Mantle composition

Sturm ME, Goldstein SJ, Klein EM, Karson JA, Mnrrell MT (2000) Uranium-series age constraints on lavas from the axial valley of the Mid-Atlantic Ridge, MARK area. Earth Planet Sci Lett 181 61-70 Sun S, McDonongh WF (1989) Chemical and isotopic systematics of ocean basalts implications for mantle composition and processes. In Magmatism in the Ocean Basins. Saunders AD, Norry MJ (eds) Blackwell Scientific Pnbl. Oxford, p 313-345... 

Sun SS, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts implications for mantle composition and processes. In Magmatism in ocean basins. Saunders AD, Norry MJ (eds) Geol Soc Lond Spec Publ 42 313-345... 

Mantle composition can also be assessed through examination of lavas from other oceanic settings. In a study of well-characterized Hawaiian lavas, Chan and Frey (2003) found a total range indH i that overlaps the range for MORE, +2.5 to +5.7. Other data from Kilauea volcano substantiate this range (Tomascak et al. 1999b). The Hawaii data, when compared with other isotopic and elemental parameters, suggested incorporation of recycled altered oceanic crust into the source of the Hawaiian plume (Chan and Frey 2003). 

Ion microprobe analyses of hydrous minerals in Martian meteorites reveal two different sources of hydrogen. One is interpreted as magmatic water, with 5D = 900 permil, and thought to reflect the mantle composition the other is thought to reflect the atmospheric composition, with 5D =4000 permil (Leshin, 2000). The incorporation of atmospheric water into these meteorites suggests some kind of cycling of water between the atmosphere and lithosphere on Mars. 

The compositions of the crusts of the Moon and Mars are distinct - one is dominated by feldspathic cumulates from an early magma ocean, and the other by basaltic lavas. Regional patterns reflect differences in subjacent mantle compositions. The compositions of the mantles and cores of these bodies can be constrained by chemical analyses of mantle-derived basalts. The interiors of both bodies have remained geochemically isolated, because of the absence of plate tectonics. 

Major-element compositions (weight ratios of Mg/Si and Al/Si) for mantle rocks (peridotites) and estimates of the primitive mantle composition of the Earth compared with various groups of chondrites and the Sun. No mixture of chondrite types provides an exact match to the primitive mantle composition, although some carbonaceous chondrites provide the closest match. Modified from Righter et al. (2006). 

Palme, H. and O Neill, H.St.C. (2004) Cosmochemical estimates of mantle composition, in Treatise on Geochemistry Volume 2 The Mantle and Core (eds R.W. Carlson, H.D. Holland and K.K. Turekian Editors-in-Chief), Elsevier Science, pp. 1-38. 

Fig. 1.4. Patterns of incompatible elements normalised against mantle compositions (Wood 1979 Sun and McDonough 1989) for some representative Italian Plio-Quatemary mafic rocks.

Sr-Nd-Pb-Hf isotope ratios display comparable range of values in the silicic and mafic rocks and are closer to crustal than to mantle compositions (Fig. 2.4 Vollmer 1976 Hawkesworth and Vollmer 1979 Conticelli et al. 2002 Gasperini et al. 2002 author s unpublished data). These crustal-like isotopic signatures have led early authors to suggest a crustal... 

REE patterns show variable fractionation, with small negative Eu anomalies, which increase in trachytes and phonolites (Fig. 6.7a). HREE depletion is observed is some phonolites. Patterns of incompatible elements normalised to primordial mantle compositions for mafic rocks (Fig. 6.7b) are fractionated and contain positive spike of Pb and negative anomalies of HFSE. However, these are less sharp than in other Italian ul-trapotassic rocks, such as those of the Roman Province, and HFSE abundances are much higher than observed in MORBs (Sun and McDounough 1989). 

Fig. 6.8. Sr-Nd-Pb isotopic variation of Campania, Pontine Islands and Vulture volcanoes. The fields of other Italian magmatic provinces and HIMU, EMI and DMM mantle compositions are also shown.

REE patterns are fractionated, with evolved rocks showing negative Eu anomalies (Fig. 6.12a). Incompatible element patterns of mafic rocks normalised to primordial mantle composition (Fig. 6.12b) show Pb spikes and relatively high concentration and moderate negative anomalies of HFSE. 

Petrological and geochemical variations along the arc are considered to result from variable relative amounts of slab-released fluids and melts added to the mantle wedge, as well as from higher amounts of subducted sediments added to the mantle beneath eastern islands. Variation of pre-metasomatic mantle composition, from MORB-type in the central arc to OIB-type in the external islands, is also considered as an important factor for compositional diversity along the arc. 

REE patterns are fractionated for all the rocks, but tholeiites show lower La/Yb ratios than alkaline products (Fig. 8.5a). Incompatible element patterns normalised to primordial mantle compositions for mafic rocks are very different from the Aeolian arc and central-southern Italian peninsula. Both tholeiitic and alkaline basalts show a marked upward convexity, with negative spikes of K (Fig. 8.5b). Note, however, that there are also negative anomalies for Hf and Ti, which are uncommon in most Na-alkaline basalts from intraplate settings (e.g. Wilson 1989). Overall, the Etna magmas have been found to be more enriched in volatile components than common intraplate magmas, and water contents up to 3-4 wt % have been found by melt inclusion studies (Corsaro and Pompilio 2004 Pompilio, personal communication). 

Overall, isotope and trace element data have led to the conclusion that the mantle sources beneath the Sicily Province are heterogeneous and result from the interaction between various mantle compositions or reservoirs. There is a lively debate on the origin and physical nature of these mantle compositions, not only in Sicily, but at a global scale (e.g. Hofmann 1997 Meibom and Anderson 2003). 

The Sardinia Province contains a wide variety of rocks, ranging from subalkaline to Na alkaline and nephelinitic, and from mafic to felsic. Most rocks have relatively unradiogenic Sr and Pb isotopic signatures, resembling EMI mantle compositions. A few outcrops from southern Sardinia have isotopic and trace element signatures very close to the rocks of the Sicily Province. Plio-Quatemary volcanism in Sardinia overlies Oligo-cene-Miocene arc-type tholeiitic to calc-alkaline volcanism. 

Fig. 10.4. Sr-Nd-Pb-Hf-He isotope diagrams for Italian Plio-Quatemary mafic rocks (MgO > 4 wt %) and for the main worldwide mantle compositions HIMU, DMM, EMI and EM2. Star represents the composition of European Astheno-spheric Reservoir.

Smooth trends of Sr-Nd-Pb-Hf-He isotopes connecting different mantle compositions (Fig. 10.4). These are suggested to derive from mixing among different mantle end-members (HIMU or FOZO, EMI and EM2), which occur worldwide and are believed to represent deep mantle plumes by several authors (e.g. Hofmann 1997) ... 

Wolf, G. H., and M. S. T. Bukowinski (1987). Theoretical study of the structural properties and equations of state of MgSiOj and CaSiOj perovskites implications for lower mantle composition. In High Pressure Research in Mineral Physics (M. Manghnani and Y. Syono, eds.) Tokyo Amer. Geophys. Union/Terra Pub. Co. 

Is the Upper Mantle Composition Representative of the Bulk Earth Mantle ... 

From Equations (2) to (4) and by using the solar abundance ratio for FetoM/Mgtotai. the hypothetical composition of the Earth s mantle is obtained as given in Table 1. The Earth s mantle composition derived from the analyses of actual upper mantle rocks, as described in the next section, is listed for comparison. 

In the following section we will derive the composition of the mantle of the Earth from the chemical analyses of upper mantle rocks. The resulting mantle composition will then be compared with the composition of chondritic meteorites. In order to avoid circular arguments, we will use as few assumptions based on the... 

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