Historical Geology

Basic Tenet of geology \#1

the present is the key to the past

Basic Tenet of geology \#2

The law of superposition (in an undisturbed sequence of rocks, the oldest will be on bottom and youngest on top)

What are the 3 rock types?

Igneous, Metamorphic, and Igneous

Most Common Elements in Mineral

Oxygen (O)

Magnesium (Mg)

Silicon (Si)

Aluminum (Al)

Iron (Fe)

Calcium (Ca)

Sodium (Na)

Potassium (K)

Oxygen and Silicon form what rock?

Quartz

What is the most common mineral in rocks?

Oxygen and Silicon

What is the unit cell?

Sets pattern for how minerals are arranged

Determines internal structure of mineral (Crystal Lattice)

Determines external shape

Each mineral has a unique:

Chemical Formula

Internal Structure and External Form

Physical Properties (the two above affect this)

What is a melting point/transformation point?

solid to liquid or liquid to solid

What determines which elements get together to form minerals?

This is a NON-RANDOM process that depends on: the availability of elements and temperature

How do Igneous Rocks form?

The solidification of molten rock

Temperature of minerals

High melting point: Magnesium, Iron, and Calcium

Low Melting Point: Silicon, Aluminum, and Potassium

What does the rate of cooling determine?

The texture of an igneous rock

Coarse texture (igneous):

cooled slowly

Fine texture (igneous):

Cooled quickly

Where's lava?

aboveground and it cools quickly

Where's magma?

belowground and it cooled quickly

What type of rocks are high temp minerals?

Mafic

What type of rock are low-temperature minerals?

felsic

Lava is often associated with which type of rock formation?

Extrusive igneous rock formation because of its reaction with air

Magma is often associated with which type of rock formation?

Intrusive rock formation because it doesn't come to the surface

How are metamorphic rocks formed?

Solid state diffusion (atoms migrate and reorganize without melting and often happens to existing rocks)

How can solid-state diffusion occur?

Elevated heat (between 200 and 800), elevated pressure, or hot fluids

What causes elevated pressure or an existing rock?

temperature

deep burial

tectonics

What can solid-state diffusion change?

composition and texture

How can you use thermal history?

Rate of cooling (can tell the texture from igneous)

Temperature (you can tell from which minerals are present in the rock)

Metamorphic Textures

foliated and non-foliated

How does a rock get foliated?

Pressure applied to rocks during metamorphism will cause segregation of different minerals and result in banding and often happen perpendicular to the direction of pressure applied

How does a rock get non-foliated?

Heat, no pressure: giving a random arrangement of minerals

Foliated Metamorphic Rocks

slate, phyllite, schist, gneiss

Slatey

low grade metamorphism of fine grained sedimentary rock (from slate)

Phyllitic

low-intermediate grade metamorphism and results in a wavy foliation of fine-grained minerals such as mica (from phyllite)

schistose

intermediate-high metamorphism and results in a medium-coarse grained rock with visible mineral grains (from schist)

Gneissic

high-grade metamorphism. comes from bands of alternating light and dark minerals and is medium-coarse grained (from gneiss)

Non-foliated metamorphic rocks

marble and quartzite

What are the most popular minerals in metamorphic rocks?

garnets and staurolite

What are garnets?

small bulbs of segregated mineral (crystal) found in a larger rock from metamorphism

What do sedimentary rocks contain?

fossils and they are deposited on earth's surface

What are the two types of sedimentary rocks?

Precipitated (chemical) and detrital (clastic)

Explain precipitated rocks

Begins with erosion and weathering of existing rock

Ions find each other in water, make a unit cell and build into a crystal

Crystal becomes heavy and falls to bed, interlocking with other deposited sediment

Precipitation Process

this begins when ions are so concentrated that the water can no longer suspend them

How does concentration increase?

taking out/evaporating water, adding more ions, and for carbonates only increasing temperature/releasing CO2 from water

How can precipitated sedimentary rocks be formed?

Physical Processes and Biological Processes

Types of physical sedimentary rocks

carbonates, gypsum, halite

How are biochemical sedimentary rocks formed?

shells/skeletons made from calcium carbonate

How are detrital sedimentary rocks formed?

Begins with weathering/erosion of existing rocks

Clasts are transported then deposited

No new minerals are formed/added, but minerals can be "eroded out"

Weathering Clasts

high temp = weather much more easily and dissolve quickly

little weather = large assortment of minerals

lots of weather = less mineral diversity and low temp minerals

more weathering = smaller, rounder clasts

Physical Weathering

physical breakdown of rock into smaller pieces caused by wind, rain, ice, gravity, plants, roots

Chemical Weathering

chemical breakdown/dissolution of rocks into original elements and occurs in water

How are detrital sedimentary rocks classified?

clast size

The more clasts are moved, the more there is a chance of:

destruction of unstable high temperature minerals, physical rounding of clasts, physical reduction of size of clasts

Which weathering techniques are the biggest transporters of clasts?

water, wind, gravity, and ice

What are the 3 phases of detrital rocks?

Weathering, Transporting, Depositing

To transport the sediment, the forces that are holding it in place need to over come with \_______

energy.

Gravity- pushing clast down with substrate

Friction- between clast and substrate, resistance to slide

In what 3 ways are clasts transported?

Suspended load (floating/carried in water)

Bedload (rolling along bed)

Dissolved loads (moving dissolved in water, what transports it also deposits it)

the higher the energy:

the more sediment and larger clasts that can be picked up

What is graded bedding?

tells us the deposit was made in a waning current of decreasing velocity (heavy on bottom, light on top)

What is the process of transportation?

different clast sizes are entrained and moved at different velocities

What is the process of deposition?

Different clasts are deposited at different velocities

What determines the structure of deposition?

Strata and Cross-Stratification,

Strata

horizontal parallel layers in deposited rock, each layer records a depositional event, and each layer is known as "stratification"

cross-stratification/cross-bedding

deposited at an angle, formed by moving sediment, deposited in ripples/waves/hills, asymmetry of deposit will tell us which way the sediment is moving (stoss slope and lee slope)

stoss slope

long side of ripple, the sediment was moving up this slope

lee slope

short side of ripple, the sediment peaks right before this and drops off to create lee slope

Earth Age Periods

Hadean (4.6 BYA), Archean (4 BYA), Proterozoic (2.5 BYA), Paleozoic (542 MYA)

Heat is earth was due to \_______ and \______

gravitational compression and radioactive decay

When internal temperature rose above 1500 C...

the dense materials (metals) moved towards the center and the lighter material (silicates) moved towards the surface

Earth Layers and their composition

Crust \n (Solid, rich in quartz, 7-70 km, stony composition) \n Upper Mantle \n (Semi-molten, rich in higher-temp silicates, 600-663 km, stony composition) \n Mantle \n (Semi-molten, composed of very high-temp silicates, 2230 km, stony composition) \n Outer Core \n (Liquid, composed of Iron (Fe) and Nickel (Ni), 2250 km, metallic composition) \n Inner Core \n (Liquid, composed of Iron (Fe) and Nickel (Ni), 1220 km, metallic composition)

What are the 3 types of seismic waves?

P waves (primary), S waves (secondary) and surface waves.

What are p-waves?

particles move the same direction as energy of wave, travels through solids and liquids, and travels fastest

What are s-waves?

particles move perpendicular to energy of wave, can only travel through solids, and travels second fastest

What are surface waves?

generated when P and S waves reach the surface, most destructive waves, and travel the slowest

How do the seismic waves differ?

Relative speeds, absolute speeds, and the materials through which they can propagate

How does the speed and direction work?

Less dense to more dense = waves speed up and bend towards surface

More dense to less dense = waves slow down and bend into the earth

What is the P-wave shadow zone?

103-142 degrees away from the origin of the earthquake

What is the S-wave shadow zone?

103-180 away from the origin of earthquake (cannot travel through inner core)

How do you record seismic waves?

Using a seismograph

By recording travels times of seismic waves and their behavior as they pass through earth we can determine:

Whether parts of interior earth are liquid or solid (how we know outer core is liquid)

How density changes from layer to layer

What is the lithosphere?

all of the crust, hard part of the upper mantle and between 75 and 125 km thick

How is the lithosphere divided?

between oceanic crust (8km thick) and continental crust (32km thick)

What is the asthenosphere?

The upper mantle below the lithosphere

How many tectonic plates are there?

27 and they are apart of the lithosphere

Which way do divergent boundaries move?

apart from each other (that's why their spreading centers)

What is magma convection?

The process of magma rising between plates, welling up and attaching to the back of plates, forming new lithosphere

What is a mid-ocean ridge?

underwater divergent boundary, forms new oceanic lithosphere

What is a triple junction?

A place where a new spreading center is trying to form. Pressure starts in one spot, 3 arms of magma stick out, helping to form spread

Which way do rocks move on a divergent boundary?

Like a conveyer belt. Oldest should be on the outside

Which way do convergent boundaries move?

towards each other

Will oceanic lithosphere win against continental?

NO

What is a subduction zone?

One plate gets pushed under another plate and it's very tectonically active producing volcanoes and earthquakes

Explain the subduction process

Subducted plate begins to melt

Magma will start to rise from melt and form a volcano

Earthquakes can also happen when there is tension between plates and a sudden release of seismic energy

Which direction will a volcano be to a subduction zone?

Parallel

Smaller Angle \=

farther volcano (the angle of subduction determines how far the volcano forms from the subduction zone)

What happens when neither plate "loses"

a mountain is formed (usually continental vs continental)

What way are the plates moving in a transform boundary?

They try to move past each other and it's never smoothly (the plates stick, build pressure, cause earthquakes)

What is a transform fault?

Break in rocks/plates where movement occurs

How do earthquakes happen?

plates collide, stick, build pressure, and release

What plates can earthquakes happen on?

Convergent and Transform boundaries

Can we predict when an earthquake will happen?

No, but we can predict where it may happen

What processes build volcanic chains?

Convergent plates (material from melting lithosphere), divergent plates (material from the mantle), rifts