Subduction zones recycling

Moriguti T, Nakamura E (1998b) Across-arc variation of Li isotopes in lavas and implications for crust/mantle recycling at subduction zones. Earth Planet Sci Lett 163 167-174... 

Seafloor spreading eventually pushes oceanic crust into subduction zones where the hydrothermal sediments and rock are recycled back into the mantle. A small fraction of these deposits is uplifted, or obducted, onto land. These rescued deposits are termed ophiolites. Because of their metal enrichments, they serve as major ore bodies and have been mined for various precious metals, such as copper, for thousands of years. 

Hilton D. R., Fischer T. P., and Marty B. (2002) Noble gases and volatile recycling at subduction zones. Rev. Mineral. Geochem. 47, 319-370. 

Sano Y., TakahataN., Nishio Y., and Marty B. (1998) Nitrogen recycling in subduction zones. Geophys. Res. Lett. 25, 2289-2292. 

Sobolev A. V. and Chaussidon M. (1996) H2O concentrations in primary melts from supra-subduction zones and midocean ridges imphcations for H2O storage and recycling in the mantle. Earth Planet. Set Lett. 137, 45—55. 

This chapter focuses on subduction zone processes and their implications for mantle composition. It examines subduction contributions to the shallow mantle that may be left behind in the wedge following arc magma genesis, as well as the changing composition of the slab as it is processed beneath the fore-arc, volcanic front and rear arc on its way to the deep mantle. Much of this chapter uses boron and the beryllium isotopes as index tracers boron, because it appears to be completely recycled in volcanic arcs with little to none subducted into the deep mantle, and cosmogenic e, with a 1.5 Ma half-life, because it uniquely tracks the contribution from the subducted sediments. 

Savov I. P., Ryan J. G., Chan L.-H., D Antonio M., Mottl M., and Fryer P. (2002) Geochemistry of Serpentinites from the S. Chamorro Seamount, ODP Leg 195, Site 1200, Mariana Forearc-Iimplications For Recycling at Subduction Zones. In Proc. V.M. Goldschmidt Conference, Davos, Switzerland. Geochemical Society. 

Using average MORE or the range of compositions of oceanic basalts (e.g., Hofmann, 1988 Chapter 3.13 and http //petdb.ldeo.columbia.edu Lehnert et al., 2000), the fluxes derived here can be applied to determine the average compositions of oceanic crust that is subducted and recycled into the mantle. These compositions thus influence the composition of subduction zone magmas (see Chapter 3.18) and bear on the chemical mass balance of the mantle. 

Fig. 1. Recycling of volatile elements in the Earth. The x-axis is the ratio of the surface (atmosphere, oceans, crust, sediments) inventory divided by the present-day flux at ridges. The y-axis is the amount of volatile elements carried by the oceanic crust and sediments to subduction zones by the volcanic flux at arcs. Neon is not represented because its volcanic flux is not known. Data sources Craig el al. (1975), Matsuo et al. (1978), Le Guern (1982), Staudacher Allegre (1988), Staudigel ct a/. (1989), Allard (1992), Marty (1992,1995), Rea Ruff (1996), Sano Williams (1996), Marty Tolstikhin (1998), Marty Zimmermann (1999), and references therein.

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