Internal Fabric of Giant Domes in the Mesoarchean Steep Rock Carbonate Platform, Superior Province, Canada
Drivers for accumulation of Archean seafloor carbonate were mostly very different than those operating today. Alternating crystal fan fabric and cuspate fenestral fabric forming meter-scale giant domes is rare in Archean carbonate platforms and limited to this time period. Their genesis is poorly understood. The oldest known examples are in the 2.8Ga Steep Rock Group of northwestern Ontario, Canada, where 200 to 500m of carbonate was deposited on a semi-restricted platform. Here the elongate domes are composed of cm to dm alternations of calcite crystal fans and microbialite, commonly separated by thin, dark ferroan dolomite and quartz replaced areas, which have herein been referred to as alteration surfaces. The cuspate fenestral fabric is formed of draping, mat-like laminae, vertically oriented support structures, and cement-filled voids. The concave-up mat-like laminae attach to the support structures, which, similar to the alteration surfaces, are primarily composed of ferroan dolomite and quartz. One...