1. Igneous and metamorphic Petrology
Mahrous M. Abu El-Enen
Faculty of Science, Mansoura University

2. ربنا ماخلقت هذا باطلا سبحانك فقنا عذاب النار
بسم الله الرحمن الرحيم
ربنا ماخلقت هذا باطلا سبحانك فقنا عذاب النار

3. Course objectives/ outcomes
The main objective of the coarse:
This introductory level course in Petrology is aimed to help the students with the basic tools needed for understanding igneous and metamorphic processes.
Specific student outcomes include:
1- identifying and describing igneous and metamorphic rocks and their structures in the field and hand specimen based on their mineralogical composition and textures.

4. Cont. Course objectives/ outcomes
Specific student outcomes include:
2- Explaining (orally and in writing) the general processes of formation of igneous and metamorphic rocks.
3- Classifying igneous and metamorphic rocks properly in hand specimen.

5. What is petrology?
Petrology is the branch of geology that dealing with study of the rocks.
Igneous Petrology: is that branch of petrology dealing with the study of rocks that were originally molten (i.e. which formed from magmas or lavas).
Metamorphic Petrology is the study of all rocks that formed by recrystallization in the solid state, beyond the field of diagenesis.

6. General divisions of Petrology
In general, all branches of petrology (whether igneous, sedimentary or metamorphic) consist of two main components:
A- Petrography: which is the descriptive component of petrology, and consists of describing rocks either in the hand or under the microscope.
B- Petrogenesis: which is that part of petrology which aims at understanding the origin of rocks.

7. What is rock meaning?
Rocks are defined as a component of the Earth’s crust that composed of one or more minerals with a geologic extension. Rocks are defined as the main unit of the Earth. Rocks could be:
1) Mono-mineralic rocks: such as quartizite and marble.
Poly-mineralic rocks: such as granites, schists and greaywackes.
This means that Meteorites are not belonged to rocks

8. Exception for rock definition
Some rocks deviate from rock definitions as:
1) Coal: which originated from organic materials
Obsidian: which composes of non-crystallized silicates.

9. Again, What is the Earth Crust
The Earth’s crust is the outer solid materials of the Earth (5-70 km) that composed of rocks. It subdivided into:
Oceanic crust: Thin (~ 10 km), dense, (Fe-Mg silicate rocks, SIMA)
Continental crust: Thick (20-70 km, ~ 35 km average), less dense (Na-K-Al-silicate rocks, SIAL)
sedimentary cover (attains 10 km thick), of sedimentary rock composition
Upper Mantle
Depth km

10. Primary rocks: Igneous rocks
Rock Cycle
The rocks are passed through a cycle during their generation in the Earth, which known as: Rock Cycle
The rocks are divided into:
Primary rocks: Igneous rocks
Secondary rocks: Sedimentary and metamorphic rocks.

11. Rock Cycle
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12. Igneous rocks Primary rocks Massive and hard Crystalline
devoid fossils and pore spaces
Example: granite, basalt

13. Metamorphic rocks Secondary, hard, and deformed Foliated
occur in tectonic active areas
Example: Schist, and gneiss

14. Sedimentary rocks Secondary, Soft, and bedded
Contain fossils, and porous
Contain petroleum, coal and phosphate
Example: Sandstone, Limestone and Claystone.

15. The source of igneous rocks is the molten materials, i. e. magma
The source of igneous rocks is the molten materials, i.e. magma. Therefore, these name of igneous rocks came from the Latin “ignis”, which meaning fire.
The igneous rocks are formed by cooling and crystallization of magma (molten silicate materials) either below the earth as Intrusive rocks (plutonic) or on the surface as extrusive rocks (Volcanic).
Then what is the magma and Lava

17. Magma and Lava
Magma: a mixture of a melt (predominantly silicate) ± crystals ± volatiles which occurs at depths and has the ability to migrate to shallower levels where it either crystallizes at depth giving rise to igneous intrusions, or erupts at the surface to form volcanic rocks. The magma occur in equilibrium.
Lava: is erupted molten material that can flow on the surface of the earth. therefore lava may be considered a magma that has lost its gases (to the atmosphere upon eruption).

18. Nature and composition of magma
Magma is a complex mixture of molten, little solid and volatile phases that occur at high temperature ( ° C) and high pressure and have a different degrees of viscosity .

19. Chemical composition of magma
All chemical elements are represented in magma, but with various proportions.
The most abundance elements are oxygen and silicon; therefore magma could be described as molten silicate materials.
 Not all magmas have the same composition, which proofed from diversity of igneous rocks that occur at the surface of the earth or at depth.

21. Chemical classification of Magmas
Petrologists were able to classify magmas into four main chemical groups:
1- Acidic magma: rich in SiO2 (66-77 wt./%), Na2O and K2O. acidic magmas are broadly known as "granitic"
2- Intermediate magma: rich in SiO2 (52-66 Wt.%), Na2O, K2O as well as CaO and Al2O3.
3- Basic magma: rich in CaO, MgO and FeO and moderate SiO2 (52-45 wt.%). Basic magmas are broadly known as "basaltic".

22. Chemical composition of magmas, cont.
4- Ultrabasic magma : Poor in SiO2 (< 45 ~ 38 wt.%) but with large amounts of FeO and MgO.
Ultrabasic (Peridotite)
Basic (Basalt)
Intermediate (Andesite)
Acidic (Granite)
Oxide
42.26
49.2
57.94
71.3
SiO2
0.63
1.84
0.87
0.31
TiO2
4.23
15.74
17.02
14.32
Al2O3
3.61
3.79
3.27
1.21
Fe2O3
6.58
7.13
4.04
1.64
FeO
0.41
0.2
0.14
0.05
MnO
31.24
6.73
3.33
0.71
MgO
5.05
9.47
6.79
CaO
0.49
2.91
3.48
3.68
Na2O
0.34
1.1
1.62
4.07
K2O
3.91
0.95
1.17
0.77
H2O
0.30
0.11
CO2
0.10
0.35
0.21
0.12
P2O5

23. Generation of magma
Temperature and pressure rises with depth, eventually reaching to a level wherein the strongest rock is melted and turned to a liquid form which is called magma.
magmas are generated by partial melting in the upper mantle or lower crust, such a process occurs over a range of depths.
Therefore rising of magma connected to the weakness area (plate margins) within the Earth.

24. Plate boundaries

25. Plate Motions

26. Magma crystallization
Crystallization of magma means that transformation of magma from molten phase to solids phase.
During crystallization of magma, all minerals not crystallized at the same time, but according to rules (melting points and specific gravity of minerals)
Generally, the minerals with high melting point and higher specific gravity crystallized early and followed by minerals with lower melting point and specific gravity.

27. A series of minerals wherein any early-formed phase will react with the melt later in the differentiation to yield a new mineral further in the series.

29. Mineral association in igneous rock.

30. Differentiation of magmas
Differentiation is the process by which magmas evolve to give rise to a variety of magmas and rock types
There are different processes of magmatic differentiation:
1- Fractional crystallization and gravity crystallization:
Is a sequence of separation of crystal from melt

31. Differentiation of magmas
2- filter Pressing
If a mixture of crystals and liquid is suddenly subjected to compressional stress, the liquid will be squeezed out of the mixture, and will therefore be separated from the crystals.
3- Magmatic assimilation
Is the reaction of the magma with the country rocks, whereby these country rocks are incorporated in the magma and eventually melt.

32. Differentiation of magmas
4- Magma Mixing
Mixing two magmas that are compositionally different will produce a magma of intermediate composition.

33. Characters of igneous rocks
The igneous rocks have the following characters:
Hard crystalline rocks: most of igneous rocks are crystalline and very little (obsidian) are hyaline
Massive: occur as large massive bodies, dykes and sills
They are not porous and devoid any fossils content

34. Classification of Igneous Rocks
The igneous rocks are classified according to the following bases:
1- Mode of occurrence of igneous rocks
2- Textures of the Igneous rocks
3- Chemical composition and corresponding Mineralogy
4- The colour of Igneous rocks

35. Classification of the Igneous rocks
Igneous rocks are classified according to the depth of generation (Mode of occurrence) into:
- Extrusive (volcanic) rocks: That formed at the Earth’s surface
Intrusive rocks: That formed under the Earth’s surface, and could be:
- Plutonic rocks: That formed at quit depth of the Earth’s crust.
- Hypabyssal rocks: formed at a depth in between the plutonic and volcanic rocks

37. Plutonic Igneous rocks: Characterize by the following:
1- They are generated at quit depth, so their magma cooled slowly
2- Their yielded rocks have coarse-grained texture
3- They form a large masses (Batholith, Boss, Stock)
4- Examples are granite and gabbros

40. Volcanic Igneous rocks: Characterize by the following:
1- They are generated at Earth’s surface from lava cooling, so their cooling is fast
2- Their yielded rocks have very fine to glassy rocks
3- They form Lava flow and occasionally contain vesicles (such as Scoria)
4- Examples are rhyolite and basalt

45. Hypabyssal Igneous rocks: Characterize by the following:
1- They are generated formed at a depth in between the plutonic and volcanic rocks, So the their rate of cooling is intermediate
2- Their yielded rocks have medium-grained texture, and porphyritic texture
3- They form dykes, sills, lacoliths, lopoliths and phacoliths forms
4- Examples are porphyrites

51. Classification of the Igneous rocks
Texture of Igneous rocks:
Texture: grain-grain relationships, and refers to degree of crystallinity, grain size, and geometrical relationships between the constituents of a rock
1) degree of crystallinity,
2) Sizes of crystals, and
3) Mutual relationships between the crystals.
1- Degree of crystallinity: is the quantity of crystal opposite to glass in a given igneous rocks.
It depends on: 1)Rate of magma cooling
2)Viscosity of the magma

52. Holocrystalline Texture
Degree of crystallinity
Generally the igneous rocks are described as:
1- Holocrystalline: composed wholly of crystals
2- Hypocrystalline: contains both glass and crystals
3- Holohayline: consists entirely of glass
Holocrystalline Texture
Holohyaline texture

53. Grain-size As well grain size depends on:
rate of cooling, 2)Viscosity of magma, and
3) volatile content in magma
Igneous rocks are classified according to their grain size into:
1-Cryptocrystalline: crystals cannot be distinguished even with a microscope
2- Aphanitic: crystals not visible to the unaided eye
3- Phaneritic: grains readily distinguished with the unaided eye. If the grains of the rock are roughly the same size:
Fine < 1 mm
Medium 1-5 mm
Coarse 5 mm-3 cm
Very coarse > 3 cm

54. Grain size Aphanitic Texture Fine-grained tex Medium-grained tex
Coarse-grained tex
Very coarse-grained tex

55. Mutual relationships between the crystals
There are different types of textures,
1- Porphyritic texture: Large (Phenocrysts) in Fine-grained (matrix). It forms due to two cycles of cooling, initially very slowly underground, then rapidly at Earth's surface.
1-Flow Texture: directive large phenocrysts in matrix. It forms due to magma flowing
3- Vesicular texture: refers to vesicles (holes, pores, or cavities) within the igneous rock. It forms as the result of gas expansion (bubbles), which often occurs during volcanic eruptions.

56. Grain size
Porphyritic Texture
Vesicular texture

57. Mineralogical composition
As we discussed, minerals separated from magma according to Bown’s reaction Series.
Most of the common essential minerals are:
1- Quartz: occur in the high-silica igneous rocks (SiO2>66 Wt.%). It is glassy in appearance.
2- K-Feldspar: include Orthoclase (buff color). It is also occur in rocks of high-silica content, and Plagioclase (milky white in color), which occur in all rocks and include (Na-plagioclase to Ca-plagioclase).
3- Mica: include white mica (muscovite) and dark mica (biotite). All are flakey.

58. Mineralogical composition
4- Amphiboles: their common mineral is hornblende. It occur in rocks with moderate-silica content. It is dark green in color.
5- Pyroxene: include complex silicate minerals (e.g. Augite, enstatite, diopside, and Aegerine). They occur in rock that poor in silica. They are dark green colour.
6- Olivine: include fyalite and forsterite varieties. They are green in colour, prismatic in habit. They occur only in rocks that are deficient in silica.

59. Common Minerals

60. Fig. 5.4

61. Compositional Classification
Granite
Compositional Classification
Quartz
Orthoclase
Biotite
Granite
Plagioclase

62. Compositional Classification
Granite
Compositional Classification
Granodiorite
Quartz
Granite
Amphibole
Plagioclase

63. Compositional Classification
Granite
Compositional Classification
Granodiorite
Diorite
Granite
Plagioclase
Amphibole

64. Compositional Classification
Granite
Compositional Classification
Granodiorite
Diorite
Granite
Gabbro
Plagioclase
Pyroxene

65. Compositional Classification
Granite
Compositional Classification
Granodiorite
Diorite
Granite
Gabbro
Pyroxene
Olivine
Peridotite

66. Chemical composition
Chemically, the igneous rocks are classified into:
1- Acidic (felsic) rocks: rich in SiO2 (66-77 wt./%), and little FeO and MgO. They contain minerals such as: quartz, Na-plagioclase, K-feldspars (orthoclase, microcline), white mica. Their rocks are leucocratic. E.g. granite, rhyolite, granodiorite
2- Intermediate rocks: Contain SiO2 (52-66 wt./%) and a moderate FeO and MgO. They contain minerals such as: Ca-Na-plagioclase, K-feldspars (orthoclase), amphibole. Their rocks are mesochratic. E.g. Diorite, andesite

67. Chemical composition
3- Basic (mafic) rocks: rich in CaO, MgO and FeO and moderate SiO2 (52-45 wt.%). They contain minerals such as: Na-Ca-plagioclase, Pyroxene. Their rocks are melanochratic. E.g. basalt and gabbro.
4- Ultrabasic (ultramafic) rocks: Poor in SiO2 (< 45 ~ 38 wt.%) but with large amounts of FeO and MgO. They contain minerals such as: Ca-plagioclase, Pyroxenes, Olivine. Their rocks are melanochratic. E.g. dunite, pyroxenite, anorthosite, peridotite

68. 5- rocks Color
The color of the rock depends on the ratios of mafic to felsic mineral constituents.

69. 5- rocks Color
The color of the rock depends on the ratios of mafic to felsic mineral constituents.
Generally, rock are classified, depends on estimating the volume % of the dark (mafic) minerals. Igneous rocks are classified into 4 groups based on C.I.:
1- leucocratic rocks: < 30% = Felsic rocks
2- Mesocratic: C.I. = 30 – 60 = Intermediate rocks
3- Melanocratic: C.I. = 60 – 90 = Mafic rocks
4- Hypermelanic: C.I. > 90. = Ultramafic rocks

70. General classification of Igneous rocks
Based on:
1- Mode of occurrences
2- Textures
3- Chemical composition and silica saturation
4- Mineralogical composition
5- Rock colour
Igneous rocks are classified into:
1- Acidic-felsic-oversaturated igneous rocks
2- Intermediate-saturated igneous rocks
3- Basic-saturated igneous rocks
4- Ultrabasic-undersaturated igneous rocks

71. Classification of igneous rocks

72. Classification of igneous rocks

73. Classification of igneous rocks

74. Classification of igneous rocks

75. Classification of igneous rocks

76. General classification of Igneous rocks
Based on:
1- Mode of occurrences
2- Textures
3- Chemical composition and silica saturation
4- Mineralogical composition
5- Rock color
Igneous rocks are classified into:
1- Acidic-felsic-oversaturated igneous rocks
2- Intermediate-saturated igneous rocks
3- Basic-saturated igneous rocks
4- Ultrabasic-undersaturated igneous rocks

77. Classification of igneous rocks
Ultrabasic – under-saturated
Basic- Saturated
Intermediate
saturated
Acidic
Oversaturated
Chemical Composition &
Silica Saturation
Pyroxene + Olivine + Ca-rich Pl
Pl + Pyroxene
Pl<Or + mica + amphibole
Or>Pl + mica + amphibole
Qtz + Na-rich Pl < Or + mica
Qtz + Or< Na-rich Pl + mica
Mineral composition
Scoria
Pumice
Vesicular
Obsidian
Glassy
Basalt
Andesite
Trachyte
Dacite
Rhyolite
Volcanic
(Fine grained
dolerite
Porphyritic andesite
Porphyritic- dacite
Pgmatite
Porphritic- rhyolite
Pegmatite
Hypapyssal (medium- grained)
Dunite
Pyroxenite
Predotite
Anorthosite
Gabbro
Diorite
Syenite
Granodiorite
Granite
Plutonic
(Coarse-grained)
Hyper-melanic
(Ultramafic)
Melano-cratic
(Mafic)
Mesocratic
(Intermediate)
Leucocratic
(felsic)
Color

78. Acidic Igneous rocks
Granite

79. Acidic Igneous rocks
Rhyolite

80. Acidic Igneous rocks
Granodiorite

81. Acidic Igneous rocks
Dacite

82. Acidic Igneous rocks
Pegmatite and Rhyolite porphyry

83. Acidic Igneous rocks
Pumice

84. Intermediate Igneous rocks
Syenite

85. Intermediate Igneous rocks
Trachyte

86. Intermediate Igneous rocks
Diorite

87. Intermediate Igneous rocks
Andesite

88. Intermediate Igneous rocks
Andesite porphyry

89. Basic Igneous rocks
Gabbro

90. Basic Igneous rocks
Basalt

91. Basic Igneous rocks
Dolerite

92. Basic Igneous rocks
Scoria

93. Ultrabasic Igneous rocks
Dunite

94. Ultrabasic Igneous rocks
Pyroxenite

95. Ultrabasic Igneous rocks
Predotite

96. Ultrabasic Igneous rocks
Anorthosite

97. Ultrabasic Igneous rocks
Obsidian

98. Syllabus of the course Igneous rocks:
1- Introduction, magmas and lavas, magma source, chemical composition of magma, crystallization of magma, Occurrence and abundance of igneous rocks
2- Characters of igneous rocks
3- Classification of igneous rocks
4- Common metamorphic rocks

99. General classification of Igneous rocks
Based on:
1- Mode of occurrences
2- Textures
3- Chemical composition and silica saturation
4- Mineralogical composition
5- Rock colour
Igneous rocks are classified into:
1- Acidic-felsic-oversaturated igneous rocks
2- Intermediate-saturated igneous rocks
3- Basic-saturated igneous rocks
4- Ultrabasic-undersaturated igneous rocks

100. Text books
1- Abu El-Enen: Lecture notes on Igneous and Metamorphic Petrology.
2- Turner, Francis J.: Igneous and metamorphic petrology
3- Best, Myron G. : Igneous and metamorphic petrology
4- The available “Physical Geology” at Literary.