A Petrographic Classification Scheme of Metamorphic Rocks Based on Fabric-Components

In this paper, a classification scheme is proposed for the common metamorphic rocks. In this scheme, the fabric-components reflecting both the structure-texture and compositions of metamorphic rocks are used as the first-order index, and the texture, structure and mineral composition are sequentially used as the secondary-, third- and fourth-order indexes for classification of the five genetic types of orogenic-regional, contact thermal, fault-related dynamic, altered-metasomatic metamorphic and migmatitic rocks. When geological occurrence of rocks is clear, the genetic type can replace the corresponding fabric component and becomes the first-order index for classification with the same procedures. Most orogenic-regional and contact thermal metamorphic rocks share the same names and features due to having the same fabric-components. However, it would be easy to distinguish a regional rock from a contact one according to their mode of occurrence and other characteristic microstructures of some diagnostic minerals. The effect of this classification is better than the petrographic classification schemes available in the world.