Final answer:
An anticline is formed from plastic strain due to compressional stress and results in older rocks at the center with younger rocks outside. In contrast, a syncline features the youngest rocks at the center..
Step-by-step explanation:
An anticline is the result of plastic strain associated with compressional stress in geologic structures. This type of fold occurs when the Earth's crust experiences compression, causing the oldest rocks to buckle upwards at the center with younger rocks on the outside. Anticlines are typically associated with convergent plate boundaries, where two plates are moving towards each other, leading to folding of the rocks. However, in a setting such as a divergent boundary or as a result of rifting where tensional stress prevails, the presence of anticlines, as well as synclines which have the youngest rocks in the center, suggests additional forces at work.
Strain refers to the deformation of materials such as rocks in response to stress. When a material is subjected to increasing stress, it undergoes elastic deformation up to a certain point known as the elastic limit. Beyond this point, the material undergoes plastic deformation, where it bends and folds, as is the case with anticlines and synclines, without returning to its original shape once the stress is removed. Synclines are characterized by a concave shape, with the youngest rocks in the middle and the oldest rocks on the exterior.