Figure 4
Conceptual model of zebra texture formation in dolomite involving the development of compaction instabilities leading to focused recrystallization and subsequent grain growth affected by second-phase particle densities. An impurity-rich limestone (1) is dolomitized by an infiltrating fluid (2). This fluid-saturated dolomite (Do I) undergoes compaction during burial, and instabilities evolve as soon as the critical values of permeability and loading are reached (3). The small plot next to sketch number 3 indicates how the solution of equation 3 is related to the localisation of high-porosity and high-pressure channels. Recrystallization is then focused in equidistant channels (Do II) whereas the second-phase is washed out and accumulated between the channels (3.1). The subsequent grain growth is now focused in the areas of low impurity densities. The high pressure then leads to fracturing in the high-pressure channels of the compaction bands as the yield stress is successively lowered during grain coarsening (Hall-Petch relation 50,51). The highest pressures occur in the centre of the compaction instabilities leading to fracturing and subsequent dissolution along the median line of the coarse grained layers (3.2). The grain growth continues whereas the grains now elongate towards the central line where stress is depleted due to the fracturing (3.3). The resulting texture is periodically layered (4). If a mineralizing fluid percolates into this structure, the sulphide (Su) will precipitate along the vuggy median line (5).
