1. Igneous Rocks

2. Summary 1. The Rock Cycle 2. Formation of Igneous Rocks 3. Classification of Igneous Rocks

3. The Rock Cycle Igneous Rock Solidification Magma Partial Melting Mantle Rock Fig 3.1 Geological Materials Transformation Processes

4. Formation of Magma How are rocks melted? 1. Heating 2. Depressurization 3. Partial Melting Where do rocks melt? Subduction zones (Silicic and Intermediate)

5. Mantle Plumes or Hot Spots Partial Melting Different rocks melt at different temperatures. Depending on the temperature, some rocks in the mixture may be liquidified and others might not.

6. Types of Igneous Rock Extrusive Fine grained rock that cooled quickly on the Earth’s surface.

7. Intrusive Course grained rock that cooled slowly under the surface. This is the most common type of rock. Also describe as Plutonic See Kehew, Fig 3-6

8. Classification of Igneous Rocks These classes of rock are based on the type of magma that cooled to create the rock. These are describe in terms of temperature, composition, viscosity, and pH level.

9. Silicic (a.k.a, felsic) Magmas Cool (<700 o C) Viscous (sticky, doesn’t flow easily) Gaseous (steam of H 2 O and C0 2 ) Silicic Rocks Usually intrusive, course-grained, Silicic (Granite) to Intermediate (Diorite). If extrusive, fine-grained rocks formed by explosive volcanoes Rhyolite or Andesite Volcanoes  Silicic Rocks

10. Intrusive Silicic Igneous Rock E.g., Granite (Silicic, Phaneritic): Crystallized (Solidified) Silicic Magma Poor in: Fe, Mg, Ca, (<20%) Rich in: Silica (>70%) Quartz Na Plagioclase Biotite

11. Mafic Rocks Mafic Magmas Hot (>1000 o C) Non-Viscous (runny, flows easily) “Dry” (no H 2 O or C0 2 ) Mafic Rocks Usually Extrusive, Fine-grained, Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Basalt Floods If Intrusive, course-grained mafic rocks are formed Gabbro. If intrusive, Dikes and Sills more common See Kehew, Fig 3-40

12. Mafic Volcanism, Hawaii Mantle Hot Spot Volcano See Kehew, 3-8

13. Hawaii 10.3 12.0 20.6 Midway 27.2 19.9 43.4 42.4 48.1 55.2 56.2 59.6 0-5 Current Plate Motion Hawaii A long chain of inactive volcanoes Island ages, millions of years

14. Shield Volcanoes Mafic Magma Low-viscosity Non-explosive eruptions Gentle slopes Covering large areas

15. Types of Eruptions (Mafic Volc.) Types of Eruptions Lava floods Lava fountains Fissure eruptions Rock Textures (Table 3-1) Aphanitic Porphyritic Vesicular Glassy (Obsidian)

16. Surface Textures (Extrusive, Mafic Rocks) Ahah (Rubbley) Mostly solid when flowing Pahoehoe (Ropey) mostly liquid when flowing)

17. Mafic Sill: Intruded between layers Mafic magma is less viscous and hotter so Does not form plutons but Cuts along layers (Sills) or even across layers (Dikes) Also Baked Zones of adjacent country rock and Chill Zones within the intrusion

18. Igneous Rock Classification Intrusive (Plutonic) Extrusive (Volcanic) Mineral Percentage Continental Crust Oceanic Mantle Crust

19. Igneous Rock Classification Silicic Intermediate Mafic Granite Diorite Gabbro Rhyolite Andesite Basalt (Porphyritic) Intrusive Extrusive

20. 1200 o C 1000 o Bowen’s Reaction Series Two series of minerals formed during crystallization of magma Intrus. Extrus. Gabbro Basalt Diorite Andesite Granite Rhyolite Low Silica Magma High Silica Magma Frame- Double Single Isolated work Sheet Chain Chain Temperature of Crystallization 750 o

21. Bowen’s Reaction Series Illustrates the relationship between the cooling magma and the crystallization of the minerals contained in the rock. Rocks on the right side of this chart are rich in calcium and sodium Rocks on the left side represents iron-rich minerals. They cool and create quartz.

22. Terminology Felsic – silicate minerals, magmas and rocks enriched in lighter elements for oxygen, aluminum, sodium, and silicon. Aphanitic – dark-coloured rock where the grains are so fine they cannot be seen by the naked eye.

23. Terminology Mafic – iron and magnesium enriched minerals are found in these rocks. They are dark in colour. Phaneritic – Grains in the rock can be seen by the naked eye.

24. Types of Igneous Rocks Granite Acidic Very pale Coarse-grained Intrusive, felsic Can be pink to dark gray.

26. Rhyolite Extrusive form equivalent to Granite Fine grained. Make up Mt Fuji.

27. Andersite Intermediate rock Less quartz that granite, thus has a darker colour. Both sizes of grains. Not as acidic as Granite. Found in the Andes Extrusive

28. Diorite Coarse grained Grey to dark gray in colour Intrusive.

29. Basalt Black to gray in colour (dark) Fine-grained Mafic Found in Ireland (Giants Causeway) and Hawaii. Basic Extrusive

31. Gabbro Dark Basic Intrusive Coarse-grained Part of the oceanic crust

32. Peridotite Ultrabasic Rare and part of the mantle Course grained Green in colour

33. Obsidian Glassy (volcanic glass) Can be green or black Extrusive

35. Pumice Glassy (Frothy) Light to dark in colour depending on its impurities. Solidified foam Extrusive

38. Homework P. 106 #1-3 P. 113 #1-4

39. Rocks in the Collection 1. Grantie 2. Rhyolite 3. Andesite 4. Obsidian 5. Pumice 6. Basalt 7. Gabbro 8. Anorthosite 9. Diorite 10. Scoria 11. Syenite 12. Peridotite