(a) The Rock Cycle

download report

Transcript (a) The Rock Cycle

ESCI 101: Lecture
Rocks
February 16, 2007
Copy of this lecture will be found at:
Banded
Iron
Formation
http://www.owlnet.rice.edu/~esci101
From http://geology.about.com/library/
bl/images/blbif.htm
With Some Graphics from Press et al., Understanding Earth, 4th Ed.
(Copyright © 2004 by W. H. Freeman & Company)
Rocks
•
A rock is a naturally occurring, solid aggregate
of minerals.
Fig 4.1
How Rocks are Made and Recycled:
Three Classes of Rocks
•
Igneous (made by “fire”) - Solidified from
molten rock (i.e., magma).
•
Sedimentary - Deposited and buried at Earth’s
surface.
•
Metamorphic (“changed form”) - Transformed
from preexisting rocks under high pressure
and temperature.
Distinguishing Characteristics
•
Mineralogy - Constituent (all together_ minerals
and their relative proportions.
•
Texture - Sizes, shapes, and arrangements of
minerals within the rock, e.g.,
1. Coarse-grained
2. Fine-grained
3. Foliated (planar fabric)
•
All are clues to a rock’s origin and history.
Three Classes of Rocks
Fig 4.2
The Rock Cycle
10. Melting & Intrusion
1. Solidification of melt
2. Mountain Building
3. Uplift & Exposure
(Metamorphism)
4. Weathering
5. Erosion & Transport
6. Accumulation of
sediments
7. Deposition & Burial
8. Melting
9. Metamorphism
Fig 4.9
Igneous Rocks
•
Minerals crystallize from melt, derived 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:
– Coarse, interlocking crystals (“Coarse”)
•
Extrusive rocks cool rapidly at (or near) the
surface of the earth:
– Fine-grained, often “glassy”
Igneous Rocks
Common in
volcanic areas &
plate boundaries
Fig 4.3
Igneous
Silicates
predominate
-High melting
temperatures
- Abundance
of silicon
Sedimentary Rocks
• Organic rock:
– The hard parts of animals, such as bones and
shells, can become cemented together over
time to make rock. Usually the bones and
shells are made of calcite, or similar minerals,
and the organic rock that is made from them
is called limestone.
– Some types of microorganisms that live in the
ocean or lakes have tiny skeletons made of
silica. The organic rock made from their
skeletons is called chert.
Sedimentary Rocks
•
Loose particles (sand, silt, marine 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
Common along
passive margins
(and other basins)
Weathering
& Erosion
Transport
Basement
Rocks
Clastic:
Sandstone
Deposition
Chemical:
Limestone
Fig 4.4
Sedimentary
Silicates
(esp. Clays)
Carbonates
Sulfates
& Halides
(Precipitates)
Metamorphic Rocks
•
High temperatures and pressures at
depth 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
• Foliated Rocks: have a layered or
banded appearance that is produced
by exposure to heat and directed
pressure
Examples are: gneiss, phyllite,
schist and slate which
• 2) Non-Foliated rocks: do not have
a layered or banded appearance.
Examples are marble and quartzite
Common at
collisional plate
boundaries
Metamorphic Rocks
Fig 4.6
Metamorphic
Silicates
predominate
-Due to silicate
source rocks
-Distinctive
mineral types
indicative of
solid state
reactions
Rock Types
Sedimentary
rocks are most
abundant near
Earth’s surface
Sediments
make up
75% surface
area
Outcrops
- poor preservation
Igneous and
Metamorphic
rocks make up
most of the
crustal volume
- limited exposure!
Sediments make
up only 5% by
volume
Fig 4.6
Fig 4.8
Fig 4.8
Fig 4.8
Fig 4.8
Fig 4.8
??
??
??
??
Fig 4.8
??
Rock Types
How can we sample
what lies below the
surface?
By drilling: e.g.,
Sediments
make up
75% surface
area
Ocean
Drilling
Oceans - all over,
- passive margins
- rifting & spreading
- convergent
- hot spots
Continents
- San Andreas Fault
- Chelungpu Fault
- Hawaii
Outcrops
Continental
Drilling
Sediments make
up only 5% by
volume
Fig 4.6
(a) The Rock Cycle
Convergent Plate Boundary
-Subducting slab
2. Mantle melting & Intrusion
-Bouyant rise of melt
Figof
4.9Melt
1. Volcano: Solidification
(b) The Rock Cycle
Convergent Plate
Boundary
-Solidification of melt
3. Mountain building
Fig 4.9
(c) The Rock Cycle
Precipitation & Weathering
-Moisture laden air
-Precipitation and run-off
-Freezing & thawing
Fig 4.9
(d) The Rock Cycle
Sediment Transport
to Oceans
-Deposition
-Burial & lithification
-Chemical precipitation
Fig 4.9
(e) The Rock Cycle
Deformation & Metamorphism
-Continental collision (i.e., orogeny)
-Burial & deformation
-Increased pressure & temperature
Fig 4.9
(a) The Rock Cycle
Convergent Plate
Boundary
-Subducting slab
-Mantle melting
4.9
-Bouyant rise ofFigmelt