Petrology Course Geo 320

Introduction To Igneous & Metamorphic Petrology Course

Course Director

Dr. Bassam A. A. Abu-Amarah Al Mohanna I. Introduction

• Petrology Definition,

 Petrology , from the Greek words petra , meaning rock, and logos , meaning knowledge, is the study of rocks and the conditions in which they form.  Petrology includes igneous, metamorphic, and sedimentary. But,

2 Introduction Petrology of Igneous And Metamorphic Petrology , from the Greek words petra , meaning rock, and logos , meaning knowledge, is the study of rocks and the conditions in which they form. Petrology includes igneous, and metamorphic, But, Metamorphic petrology is not so much concerned with the bulk In igneous petrology, the chemistry of the rocks. bulk composition of the rock is important because and It is concern with the use of mineral it gives evidence to theie assemblages to determine their tectonic environment in conditions under which the which they formed. metamorphic rock crystallized and formed

So, it is a Rocks’ study to identify their: 3 1) occurrences, 2) composition, 3)origin and 4) evolution. So, Petrological description : . Comprises rock ‘s occurrence, attitude, structure, mineralogy, chemical composition, to know its origin (Petrogenesis) of rock’s unit diversities, Furthermore,

• PETROLOGY : focuses primarily on the rock formation, or Rock’s Petrogenesis (Origin), while, • Petrography is (Microscopic rock’s study) deals with the detailed description and classification of rocks via its mineral’s4 composition, So, The Petrologists (Persons who study rocks) tasks are : 1. To carry out study on rocks which are forming parts of the lithosphere that are clearly different from their surroundings rocks, and

2. To draws conclusive (Definite) records about Evolution and Constitution of the Earth on the crust and deep init.

 It is primarily based on volcanic eruptions, shape and composition of igneous bodies that have extended to the Earth’s surface by tectonic processes and

erosion. 5 Therefore; So, the most significant Petrological processes is to focus on the following:

1. Tectonic movements of rock masses. 2. Magmas generation and its injection into the lithosphere and crust, in addition Volcanic eruptions.

3. Physical, chemical and biological weathering, and depositional processes in the earth’s surface , in the hydrosphere, and in the atmosphere. 4. Mutual chemical reactions and biological processes in aqueous solutions.

6 5. Metamorphic changes due to increasing pressure and temperature at greater depths of covering. 6. Melting, migration, recrystallization, degassing and similar events take place on rocks.

Hence,

1. In general; all Rocks types , are composed of certain minerals (minerals aggregates Components= Rock),

So, Petrology is closely associated with the mineralogy.

7  In addition; “Petrology is the study of the rocks involve their chemical composition (mineral chemistry and geochemistry) through studying the complex chemical reactions and their formation processes

 So, determination of rock’s : 1. mineral constituents and 2. chemical composition necessary to study and to distinguish among the Are rocks occurrane, and also for resolving the origin of 8 them. As a result,

Why Petrology is very important in Geophysics studies and explorations? because

1. The Petrology is also illustrating rock’s physical proparities, which are varies from one rock to another (On/within the crust and lithosphere) of the earth, and 2. It has an important role in geophysical explorations for discriminating and discovering different rocks types, 3. As well as, their potential resources encountered . 9 ConsequentlyConsequently

• Igneous petrology is the study . Metamorphic petrology is the study the of melts (magma) and the rocks changing existing rocks (Parent rocks) that that crystallize and solidify from their minerals recrystallized in the solid the melts, and emption or state within Earth’s crust or, rarely, within emplaced as eventual igneous the upper mantle. rocks, . Metamorphic rocks crystallized within the • Describing how magmas are crust involves deformation that lead to produced and how they ascend mineral reactions by introducing strain through the mantle and crust, via energy and by opening pathways for fluid 1. Their minerals content movement. characteristics of igneous . Minerals present in a metamorphic rock to rocks, and determine what its parent was (i.e., the 2. their geochemical evolution, protolith ) and to estimate the conditions and their eruption or of metamorphism

emplacement to form 10 igneous rocks. Thus, Thus,

. The chemical variations of The igneous rocks are concerned minerals in metamorphic rocks simply give and provide little with the entire spectrum of information about minerals processes minerals chemistry may abundancy , and about provide an important information metamorphic rocks conditions. . Study Metamorphic Rocks facies, about the origin (Magma) and to establish the relative their evolution. temperature and pressure conditions of metamorphism were had the ability to quantify metamorphic mineral compositions. 11 and • Study the therobarometry as quantitative calculated methods for calculating the P and T conditions that minerals’ constitute of metamorphism conditions at a specific chemical reaction within the metamorphic rocks. Thus,

The Metamorphic rocks are concerned with Pre-existing rocks (Parent) of igneous, Metamorphic and sedimentary changing their mineral contents and their chemical reaction in solid

state due to metamorphism processes. 12 In addition,

Igneous and metamorphic petrology are commonly taught together because they both depend on the use of mineral contents, chemistry and phase diagrams. Therefore,

The igneous rocks may later be transformed into metamorphic rocks, Cosequently,

In this course we will begin with igneous Petrology and takes up metamorphic petrology second.

13 that is to say

• igneous petrology, shows the understanding of how the mineralogy of igneous rocks reflects the equilibria that govern minerals crystallization of/from magma and how its geochemistry reflects its magmatic differentiation in forming rocks. • Geochemistry is using several major element discrimination diagrams including: • Fe-index, modified alkali-lime index, and aluminum saturation index, So that • We can compare and locate magmatic rocks suites that form in different tectonic environments. Thus, Magma chemistry highlight the different magmatic processes in developing magmatic suites formed environments whichever at: 1. oceanic and continental divergent plate boundaries, 2. Or in arcs formed at oceanic and continental convergent margins, and 3. Or in oceanic and continental intraplate tectonic settings.

14 conversely In metamorphic petrology, describing how mineral assemblages in progressively changes by the affect of pressure, temperature, and fluid composition and forming metamorphic rocks (Protolith) in more complex systems

Simply is to say  The metamorphic rock’s mineral assemblages depend fundamentally on: 1. upon the protolith (Pre-existing rocks) of the rock, as well as on 2. the mineral reactions that take place at successively by metamorphism agents (temperatures, pressures, hydrothermal solutions, and time). As a way

By determining the metamorphic mineral assemblages occurred, along with its specific metamorphic environments conditions will locate and found their various types of metamorphic belts at different types of tectonic significance.

15 So, this This short introduction will make you to do connections between: 1. The study of igneous and metamorphic rocks and 2. To illustrate the value of a fundamental understandingT of petrology. The Scope of Metamorphism in The Scope of Igneous Petrology metamorphic Petrology

• All igneous rocks ultimately sourced • Pre-existing rocks be subjected by: from magmas that solidify to form 1. Igneous intrusion of magmas, at low- igneous rocks plutons. temperature, or at higher temperatures, • The igneous classified and named 2. Or Pressure by tectonic loading and upon their: movements. 1. occurrence, In both minerals will react by releasing all or part 2. composition, of their volatile constituents. 3. origin, and 4. evolution of rocks formed via magmatism.

16 Igneous rocks study can be divided and • As igneous rocks, are typically dominated by classified into two catogries: anhydrous minerals, dehydrated and interact 1) Igneous petrography , which is the description with fluids after solidification from the melt, and classification of igneous rocks; and • Metamorphic rocks Study gives very 2) Igneous petrogenesis , which is the study of the origin and evolution of igneous rocks through their important information about: geochemistry: 1. the pressure and temperature conditions a) Major-element geochemistry can of/during tectonic processes and determine whether a suite of rocks 2. the nature of fluid flow in the deep crust. is related through a process such as • Changes in P, T, and fluid compositions magmatic differentiation or mixing. result in reactions among minerals to b) Trace-element geochemistry is used produce new minerals. to identify the role various minerals • In metamorphic rocks new minerals may have played as either formed in a more stable in lower- crystallizing phases or as residual temperature, pressure in metamorphism phases in a suite of rocks. conditions processes.

17 Therefore; 3. Isotope geochemistry , which can involve both radiogenic and stable • by studying mineral assemblages in isotopes, can determine whether a suite metamorphic rocks we can deduce the of rocks formed: conditions of metamorphism Agents. a) From a single magma, or whether • simple definition, metamorphism is the b) From a more complex, multisource recrystallization of a rock at conditions process was involved. below those of the liquidus . At low temperatures, metamorphism merges with the process known as diagenesis , But;

Metamorphic rocks at high temperatures of metamorphism processes condition will generate melts of igneous rocks-forming processes

18 II . Structure of The Earth:

 The Earth is an oblate spheroid in shape.  It is composed of a number of different zones in elliptical shells shape as determined by deep seismic evidence,  These layers are :

I. Crust Zone :The outer most solid silicate crust, surrounding the earth. 1) It is rigid and solid rocks layer. It is composed of granitic-rich continental crust . 19 2) The Oceanic crust is thin zone, varies in thickness from 4 to about 12 km. • It is also composed of basalt and has a density of about 3 gr/cm3. • The Continental crust thickness varies between 40 and 70 km and composed mainly of lighter granites, pegmatites and gneisses . • The density of continental crust is about 2.7 gr/cm3.

20 THE EARTH’S INTERIOR CRUST: OCEANIC CRUST THIN: 10 KM RELATIVELY UNIFORM STRATIGRAPHY = OPHIOLITE SUITE: • SEDIMENTS • PILLOW BASALT • SHEETED DIKES • MORE MASSIVE GABBRO • ULTRAMAFIC (MANTLE) Continental Crust: Thickness : 20-90 km.,with an average of ~35 km Highly variable composition Average ~ Granodiorite II. The Mantle comprises 83% of the earth volume: the top mantle zone called Lithosphere, solid and rigid.

 The crust and the top of solid mantle (Lithosphere) floats on the “Asthenosphere (middle mantle) as a components of a

plate. 22 The Earth’s Interior Mantle: Peridotite (ultramafic) Upper to 410 km (olivine  spinel)

 Low Velocity Layer 60-220 km

Transition Zone as velocity increases ~ rapidly

 660 spinel  perovskite-type  SiIV  SiVI

Lower Mantle has more gradual velocity increase

Figure Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. • The mantle comprises Lithosphere, Asthenosphere and Mesosphere zone.

• The mantle zone is surrounding the core zone, with a thickness of 2900km. • The upper mantle (Lithosphere) exists from the base of the crust down- ward to a depth of about

400 km. 24 • This region Lithosphere) of the Earth’s interior is composed of peridotite, an ultramafic rock made up of the minerals olivine and pyroxene.

• The middle mantle zone called (Asthenosphere) lies between

400 to 1000 km below earth surface. 25  This layer has a physical properties differ from the the upper mantle (lithosphere).

 It is hot and plastic, the higher pressure causes formation of minerals differ from of the upper mantle.

26  The CRUST thickness and the upper mantle (Lithosphere) is about 400 km thick,  and it has the ability to glide (Slide) over the rest of the middle mantle (Asthenosphere) and flow due to the increase in 1. Pressure, and 2. Temperature.

27 III. The core zone : it is involved of:

1) Inner core solid, rich in Fe (Iron) and Ni (Nickel), with a density of about 10.3 g/cm3 . Its radius of about 1220 km. 2) Outer Core (OC) is a liquid with a density of about 6 g/cm3. • OC surrounds the inner core and with thickness of about 2250 km.

28 The Earth’s Interior

Core: Fe-Ni metallic alloy

Outer Core is liquid

 No S-waves Inner Core is solid

Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Figure 1-3. Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford. Both 1) crust and 2) upper mantle (lithosphere) zones are forming a numerous tectonic plates that float on top of the middle mantle (Asthenosphere).

These plates move slowly due to the convection currents within the mantle across the asthenosphere causing PLATE TECTONIC.

The tectonic plates have the ability to rise and to sink, known as isostasy phynomena,

Because the crust floats on top of the mantle-like ice cubes in water. 31 The Earth’s Zones Discontinuity due to the their differences in Rocks compositions and their physical characteristics:  The ( MOHO) discontinuity , named after Andrija Mohorovicic, a Croatian Geophysicist.  It is a line separates between the Earth’s crust and the mantle. It separates oceanic crust and continental crust from the upper mantle mantle.

 It lies in about 5 to10 km (3-6 miles) below the ocean floor and 20-90 km (10 - 60 miles) beneath the 32 continents. 2. The Gutenberg discontinuity, named after German scientist Bruno Gutenberg,

 It is located at 2900 km depth beneath the Earth’s surface.

 It is determined by applying Seismic waves.

 It is separating the solid lower mantle (Mezosphere)

and the molten outer core. 33 For that reason,

At any dynamic change in Isostasy, the plates collide or move causing Earthquakes, Tsunami and related natural hazards and disasters.

Thus,

The PETROLOGY (rocks’ Studies) applied in/within the crusts and upper mantle Rocks.

34 III. ROCKS’ CLASSIFICATION

The rocks of Earth’s crust and upper mantle are divided into three main groups according to their origin, as follow: 1. Igneous Rocks

. Igneous came from “ignis” means “fire” in Latin and eruptive). These rocks are a primary rocks.

. Igneous Rocks occurred and formed in/on the Earth via two manner either by: 35 1. Inside (down in the earth); • formed by a direct slow cooling rate, crystallized, and solidified from a molten rock mass (called

magma). A light-color fine to medium grained igneous rock (granite) containing interlocking minerals of quartz (white) and feldspar (light rosy or pink) with minor OR grains (black) of hornblende, biotite and chlorite.

2. Outside in the earth’s 36 surface; . Volcanic rocks Formed via fast cooling rate (surface of the earth) fine Crystallized grains from LAVA formed on the earth’s surface we call it “lava”;

( i.e. when magma reaches to the earth’s surface or at a very shallower depth).

37 2. Metamorphic Rocks: . The metamorphic rock is a transformation status of a pre- existing rock (Original rock of igneous, metamorphic, and sedimentary) subjected to :

1. a very high heat (increases Temperature from 150 to 200 oC, and

2. Pressure increased to an about +1500 bar located at a greater depth ,  Causing changes in their physical and/or chemical in rock’s minerals crystal form (texture and structure) in solid state due to 38 active fluid and contact with magma. 39