Subduction zones upper mantle

Barth MG, Foley SF, Horn 1 (2002) Partial melting in Archean subduction zones constraints from experimentally determined trace element partition coefficients between eclogitic minerals and tonahtic melts under upper mantle conditions. Precamb Res 113 323-340... 

Kincaid C, Sacks IS (1997) Thermal and dynamic evolution of the upper mantle in subduction zones. J Geophys Res 102 12,295-12,315... 

Since hthium and boron isotope fractionations mainly occur during low temperature processes, Li and B isotopes may provide a robust tracer of surface material that is recycled to the mantle (Elhott et al. 2004). Heterogeneous distribution of subducted oceanic and continental crust in the mantle will thus result in variations in Li and B isotope ratios. Furthermore, dehydration processes active in subducdon zones appear to be of crucial importance in the control of Li and B isotope composition of different parts of the mantle. For the upper mantle as a whole Jeffcoate et al. (2007) gave an estimated 8 Li-value of 3.5%o. 

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). 

In the case of arc volcanism, the critical observation is that the C02/ He ratio of arc-related volatiles is significantly greater than that of MORBs (Marty et ai, 1989 Sano and Marty, 1995 Sano and Williams, 1996 Varekamp et ai, 1992). In a compilation of subduction zone type gases, Marty and Tolstikhin (1998) report a median value of 11.0 3.3 X 10, or 5 times that of MORBs. Consequently, an estimate of the proportion of carbon from nonmantle sources (—80%), presumably the subducted slab, can be inferred by scaling to the (upper mantle) C02/ He value. 

Sudo A. and Tatsumi Y. (1990) Phlogopite and K-amphibole in the upper mantle implication for magma genesis in subduction zones. Geophys. Res. Lett. 17, 29-32. 

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

It is increasingly apparent that there are exchanges and interactions between all the major chemical domains within the silicate earth. Communication between the upper mantle and cmst occurs at ridges, above mantle plumes, and at volcanic arcs. Geochemical smdies of OIBs, as well as seismic tomography of mantle stmcture beneath subduction zones demonstrate that there is... 

VanDecar, j. C. 1991. Upper-mantle structure of the Cascadia subduction zone from non-linear teleseis-mic travel-time inversion. PhD thesis. University of Washington, Seattle. 

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