Elements: Introduction

1. Elements: Introduction

2. Periodic table

4. Behavior of elements: Goldschmidt’s classification Elements divided into four broad categories: Lithophile • generally found within crust and mantle • Concentrate in silica-rich melts

5. Siderophile • Generally concentrate in iron-rich melt Chalcophile • Generally occurs with sulfur Atmophile • Generally found in the atmosphere

9. Reference book: This Dynamic Earth by USGS http://pubs.usgs.gov/publications/text/dynamic.html Plate tectonics: Mixing crust and mantle

10. Plate tectonics: Mixing crust and mantle Two common views of mantle convection: Whole mantle convection Stratified convection

11. Plate tectonics and Earth Materials: Why Bother? • Pressure and heat from convergent boundaries metamorphoses, melts, deforms, chemically changes rocks/minerals • Divergent boundaries bring up new materials, subduction zones recycle old materials, economic deposits • Hotspots, new land • Erosion and weathering expose new materials

12. Oceanic trenches Mid-oceanic ridges

13. Earth’s crust and mantle are rich in lithophile elements (those that concentrate in a silica-rich melt) All types of magma contain silicon and oxygen as silica (SiO2) in different amounts(~40 -70%) Igneous rocks are almost exclusively made up of SILICATE minerals Containing the (SiO4)-4 anionic group

14. Soooo… what is an ANION and what is an ANIONIC group? Return of the specter of chemistry

15. Silicate minerals • Contain the (SiO4)-4 anionic group • Make up 95% of the continental crust, and almost all of the oceanic crust and the mantle

16. SILICON-OXYGEN TETRAHEDRON (SiO4)-4 anionic group is commonly referred to as the SILICON-OXYGEN TETRAHEDRON because of its shape

17. O O Si Shared electrons O O

18. Tetrahedron= Four-sided pyramid

19. The pyramids link together by sharing oxygen atoms and reduce the total charge • Five main groups of silicate minerals are created based on how the pyramids link together • Total SIX main groups of silicate minerals

20. Isolated silicate structure (NESOSILICATES, pages 56-57) • Tetrahedron does not share oxygen atoms • Individual tetrahedrons are bonded by positively charged ions Examples: OLIVINE, GARNET

21. SOROSILICATES, (pages 56-57) • Two tetrahedra share ONE oxygen atom (Si2O7)-6 Example: EPIDOTE (not too many minerals belong in this group)

22. CYCLOSILICATES or ring silicates, (pages 56-57) • 3, 4 or 6 tetrahedra linked to form a ring • Each tetrahedra share TWO oxygen atoms with neighbors • Six-member rings are most common Examples: BERYL, TOURMALINE

23. IONOSILICATES or Chain silicates • Single-chain silicates • Each Tetrahedron shares TWO oxygen atoms with neighboring pyramids Example: PYROXENE GROUP • Double-chain silicates • Two single chains cross-linked Example: AMPHIBOLE GROUP

24. PHYLOSILICATES or Sheet silicates • Each Tetrahedron shares THREE oxygen atoms forming two-dimensional sheets Example: MICA GROUP and CLAY MINERALS

25. TECTOSILICATES or Framework silicates • Each Tetrahedron shares ALL FOUR oxygen atoms Example: FELDSPAR GROUPS and QUARTZ

26. How silicate minerals form from magma (Bowen’s reaction series) As magma begins to cool, minerals start to crystallize and REACT with the magma in a very regular manner

27. CONTINUOUS branch Mineral chemistry changes gradually Plagioclase feldspar group DISCONTINUOUS branch One mineral changes into a different mineral Iron-magnesium rich minerals Two separate “branches” or series

28. Discontinuous branch Cooling magma OLIVINE crystallizes Reacts with magma High temp PYROXENE crystallizes Reacts with magma AMPHIBOLE crystallizes Reacts with magma BIOTITE crystallizes Low temp

30. In-class exercise Using the Bowen’s Reaction Series, answer the following: • how does the silica content of the minerals change as you go down the discontinuous reaction series? • If the Bowen’s Reaction Series holds true, then no igneous rock should contain olivine, pyroxene… etc. How come those minerals exist in nature then? • Can you have quartz and olivine in the same rock? Why or why not?

31. Magma types based on silica content • Types of magma are defined by the relative proportion of silica (SiO2) to the sum of Magnesium (Mg) and Iron (Fe) oxides • When amount of SiO2 increases, Fe + Mg decreases

32. Is called Magma with high MAGNESIUM + FERROUS (iron) MAFic magma (silica ~50%) Also called BASALTIC magma after the most common mafic rock Magma with ~ 40% silica is called ULTRAMAFIC

33. At divergent boundaries and hot spots, mafic magma forms by PARTIAL MELTING (not complete melting) of the asthenosphere • Minerals with higher melting points stay in the asthenosphere. Minerals with relatively lower melting points melt to form mafic magma

35. Sometimes mafic magma is produced below continental crust (e.g. East African Rift, Yellowstone, subduction zones etc.) • When it rises through continental crust, the continental crust melts • The rocks in continental crust are silica rich and SILICIC magma is formed (silica >65%)

36. Common rocks produced from silicic magma are GRANITE and RHYOLITE • Mixing of silicic and mafic magma, as well as melting of ocean sediments produces INTERMEDIATE magma (ANDESITE, silica ~55%) in subduction zones