Rocks Tell Stories Records of Geologic Past. 1.Igneous rocks … from cooling and solidification of...
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Transcript of Rocks Tell Stories Records of Geologic Past. 1.Igneous rocks … from cooling and solidification of...
Rocks Tell Stories Records of Geologic Past
1. Igneous rocks … from cooling and solidification of lava or magma
2. Sedimentary rocks … from compacted and cemented sediments, or chemical precipitates or evaporites
3. Metamorphic rocks … meta (change) morphic (form) … rocks changed by heat and pressure –but remain solid
Rock Classification – 3 major groups based on their methods of
formation or origin
IGNEOUS ROCKS
Formation of Igneous Rocks
COOLING AND SOLIDIFICATION OF MAGMA/LAVA
INTERGROWN OR INTERCONNECTED SILICATE CRYSTALS IN A RANDOM PATTERN – NOT ORGANIZED
INTERGROWN SILICATE CRYSTALS - RANDOM
PATTERN
Magma – molten material BELOW the surface of the Earth
Lava – molten material AT OR ABOVE earth’s surface
MAGMA VS. LAVA
MAGMA LAVAIntrusive – below the surface
Extrusive - above the surface
A pluton is a body or chamber of magma deep inside the crust.
Ejected from volcano
Rocks formed when magma cools and solidifies are called
INTRUSIVE (PLUTONIC)
Rocks formed when lava cools and solidifies are called
EXTRUSIVE (VOLCANIC)
ENVIRONMENT OF FORMATION
COOLING HISTORY
IGNEOUS ROCKS ARE CLASSIFIED BASED ON 2 MAIN CHARACTERISTICS
•TEXTURE – MINERAL GRAIN SIZE
•MINERAL COMPOSITION (COLOR)
Classification of Igneous Rocks by Texture
•WHAT IS TEXTURE? It is NOT how it feels!
It’s the SIZE OF MINERAL CRYSTALS
What controls texture?What controls texture?
How fast an igneous rock cools.
What controls how fast an What controls how fast an igneous rock cools?igneous rock cools?
Where the rock is formed.
coarser crystals
slower cooling
deep in ground
ESRT – TOP OF THE IGNEOUS ROCK SCHEME TELLS THE
TEXTURE / GRAIN SIZE
Classification of Igneous Rocks – Texture or Grain Size
Extrusive Extrusive Intrusive Intrusive
Volcanic - LAVA
Volcanic- LAVA
Plutonic - MAGMA
Plutonic - MAGMA
Extremely fast cooling
Fast Cooling
SlowCooling
Extremely slow cooling
Non-crystallineGlassy vesicular (gas pockets)
Fine-grained
Coarse-grained
Very Coarse-grained
EXTRUSIVE – VOLCANIC - LAVA• When lava cools extremely fast crystals have
no time to form – JUST FROZEN IN PLACE RANDOMLY WHEN LAVA ENTERS ATMOSPHERE OR WATER
• GLASSY – NON-CRYSTALLINE Non-vesicular Vesicular gas pockets
EXTRUSIVE – VOLCANIC - LAVALava that cools fast at or near the Earth’s surface
Produces small crystals FINE-GRAINED TEXTUREnot easily seen with the naked eye.
INTRUSIVE – PLUTONIC - MAGMA
Magma that cools slowly deep underground produces large crystals COARSE-GRAINED TEXTURE easily seen with the naked eye.
EXTREMELY SLOW COOLING HAS ABNORMALLY LARGE CRYSTALS
AND IS VERY COARSE.
INTRUSIVE – PLUTONIC - MAGMA
IN THE MIDDLE OF THE IGNEOUS ROCK CHART ARE
CHARACTERISTICS BASED ON WHICH MINERALS ARE IN EACH
ROCK.
NOTICE 2 NEW WORDS
FELSIC AND MAFIC
CHARACTERISTICS OF IGNEOUS ROCKS
FELSIC VS. MAFICFELSIC MAFIC
“FEL” = FELDSPARS “MA” = MAGNESIUM
“SIC” = SILICA “F” = IRON
High % of quartz, feldspars, mica
“IC” = SILICAHigh % of pyroxene, feldspars, amphibole
LIGHTER IN COLOR LESS DENSE
DARKER IN COLORMORE DENSE
Continental mixed oceanic mantle
FELSIC MAFIC ULTRAMAFIC
THE BOTTOM OF THE IGNEOUS ROCK SCHEME TELLS YOU THE COMPOSITION
TEXTURE + COMPOSITION CAN NAME ROCK
FELSIC COMPOSITION COLUMN
+
COARSE TEXTURE ROW
Granite RhyoliteFigure 4.7 AMINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE EXTRUSIVE
DioriteAndesite
Figure 4.7 B
MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE EXTRUSIVE
Gabbro BasaltMINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
INTRUSIVE EXTRUSIVE
WHAT GRAPH BELOW SHOWS AS TIME INCREASES THE SIZE INCREASES?
A B
SEDIMENTARY ROCKS
Sedimentary Rocks• 80 % of Earth’s surface is covered
with sediments and Sedimentary Rocks (only a thin layer on top)
What is sediment????
Broken pieces of rocks called Sediments
Chemical precipitates ( dissolved solids come out of solution)
Organic fragments – shells, decayed plant matter – this is called BIOCLASTIC
Source of Sediment
When Igneous, Metamorphic Rocks, and Sedimentary Rocks are uncovered and exposed to the atmosphere and hydrosphere they start to break down
Weathering is the general term for all actions that break down or wear away rock
Erosion is the moving/transport of the sediment
Sedimentary Rocks form when sediments are transported to large
bodies of water and are …
Deposited in horizontal layers called beds or strata
Buried
Compacted – particles forced extremely close together because of the pressure of the overlying layers and water
Cemented – glued together
Sedimentary RocksSediments that are
eroded settle to the bottom of the rivers, lakes, and oceans
Layer after layer of eroded earth is deposited on top of each other
Most Sedimentary Rocks form under large bodies of water, such
as lakes, seas, and oceans
Horizontal layers deposited under water
Classification of Sedimentary Rocks
• We classify sedimentary rocks depending whether the sediments are
LAND DERIVED (came from)
CHEMICALLY - ORGANICALLY DERIVED
INORGANIC LAND DERIVED ROCKS NAMED BY GRAIN SIZE
Breccia
Sediments are pebbles, cobbles, and boulders
rounded
angular
Sand (0.2 to 0.006 cms.)
SANDSTONE
Silt (0.006 to 0.0004 cms.
SILTSTONE
Clay (less than 0.0004 cms.)
SHALE
2 TYPES OF TEXTURE
CRYSTALLINE FOR CHEMICALLY FORMED SEDIMENTARY ROCKS
BIOCLASTIC FOR ORGANICALLY FORMED SEDIMENTARY ROCKS
HOW USEFUL IS GRAIN SIZE????
CHEMICAL Sedimentary RocksSediment From Solution
All liquid water contains dissolved minerals.
These minerals precipitate (dissolved solids come out of solution/water)
Usually happens because of evaporation
Characteristics of Chemically Formed Sedimentary Rocks
They are monominerallic – consisting of intergrown crystals of just 1 mineral.
Form in shallow seas
ROCK SALT
DOLOSTONE
ROCK GYPSUM
Intergrown crystals of just 1 mineral
ORGANIC Sedimentary Rocks Bioclastic Sediment
LIMESTONE AND CORALS• Dissolved minerals taken out of solution by
marine organisms for their hard parts (shells) can pile up on the seafloor when they die.
• These fossil remains accumulate into a thick enough layer to form an “organic” sedimentary rock
• Cement is commonly calcite ( bubbles with acid)
COAL• Decayed plant remains
BIOCLASTIC LIMESTONE CHEMICALLY PRECIPITATED LIMESTONE
COAL
Summary
Inorganic Land-Derived Sedimentary Rocks are identified by Texture or Grain Size
Chemically and/or Organically Formed Sedimentary Rocks are identified by Composition
HIGH ENERGY
LOW ENERGY
Environment of Formation Ocean Derived Sedimentary Rocks
Sedimentary Rockshelp us understand our pastgeologic history
There is evidence of climatechange as well as lost speciesof plants and animals in Sedimentary Rocks
During the Cretaceous Period (about 120 mya) a shallow inland sea split North America.
We know this by the Sedimentary Rocks deposited in the former shallow sea
SALT AND GYPSUM EVAPORATION
Bedrock of Salt and Gypsum around Buffalo
What type of environment would cause salt and/or gypsum to evaporate?
Ocean environment with hot temperatures
CHARACTERISTICS OF SEDIMENTARY ROCKS
1. Horizontal layers called beds or strata
2. Clasts are rounded and sorted because they have been moved by water
3. Ripple Marks
4. Mud Cracks
5. Fossils
6. Interconnected mineral crystals of 1 mineral (monominerallic)
HORIZONTAL LAYERS
A. SHALLOW WATER B. LOW ENERGY C. DIRECTION OF FLOW
MUDCRACKS
ALTERNATING WET AND DRY CONDITIONS
Limestone - FOSSILS
SEDIMENTARY ROCK MANTRA
1.COMPACTED AND CEMENTED SEDIMENTS
FOSSILS RIPPLE MARKSMUDCRACKS
METAMORPHIC ROCKS
METAMORPHIC ROCKSMETA = CHANGE MORPH = FORM
Start with pre-existing rock and change to another rock – but these changes occur in the SOLID STATE
METAMORPHISM
Process by which igneous, sedimentary, or another metamorphic rock called the “parent rock” undergoes changes in minerals and texture
METAMORPHISM
Occurs in rocks due to the effects of
•High temperature•High pressure
HEAT EFFECTS
Temperature increases with depth or contact with magma
Recrystallization – a process that forms new mineral crystals because the mineral is no longer stable at the new temperature
• Changes to a new (high temperature) mineral
PRESSURE EFFECTS
Pressure increases with depth – weight of overlying rock (see page 10 ESRT)
Mineral crystals grow larger Mineral crystals are more dense Mineral crystals grow
perpendicular to pressure Mineral crystals are arranged in
parallel layers – PRODUCES FOLIATION
FOLIATION
Pressure actually rearranges the minerals into parallel layers.
More pressure – minerals grow larger and recrystallize and separate into layers
Even more pressure – alternating layers of light and dark minerals called
Banding
Random arrangement of minerals
Organized arrangement of minerals - banding
METAMORPHIC ROCK MANTRA
• INTERGROWN CRYSTALS IN AN ORGANIZED PATTERN
GraniteIntergrown crystals
random pattern
GneissIntergrown crystalsOrganized Pattern
2 Types of Metamorphism
1. Regional Metamorphism – Occurs over large areas where there is active mountain building
a) Convergent plate boundaries
2. Contact Metamorphism – areas in contact with magma intrusions and/or lava extrusions
MOUNTAIN
BUILDING
Classification of Regional Metamorphic Rocks
Composition is basically the same for all foliated rocks – parent rock is usually listed in comments section.
Type of texture and grain size determined by the amount of heat and pressure
GRADES OF METAMORPHISM
LOW GRADE – LESS HEAT AND PRESSURE – SLATE
HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS
Low-grade metamorphism: Occurs at about 2000 C to 5000 C. and pressure greater than 1,000 atmospheres
High-grade metamorphism:Occurs at > 5000 C
Temperature
FOLIATED METAMORPHIC ROCKS
MICA CRYSTALSBECOMELARGE AND SPANGLY
MICA SCHIST WITH GARNET
METAMORPHIC ROCKS WILL OFTEN BE DEFORMED
BECAUSE OF INTENSE HEAT AND PRESSURE
LOOK AT ROCK SYMBOL FOR GNEISS
DEFORMED GNEISS
A metamorphic rock exposed to too much heat will melt and become ???
MAGMA
CONTACT METAMORPHISM
Contact Metamorphic
• Metamorphism means "changed form".
• The Changes occur because of:
• Heat from magma intruding on the surrounding rock
• Very little pressure
Near magma chambers (plutons)
Rocks in “contact” with the magma are heated
New minerals are formed –recrystallization
Contact Metamorphism – heating the adjacent rocks
Symbol for Contact Metamorphism is a line with tick marks
When limestone undergoes contact metamorphism what rock will it metamorphose into? Sandstone??
PARENT ROCK IN THE COMMENTS
LIMESTONE METAMORPHOSES INTO MARBLE
SANDSTONE METAMORPHOSES INTO QUARTZITE