Occurrence of Th, U, Y, Zr, and REE-bearing accessory minerals in late-Variscan granitic rocks from the Sierra de Guadarrama (Spain).
Casillas, Ramon; Nagy, Géza; Pantos, Gyorgy; Brändle, Jοsé; Forizs, István
European Journal of Mineralogy Volume 7 Number 4 (1995), p. 989 - 1006
published: Aug 1, 1995
manuscript accepted: Mar 3, 1995
manuscript received: Sep 12, 1994
ArtNo. ESP147050704023, Price: 29.00 €
Abstract 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 mineralogical paragenetic sequences are found in each association. The occurrence of different minerals is controlled by the initial trace-element contents of the melt, the aluminous index, the Ca content and volatiles, as well as (F, P) contents, ƒO2 and the LREE/HREE, Th/REE, U/REE and U/Th ratios of the melts. The accessory mineral assemblages can be changed by post-magmatic hydrothermal processes. The differences between the accessory mineralogical paragenesis and the individual mineral compositions in the granitic rocks are discussed using these parameters, which play a key role in determining the crystallization of accessory REE, Th and U-bearing phases in the studied granitoids. The paper also discusses the geochemical behaviour of these elements during granite petrogenesis.