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Hot. Melting. Crystallization. Cold. Bowen’s Reaction Series . Different minerals crystallize from magmas at different temperatures. Daily Question .
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Hot Melting Crystallization Cold Bowen’s Reaction Series • Different minerals crystallize from magmas at different temperatures
Daily Question • The core (center) of the Black Hills of South Dakota is composed of granite. The Columbia River Plateau of Washington and Oregon is composed of basalt. Using a Venn Diagram, compare and contrast the two locations highlighting the composition of the rocks, the texture of the rock, and the location (depth) where the rocks formed.
Magmatic Differentiation • Formation of more than one magma from a single parent magma
Magmatic Differentiation • Crystal Settling: crystallized minerals have a density greater than the magma and settle to the bottom due to gravity • Because Fe and Mg are first removed, melt becomes rich in SiO2, Na, and K • Marbles analogy
Magmatic Differentiation • Assimilation: magma reacts with the “country rock” which is adjacent to the magma chamber • Magma composition is altered according to the composition of the assimilated country rock • Inclusions are rocksIncompletely melted chunks of country rock
Magmatic Differentiation • Magma Mixing: Magmas of different compositions are mixed together • Resulting magma is of a composition intermediate between the parents
Fig. 6.4 Viscosity Controls Violent Nature of Volcanic Eruptions
Controls of Viscosity • Magma composition – silica content • High silica content – high viscosity • Low silica content – low viscosity • Temperature • High temperature – low viscosity • Low temperature – high viscosity • Dissolved gas • Low viscosity – gases escape • High viscosity – gases cannot escape (pressure builds up)
Materials Extruded During an Eruption • Lava flows – low silica content of basalt lava allows it to flow up to 30 km/hour, typically 10 to 300 m/hour • Gases – reduction of confining pressure allows gases to escape • 70% water vapor • 15% carbon dioxide • 5% nitrogen • 5% sulfur dioxide • Trace amounts of chlorine, hydrogen, and argon • Pyroclastic material – welded ash, dust, and lava
Nuée ardente • Glowing avalanche of ash, steam, gas, and pyroclastics • Travels at speeds of 200 km/ hr (125 mph)