Engineering geology
Cross-cutting fault_geology_eng

Principle of Cross-Cutting Relationships

Figure 1 shows layers of rock that have been offset by a fault, a fracture in rock along which displacement occurs. It is clear that the strata must be older than the fault that broke them. The principle of cross-cutting relationships states that geologic features that cut across rocks must form after the rocks they cut through. Igneous intrusions provide another example.

Figure 1 – Cross-cutting fault The rocks are older than the fault that displaced them.

The dikes shown in Figure 2 are tabular masses of igneous rock that cut through the surrounding rock. The magmatic heat from igneous intrusions often creates a narrow “baked” zone of contact metamorphism on the adjacent rock, also indicating that the intrusion occurred after the surrounding rocks were in place.

Figure 2 – Cross-cutting dikes This igneous intrusion is younger than the rocks that are intruded.

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