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

5. Hirschmann 2006

6. Reverberative Interval

7. ScS Reverberation Method

9. The Transition Zone Melting at 410 km depth –Slow Layer Upon the Transition Zone –SLUTZ The 520-km story

10. ScS n Coverage

11. Paths Without LVL

12. Paths With LVL

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 > 7 to 8 GPa (Karato et al., 2005) Fully wetting thin films; gravitationally stable?

19. Wet But Not Too Wet If transition zones aren’t near capacity, is there anyplace that is?

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

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 @ 30° N

36. Mid-Mantle Reflectors

37. East-West Path

38. North-South Path

39. Mid-Mantle Reflectors

40. Grand et al., 1997

41. ScS n 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. Shieh et al. [1998] Getting Water Into the LM

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?