Igneous Rocks

1. Igneous Rocks

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

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

4. Formation ofMagma • How are rocks melted? • 1. Heating • 2. Depressurization • 3. Partial Melting • Where do rocks melt? • Subduction zones (Silicic andIntermediate)

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

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 Rocks • Silicic (a.k.a, felsic) Magmas • Cool(<700oC) • Viscous(sticky, doesn’t flow easily) • Gaseous(steam of H2O and C02) • Silicic Rocks • Usuallyintrusive, course-grained, Silicic (Granite) to Intermediate (Diorite). • If extrusive, fine-grained rocks formed by explosive volcanoes Rhyolite or Andesite Volcanoes

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

11. Mafic Rocks • Mafic Magmas • Hot(>1000oC) • Non-Viscous(runny, flows easily) • “Dry”(no H2O or C02) • Mafic Rocks • UsuallyExtrusive, 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. HawaiiA long chain of inactive volcanoes • Island ages, millions of years Convergent Plate Boundary 59.6 56.2 48.1 Current Plate Motion 55.2 Midway 27.2 19.9 43.4 42.4 Hawaii 20.6 0-5 12.0 10.3

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 CrustOceanicMantle Crust

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

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

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 • Grantie • Rhyolite • Andesite • Obsidian • Pumice • Basalt • Gabbro • Anorthosite • Diorite • Scoria • Syenite • Peridotite