The effect of titanite and other HFSE-rich mineral (Ti-bearing andradite, zircon, eudialyte) fractionation on the geochemical evolution of silicate melts

We present trace element data for HFSE-rich minerals (titanite, eudialyte,Ti-bearing andradite, zircon) from plutonic rocks of the Eocene Tamazeght complex, High Atlas Mountains, Morocco. In most lithologies significant amounts of titanite are present and as such, titanite fractionation played a major role in the evolution of the HFSE budget of the whole complex. By combining our data with published titanite-melt partition coefficients we explore the effects of titanite fractionation on the evolution of geochemical parameters (Zr/Hf, Nb/Ta. La/Lu and Th/U ratios) during differentiation of silicate melts in detail. Based upon this, we further discuss the genetic relationships between the various rock types present in the Tamazeght complex and show that the above-mentioned element ratios can potentially be useful for distinguishing geochemically distinct melt reservoirs within a given platonic rock suite. Zircon, eudialyte and Ti-bearing andradite are generally rare or are restricted to localized rock units. Despite their scarcity, each of them can have a significant effect upon the HFSE budget in their evolving magmas. Here, we derive first estimations of eudialyte-melt partition coefficients for REE. Application of these data to eudialyte-bearing rocks of the Ilimaussaq complex (South Greenland), and comparing the results to published estimations for the parental melts of these rocks yields consistent results and demonstrates the reliability of our estimations. (C) 2008 Elsevier B.V. All rights reserved.