EOSC210 P1

The Layers that form the Earth

inner core, outer core, mantle, asthenosphere, lithosphere, crust

inner core

mostly iron and nickel, solid

outer core

mostly iron and nickel, liquid

mantle

consists of lower mantle (rigid), asthenosphere (plastic), uppermost mantle (rigid)

less dense than core, mostly silicate minerals (abundant in iron and magnesium)

the crust

least dense, rigid, abundant silicate minerals

lithosphere

the uppermost mantle and the crust, together moves over the asthenosphere

oceanic crust

thinner, denser of the crusts

continental crust

thicker, less dense of the crusts

history leading to understanding of plate tectonics

continents connected, geology of land on opposite sides of ocean, fossils, the sea floor

7 different types of plate margins/boundaries

• Continent/Continent - Rift valley [divergent]

• Ocean/Ocean - Mid ocean ridge (spreading center) [divergent]

• Ocean/Ocean [convergent]

• Ocean/Continent [convergent]

• Continent/Continent [convergent]

• Transform

• Passive Margins

divergent margins

plates spreading or moving apart, symmetrical

can start as a rift valley, mature into ocean basin, with mid-oceanic ridge/spreading center

convergent margins

plates move toward each other

if plates are different densities (and at least one is oceanic), denser plate moves under the other and heads towards the core (it subducts)

no subduction if both are continental (just mountains)

transform boundaries

plates move past one another

passive margins

when continental lithosphere is connected to oceanic lithosphere and moves with it

Driving forces of movement of plate tectonics

heat and density

• mantle convection

• slab pull

• ridge push

mantle convection

earth’s heat leads to mantle undergoing convection (has convection currents) which pulls the lithosphere along its currents

slab pull

where earth subducts, increased pressure and heat cause mineralogical/chemical changes, increase density of subducting plate pulls plate down

ridge push

mid ocean ridges are spreading centers which creates slopes which cause forces away from the ridge

Mineral

Naturally occurring, inorganic solid element or compound, having an orderly internal structure, and characteristic chemical composition, physical form, and physical properties

How do minerals form?

• Cooling and crystallizing from lava or magma

  • fast cooling = small crystals

  • slow cooling = large crystals

• Precipitation from fluid

  • ex. evaporation brines lead to salt crystals

• chemical changes from metamorphism

  • New minerals in equilibrium with the conditions will grow

• Precipitation from biogenic activity (biomineralization)

  • Ex. coral reefs

How minerals are categorized into groups

Grouped based on their ions

silicate minerals

SiO₄^4-, tetrahedra arrangement

carbonate minerals

CO₃^2-, limestone, marble, tend to dissolve

sulfide minerals

S^2-, primary ores for many important minerals (Cu, Zn, Ni, etc)

Rock

an agglomeration of minerals

Igneous rock formation

crystalize from magma or lava

extrusive (volcanic) rocks

cools relatively quickly, making small crystals (hard to see) (aphanitic)

intrusive (plutonic) rocks

cool very slowly (years to millennia), large (visible) crystals (phaneritic)

Porphyritic

two stage cooling

Mineral Composition:

Felsic and Mafic

Felsic

Light colors, feldspar + silica (eg. Granite)

Mafic

dark colors, magnesium + iron (eg. Gabbro)

How to make magma

• increase temperature

• decrease pressure

• add water or other volatiles which lowers melting temp

Decompression melting

decreasing pressure to make magma

Plutons

mass of igneous rock that cools and crystallizes within the crust

Diapers

Rising bodies of magma

Batholith

large igneous bodies formed by several plutons formed together

Dykes

Flat intrusive blocks that cut through layers or follow fractures

• can be near the surface

• sometimes look extrusive

Sills

flat intrusive bodies, follow bedding and so tend to be horizontal

Laccolith

Mushroom shaped body, magma is injected between layers, inflates or puffs them up

Viscosity of magma

affected by temperature of magma

• high temp = less viscous

• low temp = more viscous

affected by composition of magma

• silicate minerals are “sticky”

• higher silica content, higher viscosity

mafic magma

• 45-55% silica

• high temp

• low viscosity (runny)

intermediate magma

• 55-65% silica

• avg temp

• avg to high viscosity

• explosive

felsic magma

• 65-75% silica

• relatively cool temp

• high viscosity

• highly explosive

Metamorphism

mineral (chemical) and crystalline changes in a rock caused by

• pressure

• temperature

• fluids

• & time

Country rock

original rock around metamorphic rock

parent rock (protolith)

sedimentary, igneous, and metamorphic rocks are the parents rocks

What drives metamorphism

• increased temp

• increased pressure

• fluid activity

• time

lithostatic

equal pressure in all directions, increases with depth

differential

directed stress (may cause compressive or shear), usually result of plate tectonics or sometimes meteorites

Foliation

as minerals recrystallize, they do so in preferred alignment, perpendicular to pressure (directed stress)

Non foliated

either formed without pressure or of minerals that don’t produce foliation

Slate

Product of low grade metamorphism

Phyllite

product of increased metamorphism of slate, can be wavy foliation, more “sheen”

Schist

the product of increased metamorphism of phyllite, micas and metamorphic minerals are visible

gneiss

increased temp and pressure on schist, visible crystals, no mica, layers of felsic and mafic

migmatite

mix of both metamorphosed and igneous material, rock finally begins to melt creating “mixed” rock

4 types of metamorphism

• contact metamorphism

• regional metamorphism

• metasomatism

• dynamic metamorphism

contact metamorphism

high temp, low pressure

• when magma moves to upper crust, high temp is added (to low pressure) to country rock

regional metamorphism

high temp, high pressure

• recrystallization and new minerals form foliated rocks

metasomatism

magma body releases fluid bodies and heats existing groundwater, convection occurs, alters composition of surrounding rocks

dynamic metamorphism

low temp, high pressure

• occur around fault zones

• rocks grind against each other and create friction (heat) and lots of pressure

weathering

the breakdown of rocks and minerals on earth’s surface without moving them

caused by factors such as:

• temp changes

• water

• chemical reactions

erosion

removal and transportation of rocks and soil from their original locations

typically due to agents such as:

• wind

• water

• ice

4 types of mechanical weathering

• frost wedging

• salt wedging

• exfoliation

• root wedging

frost wedging

water along fractures in rocks freezes (expanding), splitting the rock

• volume of ice is around 9% greater than water

salt wedging

pressure created by crystallization of salt particles in pore spaces and along fractures

exfoliation

(aka sheeting) rocks are subjugated to elastic compression, then, when brought to the surface, are released, which forms cracks and allows fluids to flow into

root wedging

plant roots grow in existing cracks, causes cracks to get larger

chemical weathering

disintegration of rock-forming minerals by chemical reactions with water or atmospheric gases

3 types of chemical weathering

• solution (dissolution)

• hydrolysis

• oxidation

dissolution

rocks dissolve when exposed to water

hydrolysis

chemical reaction that creates a new mineral

oxidation

reaction of free oxygen with metallic minerals

what aids in mechanical and chemical weathering of rocks

• fractures, faults, conduits

• porosity of the rocks

• increase of exposed surface area

• climate (temp, moisture)

• composition of minerals

physical products of weathering

sand and clastic sediment such as gravel silt

chemical products of weathering

clay, ions in solution

sediment

the product of weathering, physical fragments or ions in solution

sedimentary rock

sediment that has undergone lithification

Clastic rocks - formation of sedimentary rocks

material from physical weathering is transported and deposited, then compacted, then cemented by precipitated materials

Chemical Precipitates - formation of sedimentary rocks

ions in solution (sediment, but not clastic rock) are transported and then precipitated, creating chemical sedimentary products

Ways to classify sedimentary rocks

• grain size

• grain sorting

• grain shape

• sedimentary structures

Breccia

angular particles the size of boulders, cobble, or pebble (Gravel)

Conglomerate

rounded particles the size of boulders, cobble, or pebble (gravel)

Sandstone

sediment the size of sand

Siltstone

sediment the size of silt

shale or mudstone

sediment the size of clay

grain sorting

distribution of grain sizes or types

sediment maturity

relates to how far a sediment has been transported

immature sediment

• hasn’t traveled far

• variety of particle sizes

• mix of rock fragments

• angular particles

mature sediment

• travelled far

• clay or sand sized particles

• one mineral composition

• well rounded, similar sized particles

sedimentary structures

• bedding

• cross beds

• mud cracks

• ripple marks

bedding

arrangement of sedimentary rocks into layers, initially horizontal

cross beds

layers which cross over each other, slope swoop falls in direction of wind

mud cracks

arid environment with seasonal precipitation

ripple marks

indicate currents or waves

conformable parallel contacts

no “missing rock”

unconformity

type of contact with missing rock, often occurs when there is lots of time before deposition of next layer so top layer can be eroded away

faunal succession

organisms evolve through time, fossils in types of rocks give ages to said rocks