Transcript
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Rocks and RockRocks and Rock--FormingForming
ProcessesProcesses
Smith & Pun, Chapter 3Smith & Pun, Chapter 3
3.4 How are the rock classes3.4 How are the rock classes
related to one another?related to one another?
The Rock Cycle
Processes link
typesPlate tectonics is
driving force
3.13.1 How and where do rocks form?How and where do rocks form?
If we look closely at the loose materials undIf we look closely at the loose materials und
our feet what might we expect to find?our feet what might we expect to find?
Consider a beach along a sandstone cliff.Consider a beach along a sandstone cliff.
Fig 3.2a
3.13.1 How and where do rocks form?How and where do rocks form?
Bits of shell; calcite or aragonite
Small glassy
grains of quartz Some few dark
grains of magnetite
If we look closely we see
minerals of various sorts
Fig 3.2b
3.13.1 How and where do rocks form?How and where do rocks form?
But what else can we tell from observing?
The quartz
grains are
small, and
very round
Even the
dark grains
are round-
ish, if small
and the shell fragments, while flat, have rounded edges. What
processes are involved? Watch the waves moving the sand
Fig 3.2b
3.13.1 How and where do rocks form?How and where do rocks form?
So, we know for some rocksSo, we know for some rocksThey are made from bits of other rocks and/orThey are made from bits of other rocks and/or
organically derived mineralorganically derived mineral--like matterlike matter
(shells)(shells)
An abrasive process moves and reshapes theAn abrasive process moves and reshapes the
fragmentsfragments
Fragments of older rock consolidate into newFragments of older rock consolidate into new
rock with a mineral cementrock with a mineral cement
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3.13.1 How and where do rocks form?How and where do rocks form?
Water coming from a spring atop a rock. The
entombed trees bear evidence that a rock-forming
process is ongoing...The rock around the spring
itself appears to be made of
layered crystalline materialwith sponge-like holes.
Fig 3.3
3.13.1 How and where do rocks form?How and where do rocks form?
So, we now know that some other rocks:So, we now know that some other rocks:
Form by precipitation of minerals from waterForm by precipitation of minerals from water
These minerals cement together other looseThese minerals cement together other loose
sediments, ORsediments, OR
These precipitating mineralsThese precipitating minerals intergrowintergrow
3.13.1 How and where do rocks form?How and where do rocks form?At a volcano lava quickly
freezes into rock. That rock
(bottom left) is made of very small
mineral crystals. Other rocks
coughed up from deep within the
volcano (bottom right) show
mosaics oflarger crystals and
banded structures.
Fig 3.4
3.13.1 How and where do rocks form?How and where do rocks form?
Rocks around a volcano form by much differentRocks around a volcano form by much different
processes than in the previous examinations ofprocesses than in the previous examinations of
sediments and sedimentary rockssediments and sedimentary rocks
Minerals in these rocks have angular shapesMinerals in these rocks have angular shapes
Must have crystallized in place from molten rockMust have crystallized in place from molten rock
Both the spring and volcano have intergrownBoth the spring and volcano have intergrown
crystals, but the origins of crystals are differentcrystals, but the origins of crystals are different
3.13.1 How and where do rocks form?How and where do rocks form?
Most natural rocks areMost natural rocks are aggregates of mineralaggregates of mineralgrainsgrains..
Many rocks originate from observableMany rocks originate from observable
processes on or near Earthprocesses on or near Earths surface.s surface.
The presence of rocks that are not related toThe presence of rocks that are not related to
surface processes suggests a relation tosurface processes suggests a relation to
internal processes.internal processes.
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
ClassificationClassification is a central theme of scienceis a central theme of scienceOur observations ofOur observations ofexternal processesexternal processes atat
EarthEarths surface show that active surfaces surface show that active surface
processes produce minerals and hence rocksprocesses produce minerals and hence rocks
Internal processesInternal processes observations of rocksobservations of rocks
unassociated with surface processes must beunassociated with surface processes must be
related to some other group of phenomenarelated to some other group of phenomena
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3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
The three classes of rocks: sedimentary, igneous, and
metamorphic
Rock CycleRock Cycle
Proportions of Rock Types onProportions of Rock Types on
the Earththe Earth
Soil, sediment,
weathered rock,
regolith
gneousgneous
RocksRocks
IdentificaIdentifica
tiontion
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Igneous rocksIgneous rocks
Fig 3.6
Form from moltenForm from molten
magmamagma
Volcanic rocks formVolcanic rocks form
above ground =above ground =
extrusiveextrusive
Plutonic form belowPlutonic form below
ground =ground = intrusiveintrusive
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3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Layered extrusiveLayered extrusive
rocksrocks
Massive plutonic rockMassive plutonic rockbodiesbodies
Fig 3.7
on:on:CompositionComposition
What minerals makeWhat minerals makeup the rock?up the rock?
TextureTexture
What is the shape,What is the shape,size and orientationsize and orientationof the mineral grainsof the mineral grainsthat make up thethat make up therock?rock?
Major Difference:Major Difference:Crystalline (below)Crystalline (below)vs. fragmental (left)vs. fragmental (left)
Igneous CompositionIgneous CompositionMafic
Felsic
Richer in Magnesium and Iron
(Fe) and poorer in silica;
example, basalt.
Richer in feldspar and quartz,
and thus richer in silica;
example, rhyolite.
Igneous TexturesIgneous Textures -- CrystallineCrystalline
Coarse Grained Fine Grained
Aka: phaneritic Aka: aphanitic
Igneous TexturesIgneous Textures -- CrystallineCrystalline
Porphyritic
Phenocrysts
Groundmass
Igneous TexturesIgneous Textures -- CrystallineCrystalline
Glassy
Vesicular
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Igneous TexturesIgneous Textures volcaniclasticvolcaniclastic
or fragmentalor fragmental
Made of rock fragments
rather than crystals
Igneous RocksIgneous Rocks
GraniteDioriteGabbro
RhyoliteAndesiteBasalt Dacite
Granodiorite
Mafic Intermediate Felsic
Fine
Coar
se
Increasing silica
Ultramafic RockUltramafic Rock
-- DuniteDuniteGrain Size:Grain Size:
Plutons and VolcanoesPlutons and Volcanoes
Fine
Grained
Coarse
Grained
Name this Igneous FeatureName this Igneous Feature
Igneous Dike
Figure 4.7aFigure 4.7a
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Figure 4.7bFigure 4.7b Figure 4.8bFigure 4.8b
Figure 4.10bFigure 4.10b
Plutonic StructuresPlutonic Structures
Inclusions: Xenoliths
Source: William E. Ferguson
Why do we find Plutons at theWhy do we find Plutons at the
Surface?Surface?
Sierra Nevada Mountains Batholith, California
Uplift & Erosion
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Intermission: QuizIntermission: uizWhat Can you say about theWhat Can you say about the
history of this rock?history of this rock?
Basalt
Magma produced by
partial melting of the
mantle that erupted
from a volcano at adivergent zone or hot
spot.
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nterm ss on: u znterm ss on: u z
What Can you say about theWhat Can you say about the
history of this rock?history of this rock?
Gabbro
Magma produced by
partial melting of
mantle that cooledunderground (plutonic)
at a divergent zone or
hot spot.
nterm ss on: u znterm ss on: u z
What Can you say about theWhat Can you say about the
history of this rock?history of this rock?
Granite
Magma produced by
partial melting of the
continental crust that
cooled underground
(plutonic) at a
subduction zone or
continental hot spot.
nterm ss on: u znterm ss on: u z
What Can you say about theWhat Can you say about the
history of this rock?history of this rock?
Andesite
Magma produced by
partial melting of the
mantle, ocean crust &
continental crust, that
erupted from a volcano
at a subduction zone.
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Sedimentary RocksSedimentary Rocks
Formed byFormed by depositiondeposition andand
precipitationprecipitation of materialsof materials
coming from the breakdowncoming from the breakdown
of older rocksof older rocks
Weathering breaks downWeathering breaks down
and/or dissolves parts of aand/or dissolves parts of a
rockrock
Dissolved ionsDissolved ions
Clastic sedimentClastic sediment
Fig 3.5
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Fragments formFragments form clasticclastic sedimentary rocksedimentary rock
Dissolved ions formDissolved ions form chemicalchemical sedimentary rockssedimentary rocksPrecipitatesPrecipitates such as halitesuch as halite
Generally carbonates, halides, some oxides also areGenerally carbonates, halides, some oxides also are
the cement for clastic materialsthe cement for clastic materials
LithificationLithification sediments of either typesediments of either type
accumulate in layers, compress under their ownaccumulate in layers, compress under their own
mass and/or what buries them, and, withmass and/or what buries them, and, with
cements, form a hardened masscements, form a hardened mass
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3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Metamorphic rocksMetamorphic rocks
rocks that have changedrocks that have changed
Increased temperature (butIncreased temperature (but
not melted)not melted)
Increased pressureIncreased pressure
Presence of hot fluidsPresence of hot fluids
(chemical reactions)(chemical reactions)
Changes to:Changes to:
Shape and/or orientation ofShape and/or orientation of
crystalscrystals
The mineralsThe minerals
Fig 3.8
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Three classes of metamorphic rocksThree classes of metamorphic rocks
RegionalRegional metamorphic rocks exmetamorphic rocks ex = schist &= schist &
gneissgneiss
PressurePressure--drivendriven ; occur across vast regions =>ccur across vast regions =>convergentconvergent plate boundariesplate boundaries
ContactContact metamorphic rocksmetamorphic rocks--exex = hornfels= hornfels
Thermally driven and common along boundaries ofThermally driven and common along boundaries of
igneous intrusionsigneous intrusions or under lava flow zonesor under lava flow zones
HydrothermalHydrothermal metamorphic rocksmetamorphic rocks
Driven byDriven by hothot--fluid chemical changesfluid chemical changes
Often associated with previous typesOften associated with previous types
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Classic regional metamorphic structures in Scotland
Note bands, but also that they are folded
back on one another, attesting to the
pressure that drives such change.
3.2 Can rocks be classified according3.2 Can rocks be classified according
to the processes that form them?to the processes that form them?
Igneous rocksIgneous rocks crystallize as intergrown mineral massescrystallize as intergrown mineral massesfrom thefrom the molten statemolten state in extrusive or intrusive fashionin extrusive or intrusive fashion
SedimentarySedimentary rocks derive from weathering ofrocks derive from weathering ofpreviously existing rocks as particles or dissolved ions.previously existing rocks as particles or dissolved ions.Clastic sed. rocks form from the fragments, andClastic sed. rocks form from the fragments, andchemicalchemical sedsed rocks from the dissolved portion...rocks from the dissolved portion...
MetamorphicMetamorphic rocks form by the reaction of preexistingrocks form by the reaction of preexistingrocks in the presence of heat, pressure, fluids, orrocks in the presence of heat, pressure, fluids, or
combinations thereof, producing new minerals andcombinations thereof, producing new minerals and
rocks.rocks.
Rocks can be classifiedRocks can be classified descriptivelydescriptively ororgeneticallygenetically.. TheThe
three classes of rocks are genetic categories...three classes of rocks are genetic categories...
3.3 How do we know3.3 How do we know how tohow to
determine rock origins?determine rock origins?
How do geologists use observations of rocks toHow do geologists use observations of rocks toinfer process?infer process?
TheThe 33--classclass ggeneticenetic grouping isgrouping is newnew (only ~200(only ~200
yr oldyr old----Prior to the current genetic groups, therePrior to the current genetic groups, there
were competing thoughts)were competing thoughts)
DescriptiveDescriptive classes require only keen observationclasses require only keen observation
and sufficient adjectives.and sufficient adjectives.
3.3 How do we know3.3 How do we know how tohow to
determine rock origins?determine rock origins?
Neptunism:Abraham Werner
(17491817) believed that all rocksderived from processes of chemical
precipitation.
Concluded that the bottom layers of
Earths rocks were least soluble and
thus first to precipitate (primitive
rocks), and that they were overlain
by stratified rocks and finally
washed deposits of loose
materials. Volcanic activity was
caused by coal fires underground
melting rock overhead.
Fig 3.10
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3.3 How do we know3.3 How do we know how tohow to
determine rock origins?determine rock origins?Vulcanism (or plutonist)Vulcanism (or plutonist) the belief that most rocksthe belief that most rocks
were formed by igneouswere formed by igneous--like origins.like origins.
Championed byChampioned by James HuttonJames Hutton (1726(17261797)1797)
Noted that veins ofNoted that veins ofPrimitive RockPrimitive Rock extended up into theextended up into the
Stratified FormationsStratified Formations and that the boundaries of contactand that the boundaries of contact
with the latter werewith the latter were baked.baked.
Posited that layered rocks were mainly lava flows of somePosited that layered rocks were mainly lava flows of some
kind.kind.
One of Huttons sketches
3.3 How do we know3.3 How do we know how tohow to
determine rock origins?determine rock origins?
Neptunists, led by A. Werner, asserted that nearlyNeptunists, led by A. Werner, asserted that nearly
all rocks came from precipitates. Agreed with aall rocks came from precipitates. Agreed with a
view by many at the time, that Earth wasview by many at the time, that Earth was
internally coldinternally cold
VulcanistsVulcanists, following Hutton, used careful, following Hutton, used careful
observation to refute Neptunistsobservation to refute Neptunists claims byclaims by
demonstrating the presence of igneous rocks anddemonstrating the presence of igneous rocks and
showing evidence of Earthshowing evidence of Earths internal heat...s internal heat...
So how did geologists resolve these competing views?So how did geologists resolve these competing views?
Competing views met in the middleCompeting views met in the middle ----Hypothesized andHypothesized and
tested the observations they madetested the observations they made
3.4 How are the rock classes3.4 How are the rock classes
related to one another?related to one another?
Metamorphic rocks are preexisting rocks thatMetamorphic rocks are preexisting rocks that
have changed.have changed.
Igneous rocks are made from any rocks thatIgneous rocks are made from any rocks that
have melted and recrystallized.have melted and recrystallized.
Sedimentary rocks come from weathered bits ofSedimentary rocks come from weathered bits of
other preexisting rocks.other preexisting rocks.
Thus, all three rock types are connected in some manner.Thus, all three rock types are connected in some manner.
3.4 How are the rock classes3.4 How are the rock classes
related to one another?related to one another?
The Rock Cycle
Processes link
typesPlate tectonics is
driving force
top related