Chapter 3 – Igneous Rocks, the Origin and Evolution of Magma Rocks are composed of an aggregate of one or more minerals. One exception: obsidian (rock) is composed of volcanic glass with no orderly internal arrangement of atoms. Three rock types.

Igneous Rocks Igneous rocks: rocks “born of fire”; all igneous rocks were once molten. Intrusive igneous rocks cool and solidify deep inside earth. Form from solidified magma. Extrusive igneous rocks cool and solidify on earth’s surface. Form from solidified lava.

Igneous Rock Pictures Intrusive (Plutonic) Igneous Rock Extrusive (Volcanic) Igneous Rock

Sedimentary Rocks Sedimentary rocks are composed of sediment. Sediment can be either clastic (pieces) or chemical. Clastic sediment is pieces of pre- existing rock like gravel, sand, silt and clay. Chemical sediment is chemicals dissolved in water.

Sedimentary Rock Pictures Gravel clasts. Chemical sedimentary rock.

Metamorphic Rocks Metamorphic rocks: Changed by heat and pressure. Change is accomplished without melting.

Rock Cycle One of the three rock types can become any other rock type through various geologic processes. This is known as the rock cycle.

Rock Cycle Diagram One of the three rock types can become any other rock type through various geologic processes. This is known as the rock cycle.

Rock Cycle Diagram

Igneous Rocks 90% of all crustal rocks. Most covered by sedimentary rocks. Hard to see. Magma: molten rock underground. Cools slowly. Large crystals. 1 MY cooling history Plutonic: Pluto-god of underworld. Lava: molten rock on earth’s surface. Cools quickly. Small or no crystals. Hours-weeks cooling. Volcanic: Vulcan-god of fire

Eight Major Igneous Rocks

Start Chemistry of Igneous Rock felsic - high in silica - ≈70%+ granite/rhyolite intermediate - in-between felsic and mafic - ≈60% diorite/andesite mafic - low in silica - ≈ 50% gabbro/basalt ultramafic - really low in silica - below 44% peridotite/xxx

Granite Picture

Rhyolite Picture

Diorite Picture

Andesite Picture

Gabbro Picture

Basalt Picture

Bowen’s Reaction Series Could you create every igneous rock by melting the upper mantle? assumption - chemistry of the magma is the same as the upper mantle BRS - yes, order in which minerals crystallize fractional crystallization crystal separation filter pressing crystal settling crystal flotation

Bowen’s Reaction

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Fig a

What if the Magma Stays Underground? magmatic stoping - moving through the solid rock (country rock) wedging breaking (xenolith) melting plutons batholith - larger than 100 km 2 most batholiths contain multiple intrusions stock - smaller 10km 2 or less dike – discordant intrusion sill – concordant intrusion

Fig. 7.18