The movement of tectonic plates is often thought of on a very large scale, but what actually happen to rocks at plate boundaries? In simple terms, rheology tells us how a rock will behave when a force is applied to it. Forces on rocks can come from a variety of places, such as the weight of overlying rock or the pulling apart of crust at divergent boundaries.
An understanding of rheology is crucial for understanding important concepts in geophysics, such as what happens during an earthquake, how mountains and faults are formed, and how rocks behave in the mantle. Rheology is an important concept in structural geology and can help geophysicist to make observations about what forces lead to the creation of a geologic structure, and how those forces may act over a regional scale.
FIGURE of a fold or other deformation structure
By the end of this chapter, you should be comfortable with the various forces that act on a rock, the different ways a rock can responds to those forces, and what geologic structures are produced by a rock's response to stress. First, we will examine stress and strain in a 1-D context and some of the plate boundaries the various types of stress occur in. Second, we will look at various types of deformation (elastic, viscous, and plastic), the timescales deformation occurs on, and the effect this has on geologic structures. Finally, we will cover why rocks fail (brittlely, ductility, or plastically) and what happens when they do.