GG231 Chapter Notes - Chapter 5: Pyroclastic Rock, Mount Meager, Silicate Minerals
Document Summary
Magma (molten rock) reaches the surface at mid-ocean ridges and subduction zones and then erupts as lava. Ring of fire = 2/3s of all active volcanoes (pacific ocean) How magma forms: decompression: when the pressure exerted on hot rock within the asthenosphere is reduced (1200 degrees) Divergent plate boundaries, continental rifts, and hot spots: addition of volatiles (i. e. dissolved gas): lowers the melting temp of rocks by helping to break chemical bonds within silicate minerals. Volatiles are chemical compounds that exist in a gaseous state at earth"s surface and evaporate easily. Subduction zones: addition of heat: induce melting if the temp of the rocks exceeds the melting temp of silicate rocks at that depth. Melted silicate minerals and dissolved gases: oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, and potassium. Basalt (most common volcanic rock on earth) = 45-52% of silica. Andesite = 52-63% silica, not as common.
