Transcript Igneous Rocks and Intrusive Igneous Activity

Bowen’s Reaction Series
Hot
Melting
minerals
crystallize from
magmas at
different
temperatures
Crystallization
 Different
Cold
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 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
Magma Mixing
Magma Mixing
Fig. 7.21
Igneous Activity
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)
Magma Properites
Composition Silica
Content
Mafic
Least (< 50%) Least
Intermediate Intermediate
(~60%)
Felsic
Viscosity
Most (~70%)
Gas Content Tendency to
form
Pyroclastics
Least (1-2%)
Least
Intermediate
Intermediate
(3-4%)
Intermediate
Greatest
Most (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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