Chapter 6 Section 1 PDF

24/10/20 Chapter 6 Section 3 What are the different types and causes of metamorphism? 1  24/10/20 How are rocks classified using the rock cycle?...

24/10/20 Chapter 6 Section 3 What are the different types and causes of metamorphism? 1  24/10/20 How are rocks classified using the rock cycle? 2  24/10/20 When rocks are baked by heat of molten magma or squeezed by the movements of huge tectonic plates or by the pressure of overlying thick succession of rocks They are altered or changed beyond their recognition, i.e. change in Chemical composition, texture and structure Fig. Ta 7.1 3  24/10/20 Recognizing Metamorphic Rock When high temperature and pressure combine and change the texture, mineral composition, or chemical composition of a rock without melting it, a metamorphic rock forms. Copyright © McGraw-Hill Education Metamorphic Rocks Recognizing Metamorphic Rock The high temperatures required for metamorphism are ultimately derived from Earth’s heat, either through deep burial or from nearby igneous intrusions. The high pressures required for metamorphism come from deep burial or from compression during mountain building. Metamorphic Rock Copyright © McGraw-Hill Education Metamorphic Rocks 4  24/10/20 Compressive Stress Shearing min max inter Directed Stress Uniform Stress 5  24/10/20 Granite Granite-Gneiss Recognizing Metamorphic Rock Metamorphic minerals During metamorphism, the minerals in a rock undergo solid-state alterations, which means that they change into new minerals that are stable under the new temperature and pressure conditions. Copyright © McGraw-Hill Education Metamorphic Rocks 6  24/10/20 Effects of Metamorphism Mineralogical: - change minerals to reflect new P-T (equilibrium) conditions. Recrystallization: change of existing crystal size and shape to form layers (e.g., shale to schist), interlocking crystals (e.g., sandstone to quartzite). Recombination: Recombination of elements in pre-existing minerals to form stable new ones. Addition/subtraction of ions common when fluid is present. Recognizing Metamorphic Rock Metamorphic textures Foliated metamorphic rocks are characterized by layers and bands of minerals caused by high pressure during metamorphism. Foliation develops when pressure is applied from opposite directions. The foliation develops perpendicular to the pressure direction. Copyright © McGraw-Hill Education Metamorphic Rocks 7  24/10/20 Development of Foliation Recognizing Metamorphic Rock Metamorphic textures Nonfoliated metamorphic rocks are composed mainly of minerals that form with blocky crystal shapes. Copyright © McGraw-Hill Education Metamorphic Rocks 8  24/10/20 Recognizing Metamorphic Rock Metamorphic textures Increasing grain size parallels changes in composition and development of foliation. Grain size is not a factor in nonfoliated rocks. Copyright © McGraw-Hill Education Metamorphic Rocks Grades of Metamorphism Different combinations of temperature and pressure result in different grades of metamorphism. Each of the grades—low, intermediate, and high—is associated with a different suite of minerals and textures. Copyright © McGraw-Hill Education Metamorphic Rocks 9  24/10/20 Grades of Metamorphism Metamorphism of shale results in the formation of minerals that provide the wide variety of color observed in slate. Copyright © McGraw-Hill Education Metamorphic Rocks Metamorphic Grade: Degree of parent rock alteration, mostly dependent on increasing temperature for increasing grade Prograde: SLATE - phyllite-schist-gneiss- migmatite (melting). SLATE: oriented clay minerals allows the rock to be easily cleaved. 10  24/10/20 Types of Metamorphism Regional metamorphism When high temperature and pressure affect large regions of Earth’s crust, they produce large belts of regional metamorphism, ranging from low grade to high grade. Regional metamorphism results in changes in minerals and rock types, plus folding and deforming of the rock layers that make up the area. Copyright © McGraw-Hill Education Metamorphic Rocks Types of Metamorphism: Meteorite impact – sudden and intense deformation. 11  24/10/20 Types of Metamorphism: High-pressure polymorph of quartz – coesite – can form. Impact melt can form. Lots of rock fragmentation & mineral deformation. Moon – no atmosphere so lots of meteorite impacts (micro and macro!). Produces regolith, rock flour, impact melt, breccias. Types of Metamorphism Contact metamorphism When molten material, such as that in an igneous intrusion, comes in contact with solid rock, a local effect called contact metamorphism occurs. High temperatures and moderate-to-low pressure form mineral assemblages that are characteristic of contact metamorphism. Copyright © McGraw-Hill Education Metamorphic Rocks 12  24/10/20 SCHIST: strongly foliated with visible micas & feldspars. Prograde: slate-phyllite-SCHIST-gneiss-migmatite. 13  24/10/20 Garnet Schist GNEISS: strongly banded rock with dark bands of micas & pyroxenes and light bands of feldspars and quartz. Prograde: slate- phyllite-schist- GNEISS- migmatite. 14  24/10/20 Gneissose Banding 0065 15  24/10/20 Types of Metamorphism Hydrothermal metamorphism When very hot water reacts with rock and alters its chemical and mineral composition, hydrothermal metamorphism occurs. Chemical changes are common during contact metamorphism near igneous intrusions and active volcanoes. Copyright © McGraw-Hill Education Metamorphic Rocks 16  24/10/20 Economic Importance of Metamorphic Rocks and Minerals Many of the economic mineral resources that make the modern way of life possible are produced by metamorphic processes. Copyright © McGraw-Hill Education Metamorphic Rocks Economic Importance of Metamorphic Rocks and Minerals Metallic mineral resources Although deposits of pure metals are occasionally discovered, many metallic deposits are precipitated from hydrothermal solutions. Copyright © McGraw-Hill Education Metamorphic Rocks 17  24/10/20 Economic Importance of Metamorphic Rocks and Minerals Nonmetallic mineral resources Many nonmetallic resources are also produced by metamorphism, including talc, asbestos, and graphite. Copyright © McGraw-Hill Education Metamorphic Rocks Marble Mine 18  24/10/20 The Rock Cycle The three types of rock are grouped according to how they form. Igneous rocks crystallize from magma; Sedimentary rocks form from cemented or precipitated sediments; and Metamorphic rocks form from changes in temperature and pressure. Copyright © McGraw-Hill Education Metamorphic Rocks The Rock Cycle Any rock can be changed into any other type of rock. This continuous changing and remaking of rocks is called the rock cycle. The rock cycle shows some of the series of changes rocks undergo above and beneath Earth’s surface. Copyright © McGraw-Hill Education Metamorphic Rocks 19