Bowen’s Reaction Series  Different minerals crystallize from magmas at different temperatures Melting CrystallizationHotCold

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 SiO 2, 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 rocks Incompletely 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

Magma Mixing

Fig. 7.21

Igneous Activity

Viscosity Controls Violent Nature of Volcanic Eruptions Fig. 6.4

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)

Magma Properites Composition Silica Content Viscosity Gas Content Tendency to form Pyroclastics Mafic Least (< 50%)LeastLeast (1-2%)Least Intermediate Intermediate (~60%) IntermediateIntermediate (3-4%) Intermediate Felsic Most (~70%)GreatestMost (4-6%)Greatest

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)

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