GEO Exam 2 Study Guide

Magma

Molten rock below ground

Lava

Molten rock once it has reached the surface

Intrusive settings

Cool at depth/underground; loses heat slowly, crystals often grow large

Extrusive settings

Cool at or near the surface; cools rapidly, chill too fast to grow big crystals

decompression, addition of volatiles (water), and heat transfer from rising magma

How does Magma form?

Different rocks melt at different temperatures/pressures depending on their composition. Mafic minerals melt last, while felsic minerals melt first

Why do different rocks melt at different temperatures/pressures?

Aphanitic: fine-grained

Phaneritic: coarse-grained

Porphyritic: has phenocrysts distributed throughout a finer matrix; indicates two stages of cooling

What texture does aphanitic, phaneritic, and porphyritic have?

source rock, partial melting, assimilation, and magma mixing

What factors control magma composition?

Partial melting: when a rock is exposed to higher temperatures the felsic minerals melt first, while mafic minerals melt last

Assimilation: while magma slowly moves upward, it may incorporate the chemistry of surrounding rock that melt due to the heat of the magma

How does magma composition change with partial melting and assimilation?

Geysers

A natural hot spring that intermittently shoots jets of hot water and steam high into the air

They are both created by the same underground plumbing system where there is a circulation of hot, mineral-rich water powered by magma

Why are geysers found near ores?

Gabbro

Is Mafic and can be found in lower oceanic crust

Basalt

Is mafic and can be found in oceanic floor

Granite

Is felsic and is found deep within continental crust

Rhyolite

Is felsic and is found in continental volcanic regions and along convergent plate boundaries

Diorite

Is intermediate and can be found at convergent plate boundaries

Andesite

Is intermediate and can be found at subduction zones and convergent plate boundaries

Volcanic eruptions causes cooling in the short-term because of ash, but causes heating in the long-term because of gases emitted

How can volcanic eruptions affect climate in both the short-term and long-term?

caldera

A large volcanic crater that forms primarily through the collapse of a volcano after a significant eruption, where the ground above an emptied magma chamber sinks inward due to the removal of magma that once supported it

1. Shield volcano: divergent plate boundaries and hot spots

2. Cinder cones: flanks of larger volcanoes and in volcanic fields

3. Stratovolcanoes (composite): convergent plate boundaries where an oceanic plate subducts beneath a continental plate

What are the three main types of volcanoes and where are they found?

Volcanic domes

A steep-sided mound formed by the slow accumulation of viscous lava that cannot flow away easily

Volcanic fissures

A linear volcanic vent through which lava erupts, typically without explosive activity

Volcanic craters

A bowl-shaped depression atop a volcano

its viscosity determines that; the thicker it is the more explosive the volcano

How does magma composition determine the explosivity of a volcano?

Pyroclastic flow

A dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at a great speed

Lahar

A destructive mudflow on the slopes of a volcano

Mt. Vesuvius (Pompeii, Italy)

City buried under 13-20 feet of volcanic ash. Eruption occurred in 79 AD

Mt. Saint Helens

Eruption in 1980 in Washington State. Caused 61 casualties. There was a vertical and lateral blast from the volcano.

Hotspot

An area where hot material from deep within earth’s mantle rises toward the surface, creating volcanic activity

magma is usually basaltic and runny

What is the effect of oceanic crust over a hot spot?

Magma can interact with and melt continental rocks, making it higher in silica and thicker/ more viscous, leading gases to become trapped more easily, causing more explosive eruptions

What is the effect of continental crust over a hot spot?

very explosive magma meaning it has high viscosity and is thick

What magma do you see with a stratovolcano?

Basaltic magma (explosive/runny)

What magma do you see with a cinder cone volcano?

Basaltic magma (gentle/flowing)

What magma do you see with a shield volcano?

1. earthquake activity

2. changes in shape

3. changes in heat flow

4. increases in gas emission and steam

What are the 4 ways we can predict volcanic eruptions?

freeze/thaw (frost wedging), exfoliation and sheeting, salt wedging, and biological

What are the main types of physical weathering?

dissolution, oxidation, and hyrdolysis

What are the main types of chemical weathering?

They are complementary. Chemical weathering acts on surfaces, which increase due to physical weathering.

How do chemical and physical weathering exacerbate one another?

Soil is the loose material on Earth’s surface that supports plant growth, while sediment mainly consists of rock/mineral particles that can be transported and deposited

What is soil and how is it different from sediment?

The process by which loose sediment is turned into solid sedimentary rock; its two main processes are compaction and cementation

What is lithification and its two main processes?

Siliciclastic (detrital), chemical (biochemical), and organic

What are the main types of sedimentary rock?

conglomerate, breccia, sandstone, siltstone, shale/mudtone

What are the different types of clastic/detrital sedimentary rocks?

As sediment travels farther from its source sorting increases, roundness increases; if its angular and poorly sorted it is usually closer to the source

How do sorting and angularity change with maturity/distance from their source?

tells you the energy of the environment; large grains = high energy, small grains = low energy

What does grain size indicate?

chemical/biochemical, commonly forms from calcium carbonate

What kind of sedimentary rocks are limestone and where/how does it form?

chemical

What kind of sedimentary rocks are evaporites?

biochemical/chemical

What kind of sedimentary rocks are chert?

bedding/layering, cross-bedding, graded bedding, mud cracks, and ripple marks

What are the kind of structures we see in sedimentary rocks?

Metamorphism

Solid-state change due to change in preexisting rock’s environment

heat, pressure, fluids

What are the different types of metamorphic agents/causes?

temperature change, pressure change, compression/shear

What are the different types of metamorphic processes?

Foliated metamorphic rock

Have a layered, or foliated, pattern from the rearrangement or recrystallization of minerals

Nonfoliated metamorphic rocks

Monomineralic rocks with equant grains or not subjected to high enough pressure

slate, phyllite, schist, gneiss

What is the order from low to high grade of these four things? phyllite, schist, gneiss, and slate

shear stress

Causes foliation; crystal grains become elongated, flattened, or aligned in a particular direction

confining stress

Pressure is applied equally in all directions, so crystals tend to become more compact without a preferred alignment (more rounded/compact)

quartzite

What rock forms from the metamorphism of sandstone?

marble

What rock forms from the metamorphism of limestone?

hornfels

What rock forms from the metamorphism of contact metamorphism?

contact (thermal), burial (weight), dynamic (shearing), dynamothermal (regional), hydrothermal, subduction zones, shock

What seven tectonic environments/geological settings do we see metamorphism?

erosion and lithification

How can you change an igneous rock into a sedimentary?

heat and pressure

How can you change sedimentary into metamorphic?