Abstract
The interaction of pressure solution with extensional strain is the most important factor influencing boudinage and vein structures in a mesoscopically folded sequence of subgreenschist-grade carbonate rocks from the overturned limb of the Lebanon Valley fold nappe at Rheems, Pennsylvania. The formation of stylolites and slickolites in association with boudins and veins indicates that extreme bed-normal contraction is intimately connected with bed-parallel extension. A variety of boudin shapes in dolomitic beds, from rectilinear to pinch-and-swell and fish-mouth structures, are formed by a combination of cataclastic flow and heterogeneous pressure solution.
Many veins record catastrophic failure and collapse of wallrock prior to or during crystallization of the vein-fill. At the earliest stage of boudinage, veins in boudin necks are straight and perpendicular to bedding. With continued extension, they adopt a bow-tie form in cross section as a result of inward flow of the surrounding matrix and pressure solution of the fragment corners and vein margins. With continued stylolitization and separation of boudins, bow-tie veins are converted into transverse veins of extraordinary dimension.
Failure to recognize the role of pressure solution in the formation of boudinage structure may result in inaccurate estimates of extension, erroneous assumptions regarding volume change, and incorrect interpretations of the changes in stress regime with time.
