Ocean island basalt

Piton de la Fournaise erupting OIB in 2004

Ocean island basalts or OIBs are basaltic rocks found on many volcanic islands away from tectonic plate boundaries typically associated with hot spots. Islands hosting ocean island basalts always lie above the oceanic crust and are not limited to volcanic islands but occur also on volcanoes of any size under the sea. The chemical composition of these basalts can vary from tholeiite to alkali basalt within the same island group, but is never calc-alkaline. During the shield volcano stage of many hotspot islands, tholeiitic OIBs build up most of the volcano's structure. Following the post-erosional stage this is usually accompanied by violent eruptions of alkali basalt and other more evolved volcanic rocks with high alkali content.

Types of basalts

Basalts by tectonic setting	Flood basalt Mid-ocean ridge basalt Ocean island basalt Volcanic arc basalt

Basalts by form and flow	Columnar basalt Pillow basalt Aa lava Pahoehoe lava

Basalts by chemistry	Tholeiitic basalt Calc-alkaline basalt Alkali basalt Trachybasalt Hawaiite Mugearite Picrite

Important minerals	Olivine Pyroxene Plagioclase Amphibole Magnetite Ilmenite Quartz Cristobalite Trydimite

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