Photo: Prof.  Mário Cachão.

Dyke is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.

Intrusion of basaltic and trachytic dykes in volcanic rocks from Middle Miocene (Porto Santo island, Portugal).

Intrusão de diques basálticos e traquíticos em rochas vulcânicas do Miocénico Médio (ilha de Porto Santo, Portugal).
 
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