Section through Japan of

1
(No Transcript)
2
(No Transcript)
3
Section through Japan of Wadati-Benioff Zone
defined by earthquakes. Most EQ near top of
slab. Second line. Within plate. Perhaps at the
base of the brittle lithosphere
Fig from SubFac science plan
4
Earthquakes extend to 600 km beneath Lau
Basin Note that tomographic image slab appears to
terminate at 660 km discontinuity
Fig from SubFac science plan
5
Limit for hydrated minerals
High P reactions in slab
Density H2O
6
(No Transcript)
7
Island Arc Petrogenesis
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. Slide from J Winter, Whitman College
8
Hydrated Solidus
Melts from slab
Phlogopite breakdown
9
(No Transcript)
10
(No Transcript)
11
Natural Abundances
Natural elemental abundances are higher for even
atomic numbers (Oddo-Harkins rule)
Basalts
Mantle
Chondrite-normalized Abundances
This variation obscures petrogentic info. So we
normalize to (divide by) a reference composition
-- most commonly to a chondritic meteorite that
is close to a bulk-Earth composition
Basalts
Mantle
12
LIL -- Large Ion Lithophile Large, lower charge
cations with an affinity for aqueous or fluid
phase
HFS -- High Field strength. Small, highly charged
cations
In this case the data are normalized to a
primitive Mid-ocean ridge basalt (NMORB) --
representing a bulk ocean crust composition. This
Spider Diagram provides a quick visual
representation of how much two typical arc lavas
differ from MORB.
13
(No Transcript)
14
Ba/La
U/Th
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)