-High resolution Rb_Sr and Pb isotope geochemistry: applications in archeometry and geological research

-The determination of the origin of rocks is largely based on geochemical studies. The genesis can be specified from the main and trace element composition and from the isotopic signature of minerals and rocks. Initially, total rock analysis were used to unravel the origin, but the necessity of in situ analysis, during which individual grains or zones in minerals are measured, is generally accepted. Geochemical variations result from changes in formation conditions, such as varying compositions of magma, changes in the crystallisation temperature, pressure and redox conditions ... In palaeoenvironmental studies, geochemical variations are explained by changes in the temperature and/or the chemical composition of sea water. Although interesting conclusions regarding the genesis of minerals and rocks can be drawn from the main and trace element composition, isotope signatures are essential to obtain a profound insight in the formation conditions. Multi-collector inductively coupled plasma - mass spectrometry (MC-ICPMS) is a new and extremely powerful technique to determine isotope ratios. In situ analyses are possible by coupling a laser ablation unit to the MC-ICPMS. With exception of the light elements H, C, N and O and the noble elements, MC-ICPMS can be used for the isotopic analyses of almost all elements. The research themes of the Geology research group at the Vrije Universiteit Brussels (VUB) especially focuses on palaeoenvironmental reconstructions based on isotope geochemistry (stable isotopes, Hellings et al., 2000, Felder et al., 2003, but also Sr and Pb isotope ratios, Verheyden et al., 2000, Lazareth et al., 2000). The VUB has three stable isotope mass spectrometers, but until now Sr and Pb isotope measurements had to be carried out abroad. The recent award of a grant (Financing of 'heavy equipment' -call 2004) for the purchase of an LA-MC-ICPMS in Flanders, offers enormous perspectives for the study of small variations in the isotopic composition in geological processes, applications that require large amounts of analyses or situ analysis of mineral grains.