helium and other noble gases sampling and analysing from marmara sea seepages sylvain bourlange...
DESCRIPTION
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 3 He/ 4 He) = crustal Non-radiogenic (high 3 He/ 4 He) = mantleTRANSCRIPT
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• Role of the gas fluxes on the seimogenic
behavior of the fault
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
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
(Gulec, Hilton and Mutlu, 2002)
(Gulec, Hilton and Mutlu, 2002)
Results• Presence of mantle-derived helium along
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)
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
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
Estimated vertical fluid flux in the fault zone
• « 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 ?
What about such a process in NAFZ