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The deep structure of continents

Anderson, Don L. (1979) The deep structure of continents. Journal of Geophysical Research B, 84 (B13). pp. 7555-7560. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20150223-105154987

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Abstract

The Lehmann discontinuity at 220-km depth is an important global feature which occurs under both oceans and continents. It is a barrier to penetration by young lithosphere and marks the base of seismicity in regions of continent-continent collision. The strong lateral variation in upper mantle velocities occurs mainly above this depth. Continental roots extend no deeper than about 150–200 km. The basalteclogite transformation and eclogite-harzburgite separation may be responsible for the geometry of intermediate depth earthquakes. Oceanic and continental geotherms converge above about 200 km and become less steep than the melting gradient at greater depth. This implies a low viscosity channel near 250 km. This would give a decoupling zone of maximum shear beneath continental shields. The Lehmann discontinuity may be the interface between two distinct geochemical reservoirs. The velocity jump, and the inferred density jump, at 220 km are consistent with an increase in garnet content. The mantle may be garnet lherzolite above and eclogite immediately below the Lehmann discontinuity. The transition region may be mainly eclogite and be the source region for oceanic tholeiites.


Item Type:Article
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http://dx.doi.org/10.1029/JB084iB13p07555DOIArticle
http://onlinelibrary.wiley.com/doi/10.1029/JB084iB13p07555/abstractPublisherArticle
Additional Information:© 1979 by the American Geophysical Union. Paper number 9B0991. Received March 28, 1979; revised May 25, 1979; accepted July 2, 1979. I thank Tom Jordan, Frank Richter, Hiroo Kanamori, and Raymond Jeanloz for stimulating discussions, and Thomas Jordan, Michel Cara, David Jackson, and Geoffrey Davies for copies of preprints. This research was supported by NSF grant EAR 77-14675. Contribution 3212, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
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NSFEAR 77-14675
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Caltech Division of Geological and Planetary Sciences3212
Record Number:CaltechAUTHORS:20150223-105154987
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20150223-105154987
Official Citation:Anderson, D. L. (1979), The deep structure of continents, J. Geophys. Res., 84(B13), 7555–7560, doi:10.1029/JB084iB13p07555
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55100
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:23 Feb 2015 19:38
Last Modified:23 Feb 2015 19:38

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