Fuji Kao Mayan
Bali
Pinatubo
Cinder Cones Stratovolcanoes Fountains: shields and plateaus Domes Gas Content Viscosity
Classification of Igneous Rocks Figure 2-5. Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1,
Wt. % oxides Wt. % SiO FeO, MgO, CaO Na 2 O, K 2 O H2OH2O
Water content (wt. %) Composition Basalt Andesite Rhyolite Water Saturation Exsolution of a vapor of a magma
Fractional Crystallization Basalt Andesite Rhyolite low H 2 O Explosive volcanism 50 % SiO 2 75% SiO 2 ? Water content of a rhyolitic magma ????
Mt. St. Helens
Granites
Origin of Andesites Fractional crystallization of basaltic magma Contamination of basaltic magma by continental crust Both of the above Partial melting of “special (wet ?) manlte”
Origin of Granite/ Rhyolite Fractional crystallization of basaltic magma ( volume problem for some areas) Partial melting of continental crust