1. Continued intro & classification

2. Updates Lab starts this week Monday 9.30-12.20 lab, Wednesday 2.30-5.30 lab Today’s topics: 1a. Heat, pressure and the geotherm 1b. Geotherm and melting 1c. Different ways to melt 2. Classification of igneous rocks

3. The Pressure Gradient P increases =  gh Nearly linear through mantle –~ 30 MPa/km –  1 GPa at base of ave crust Core:  incr. more rapidly since alloy more dense 1020 30 0 1000 2000 3000 4000 5000 6000 Depth (km) Pressure (GPa) 40 Mantle Core Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science.

4. Heat

5. Heat Sources in the Earth

6. The Geothermal Gradient Crust Mantle Outer Core Temperature(K) 0510 1000 2000 3000 4000 5000 6000 Depth (km) S waves P waves Inner Core Lithosphere Astheno- sphere Solid Liquid Meso- sphere S waves

7. Rocks at different depth: change in P & T: Phase change TT P P

8. Atoms have a “choice” as to how they want to arrange themselves in a phase

9. Plate Tectonic - Igneous Genesis ? ? ? ? 600 km 400 200 km Continental Crust Oceanic Crust Lithospheric Mantle Sub-lithospheric Mantle Source of Melts 15 3 4 6 7 2

10. Geotherm and solidus: how to melt

11. Processes That Form Magma

12. Processes that form magma and rock

13. Environments of Magma Formation

18. Partial Melting: The Origin of Basalt and Granite Asthenosphere 40% Silica Melting Basaltic magma = 50% silica (1100 o C) Forms the rock basalt

19. Partial Melting: The Origin of Basalt and Granite Continental Crust (Mainly low melting point minerals such as quartz, feldspar, mica) Melting Granitic magma ~ 70% silica (700-900 o C) Forms granite (a mixture of quartz and feldspar)

20. Classification of Igneous Rocks Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.

21. Classification of Igneous Rocks Figure 2-1b. Method #2 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall. 100 0 %X

26. Classification of Igneous Rocks Figure 2-2. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.OlivineClinopyroxene Orthopyroxene Lherzolite Harzburgite Wehrlite Websterite Orthopyroxenite Clinopyroxenite Olivine Websterite Peridotites Pyroxenites 90 40 10 Dunite (c)

27. Classification of Igneous Rocks Figure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.

28. Classification of Igneous Rocks Figure 2-5. Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298. Ash (< 2 mm) Blocks and Bombs (> 64 mm) Lapilli Tuff Lapilli -Tuff Breccia Tuff Lapilli- stone (b) 30 70 Pyroclastic Breccia or Agglomerate Lapilli (2-64 mm)