Metamorphism Metamorphic Rocks & the Rock Cycle Types of Metamorphism Patterns of Metamorphic Grade Mineral Assemblages in Metamorphic Rocks METAMORPHIC ROCKS Metamorphic Textures Index Minerals Phase Diagrams Factors affecting type of metamorphic rock Metamorphic Rocks By the end of this lesson you will be able to: • Classify metamorphic rocks into two groups • Explain the concept of metamorphic grade • Describe the causes of the different types of metamorphism • Explain how metamorphic reactions occur during metamorphism Metamorphic Rocks List down as many metamorphic rocks as you can remember: • spotted rock • hornfels • marble • metaquartzite • slate • phyllite • schist • gneiss Metamorphic Rocks Which ones are foliated and which ones are unfoliated? • spotted rock • hornfels • marble unfoliated • metaquartzite • slate • phyllite • schist • gneiss foliated Metamorphic Rocks Which can be formed due to contact metamorphism & which can be formed due to regional metamorphism? • spotted rock • hornfels • marble unfoliated Contact metamorphism • metaquartzite • slate • phyllite • schist foliated Regional metamorphism • gneiss • mylonite/fault breccia Dynamic metamorphism Metamorphic Processes • Mineral alignment • Recrystallisation • New minerals formed from metamorphic reactions Metamorphic Reactions Low temperature minerals Change in stability High temperature minerals PROGRADE REACTION reactants temp by 550 °C products (increase in metamorphic grade) muscovite + quartz = feldspar + sillimanite + water vapour products temp by 550 °C reactants (decrease in metamorphic grade) RETROGRADE REACTION Low temperature minerals Change in stability High temperature minerals Metamorphic Reactions Low temperature minerals Change in stability High temperature minerals PROGRADE REACTION reactants temp by 550 °C products Escapes from rock (increase in metamorphic grade) muscovite + quartz = feldspar + sillimanite + water vapour Metamorphic mineral Metamorphic Texture • Recrystalline • Interlocking • Coarse-grained • Foliated • Gneissose banding Metamorphic Minerals • Quartz • Feldspar • Hornblende • Augite Metamorphic Rock Identification Checklist for describing metamorphic rocks A – H: 1.Texture • Recrystalline • Interlocking • Grain size (coarse >2mm, medium 2mm-0.05mm, fine [...]... Describe the causes of the different types of metamorphism Write the cause of the metamorphic change next to the types of metamorphism below Dynamic metamorphism - Localised deformation along fault zones Contact metamorphism - Heat from igneous intrusions Regional metamorphism - Heat & pressure due to orogenesis • Explain how metamorphic reactions occur during metamorphism Use clay & its polymorph andalusite... describe the metamorphic textures associated with the different types of metamorphism • Explain how these metamorphic textures form Dynamic Metamorphism large, angular fragments (fault breccia) fine-grained matrix (fault gouge) Mylonite Fault Breccia elongation of minerals foliation Contact Metamorphism A B E G D C F Contact Metamorphism A B F E D C H Interlocking quartz, feldspar & mica grains (granoblastic)... Describe the differences between the three types of metamorphism Metamorphic Rocks The intended learning outcomes from last lesson were to be able to: • Classify metamorphic rocks into two groups • Explain the concept of metamorphic grade • Describe the causes of the different types of metamorphism • Explain how metamorphic reactions occur during metamorphism • Classify metamorphic rocks into two... different types of metamorphism • Explain how these metamorphic textures form • Identify & describe the metamorphic textures associated with the different types of metamorphism 2mm Thin section of a metamorphic rock 1 Describe the texture of this rock 2 Name this rock 3 How did this rock form? • Identify & describe the metamorphic textures associated with the different types of metamorphism Thin section... metaquartzite 4 Phyllite • migmatite 5 Gneiss 6 Migmatite • Classify metamorphic rocks into two groups Put these metamorphic rocks into a Venn diagram to show whether they are formed by contact metamorphism or regional metamorphism, or by both • • • • • • • • • • • schist mylonite fault breccia spotted rock hornfels slate phyllite marble gneiss metaquartzite migmatite Marble Spotted rock Metaquartzite Hornfels... stability field Phase boundary Sillimanite stability field Andalusite stability field Al2SiO5 All have same formula but each mineral has a different crystal structure = POLYMORPH Metamorphism & Metamorphic Reactions 1 Define metamorphism 2 What does the term metamorphic grade mean? 3 Why do metamorphic reactions occur? 4 What do these reactions typically form? 5 Explain prograde and retrograde reactions... • Clay • Chlorite Mica Metamorphic Texture • Recrystalline • • • • • Interlocking Medium-grained Foliated Schistosity Porphyroblastic Metamorphic Minerals • Quartz • Feldspar • Mica • Garnet Regional Metamorphism Granite Gneissose Banding (foliation) Migmatite Gneiss Increasing metamorphic grade Metamorphic Texture • Recrystalline • Interlocking • Coarse-grained • Foliated • Gneissose banding Metamorphic... Metamorphic Minerals • Quartz • Feldspar • Mica • Sillimanite Metamorphic Texture • Recrystalline • • • • Interlocking Medium-grained Granoblastic Non-foliated Metamorphic Minerals • Calcite Regional Metamorphism Schistosity (foliation) Schist Slaty cleavage (foliation) Clay & mica Phyllite Slate Increasing metamorphic grade Metamorphic Texture • Partially recrystalline • Fine-grained • Foliated •