Question

Why are some rock units folded and others of similar rock type faulted?

32. Why are some rock units folded and others of similar rock type faulted?

Answer 1

• The phenomenon of faulting and folding depends on material behavior.
• Material or rock behavior changes with respect to temperature and pressure.
• If some rock of composition "X" undergoes deformation on surface it will develops fault because at surface rock behaves as brittle material which can withstand certain amount of stress but when stress exceeds beyond rock limit to hold stress and rock will fracture and develops fault.
• if same rock of composition "X" undergoes deformation at deeper level in the earth crusts it will develops fold because at deeper level rock behaves as ductile material which on stress application withstand up to certain limit and when stress exceeds that limit it will develops fold.

Landscape Interactions (uplift is opposed by erosion, rates of each may vary with time) Brittle Upper Crust (rocks closer to the Earth's splaying faults closer to the surface surface are cool and under less confining pressure Harder materials will break, forming faults, whereas softer material may fold) Earthquakes occur along faults at any depth 8 to 11 Brittle-Ductile Transition Zone miles 250-400°C (strongest part of Earth's crust) Lower Crust (due to high heat and confining pressure, rocks deform like plastic and stretch rather than breaking)

   Fig:- Brittle-Ductile transition