Download Midterm Review 1

Where did we come from and how did we get here?
The Universe formed about 14 billion years ago
The Solar System and Earth formed about 4.6 billion years ago
We are a planet, revolving around a star that is one of about four hundred billion
stars in a galaxy (The Milky Way), that is one of more than 80 billion galaxies in the
observable Universe.
Our Star, the Sun, like most stars is composed of mostly Hydrogen, with some
Helium
The outer planets (Jupiter, Saturn, Neptune and Uranus) are gas giants (H and He)
The Earth is one of four ‘terrestrial’ planets (Mercury, Venus, Earth and Mars) in the
inner Solar System, and like those planets, is composed largely of a silicate (SiO2)
and Iron (Fe)
Unlike most of the other ‘terrestrial’ planets, the Earth is a dynamic planet, with a
constantly changing lithosphere (rocks), atmosphere (wind), hydrosphere (water),
and biosphere (life).
That is why the surface of the Earth is largely free of meteorite impact craters.
Much of this dynamism is due to heat-driven convection
~14 GA
(GigaAnnum, i.e,
Billion Years)
But first things
first
today
Typical spiral galaxy. Similar to ‘our’ Milk Way Galaxy’
We are not alone.
About 80 billion galaxies in the
observable universe.
About 400 billion stars in the
Milky Way galaxy (but that may
be a bit larger than average)
Many (most?) of those probably
have planets.
How many of those planets are
terrestrial (Earth-like?)
How many have life?
The Crab Nebula in Lyra
Remnants of a supernova
The Surface of our Sun ( a very close star)
SUN
Hydrogen (74%),
some helium (24%)
Rocky inner
planets
Silicates with
Iron/Nickel
cores
The giant Gas planets of the outer solar system
Hydrogen, Helium, methane, water,
ammonia
plus small icy planets like Titan
Gaseous Outer Giant
‘terrestrial planets’
Mars
‘terrestrial planets’
The surface of Mars – close up
‘terrestrial planets’
The surface of Idaho – close up
Earth
Our moon: Luna
Close up of Tycho
Earth’s Outermost Layers
• The most dynamic portion of the Earth
– Atmosphere
• Thin gaseous envelope surrounding Earth
– Hydrosphere
• Water layer dominated by the oceans
– Biosphere
• All living things on the planet
– Lithosphere
• Rocky outer shell
Heat driven
convection
1. Bottom water is warmed
2. It expands an is therefore less dense
3. It rises to the surface and then
spreads out
4. Cooler water at the sides descends to
fill the void
A convective thunderstorm
Atoms and Minerals
What are we (the Earth) made of?
All matter is composed of atoms, which consist of a nucleus with protons and
neutrons, and electrons which ‘orbit’ the nucleus
Bonds are formed between the valence electrons of atoms to form molecules
Minerals are ‘naturally occurring inorganic solid that has an exact (or clearly
defined range) chemical composition with an orderly internal arrangement of
atoms generally formed by inorganic processes’.
The nature of the bonds results in the physical properties of minerals, including
crystal form, cleavage, fracture, hardness, density, color, luster, streak, etc.
Rocks are formed of minerals
The rock-forming minerals include silicates, carbonates, evaporites and secondary
minerals such as clays
Rocks are formed of minerals
Most rocks are silicates and are composed of cations linked by silicate tetrahedra,
chains, sheets and solids
Matter
• Atoms
– The smallest unit of an element that
retain its properties
• Molecules - a small orderly group of atoms
that possess specific properties - H2O
– Small nucleus surrounded by a cloud of
electrons
– The nucleus contains protons and
neutrons
Bonding
• Atoms are stable when their outmost
electron shell is filled
– Atoms lose, gain or share electrons to
achieve a noble gas structure
• Types or bonds
– Ionic
Covalent
Metallic
The Nature of Minerals
• Mineral
– A naturally occurring inorganic solid that
has an exact (or clearly defined range)
chemical composition with an orderly
internal arrangement of atoms generally
formed by inorganic processes.
Physical Properties
Crystal Form
Cleavage and Fracture
Hardness
Density
Color
Luster: Metallic vs Non-metallic
Streak
Taste, magnetism, etc.
Rock-Forming Minerals
• About 20 common minerals make up
most rocks
– Silicates dominate
– Quartz, Feldspars, Mica, Amphiboles, Pyroxenes
– Carbonates are common
– Evaporite minerals
– Secondary minerals formed during
weathering
Silicate Minerals
• Silica tetrahedron may polymerize to
form a variety of geometric structures,
alone or in combination with other
cations
• Isolated tetrahedron
• Single chains
• Double chains
• 2-D sheet
• 3-D frameworks
Silica Tetrahedron
Silicate Structures
Isolated
Single chain
Double chain
Sheet
Solid
Nonsilicate Minerals
– Carbonates (biologic)
• Calcite - Ca CO3
• Dolomite - CaMg(CO3)2
– Evaporite Minerals (seawater evaporation)
• Gypsum - CaSO4-2H2O
• Halite – NaCl
– Clays and Oxides (rust and weathering)
• Hematite
• Bentonite, Kaolinite
Rocks
Imagine the first rock and the cycles that it has been
through.
Igneous Rocks
Igneous Rocks
• Form from Magma (hot, liquid rock)
• Cool and solidify underground (plutonic) or as lavas above
ground (volcanic)
• Most properties are controlled by silica (SiO2) content:
classification, melting point, minerals, appearance, etc.
• Viscosity of magma is controlled by temperature, silica content,
and to a lesser extent, water.
• Silica-rich magmas are more likely to erupt explosively than are
mafic magmas, which are runny
• Texture (size and shape of xtals) is controlled by the rate cooling
history of the rock.
Igneous Rocks (cont)
• Faster cooling results in finer-grained crystals
• Common textures include aphanitic (fine-grained), phaneritic
(coarse-grained), porphyritic (big xtals in a fine-grained matrix),
pyroclastic (explosive) and glassy
• The kind of volcanism depends upon the viscosity of magma
• Plutonic bodies include plutons, batholiths, sills, dikes etc.
• Magmas originate in the upper Mantle
• Magmas differentiate (change composition) through mixing,
melting of country rock, and partial melting
• The Bowen’s Reaction series describes the order in which silicate
minerals solidify in a magma
Mafic (Fe,Mg –rich) Magmas
• Silica content of ~ 50%
• High concentrations of Fe, Mg and Ca
• High temperature of molten magma
– 1000o to 1200oC
• Major minerals
– Olivine
– Pyroxene
- Ca-rich Plagioclase
Felsic (Si,Al-rich) Magma
• Silica content of 65-77%
• High concentrations of Al, Na and K
• Lower temperature magmas
– Less than 850oC
• Major minerals
– Feldspars
– Quartz
- Micas
Magma Viscosity
• Controlled by silica temperature
• As magma cools, silica tetrahedron form links
– Similar to polymers - e.g., nylon
• Increasing linkages
– Higher silica & lower temp
• Linkages increase viscosity
Note: this is just like oils, fats and other organic compounds
used in the household
Igneous Textures
• Texture - the size, shape and relationship of
mineral crystals in the rock
• Reflects cooling history of the magma or
lava
Big crystals
• Slow cooling rate
>>
• Fast cooling rate
• Very fast cooling rate
>> Small crystals
>> glass
Glassy texture in obsidian
Aphanitic Texture
• Fine grained texture
• Few crystals visible in hand specimen
• Relatively rapid rate of cooling
Aphanitic texture in rhyolite
Phaneritic Texture
•
•
•
•
•
Coarse grained texture
Relatively slow rate of cooling
Equigranular, interlocking crystals
Slow cooling = crystallization at depth
Pegmatites - very coarse grained
texture
Phaneritic texture in granite
Porphyritic Texture
• Well formed crystals (phenocrysts)
• Fine grained matrix (groundmass)
• Complex cooling history
– Initial stage of slow cooling
• Large, well formed crystals form
– Later stage of rapid cooling
• Remaining magma crystallizes more rapidly
Porphyritic igneous rock:
Big xtals in a fine grain matrix
Pyroclastic Texture
• Produced by explosive volcanic eruptions
• May appear porphyritic with visible crystals
– Crystals show breakage or distortion
• Matrix may be dominated by glassy fragments
– Fragments also show distortion
– Hot fragments may “weld” together
Concept Art, p. 105
Fine grained
Coarse
grained
Classification of common igneous rocks
Volcanic Eruptions
• Basaltic eruptions are runny
• Low Silica + High T = Low Viscosity
• Produce
– Lava Flows - Pahoehoe or Aa
– Flood basalts
– Shield Volcanoes
– Pillow lavas
Fig. 4-1, p. 102
Flood basalts with several thick and
thin layers. Each layer represents a separate eruption.
Fig. 5-12d, p. 145
Intermediate & Silicic Eruptions
• Higher Silica + Lower T = Higher Viscosity
– Composite or Stratovolcanos
– Lava Domes
– Ash Flow Calderas
Concept Art, p. 155
Mt Fuji: Stratovolcano
Caldera Explosions:
Super volcanoes
Fig. 5-9b, p. 142
Fig. 5-9c, p. 142
Fig. 5-9d, p. 142
Fig. 5-9e, p. 142
Basalt
River Gravels
Rhyolite
Basalt
Fig. 5-21c, p. 157
Concept Art, p. 104
Plutonic Rocks
• Less dense magmas rise through the
crust
• Intrusions form as magma solidifies
beneath the surface
Figure 4.18. Types of magmatic intrusions
Half Dome; part of the Sierra Nevada batholith
Sill; parallels layers in the country rock
Dike; cuts across layers in the country rock
Origin of Magmas
• Solid rock is at equilibrium with its
surrounding
• Changes in the surroundings may cause
solid rock
magma
– Raising T
– Lowering P
– Changing composition
Magma Differentiation
• Magmas, and the resulting igneous rocks,
show a wide range of compositions
• Source Rock
– variations cause major and minor
variations in the magma
• Magma Mixing
• Assimilation
Bowen’s Reaction Series
Metamorphic Rocks
•
•
•
•
•
•
•
•
•
•
Rocks can be metamorphosed (changed) into other rocks when subjected to
high temperatures and pressures.
The presence of fluids increases the rate of metamorphism
Metamorphic changes occur in the solid state
The three kinds of metamorphism are Regional, Contact and Hydrothermal
Regional metamorphism involves large scale pressures and temperatures
caused by collision of plates in subduction zones or continental collisions
Contact metamorphism involves baking of adjacent rocks by hot magma
intrusions
Hydrothermal alteration involves alteration of minerals through percolation of
hot, mineral-rich fluids through the rock
The ‘Parent’ rock is an important control on the type of metamorphic rock
formed
Index minerals form at specific temperatures and pressures and thus record the
T and P ‘experienced’ by the rock
Metamorphic rock textures are either foliated (layered due to directional
pressure) or non-foliated
Metamorphic Rocks
• The transformation of rock by
temperature and pressure
• Alters igneous, sedimentary and even
other metamorphic rocks
What causes metamorphism?
• Heat
• Most important agent
• Heat drives recrystallization - creates new, stable minerals
• Pressure (stress)
• Increases with depth
• Pressure can be applied equally in all directions or differentially,
i.e. directed
• Fluids
• The flow of hot mineral-rich water through the rock can have a
big impact on metamorphism
• Referred to as hydrothermal alteration and creates specific easily
identified minerals
Main factor affecting metamorphism
• Parent rock
• Metamorphic rocks typically have the same
chemical composition as the parent rock.
• They contain different minerals, but the same
chemicals; just rearranged.
• Exception: at sometimes gases like carbon
dioxide (CO2) and water (H2O) are released
• Examples:
– Quartz SandstoneQuartzite
– ShaleSlate  Schist Gneiss
– GraniteGranite, though minerals might align
Source of Heat
Source of Fluids
Ocean-Continent convergence
Regional Metamorphism:
Subduction zones …..
High T
Low P
High T
High P
High P
Low T
Why it is called regional
Colors represent
Fig.
6.15. levels of
different
Temperature and
Regional
Pressure
as recorded in
Metamorphic
the minerals.
Gradients
This regional pattern
was caused by the
collision of two
continents
Other minerals behave similarly
Metamorphic Index Minerals
Index Minerals in metamorphic rocks
Each of these minerals is an index of T and P
Metamorphic textures
• Foliation
• Foliation can form in various ways:
– Rotation of platy or elongated minerals
– Recrystallization of minerals in a preferred
orientation
– Changing the shape of equidimensional
grains into elongated and aligned shapes
Development of foliation due to
directed pressure
Change in metamorphic grade with depth
Progressive metamorphism of a shale
Shale
Progressive metamorphism of a shale
Schist
Progressive metamorphism of a shale
Gneiss
Common metamorphic rocks
• Nonfoliated rocks
• Quartzite
– Formed from a parent rock of quartz-rich
sandstone
– Quartz grains are fused together
– Forms in intermediate T, P conditions
Sample of
quartzite
Thin section
of quartzite
Marble (Random fabric = annealing; nonfoliated)