Vitim peridotites

The Vitim peridotite with the least disturbed extended-PGE pattern in Fig. 8 sample 314-5, also has similar Trd and Tma ages (1.8 and 2.0 Ga, respectively). The Trd age of 1.8 Ga is the oldest of this suite of peridotites and is similar to the Sm-Nd clinopyroxene model ages in these rocks (Ionov Jagoutz 1989). In contrast to cratonic rocks, the Sm-Nd isotope systema-tics of most Vitim peridotites are characteristic of melt depletion, i.e. clinopyroxenes have Sm/Nd > chondrite and mineral REE patterns do not show the complexity of enriched cratonic rocks (Ionov Jagoutz 1989 Ionov et al. 1993). Hence, in contrast to cratonic rocks (Pearson 19996), the Sm-Nd model ages of Vitim rocks may reflect the partial melting event that produced them. This possibility is supported by the coincidence of Sm-Nd and Re-Os model ages... 

Fig. 9. AhOj- Os/ Os correlation for the Vitim peridotites suite (Pearson et al. 19986). The y-intercept of this correlation gives a Os/ Os value of 0.107, = 0.974, for samples with <4wt% AI2O3. Louwrencia data from...

Figure 6 P-T arrays compiled for garnet peridotite xenoliths from several suites using two-pyroxene thermometry and Al-in-orthopyroxene barometry (Tbkn and Rbkn methods, Table 5). Data sources given in Rudnick and Nyblade with additional data here for Vitim (Ionov et al., 1993a) and Canada (MacKenzie and Canil, 1999 Schmidberger and Francis, 1999). The best-fit line for the Kaapvaal data is plotted in each figure for reference. Intersection of P-T array with mantle adiabats (shaded field) represents an estimate of the thickness of lithosphere at the time of sampling.

The best characterized noncratonic, spinel peridotite xenoliths for PGEs are those from southeastern Australia (Handler and Bennett, 1999), the Massif Central, France (Lorand and Alard, 2001), Western USA (Morgan et al., 1981 Lee, 2002) and Vitim, Siberia (Pearson et al,... 

Glaser S. M., Foley S. F., and Gunther D. (1999) Trace element compositions of minerals in garnet and spinel peridotite xenoliths from the Vitim volcanic field, Transbaikalia, eastern Siberia. Lithos 48, 263 —285. 

Ionov D. A. (2004) Chemical variations in peridotite xenoliths from Vitim, Siberia inferences for REE and Hf behaviour in the garnet facies upper mantle. J. Petrol. 45. 

Ionov D. A., Ashchepkov I. V., Stosch H.-G., Witt-Eickschen G., and Seek H. A. (1993a) Garnet peridotite xenoliths from the Vitim volcanic field, Baikal Region the nature of the garnet-spinel peridotite transition zone in the continental mantle. J. Petrol. 34, 1141—1175. 

Pearson D. G., Ionov D., Carlson R. W., and Shirey S. B. (1998a) Lithospheric evolution in circum-cratonic settings a Re-Os isotope study of peridotite xenoliths from the Vitim region, Siberia. Mincra/. Mag. 62A, 1147-1148. 

Table 1. PGE and Os isotope data for selected whole-rock peridotites from the Slave Craton, Namibia and Vitim... 

To illustrate the appUcation of these methods we have analysed selected samples from different suites of cratonic peridotites for PGE abundances and Re-Os isotopic composition that had been previously analysed for major elements (Table 1). The sample set comprises three peridotites from the Jericho kimberlite, Northern Slave Craton (Irvine et al. 1999 Kopylova Russell 2000) two peridotites from the Kaapvaal Craton (Pearson et al. 1995a Carlson et al. 1999) three peridotites from the Farm Louwrencia kimberlite, Southern Namibia, on the periphery of the Kaapvaal Craton (Pearson et al. 1994, 1998a Hoal et al. 1995 Frantz et al. 1996) three peridotites from the Vitim alkali basalt field, on the southern margin of the Siberian Craton (Ionov et al. 1993 Pearson et al. 19986). 

Fig. 8. Chondrite-normalized PGE patterns of whole-rock peridotites from the Vitim region and Namibia (see data in Table 1). Normalizing values taken from McDonald et al. (1995).

Ionov, D. A. Jagoutz, E. 1989. Sr and Nd isotopic composition in minerals of garnet and spinel peridotite xenoliths from the Vitim Highland first data for mantle inclusions in the USSR. Transactions Doklady J of the USSR Academy Sciences, Earth Science Section, 301, 232-236. 

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