Final answer:
Brittle deformation is favored under cooler temperatures because, at shallower depths where it is colder, rocks tend to fracture rather than bend.
Step-by-step explanation:
Brittle deformation would be favored over plastic deformation in cooler temperatures. When rocks are exposed to stress, they initially undergo elastic deformation, returning to their original shape upon release of the stress. However, once they reach the elastic limit, they will either deform in a ductile (plastic) or brittle manner. The type of deformation depends on several conditions, including temperature, type of rock, pressure, depth, and duration of the stress. At high confining pressures or deeper within the Earth where it's warmer, rocks tend to behave more plastically. Conversely, at shallow depths and under cooler temperatures, rocks are more likely to experience brittle deformation, leading to fractures and breaks rather than bending or folding.