Title: The Transition Zone and Uppermost Lower Mantle in Subduction Zones
1The Transition Zone and Uppermost Lower Mantle in
Subduction Zones
- Justin Revenaugh
- Anna Courtier
- Geology and Geophysics
- University of Minnesota
2Outline
- All about water
- Quick review of water in mantle
- New seismic constraints
- Conclusions
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5Hirschmann 2006
6Reverberative Interval
7ScS Reverberation Method
8ScS Reverberation Method
9The Transition Zone
- Melting at 410 km depth
- Slow Layer Upon the Transition Zone
- SLUTZ
- The 520-km story
10ScSn Coverage
11Paths Without LVL
12Paths With LVL
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14LVL Geography
Yes No
15Problems!
- Melt layer is too thick!
- Not obvious upwelling zones
16Bercovici and Karato 2003
- Upwelling wet transition zone mantle melts upon
passage through 410-km discontinuity. - Calculations ignore dynamics
17Limits
Transition width is limited by melt production
180 Dihedral Angle
- Melt and olivine-basalt aggregate at 1 Gpa
(Cmiral et al., 1998) - Silicate melt and olivine at P gt 7 to 8 GPa
(Karato et al., 2005) - Fully wetting thin films gravitationally stable?
19Wet But Not Too Wet
- If transition zones arent
- near capacity, is there
- anyplace that is?
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21Obayashi et al., EPSL 2006
22Paths Examined
23Paths With Melt
24Melt Profiles
25Courtier and Revenaugh, 2006
26Hirschmann et al., 2006
27Strong 520/Weak 410
- 520-km discontinuity
- Wadsleyite to Ringwoodite transition
- Narrower, brighter when wet
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29Another Strong 520-km
Strong 520 coincident with LVL
30Niu and Kawakatsu, 1997
31Niu, et al. 2002
32Reverberation Paths
33Path 2 Eastern US/Gulf of Mexico
34Path 3 Mid-Continent/Gulf of Mexico
35Farallon Slab?
Grand et al., 1997 _at_ 30 N
36Mid-Mantle Reflectors
37East-West Path
38North-South Path
39Mid-Mantle Reflectors
40Mid-Mantle Reflectors
Grand et al., 1997
41ScSn Coverage
42Two Mid-Mantle Reflectors
43Paths in Coral Sea
44Two Mid-Mantle Reflectors
45850-km Reflector
461100-km Reflector
47Hall and Spakman, 2002
48Hall and Spakman, 2002
49Getting Water Into the LM
Shieh et al. 1998
50Conclusions
- SLUTZ
- Marker of locally wet transition zone
- Slab-displaced TZ material pushed through 410
- Below maximum UM storage capacity.
- 520
- Another marker of locally wet TZ
51Conclusions
- Frequent lower mantle reflectors
- Associated with mid-mantle slabs
- Signal of dewatering?
- Decarbonatization?
- Lower mantle wet pools
- Triggers for LIPs?
- Agents of eustasy?
- Chemical filters?