Grain coarsening and hydrothermal alteration in metacarbonates of the Damara Orogen, Namibia

Abstract

Grain coarsening is a process that occurs in a wide variety of rock types. The application of grain growth theory to natural geologic materials has its beginnings in the theoretical foundations of the metallurgical and material sciences. Two types of grain growth can be statistically defined: 1) normal grain growth describing a uniform grain structure and 2) abnormal grain growth, where some grains grow more rapidly in size at the expense of matrix grains, thus creating a bimodal grain size distribution. This study aims to understand the grain coarsening phenomenon in metacarbonate rocks, to determine the mechanisms involved and to elucidate the role of fluids (e.g. hydrothermal alteration). Metacarbonate units exhibiting coarsely crystalline fabrics, representing abnormal grain growth, and hydrothermal alteration have been investigated from two major geologic formations of the Damara Orogen (Namibia)...