Melt-mineral-fluid interaction in peralkaline silicic intrusions in the Oslo Rift, Southeast Norway. I. Distribution of elements in the Eikeren ekerite.

Abstract

The behaviour of different elements during formation of the Eikeren ekerite (alkali granite) has been studied with the help of an element correlation matrix. The compositional relations are the result of partitioning of elements between a F-rich silicic melt, crystallizing phases (feldspar, sodic amphibole, acmitic pyroxene, sphene, apatite and ilmenite) and a Cl-F-rich fluid phase. The behaviour of the trace and minor elements Ba, Eu, Sm, Ca (and Sc) was governed by melt\/crystal partitioning, and the melt\/vapour distribution coefficients (D) were high. Also Cr, U and Rb were concentrated in the melt (D>1). Elements such as Zr, Hf, intermediate to hevay REE, Ta and Th were apparently stabilized in the fluid in F-complexes. D was slightly above 1 for Zr, Nb, and REE. Ni, Zn and Co appear to have the lowest D-values (<1) in the system. Element transport by the fluid phase continued at subsolidus temperatures.