1. Bowen’s Reaction Series
Melting
Crystallization
Hot
Cold
Different minerals crystallize from magmas at different temperatures

2. Daily Question
The core (center) of the Black Hills of South Dakota is composed of granite. The Columbia River Plateau of Washington and Oregon is composed of basalt. Using a Venn Diagram, compare and contrast the two locations highlighting the composition of the rocks, the texture of the rock, and the location (depth) where the rocks formed.

3. Magmatic Differentiation
Formation of more than one magma from a single parent magma

4. Magmatic Differentiation
Crystal Settling: crystallized minerals have a density greater than the magma and settle to the bottom due to gravity
Because Fe and Mg are first removed, melt becomes rich in SiO2, Na, and K
Marbles analogy

5. Magmatic Differentiation
Assimilation: magma reacts with the “country rock” which is adjacent to the magma chamber
Magma composition is altered according to the composition of the assimilated country rock
Inclusions are rocks Incompletely melted chunks of country rock

6. Magmatic Differentiation
Magma Mixing: Magmas of different compositions are mixed together
Resulting magma is of a composition intermediate between the parents

7. Magma Mixing

8. Magma Mixing

9. Magma Mixing

10. Fig. 7.21

11. Igneous Activity

12. Viscosity Controls Violent Nature of Volcanic Eruptions
Fig. 6.4
Viscosity Controls Violent Nature of Volcanic Eruptions

13. Controls of Viscosity Magma composition – silica content Temperature
High silica content – high viscosity
Low silica content – low viscosity
Temperature
High temperature – low viscosity
Low temperature – high viscosity
Dissolved gas
Low viscosity – gases escape
High viscosity – gases cannot escape (pressure builds up)

14. Magma Properites Composition Silica Content Viscosity Gas Content
Tendency to form Pyroclastics
Mafic
Least (< 50%)
Least
Least (1-2%)
Intermediate
Intermediate (~60%)
Intermediate (3-4%)
Felsic
Most (~70%)
Greatest
Most (4-6%)

15. Materials Extruded During an Eruption
Lava flows – low silica content of basalt lava allows it to flow up to 30 km/hour, typically 10 to 300 m/hour
Gases – reduction of confining pressure allows gases to escape
70% water vapor
15% carbon dioxide
5% nitrogen
5% sulfur dioxide
Trace amounts of chlorine, hydrogen, and argon
Pyroclastic material – welded ash, dust, and lava

16. Nuée ardente Glowing avalanche of ash, steam, gas, and pyroclastics
Travels at speeds of 200 km/ hr (125 mph)

17. Page 160