Spinel oceanic mantle

Figure 13 Normative spinel Iherzolite mineral abundances (wt.%) versus rock Mg for oceanic mantle (as in Figure 7) relative to trends for 0-25% batch melt extraction at 0.5-2 GPa. The starting composition is fertile upper mantle as determined in this study (Table 1, 8), and residues are calculated using the melting model of Kinzler and Grove (1992a, 1993).

Figure 11 CaO/Al203 versus spinel Iherzolite normative cpx/opx for the off-craton mantle subset (shaded circles) and reconstructed oceanic mantle (open circles). Primitive mantle compositions from Table 2 are also shown and the symbols are the same as in Figure 9.

Byndzia, L.T., Wood, B.J., and Dick, H.J.B., 1989. The oxidation state of the earth s sub-oceanic mantle from oxygen thermobarometry of abyssal spinel peridotites. Nature, 341, 526-7. 

Hellebrand E., Snow J. E., and Muhe R. (2002) Mantle melting beneath Gakkel Ridge (Arctic Ocean) abyssal peridotite spinel compositions. Chem. Geol. 182, 227-235. 

Figure 8 Mg/(Mg + Fe) versus Mg/Si for (a) off-craton spinel peridotite xenoliths and (b) cratonic garnet and spinel peridotite xenoliths. Arrows mark the oceanic trend (Boyd, 1989, 1997) defined by abyssal peridotites. Also shown are various estimates for primitive upper mantle (polygons from Table 7).

In the oceanic setting, spinel Iherzolite xenoliths from Pali (Hawaii) have olivine 5 0 values of 5.09-5.12 per mil, typical of olivines from other oceanic and continental mantle rocks (Ducea et al., 2002). In contrast, olivines from plagioclase peridotites are enriched by 0.5 per mil. This is interpreted to be due to the formation of plagioclase by reaction with or crystallization from melts intruding the Pacific lithospheric mantle. 

Stolz A. J. and Davies G. R. (1988) Chemical and isotopic evidence from spinel Uierzolite xenoliths for episodic metasomatism of the upper mantle beneath southeast Australia. In Oceanic and Continental Lithosphere Similarities and Differences J. Petrology (Spec, volume) (eds. 

Normal mantle melting, such as that which leads to the formation of oceanic crust and oceanic islands, produces magma of basaltic to picritic composition and leaves a residue consisting of olivine, orthopyroxene, chnopyroxene and an aluminous phase. The compositions of minerals in this residue, and their relative proportions, are unlike those in old subcontinental hthosphere Mg-Fe ratios of the ferromagnesian minerals are too low, and the amount of chnopyroxene and spinel or garnet is too high. 

Alkali basalt xenoliths Xenoliths in alkali basalts are most commonly spinel-bearing peridotites. They have been divided into two main groups (Frey Prinz, 1978). Primitive xenoliths have chemical compositions which suggest that they have had a melt extracted from them. Menzies (1983) showed that this "depleted" character is similar in alkali basalt xenoliths beneath both the oceans and the continents and proposed that a depleted mantle layer underlies both... 

McKenzie D, O Nions RK (1995) The source regions of ocean island basalts. J Petrol 36 133-159 Meen JK, Eggler DH, Ayers JC ((1989) Experimental evidence for very low solubility of rare earth elements in C02-rich fluids at mantle conditions. Nature 340 301-303 Menzies M, Chazot G (1995) Fluid processes in diamond to spinel facies shallow mantle. J Geodynamics 20 387-415... 

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