Fractionation metal-silicate

With the exception of metal-silicate equilibrium, (which is relevant to mantle-core segregation), igneous processes seem to be inefficient at fractionating Cu and Zn isotopes. 

This indicates that the volatility fractionations affecting silicates and metal occurred under different conditions. Since chondrites are sedimentary rocks consisting largely of chondrules that were melted and rapidly cooled in zero gravity, the volatility depletions in bulk chondrites almost certainly arose in the nebula, likely during the thermal processing events that melted chondrules (see Chapters 7 and 8). 

Another approach for overcoming the problems posed by conventional cracking catalysts has been disclosed recently by Reverse et al. [101]. In this case, direct cracking is performed by using as catalyst a molten bed of pure metal or a metal mixture (mainly lead, zinc, tin) at a temperature of 460-550°C wherein the waste polymer is loaded inside the reactor at a certain depth. The authors point out that the products are indeed a result of the combination of both thermal and catalytic cracking. The catalyst composition may also include some acidic component such as metal silicates, metal carbonates and their mixtures. The process can be applied to pure and mixed polymers (PE, PET, PP, PVC), as well as to the plastic fraction of municipal solid wastes. 

Lewis J. S. (1972) Metal/silicate fractionation in the solar system. Earth Planet. Set Lett. 15, 286-290. 

Sasaki S. and Nakazawa K. (1986) Metal-silicate fractionation in the growing Earth energy source for the terrestrial magma ocean. J. Geophys. Res. 91, B9231-B9238. 

SNC meteorites (Harper et al., 1995 Borg et al., 1997). This isotopic anomaly requires early differentiation of mantle and crust. Because hafnium and mngsten fractionated into silicate and metal, respectively, the short-lived Hf- W system can be used to determine that martian core formation occurred within —13 milhon years of the planet s accretion (Kleine et al., 2002 Yin et al., 2002). Correlation between Nd and isotope anomalies, as well as the initial Os/ Os ratios for martian meteorites (Brandon et al., 2000), indicate synchronous differentiation of core, mantle, and cmst (Figure 14). On Earth, core formation took substantially longer, convection has stirred the mantle sufficiently to erase any evidence of early isotopic heterogeneity, and cmst formation continues throughout geologic history. 

RSEs comprise two groups of metals the HSEs—osmium, rhenium, ruthenium, iridium, platinum, and rhodium with metal/silicate partition coefficients >10" —and the two moderately siderophile elements—molybdenum and tungsten (Table 2). As the major fractions of these elements are in the core of the Earth, it is not possible to establish independently whether the iDulk Earth has chondritic ratios of RLE to RSE, i.e., whether ratios such as Ir/Sc or W/Hf are chondritic in the bulk Earth. Support for the similar behavior of RLE and RSE in chondritic meteorites is provided by Figure 9. The ratio of the RSE, Ir, to the nonrefractory siderophile element, Au, is plotted against the ratio of the RLE, Al, to the nonrefractory lithophile element, Si. Figure 9 demonstrates that RLEs and RSEs are correlated... 

Meteorites, as rocks produced in a solar nebula, have formed through a range of processes, some of which are quite different from those observed on Earth. Thus while igneous differentiation processes and metamorphism are recognized in meteorites, there also other processes operating which are not observed in terrestrial rocks. These include evaporation and condensation events related to melting in a gas-rich medium (as discussed in Section 2.3.2), impacting events, and metal-silicate fractionation. 

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