Subduction zones composition

Several authors have suggested that the composition of subduction zone fluids is likely to change by chromatographic interaction during their passage through the mantle... 

Davies JH, Biekle MJ (1991) A physical model for the volume and composition of melt produeed by hydrous fluxing above subduction zones. Phil Trans R Soc Lond 335 355-364 Davies JH, Stevenson DJ (1992) Physical model of source region of subduction zone voleanies. J Geophys Res 97 2037-2070... 

Keppler H (1996) Constraints from partitioiung experiments on the composition of subduction-zone fluids. Nature 380 237-240... 

Regardless of the ultimate sources of these compositions, these results clearly show that strongly isotopically fractionated Li from crustal sources plays a role in the mantle. Processes active in subduction zones appear to be cardinal in the control of the Li isotopic composition of different parts of the mantle. The results to date imply that both isotopically enriched (8 Li > MORE) and depleted (5T i < MORE) material are available for deep subduction, and that areas of the continental lithosphere may retain these records on long time scales. 

Chan LH, Edmond JM (1988) Variation of lithium isotope composition in the marine environment A preliminary report. Geochim Cosmochim Acta 52 1711-1717 Chan LH, Kastner M (2000) Lithium isotopic compositions of pore fluids and sediments in the Costa Rica subduction zone implications for fluid processes and sediment contribution to the arc volcanoes. Earlh Planet Sci Lett 183 275-290... 

Rudnick RL, McDonough WF, Tomascak PB, Zack T (2003) Lithium isotopic composition of eclogites implications for subduction zone processes. Eighth Int Kimberlite Conf Abst Ryan JG, Langmuir CH (1987) The systematics of lithium abundances in young volcanic rocks. Geochim Cosmochim Acta 51 1727-1741... 

Ransom B, Spivack AJ, Kastner M (1995) Stable Cl isotopes in subduction-zone pore waters implications for fluid-rock reactions and the cycling of chlorine. Geology 23 715-718 Reddy CM, Heraty LJ, Holt BD, Sturchio NC, Eglinton XI, Drenzek NJ, Xu L, Lake JL, Maruya KA (2000) Stable chlorine isotopic compositions of aroclors and aroclor- contaminated sediments. Env Sci Tech 34(13) 2866-2870... 

A summary of the observed natural chlorine isotope variations is presented in Fig. 2.23. Ransom et al. (1995) gave a natural variation range in chlorine isotope composition of about 15%c with subduction zone pore waters having S Cl values as low as —8%c whereas minerals in which Cl substitutes OH have 5 Cl values as high as 7%c. 

Perhaps one of the most important consequences of a peridotite composition for the upper mantle is that the phase transitions in olivine that are manifested as seismic discontinuities should exhibit thermally controlled variations in their depth of occurrence that are consistent with the measured Clapeyron slopes (Bina and Helffrich, 1994) of the transitions. In particular, the olivine-wadsleyite transition at 410 km should be deflected upwards in the cold environment of subduction zones while the disproportionation of ringwoodite to silicate perovskite and magnesiowiistite at 660 km should be deflected downwards, thereby locally thickening the transition zone. In anomalously warm regions (such as the environs of mantle plumes as described below), the opposite deflections at 410 and 660 should locally thin the transition zone. The seismically observed topography of 20-60 km on each of the 410 and 660 is consistent with lateral thermal anomalies of 700 K or less (Helffrich, 2000 Helffrich and Wood, 2001). 

Kennett B. L. N. and Hilst R. D. V. d. (1998) Seismic structure of the mantle from subduction zone to craton. In The Earth s Mantle Composition, Structure and Evolution (ed. 

Subduction Zone Processes and Implications for Changing Composition of the Upper and Lower Mantle... 

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. 

Ono S. (1998) Stability limits of hydrous minerals in sediment and mid-ocean ridge basalt compositions implications for water transport in subduction zones. J. Geophys. Res. 103, 18253-18267. 

Rea D. K. and Ruff L. J. (1996) Composition and mass flux of sediment entering the worlds subduction zones implications for global sediment budgets, great earthquakes and volcan-ism. Earth Planet. Sci. Lett. 140, 1-12. 

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