Shearing of a discontinuity may produce splay pressure solution seams in the compressive quadrants around the end region of the sheared fracture of a fault (Figure 1 and Figure 2), in contrast to splay joints forming in the extensional quadrants (Figure 1). Most aspects of splay pressure solution seams including the angle they make with the sheared discontinuity are conceptually similar to splay joints, so please refer to the sections on Splay Joints for analogy. Splay pressure solution seams commonly occur in materials that have a greater tendency to dissolve under pressure. However, it is quite common that both splay pressure solution seams and splay joints or veins may form around the same sheared discontinuities within the same lithology as shown by Figures 1 and 2.

Figure 1. Splay joints and veins and splay pressure solution seams associated with small strike-slip faults in limestone. From Rispoli (1981).

Figure 2. (a) and (b) Outcrop photographs of pressure solution seams (PSS), splay PSSs, and splay veins in limestone from Languedoc, France. From Petit and Mattauer (1995). (c) and (d) are annotated copies by us. In each case left-lateral faults (red lines) are quite clear. Splay PSS (turquoise lines) and nearly symmetric splay veins (white lines) show interesting distributions and orientations. Splay PSSs within the overlapping faults are closely-spaced and make higher angles to the faults. Dotted white lines are veins either formed along the PSSs or formed at right angle to the existing splay veins.

It is common to observe pressure solution seam geometric patterns which are similar to joint or crack branching geometries. Figure 3 and Figure 4 are two examples for such geometries. We will refer to these cases as apparent pressure solution seam branching because they can also be explained by transverse mergers of the neighboring seams through dissolution of material slabs between the neighboring seams.

Figure 3. Apparent branching of pressure solution seams in limestone. From Mardon (1988).

Figure 4. Apparent branching of pressure solution seams in detrital rocks. From Geiser and Sansone (1981).