Bimodal volcanism of back-arc basin formation and in the products of both continental and oceanic hotspots (e.g. Yellowstone and the Canary Islands). Bimodal volcanism is normally explained as a result of partial melting of the crust, creating granitic magmas, during the emplacement of large volumes of relatively hot basaltic magma from a mantle source. The two magma types then form separate magma chambers giving rise to periodic eruption of both types of lava. 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
Archean felsic volcanic rocks are distributed only in the preserved Archean greenstone belts, where deformed sequences of volcanic-sedimentary rocks are common. Felsic volcanic rocks are rare in the early Earth and only contribute to less 20% of rocks in the Archean greenstone belts worldwide. Nonetheless, mafic volcanic rocks (such as basalt and komatiite, silicate content <52%) occupy about 50% in the greenstone belts. Thus, felsic volcanic rocks are rare members in the Archean terranes. Archean felsic volcanic activities commonly occur in submarine environments. The composition of Archean felsic volcanic rocks are equivalent to a spectrum between dacite and rhyolite. They can be distinguished by