Agents of MetamorphismHeat

6.3 Lecture Notes

Heat causes rocks to expand & mineral bonds weaken or break. Once broken, they can form new minerals!1. Geothermal Gradient (increasing temps within

Earth)

2. Magma.

Effects:

Sources:

METAMORPHIC ROCKS- “MORPHED” FROMSEDIMENTARY OR IGNEOUS ROCKS

Chemically Active FluidsIons in fluids can mix with ions in minerals & actas a “seed” for new mineral growth.

1. Ionic solutions deep within Earth.

2. Ionic solutions in heated water, near magma chambers.

Effects:

Sources:

PressurePressure compacts rocks & can break ionic bonds.This creates more-compact mineral structures.

1. Weight of overlying rocks deeper in Earth.

2. At convergent boundaries.

3. Along fault lines.

Effects:

Sources:

Types of Metamorphism

1. Heat 2. Pressure

When a meteorite hits Earth, extreme pressure& heat alter rocks that are hit.

Primary Agents:

Describe:

Impact

DynamicPressure

Pressure changes rock structure along a fault line as rocks are crushed.

Primary Agents:

Describe:

RegionalPressure, temp, chemically active fluids

All 3 agents together can cause huge areas of rocks to metamorphose. Example: Mountain Building.

Primary Agents:

Describe:

ContactHeat

A tremendous heat sources contacts a pre-existingrock. Example: Igneous intrusions.

Primary Agent:

Describe:

Rock texture & minerals usually change.Characterisitcs:

BurialPressure

As rock gets buried deep in Earth, equal pressurescompress it from all sides.

Primary Agent:

Describe:

No banding pattern compared to Sedimentary rocks that get buried and compressed.

Characteristics:

Burial metamorphic Compressed Sedimentary

RecrystallizationThe growth of new mineral grains are biggerthan the original grains of minerals.

Describe:

Types of Change

Occurs when grains move closer together &reduce pore size (spaces between grains) due toIncreased pressure.

Describe:

Compaction

Under pressure, grains of rocks become aligned parallel to each. This changes the texture.

Describe:

Foliation