Igneous and metamorphic Petrology Mahrous M. Abu El-Enen Faculty of Science, Mansoura University E-mail: mahrous@mans.edu.eg

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

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.

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.

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.

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.

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

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.

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

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.

Rock Cycle Kjxckjx دورة الصخور

Igneous rocks Primary rocks Massive and hard Crystalline devoid fossils and pore spaces Example: granite, basalt

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

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

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

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).

Nature and composition of magma Magma is a complex mixture of molten, little solid and volatile phases that occur at high temperature (700-1300° C) and high pressure and have a different degrees of viscosity .

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.

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".

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

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.

Plate boundaries

Plate Motions

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.

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.

Mineral association in igneous rock.

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

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.

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

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

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

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

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

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

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

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

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

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

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

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.

Grain size Porphyritic Texture Vesicular texture

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.

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.

Common Minerals

Fig. 5.4

Compositional Classification Granite Compositional Classification Quartz Orthoclase Biotite Granite Plagioclase

Compositional Classification Granite Compositional Classification Granodiorite Quartz Granite Amphibole Plagioclase

Compositional Classification Granite Compositional Classification Granodiorite Diorite Granite Plagioclase Amphibole

Compositional Classification Granite Compositional Classification Granodiorite Diorite Granite Gabbro Plagioclase Pyroxene

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

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

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

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

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

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

Classification of igneous rocks

Classification of igneous rocks

Classification of igneous rocks

Classification of igneous rocks

Classification of igneous rocks

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

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

Acidic Igneous rocks Granite

Acidic Igneous rocks Rhyolite

Acidic Igneous rocks Granodiorite

Acidic Igneous rocks Dacite

Acidic Igneous rocks Pegmatite and Rhyolite porphyry

Acidic Igneous rocks Pumice

Intermediate Igneous rocks Syenite

Intermediate Igneous rocks Trachyte

Intermediate Igneous rocks Diorite

Intermediate Igneous rocks Andesite

Intermediate Igneous rocks Andesite porphyry

Basic Igneous rocks Gabbro

Basic Igneous rocks Basalt

Basic Igneous rocks Dolerite

Basic Igneous rocks Scoria

Ultrabasic Igneous rocks Dunite

Ultrabasic Igneous rocks Pyroxenite

Ultrabasic Igneous rocks Predotite

Ultrabasic Igneous rocks Anorthosite

Ultrabasic Igneous rocks Obsidian

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

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

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.