EarthStructure An Introduction to Structural Geology and Tectonics

13. Deformation, Metamorphism and Time - Essay

Unraveling the deformation history of a region can be like a detective story. Well, maybe solving how an area became deformed isn't quite as exciting as some of the stuff in the movies, but a mystery it is. Just like any sleuth you have many tools available in the modern forensic lab to solve the geologic 'crime'; in fact, many of these tools have only been developed during the last decade or so. It is impossible to be expert in all these methods (which range from physics to chemistry of materials), but a basic knowledge will help you to decide which may be useful for your particular problem.

In this chapter we look at some approaches, mainly from the fields of metamorphic petrology and isotope geochemistry, that are increasingly used in the study of deformed regions. We concentrate on medium- to high-grade metamorphic areas, which are representative of processes active in the deeper levels of the crust, to complement the emphasis on relatively shallow-level deformation in much of the book. In this chapter we will use a hypothetical area with hypothetical (= perfect?) rocks , with the purpose to show the complementary nature of these methods to 'traditional' structural analysis. As we go along, you will see that this chapter is far from comprehensive, so we call it an essay.