Geology in the news presentation by Michael Zara. Classification of igneous rocks. Nature and classification of igneous

1. In Lecture Today: • Geology in the news presentation by Michael Zara. • Classification of igneous rocks. • Nature and classification of igneous plutons. • Origins of magma and relationship to plate tectonic setting.

2. Naming Igneous Rocks Igneous rocks are classified by their: • Texture • Mineral Composition depends on: how fast/slow magma cools depends on: chemical makeup of parent magma

4. Cooling rate in igneous rocks is determined by cooling rate, which is in turn, determined by proximity to the surface. Fig. 6.15 W. W. Norton

5. Coarse-grained or “phaneritic” Fine-grained or “aphanitic” Fig. 6.16a Photod by Dr. Kent Ratajeski, Dept. Geology and Geophysics, University of Wisconsin, Madison 0 Mm 0.5 0 Mm 0.5 Grain size in igneous rocks is determined by cooling rate.

7. Fig. 6.14cd Stephen Marshak

8. Fig. 6.12 W. W. Norton

9. Fig. 6.19 Stephen Marshak

10. magnesium + ferrum feldspar + silica (quartz) Naming Igneous Rocks Basic magma types: • Mafic • Felsic High in Mg, Fe. Dark, dense High in Si. Lighter, less dense

11. Naming igneous rocks Zooming in: Basalt volcanic Aphanitic M a f i c Gabbro plutonic Phaneritic

12. Fig. 6.17a Figure 6.17 Text, page 155

13. Naming igneous rocks Zooming in Andesite volcanic Aphanitic In t e r m e d i a t e plutonic Diorite Phaneritic

14. Fig. 6.17a Figure 6.17 Text, page 155

15. Granite Rhyolite Naming igneous rocks Zooming in: volcanic Aphanitic F e l s i c plutonic Phaneritic

16. Fig. 6.17a W. W. Norton. Mineral proportions after Hamblin and Howard.

17. Naming Igneous Rocks: Ultramafic: ~ 40% Silica (less than gabbro/basalt, with more Fe and Mg). Upper mantle plutonic igneous rocks, “peridotite” or “dunite”. (Near Globe, AZ)

18. Naming Igneous Rocks: Glassy Volcanic Rocks Volcanic Glass Obsidian F e l s i c Volcanic “Froth” Pumice

19. Bowen’s Reaction Series Magmas don’t crystallize all at once! • Minerals with the highest melting temperatures come out first, followed by minerals with successively lower melting temperatures. • The sequence of silicate mineral crystallization in magmas was first studied by University of Chicago geologist, N.L Bowen, in the 1920’s.

20. Bowen’s Reaction Series Box 6.2 Text, page 145. Fig. 6.06 W. W. Norton This diagram shows the order in which silicate minerals crystallize from magma and how that Relates to mineral content and rock type.

21. Basaltic lavas are very fluid and travel far from the vent to produce volcanoes with low profiles.

22. Basalt eruptions on land produce flows that travel great distances. Fig. 6.20a W. W. Norton Columbia River basalts

23. Basaltic lavas erupted under water produce “pillows” Fig. 6.21a W. W. Norton

24. Fig. 6.21b Stephen Marshak

25. Fig. 6.21c © Peter Kresan

26. Products of volcanic eruptions includes more than just lava flows! Fig. 6.02 W. W. Norton

27. Explosive Volcanic Eruptions • Violently explosove volcanic • eruptions produce: • Rock fragments • (all sizes) • Finely-fragmented ash • Molten bombs These accumulate to form: Pyroclastic Volcanic Rocks

29. Fig. 6.08a W. W. Norton

30. Naming Igneous Rocks • Pyroclastic volcanic rocks: Composed of rock fragments ejected during eruptions. Types include: “Tuff”: Composed of ash, finely fragmented volcanic rock. Welded tuffs form when ash is so hot, it deforms plastically. Scoria: Red or black, frothy lava, denser than pumice. Volcanic Breccia: Coarse, angular rock fragments, usually in an matrix of fine to coarse ash.

31. Pumice: Formed by the quenching of gas-charged lava. Obsidian: Volcanic glass. Formed by quenching of lava. Volcanic ash: Lithifies to form a volcanic tuff.