bowen’s reaction series different minerals crystallize from magmas at different temperatures...
TRANSCRIPT
Bowen’s Reaction SeriesBowen’s Reaction Series
Different minerals crystallize from magmas at different temperatures
Melting
Melting
Crystallization
Crystallization
HotHot
ColdCold
Daily QuestionDaily 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 DifferentiationMagmatic Differentiation Formation of more than one magma from a single
parent magma
Magmatic DifferentiationMagmatic 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 DifferentiationMagmatic Differentiation Assimilation: magma reacts with the “country rock” which
is adjacent to the magma chamberMagma composition is altered according to the composition of the assimilated country rockInclusions are rocksIncompletely melted chunks of country rock
Magmatic DifferentiationMagmatic Differentiation Magma Mixing: Magmas of different
compositions are mixed togetherResulting magma is of a composition intermediate between the parents
Viscosity Controls Violent Nature of Volcanic Eruptions
Viscosity Controls Violent Nature of Volcanic Eruptions
Fig. 6.4
Controls of ViscosityControls of Viscosity Magma composition – silica content
High silica content – high viscosityLow silica content – low viscosity
TemperatureHigh temperature – low viscosityLow temperature – high viscosity
Dissolved gasLow viscosity – gases escapeHigh viscosity – gases cannot escape (pressure builds up)
Magma ProperitesMagma ProperitesCompositionComposition Silica Silica
ContentContentViscosityViscosity Gas ContentGas Content Tendency to Tendency to
form form PyroclasticsPyroclastics
Mafic Least (< 50%) Least Least (1-2%) Least
Intermediate Intermediate (~60%)
Intermediate Intermediate (3-4%)
Intermediate
Felsic Most (~70%) Greatest Most (4-6%) Greatest
Materials Extruded During an EruptionMaterials 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 vapor15% carbon dioxide5% nitrogen5% sulfur dioxideTrace amounts of chlorine, hydrogen, and argon
Pyroclastic material – welded ash, dust, and lava
Nuée ardenteNuée ardente Glowing
avalanche of ash, steam, gas, and pyroclastics
Travels at speeds of 200 km/ hr (125 mph)