Os isotope evolution

Fig. 2. Os isotope evolution diagram showing details of Re-Os model age systematics. The Trd age assumes that all Re was removed during a single stage of melting whereas the Tma age uses the measured Re concentration to calculate a model age with respect to the mantle evolution line. The equations for each age calculation are ...

Hf Isotopic Constraints on the Evolution of the Archean and Hadean Mantle " Nd Isotopic Signatures Os Isotopic Evolution Sr Isotopic Evolution... 

Figure 37 Frequency distribution plots for Os, Nd, and Sr isotope compositions of cratonic and noncratonic peridotite xenoliths. Upper right plots give the range for ocean island basalts (OIB) and arrows show the direction of isotopic evolution for melt depletion and enrichment events. Data compiled from sources cited in Menzies (1990b), Pearson (1999a,b), and those given in Figure 21 (after Pearson and Nowell, 2002).

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. 

Singh S. K., Trivedi J. R., and Krishnaswami S. (1999) Re-Os isotope systematics in black shales from the Lesser Himalaya their chronology and role in the Os/ Os evolution of seawater. Geochim. Cosmochim. Acta 63(16), 2381-2392. 

S. B. 19986. Lithospheric evolution in circum-cratonic settings a Re-Os isotope study of peridotite xenoliths from the Vitim region, Siberia. Mineralogical Magazine, 62A, 1147-1148. 

Table 3.2 the initial compositions and the temporal evolution of the Nd-, Hf-, Pb- and Os-isotopic systems are given in Section 3.2.3. Finally, the volatile content of the Archaean mantle is discussed in Chapter 5, Section 5.2). 

In this section mantle evolution curves are presented for neodymium (Nd), hafnium (Hf), lead (Pb) and osmium (Os) isotopes. A summary of these isotopic systems is given in Text Box 3.2. Earlier studies based upon the study of Sr isotopes in the mantle (e.g. Bell et al., 1982) are now known to be unreliable because of its high geochemical mobility (Goldstein, 1988). The significance of the mantle evolution curves described here is that they demonstrate that the mantle does not operate as an isolated system but that it has evolved in its composition over time, in response to core formation, crust extraction, and the recycling of crustal material. 

As an aside, it is also worth noting that a close look at the isotopic evolution of the Earth s mantle challenges the chondritic model for the Earth. This is particularly clear for the Lu-Hf and Re-Os isotope systems, where there is uncertainty about which meteorite type is the most appropriate starting point for the isotopic evolution of the Earth. Recent studies of chondritic Sm-Nd ratios by Boyet and Carlson (2005) further support the nonchondritic view of the bulk Earth. 

Certainly the globally uniform seawater isotope evolution of Sr, Os, and potentially also Be, offer excellent tools for isotope stratigraphy on long (My) timescales. 

---