Magmas subduction slabs

Honma et al. (1991) have shown that the Okinawa Trough basalts have significantly high K, Rb and Sr contents and D/H, 0/ 0 and Sr/ Sr ratios than N-Morb have and these are due to generation of magma from normal-type mantle peridotite modified by component from the subducted slab and crustal contamination. 

O, H, C, S, and N isotope compositions of mantle-derived rocks are substantially more variable than expected from the small fractionations at high temperatures. The most plausible process that may result in variable isotope ratios in the mantle is the input of subducted oceanic crust, and less frequent of continental crust, into some portions of the mantle. Because different parts of subducted slabs have different isotopic compositions, the released fluids may also differ in the O, H, C, and S isotope composition. In this context, the process of mantle metasomatism is of special significance. Metasomatic fluids rich in Fe +, Ti, K, TREE, P, and other large ion lithophile (LIE) elements tend to react with peridotite mantle and form secondary micas, amphiboles and other accessory minerals. The origin of metasomatic fluids is likely to be either (1) exsolved fluids from an ascending magma or (2) fluids or melts derived from subducted, hydrothermally altered crust and its overlying sediments. 

It is beyond the scope of this review to discuss in detail the statistical parameters of subduction zones, and Figure 10 is intended to demonstrate that conditions attained in subducting slabs are highly variable, even for similar convergence parameters, and that interplay between thermomechanical properties and reaction paths are responsible for a complex pattern of fluid release and magma genesis. Furthermore, any correlation of kinematic subduction parameters with volcano location tacitly assumes steady state, which is not necessarily the case. 

Furukawa Y. and Tatsumi Y. (1999) Melting of a subducting slab and production of high-Mg andesite magmas unusual magmatism in SW Japan at 13 approximately 15 Ma. Geophys. Res. Lett. 26(15), 2271-2274. 

The quest of recent research into arc magma-tism has been to assess the relative contributions of the different components of arc magmatism. These include the mantle wedge, a fluid phase, subducted sediment, and the subducted slab. In each case these differing contributions can be identified by a geochemical fingerprint. A further potential magma source, present in some arcs, is continental... 

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