Subducted crust q q q the lilhfs trace element data

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Unformatted text preview: HFS trace element data underscore The the importance of slab-derived water and a MORB-like mantle wedge source MORB-like The flat HREE pattern argues against a The garnet-bearing (eclogite) source garnet-bearing Thus modern opinion has swung toward the Thus non-melted slab for most cases non-melted Mantle Wedge P-T-t Paths Mantle q q Amphibole-bearing hydrated peridotite should melt at ~ 120 km -bearing melt Phlogopite-bearing hydrated peridotite should melt at ~ 200 km -bearing melt → second arc behind first? second Figure 16-18. Some calculated P-T-t paths for peridotite in the mantle wedge as it follows a path similar to the flow lines in Figure 16-15. Included are some P-T-t path range for the subducted crust in a mature arc, and the wet and dry solidi for peridotite from Figures 10-5 and 10-6. The subducted crust dehydrates, and water is transferred to the wedge (arrow). After Peacock (1991), Tatsumi and Eggins (1995). Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Crust and Mantle Wedge Island Arc Petrogenesis Island Figure 16-11b. A proposed model for subduction zone magmatism with particular reference to island arcs. Dehydration of slab crust causes hydration of the mantle (violet), which undergoes partial melting as amphibole (A) and phlogopite (B) dehydrate. From Tatsumi (1989), J. Geophys. Res., 94, 4697-4707 and Tatsumi and Eggins (1995). Subduction Zone Magmatism. Blackwell. Oxford. A multi-stage, multi-source process multi-stage, q q 10 Dehydration of the slab provides the LIL, 10Be, B, Dehydration Be, etc. enrichments + enriched Nd, Sr, and Pb isotopic signatures signatures 3 These components, plus other dissolved silicate These materials, are transferred to the wedge in a fluid phase (or melt?) phase The mantle wedge provides the HFS and other The depleted and compatible element characteristics depleted q q Phlogopite is stable in ultramafic rocks beyond the conditions at Phlogopite which amphibole breaks down which P-T-t paths for the wedge reach the phlogopite-2-pyroxene P-T-t dehydration reaction at about 200 km depth Figure 16-11b. A proposed model for subduction zone magmatism...
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