A fluidization breccia in granite at Skaget, Svellingen, Frøya.

Abstract

The breccia consists of fragmented and comminuted host rock material and small amounts of hydrothermal quartz, epidote, laumontite, ?stilbite, calcite and montmorillonite. At least three brecciation and mineralization events have occured. The breccia is considered to have formed bu hydraulic fracturing by a mixed, high-pressure CO2-H2O fluid. Upon explosive venting to the surface, the fluid is thought to have fluidized and fragmented the fractured rock. The carbon dioxide of the fluid may have originated in the mantle, and could have ascended through the crust by hydraulic fracture propagation. It is suggested that the occurence within the same region of the Skaget Breccia, Tertiary olivine-nephelinite plugs, and scattered zeolite mineralization may possibly define a palaeo-geothermal province.