Upper mantle

The outer shell of the earth, consisting of the upper mantle and the crust (Figure I4. lO), is formed of a number of rigid plates. These plates are 20 in number and are shown in Figure 14.1 I. Of these, six or seven are major plates, as can be seen in the map. The edges of these plates define their boundaries and the arrows indicate the direction of their movement. These plates contain the continents, oceans and mountains. They almost float on the partially molten rock and metal of the mantle. The outer shell, known as the lithosphere, is about 70 to 1,50 km thick. It has already moved great distances below the etirth s surface, ever since the earth was formed and is believed to be in slow and continuous motion all the time. The plates slide on the molten mantle and move about lO to 100 mm a year in the direction shown by the arrows. The movement of plates is believed to be the cause of continental drifts, the formation of ocean basins and mountains and also the consequent earthquakes and volcanic eruptions. 

The way to think of them all is as Si04 tetrahedra (or, in polymer terms, monomers) linked to each other either directly or via a metal ion (M) link. When silica is combined with metal oxides like MgO, CaO or AI2O3 such that the ratio MO/SiOj is 2/1 or greater, then the resulting silicate is made up of separated Si04 monomers (Fig. 16.4a) linked by the MO molecules. (Olivene, the dominant material in the Earth s upper mantle, is a silicate of this type.)... 

Figure 1.164. Distribution of Cenozoic basalts and active rift systems in the northeast China region. Arrows indicate the horizontal convective current in the upper mantle associated with the upwelling of the asthenosphere beneath the region. A Baikal Rift B Shanxi Graben C Tancheng-Lujiang Fault D Okinawa Trough (Tatsumi et al., 1990).

Barth MG, Foley SF, Horn 1 (2002) Partial melting in Archean subduction zones constraints from experimentally determined trace element partition coefficients between eclogitic minerals and tonahtic melts under upper mantle conditions. Precamb Res 113 323-340... 

Guo J, Green TH (1990) Experimental study of barium partitioning between phlogopite and sihcate liquid at upper-mantle pressure and temperature. Lithos 24 83-96 Harrison WJ, Wood BJ (1980) An experimental investigation of the partitioning of REE between garnet and liquid with reference to the role of defects. Contrib Mineral Petrol 72 145-155 Hart SR, Duim T (1993) Experimental cpx/melt partitioning of 24 trace elements. Contrib Mineral Petrol 113 1-8... 

Zindler A, Hart SR (1986) Chemical geodynamics. Aim Rev Earth Planet Sci 14 493-571 Zindler A, Standigel H, Batiza R (1984) Isotope and trace element geochemistry of young Pacific seamounts implications for the scale of upper mantle heterogeneity. Earth Planet Sci Lett 70 175-190... 

Blatter DL, Carmichael ISE (1998) Hornblende peridotite xenoliths from central Mexico reveal the highly oxidized nature of subarc upper mantle. Geology 26 1035-1038 Blundy J, Wood B (2003) Mineral-melt partitioning of uranium, thorium and their daughters. Rev Mineral Geochem 52 59-123... 

Kay RW (1980) Volcaiuc arc magmas implications of a melting-mixing model for element recycling in the crast-upper mantle system. J Geol 88 497-522... 

Kincaid C, Sacks IS (1997) Thermal and dynamic evolution of the upper mantle in subduction zones. J Geophys Res 102 12,295-12,315... 

Mysen BO, Kushiro I, Fuji T, (1978) Preliminary experimental data bearing on the mobility of H2O in crystalline upper mantle. Carnegie Inst Washington Yearbook 77 793-797 Navon O, Stolper E (1987) Geochemical consequences of melt percolation the upper mantle as a chromatographic colunm. J Geol 95 285-307... 

Fig. 1.6. The rock cycle. Rocks are weathered to form sediment, which is then buried. After deep burial, the rocks undergo metamorphosis or melting, or both. Later they are deformed and uplifted into mountain chains, only to be weathered again and recycled. Some injection of rock from the upper mantle is irreversible, that is, non-cyclic. (Adapted from M.J. Pidwimy, www.geog.ouc.bc.ca/phys.geog/)...

Eaton, D.W. Hope, J. 2003. Structure of the crust and upper mantle of the Great Slave Lake shear zone, northwestern Canada, from teleseismic analysis and gravity modelling. Canadian Journal of Earth Sciences, 40, 1203-1218. 

Olivine is the principal mineral (in terms of mass) of the earth s upper mantle where it is present as a combination of the two main components forsterite (85-95 mol.%) and fayalite (5-15 mol.%). In the earth mantle the increase in seismic velocity with depth is believed to be due to the presence of denser modifications of common minerals. 

Elderfleld H, Wheat CG, Mottl MJ, Monnin C, Spiro B (1999) Fluid and geochemical transport through ocean crust a transect across the eastern flank of the Juan de Fuca Ridge. Earth Planet Sci Lett 172 151-165 Elliott T, Thomas A, Jeffcoate AB, Niu Y (2003) Li isotope composition of the upper mantle. EOS Trans, Am Geophys Union 84 1608... 

Edwards R, Sedwick PN, Morgan V, Boutron CF, Hong S (1998) Iron in ice cores from Law Dome, east Antarctica implications for past deposition of aerosol iron. Ann Glaciol 27 365-370 Filer JM (2001) Oxygen isotope variations of basaltic lavas and upper mantle rocks. Rev Mineral Geochem 43 319-364... 

The contribution of petroleum of abiotic origin to the natural deposits is a topic of enormous importance and actuality. The geologic conditions of the Earth s upper mantle can be easily reproduced by using the diamond anvil cell in combination with different heating methods. The first experimental study of an abiotic hydrocarbons synthesis was performed by Kenney et al. [471]. The... 

The pre-human natural rate at which rivers were carrying secondary minerals into the ocean was 1.4 x lO g/y. Assuming that these solids have an average settled density of 1.6g/cm, this input would have filled the ocean basins (volmne= 1.37 x 10 cm from Figure 2.1) within 157 million years. This has not happened because the sediments are recycled through the crust and the upper mantle (Figure 1.2). 

Table 21.5 Masses (in grams) of the Five Major Volatiles in the Upper Mantle, Crust, and Surface Reservoirs. ... 

Species Upper Mantle Oceanic Continental Crust Crust Earth Surface Sediments Ocean Atmosphere ... 

Crustal-ocean-atmosphere factory The conceptual model that describes the material flows between the crust, ocean, atmosphere, and upper mantle. 

Lithosphere The outer, solid portion of Earth, including the crust and upper mantle. 

The variety of symmetries in the garnet structure (coordinations 4, 6, and 8) allows considerable compositional range. Table 5.16 lists the elements commonly present in positions X, X and Z. The diadochy of Al, Ti" ", and Fe in the tetrahedral site has been confirmed by Mossbauer spectroscopy on natural Fe-Ti-bearing garnets (Schwartz and Burns, 1978), and the presence of phosphorus in these sites, observed in upper mantle garnet, is attributable, according to Bishop et al. (1976), to coupled substitutions of the type... 

Because of the importance of garnet in upper-mantle parageneses, the compressibility of this phase has been the subject of many experimental studies. Ha-zen and Finger (1978), studying the compressibility of pyrope, observed that the... 

Samples 6 and 7 in table 5.32 are from the Zabargad peridotite (Red Sea) and are representative of the chemistry of upper mantle pyroxenes (Bonatti et al., 1986). The absence of Fe203 in these samples is due to the fact that microprobe analyses do not discriminate the oxidation state of iron, which is thus always expressed as FeO. It must be noted here that the observed stoichiometry (based on four oxygen ions) is quite consistent with the theoretical formula and that no Fe is required to balance the negative charges of oxygen. 

The importance of aqueous solutions in geochemistry can be appreciated if we recall that two-thirds of the surface of our planet is covered by water and that aqueous fluids of various salinities are determinant in the development of volcanic and metamorphic processes in the earth s upper mantle and crust. 

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