Class 10

GEOLOGY 101Class 10

Spring 2014

Objectives –Chapter 6

Explain the distinctive characteristics of metamorphic rock

List what the major sedimentary rocks become under metamorphic processes

Describe the three metamorphic processes and where metamorphic rocks form

Describe the potential significance of the discovery in 1977 of “Black Smokers”

Rock Cycle Simplified

Start with molten magma heavy in silicates or ions of calcium and carbonate in water

Allow magma to cool and crystalize into igneous minerals and rocks Or promote biochemical or straight chemical combination of

calcium and carbonate to form calcite Expose igneous rocks to water and let them deteriorate to small

pieces and clay minerals Gather small pieces, clays, and calcites and cement together into

sedimentary rocks OPTIONAL STEP – To any rock created above, raise to high

temperatures and pressure, allowing re-crystallization into igneous minerals or marble (from calcite)

WARNING, if temperatures get too high , you melt the rock and start over as magma

MetamorphismMetamorphic Rocks

Definition: Re-crystallization of

minerals while still solid into minerals that are

stable at different temperatures and

different pressures

Characteristics of Metamorphic Rocks

High temperatures can change chemical structure of minerals

Pressure + heat – flattened crystals and create characteristic foliation Slaty cleavage Increasing Phyllitic cleavage degree of Schistose metamorphism Gneissic structure

Metamorphic rocks are not all foliated

Foliation – How Rock Metamorphic Rocks Show Stress

Characteristics of Metamorphic processes

Work on all kinds of rocks Varying degrees of Metamorphism Heat and pressure to re-form crystals in

existing rock

Step 1 - Metamorphism of Shale

Shale: Fine grained Clay (and quartz) minerals stable under atmospheric T&P

Compacted by overburden

Laminated sheets Water bound in crystalline structure of clay

Increase pressure and temperature –create Slate Clays converted to mica and

chlorite - fine grained plates Water expelled from

crystalline structure of clay New minerals stable Slaty Cleavage due to realignment of platy minerals Result of Low Grade

Metamorphism - Slate POOL TABLES and ROOF SHINGLES

Heat Slate to Higher Temperature and Pressure More Grow more and larger

grains of Mica and quartz

All clays convert to mica Slaty cleavage takes on a

sheen surface of sheets of mica aligned with stressesMedium-Grade Metamorphism

Phyllite

Of mica

Still more heat and pressure on Phyllite

Create larger grains of Mica and Quartz

Garnets, amphibole and biotite may be created

Schistosity created by alignment of platy and needle-like minerals Medium to High-Grade Metamorphism Schist

Still hotter temperature on Schist OR Granite

Create course grained Feldspar, Quartz, Amphibole, Biotite

Less mica or amphibole because of dehydration

Minerals tend to migrate into separate parallel bands of dark and light

High-Grade Metamorphism Gneiss

Fig 7.12

Cook the Gneiss Even Hotter

Silica rich minerals melt first (quartz and feldspar)

Forming silicic magma Injected into fractures

resulting in silicic veins if intrusive igneous rock

Very High-Grade Metamorphism and partial melting Migmatite

Fig 7.12

Metamorphic Rocks of other Parent Rocks Limestone Marble

Bioclastic calcite Crystalline calciteNonfoliated

Metamorphic Rocks of other Parent Rocks Quartz Sandstone Quartzite

Granular quartz Crystalline quartzNonfoliated

Metamorphic Rocks of other Parent Rocks Basalt Amphibole Schist Granite Gneiss

Uniform texture Foliation (schistosity and gneissic banding)

Types of metamorphic rocks

Slate – Shale – Low grade Phyllite – Sheen, more mica, higher gradeSchist – Most abundant – mineral first name

lot around Enchanted RockGneiss – Coarse grained – high grade regional - granite or gabbroMarble – Limestone or dolostone, contact or regionalQuartzite – non-foliated quartz sandstone

How deep and how hot?

Regional Metamorphic Environments

Regional metamorphism occurs where rocks are squeezed between two converging lithospheric plates during mountain building.

DEEPEST, HOTTEST and LARGEST AREA

Contact Metamorphic Environment

There are a number of environments in which metamorphism occurs. Most are in the vicinity of plate margins, and many are associated with igneous activity.

Contact or thermal metamorphism occurs when rocks immediately surrounding a molten igneous body are “baked” and therefore altered from their original state.

Hydrothermal Metamorphic

Hydrothermal metamorphism occurs when hot fluids circulate through fissures and cracks that develop in rock. This hot fluid chemically alters rocks and is closely related to igneous activity.

Mid-ocean ridge

Mid-ocean ridge

Black Smoker off Galapagos Islands

Black Smokers first discovered 1977

Concentrated high value minerals from magma(mostly sulfides) in hot water

Quickly cool and minerals come out of solution

Home to exotic plant and Animal life

Anatomy of a Black Smoker

Objectives –Chapter 6

Explain the distinctive characteristics of metamorphic rock

List what the major sedimentary rocks become under metamorphic processes

Describe the three metamorphic processes and where metamorphic rocks form

Describe the potential significance of the discovery in 1977 of “Black Smokers”