1. Imaging the mantle transition zone beneath the Transantarctic Mountains, Antarctica: There is no plume! Mouse Marie Larson PSU Geodynamics seminar 30 November 2006

2. Acknowledgements Thanks to: Andy Nyblade Maggie Benoit Tim Watson Paul Winberry

3. 1.What’s the point/Backgroud 2.How 3.Results 4.Weird Results?!? 5.What does it mean? Talk outline

4. This study uses receiver functions to place depth constraints on any thermal anomaly beneath the TAMs The main question addressed here: 1.Is there evidence for thinning of the transition zone between the 410 and 660? http://home.freeuk.com/gtlloyd/tam/main.htm No

6. East and West Antarctica are geologically distinct Modified from Anderson (1999)

7. Geologic Overview-I The West Antarctic Rift System (WARS) –Extensional tectonism since the Jurassic (Dalziel and Lawver, 2001). –Previous studies estimate crustal thickness between 18-25 km.

8. Geologic Overview-II The East Antarctic Craton (EAC) –Stable Precambrian shield –Unusually topographically high, >1km (Cogley, 1984) –Thicker crust, 35-40km

9. Geologic Overview-III The Transantarctic Mountains (TAM) –Geologic boundary between the EAC and the WARS –The mountains extend ~3500km and reach heights of 4500m –Lack evidence of compressional tectonics.

10. Many different mechanisms have been proposed for creating the tectonic features of Antarctica http://mitglied.lycos.de/mapu2001/dryvalleys.html

11. Tectonic Models Isostatic uplift induced by crustal thickening and hot mantle (Fitzgerald et al, 1986)

12. Tectonic Models Flexural uplift of a broken plate supported by a thermal load (Stern and ten Brink, 1989; ten Brink and Stern, 1992) Decoupling between EA and WARS lithosphere in response to transtensional plate motion @ 61-53 Ma (ten Brink et al, 1997)

13. Tectonic Models Flexural uplift of a continuous plate. Crustal thickening during Ross Orogeny and then erosion induced uplift @ c. 55 Ma triggered by climate change. (Karner et al, 2005 and Studinger et al, 2004)

14. Previous studies show a negative anomaly beneath the Ross Sea Seiminski et al, 2003 at 300 km

15. Watson 2005

17. Ok, so what am I going to do? From Brian White’s TAMSEIS photos

18. Figure courtesy of Lars Stixrude

19. Phase transformation at ~ 410 km Phase transformation at ~660 km Bina and Helffrich, 1994 Clapeyron Slopes

20. The thermal anomalies affect the depth of the major phase transformations Lebedev et al, 2002

21. The Transantarctic Mountains Seismic Experiment (2000 - 2003) included 41 portable broadband seismometers TAMSEIS http://epsc.wustl.edu/admin/whatsnew/tamseis/

22. Three arrays: 1.Coastal array 2.North array 3.East array http://epsc.wustl.edu/admin/whatsnew/tamseis/

23. Photos from Brian White’s TAMSEIS website

24. Sometimes there can be problems…

25. Receiver functions generated using Ammon’s water level- deconvolution code and stacked using Owen’s stacking codes. http://epsc.wustl.edu/admin/whatsnew/tamseis/ http://eqseis.geosc.psu.edu/~cammon/HTML/RftnD ocs/rftn01.html

26. Geographical binning reduces bias based on azimuth longitude latitude

27. Each bin table is populated by the names of station/event pairs for which the wave passed through that node as well as the time that this occurs Station1-eventA Station1-eventG Station3-eventA, etc t*

28. Maps of the points show the lateral extent of the ray sampling from teleseismic events 410 km cross-sectional slice 660 km cross-sectional slice

29. The EW line

30. Some results TZT=260km

31. Small vs big bins

32. Going Coastal

33. ? ? ? NorthSouth

34. ? ? ?

36. The mysterious NS line

37. The NS line

38. The average global thickness of the mantle transition zone is 242 +/- 2km - Lawrence and Shearer 2006

40. Preliminary Results: AND http://home.freeuk.com/gtlloyd/tam/main.htm The ice layer may be causing the double peak…more study is needed. The average transition zone thickness is greater than 250 km (the global average) -- currently no evidence for a plume or thermal anomaly in the transition zone

41. Any questions?