I would fully support Dugald's statement. Can anybody tell me how to differentiate between hornblende-hornfels facies and amphibolite facies when looking at a hand specimen? What defines the upper pressure limit of the "shallow contact metamorphic facies"? If we can use these facies terms only in a field-related sense, where does "pure" contact metamorphism end and where does low-pressure, regional-style thermal metamorphism start?
The idea that aureoles generally contain hornfelses is clearly wrong. Do we then explain to students that a foliated hornblende-plagioclase rock cannot be called a hornblende-hornfels, but rather an amphibolite that originated in the hornblende-hornfels facies? What is lost if we abandon these contact-metamorphic facies terms?
School of Geological & Computer Sciences
University of Natal