Metamorphism Metamorphic Rocks the Rock Cycle Types of

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

Phase Diagrams Kyanite stability field. Phase boundary Sillimanite stability field. Andalusite stability field. Al 2 Si. O 5 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 using the muscovite + quartz metamorphic reaction. 6. In reality most metamorphic reactions do not return to their original starting point. Why? 7. Metamorphic reactions are slow. What could cause them to speed up and how is this done? 8. What is a phase diagram and what does it show? (note: explain these words phase/phase transformation/ stability field - using the kyanite, andalusite & sillimanite example) 9. Why might a mineral be termed metastable? 10. 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 groups. Put these metamorphic rocks into 2 groups – unfoliated & foliated. Unfoliated • schist 1. Fault breccia • mylonite 2. Spotted rock • fault breccia 3. Hornfels 4. Marble • spotted rock 5. Metaquartzite • hornfels • slate Foliated • phyllite 1. Schist • marble 2. Mylonite • gneiss 3. Slate • 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 Contact Schist Slate Phyllite Gneiss Migmatite Regional Fault Breccia Mylonite Dynamic

• Explain the concept of metamorphic grade. Put these regional metamorphic rocks into a linear order to show increasing metamorphic grade. • schist • slate • phyllite • migmatite • gneiss slate phyllite schist gneiss Increasing metamorphic grade migmatite

• 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 to show metamorphic reactions occur. Prograde reaction Clay Andalusite Retrograde reaction

Metamorphic Rocks By the end of this lesson you will be able to: • Identify & 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) F Cordierite minerals (porphyroblastic) Recrystallised mica minerals (unfoliated) E G Interlocking coarse calcite crystals (granoblastic) H Partially recrystallised clay minerals (unfoliated) Interlocking quartz grains (granoblastic) D B

Metamorphic Texture • Recrystalline • Interlocking • Medium-grained • Granoblastic • Non-foliated 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 • Slaty cleavage • (porphyroblastic) Metamorphic Minerals • Quartz • Clay • Mica • Pyrite (porphyroblasts)

Metamorphic Texture • Partially recrystalline • Fine-grained • Foliated • Slaty cleavage Metamorphic Minerals • Quartz • 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 Minerals • Quartz • Feldspar • Hornblende • Augite

Metamorphic Rock Identification Checklist for describing metamorphic rocks A – H: 1. Texture • Recrystalline • Interlocking • Grain size (coarse >2 mm, medium 2 mm-0. 05 mm, fine <0. 05 mm) • Granoblastic • Porphyroblastic • Foliated (slaty cleavage, schistosity, gneissose banding) 2. Mineralogy • Quartz, feldspar, hornblende, augite • Chlorite mica, muscovite mica, biotite mica, andalusite, garnet

A. B. C. D. E. F.

Metamorphic Rocks The intended learning outcomes from last lesson were to be able to: • Identify & describe the metamorphic textures associated with the different types of metamorphism. • Explain how these metamorphic textures form.

• Identify & describe the metamorphic textures associated with the different types of metamorphism. 2 mm 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 of a metamorphic rock Cordierite Andalusite Clay 1. Describe the texture of this rock. 2. Name this rock. 3. How did this rock form?

Metamorphic Rocks By the end of this lesson you will be able to: • Interpret pressure-temperature graphs. • Recognise the type of metamorphism from the patterns of changing metamorphic grade. • Use index minerals to indicate the direction of increasing metamorphic grade & the location of metamorphic mineral isograds.

P-T Graph Spotted Rock Hornfels CONTACT METAMORPHISM RE GI O Sla te nite lo My ISM RPH MO ETA C M MI NA DY cia rec lt-b Fau NA LM ET AM OR Ph PH yll IS ite M Sc h ist Gn eis s Ig ne ous

Metamorphic Mineral Isograds Index minerals North Kyanite zone Staurolite zone me I ta ncr mo e rp asi hi ng c gr ad e Key: Kyanite Staurolite Garnet Biotite Garnet zone Chlorite Biotite zone Chlorite zone isograd

Contact Metamorphism UNALTERED COUNTRY ROCKS Metamorphic aureole Increasing metamorphic grade andalusite cordierite GRANITE sillimanite • concentric metamorphic zones • associated with a batholith • index minerals (andalusite, cordierite & sillimanite) • hornfels at contact (granoblastic texture) Increasing metamorphic grade

Regional Metamorphism • linear metamorphic zones • not associated with a batholith • index minerals (muscovite mica, chlorite mica, biotite mica, garnet, staurolite, kyanite & sillimanite) • foliated textures (slaty cleavage, schistosity & gneissose banding) Increasing metamorphic grade

Phase Diagrams Using the phase diagram: 1. Which mineral is stable at 700°C and 400 Mpa? 2. At what temperature do andalusite & sillimanite coexist in equilibrium at a pressure of 200 Mpa? 3. Which mineral is high temperature, low pressure metamorphic mineral? 4. Which mineral is high pressure, low pressure?

Metamorphic Rocks By the end of this unit you should now 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 processes occur during metamorphism. • Identify & describe the metamorphic textures associated with the different types of metamorphism. • Explain how these metamorphic textures form. • Name metamorphic rocks from their metamorphic texture. • Interpret P-T graphs and phase diagrams. • Recognise the type of metamorphism from the patterns of changing metamorphic grade. • Use index minerals to indicate the direction of increasing metamorphic grade & the location of metamorphic mineral isograds.