Post on 03-Oct-2020
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Banded Iron Formation
Rocks and the Rock Cycle
Rocks
Big rocks into pebbles,
Pebbles into sand.
I really hold a million, million
Rocks here in my hand. Florence Parry Heide
How are rocks formed?
How do rocks change?
How are rocks treasured?
Volcanoes
Earthquakes
Heat and earth’s movement change what rocks
look like and change landforms. What landforms
do volcanoes and earthquakes form?
Earthquakes
Water Wind
Ice Erosion and weathering change rocks and
land formations. What changes do you see?
Water
Wind
Ice
What are the main parts of the rock cycle
that you should know?
Man changes rocks
in many ways. Look for
ways that rocks are used.
Rocks
A rock is a naturally occurring, solid mixture of minerals.
Fig 4.1
Three Classes of Rocks
• Igneous (made by “fire”) - Solidified from
molten rock (magma & lava).
• Sedimentary - Deposited and buried at Earth’s
surface.
• Metamorphic (“changed form”) - Transformed
from pre-existing rocks under high pressure
and temperature.
Three Classes of Rocks
Fig 4.2
Igneous Rock
Igneous rock comes from cooled magma
and lava. What are some names of igneous
rock?
Sedimentary Rock
Pieces of rock erode and pile up in layers
to create sedimentary rocks. This is where
you can find fossils. What other types of
rock are sedimentary rocks?
Metamorphic Rocks
Metamorphic rock are sedimentary or igneous
rocks that have been changed under pressure
while deep in the crust of the earth. What kinds
of rocks are metamorphic rock?
Distinguishing Characteristics
• Mineralogy – The different minerals that make
up the rock and their relative proportions
• Texture - Sizes, shapes, and arrangements of
minerals within the rock:
– Course-grained
– Fine-grained
– Foliated (layered)
All are clues to a rock’s origin and history.
Igneous Rocks
• Minerals crystallize out of melted rock from deep within Earth’s crust or mantle
– High temperatures, up to 700 C or more!!
– Crystal size depends on cooling rate.
• Intrusive rocks cool slowly within deep magma chambers:
– Large, coarse crystals form
• Extrusive rocks cool rapidly at (or near) the surface of the earth:
– Fine-grained, often “glassy”
Igneous Rocks
Common in volcanic areas & plate boundaries
Igneous
High melting temperatures
- Abundance of silicon and
oxygen
Sedimentary Rocks
• Loose particles (sand, silt, ocean shells) accumulate on shorelines, basins, rivers, etc.,
– Clastic Sediments
• Minerals precipitate from dissolved chemicals in water
– Chemical & Biochemical Sediments
• All are the products of Weathering - that breaks up and decays rocks, and Erosion - that transports from source to point of deposition
Weathering & Erosion
Transport
Deposition
Basement Rocks
Chemical: Limestone
Common along passive margins
(and other basins)
Clastic: Sandstone
Sedimentary
Silicates (esp. Clays)
Carbonates
Sulfates & Halides
(Precipitates)
Metamorphic Rocks
• High temperatures and pressures deep inside the Earth cause changes in mineralogy, texture, and composition
– Changes take place in Solid State by recrystallization and chemical reactions
– Temperatures greater than 250 , less than 700
Metamorphic Rocks Common at collisional plate
boundaries
Metamorphic Rocks
Fig 4.6 • Foliated - Layers defined by
– Alignment of minerals (micas & clays)
– Alternating bands of mineral types
• Indicative of high pressures and deformation during formation
• Not Foliated
• Distinct low- pressure minerals
Metamorphic
Silicates predominate
-Due to silicate
source rocks
Characteristic Metamorphic Minerals
For more images: http://skywalker.cochise.edu/wellerr/mineral/
kyanite
andalusite
sillimanite
staurolite garnet
Rock Types
Sedimentary rocks are most abundant near Earth’s surface
- poor preservation
Igneous and
Metamorphic rocks make up
most of the crustal volume
- limited exposure!
Outcrops
Sediments make up only 5% by
volume
Sediments make up
75% surface area
Outcrop
Exposures
-Measure orientation & thickness
- Record regional
patterns on geologic
maps
- Infer what lies below
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Rock Types
How can we sample what lies below the
surface? Ocean
Drilling
Continental Drilling
Outcrops
Sediments make up only 5% by
volume
Sediments make up
75% surface area
By drilling: e.g., Oceans - all over, - passive margins - rifting & spreading - convergent - hot spots Continents - San Andreas Fault - Chelungpu Fault - Hawaii
The Rock
Cycle
-Melting & Intrusion
-Solidification of melt
-Mountain Building
-Uplift & Exposure
-Weathering
-Erosion & Transport
-Deposition & Burial
-Metamorphism
-Melting & Intrusion
(a) The Rock Cycle
Convergent Plate
Boundary
-Subducting slab
-Mantle melting
-Buoyant rise of melt
(b) The Rock Cycle
Convergent Plate
Boundary
-Solidification of melt
-Mountain building
(c) The Rock Cycle Precipitation &
Weathering
-Moisture laden air
-Precipitation and run-off
-Freezing & thawing
(d) The Rock Cycle
Sediment Transport
to Oceans
-Deposition
-Burial & lithification
-Chemical precipitation
(e) The Rock Cycle
Deformation & Metamorphism
-Continental collision (i.e., orogeny)
-Burial & deformation
-Increased pressure & temperature
(a) The Rock Cycle
Convergent Plate
Boundary
-Subducting slab
-Mantle melting
-Buoyant rise of melt
Plate Tectonics & Climate
-Plate tectonics
drives uplift &
subsidence
-Climatic processes
weather & transport
sediment
-Interactions control
the rock cycle