Mechanics of the formation of orthogonal sets of solution seams, and solution seams and veins and parallel solution seams and veins

Abstract

Commonly observed networks of pressure solution seams (PSSs) and PSSs and veins can be broken down to three basic assemblages: orthogonal PSS sets, orthogonal PSS/vein sets, and parallel PSS/vein sets. We investigate stress distributions around PSSs idealized as localized volume reduction structures (LVRSs) to identify the conditions for forming these three fundamental assemblages. Various geometries of LVRSs are taken into account, including elliptical LVRSs with smooth flanks, LVRSs with triangular and rectangular asperities on their flanks, and LVRSs with overall irregular geometries, such as columnar and conical shapes. The modeling results indicate that if the first PSS set has elliptical shapes with smooth flanks, the conditions for generating the fundamental assemblages listed above are highly restrictive, primarily due to relatively large average aspect ratios of PSSs as measured in the field, which indicate lower stresses around PSSs as they grow. However, both laboratory and field observations have shown that PSS surfaces are extremely rough. We find that PSSs with relatively rough flanks and PSSs with overall irregular trace geometry such as sutured and zig-zag or wiggly are much more favorable for generating the stresses for the formation of these fundamental structural assemblages. Based on a series of stress domain maps from our mechanical model, we evaluated the stress, strain, and geometric conditions for the formation of each of the three assemblages. It turns out that there are a wide variety of loading and geometric factors favoring the formation of a particular type of assemblage.