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Ch. 5 Sec. 1

Ch. 5 Sec. 1. Igneous Rocks. Igneous rocks are the rocks that form when molten material cools and crystallizes. Review Vocabulary. silicate: mineral that contains silicon and oxygen, and usually one or more other elements. I. Igneous Rock Formation. Formation 1. Molten material

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Ch. 5 Sec. 1

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  1. Ch. 5 Sec. 1 Igneous Rocks

  2. Igneous rocks are the rocks that form when molten material cools and crystallizes. Review Vocabulary silicate:mineral that contains silicon and oxygen, and usually one or more other elements

  3. I. Igneous Rock Formation Formation 1. Molten material a. Upper mantle & lower crust b. Thermal energy (800oC – 1200oC) i. Earth’s early formation ii. Radioactive decay 2. Lava or magma cools 3. Minerals crystallize

  4. B. Composition of Magma (molten rock, dissolved gas, and mineral Xl’s) Elements – same as Earth’s crust (Si, O, Al, Fe, Mg, Ca, K, Na) Silicon most abundant a. Basaltic – low Si b. Andesitic c. Rhyolitic – high Si 3. Si content affects melting & flow

  5. Page 112

  6. C. Magma Formation b. Pressure increases with depth c. As water content increases, MP decreases d. Mineral content i. Different minerals have different MP Melting in crust or mantle affected by a. Temperature increases with depth

  7. Magma formation Temperature generally increases with depth in Earth’s crust. This temperature increase is known as the geothermal gradient. Fig 5.1 - pg. 113

  8. D. Partial Melting – process by which some minerals melt at relatively low temperatures while others remain solid New elements added to melted minerals Changes composition of magma, resulting in different types of rocks

  9. Partial melting If temperatures are not high enough to melt the entire rock, the resulting magma will have a different composition than that of the original rock.

  10. II. Bowen’s Reaction Series Bowen discovered two main patterns, or branches, of crystallization. Predictable pattern of Xl formation Fig. 5.4 pg. 114

  11. 1. Feldspars – continuous composition change a. Calcium (Ca) rich b. Sodium (Na) rich The right branch of Bowen’s reaction series represents the plagioclase feldspars, which undergo a continuous change of composition as magma cools.

  12. 2. Iron-rich minerals : abrupt changes The left branch of Bowen’s reaction series represents the iron-rich minerals, which undergo abrupt changes as magma cools and crystallizes.

  13. III. Fractional Crystallization When magma cools, the first minerals that crystallize are the last minerals that melted during partial melting. This process is called fractional crystallization.

  14. A. As magma cools, Si content increases B. Quartz 1. Occurs in veins 2. Last to crystallize 3. Magma squeezes into rock fractures

  15. Visualizing Fractional Crystallization and Crystal Settling In the basaltic intrusion of the Palisade Sills in the Hudson River valley of New York and New Jersey, small crystals formed in the chill zone as the outer areas of the intrusion cooled more quickly than the interior.

  16. Under certain conditions, newly formed crystals can be removed from magma, ending the chemical reactions between the magma and the minerals, thus ending Bowen’s reactions.

  17. Magmas of several different compositions have erupted from the same volcano. How can this be explained by the concept of fractional crystallization?

  18. Answer: Fractional crystallization is one way that different magmas can be produced at the same volcano. If magma is injected beneath the volcano and begins to crystallize, the composition of the remaining magma will change as the crystals form. The magma may then erupt from the volcano at any time.

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