Unformatted text preview: HFS trace element data underscore
the importance of slab-derived water and a
MORB-like mantle wedge source
The flat HREE pattern argues against a
garnet-bearing (eclogite) source
Thus modern opinion has swung toward the
non-melted slab for most cases
non-melted Mantle Wedge P-T-t Paths
q Amphibole-bearing hydrated peridotite should melt at ~ 120 km
Phlogopite-bearing hydrated peridotite should melt at ~ 200 km
→ 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
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
Oxford. A multi-stage, multi-source process
q q 10
Dehydration of the slab provides the LIL, 10Be, B,
etc. enrichments + enriched Nd, Sr, and Pb isotopic
3 These components, plus other dissolved silicate
materials, are transferred to the wedge in a fluid
phase (or melt?)
The mantle wedge provides the HFS and other
depleted and compatible element characteristics
depleted q q Phlogopite is stable in ultramafic rocks beyond the conditions at
which amphibole breaks down
P-T-t paths for the wedge reach the phlogopite-2-pyroxene
dehydration reaction at about 200 km depth Figure 16-11b. A proposed model for
subduction zone magmatism...
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- Spring '13
- Plate Tectonics, Basalt, Mantle, Gill, subduction zone, Tatsumi