微量元素地球化学课件（中国地质大学） 2微量元素的地球化学分类.pptVIP

* * * * Members of Group IIIA of the Periodic Table La - to Lutetium (Z = 57 ? 71) All have very similar chemical and physical properties - behave as a coherent series All have a 3+ oxidation state Ionic radius decreases steadily with increasing atomic number (lanthanide contraction) * * * * * * * * * * Chondrite normalization: Normalize to chondrite meteorites to: 1) avoid Oddo-Harkins (even Z more common) 2) think chondrite = primitive earth, so can compare to initial distribution * * * * * * * * * * * * * * * Since the concentration of a trace element (unlike major elements--note Fo-Fa) in any phase is proportional to the coverall concentration of that element, a more convenient constant is commonly used for them. It is commonly referred to as D for TEs (although some authors still use KD) and is called a partition coefficient: ? D = C(S)/C(L) ? Where CS and CL are the concentration of a trace element in the solid and liquid phases, respectively (the wt% or ppm value directly). As long as the element occurs in very dilute concentrations, D is a constant. * * * * * * * * * * * * * * * Note that 85% Ol + Opx, but 5% Grt raises bulk D to 0.366 * * * * * * A bit ambiguous, since many variables (country rx, %PM, %FX) ? Need immobile TEs, so met has no effect. Ti, Zr, Y, Hf ? apply to basic volcs to eliminate high %FX * * * * Not exact, since D varies with the composition of mins melt * * Depends on the minerals involved! Sr - melt as ol px separate - plag (Ca) not melt if plag is phenocryst phase Commonly standardized to mantle compositions (olivine, pyroxenes, and perhaps garnet) Thus the major elements Mg and Fe would usually be referred to as compatible, while K and Na as incompatible * Depends on the minerals involved! Sr - melt as ol px separate - plag (Ca) not melt if plag is phenocryst phase Commonly standardized to mantle compositions (olivine, pyroxenes, and perhaps garnet) Thus the major elements Mg and Fe would usually be refe