Basalts neodymium isotopes

Salters V. J. M. and Dick H. J. B. (2002) Mineralogy of the midocean-ridge basalt source from neodymium isotopic composition of abyssal peridotites. Nature 418, 68-72. 

Because of the generally high LREE contents of all the western USA alkali basalts, their neodymium-isotopic compositions are likely to represent those of their mantle source regions. The high-SKfd (low-LIL/HFSE) and low-8Nd (high-LILE/HFSE) alkali basalts are typically. 

DePaolo D. J. and Daley E. E. (2000) Neodymium isotopes in basalts of the southwest basin and range and lithospheric thinning during continental extension. Chem. Geol. 169, 157-185. 

Horan M. F., Walker R. J., Fedorenko V. A., and Czamanske G. K. (1995) Osmium and neodymium isotopic constraints on the temporal and spatial evolution of Siberian flood basalt sources. Geochem. Cosmochim. Acta 59, 5159—5168. 

Brimhall et al. (1991) used lead isotopes in zircons within a bauxite profile from Western Australia to differentiate between zircons derived from the underlying bedrock and zircons of eolian origin. Borg and Banner (1996) applied both neodymium and strontium isotopes to constrain the sources of soil developed on carbonate bedrock. Using these isotopes and Sm/Nd ratios, they were able to delineate the importance of atmospheric versus bedrock contributions in controlling the composition of the soil. Kurtz et al. (2001) used neodymium and strontium isotopes to determine the amount of Asian dust in a Hawaiian soil chronosequence. They found that the basaltic bedrock isotope signatures in soils had, in many cases, been completely overprinted by dust additions, demonstrating the profound effect of Asian dust on soil nutrient supplies. 

Beyond the broad major-element constraints afforded by seismic imaging, the abundance of many trace elements in the mantle clearly records the extraction of core (Chapters 2.01 and 2.15) and continental crust (Chapter 2.03). Estimates of the bulk composition of continental cmst (Volume 3) show it to be tremendously enriched compared to any estimate of the bulk Earth in certain elements that are incompatible in the minerals that make up the mantle. Because the crust contains more than its share of these elements, there must be complementary regions in the mantle depleted of these elements—and there are. The most voluminous magmatic system on Earth, the mid-ocean ridges, almost invariably erupt basalts that are depleted in the elements that are enriched in the continental crust (Chapter 2.03). Many attempts have been made to calculate the amount of mantle depleted by continent formation, but the result depends on which group of elements is used and the assumed composition of both the crust and the depleted mantle. If one uses the more enriched estimates of bulk-continent composition, the less depleted estimates for average depleted mantle, and the most incompatible elements, then the mass-balance calculations allow the whole mantle to have been depleted by continent formation. If one uses elements that are not so severely enriched in the continental cmst, for example, samarium and neodymium, then smaller volumes of depleted mantle are required in order to satisfy simultaneously the abundance of these elements in the continental cmst and the quite significant fractionation of these elements in the depleted mantle as indicated by neodymium isotope systematics. 

Volcanics from the Onverwacht Group, Swaziland and South Africa, comprise the basal part of the Early Precambrian Barberton greenstone belt found both in Swaziland the Transvaal. Data from them gave an age of about 3.54 Ga calculated using an initial [ Nd/ Nd]o ratio of 0.50809 00004 (Hamilton et aL 1979). The strontium and neodymium isotopic record of Apollo-12 basalts from the Moon were examined. Isochrons were derived for an achondrite (eucrite) and another meteorite and gave ages of about 4.58 and 4.562 Ga, respectively, with primordial [ Nd/ Nd]p ratios of 0.50684 0.00008 and 0.506664. An initial [ Sr/ Sr]o ratio was termed ADOR. The isotopic evolution of neodymium in the Earth has been described by means of a model termed CHUR (GHondritic Uniform Reservoir). And the present value of the [ Nd/ Nd] ratio is 0.512638 relative to a [ Nd/ Nd] ratio of 0.7219. The present value of the [ Sm/ Nd] ratio of CHUR is 0.1967, which permits calculation of [ Nd/ Nd] ratio in any past time interval. 

Stracke A, Salters VJM, Sims KWW (1999) Assessing the presence of gamet-pyroxenite in the mantle sources of basalts through combined hafnium-neodymium-thorium isotope systematics. Geochem Geophys Geosyst L1999GC000013... 

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