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Rocks:Ig
neou
s
Igne
ous Se
dim
enta
ry
Sedi
men
tary
Metamorp
hic
Metamorp
hic
Keepers of Earth’s HistoryKeepers of Earth’s History 1
What’s in your rock?:
Hornblende
Orthoclase
Quartz
aggregates of minerals
Granite
Biological material
Fossil fragments
Plant material
3
Understanding rocks is the basic foundation ofknowledge for earth scientists and materials thatmake up the earth.
Understanding rocks is the basic foundation ofknowledge for earth scientists and materials thatmake up the earth.
• Every rock “speaks” to the observer and gives clues about where and how it was formed.• Rocks are divided into 3 major groups:
• Igneous• formed from solidifying hot molten
rock (magma)
• Every rock “speaks” to the observer and gives clues about where and how it was formed.• Rocks are divided into 3 major groups:
• Igneous• formed from solidifying hot molten
rock (magma)• Sedimentary
• formed on the surface of the earth from weathering processes
• Sedimentary• formed on the surface of the earth from
weathering processes
• Metamorphic• pre-existing rocks are subjected to
various pressure and temperature relationships
• Metamorphic• pre-existing rocks are subjected to
various pressure and temperature relationships
4
How does an earth scientist distinguish betweenthe three rock types (Ig, Seed, and Met)?
Texture:• the appearance of the rock
• size, shape, and arrangement of mineral grains.
Composition (mineral assemblages)• types and relative proportions of minerals
making up a rock
• composition, mineral make-up, chemistry--all indicators of a rock’s composition
All rocks are identified based on their texture and composition. 5
The Rock Cycle:• where the earth’s internal forces meet the earth’s external forces (at the earth’s surface)
Earth’s internal forces Earth’s external forces
• moving continents (PT)• earthquakes• elevation of mountains• volcanic eruptions
• the hydrosphere (HC)• atmosphere• erosion (wind, water, ice)• biosphere activities
Produce a continuous cycle of rising mountains only to beweathered down and uplifted repeatedly. As a result, igneoussedimentary, and metamorphic rocks are created.
7
I I Earth Science, especiallythe rock cycle !!!!!!!!!!!!! Earth Science, especiallythe rock cycle !!!!!!!!!!!!!
I will get an A on my exams and quizzes.
Discuss with a friend:
1.Briefly identify each rock group and its geologic environment.
2. Draw the rock cycle, and explain how the rock cycle works to your neighbor.
3. Why is the rock cycle a “cycle”???
8
MagmaMagma
Extrusive - igneous rocks – above the earth’s surface volcanic rocks lava flows Example – Hawaiian Volcanoes
Intrusive - igneous rocks – below the earth’s surfaceplutonic rockslarge granite mountainsExample – Sierra Nevada Mountain Range
• the parent material for igneous rocks (if not all rock groups)
• typical temperature 1,200oC (2,200oF)• forms about 250 km or 150 miles below the earth’s surface
Grain size determines if the ig rock is extrusive orintrusive. Magma determines the rock’s composition.
10
When observing “frozen magma” (an igneous rock), how does a geologist know if the rock is an Extrusive orIntrusive igneous rock?
When observing “frozen magma” (an igneous rock), how does a geologist know if the rock is an Extrusive orIntrusive igneous rock?
checking the crystal size - Does the rock contain visible crystals, or are crystals non-existent?checking the crystal size - Does the rock contain visible crystals, or are crystals non-existent?
Factors that affect crystal size in an igneous rock:The rate at which magma cools
• slow cooling – visible minerals• rapid cooling – non-visible minerals
Factors that affect crystal size in an igneous rock:The rate at which magma cools
• slow cooling – visible minerals• rapid cooling – non-visible minerals
Igneous Rock TexturesIgneous Rock Textures
• non-visible minerals• rapid cooling magma• extrusive ig rock
• non-visible minerals• rapid cooling magma• extrusive ig rock
• visible minerals• slow cooling magma• intrusive ig rock
• visible minerals• slow cooling magma• intrusive ig rock
Cooled above thesurface (fine-grained)
Cooled above thesurface (fine-grained)
Cooled below the surface (coarse-grained)
Cooled below the surface (coarse-grained) 11
Composition of Igneous RocksHow much silica (SiO2) is in your igneous rock?Felsic compositions (feldspar + silica)
• light-colored igneous rocks• common minerals: feldspar and quartz• 70% SiO2
Mafic compositions (magnesium + iron)• dark-colored igneous rocks• common minerals: olivine and pyroxene• 50% SiO2
• ultramafic: composed entirely of olivine and pyroxene and less than 50% silica (SiO2)
Intermediate compositions:• mixture of felsic and mafic minerals• about 60% silica (SiO2)
14
How are igneous rocks classified?• Using their TEXTURE and COMPOSITION
Igneous rocks are classified based on TEXTURE andCOMPOSITION.
TE
XT
UR
E
CO
AR
SE
ph
aneritic
FIN
Eap
han
itic
COMPOSITIONFelsic (light color)
70% silicaMafic (dark color)
50% silicaIntermediate color
60% silica
Granite Diorite Gabbro
Rhyolite Andesite Basalt
Igneous rocks have the same chemistry but different textural characteristics due to the type of geologic environment (cools quickly or slowly).
I I Earth Science, especiallyigneous rocks. Earth Science, especiallyigneous rocks.
I will get an A on my exams and quizzes.
1.What is the difference between extrusive and intrusive igneous rocks?2. How can one tell the difference between an extrusive and intrusive rock texture?3. The composition of a mafic ig rock is…. The composition of a felsic ig rock is ….4. A fine-grained, light-colored ig rock is called a ………………….
17
How is a sedimentary rock formed???How is a sedimentary rock formed???
Pre-existingRock
Pre-existingRock
erosionerosion
water, wind, ice
water, wind, ice
breaks downpre-existing rockbreaks downpre-existing rock
sedimentsediment
transportedtransportedLakesLakes
RiversRivers
Depos
ited
Depos
ited
compactedcemented
compactedcemented
lithifiedlithified SedimentaryRock
SedimentaryRock
Why is the earth’s surface 75% sedimentary rocks?Why is the earth’s surface 75% sedimentary rocks?19
Erosional processes – later (Chapter 4)Erosional processes – later (Chapter 4)
Sediments are separated into 3 broad categories:
• Clastic sediments: inorganic grains or mineral fragments ranging in size from boulders to clay particles (flour size)
• Chemical sediment: formed by the precipitation of minerals dissolved in lakes, rivers, or seawater environments
• Biogenic (bioclastic) sediment: sediment composed of animal and plant remains or material precipitated by biological processes
Sediments are separated into 3 broad categories:
• Clastic sediments: inorganic grains or mineral fragments ranging in size from boulders to clay particles (flour size)
• Chemical sediment: formed by the precipitation of minerals dissolved in lakes, rivers, or seawater environments
• Biogenic (bioclastic) sediment: sediment composed of animal and plant remains or material precipitated by biological processes To be a sedimentary rock, it must be lithified.To be a sedimentary rock, it must be lithified.
21
Lithification: processes by which sediment is transformed into sedimentary rockLithification: processes by which sediment is transformed into sedimentary rock
Sediment can be lithified in three common processes: Sediment can be lithified in three common processes: Compaction: Overlying weight of the sediment “squeezes”and compresses pore spaces, which pushes particles together.Compaction: Overlying weight of the sediment “squeezes”and compresses pore spaces, which pushes particles together.
A B
A. loose, unconsolidated sediment with abundant pore spaceB. compacted, compressed sediment with reduced pore space
A. loose, unconsolidated sediment with abundant pore spaceB. compacted, compressed sediment with reduced pore space
Cementation: Pore water is expelled from voids, and risingwater carries iron, calcium carbonate, and silica which precipitates as geological glue (cement) holding the grains together.
Cementation: Pore water is expelled from voids, and risingwater carries iron, calcium carbonate, and silica which precipitates as geological glue (cement) holding the grains together.
Grains are cemented together by three types of cements:
• iron cement• calcium carbonate cement• silica cement
Grains are cemented together by three types of cements:
• iron cement• calcium carbonate cement• silica cement 22
Lithification processes
Recrystallization: Overlying pressure causes less stableminerals to convert to more stable minerals, producing new substances that cement pre-existing grains.
Recrystallization: Overlying pressure causes less stableminerals to convert to more stable minerals, producing new substances that cement pre-existing grains.
Overlying pressureOverlying pressure Grain boundaries convertto more stable mineral
compositions, “cementing”grains together.
Grain boundaries convertto more stable mineral
compositions, “cementing”grains together.
23
Clastic Sediment:Clastic Sediment:
lithifiedlithifiedgravel sediment rangingfrom pea-sized to largergravel sediment rangingfrom pea-sized to larger conglomerateconglomerate
sand-sized particles (fine to coarsesandpaper)
sand-sized particles (fine to coarsesandpaper)
sandstonesandstone
finer particles – size of table saltfiner particles – size of table saltsiltstonesiltstone
finest sedimentaryparticles (flour-size)finest sedimentaryparticles (flour-size) shaleshale
lithifiedlithified
lithifiedlithified
lithifiedlithified
24
Chemical Sediments and Sedimentary Rocks
Chemical Sediment: sediment formed by the precipitationof minerals dissolved in a lake, river, or seawaterChemical Sediment: sediment formed by the precipitationof minerals dissolved in a lake, river, or seawater
All surface water and groundwater contain dissolved ions (chemicals), creating a venue for precipitation of chemical sediment.
All surface water and groundwater contain dissolved ions (chemicals), creating a venue for precipitation of chemical sediment.
Precipitation of chemical rocks takes place in two ways:
• Plants and animals alter the chemical balance of the water body (lake, ocean).
Increasing amounts of calcium carbonate cause precipitation of limestone.
• evaporation of chemically saturated water bodies
Precipitation of chemical rocks takes place in two ways:
• Plants and animals alter the chemical balance of the water body (lake, ocean).
Increasing amounts of calcium carbonate cause precipitation of limestone.
• evaporation of chemically saturated water bodies 26
Evaporation of chemically saturated water createsa chemical sedimentary rock (evaporite).
Na+Na+ Na+Na+
Na+Na+ Na+Na+
Cl-Cl-
Cl-Cl-
Cl-Cl-Cl-Cl- a lake containing sodium (Na+)
and chlorine (Cl-)--free ionsa lake containing sodium (Na+)and chlorine (Cl-)--free ions
EvaporationEvaporation
NaCl
Lake water is evaporated,concentrating sodium andchloride ions (saturation).
Sodium and chlorine combineto form halite (table salt).
Lake water is evaporated,concentrating sodium andchloride ions (saturation).
Sodium and chlorine combineto form halite (table salt).
27
The Great Salt Lake, Utah(evaporite halite)
The Great Salt Lake, Utah(evaporite halite)
UtahUtah
As lake becomes saturated,density of water increases.As lake becomes saturated,density of water increases.
28
Chemical – sedimentary rocks that have beenprecipitated or are the result of evaporation Chemical – sedimentary rocks that have beenprecipitated or are the result of evaporation
Gypsum – evaporite CaSO4Gypsum – evaporite CaSO4
Halite – evaporiteNaCl
Halite – evaporiteNaCl
Limestone--precipitated
calcium carbonate
Limestone--precipitated
calcium carbonate
29
Biogenic Sediments and Biogenic Rocks:Biogenic sediment is composed of organic remains of plants andanimals (bioclastic rocks).
• shell, bones, teeth, plant fragments, wood, roots
Biogenic Sediments and Biogenic Rocks:Biogenic sediment is composed of organic remains of plants andanimals (bioclastic rocks).
• shell, bones, teeth, plant fragments, wood, roots
Common Biogenic Rocks:• Limestone
• most abundant biogenic sedimentary rock• composed of calcium carbonate CaCO3(calcite, dolostone,
aragonite)• lithified shells, skeletal material
Common Biogenic Rocks:• Limestone
• most abundant biogenic sedimentary rock• composed of calcium carbonate CaCO3(calcite, dolostone,
aragonite)• lithified shells, skeletal material
• Chert• composed of silica SiO2
• precipitated silica shells (made by sea animals) that protect microscopic sea animals – Animals die, and silica shells sink, creating layers of chert beds on the ocean floor.
• Chert• composed of silica SiO2
• precipitated silica shells (made by sea animals) that protect microscopic sea animals – Animals die, and silica shells sink, creating layers of chert beds on the ocean floor.
30
“When the animal dies, it loses the chert off its back.”“When the animal dies, it loses the chert off its back.”
Common Biogenic RocksCommon Biogenic Rocks
Peat to Coal• accumulated remains of terrestrial plants• with time and pressure ---- peat• continued pressure and lithification ------ coal
Peat to Coal• accumulated remains of terrestrial plants• with time and pressure ---- peat• continued pressure and lithification ------ coal
PeatPeat
Bituminous coalBituminous coal
Anthracite coalAnthracite coal
Increasing pressure
Increasing pressuremetamorphismmetamorphism
lithificationlithification
31
Biogenic (bio-clastic) rocks –
result from animal and plant secretions -- The term “clastic” indicates that these rocks contain fossils or parts of plants, shells, compacted plant material
Biogenic (bio-clastic) rocks –
result from animal and plant secretions -- The term “clastic” indicates that these rocks contain fossils or parts of plants, shells, compacted plant material
Animal partsAnimal parts
Cemented shell fragmentsCemented shell fragments
CoquinaCoquina
Fossil LimestoneFossil Limestone
Chalk
Microscopic fossils
32
What do sedimentary rocks tell the earthscientist?What do sedimentary rocks tell the earthscientist?
These rock “layers” weredeposited one layer at a time and lithified.
The banded appearanceis known as bedding orgroups of layers called strata.
The boundary between each stratum is called a bedding surface.
These rock “layers” weredeposited one layer at a time and lithified.
The banded appearanceis known as bedding orgroups of layers called strata.
The boundary between each stratum is called a bedding surface.
stratastratabeddingbedding
Bedding surface
By observing the sedimentary rock type (clastic, chemical,biogenic) and depositional patterns, an earth scientist candecipher the geologic history – like reading pages in a book.
By observing the sedimentary rock type (clastic, chemical,biogenic) and depositional patterns, an earth scientist candecipher the geologic history – like reading pages in a book.33
Sedimentary Rock Classification Summary TreeSedimentary Rocks are divided into 3-classification categories:
Clastic sediments Chemical sediments Bio-clastic (chemical)sediments
composed of inorganicgrains
formed by precipitation
plants andanimals
evaporationprocesses
composed of “animal parts”from
classification based on distribution of grain sizes
Conglomerate
Sandstone
Shale
Siltstone
Decreasing grain size
Classification based onlack of grains and chemical
composition
Gypsum (CaSO4)
Halite (NaCl)
Limestone (CaCO3)
Classification based onObserved fossils, animal parts,
Plant/animal secretions
Fossil-limestone
Coquina
Chalk
I I sedimentary rock classification. sedimentary rock classification.
I will get an A on my exams and quizzes.
Discuss with a friend:
1.Describe at least 2 characteristics of each sedimentary rock classification (clastic, biogenic, chemical).
2.Give a rock example for each classification.
36
What is “metamorphism?” What is “metamorphism?”
• transformation of pre-existing rock to a metamorphic rock through pressure and temperature relationships
• transformation of pre-existing rock to a metamorphic rock through pressure and temperature relationships
• meta (change) morphism (form)• meta (change) morphism (form)
• All changes take place through solid state transformation.
• All changes take place through solid state transformation.
38
Types of Metamorphism• takes place around 150oC (Temperature) • typically at depths of 5 km below the earth’s surface (Pressure)
Types of Metamorphism• takes place around 150oC (Temperature) • typically at depths of 5 km below the earth’s surface (Pressure)
At this temperature and pressure, new mineralsare formed – changed from one mineral to another.
At this temperature and pressure, new mineralsare formed – changed from one mineral to another.
39
I I metamorphic rocks. metamorphic rocks.
I will get an A on my exams and quizzes.
Discuss with a friend:
1.How do you define metamorphism? – Be specific.
2.What two major factors are necessary for pre-existing rocks to become metamorphosed?3. Where does metamorphism typically take place within the earth?
40
2 Common types of metamorphism2 Common types of metamorphism
• contact metamorphism
• regional metamorphism
44
What is contact metamorphism?What is contact metamorphism?
• Contact metamorphism:
magma “contacts” solid rock – heat is transferred into overlying
rocks through conduction – changing the pre-existing rock it intruded
• high heat/low pressure• localized metamorphism• “fast-acting,” like touching a
hot frying pan
• Contact metamorphism:
magma “contacts” solid rock – heat is transferred into overlying
rocks through conduction – changing the pre-existing rock it intruded
• high heat/low pressure• localized metamorphism• “fast-acting,” like touching a
hot frying pan 45
What is regional metamorphism?What is regional metamorphism?
Regional Metamorphism
Pre-existing rock is subjected to intensestresses and strains (deformation) usuallyfrom the forces of mountain building.
• high heat/high pressure• very widespread geographically• like experiencing a slow sunburn
Regional Metamorphism
Pre-existing rock is subjected to intensestresses and strains (deformation) usuallyfrom the forces of mountain building.
• high heat/high pressure• very widespread geographically• like experiencing a slow sunburn
47
I I the different ways to createMetamorphism. the different ways to createMetamorphism.
I will get an A on my exams and quizzes.
Discuss with a friend:
Describe the conditions necessary for eachtype of metamorphism:
• contact metamorphism• regional metamorphism
49
Heat sources:contact with hot magma – heat penetrates
overlying rocks (conduction)
geothermal gradient – heat increases with depth – rocks are hotter when buried
Heat sources:contact with hot magma – heat penetrates
overlying rocks (conduction)
geothermal gradient – heat increases with depth – rocks are hotter when buried
50
Metamorphic heat sources:
Geothermal Gradient
• Temperature increases as depth increases.
• Large thermal gradient is at the surface.
• Gradient decreases after 1000 km depth.
Geothermal Gradient
• Temperature increases as depth increases.
• Large thermal gradient is at the surface.
• Gradient decreases after 1000 km depth.
10001000 20002000 30003000 4000400000
Steep gradientSteep gradient
51
Pressure – increases with depth,various types of pressure rearrangeminerals – minerals compact or elongate
Pressure – increases with depth,various types of pressure rearrangeminerals – minerals compact or elongate
Confining pressure Differential pressure
52Pressure associated with metamorphism
How does one know how much metamorphismhas taken place in a rock?• reflected in the rock’s texture
How does one know how much metamorphismhas taken place in a rock?• reflected in the rock’s texture
Not MetamorphosedNot Metamorphosed
Metamorphosed – mineralgrains are in a preferred direction -- FOLIATION
Metamorphosed – mineralgrains are in a preferred direction -- FOLIATION
53
I I to metamorphose. to metamorphose.
I will get an A on my exams and quizzes.
Discuss with a friend:
1.Describe two heat sources associated with metamorphism.2.Define the differences between confining and differential pressures.3. Draw a diagram that shows mineral orientation due to confining and differential type pressures.
54
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