DISTRIBUTIONCOEFICIENTSOF TRACE ELEMENTS INCLINOPYROXENEANDPLAGIOCLASEOF BASALTIC SILLS FROM SERRA GERAL FORMATION, BRAZIL

Abstract

The use of an electron microprobe (EPMA) integrated with inductively coupled plasma mass spectrometer laser ablation (LA-ICP-MS) for the determination of major and trace elements in igneous minerals advances the knowledge of the distribution coefficients “D”in cores, intermediate portions and rims of crystals. Crystals of clinopyroxene and plagioclase of tholeiitic sills from the Serra Geral Formation, Paraná Basin, Brazil, display positive correlations between many major and trace elements. Plagioclase has core concentrations of SiO2 and Na2O wt.% which increase to the rim and Al2O3 and CaO wt.% decreasing from the core to the rim, corroborated by similar variations of distribution coefficients of Sr and Eu as a result of substitution of these compatible elements for Na in the structure of plagioclase. Clinopyroxene has the decreases in MgO, Al2O3 and CaO wt.% core to the rim and decreased D of Ni, Zn and V, and to increased concentration of FeOtotal wt.% core to the rim related increase in D of Sc, Y andHREE. This investigation is innovative because it presents the study of distribution coefficients oftrace elements with spatial control of the analyses, taking into account the effect of inclusions, fractures and compositional zoning.