|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).