trace elements

trace elements - 1 The Use of Trace Elements in Igneous...

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1 The Use of Trace Elements in Igneous Petrology Introduction: Trace elements are those which occur in very low concentrations in common rocks (usually < 0.1 % by weight). Their concentrations are therefore commonly expressed in parts per million (ppm; 1 ppm = 10 -4 weight%). Unlike major elements, trace elements tend to concentrate in fewer minerals, and are therefore more useful in formulating models for magmatic differentiation, and in some cases, in predicting the source of a particular magma. Trace elements most commonly used for the interpretation of the petrogenesis of igneous rocks include: Ni, Cr, Sc, V, Rb, Ba, Sr, Zr, Y, Nb and the rare earth elements (La to Lu). Keep in mind that the concentration of trace elements will vary with the rock type; whereas Ni and Cr show higher concentrations in mafic and ultramafic rocks, Zr and Rb are more concentrated in acidic rocks. Accordingly, some major or minor elements as K and P, which occur in very low concentrations in basalts (approaching trace levels), are just as useful in petrogenetic interpretations as some trace elements (in the case of basalts only, . . of course!). The incorporation of a trace element in the crystal structure of one or more minerals depends largely on its charge and radius, but also on the electronegativity of this element, and crystal field effects. Accordingly, a trace element will either substitute for a major element in the structure of a crystallizing mineral, or remain in the liquid. Types of trace elements: In addition to this simple classification of trace elements into compatibles and incompatibles, trace elements are perhaps better classified on the basis of their geochemical characteristics (which will naturally influence whether the element becomes compatible or incompatible). 1) Large ion lithophile elements (LILE): These elements are characterized by large
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trace elements - 1 The Use of Trace Elements in Igneous...

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