Chapter 4 1-Know the characteristics and differences between extrusive/volcanic

Question

Chapter 4

1-Know the characteristics and differences between extrusive/volcanic and intrusive/plutonic.

2-Igneous rocks are classified by (2 ways) and what controls each classification?

3-What are the three factors that affect igneous textures? (cooling rate, % silica,

dissolved gases).

4-Know the following terms: aphanitic, vesicular, phaneritic, phenocrysts, groundmass or matrix, pegmatite, pyroclastic,

5-How does heat, pressure, and the presence of volatiles effect melting and magma formation?

6-Understand how magmatic differentiation, asssimilation, magma mixing, and partial melting effects magma composition.

8-Be able to describe and identify the following concordant and discordant intrusive structures: pluton, batholith, lacolith, dike, sill.

Chapter 5

1-Know how magma viscosity relates to silica content.

2-Know order of magma viscosity.

3-How do dissolved gases affect magma and intensity of volcanic eruptions?

4-Know and be able to describe the characteristics of the three volcano types (shield, cinder, composite)?

5-Know how eruptions are predicted.

6-Know the following terms: pyroclastic flow, lahar, caldera, crater, vent, flood basalt, lava dome, fissure eruption.

7-Be able to identify and describe the types of igneous activity associated with plate boundaries and intraplate activity.

9-Understand the relation between hot spots and flood basalts (figures 5.30).

Explanation / Answer

1-Know the characteristics and differences between extrusive/volcanic and intrusive/plutonic.

---->characteristics:-

volcanic rocks are rocks that have been expelled, as lava or other "extrusive" onto the earth's surface (or underwater). Examples include basalt, rhyolite- rocks.

Plutonic rocks also develop from an initially molten mass (molten rock is called "magma", unless and until it is exposed by volcanism). By contrast, though, plutonics, or "intrusive" rocks, are generally not exposed at the earth's surface during formation.

Fundamental differences:-

1)Fine-grained versus coarse-grained, because of very small (or absent) crystals

versus larger, well-developed crystals;
2)Rapid cooling at the earth's surface

versus slow cooling at-depth;

2-Igneous rocks are classified by (2 ways) and what controls each classification?

ans)

--->Igneous rocks are classified by two things, first, the magma type, which depends on the amount of silica present. They are further classified by how big the crystals are. The crystal

---->Igneous rocks are generally classified first on the basis of their formation (and therefore their texture) as intrusive or extrusive. Intrusive rocks are solidified from magma under the surface resulting in a visible crystalline texture, and extrusive igneous rocks are solidified from lava at or near the surface, resulting in a small or nearly invisible crystalline texture.

--->Igneous rock can additionally be classified by general chemistry composition as felsic,intermediate, mafic, and ultramafic. Felsic rocks are higher in silica and aluminum. Mafic rocks are higher in magnesium and iron.

3-What are the three factors that affect igneous textures? (cooling rate, % silica,

dissolved gases).

ans)Three factors that affect igneous textures are:-

1)rate at which magma cools

            very rapid cooling - glass
            rapid cooling - fine-grained
            slow cooling - coarse grined

2)amount of silica (SiO2) present

silica varies between 50% and 80%

low silica

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