Neodymium isotopic composition

Vervoort, J.D., Blichert-Toft, J., Patchett, P.J., and Albar de, F. (1997) Hafnium-neodymium isotopic composition of the crust and mantle through time new directions with hafnium whole rock studies. In Seventh Annual V.M. Goldschmidt Conference, 212, LPI Contribution No. 921, Lunar and Planetary Institute Houston. 

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. 

Sharma M. and Wasserburg G. J. (1996) The neodymium isotopic compositions and rare earth patterns in highly depleted ultramafic rocks. Geochim. Cosmochitn. Acta 60, 4537-4550. 

Mica from mantle xenohths is very poor in REE, especially LREE (Table 9). Where reported, Sm/Nd values vary widely both above and below the PUM values (Figure 25) however, the low levels present could be easily influenced by small inclusions or analytical artifacts. Neodymium levels are so low that even the presence of tens of percent mica in a peridotite mineralogy do not significantly influence the neodymium budget of the rock. As such, the presence of mica in a peridotite is not sufficient to generate LREE enrichment and hence its presence alone, is unlikely to cause a bulk peridotite to evolve to enriched neodymium isotopic compositions (Pearson and Nowell, 2002). 

If continental peridotite xenoliths are divided into cratonic and noncratonic compositions, the vast majority of highly enriched neodymium isotope compositions originate in cratonic mantle and very few are evident in noncratonic mantle. Enriched neodymium isotope compositions can also be found in mantle sampled by orogenic peridotites (Reisberg and Zindler, 1986 Pearson et ai, 1993 Chapter 2.04) but not the extreme values evident in cratonic CLM. This is expected, given the great antiquity of cratonic CLM. Further subdivision of cratonic samples (Figure 37) shows... 

Four cratonic, ultradeep xenoliths from S. Africa and Sierra Leone have been analyzed for their strontium and neodymium isotopic compositions (Macdougall and Haggerty, 1999). The neodymium isotopic compositions of minerals from these xenoliths suggest that they were emplaced into the African lithosphere at times ranging from approximately the time of kimberlite emption to hundreds of millions of years earlier. The samples show a complex history of melt... 

There are few pubhshed Lu-Hf isotope studies of mantle xenohths because of difficulties in efficient ionization of hafnium by thermal ionization mass spectrometers. Multicollector plasma mass spectrometers are a solution to this problem and data are emerging that promise to be a more revealing tool in mantle environments than neodymium isotopes. The variety of Lu/Hf fractionation displayed by mantle minerals (Figure 42) indicates that, as with other isotope systems, isotopic variation should be considerable and initial results are confirming this. Salters and Zindler (1995) found very radiogenic Hf/ Hf at relatively unradiogenic neodymium isotope compositions in spinel peridotites from Salt Lake Crater, Hawaii. Radiogenic Hf/ Hf also characterizes low-T circum-cratonic... 

Figure 52 Initial ENd ssr isotope plot of calculated whole-rock eclogites from Africa (Koidu—Hills and Haggerty, 1989 Orapa—Smith et al., 1989 Viljoen et al, 1996 Roberts Victor—Jagoutz et al, 1984 Smith et al., 1989 Jacob and Jagoutz, 1994 Bellsbank—Neal et al., 1990), Yakutia (Snyder et al, 1993 Jacob et al, 1994 Pearson et al., 1995a Snyder et al, 1997), and eclogitic inclusions in diamonds (Richardson, 1986 Richardson et al, 1990 1999 Smith et al, 1991). Eclogite data are initial calculated whole-rock neodymium isotope compositions. Strontium isotope compositions are from clinopyroxene only. Cratonic peridotite minerals and diamond inclusions are plotted for comparison. Arrow points to a sample from Udachnaya that has a calculated initial SNd of 484. dashed lines are...

Mantle evolution curves for neodymium isotopic compositions in the Earth prior to 2.7 Ga are much less well defined than for younger time periods. Many studies have elected simply to extrapolate a linear evolution from 2.7 Ga to the composition of the primitive mantle (snu = 0) at 4.56 Ga (e.g., Goldstein et al., 1984). In contrast, other studies have attempted a more precise definition of the neodymium mantle evolution curve for the Archean based on observed compositions (e.g., Bennett et al., 1993 Bowring and Housh, 1995 Vervoort and Blichert-Toft, 1999). The justification of these efforts is that Archean mantle chemistry, particularly for the long-lived isotopic systems, provides a window into the first 700 Myr of Earth s history, prior to establishment... 

Ga would be extremely important, as this would require extreme early differentiation of the Earth s mantle within the first 100-400Myr of Earth history. As shown in Figure 2, to generate SNd of - -2 to - -4 at 3.8 Ga requires ratios in the pre-3.8 Ga upper mantle similar to those in the present-day depleted mantle, yet the modem mantle records the effects of extraction of the whole of the continental cmst. Thus, neodymium isotopic compositions of the early preserved continental cmst provide strong evidence that portions of the Earth s upper mantle in the Early Archean were significantly lithophile-element-depleted requiring very early (>4.0 Ga) differentiation. 

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. 

Chen C. H., DePaolo D. J., Nakada S., and Shieh Y. N. (1993) Relationship between emption volume and neodymium isotopic composition at Unzen volcano. Nature 362, 831-834. 

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... 

Albarede F., Goldstein S. L., and Dautel D. (1997) The neodymium isotopic composition of manganese nodules from the Southern and Indian oceans, the global oceanic neodymium budget, and their bearing on deep ocean circulation. Geochim. Cosmochim. Acta 61, 1277-1291. 

Lacan E. and Jeandel C. (2001) Tracing Papua New Guinea imprint on the central Equatorial Pacific Ocean using neodymium isotopic compositions and rare earth element patterns. Earth Planet. Sci. Lett. 186(3-4), 497-512. 

Spivack A. J. and Wasserburg G. J. (1988) Neodymium isotopic composition of the Mediterranean outflow and the eastern North-Atlantic. Geochim. Cosmochim. Acta 52(12), 2767-2773. 

Alibert, C. McCulloch, M. T. 1993. Rare earth element and neodymium isotopic compositions of the banded iron-formations and associated shales from Hamersley, Western Australia. Geochimica et Cosmochimica Acta, 57, 187-204. 

Nd/ Nd low 8nfrequency distribution for CLM as a whole is that the pronounced mode is within 58 units of bulk Earth and the mean 8j,jd value is 1.8. On this basis, the dominant neodymium isotopic characteristic of CLM is not enriched but is close to, or slightly more depleted than bulk Earth. Of course, if Depleted Mantle is used as a reference point then the CLM mode is enriched. The strontium isotope frequency distribution has a long tail out to very radiogenic ( enriched ) compositions but the mean Sr/ Sr is 0.7047 very close to estimates of bulk Earth. It is important to bear in mind that this statistical view of CLM geochemistry could... 

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