Bimodal volcanism Bimodal volcanism Bimodal volcanism is the eruption of both mafic and felsic lavas from a single volcanic centre with little or no lavas of intermediate composition. This type of volcanism is normally associated with areas of extensional tectonics, particularly rifts. Most occurrences of bimodal volcanism are associated with thinning of the crust and the presence of such rocks in metamorphic sequences has been used to provide evidence for past rifting events. Most examples come from areas of active continental rifting such as the Basin and Range Province. Bimodal volcanism has also been described from areas of transtension, the early phases
Archean felsic volcanic rocks violent pyroclastic flows. Coarse breccia would be formed as a result. Submarine sediments would subsequently be deposited along the steep flank of the volcano. Submarine landslides would occur to form turbidites. Archean felsic volcanic rocks is important to deduce absolute age of the rock units in greenstone belts. Felsic eruptions are episodic so that the felsic volcanic layers are distinctive stratigraphic units. Also, felsic volcanic rocks are distributed vastly across long distances because of its extensive deposition. However, the rock sequences of greenstone belts are commonly disputed by later deformation, such as regional folding or intrusion of granitoids. By identifying