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3 MAIN ROCK TYPES:
IGNEOUS, SEDIMENTARY, &
METAMORPHIC
IGNEOUS- COOLS FROM MOLTEN ROCK
SEDIMENTARY- RECOMBINED
FRAGMENTS OF MINERALS, ROCKS,
&/OR ORGANIC ORIGIN
METAMORPHIC- PRE-EXISTING ROCKS
CHANGED IN COMPOSITION,
MINERALOGY, OR TEXTURE FROM HIGH
TEMPERATURES, PRESSURES, &/OR
FLUIDS
THE ROCK CYCLE - CONSTANT
REWORKING OF ROCKS IN THE EARTH'S
INTERIOR & AT SURFACE BY
DEFORMATION, WEATHERING, EROSION,
ETC... TO FORM NEW ROCKS
Phase (Pressure-Temperature) Diagram for
Lithospheric & Asthenospheric Depths
Most regions of the outer 200 km of the earth
DO NOT have melt!
Davidson 4.2
TEMPERATURE VS DEPTH (GEOTHERM)
IGNEOUS ROCKS
SILICATE MATERIAL (WITH GASSES)
MELTS AT DEPTH
MELTED MAGMA LESS DENSE THAN
SURROUNDING SOLID SO RISES
INTRUSIVE ROCK: SOLIDIFIES
("CRYSTALLIZES”/"FREEZES") AT
DEPTH
EXTRUSIVE ROCK: LAVA ERUPTS AT
SURFACE & FORMS.
COOLING LAVA RELEASES GASSES
INTO ATMOSPHERE
IGNEOUS ROCKS CLASSIFIED BY
THEIR CHEMICAL COMPOSITION (HOW
MUCH SiO2 ), MINERALS, AND
INTRUSIVE OR EXTRUSIVE
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“every rock and tree and creature has a life, has a spirit,
has a name…”
LESS DENSE
IGNEOUS
ROCKS classified
by chemical
composition &
cooling rate
Felsic- more
FELdspar and
SIlica
Mafic- more
Magnesium and
iron (Fe)
---------------------Texture reflects
cooling:
MORE DENSE
LESS SiO2
SiO2
(Mg,Fe)2SiO4
Extrusive/Fine
Grain
Intrusive/Coarse
Grain
Davidson 4.4
THREE IMPORTANT PAIRS OF IGNEOUS ROCKS
RHYOLITE / GRANITE (>63% SiO2): MOST OF
CONTINENTAL CRUST, DENSITY ABOUT 2.8 g/cm3 ,
FORMS BY MELTING CONTINENTAL CRUST
ANDESITE */ DIORITE (63-52% SiO2) FROM MELTING
OCEANIC CRUST, OFTEN AT SUBDUCTION ZONES
BASALT / GABBRO (<52% SiO2) MOST OF OCEANIC
CRUST, DENSITY ABOUT 3.3 g/cm3, FROM MELTING
MANTLE, OFTEN AT MIDOCEAN RIDGES
BECAUSE GRANITE IS LESS DENSE THAN BASALT:
CONTINENTS "FLOAT" HIGHER THAN THE OCEAN CRUST SO
WE LIVE ABOVE SEA LEVEL
CONTINENTS NEVER SUBDUCT BACK INTO THE MANTLE SO
FORMED EARLY IN EARTH HISTORY & ARE OLD (LESS THAN
500 MYR TO 4 BYR), COMPARED TO OCEANIC CRUST THAT
SUBDUCTS SO IS YOUNG (0-200 MYR)
*LIKE ANDES
Igneous rock textures formed primarily by cooling rate
MICROSCOPE IMAGE
LARGE GRAINS
SMALL GRAINS
LARGE & SMALL GRAINS
Davidson 4.4
SINGLE CRYSTAL GROWING FOR INTEGRATED CIRCUIT (IC or
MICROCHIP) PRODUCTION
ICs are built on single-crystal silicon substrates of high purity and perfection.
Single-crystal silicon is used instead of polycrystalline silicon since the
former does not have defects associated with grain boundaries.
- Silicon inside the chamber is melted (Si melts at 1421 deg C).
- A slim seed of crystal silicon (5 mm dia. and 100-300 mm long) is introduced
into the molten silicon.
- The seed crystal is withdrawn at a very controlled rate, and grows.
- Wafers are sliced off the crystal and circuits built on them
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FRACTIONAL CRYSTALIZATION /PARTIAL MELTING
AS MAGMA COOLS SOLID MINERALS THAT "FREEZE" OUT DIFFER
IN COMPOSITION FROM REMAINING LIQUID
AS MAGMA COOLS
MINERALS FORM
DEPEND ON
TEMPERATURE
("FRACTIONAL
CRYSTALIZATION")
REVERSE PROCESS
OCCURS DURING
MELTING ("PARTIAL
MELTING")
PROCESS
ILLUSTRATED WITH
HALF-FROZEN APPLE
JUICE
CRYSTALLIZATION OF MAGMA AS TEMPERATURE DROPS
CRYSTALS
SINK TO
BOTTOM
SiO2-POOR
MINERALS
FREEZE
OUT
MAGMA
BECOMES
MORE
SiO2-RICH
Evanston’s population “ages” over summer break
Davidson 4.6
http://science.howstuffworks.com/oil-refining2.htm
MAGMA VISCOSITY- VOLCANIC ERUPTION CHARACTERISTICS LARGELY
CONTROLLED BY THE VISCOSITY - "GOOEYNESS" (RESISTANCE TO
FLOW) - OF THE MAGMA: LOW VISCOSITY FLUIDS FLOW MORE EASILY
THAN HIGH VISCOSITY FLUIDS
Higher temperature, lower viscosity (warm syrup flows more easily than cold)
Viscosity increases with increasing silica content due to silica chains
High viscosity lavas flow slowly and typically cover small areas.
Low viscosity magmas flow more rapidly and cover thousands of square km.
Low viscosity magmas allow gases to escape easily.
Gas pressures can build up in high viscosity magmas - so violent eruptions
(Blowing through a straw, it's easier to get water to bubble than a milk shake)
High viscosity magma- SiO2 rich
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Low viscosity magma- low SiO2
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MAGMA VISCOSITY & VOLCANO TYPE
High viscosity lava flow slowly & typically
cover small areas, forming composite
volcanoes (stratovolcanoes) (e.g. Mt. St.
Helens) that explode violently due to
trapped gas
Low viscosity lavas flow rapidly & form
shield volcanoes (e.g. Hawaii) with flows
covering thousands of square kilometers
Mount Saint Helens- stratovolcano (composite volcano) with
viscous dacitic (SiO2-rich) magma containing lots of dissolved gas
(mostly water vapor), before 1980 explosive eruption, after, & today
AFTER
BEFORE
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JANUARY 2005- NEW ASH &
DOME FORMING IN CALDERA
Successive stages of development of Crater Lake, Oregon
Davidson 4.15
2002 ERUPTION: BIG
ISLAND OF HAWAII
Brian White (CAS 2000)
Seth Stein
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http://hvo.wr.usgs.gov/cam/index.htm
Different types of volcanoes at different tectonic settings
Japan,
Aleutians
St Helens,
Andes
East
African
Rift
Davidson 4.16
The two main ways in which melting occurs in the mantle
SOLIDUS - MELTING CURVE
GEOTHERM TEMPERATURE
vs DEPTH
MIDOCEAN RIDGE
MELTING AT LOWER PRESSURE
SUBDUCTION ZONE
WATER LOWERS MELTING
TEMPERATURE
ACTIVE VOLCANOES CONCENTRATED AT PLATE BOUNDARIES
MARS: Olympus Mons
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Stands 27 kilometres (88,600 feet) high over its base
(about three times the height of Everest above sea
level)
Caldera is 85 km (53 miles) long, 60 km (37 miles)
wide, and up to 3 km (1.8 miles) deep with six
overlapping pit craters.
Outer edge is defined by an escarpment up to 6 km (4
miles) tall unique among the shield volcanoes of Mars.
Olympus Mons is roughly the size of the state of
Missouri
What type of volcano is Mt. Doom (Orodruin) in the “Lord of the Rings”?