On the arrangement of solid inclusions in fibrous veins and the role of the crack-seal mechanism

The arrangement of solid inclusions in veins was examined in three different rock types and tectonic settings. Common to all samples is a new type of sinusoidal inclusions, associated with inclusion bands oriented parallel to the vein wall and inclusion trails at high angle to the vein wall. Crosscutting relationships of inclusion bands and the sinusoidal inclusions imply that inclusion bands do not reflect individual crack-seal increments. In our veins, inclusion bands are not a sufficient criterion to infer the crack-seal mechanism. Further evidence for solid inclusions not formed by the classic crack-seal mechanism is given by inclusion bands in gypsum crystals grown in soft clay. During incorporation, solid inclusions can become folded or boudinaged, depending on their orientation with respect to the opening direction. The complex displacement field within the vein is recorded by curved crystal fibres, which track the opening direction. Based on the arrangement of solid inclusions within the vein we suggest that our veins grew continuously during syntectonic vein formation. Solid inclusions formed by a fluctuation of adhesion at the vein wall interface rather than by crack-sealing, and vein growth was at least partly driven by the force of crystallisation. (c) 2005 Elsevier Ltd. All rights reserved.