CH. 3 – METAMORPHIC RX

Metamorphic Rx

“meta” = change; “morphos” = shape/form

Parent Rock = pre-existing rock that undergoes metamorphism

Metamorphism

Caused by:- increase in pressure- increase in temperature- exposure to chemically active

fluid

Metamorphism

Occurs within Earth’s crust- minerals change until they are

stable under the new conditions

Metamorphic Conditions

1) Increasing pressure Two methods:

a) deep burialb) mountain building

Types of pressure

a) Differential pressure - applied unequally from different

directions- produces foliated texture

Foliation

Linear arrangement of minerals- creates a layered appearance- associated w/mountain building

Foliated diagram

Types of pressure

b) Confining pressure- applied equally from all sides- associated with deep burial- produces nonfoliated texture

Quartzite

Metamorphic Conditions

2) Increasing temperatureNOTE: Temperature cannot

exceed the melting point of all minerals in rock

Why?

Increasing temperature

Two methods:a) deep burial

- geothermal gradient- increases 30o C per km

b) magma intrusion

Increasing temperature

Changes to parent rock:a) Compositional change- unstable minerals either melt or

rearrange into new minerals

Compositional Change

Ex: Shale Slate(clay minerals) (microscopic

micas)

Bowen’s Reaction Series

Increasing temperature

b) Textural Change- partial melting allows minerals to

recrystallize- produces nonfoliated texture

Textural Change

Ex: Sandstone Quartzite(quartz) (quartz)

Note: The composition is still the same!

Sandstone Quartzite

Metamorphic Conditions

3) Chemically active fluid- superheated water with ions in

solution- “hydrothermal solution”- occurs near magma chambers

Metamorphic Rock Classification

Foliated textures - in order of increasing

metamorphic intensity (temperature, pressure)

Foliated textures

Parent rock = shale Degree Rock

Low slate(microscopic micas)

Foliated textures

Degree Rock Low Slate

Medium Schist(visible micas)

Foliated textures

Degree Rock Medium Schist

High Gneiss(black & white layers)

Foliated textures

Low degree Slate

Medium degree Schist

High degree Gneiss

Nonfoliated textures

Composition controlled by parent rock

Parent Rock Meta. Rock Sandstone Quartzite Limestone Marble

Metamorphic Settings

1) Contact Metamorphism- caused by contact with magma- heat from magma partially melts

minerals- minerals recrystallize into

nonfoliated texture

Contact Metamorphism

Metamorphic zone is narrow (1’-10’ wide)

Zone of contact metamorphism referred to as a “baked zone”

Metamorphic Settings

2) Regional Metamorphism- associated w/mountain building- large-scale metamorphism (100’s

miles wide)- produces foliated textures

Regional Metamorphism

Foliated rocks are often folded within mountain ranges

ROCK CYCLE

One rock is the raw material for another