http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Localization of pressure solution and the formation of discrete solution seams
This dissertation comprises a two-part observational and theoretical investigation of localization of pressure solution leading to the formation and propagation of discrete solution seams. In the observational study, bed-normal tectonic solution seams in a bed of fine grained limestone from the Valley and Ridge province, central Pennsylvania, are examined at scales between 1:4 and about 1000:1. Several characteristics of seams are (1) crack-like and (2) scale-invariant. Seams of all lengths form an echelon arrays and branching arrays. Individual seams consist of a laminated main segment which tapers toward dispersing tip arrays of finer seams. Maximum thickness on the main seam and the size of tip arrays scale with total seam length. Seams forming tip arrays themselves terminate in tip arrays and the hierarchy persists down to the grain scale where all seams terminate as clay rims on calcite grain boundaries. At scales coarser than the grain size, all seams are composites which propagate by coalescence in their tip arrays. The en echelon arrangement of seams and tip-to-plane curvature observed for linked and separate seams are interpreted in terms of the mechanics of anticracks (Fletcher and Pollard, 1981). Scale-invariance is due to mechanical interaction between seams over the entire range of seam lengths (~ 1 m to ~ 10^-5 m) and implies that pressure solution is strongly localized on seams of all lengths. The grain scale mechanism of seam formation is inferred to consist in a reduction of the viscosity in pressure solution on calcite-clay grain contacts relative to calcite-calcite contacts. The theoretical study examines the role of diffusional mass transport in the early stages of localization of pressure solution about a wavy interface between stiff and soft rock masses. The results are used to interpret an example described by Ward and Beutner (1984) in which solution seams have formed in tectonically shortened sandstone underlying shale about the troughs of ripple marks on the intervening bedding surface. The analyses illustrate some general effects of coupling between diffusion and deformation which may apply to seam tips.