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!
TEMPERATURE VS DEPTH (GEOTHERM)Davidson 4.2
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
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.“every rock and tree and creature has a life, has a spirit, has a name…”
IGNEOUS ROCKS classified by chemical composition & cooling rate
Felsic- more FELdspar and SIlica
Mafic- more Magnesium and iron (Fe) ----------------------Texture reflects cooling:
Extrusive/Fine Grain
Intrusive/Coarse Grain
LESS DENSE MORE DENSE
LESS SiO2
SiO2
(Mg,Fe)2SiO4
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
LARGE GRAINS SMALL GRAINS LARGE & SMALL GRAINS
MICROSCOPE IMAGE
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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AS MAGMA COOLS MINERALS FORMDEPEND ON TEMPERATURE ("FRACTIONAL CRYSTALIZATION")
REVERSE PROCESS OCCURS DURING MELTING ("PARTIAL MELTING")
PROCESS ILLUSTRATED WITH HALF-FROZEN APPLE JUICE
FRACTIONAL CRYSTALIZATION /PARTIAL MELTINGAS MAGMA COOLS SOLID MINERALS THAT "FREEZE" OUT DIFFER IN COMPOSITION FROM REMAINING LIQUID
CRYSTALLIZATION OF MAGMA AS TEMPERATURE DROPS
Davidson 4.6
CRYSTALS SINK TO BOTTOM
SiO2-POOR MINERALS FREEZE OUT
MAGMA BECOMES MORE SiO2-RICH
Evanston’s population “ages” over summer break
http://science.howstuffworks.com/oil-refining2.htm
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)
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
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High viscosity magma- SiO2 rich
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Low viscosity magma- low SiO2
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
BEFORE
AFTER
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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
http://hvo.wr.usgs.gov/cam/index.htm
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Different types of volcanoes at different tectonic settings
Davidson 4.16
Japan,Aleutians
East African Rift
St Helens,Andes
The two main ways in which melting occurs in the mantle
MELTING AT LOWER PRESSUREWATER LOWERS MELTING
TEMPERATURE
MIDOCEAN RIDGE SUBDUCTION ZONE
GEOTHERM - TEMPERATURE vs DEPTH
SOLIDUS - MELTING CURVE
ACTIVE VOLCANOES CONCENTRATED AT PLATE BOUNDARIES
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
MARS: Olympus Mons
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What type of volcano is Mt. Doom (Orodruin) in the “Lord of the Rings”?