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Preservation of ancient and fertile lithospheric mantle beneath the southwestern United States

Lee, Cin-Ty and Yin, Qingzhu and Rudnick, Roberta L. and Jacobsen, Stein B. (2001) Preservation of ancient and fertile lithospheric mantle beneath the southwestern United States. Nature, 411 (6833). pp. 69-73. ISSN 0028-0836. doi:10.1038/35075048.

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Stable continental regions, free from tectonic activity, are generally found only within ancient cratons—the centres of continents which formed in the Archaean era, 4.0–2.5 Gyr ago. But in the Cordilleran mountain belt of western North America some younger (middle Proterozoic) regions have remained stable, whereas some older (late Archaean) regions have been tectonically disturbed, suggesting that age alone does not determine lithospheric strength and crustal stability. Here we report rhenium–osmium isotope and mineral compositions of peridotite xenoliths from two regions of the Cordilleran mountain belt. We found that the younger, undeformed Colorado plateau is underlain by lithospheric mantle that is 'depleted' (deficient in minerals extracted by partial melting of the rock), whereas the older (Archaean), yet deformed, southern Basin and Range province is underlain by 'fertile' lithospheric mantle (not depleted by melt extraction). We suggest that the apparent relationship between composition and lithospheric strength, inferred from different degrees of crustal deformation, occurs because depleted mantle is intrinsically less dense than fertile mantle (due to iron having been lost when melt was extracted from the rock). This allows the depleted mantle to form a thicker thermal boundary layer between the deep convecting mantle and the crust, thus reducing tectonic activity at the surface. The inference that not all Archaean crust developed a strong and thick thermal boundary layer leads to the possibility that such ancient crust may have been overlooked because of its intensive reworking or lost from the geological record owing to preferential recycling.

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Additional Information:© 2001 Macmillan Magazines Ltd. Received 1 September 2000; Accepted 27 February 2001. All samples, except for CiP98-8 and CiP98-64, were borrowed from the Smithsonian Institution (we thank S. Sorensen for her curation of these specimens).We thank J. Chesley, M. Handler, A. Nyblade, D.G. Pearson, D. Smith and R.J. Walker for comments on the manuscript. This work was supported by the NSF, and C.-T.L. was supported in part by an NSF graduate fellowship and a Mineralogical Society of America grant for research.
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NSF Graduate FellowshipUNSPECIFIED
Mineralogical Society of AmericaUNSPECIFIED
Issue or Number:6833
Record Number:CaltechAUTHORS:20150331-075353170
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Official Citation:Preservation of ancient and fertile lithospheric mantle beneath the southwestern United States p69 Cin-Ty Lee, Qingzhu Yin, Roberta L. Rudnick and Stein B. Jacobsen doi:10.1038/35075048
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56226
Deposited By: Ruth Sustaita
Deposited On:31 Mar 2015 16:10
Last Modified:10 Nov 2021 20:56

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