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![Page 1: Imaging the mantle transition zone beneath the Transantarctic Mountains, Antarctica: There is no plume! Mouse Marie Larson PSU Geodynamics seminar 30 November.](https://reader035.fdocuments.us/reader035/viewer/2022062309/56649cc05503460f94986d78/html5/thumbnails/1.jpg)
Imaging the mantle transition zone beneath the Transantarctic
Mountains, Antarctica:
There is no plume!
Mouse Marie LarsonPSU Geodynamics seminar
30 November 2006
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Acknowledgements
Thanks to:
Andy NybladeMaggie BenoitTim WatsonPaul Winberry
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1. What’s the point/Backgroud
2. How
3. Results
4. Weird Results?!?
5. What does it mean?
Talk outline
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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
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East and West Antarctica are geologically distinct
Modified from Anderson (1999)
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Geologic Overview-IGeologic 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.
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Geologic Overview-IIGeologic Overview-II• The East Antarctic Craton (EAC)
– Stable Precambrian shield– Unusually topographically high, >1km (Cogley, 1984)– Thicker crust, 35-40km
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Geologic Overview-IIIGeologic 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.
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Many different mechanisms have been proposed for creating the tectonic features of Antarctica
http://mitglied.lycos.de/mapu2001/dryvalleys.html
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Tectonic Tectonic ModelsModels
• Isostatic uplift induced by crustal thickening and hot mantle (Fitzgerald et al, 1986)
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Tectonic ModelsTectonic 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)
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Tectonic ModelsTectonic 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)
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Previous studies show a negative anomaly beneath the Ross Sea
Seiminski et al, 2003
at 300 km
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Watson 2005
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Ok, so what am I going to do?
From Brian White’s TAMSEIS photos
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Figure courtesy of Lars Stixrude
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Phase transformation at ~ 410 km
Phase transformationat ~660 km
Bina and Helffrich, 1994
Clapeyron Slopes
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The thermal anomalies affect the depth of the major phase transformations
Lebedev et al, 2002
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The Transantarctic Mountains Seismic Experiment (2000 - 2003) included 41 portable broadband seismometers
TAMSEIS
http://epsc.wustl.edu/admin/whatsnew/tamseis/
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Three arrays:
1. Coastal array
2. North array
3. East array
http://epsc.wustl.edu/admin/whatsnew/tamseis/
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Photos from Brian White’s TAMSEIS website
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Sometimes there can be problems…
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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/RftnDocs/rftn01.html
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Geographical binning reduces bias based on azimuth
longitude
latit
ude
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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*
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Maps of the points show the lateral extent of the ray sampling from teleseismic events
410 kmcross-sectional slice
660 kmcross-sectional slice
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The EW line
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Some results
TZT=260km
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Small vs big bins
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Going Coastal
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??
?
North South
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??
?
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The mysterious NS line
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The NS line
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The average global thickness of the mantle transition zone
is 242 +/- 2km - Lawrence and Shearer 2006
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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
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Any questions?
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