TYPES OF ROCKS

© 2008, John Wiley and Sons, Inc.

Tectonics and Metamorphism

Figure 10.13

Zone of burial metamorphism

Blueschist and eclogite metamorphism

Regional metamorphism

Granitic magma rises and causes contact metamorphism

What’s metamorphism?

The set of changes that occur in rocks as a result of elevated temperatures and pressures. It takes place in solid state, without melting.

Where does it occur?

Underground, very deep but specially where there are stress forces

Factors in metamorphism?

Temperature and pressure.

© 2008, John Wiley and Sons, Inc.Figure 10.2

Types of metamorphism

Metamorphism is a complex process including:•Loss of water•Orientation of minerals.•Recrystallization.•New minerals formation.

Second process: orientation.Extreme pressure produces foliation, a planar arrangement of mineral grains giving a layered texture. (Esquistosidad)

See animation: http://www.bioygeo.info/Animaciones/Foliation1.swf

Third process: recrystallization.Increasing the size of some minerals.

© 2008, John Wiley and Sons, Inc.

Shale Slate Phyllite

SedimentaryRock

Fine grained, low grade metamorphic rock with slaty cleavage.

Fine grained, high grade metamorphic rock with foliation.

© 2008, John Wiley and Sons, Inc.

From shale to gneiss Figure 10.3

Shale

Slate

Phyllite

Gneiss

Diagenesis

Low-Grade

Medium-Grade

High-Grade

* Sillmanite and KyaniteAl2O3 with different

crystal structures

There are some metamorphic rocks without foliation. Why?

If the previous rock hasn’t got planar components foliation is impossible

Sandstone Quartzite

Dominantly quartz minerals Very little foliation due to low diversity of minerals.

Video sobre recristalización: http://www.youtube.com/watch?v=J_2FdkRqmCA&feature=related

Quarzite and marble are metamorphic rocks without foliation

Made of cacite Made of quartz

From limestones From sandstones

Soft, it reacts with acid Hard, it doesn’t react

A collection of metamorphic rocks