea seepages. Sylvain Bourlange Pete Burnard Bernard Marty CRPG – CNRS Vandoeuvre-lès-nancy. Scientific Objectives. Fluid origin Is the MOHO permeable across a plate boundary? He and other gas fluxes at a major plate limit

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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 ?

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