OCCURRENCE OF TH-BEARING, U-BEARING, Y-BEARING, ZR-BEARING, AND REE-BEARING ACCESSORY MINERALS IN LATE-VARISCAN GRANITIC-ROCKS FROM THE SIERRA DE-GUADARRAMA (SPAIN)

The paragenesis of Y, Th, U, Zr and REE accessory minerals (monazite, apatite etc.) in four different late-Variscan granitic associations of the Sierra de Guadarrama are discussed. Characteristic accessory mine ralogical paragenetic sequences are found in each association. The occ urrence of different minerals is controlled by the initial trace-eleme nt contents of the melt, the aluminous index, the Ca content and volat iles, as well as (F, P) contents, fO(2) and the LREE/HREE, Th/REE, U/R EE and U/Th ratios of the melts. The accessory mineral assemblages can be changed by post-magmatic hydrothermal processes. The differences b etween the accessory mineralogical paragenesis and the individual mine ral compositions in the granitic rocks are discussed using these param eters, which play a key role in determining the crystallization of acc essory REE, Th and U-bearing phases in the studied granitoids. The pap er also discusses the geochemical behaviour of these elements during g ranite petrogenesis.