Microveins in limestones of the Oman Mountains : a structural study of the fundamental building blocks of a crack-seal-system

摘要

Crack seal is a ubiquitous process in the upper crust. It has been studied and know for a long time but it’s details are not well understood. In particular the individual events of crack seal have not been studied in great detail. In this work microveins are hypothesized to be the fundamental building blocks representing one crack-seal event and that they have a minimum opening aperture. In this study rocks from the Oman Mountains were sampled which contain a wide range of calcite veins in limestone and it was aimed to find rock samples which were devoid of veins. Many of these rock samples do not have macroscopic veins. In all these samples many microveins were found and based on a series of criteria to identify veins that belong to single crack-seal events they were selected and their properties were analyzed. The microveins typically are coarser in grain size than the surrounding matrix and based on the observed data the hypothesis that there is a minimum opening width of crack seal veins can not be rejected. The coarser grain fill is epitaxially grown inside the grain-boundary fractures in the matrix. It is proposed that these microveins represent the fundamental building blocks of crack seal and are the product of one crack seal event.