Geology Midterm 1

What are the two ways to classify Earth's structure?

Rheologic and compositional

What is rheology?

How materials deform and flow under force

What is the lithosphere?

Rigid outer shell of Earth (crust + upper mantle)

What is the asthenosphere?

Weak, partially molten layer beneath lithosphere

What is the mesosphere?

Deeper mantle layer, denser and convecting

State of the outer core

liquid

State of the inner core

solid

What distinguishes layers in the rheologic scheme?

Physical properties (strength, rigidity, flow)

What distinguishes layers in the compositional scheme?

Chemical composition

Composition of continental crust

Felsic/intermediate rocks

Composition of oceanic crust

Mafic rocks

Composition of mantle

Ultramafic rock (peridotite)

Why is oceanic lithosphere lower than continental lithosphere?

It is denser and thinner

What evidence supports continental drift?

Fit of continents, fossils, connection of mountain ranges, glacial deposit

Why was continental drift rejected?

No mechanism for how continents moved was known and where does the oceanic floor come from

What does the lithosphere consist of?

Crust and upper mantle

Where do deep ocean trenches form?

Subduction zones

Why doesn't continental lithosphere subduct?

Too buoyant (low density)

Motion at transform boundaries

Plates slide past each other

Mineral

Naturally occurring, inorganic solid having a specific elemental composition and a specific arrangement of atoms

What is a rock?

an aggregate consisting of more than one mineral

Cation

Positively charged ion

Anion

Negatively charged ion

Strongest bond type

Covalent (diamond)

Ionic bond

electron exchange (halite)

Weak bonds significance

Control cleavage and softness, electron spin, opposite charge attraction

What is the serpentine mineral family?

Lizardite, antigorite, chrysotile (asbestos insulation)

What is serpentinite?

Rock made of serpentine minerals

Difference between serpentine and serpentinite

Serpentine = minerals; serpentinite = rock

What is chrysotile?

Fibrous serpentine mineral (white asbestos)

Difference between chrysotile and lizardite/antigorite

Different crystal structures/habits

White asbestos

Chrysotile

Brown and blue asbestos similarity

Both are amphibole minerals

Why is chrysotile less harmful?

Different structure than amphiboles

Silicate minerals

the most abundant and significant "family" of rock-forming minerals

What is a silica tetrahedron?

SiO₄ structure

Shape of silica tetrahedron

4-sided pyramid

what influences structure of silicate minerals

minerals having a higher proportion of silica have more complex structures (Higher silica = more complex structures)

Cleavage

Tendency to break along planes of weakness

Mica cleavage

1 direction "perfect cleavage"

Halite cleavage

3 directions at 90° (consists of weak bonds)

Quartz cleavage

none (fracture) very strong bonds and symmetrical

Why graphite is soft

Weak bonds between layers

Why diamond is hard

Strong covalent bonds throughout

Al₂SiO₅ polymorphs

Kyanite, sillimanite, andalusite

Why are these minerals significant?

Indicate pressure and temperature conditions

What are index minerals?

Minerals that form at specific P-T conditions

Glaucophane indicates

High pressure, low temperature

What environment forms blueschist?

Subduction zones

Magma

Molten rock below surface

Lava

Molten rock above surface

Intrusive rock

Forms below surface

Extrusive rock

Forms at surface

Batholith

Large intrusive body

Sill

Parallel to layers

Dike

Cuts across layers

Felsic rocks

High silica, light minerals

Mafic rocks

Magnesium and iron rich

Intermediate rocks

Between felsic and mafic

Ultramafic Rocks

Mantle composition

Felsic intrusive/extrusive pair

Granite/ rhyolite

Intermediate pair

Diorite / andesite

Mafic pair

Gabbro / basalt

What does Bowen's reaction series show?

Order minerals crystallize from magma

Which minerals crystallize first?

Mafic

Which crystallize last?

Felsic

What is partial melting?

Only some minerals melt, partial melting at subduction zones when oceanic lithosphere is forced into the mantle - melting occurs

Which minerals melt first?

Lowest melting point, only part of the mass melts

Resulting magma composition

More silicic/ less mafic than source rock

Where does magma form at subduction zones?

Mantle wedge above subducting plate

What causes melting at subduction zones?

Water lowers melting temperature

What is decompression melting?

Melting due to reduced pressure and decreased melting point

Where does decompression melting occur?

Mid-ocean ridges and rift zones

What is a slab window?

Gap where mantle rises and melts

What led to development of magma 7 sisters?

slab window

What is a hot spot?

Mantle plume causing volcanism, originate below the asthenosphere

What controls eruptive style?

Magma composition

Why are felsic eruptions explosive?

High viscosity and trapped gases

Where do composite volcanoes form?

Subduction zones

What are composite volcanoes made of?

Pyroclastic material and lava

What is a pyroclastic flow?

Hot, fast-moving ash and gas

What is a caldera?

Collapsed volcanic crater (common in composite volcanoes) depression in the center of a volcano surrounded by "ring faults "

How does a caldera form?

collapse occurs after a large eruption and the magma chamber below the volcano is emptied

Why do lakes form in calderas?

Water fills depression if the caldera rims aren't breeched by streams ( crater lake)

Shield volcano characteristics

Broad, gentle slopes, low viscosity magma

Composite volcano characteristics

Steep, explosive, pyroclastic deposits

What rock forms at spreading centers?

Pillow basalt

Why pillow basalt forms

Rapid cooling in water

What are black smokers?

Hydrothermal vents

Energy source for life at vents

Chemical energy

What volcano type forms at hot spots?

Shield volcanoes

Why hot spots are useful

provide fixed reference frame for evaluating plate motions

What are seamounts?

Underwater volcanic mountains

What is a lahar?

volcanic mudflow

Why are lahars dangerous?

Fast-moving and long-lasting

Why is decreased gas emission dangerous?

Indicates pressure buildup

What was unexpected about the 2011 Japan earthquake?

Unusual fault behavior and complexity

Tsunami height

very large waves (up to 35m tall)

Tsunami inland distance

traveled 10 kilometers inland

Direction Japan moved

eastward