Quiz Question

• Do you expect that the earthquake in Hawaii was:– Tensionsal (pull-apart movement)– Compressional (push-together movement)– Shear (moving-past movement)

• Given the geologic setting of Hawaii, why do you expect this?

Where does continental crust come from?

Continental Crust

What defines a specific mineral?

Crystal structure and Chemical Composition

Mineral Name

Quartz

Corundum

Diamond

Graphite

Chemical Composition

SiO2

Al2O3

C

C

Crystal structure

Framework Silicate

3-D framework

Sheets

The Silicate MineralsBasic Building Block

Silicate ion: SiO4-4

One Si surrounded by 4 O in a tetrahedron. Can be combined in different ways:

•Isolated tetrahedra

•Chains

•Sheets

•3-D Framework

Isolated Tetrahedra

Chains Sheets

FrameworkSilicates

In framework silicates, every O is shared with two Si tetrahedra:

Quartz: SiO2

Rocks, some context

• What is a rock?– A coherent, natural, aggregate of minerals (or

glass)

• Types of rocks– Igneous - formed from melt– Sedimentary - formed by surface processes– Metamorphic - formed by transforming other

rocks

Let there be… magma

• Where is magma formed? In the lithosphere– At subduction zones (addition of water)– At midocean ridges (decompression)– At rifts (decompression)– At hot spots (decompression)– In next to other magma (contact)

PlateBoundaries

Decompression meltingS

olid

mat

eria

l ris

esP

ress

ure

decr

ease

s

Surface

Hot Spot Vulcanism

Addition of volatiles (water and CO2)

Contact Melting

Where are Igneous Rocks Formed?

Intrusive (Plutonic) vs. Extrusive (Volcanic) Rocks

What is a Metamorphic Rock

• Metamorphic rocks are formed by metamorphism of other rocks– Changes in physical, chemical, and

mineralogical characteristics– In Solid State

Metamorphism

• What causes rocks to metamorphose?– Heat (different mineral stability, faster reactions)

– Hot water (addition/removal of elements)

– Confining Pressure (different mineral stability)

– Directional forces due to deformation

Kinds of Metamorphism

• Contact Metamorphism with hot rocks

Kinds of Metamorphism

• Burial Metamorphism of Sediments(think isostacy! And then think geotherm!)

Kinds of Metamorphism

• Regional Metamorphism from mountain building

Where do Metamorphic Rocks Form?

Weathering

• The conversion of solid rock to smaller pieces or other (non-rock-forming) minerals

• Physical v. Chemical weathering (they work together!)

Physical weathering

• … the process whereby large rocks are broken into smaller rocks.

• Many different processes

Chemical Weathering

• Dissolution = dissolving salt in water

• Hydrolysis

2 KAlSi3O8 + 2 H2CO3 + H2O

Al2Si2O5(OH)4 + 4SiO2 + 2K+ + 2HCO3-

• Oxidation (where does the Fe+2 come from?)

4 Fe+2 + 3 O2 2 (Fe+3)2O3

• The role of organisms

Transport (erosion)

• What transports sediments?– Water, primarily– Wind

• Why?– Ultimately, for water: gravity

Sedimentary Rocks

• Sediments: layers of loose particles that originate from the weathering of the continents (solid debris or dissolved substances)

• Sedimentary Rocks: Rocks formed from sediments by the process of lithification.

• Two types

– Clastic Sediments

– Chemical and Biochemical Sediments• Requirements

– Weathering– Erosion– Deposition– Lithification

Sedimentary Environments

Principal of Original Horizontalityand the

The Law of Superposition

Sediments (and sedimentary rocks) record conditions on the (local) earth’s surface at the time they were formed.

1000 mya

600 mya

600-240 mya

420 mya

370 mya

270 mya

180 mya