HR: 14:40h
AN: U33B-05    [Abstracts]
TI: Numerical modeling of noble gas recycling into the mantle
AU: * Ballentine, C J
EM: chris.ballentine@man.ac.uk
AF: University of Manchester, Dept Earth Sciences, Manchester, M13 9PL United Kingdom
AU: Van Keken, P E
EM: keken@umich.edu
AF: University of Michigam, Dept Geological Sicences, Ann Arbor, MI 48109-1063 United States
AU: Holland, G
EM: g.holland@man.ac.uk
AF: University of Manchester, Dept Earth Sciences, Manchester, M13 9PL United Kingdom
AU: Hauri, E H
EM: hauri@dtm.ciw.edu
AF: Carnegie Institute of Washington, Dept Terrstrial Magnetism 5241 Broad Branch Road, Washington DC, DC 20015 United States
AU: Brandenburg, J
EM: jpbrande@umich.edu
AF: University of Michigam, Dept Geological Sicences, Ann Arbor, MI 48109-1063 United States
AB: Numerical simulations of mantle convection have provided a unique insight into the use of geochemical tracers such as 3He/4He and 40Ar [1]. Almost no attention has been paid to information about convective mixing in the mantle from integrated analyses of Ne, Ar, Kr and Xe: Solar Ne, Xe and now Ar [2] have been resolved in upper mantle volatiles. Holland and Ballentine [2] show how the convecting mantle Ar and Xe isotopic composition can be accounted for by mixing between a Solar noble gas component trapped during the accretionary process, with atmosphere-derived noble gases, most likely recycled into the mantle dissolved in seawater. From mass balance, He and Ne isotopic compositions are little affected by this process. We present here numerical models that investigate the subduction of seawater-derived noble gases into the mantle as a constant proportion of recycled oceanic crust. These models constrain the amount of unmodified seawater that can be subducted and are compared with observed concentrations in oceanic crust to assess the efficiency of volatile return in arc processes. We show how a whole-mantle convective regime efficiently mixes these recycled heavy noble gases with residual Solar noble gases to provide the He, Ne, Ar, Xe abundance and isotopic composition observed in the convecting mantle. Low 40Ar/36Ar and low 129Xe/130Xe isotopic ratios in OIB relative to MORB are observed and has been used to argue that the OIB source is rich in primitive Ar and Xe. We further use the numerical simulations to test the hypothesis that because of the higher proportion of recycled material in the OIB-source, low 40Ar/36Ar and low 129Xe/130Xe isotopic ratios would be produced as a result of seawater recycling into this portion of the mantle. [1] Van Keken, P.E., C.J. Ballentine and E.H. Hauri, Convective mixing in the Earth's mantle, in The Mantle and Core, edited by R.W. Carlson, pp. 471-492, Elsevier, New York, 2003. [2] Holland. G and C.J. Ballentine, AGU abstract, This meeting.
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8125 Evolution of the Earth
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
SC: Union [U]
MN: 2004 AGU Fall Meeting