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The Transition Zone and Uppermost Lower Mantle in Subduction Zones

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Mid-Mantle Reflectors. East-West Path. North-South Path. Mid ... Frequent lower mantle reflectors. Associated with mid-mantle slabs. Signal of dewatering? ... – PowerPoint PPT presentation

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Title: The Transition Zone and Uppermost Lower Mantle in Subduction Zones


1
The Transition Zone and Uppermost Lower Mantle in
Subduction Zones
  • Justin Revenaugh
  • Anna Courtier
  • Geology and Geophysics
  • University of Minnesota

2
Outline
  • All about water
  • Quick review of water in mantle
  • New seismic constraints
  • Conclusions

3
(No Transcript)
4
(No Transcript)
5
Hirschmann 2006
6
Reverberative Interval
7
ScS Reverberation Method
8
ScS Reverberation Method
9
The Transition Zone
  • Melting at 410 km depth
  • Slow Layer Upon the Transition Zone
  • SLUTZ
  • The 520-km story

10
ScSn Coverage
11
Paths Without LVL
12
Paths With LVL
13
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14
LVL Geography
Yes No
15
Problems!
  • Melt layer is too thick!
  • Not obvious upwelling zones

16
Bercovici and Karato 2003
  • Upwelling wet transition zone mantle melts upon
    passage through 410-km discontinuity.
  • Calculations ignore dynamics

17
Limits
Transition width is limited by melt production
18
0 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?

19
Wet But Not Too Wet
  • If transition zones arent
  • near capacity, is there
  • anyplace that is?

20
(No Transcript)
21
Obayashi et al., EPSL 2006
22
Paths Examined
23
Paths With Melt
24
Melt Profiles
25
Courtier and Revenaugh, 2006
26
Hirschmann et al., 2006
27
Strong 520/Weak 410
  • 520-km discontinuity
  • Wadsleyite to Ringwoodite transition
  • Narrower, brighter when wet

28
(No Transcript)
29
Another Strong 520-km
Strong 520 coincident with LVL
30
Niu and Kawakatsu, 1997
31
Niu, et al. 2002
32
Reverberation Paths
33
Path 2 Eastern US/Gulf of Mexico
34
Path 3 Mid-Continent/Gulf of Mexico
35
Farallon Slab?
Grand et al., 1997 _at_ 30 N
36
Mid-Mantle Reflectors
37
East-West Path
38
North-South Path
39
Mid-Mantle Reflectors
40
Mid-Mantle Reflectors
Grand et al., 1997
41
ScSn Coverage
42
Two Mid-Mantle Reflectors
43
Paths in Coral Sea
44
Two Mid-Mantle Reflectors
45
850-km Reflector
46
1100-km Reflector
47
Hall and Spakman, 2002
48
Hall and Spakman, 2002
49
Getting Water Into the LM
Shieh et al. 1998
50
Conclusions
  • 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

51
Conclusions
  • 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?
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