Geochemistry of Coexisting Biotite and Muscovite of Portuguese Peraluminous Granitic Differentiation Series

Abstract

In nine Portugese peraluminous Hercynian granitic series of differentiation, Cr, V, Sc and Ba decrease, whereas Nb, Zn, Sn, Li, Rb and Cs increase in the sequence of micas crystallization. Commonly equilibrium was not attained for trace elements between coexisting primary biotite and muscovite. Correlations of Cr, V, Nb, Li, Rb and Cs were found for biotite-muscovite pairs. The same correlation has a different slope in distinct series due to distinct degree of fractional crystallization, but also to solid-liquid reequilibration during late-magmatic evolution, as suggested by regression lines, which do not generally pass through the origin. Most trace elements partition in favour of biotite, while Sn, Sc, Sr and Ba prefer muscovite. These micas probably crystallized simultaneously as suggested by intergrowths. The partition ratio for Cs is one series is similar to that found experimentally.