The vocabulary of deformation in the rock cycle primarily includes terms describing how forces change rock shape, such as deformation itself, folding, faulting, and re-crystallisation.
Understanding Rock Deformation
Within the dynamic rock cycle, rocks are constantly subjected to immense forces from Earth's internal processes. These forces, often driven by tectonic plate movements, can cause rocks to change their shape and orientation, a process known as deformation.
According to the provided reference, deformation is defined as:
where forces acting on rocks change their shape through folding, faulting and re-crystallisation.
This definition highlights the key terms that constitute the core vocabulary of deformation in this geological context.
Key Vocabulary Terms
Let's break down the essential terms associated with rock deformation:
- Deformation: This is the overarching term for any process that changes the shape, size, or volume of a rock body. It is caused by stress (the force applied per unit area).
- Forces: The external pressures or stresses applied to the rocks. These can be compressional (squeezing), tensional (stretching), or shear (sliding past each other).
- Folding: When compressional forces are applied gradually, rocks that are relatively ductile (can bend without breaking) may deform by folding. This creates wave-like bends or curves in rock layers. Folds have specific features like anticlines (upward curves) and synclines (downward curves).
- Faulting: When stresses exceed the rock's strength, or if the rock is brittle, it will break and the pieces will move relative to each other. This process is called faulting, and the break itself is a fault. Faults can be categorized by the direction of movement (e.g., normal faults, reverse faults, strike-slip faults).
- Re-crystallisation: Often occurring under high pressure and temperature during processes like metamorphism, re-crystallisation involves the rearrangement of mineral grains within a rock. This changes the rock's texture and fabric, contributing to the overall deformation and potentially strengthening or weakening the rock structure. While technically a metamorphic process, it's intrinsically linked to deformation as stress can drive or influence it.
How These Terms Fit in the Rock Cycle
Deformation is a crucial stage in the rock cycle, bridging different rock types:
- Igneous, Sedimentary, and Metamorphic rocks can all undergo deformation.
- Folding and faulting are major processes that shape landscapes, creating mountains, valleys, and rift systems.
- Deformation, particularly under pressure and heat, can lead to metamorphism, transforming existing rocks into metamorphic rocks with new textures and mineralogy often influenced by the stress (e.g., foliation).
Understanding these vocabulary terms is essential for comprehending how rocks are shaped and transformed by Earth's powerful internal forces throughout the rock cycle.
Summary Table
| Term | Description | Related Process/Cause | Example Feature |
|---|---|---|---|
| Deformation | Change in rock shape/size/volume due to forces. | Stress, Tectonics | Bent layers, Broken rocks |
| Forces | External pressures (compression, tension, shear) applied to rocks. | Tectonic Plate Movement | --- |
| Folding | Rock layers bending under compressional stress. | Compression (ductile rock) | Anticlines, Synclines |
| Faulting | Rock breaking and moving along a fracture plane. | Stress (brittle rock) | Fault lines, Scarps |
| Re-crystallisation | Rearrangement/growth of mineral grains under stress and often heat/pressure. | Metamorphism, Stress | New textures (foliation) |
