2/3/2017 - concord.edu · A chemical classification of volcanics based ... idealized calculation...
Transcript of 2/3/2017 - concord.edu · A chemical classification of volcanics based ... idealized calculation...
2/3/2017
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Classification of Igneous Rocks
Texture - largely volcanic vs. plutonic
• Volcanic, shallow intrusivemust have significant aphanitic or glassy fraction
• Other intrusivephaneritic
Composition – mineralogy, bulk chemistry (color)
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Fig 4.8 Understanding Earth
Composition
Felsic Intermediate Mafic Ultramafic
Extrusive (glassy, aphanitic, porphyritic, fragmental, vesicular, etc.)
Rhyolite Dacite Andesite Basalt Komatiite (rare)
Te
xtu
re
Intrusive (phaneritic, pegmatitic)
Granite Granodiorite Diorite Gabbro Peridotite
Simplified classification
more silica; less iron & magnesium
less silica; more iron & magnesium
lighter darker
3 Major MineralsSimplified View
More silica (SiO2), sodium, potassium
More iron, magnesium, calcium
Lighter color Darker color
mod
ifie
d fr
om F
ig 4
.6 U
nder
stan
ding
Ear
th
Rhyolite or Granite
Dacite or Granodiorite
Andesite or Diorite
Basalt or Gabbro
Komatiite or Peridotite
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Textural Classification of Pyroclastic Rocks
Figure 2.5. Classification of the pyroclastic rocks. After Fisher (1966) Earth Sci. Rev., 1, 287-298.
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Note: The compositional classification still applies and is typically used in
conjunction with the textural classification.
Ternary Diagrams
Figure 2.1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.
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Figure 2.2a. A classification of the phaneritic igneous rocks: Phaneritic rocks with more than 10% (quartz + feldspar + feldspathoids). After IUGS.
Figure 2.3. A classification and nomenclature of volcanic rocks. After IUGS.
IUGS Classifications7
Phaneritic Volcanic
Figure 2.2a. A classification of the phaneritic igneous rocks: Phaneritic rocks with more than 10% (quartz + feldspar + feldspathoids). After IUGS.
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Phaneritic Classification
Further sub-divided
on later slides
9Phaneritic Classification Quartz-bearing10
Phaneritic Classification
Feldspathoid-bearing
5%
Mafic & Ultramafic, Phaneritic Rock Classification
Figure 2.2b. A classification of the phaneritic igneous rocks: Gabbroic rocks. After IUGS.
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Bottom of diagram
further sub-divided on next slide
Figure 2.2c. A classification of the phaneritic igneous rocks: Ultramafic rocks. After IUGS.
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Mafic & Ultramafic, Phaneritic Rock ClassificationUnderstanding Earth
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Classification of Volcanic Rocks
Figure 2.3. A classification and nomenclature of volcanic rocks. After IUGS.
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Classification of Volcanic
Rocks
Figure 2.4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Maitre (2002) . Igneous Rocks: A Classification and Glossary of Terms. Cambridge University Press.
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Lamprophyres
a group of potassium-rich mafic to ultramafic rocks
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1996 - Classification of lamprophyres, lamproites, kimberlites, and the kalsilitic, melilitic, and leucitic rockshttp://canmin.geoscienceworld.org/content/34/2/1752005 - Integrating Ultramafic Lamprophyres into the IUGS Classification of Igneous Rocks: Rationale and Implications https://academic.oup.com/petrology/article/46/9/1893/1385496/Integrating-Ultramafic-Lamprophyres-into-the-IUGS
Average compositions (% by weight) and liquidus temperatures of different magmas
Composition: Ultramafic Mafic Intermediate Felsic
Volc. rock name: Komatiite (rare) Basalt Andesite Rhyolite
SiO2 47.9 50.9 58.9 73.7
TiO2 0.4 1.7 0.9 0.2
Al2O3 4.1 14.6 17.1 14.3
FeO 9.7 14.6 6.2 2.1
MgO 27.5 4.8 3.8 0.3
CaO 7.5 8.7 5.3 1.4
Na2O 0.2 3.1 4.3 5.2
K2O 0.02 0.8 1.2 4.1
Temp (°C) ~1600 ~1200 ~1000 ~900
Eruption temperatures can be a little lower than liquidus temperatures.
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“Normative” mineral abundances
A standardized, idealized calculation based on a bulk chemical analysis
Uses pure end-member mineral compositions (no solid-solutions)Sometimes used to categorize rock (e.g. “normative olivine”)
CIPW Norm19
http://minerva.union.edu/hollochk/c_petrology/norms.htm
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Brownlow's Geochemistry