Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u52a..08s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U52A-08
Physics
1000 Geochemistry, 1030 Geochemical Cycles (0330), 1031 Subduction Zone Processes (3060, 3613, 8170, 8413), 1038 Mantle Processes (3621), 1040 Radiogenic Isotope Geochemistry
Scientific paper
Subduction volcanism is generally considered to form a 'subduction barrier' that efficiently recycles volatile components contained in subducted slabs back to the Earth's surface (Staudacher and Allegre, 1988). Nevertheless, subduction of sediment and seawater-dominated pore fluids to the deep mantle has recently been proposed to account for the convecting mantle heavy noble gas (Ar, Kr and Xe) non-radiogenic elemental abundance and isotopic pattern (Holland and Ballentine, 2006). To verify whether and how subduction fluids preserve a seawater signature, we have determined noble gas and halogen compositions of the Higashi-akaishi peridotite body in the Sanbagawa metamorphic belt, southwest Japan, in which former water-rich inclusions exhumed from depths greater than 100 km are contained as serpentine dominated micro-inclusions (Mizukami et al., 2004). The striking similarities of the observed noble gas and halogen compositions with marine pore fluids challenge a popular concept, in which the water flux into the wedge mantle is only by hydrous minerals in altered oceanic crust and sediment (e.g., Schmidt and Poli, 1998). Subduction and closed system retention of unbound marine pore fluid to at least 100 km depth is required. The subducted halogen and noble gas elemental ratios are clearly distinct from those of arc volcanic gases. This implies that the Higashi-akaishi peridotite body has frozen in and preserved an inferred but previously unseen part of the volatile recycling process. Return of these volatiles to the atmosphere via arc volcanism requires the addition of a mantle component and fractionation during degassing. A small proportion preserved in the downgoing slab can explain the heavy noble gases observed in the convecting mantle. References: Holland G. and Ballentine C. J., Nature, 441, 186-191 (2006). Mizukami T. et al., Nature, 427, 432-436 (2004). Schmidt M.W. and Poli S., Earth Planet. Sci. Lett., 163, 361-379 (1998). Staudacher, T. and Allegre C.J., Earth Planet. Sci. Lett., 89, 173-183 (1988).
Ballentine Chris J.
Burgess Ray
Holland Glenn
Mizukami Tomoyuki
Sumino Hirochika
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