Lithospheric mantle evolution

Irvine G. J., Pearson D. G., and Carlson R. W. (2001) Lithospheric mantle evolution in the Kaapvaal craton A Re-Os isotope study of peridotite xenoliths from Lesotho kimberlites. Geophys. Res. Lett. 28, 2505—2508. 

Beccaluva L, Bianchini G, Coltorti M, Perkins WT, Siena F, Vaccaro C, Wilson M (2001) Multistage evolution of the European lithospheric mantle new evidence from Sardinian peridotite xenoliths. Contrib Mineral Petrol 142 284-297... 

To explain the denudation of peridotites on the seafloor before the onset of oceanic accretion, Lemoine et al. (1987) and Trommsdorff et al. (1993) proposed a model involving extensional exhumation of subcontinental mantle along a major, normal detachment fault rooted in the crust-mantle boundary (Wernicke, 1981,1985). In most cases, however, the peridotites record a higher-temperature evolution than would be expected from stable lithospheric mantle. This suggests that ... 

McDonough W. F. and McCuUoch M. T. (1987) The southeast Austrahan lithospheric mantle isotopic and geochemical constraints on its growth and evolution. Earth. Planet. Sci. Lett. 86, 327-340. 

Pearson D. G. (1999b) Evolution of cratonic lithospheric mantle an isotopic perspective. In Mantle Petrology Field Observations and High Pressure Experimentation (eds. Y. Fei, C. M. Bertka, and B. O. Mysen). The Geochemical Society, Houston, vol. 6, pp. 57—78. 

Bedini R. M., Bodinier J.-L., Dautria J.-M., and Morten L. (1997) Evolution of LILE-enriched small melt fractions in the lithospheric mantle a case study from the East African Rift. Earth Planet. Sci. Lett. 153, 67-83. 

Siena F., Beccaluva L., Coltorti M., Marchesi S., and Morra V. (1991) Ridge to hot-spot evolution of the Atlantic lithospheric mantle evidence from Lanzarote peridotite xenoliths (Canary Islands). J. Petrol. (Special LherzoUtes Issue) 271-290. 

First, volatiles exert an important control on the physical properties of the mantle. For example, the presence of water reduces the strength of olivine aggregates and seriously alters the viscosity of the mantle. Experimental studies show that at 300 MPa, in the presence of water, the viscosity of olivine aggregates deformed in the dislocation creep regime is reduced by up to a factor of 140. Thus a wet mantle is a low viscosity mantle. Conversely a mantle that is dried out by partial melting will be stiffer and more refractory, as is the case for the lithospheric "lid" to modern oceanic mantle. Thus, if it is possible to estimate the volatile content of the mantle both now and in the Archaean, it will be possible to set some physical constraints on models of mantle evolution over time. 

Even without fractionation of parent elements and noble gases, the lithospheric isotopic evolution may diverge from the underlying mantle reservoirs. For example, the upper mantle evolves as an open system, with losses to the atmosphere and possible inputs from other mantle reservoirs (see Porcelli and Ballentine 2002, this volume). Therefore, lithospheric regions that are isolated from the relatively well-mixed upper mantle reservoir and are evolving as closed systems may have different isotopic evolution paths. Clearly, this will be more pronounced over greater time periods. 

Xenoliths from Siberian continental lithosphere, with Archean model ages, had b Li as low as +0.5 (Eouman et al. 2000). If these values accurately represent the Archean mantle, they suggest the potential for Li isotopic evolution in the Earth, from lighter compositions in the ancient mantle to what is seen in present-day MORE. In spite of the analytical challenges presented by ultramafic rocks, more data from these materials are crucial to an understanding of Li in the mantle, and in resolving questions about the appropriateness of the accepted MORE mantle range. 

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