Fractionation igneous

The fractionated igneous and sedimentary rocks in Figure 20 have Rb/Sr and Eu/Sr ratios that are much higher than those in current estimates for the upper continental crust. The latter can be constrained by the strontium isotope ratios of continental run-off (—0.712), and its model neodymium age (—1.8 Ga). According to this method, a minimum time-integrated upper crustal Rb/Sr ratio of 0.14 is indicated. 

Soil water flow is decidedly episodic. During dry times the water solutions in the soil are probably fairly concentrated and not very reactive. Time-averaged reaction rates should be roughly proportional to the fraction of time reacting minerals are in contact with thermodynamically imdersaturated (and reactive) water. In a study of the relationship between denudation rate and runoff for rivers draining igneous and metamorphic rock in Kenya, Dunne (1978) obtains the relationship of (denudation rate in tons/km per year) = 0.28 (runoff in mm/ year)°. ... 

Such alpha-recoil plays a fundamental role in fractionating the nuclides from one another in the low-temperature environment. During igneous processes, on the other hand, alpha recoil is probably not important in the generation of disequilibria ( °Th, Ra, and Pa). Beattie (1993) pointed out that the time scale of annealing of alpha decay damage at high temperatures was much shorter than the time scale of decay of these nuclides. 

Van Orman J, Saal A, Bourdon B, Hauri E (2002a) A new model for U-series isotope fractionation during igneous proeesses with finite diffusion and multiple solid phases. EOS Trans, Am Geophys Union 83(47) Fall Meet Suppl Abstract V71C-02... 

Allegre, C. J., Treuil, M Minster, J.-F., Minster, B. Albarede, F. (1977). Sytematic use of trace element in igneous process. Part I fractional crystallization processes in volcanic suites. Contrih. Mineral. Petrol., 60, 57-75. 

Taylor, H. P., Jr. Sheppard, S. M. F. (1986). Igneous rocks I. Processes of isotopic fractionation and isotope systematics. In Rev. Mineral. 16 Stable Isotopes in High Temperature Geological Processes, ed. J. W. Valley, H. P. Taylor Jr. J. R. O Neil, pp. 227-71. Washington Mineral. Soc. Amer. 

INTERNAL-PLANETARY SYSTEMS Mass fractionation in igneous systems... 

With the exception of these fractionation pathways, studies of igneous systems chiefly focus on the potential of Li isotopes as geochemical tracers fingerprinting the cycling of Li derived from specific (low-temperature) sources through the solid Earth. The sections below deal with observations of Li isotopes in high-temperature systems, and the mechanisms for low-temperature fractionation processes are discussed after, imder the heading, Planetary surface systems. ... 

Figure 17. Comparison of 5 Fe values for bulk igneous rocks (O), suspended river loads ( ) and individual minerals from volcanic rocks (right panel). Left panel shows the fraction of Fe that exists as oxides (data for igneous rocks arbitrarily plotted as 0.02). Right panel shows 6 Fe values for coexisting magnetite ( ), olivine (+), hornblende (O), and biotite (O) in four volcanic rocks. Data from Canfield (1997), Beard et al. (2003a), and Beard and Johnson (2004).

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. 

Archean and Himalayan (Tertiary). The coherence of these samples suggests that Mo isotope fractionation during igneous processing is small compared to current analytical limits (Siebert et al. 2003). 

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