Theme 5. Igneous rocks

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2 Theme 5. Igneous rocks 5.1. Igneous rocks and plate tectonics 5.2. Igneous structures and forms 5.3. Classification of igneous rocks

3 5.1. Igneous rocks and plate tectonics Remember! Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever The lithosphere is underlain by a plastic layer of the mantle, the asthenosphere, over which the plates can move.

4 Remember! 5.1. Igneous rocks and plate tectonics The theory of plate tectonics describes: -the movement of plates; -the forces acting between them. The theory of plate tectonics explains: The theory of plate tectonics explains: -continental drift; -volcanoes; -earthquakes; -the distribution of mountain chains; -rock assemblages; -structures on the seafloor.

5 Remember! 5.1. Igneous rocks and plate tectonics Source: USGS

6 5.1. Igneous rocks and plate tectonics There are two major magmatic geosystems: -mid-ocean ridges (where basalt wells up from the upper mantle and melts during decompression to form oceanic crust); -subduction zones (where subducting oceanic lithosphere partially melts by addition of fluid to generate differentiated magmas that rise through the crust and form island or continental volcanic arcs).

7 5.1. Igneous rocks and plate tectonics Mid-ocean ridges (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

8 5.1. Igneous rocks and plate tectonics Mid-ocean ridges (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

9 5.1. Igneous rocks and plate tectonics Mid-ocean ridges (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

10 5.1. Igneous rocks and plate tectonics Mid-ocean ridges (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

11 5.1. Igneous rocks and plate tectonics Mid-ocean ridges (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

12 5.1. Igneous rocks and plate tectonics Subduction zones (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

13 5.1. Igneous rocks and plate tectonics Subduction zones (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

14 5.1. Igneous rocks and plate tectonics Subduction zones (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

15 5.1. Igneous rocks and plate tectonics Subduction zones (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

16 5.1. Igneous rocks and plate tectonics Subduction zones (magmatic geosystem) Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

17 5.2. Igneous structures and forms Basic extrusive and intrusive structures are: -volcanic cone; -ash falls and pyroclastic rock; -lava flow; -volcanic neck; -batholith; -stock; -dyke; -sill; -mineral vein. Extrusive structures Intrusive structures

18 5.2. Igneous structures and forms Plutonsare large igneous bodies formed at depth in Earth's crust. Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

19 5.2. Igneous structures and forms Volcanic cones mark the magma duct or vent. These are composed of layers of ash and lava, and they vary in the steepness of their sides according to the composition of the lava and the amount of ash and dust ejected. Source: Internet

20 5.2. Igneous structures and forms The ash and dust ejected from volcanoes is pyroclastic rock. The dust and fine ash may settle on land or in water to form tuffs. Source: Internet

21 5.2. Igneous structures and forms Volcanic neck Lava flow Source: Internet

22 5.2. Igneous structures and forms Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

23 5.2. Igneous structures and forms Plutons are large igneous bodies formed at depth in Earth's crust. Theyrangeinsizefrom1km 3 tohundredsofkm 3. Batholiths, the largest plutons, are great irregular masses of coarse-grained igneous rock that by definition cover at least100km 2. Batholiths are found in the cores of tectonically deformed mountain belts. The rest of the plutons, similar but smaller, are called stocks.

24 5.2. Igneous structures and forms Batholiths and stocks Source: Internet

25 5.2. Igneous structures and forms Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

26 5.2. Igneous structures and forms Sills and dikes are similar to plutons, but they are smaller and have a different relationship to the layering of the surrounding intruded rock. Asillisasheetlikebodyformedbytheinjectionofmagma between parallel layers of preexisting bedded rock. Sills are concordant intrusions. Dikes are the major route of magma transport in the crust. They are like sills in being sheetlike igneous bodies, but dikes cut across layers of bedding in country rock and so are discordant intrusions.

27 Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever 5.2. Igneous structures and forms

28 5.2. Igneous structures and forms Mineral veins are deposits of minerals found within a rock fracture that are foreign to the host rock. Irregular pencil-shaped or sheetshaped veins branch off the tops and sides of many intrusive bodies. They may be a few millimeters to several meters across, and they tend to be tens of meters to kilometers long or wide. Mineral veins can contain economic metals or gems. Source: Internet

29 5.3. Classification of igneous rocks God Remember! Wholeness Rocks Minerals (Chemical bonds, Crystals) Chemical elements Atoms Something Nothing God

30 5.3. Classification of igneous rocks Rocks are aggregates of one or more mineral. Thenatureandpropertiesofarockaredeterminedbythe: -minerals in it; -manner in which the minerals are arranged relative to each other(the texture of the rock); -weathering(affect the engineering properties of a rock).

31 5.3. Classification of igneous rocks According to their manner of formation, rocks are of three main types: -igneous rocks; -sedimentary rocks; -metamorphic rocks Granite Sandstone Gneiss Source: Internet

32 5.3. Classification of igneous rocks Igneous rocks are formed from magma, which has: -originated well below the surface; -ascended towards the surface; -crystallised as solid rock either on the surface or deep within the Earth s crust as its temperature fell. Source: Internet

33 5.3. Classification of igneous rocks Each mineral starts to crystallise at a particular temperature and continues to form throughout a limited temperature range as the magma cools. Since the crystals formed early have a higher specific gravity than the remaining liquid of the magma, they settle downwards. As time progresses, different minerals crystallise from the magma. This process is named magma differentiation.

34 5.3. Classification of igneous rocks Source: Geology for Civil Engineers A.C.McLean, C.D. Gribble

35 5.3. Classification of igneous rocks Source: Geology for Civil Engineers A.C.McLean, C.D. Gribble

36 5.3. Classification of igneous rocks commenest mineral volcanic (extrusive) hypabyssal plutonic (intrusive) acid Quartz Orthoclase Oligoclase intermediate little or no Quartz Orthoclase Plagioclase basic no Quartz Plagioclase Muscovite Biotite Biotite Biotite Hornblende Hornblende Hornblende Augite Augite Augite Rhyolite Quartz Porphyries Orthoclase Porphyries Plagioclase Porphyries Olivine Trachyte Andesite Basalt Granite Syenite Diorite Dolerite Gabbro

37 5.3. Classification of igneous rocks Texture of igneous rocks crystalline texture Medium-grained rock Coarse-grained rock Fine-grained rock Source: Internet

38 5.3. Classification of igneous rocks Texture of igneous rocks glassy texture Source: Internet

39 5.3. Classification of igneous rocks Texture of igneous rocks porphyfiritic texture Extrusive rock Intrusive rocks Source: Internet

40 5.3. Classification of igneous rocks Texture of igneous rocks vesicular and amigdaloidal texture Source: Internet

41 5.3. Classification of igneous rocks Texture of igneous rocks pegmatitic texture Source: Internet

43 Theme 6. Sedimentary rocks 6.1. Sedimentary rocks formation 6.2. Classification of sedimentary rocks 6.3. Features of sedimentary rocks

44 6.1. Sedimentary rocks formation Sedimentary rocks are formed from the solid debris and the dissolved mineral matter produced by: -the mechanical and chemical weathering of preexisting rocks, -or from the skeletal material of dead plants and animals.

45 6.1. Sedimentary rocks formation The processes involved in the disintegration of rocks by weathering and erosion, and the transport of these products to the place where they are deposited, are all very important. The deposits of sedimentary rocks recently formed are the natural material encountered and dealt with in nearly every shallow excavation. Source: Internet

The nature of a sedimentary rock, and its position in a scheme of rock classification, are partly

46 6.1. Sedimentary rocks formation Sedimentary rocks were once sediments, and so they are records of the conditions at Earth's surface when and where the sediments were deposited. The nature of a sedimentary rock, and its position in a scheme of rock classification, are partly dependent on these original conditions of transport and deposition. Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

47 According to the type of environment in which it accumulated there are: -continental deposit; -intermediate deposit; -marine deposit Sedimentary rocks formation Source: Internet

or adjacent to volcanic arcs, rift valleys, or collisional mountains.

48 6.1. Sedimentary rocks formation Sedimentary rocks also reveal former plate tectonic events and processes by their presence within or adjacent to volcanic arcs, rift valleys, or collisional mountains. Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

49 6.1. Sedimentary rocks formation Sediments, and the sedimentary rocks formed from them, are produced by the surface processes of the rock cycle. They form after rocks have been moved from Earth's interior to its surface by mountain building and before they are returned to Earth's interior by subduction. These processes involve a source area, where the sediment particles are created, and a sink area where they are deposited in layers.

50 6.1. Sedimentary rocks formation the sedimentary stages of the rock cycle Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

51 6.1. Sedimentary rocks formation Weathering is the general process by which rocks are broken down at Earth's surface to produce sediment particles. There are two types of weathering: -Physical weathering; -Chemical weathering. Source: Internet

52 6.1. Sedimentary rocks formation Erosion mobilizes the particles produced by weathering, most commonly by rainwater running downhill. Source: Internet

53 6.1. Sedimentary rocks formation Transportation occurs when currents of wind and water and the moving ice of glaciers transport particles to new locations sediment sinks downhill or downstream. Source: Internet

54 6.1. Sedimentary rocks formation Deposition(sedimentation) occurs when sedimentary particles settle out as winds die down, water currents slow, or glacier edges melt. These particles form layers of sediment on land or under the sea in sedimentary basins. Source: Internet

55 6.1. Sedimentary rocks formation Diagenesis refers to the physical and chemical changes (pressure, heat, and chemical reactions) by which sediments buried within sedimentary basins are lithified, or converted into sedimentary rocks. Source: Internet

56 6.2. Classification of sedimentary rocks The four major groups of sedimentary rocks are: -detrital (clastic) sedimentary rocks (which are formed from minerals or rock fragments derived from the breakdown of preexisting rocks); -chemical sedimentary rocks (which are formed from the precipitation of salts dissolved in water); -organic sedimentary rocks (which are formed from the skeletal remains of plants and animals); -limestones and dolomites (which are sedimentary rocks consisting of more than 50% carbonate, and can include chemical, clastic and biological material).

57 6.2. Classification of sedimentary rocks Source: Internet

58 6.2. Classification of sedimentary rocks Source: Internet

59 Source: Internet 6.2. Classification of sedimentary rocks

60 6.2. Classification of sedimentary rocks Source: Internet

61 6.2. Classification of sedimentary rocks Source: Internet

62 6.2. Classification of sedimentary rocks From an engineering perspective soilsgenerally refer to sedimentary materials that have not been cemented and have not been subjected to high compressive stresses.

63 6.2. Classification of sedimentary rocks Coarse-grained soils These include sands, gravels and larger particles. For these soils the grains are well defined and may be seen by the naked eye. The individual particles may vary from perfectly round to highly angular reflecting their geological origins.

64 6.2. Classification of sedimentary rocks Very Coarse-grained soils Coarse-grained soils Symbol /Type of soil Particle size (mm) LBo (large boulders) > 630 Bo (boulders) Co (cobbles) Gr (gravel) CGr (coarse gravel) MGr (medium gravel) FGr (fine gravel) Sa (sand) CSa (coarse sand) MSa (medium sand) FSa (fine sand) SR EN ISO :2004

65 6.2. Classification of sedimentary rocks

66 6.2. Classification of sedimentary rocks Fine-grained soils These include the silts and clays and have particles smaller than 63 µm. Silts These can be visually differentiated from clays because they exhibit the property of dilatancy. If a moist sample is shaken in the hand water will appear on the surface. If the sample is then squeezed in the fingers the water will disappear. Their gritty feel can also identify silts.

67 6.2. Classification of sedimentary rocks Fine-grained soils These include the silts and clays and have particles smaller than 63 µm. Clays Claysexhibit plasticity, they may be readily remouldedwhen moist, and if left to dry can attain high strengths

68 6.2. Classification of sedimentary rocks Symbol /Type of soil Particle size (mm) Si (silt) CSi (coarse silt) Fine-grained soils MSi (medium silt) FSi (fine silt) Cl (clay) SR EN ISO :2004

69 6.2. Classification of sedimentary rocks

70 6.3. Features of sedimentary rocks The composition of a sedimentary rock will depend on the source from which the waste material came, on the resistance, chemical and mechanical, of each component during transport, and on the distance travelled. The main constituents of detrital sedimentary rocks are fragments from pre-existing rocks and minerals. These may be fresh and unaltered, or may be alteration products of weathering (clay minerals). Quartz is the most common mineral. Some minerals in sedimentary rocks may be formed in the area of deposition: minerals precipitated from solution to form the chemical sedimentary rocks (calcite, dolomite and siderite, gypsum and anhydrite, chlorides, silica).

71 6.3. Features of sedimentary rocks The texture of sedimentary rocks is dependent on the sizes, shapes and arrangement of these fragments. The size of grains is an important textural feature. Thedegreeofroundnessofgrainsisrelatedtotheamount of abrasion suffered during transport, and hence to distance travelled from their source before deposition.

GLY 155 Introduction to Physical Geology, W. Altermann. Grotzinger Jordan. Understanding Earth. Sixth Edition

GLY 155 Introduction to Physical Geology, W. Altermann. Grotzinger Jordan. Understanding Earth. Sixth Edition Grotzinger Jordan Understanding Earth Sixth Edition Chapter 4: IGNEOUS ROCKS Solids from Melts 2011 by W. H. Freeman and Company Chapter 4: Igneous Rocks: Solids from Melts 1 About Igneous Rocks Igneous