iv. igneous rocks minerals crystallized from melts
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IV. Igneous Rocks Minerals Crystallized from Melts. 1. The Rock Cycle 2. Formation of Igneous Rocks (and Bowen’s Reaction Series) 3. Classification of Igneous Rocks 4. Igneous Rocks and Plate Tectonics. Geological Materials Transformation Processes. The Rock Cycle. Igneous Rock - PowerPoint PPT PresentationTRANSCRIPT
IV. Igneous RocksMinerals Crystallized from Melts
1. The Rock Cycle
2. Formation of Igneous Rocks (and
Bowen’s Reaction Series)
3. Classification of Igneous Rocks
4. Igneous Rocks and Plate Tectonics
The Rock Cycle
Igneous Rock
Solidification
Magma
Partial Melting
Mantle Rock Fig 3.1
Geological Materials
Transformation Processes
Fig 1.15
Fig. 2.9 From bottom to
top Increasing
Fe/Mg/Ca Decreasing silica Increasing density Darker minerals Decreasing
Silica
29% 14%
<20% 20%
<3% 23%
<2% 25%
(0) 33% (0) 23% (0) 15%*
% of Tot. # of atoms Fe/Mg: Silicon:
IncreasingFe/Mg/Ca Quartz
K and Na Feldspar
Ca Feldspar
Systematic SilicateMineralogy
IncreasingDensity
Olivine
PyroxeneGroup
AmphiboleGroup
MicaGroup
Fig. 2.9 From bottom to
top Increasing
Fe/Mg/Ca Decreasing silica Increasing density Darker minerals
29% 14%
<20% 20%
<3% 23%
<2% 25%
(0) 33% (0) 23% (0) 15%*
% of Tot. # of atoms Fe/Mg: Silicon:
Quartz
K and Na Feldspar
Ca Feldspar
Melting Points ofSilicate Minerals
IncreasingMelting
Temperature
Olivine
PyroxeneGroup
AmphiboleGroup
MicaGroup
Felsic>65% silica
Intermediate53-65%
Mafic45-52%
<700oC
>1000oC
Melting of Granite (Quartz, Na Plagioclase, Biotite)
SilicicMelt
~600oC ~700o ~800o
Quartz Melts Na-Feldspar First Begins to melt
~900o ~1000o
Biotite begins Magma is enriched to melt in Si, Na, Al (K)
Partial Melting and MagmaE.g., Progressive Silica Enrichment Results in Silicic Magma Fig. 3.1, 3.12, 3.13
Enriched: O, Si, Al, Na, K, Depleted: Ca, Fe, Mg
Gasses: (H2O, CO2) Poor in: O, Si, Al, Na, K, (<50%)
Magma Partial Melting Rich in: Ca, Fe, Mg (>50% wght)
Fig 3.13
Fig 1.15
Solidification of Melts
• Magma, Intruded or Extruded,• Solidifies (crystallizes) to form
• Intrusive or Extrusive • Igneous Rocks
Fig 3.12, 3.13
Igneous RockE.g., Granite (Silicic, Intrusive Igneous Rock):
Crystallized (Solidified) Silicic Melt Poor in: Fe, Mg, Ca, (<20%) Rich in: Silica (>70%)
See Fig. 3.7a
Quartz
Na Plagioclase
Biotite
Formation of Magma
How are rocks melted? Pg. 61
1. Heating ■ 2. Depressurization 3. Increase water content 4. Increased silica content
Where do rocks melt? Subduction zones (Silicic
and Intermediate) Mantle Plumes (“Hot Spots”) not only at
Divergent
Boundaries
Mafic
Hot andHigh Pressure
Hot andLow Pressure
Intrusive vs. Extrusive
Silicic (a.k.a, felsic) Magmas Cool (<700oC) Viscous (sticky, doesn’t flow easily) Gaseous (steam of H2O and C02)
Silicic Rocks Usually intrusive, course-grained, Silicic (Granite) to Intermediate
(Diorite) rock forms plutons If extrusive, fine-grained rocks
formed by explosive volcanoes (fig. 4.21)
Rhyolite or Andesite Volcanoes Also injects surrounding rocks with silica laden steam
Batholith made of Plutons
Composite Volcano
Dikes: Intruded near a pluton Silica rich fluids
are injected into cracks in all directions
Discordant: cutting across layers
Extrusive vs. Intrusive
Mafic Magmas Hot (>1000oC) Non-Viscous (runny, flows easily) “Dry” (no H2O or C02)
Mafic Rocks Usually Extrusive, Fine-grained,
Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Basalt Floods
If Intrusive, course-grained mafic rocks are formed Gabbro.
If intrusive, Dikes and Sills more common. (Plutons don’t form)
Mafic Sill: Intruded between layers Mafic magma is less
viscous and hotter so Does not form plutons
but Cuts along layers (Sills)
or even
across layers (Dikes) Also Baked Zones
of adjacent country rock and Chill Zones within the intrusion
Igneous Rock ClassificationIntrusive (Plutonic)Extrusive (Volcanic) E.g., Basalt
and Gabbro have two minerals Pyroxene Ca-Feldspar
Fig. 4.10
Vo
lum
e P
erce
nt
of
Min
eral
s
Continental Crust Oceanic Mantle Crust
Igneous Rocks and Silicates
The
Igneous Rock Classification
parallels the
systematic
Silicate Minerals Classification
Fig. 3.11
and Fig. 4.10
Vo
lum
e P
erce
nt
of
Min
eral
s
Frame- Double Single Iso. work Sheet Chain Chain
Fig. 2.9
Igneous Rock ClassificationIn
tru
sive
Ext
rusi
ve
Silicic Intermediate Mafic
Granite Diorite Gabbro
Rhyolite Andesite Basalt
Fig. 3.7 (Porphyritic)
1200
oC
1000
o
Bowen’s Reaction SeriesTwo series of minerals formed during crystallization of magma
Intrus. Extrus.
Gabbro Basalt
Diorite Andesite
Granite Rhyolite
Intrus. Extrus.
Gabbro Basalt
Diorite Andesite
Granite Rhyolite
Low Silica Magma
High Silica Magma
Fra
me-
D
oubl
e
S
ingl
e
Isol
ated
wor
k
S
heet
Cha
in
Cha
in
Temperature ofCrystallization
750
o