Continental evolution

Veizer, J. Jansen, S. L. (1979). Basement and sedimentary recycling and continental evolution. J. Geol., 87, 341-70. 

Anderson A. T. (1982) Parental basalts in subduction zones implications for continental evolution. J. Geophys. Res. 87, 7047-7060. 

Clowes R., Cook F., Hajnal Z., Hall J., Lewry J. F., Lucas S., and Wardle R. (1999) Canada s Lithoprobe project (collaborative, mutildisciphnary geoscience research leads to new understanding of continental evolution). Episodes 22, 3-20. 

Bostock, M. G. 1999. Seismic imaging of lithospheric discontinuities and continental evolution. Lithos, 48, 1-16. 

Rapp, R. P. 1991. Origin of Archaean granitoids and continental evolution. EOS Transactions, American Geophysical Union, 22, 225—229. 

Godderis, Y. and Francois, L.M. (1995) The Cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchange. Chem. Geol., 126, 169-190. 

Dating of whole rocks from the measurements of their °Th- U or Pa- U disequilibria has been successful in the case of MORE, and can also be applied to volcanoes for which the evolution of these disequilibria through time has been studied in detail (e.g., Piton de la Foumaise). Similarly Ra- Th disequilibria may be useful dating tools in the age range 0 to 8 ka, for MORE or continental volcanoes where a detailed knowledge of their variations in well dated samples is available. 

Taylor S.R., McLennan S.M. The continental crust Its composition and evolution, Oxford Blackwell, 1985. 

Let us first introduce some important definitions with the help of some simple mathematical concepts. Critical aspects of the evolution of a geological system, e.g., the mantle, the ocean, the Phanerozoic clastic sediments,..., can often be adequately described with a limited set of geochemical variables. These variables, which are typically concentrations, concentration ratios and isotope compositions, evolve in response to change in some parameters, such as the volume of continental crust or the release of carbon dioxide in the atmosphere. We assume that one such variable, which we label/ is a function of time and other geochemical parameters. The rate of change in / per unit time can be written... 

Albarede, F. Brouxel, M. (1987). The Sm/Nd secular evolution of the continental crust and depleted mantle. Earth Planet. Sci. Letters, 82, 25-35. 

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. 

Coleman ML (1971) Potassium-calcium dates from pegmatitic micas. Earth Planet Sci Lett 12 399-405 Condie KC (1993) Chemical composition and evolution of the upper continental crust contrasting results from surface samples and shales. Chem Geol 104 1-37... 

Richter FM, Davis AM, Ehel DS, Hashimoto A (2002) Elemental and isotopic fractionation of Type B calcium-, aluminum-rich inclusions Experiments, theoretical considerations, and constraints on their thermal evolution. Geochim Cosmochim Acta 66 521-540 Richter FM, Davis AM, DePaolo DJ, Watson EB (2003) Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochim Cosmochim Acta 67 3905-3923 Rudnick RL, Fountain DM (1995) Nature and composition of the continental crust—a lower crustal perspective. Rev Geophys 33 267-309... 

Taylor SR, Mclennan SM (1995) The geochemical evolution of the continental crust. Rev Geophys 33 241-265... 

Taylor SR, McLennan SM (1985) The Continental Crust Its Composition and Evolution. Blackwell, Boston Tuit CB, Ravizza G (2003) The marine distribution of molybdenum. Geochim Cosmochim Acta 67 A4950 Tumlund JR, Keyes WR, Peiffer GL (1993) Isotope ratios of molybdenum determined by thermal ionization mass spectrometry for stable isotope studies of molybdenum metabolism in humans. Anal Chem 65 1717-1722... 

Taylor S.R. McLennan S.M. 1985. The Continental Crust Its Composition and Evolution. Blackwell Science Publisher, Oxford. 

In order to trace the migration of basalt-derived REE in the salt, REE distribution patterns (Fig. 7) and Nd isotopic compositions (Fig. 8) have been determined in a salt horizon adjacent to a basalt dyke (Fig. 2). The flat REE distribution patterns and the almost basaltic Nd isotopic composition of the salt samples collected at the basalt-salt contact point to a basaltic origin of the REE for this sample. With increasing distance from the contact, the patterns are more and more depleted in Ce, Pr, Nd, Sm, and Eu and the Nd isotopic compositions are slightly shifted towards lower eNd values, which, however, still remain above values typical for continental crust or Permian seawater (Stille et al. 1996, and citations therein). This evolution of the REE distribution patterns and the Nd isotopic compositions could basically be due to mixing between a basalt and a salt end member or, alternatively, it could have been fractionation of the REE during migration in the salt that modified the REE patterns. 

Fig. 8. The evolution of the Nd isotopic compositions with distance in the salt profile together with the compositions of average basalt and average continental crust. The error bars represent 2 sigma mean values of the individual measurements.

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