Oceanic mantle

Sobolev, A. V. Shimizu, N. (1992). Ultra-depleted melts and permeability of oceanic mantle (in Russian). Dokl. Acad. Sci. Russia, 236, 354-69... 

Sobolev, A.V. and Shimizu, N., 1992. Superdepleted melts and ocean mantle permeability. Doklady Rossiyskoy Akademii Nauk, 326, 354-360. 

Clague, D.A. and Frey, F.A., 1982. Petrology and trace element geochemistry of the Honolulu volcanics, Oahu Implications for the oceanic mantle below Hawaii. J. Petrol., 23 447-504. 

Snow J. E. and Schmidt G. (1998) Constraints on Earth accretion deduced from noble metals in the oceanic mantle. Nature 391, 166-169. 

Rehk per M., Halliday A. N., Alt J., Eitton J. G., Zipfel J., and Takzawa E. (1999) Non-chondritic platinum-group element ratios in oceanic mantle lithosphere petrogenetic signature of melt percolation Earth Planet. Sci. Lett. 65, 65-81. 

Isotope decoupling between oceanic mantle and crust evidence for marble-cake or veined mantle 156... 

The abyssal peridotites are samples from the oceanic mantle that were dredged on the ocean floor, or recovered from drill cores (e.g., Bonatti et al., 1974 Prinz et al., 1976 Hamlyn and Bonatti, 1980). 

In spite of their variable provenance (subcontinental lithosphere, supra-subduction mantle wedge, or oceanic mantle), most of the tectonically emplaced and abyssal peridotites show coherent covariation trends for major elements (Eigure 5). These variations reflect their variable modal compositions between a fertile end-member— comparable to proposed estimates for pristine... 

As noted above, isotope decouphng between oceanic mantle and crust was observed both in ophiolites (Claesson et al., 1984 Gopel et al., 1984 Jacobsen et al., 1984 Brouxel and Lapierre, 1988 Rampone et al., 1996, 1998) and in abyssal rocks (Snow et al., 1994 Kempton and Stephens, 1997 Salters and Dick, 2002). In most examples, the mantle rocks are distinguished from the oceanic crust by more depleted isotopic compositions, generally reflected by higher Nd/ Nd values. However, the interpretations proposed for the ophiolites and for the abyssal peridotites are markedly different. 

Bodinier J.-L., Menzies M. A., and ThirlwaU M. (1991) Continental to oceanic mantle transition—REE and Sr-Nd isotopic geochemistry of the Lanzo Iherzohte massif. J. Petrol. (Orogenic Iherzolites and mantle processes) (sp. vol.) 191-210. 

Schiano P. and Clocchiatti R. (1994) Worldwide occurrence of silica-rich melts in sub-continental and sub-oceanic mantle minerals. Nature (London) 368, 621-624. 

Boyd (1989) compiled modes of major minerals in peridotite xenoliths from on and off-craton localities and compared the results with mantle residues from oceanic mantle represented by... 

Figure 38 Nd-Sr isotope variation of clinopyroxenes and garnet in peridotite xenoliths. (a) Compares cratonic and noncratonic peridotite xenoliths with continental crust. Inset shows restricted field for oceanic mantle. Arrow points to a peridotite from Lashaine, Tanzania, that lies at an Sr/ Sr value of 0.83. (b) Compares cratonic peridotites from the Kaapvaal, Wyoming, and Siberian cratons.

Canil D. and Fedortchouk Y. (2000) Clinopyroxene-liquid partitioning for vanadium and the oxygen fugacity during formation of cratonic and oceanic mantle lithosphere. J. Geophys. Res. 105, 26003-26016. 

Nixon P. H. and Boyd F. R. (1979) Garnet bearing Iherzohtes and discrete nodules from the Malaita alnoite, Solomon Islands S. W. Pacific, and their bearing on oceanic mantle composition and geotherm. In The Mantle Sample Inclusions in Kimberlites and Other Volcanics (eds. F. R. Boyd and H. O. A. Meyer). American Geophysical Union, Washington, DC, pp. 400-423. 

Luguet A., Alard O., Lorand J. P., Pearson N. J., Ryan C., and O Reilly S. Y. (2(X31) Laser-ablation microprobe (LAM)-ICPMS unravels the highly siderophile element geochemistry of the oceanic mantle. Earth Planet. Sci. Lett. 189, 285-294. 

Peacock S. M. (2001) Are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle Geology 29, 299-302. 

Direct evidence for the compositional effects of partial melt extraction is preserved in samples of upper-mantle lithosphere with a range of ages, including Archean cratonic mantle, Proterozoic subcontinental mantle, and modern oceanic mantle. Samples of upper mantle are collected as xenoliths, peridotites dredged from oceanic fracture zones, and slices of upper mantle tectonically exposed at the surface, and extensive samples exist from both oceanic and continental settings (see Chapters 2.04 and 2.05). Here, data sets are assembled for oceanic and subcontinental mantle lithosphere, and compositional trends are compared to those predicted for partial melt extraction from fertile peridotite in order to deduce the role that melt extraction has played in producing compositional variability in upper-mantle lithosphere, and to place constraints on the thermal evolution of the mantle. 

Modern oceanic mantle is defined solely by abyssal peridotites, which are samples of harzbur-gite and Iherzolite collected from fracture zones at oceanic spreading centers, and these samples are representative of shallow oceanic lithosphere that has been processed at mid-ocean ridges (see Chapter 2.04). Two types of continental mantle lithosphere are considered (i) cratonic mantle, which refers to xenoliths collected from kimberlites that sample portions of mantle beneath stable, Archean cratons and (ii) off-craton mantle, which refers to xenoliths collected from alkalic basalts that have sampled portions of the subcontinental mantle adjacent to ancient cratonic mantle (see Chapter 2.05). Also included with off-craton lithosphere are orogenic Iherzolites and ophiolites, which are slices of mantle tectonically emplaced typically at convergent margins. 

Any method for reconstructing abyssal peridotite bulk compositions involves assumptions and uncertainties. Rather than choosing a single reconstruction method as superior, we consider that in total these reconstructions are highly representative of depleted oceanic mantle beneath the axis of mid-ocean ridges. 

Figure 10 shows major-element oxides versus Mg for off-craton and oceanic mantle, as well as some estimated compositions for primitive mantle (Table 1). As expected from the normative plots, the two sets of mantle compositions have distinct trends for all oxides. Previous models for primitive upper mantle have a range in Mg from 89 to 90, and Figures 9 and 10 show that the oceanic and off-craton trends also converge within this range. Assuming that the off-craton and abyssal mantle trends are due primarily to melt extraction from a common protolith, then the intersection of the trends should provide a good estimate for the composition of fertile upper mantle for major elements. 

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).

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... 

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