EESC Unit 2 Exam (Concise)

3 rock types and how they form

Igneous = melt cools. Sedimentary = pieces cemented or minerals precipitated from water. Metamorphic = solid rock changed by heat/pressure, no melting

How to tell rock types apart

Igneous = smooth, no layers. Sedimentary = layers/bedding, fossils. Metamorphic = folded, minerals lined up

Where does igneous rock form in plate tectonics?

Mid-ocean ridges and volcanic arcs above subduction zones (plus hot spots, rifts)

Where does metamorphic rock form in plate tectonics?

Cores of mountain belts (continents colliding) and subduction zones

Magma vs. lava

Magma = underground, intrusive, cools slowly. Lava = at surface, extrusive, cools fast

Two sources of Earth's internal heat

Leftover heat from Earth's formation (accretion) and radioactive decay

Partial melting

Only the minerals with the lowest melting points melt. The rest stays as solid residue

Crystallization order

Opposite of melting: highest-melting-point minerals crystallize first (e.g., olivine). Caused by cooling

Fractional crystallization

Growing minerals use up certain ingredients, so the leftover melt's composition changes over time

Cooling speed and grain size

Slow = coarse (granite). Fast = fine. Instant (quenching) = glass (obsidian)

3 places melting happens

1) Rising mantle plume (pressure drops) = hot spot. 2) Subduction zone (water lowers melting point). 3) Base of crust (heated by magma)

Why do almost all subduction zones have volcanic arcs?

Water released from the sinking plate lowers the melting point of the mantle above

Dike vs. sill

Dike cuts across layers. Sill slides between layers

Xenolith, and why at the border of a pluton?

Chunk of wall rock that fell into magma. Comes from the wall, and the edge cools first and freezes it in place

Viscosity

Resistance to flow (honey = high, water = low)

What raises viscosity?

More silica (SiO2), more gas, more crystals

What lowers viscosity?

Higher temperature

Low vs. high viscosity eruption

Low = effusive, lava flows. High = explosive, pyroclastics

Shield volcano

Gentle slopes, runny basaltic lava, effusive. Hot spots (Hawaii)

Stratovolcano

Steep, thick silica-rich lava, explosive. Subduction zones (Ring of Fire)

Mid-ocean ridges produce…

Fissure eruptions and pillow basalts

Crater vs. caldera

Crater = small bowl at top. Caldera = huge collapse after magma chamber empties

Pyroclastics are like sediment because…

Loose material (ash) that becomes rock (tuff) when consolidated

Look-alike trap: layered basalt flows

Look like sedimentary layers from far away but are igneous

Pyroclastic flow vs. lahar

Pyroclastic flow = debris + air. Lahar = debris + water. Both too fast to outrun

Main volcanic gases

H2O (steam, most), CO2, SO2, H2S

Volcanic emissions that cool climate

Sulfate aerosols and ash (reflect sunlight)

Volcanic emissions that warm climate

CO2 and methane (greenhouse gases)

Records of past climate change

Tree rings, ice layers, fossil shells, extinctions

Hazards by distance

Lava (~50 km) < lahar (~150 km) < pyroclastic flow (~200 km) < ash fall (~2,500 km)

Why limnic eruptions are deadly

CO2 is heavier than air, sinks, and suffocates people and animals

Pompeii

Destroyed in 79 CE by Vesuvius, buried under ~25 m of ash (tuff)

Benefit of volcanoes

Fertile soils for farming

Weathering vs. erosion

Weathering = breaks rock in place. Erosion = moves pieces away

Physical vs. chemical weathering

Physical = smaller pieces, same chemistry. Chemical = changes the minerals

Chemical weathering needs…

Water (rain or humidity). Some types also need oxygen

Where is chemical weathering strongest/weakest?

Strongest in tropics (warm, wet). Weakest at poles and high altitudes

Selective weathering

Different rock types weather at different speeds

Why does weathering happen?

Rocks formed under different conditions are unstable in water and air at the surface

Regolith vs. soil

Regolith = inorganic only. Soil = inorganic + organic, supports plants

Erosion needs…

Gravity, wind, water, or ice

Fragments with longer transport become…

Smaller, more similar in size, more rounded, more single-mineral

Sediment vs. sedimentary rock

Loose vs. consolidated (= cemented = lithified). Sand → sandstone, mud → shale, pebbles → conglomerate

4 types of sedimentary rock

Clastic (rock pieces), biochemical (shells), organic (plants), chemical (precipitated from water)

Why chemical rocks precipitate

Water evaporates, ions concentrate until saturated, so minerals must crystallize (salt lakes)

Delta

River slows, loses energy, dumps coarse sediment near shore. Fine clay goes far out to abyssal plains

What layering, ripples, coral debris, fossils reveal

The depositional environment

Why protoliths become metamorphic

Higher temperature and/or pressure, or changed chemistry, deep in the crust

Does metamorphism melt rock?

No, solid state. Partial melting only at the highest grade

What changes during metamorphism?

Mineral content and texture (size, shape, arrangement, fossils destroyed)

Protolith composition determines…

Which minerals form after metamorphism

Temperature and reaction speed

Higher temperature = faster reactions

Confining pressure vs. stress

Confining = equal all directions, no shape change. Stress = one direction (plate collisions), changes shape

Foliation

Minerals lined up, caused by stress, always perpendicular to the squeeze

Role of fluids in metamorphism

Carry mineral "nutrients" faster than diffusion through solid, speeding growth

3 types of metamorphism

Subduction-zone (high P, low T). Mountain-belt (T and P rise together). Contact (heat only, no foliation)

3 ways rocks deform

Displacement (moves), rotation (tilts), distortion (changes shape)

Brittle vs. plastic

Brittle = breaks, near surface. Plastic = bends, deeper (hotter, more pressure)

Compression vs. extension

Squeezing together vs. pulling apart

Thrust vs. normal fault

Thrust = compression, block goes up and over. Normal = extension, block drops down

Conditions for folding

Plastic deformation + compression

Anticline vs. syncline

Anticline = arch, oldest in center. Syncline = trough, youngest in center. Either can plunge (tilt)

Fold-and-thrust belt

Stacked thrust faults over a detachment fault. Forms where continents collide (Alps, Himalaya)