Fig. 2
Outcrop-scale fault mirror characteristics of the Hebgen Lake Fault, optical photomicrographs, and Scanning Electron Microscopy (SEM) backscatter images of fault rocks cut perpendicularly to fault mirror (fm) across the three types of fault mirrors (carbonate, goethite and hematite). (A) Carbonate fault mirror (A1), carbonate with slickenlines (s). (B) Goethite fault mirror (A2), ochre botryoidal goethite (b), ochre goethite slickenlines (g) grading into reddish hematite slickenlines (h), and tension fractures (f). (C) Reddish hematite-rich (h) mirror A3 with slickenlines (s); note fault mirror undulations perpendicular to downslip direction. (D) HL001—across carbonate mirror, showing juxtaposed coarse (co) and fine (fi)-grained domains, with nanocalcite along the fault mirror and two sets of fractures (f and fʹ); (E) HL008—across the goethite mirror, showing carbonate clasts, banding and asymmetric sigmoidal microstructures indicative of local shear; (F) HL006 – across carbonate (Cal), goethite (Gth) and hematite (Hem) layers; also note showing the paucity of carbonate clasts in the hematite zone; (G) HL001—showing details of the nanocalcite zone along the carbonate fault mirror (fm); inset showing the uniform and equant nanocalcite grain size; (H) HL008—across a goethite-rich layer, showing a polycrystalline carbonate clast (cl), banding and shape preferred orientation (SPO) of carbonate and goethite grains; (I) HL006—across a A3 hematite-rich layer, showing shape preferred orientation (SPO) of carbonate, goethite and hematite grains. The mid gray tones are goethite (Z ~ 89) while the bright gray tones are hematite (Z ~ 160). The goethite clusters probably resulted from flocculation.
