Peridotites composition

Falloon TJ, Green DH (1987) Anhydrous partial melting of MORE pyrolite and other peridotite compositions at 10 kbar implications for the origin of primitive MORE glasses. Mineral Petrol 37 181-219... 

McGregor I. D. (1974). The system Mg0-Al203-Si02 Solubility of AI2O3 in enstatite for spinel and garnet peridotite composition. Amer. Mineral, 59 110-119. 

Perhaps one of the most important consequences of a peridotite composition for the upper mantle is that the phase transitions in olivine that are manifested as seismic discontinuities should exhibit thermally controlled variations in their depth of occurrence that are consistent with the measured Clapeyron slopes (Bina and Helffrich, 1994) of the transitions. In particular, the olivine-wadsleyite transition at 410 km should be deflected upwards in the cold environment of subduction zones while the disproportionation of ringwoodite to silicate perovskite and magnesiowiistite at 660 km should be deflected downwards, thereby locally thickening the transition zone. In anomalously warm regions (such as the environs of mantle plumes as described below), the opposite deflections at 410 and 660 should locally thin the transition zone. The seismically observed topography of 20-60 km on each of the 410 and 660 is consistent with lateral thermal anomalies of 700 K or less (Helffrich, 2000 Helffrich and Wood, 2001). 

The properties of upper-mantle seismic reflectors, especially the observed lateral variations in the seismological properties of the mantle transition zone, indicate that the upper mantle possesses a peridotite composition, approaching... 

Michael P. J. and Bonatti E. (1985) Peridotite composition from the North Atlantic regional and tectonic variations and implications for partial melting. Earth Planet. Sci. Lett. 73, 91-104. 

Green D. H. and Ringwood A. E. (1970) Mineralogy of peridotitic compositions under upper mantle conditions. Phys. Earth Planet. Int. 3, 359-371. 

Hirschmann M. M. (2000) Mantle solidus experimental constraints and the effects of peridotite composition. Geochem. Geophys. Geosys. 1 (20001024). 

Figure 12 Molar compositions of phases in the system MgO AI2O3 Si02-H20, projected from H2O into the Mg0-Al203-Si02 ternary. Solid circles are anhydrous phases, open circles are hydrous phases. Abbreviations as in Table 1. The shaded box represents plausible mantle peridotite compositions, with the upper hound being at —5 wt.% AI2O3.

Evans B. and Trommsdorff V. (1983) Fluorine hydroxyl titanian clinohumite in Alpine recrystallized garnet peridotite compositional controls and petrologic significance. Am. J. Sci. 283A, 355-369. 

Figure 4 Normative spinel Iherzolite mineral abundances (wt.%) in batch partial melt extraction residues (0-25%) from fertile peridotite (composition 8, Table 1) as a function of Mg (molar Mg/(Fe + Mg)) at 0.5 GPa, 1 GPa, and 2 GPa, based on the melting model of Kinzler and Grove (1992a, 1993). Normative mineral compositions are calculated using the spinel Iherzolite normative algorithm of Kelemen et ai, (1992).

Figure 7 Normative spinel Iherzolite mineral abundances (wt.%) versus rock Mg for a set of reconstructed abyssal peridotite compositions. Reconstructions were made using mineral modes and phase composition data (see text Niu et al. (1997), Baker and Beckett (1998), and Asimow (1999) for details). Circles are from Baker and Beckett (1998), and filled circles are reconstructions based on site-averages, whereas open circles are reconstructions based on single thin section modes. Crosses are from Asimow (1999), and are reconstructions based on single thin section modes after the method of Niu et al (1997).

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.

Figure 10 Major-element oxides versus Mg for the off-craton mantle subset (shaded circles) and reconstructed abyssal peridotite compositions (open circles). Primitive mantle compositions from Table 2 are also shown with symbols as in Figure 9.

In order to explore the role of melt extraction more fully in generating abyssal peridotite compositions, Asimow (1999) used the MELTS model to investigate a variety of melt extraction scenarios including polybaric batch and mixtures of polybaric near-fractional and batch melting. 

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