Olivine cratonic mantle

Figure 9 Normative spinel Iherzolite mineral abundances (wt.%) versus rock Mg for a subset of 292 off-craton mantle compositions (shaded circles). Data from a given locality were included if compositions had a correlation between Mg and normative olivine with a correlation coefficient (i ) of 0.6 or better. Data sources for xenoliths are Beccaluva et al. (2001a,h), Reid and Woods (1978), Rivalenti et al. (2000), Stem et al. (1999), Vaselli et al. (1995), Wiechert et al. (1997), Xu et al. (1988), and Zangana et al. (1999). Data sources for orogenic Iherzolites are Bodinier et al. (1988), Frey et al. (1985, 1991), Hartmann and Wedepohl (1993), and Lugovic et al. (1991). Open circles are the reconstmcted abyssal peridotite compositions from Figure 7. Also shown are estimates of primitive mantle from Table 2 white square = 1, circle = 2, triangle = 3, diamond = 5, inverted triangle = 6, ex = 7, and shaded star = 8.

The off-craton mantle subset is shown relative to isobaric batch melt extraction curves on plots of normative olivine and major-element oxides versus Mg in Figure 17. Generally speaking, off-craton mantle compositions are consistent with effectively 0-30% melt extraction from fertile upper mantle in the range of 1-5 GPa. The chemical signature recorded in off-craton mantle mimics closely the maximum degree of melt extraction recorded in oceanic mantle, but in contrast there are many samples that show little or... 

Figure 18 Normative olivine and opx (garnet Uierzo-Ute norm) versus rock Mg showing low-T cratonic mantle relative to batch melt extraction trends from 3 GPa to 7 GPa (see Figure 6). Open circles are compositions from the Kaapvaal, Siberian, and Slave cratons, and the filled circles are compositions from the Tanzanian, Canadian, and Greenland cratons.

Boyd, F. R. 1996. Origins of peridotite xenoliths major element considerations high pressure and high temperature research on lithosphere and mantle materials. Proceedings of the International School of Earth and Planetary Sciences, Siena, 89-106. Boyd, F. R. 1997. Correlation of orthopyroxene abundance with the Ni-content of eoexisting olivine in cratonic peridotites. EOS Transactions, American Geophysical Union, 78, 746. 

The mineralogical and chemical composition of peridotite from subcontinental lithosphere differs from that of peridotite from other parts of the mantle (Boyd 1989 Berstein et al. 1997). Peridotites from subcontinental lithosphere is depleted , which means it contains only a small amount of clinopyroxene and an aluminous phase, which together make up the so-called basaltic component. The lithosphere beneath the oldest Archaean cratons has a composition markedly different from that of younger subcontinental lithosphere (Boyd Mertzman 1987 Griffin et al. 1999). Old unmetasomatized lithosphere is harzburgitic, a mixture of olivine... 

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