Slickensides vs. Slickenfibres

Here are a couple images of a feature we've been seeing on fracture surfaces lately.  The striations on the photos below look like slickensides.

Slickensides are striations on rock, created by the friction between rocks when they slide past each other along a fault plane.  The slickensides shown here are probably not part of a major fault, but they may be part of small regions within a larger fault zone where rocks under stress slide against each other.  We have seen more than a handful of slickensides within the past few days, these two are the most photogenic.

It should be noted that these slickensides may be made up of secondary minerals rather than the original rock itself.  Such minerals are called slickenfibres, and they commonly form along fault surfaces in areas where the rocks slowly creep past each other along a fault, instead of sliding suddenly.  In these photographed examples the striated surfaces look and feel much different than the surrounding rock, so we might be seeing slickenfibres rather than slickensides.  Either way, they indicate at least a small amount of motion among fault surfaces within this borehole.

Drilling Update: We processed core to a depth of 1768 ft today.