Melt-mineral-fluid interaction in pealkaline silicic intrusions in the Oslo Rift, Southeast Norway. II. High temperature fluid inclusions in the Eikeren-Skrim.

Abstract

The Eikeren-Skrim subvolcanic granite complex consists of mildly peralkaline rocks, most of which contain abundant miarolitic cavities. Optical microscope studies reveal that several generations of fluids and solids were trapped in rock-forming (magmatic) and miarolitic quartz. A fluid evolution history has been worked out, involving (1) magmatic, (2) submagmatic (i.e. sub-solidus fluids possessing hte chemical characteristics of the magmatic fluids) and (3)post-magmatic fluids. Combined energy dispersive analyses and laser Raman microprobe studies were used for the identification of daughter minerals. Primary magmatic inclusions comprise single mineral grains, grain clusters (\u00B1glass)(interpreted as crystallized samples of silicate melts), and high-salinity fluid inclusions, which are best described as hydrosaline melts. Optical estimates of phase ratios between vapour, liquid and identified solids in fluid inclusions show high concentrations of Cl, S, Na, k, Ca (and possibly Fe) in the magmatic and submagmatic fluids. Early post-magmatic fluids were mainly characterized by high Cl, Na and K contents, and represent a change in fluid regime from sulphur-rich and highly peralkaline to alkali chloride dominated. Post-magmatic fluids were gradually diluted through mixing with meteoric water.