Sm-Nd isotopic systematics

Torigoye-Kita N., Misawa K., and Tatsumoto M. (1995a) U-Th-Pb and Sm-Nd isotopic systematics of the Goalpara ureilite resolution of terrestrial contamination. Geochim. Cosmochim. Acta 59, 381-390. 

Figure 36 Sm-Nd isotope systematics of minerals from Kimberley peridotites. Data for AJE165 from Richardson el al. (1985), and for EJ8601 from Gunther and Jagoutz (1994).

McCulloch M. T. and Black L. P. (1984) Sm-Nd isotopic systematics of Enderby Land granuUtes and evidence for the redistribution of Sm and Nd during metamorphism Earth Planet. Sci. Lett. 71, 46-58. 

Thoni M. (2002) Sm-Nd isotope systematics in garnet from different lithologies (eastern Alps) age results, and an evaluation of potential problems for garnet Sm-Nd chronometry. Chem. Geol. 185(3-4), 255-281. 

Mork M. B. E. and Mearns E. W. (1986) Sm-Nd isotopic systematics of a gabbro-eclogite transition. Lithos 19, 255-267. 

Sm-Nd isotopic systematics are compatible with Cl chondritic meteorite ratios for the bulk earth. Use of this assumption is a valuable asset in establishing other geochemical abundances. Since both Sm and Nd are relatively refractory, it is a reasonable assumption to take their bulk earth ratios as chondritic. When Nd isotopic ratios are plotted against Sr isotopic ratios (fig. 13), the points from mantle derived samples fall along a narrow zone, the so-called mantle array. The intersection of this zone with the Sm/Nd chondritic ratio provides an estimate of the bulk terrestrial Rb/Sr ratio (=0.03). Since Sr is refractory, the Sr/lanthanide ratios... 

The lanthanide abundance patterns provide unequivocal evidence of a terrestrial sedimentary parent material for tektites. This conclusion is reinforced by the Sm-Nd isotopic systematics (Shaw and Wasserburg 1982) which demonstrate an origin for the various tektite groups from terrestrial crustal source material. Many other isotopic and chemical (e.g. a negative correlation between Si02 and K2O) parameters reinforce this conclusion and all the evidence points unequivocally to an origin for tektites by meteoritic, cometary or asteroidal impact on terrestrial sedimentary rocks. 

Frei, R. and Jensen, B.T., 2003. Re-Os, Sm-Nd isotope and REE systematics on ultramafic rocks and pillow basalts from the Earth s oldest oceanic crustal fragments (Isua supracrustal belt and Ujaragssuit nunat area, W. Greenland). Chem. Geol., 196, 163-91. 

Misawa, K., Shih, C.-Y., Reese, Y., Bogard, D. D. andNyquist, L. E. (2006) Rb-Sr, Sm-Nd and Ar-Ar isotopic systematics of Martian dunite Chassigny. Earth and Planetary Science Letters, 246, 90-101. 

The robustness of the Lu-Hf isotope system in some mantle environments is demonstrated by the precise Lu-Hf isochron of 1,413 67 Myr dehned by clinopyroxene separates from the Beni Bousera peridotite massif (Pearson and Nowell, 2003). This age probably dates the time of melt extraction from these rocks and is considerably more precise than the Sm-Nd isochron or the scattered Re-Os isotope systematics of these rocks. This indicates the potential power of this system in dating mantle rocks. The initial results from the Lu-Hf isotope system indicate that of the incompatible element isotope systems, it is the more robust to metasomatic effects, with signatures frequently recording the time-integrated response to melt depletion. 

Gruau G. M., Rosing M., Bridgwater D., and Gill R. C. O. (1996) Resetting of Sm-Nd systematics during metamorphism of >3.7-Ga rocks implications for isotopic models of early Earth differentiation. Chem. Geol. 133(1-4), 225-240. 

Miller C. and Thoni M. (1995) Origin of eclogites from the Austroalpine Otztal basement (Tirol, Austria) geochemistry and Sm-Nd vs. Rb-Sr isotope systematics. Chem. Geol. 122, 199-225. 

The rather constant fractionation of Sm/Nd ratios in upper continental cmstal rock reservoirs is the basis for the widely applied neodymium model age that is illustrated in Figure 3. The Sm-Nd systematics of chondritic meteorites serve as a reference for the parent/daughter ratio of the undifferentiated Earth (Jacobsen and Wasserburg, 1984), labeled as CHUR for chondritic uniform reservoir. The evolution of this undifferentiated Earth is the basis for calculation of CHUR model ages (McCulloch and Wasserburg, 1978), while the neodymium isotopic evolution of the depleted upper part of the mantle is a more valid reference for most cmstal materials, resulting in the DM model age (DePaolo, 1981). Neodymium isotopic compositions are usually given by s d, where the deviations of Nd/ Nd above or below... 

Lu-Hf isotope systematics provide an important complement to Sm-Nd in the study of the cmst and mantle (e.g., Patchett et al., 1981 Salters and Hart, 1991 Vervoort and Blichert-Toft, 1999). In the crustal context, Lu-Hf is extremely important because of the —1% hafnium content of zircon, and the consequent ability to isotopically characterize the hafnium within grains that have been U-Pb dated (Patchett et al., 1981 Corfu and Stott, 1996 Vervoort et al., 1996 Amelin et al., 1999). However, the Lu-Hf isotopic system is currently overshadowed by a controversy over the decay constant. For many years, a value for the Lu decay constant of 1.94 X 10 yr, based on the eucrite meteorite isochron of Patchett and Tatsumoto (1980) and Tatsumoto et al. (1981) was used. More recent physical determinations reviewed by Begemann et al. (2001) have high dispersion, but do not seem to corroborate the 1.94 X 10 value. At the present time, there is a discrepancy between values based on U-Pb-dated terrestrial Precambrian REE-rich minerals, such... 

Carlson R. W., Hunter D. R., and Barker F. (1983) Sm-Nd age and isotopic systematics of the bimodal suite, ancient gneiss complex, Swaziland. Nature 305, 701-704. 

Figure 1 Systematics of Nd- and Hf-isotopic evolution in the bulk Earth, continental crust, and mantle. Daughter elements Nd and Hf are more incompatible during mantle melting (more likely to go into a partial melt of mantle rock) than Sm and Lu, respectively. As a result, the continental crust has a lower Sm/Nd and Lu/Hf ratio than the mantle, and lower Nd- and Hf-isotope ratios. Young continental crust has isotope ratios similar to the mantle, and the older the continental terrain, the lower the Nd- and Hf-isotope ratios. Rb-Sr behaves in the opposite sense, such that the parent element Rb is more incompatible than the daughter element Sr. (a) Schematic example of the evolution of Nd- and Hf-isotope ratios of a melt and the melt residue from a melting event around the middle of Earth history from a source with the composition of the bulk Earth, (b) The same scenario as in (a), but with the isotope ratios plotted as e d and snf. The bulk Earth value throughout geological time is defined as e d and SHf = 0> and e-value of a sample is the parts per 10 deviation from the bulk Earth value.

Since a number of isotope systematics (U, Th/Pb, Lu/Hf, Sm/Nd) in clastic sediments is essentially controlled by the heavy mineral fraction, such considerations are of considerable importance for any geological interpretations. 

The discussion of the chemistry of clastic sediments suggested an overall mafic to felsic evolution of global sediments, and presumably of UCC, their ultimate source, in the course of geologic history, with a major evolutionary step across the Archean/Proterozoic transition. The response of isotopes to this evolutionary scenario can best be gauged by consideration of the REE isotope systematics, such as the Sm/Nd and Lu/Hf. 

Figure 21 Stratigraphic age versus Nd- and Hf-crustal residence ages. Model ages were calculated using hnear E evolution from 0 to - -10 for Nd and 0 to - -16 for Hf, from 4.56 Gyr to present. The similarity of the model age systematics underscores the overall coherent behavior of the Sm-Nd and Lu-Hf isotopic systems in the sedimentary environment (after Vervoort et al., 1999).

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