1. ESCI 101: Lecture The Rock Cycle & Igneous Rocks February 23, 2007 Copy of this lecture will be found at: http://www.owlnet.rice.edu/~esci101 With Some Graphics from Press et al., Understanding Earth, 4th Ed. (Copyright © 2004 by W. H. Freeman & Company) Enchanted Rock

2. The Rock Cycle -Melting & Intrusion -Solidification of melt -Mountain Building -Uplift & Exposure -Weathering -Erosion & Transport -Deposition & Burial -Metamorphism -Melting & Intrusion Fig 4.9

3. ESCI 101 - “Pop” Homework #4 (Due Wednesday, 2/28/07, 5 PM) Assignment: -For this exercise, trace the alternate pathway of the rock cycle: (1) igneous rocks are formed, (2) become metamorphosed, (3) exposed, and (4) evolve into sandstone. Describe the main processes and events that might take place at each step along the way, and the plate tectonic settings in which they are likely to occur. (Your answer should not exceed one page.) -See the accompanying plot on the following page.

4. Pop-HW#4 An Alternate Rock Cycle -Melting & Intrusion -Solidification of melt -??? --> Sandstone Fig 4.9 X X X

5. (a) The Rock Cycle Fig 4.9 E.g., Convergent Plate Boundary -Subducting slab -Mantle melting -Bouyant rise of melt

6. (b) The Rock Cycle Fig 4.9 E.g., Convergent Plate Boundary - Solidification of melt - Volcanic activity Intrusive rocks Extrusive rocks

7. Genetic Classification of Igneous Rocks Granite Gabbro IntrusiveIntrusive: crystallized from slowly cooling magma intruded within the Earth’s crust; e.g. granite, gabbro.

8. Rock Texture Fig. 5.1 Intrusive: Course-grained, interlocking

9. Genetic Classification of Igneous Rocks Rhyolite Basalt ExtrusiveExtrusive: crystallized from rapidly cooling magma extruded on the surface of the Earth as lava, …

10. Rock Texture Fig. 5.1 Intrusive: Course-grained, interlocking Extrusive: Fine-grained, discrete crystals, often glassy

11. Genetic Classification of Igneous Rocks ExtrusiveExtrusive: … or erupted as pyroclastic material, i.e., fragmented pieces of magma ejected and cooled in the air. Pumice Scoria Ash

12. Formation of Igneous Rocks Pyroclasts Extrusive Intrusive Porphyry: partially crystalline Fig. 5.3

13. Process of Intrusion Intrusive rocksIntrusive rocks fracture and cross-cut the “country rock”. Igneous rocks cool quickly near the intrusive contacts, and cause contact metamorphism. Fig. 5.2

14. Composition and Classification of Igneous Rocks Chemistry: e.g. % SiO 2 Mineralogy: e.g. –Felsic - high silica –Intermediate - intermediate silica –Mafic - low silica –Ultramafic - very low silica (continental crust) (oceanic crust) (mantle)

15. Felsic Igneous Rocks: Igneous rocks rich in minerals high in silica and low in iron and magnesium. They include: GraniteRhyolite

16. Mafic Igneous Rocks: Igneous rocks rich in minerals low in silica and high in iron and magnesium. They include: GabbroBasalt

17. Common Minerals

18. Intermediate Igneous Rocks: Igneous rocks intermediate in composition between felsic and mafic igneous rocks. They include: Granodiorite (Dacite) Diorite (Andesite)

19. Ultramafic Igneous Rocks: Igneous rocks with very low silica content, consisting dominantly of mafic minerals. The most common ultramafic rock is: Peridotite (no extrusive equivalent)

20. Fig. 5.4

21. Compositional Classification Granite Quartz Orthoclase Biotite Plagioclase

22. Compositional Classification Granite Granodiorite Quartz Amphibole Plagioclase

23. Compositional Classification Granite Granodiorite Diorite Plagioclase Amphibole

24. Compositional Classification Granite Granodiorite Diorite Gabbro Plagioclase Pyroxene

25. Compositional Classification Granite Granodiorite Diorite Gabbro Peridotite Pyroxene Olivine

26. Table. 5.2 Felsic IntermediateMafic GraniteGranodioriteDioriteGabbro Basalt AndesiteDaciteRhyolite Viscosity Melting Temperature

27. How do magmas form? When rocks melt (or partially melt). When do rocks melt? When the temperature exceeds the melting point of the rock or some minerals within the rock.

28. Factors that Affect Melting of Minerals (and Rocks) CompositionComposition: Felsic minerals melt at lower temperatures than mafic minerals PressurePressure: Increased pressures raises melting points Water ContentWater Content: Increased water content lowers melting points

29. The Formation of Magma Chambers Partial melting Less dense magma Magma rises Magma pools in magma chamber Some minerals melt before others. Results in mixture of melt and solid. Melt is less dense than solid. Low density minerals tend to melt first. Buoyant melt migrates through rock pores and fractures.

30. - Covers 15,400 mi 2 !! - Composition - Granite - Monzonite - Granodiorite - Diorite - Even Gneiss - All in one “magma chamber”

31. Why do magmas have such different compositions - even when derived from a single “parent magma” e.g., granite, granodiorite, diorite

32. Magma Differentiation The process by which rocks of various compositions can arise from a uniform parent magma Occurs because different minerals crystallize at different temperatures (i.e., the opposite of partial melting) Tune in Wednesday for the exciting conclusion!