esci 101: lecture rocks february 16, 2007 copy of this lecture will be found at: esci101 with some...
TRANSCRIPT
ESCI 101: Lecture ESCI 101: Lecture RocksRocks
February 16, 2007February 16, 2007
Copy of this lecture will be found at:http://www.owlnet.rice.edu/~esci101
With Some Graphics from Press et al., Understanding Earth, 4th Ed. (Copyright © 2004 by W. H. Freeman & Company)
From http://geology.about.com/library/bl/images/blbif.htm
Banded Iron
Formation
Three Classes of RocksThree 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 CharacteristicsDistinguishing 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.
The Rock CycleThe Rock Cycle
10. Melting & Intrusion1. Solidification of melt2. Mountain Building3. Uplift & Exposure(Metamorphism)4. Weathering5. Erosion & Transport6. Accumulation of sediments7. Deposition & Burial8. Melting 9. Metamorphism
Fig 4.9
Igneous RocksIgneous 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”
Sedimentary RocksSedimentary 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 RocksSedimentary 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
Weathering & Erosion
Transport
Deposition
Basement Rocks
Chemical: Limestone
Fig 4.4
Common along passive margins
(and other basins)
Clastic: Sandstone
Metamorphic RocksMetamorphic 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 RocksMetamorphic 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
Metamorphic
Silicates predominate
-Due to silicate source rocks
-Distinctive mineral types indicative of solid state reactions
Rock TypesRock Types
Fig 4.6
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
Rock TypesRock Types
Fig 4.6
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
(a) The Rock Cycle(a) The Rock Cycle
Fig 4.9
Convergent Plate Boundary-Subducting slab
2. Mantle melting & Intrusion-Bouyant rise of melt
1. Volcano: Solidification of Melt
(b) The Rock Cycle(b) The Rock Cycle
Fig 4.9
Convergent Plate Boundary
-Solidification of melt3. Mountain building
(c) The Rock Cycle(c) The Rock Cycle
Fig 4.9
Precipitation & Weathering-Moisture laden air
-Precipitation and run-off-Freezing & thawing
(d) The Rock Cycle(d) The Rock Cycle
Fig 4.9
Sediment Transport to Oceans
-Deposition-Burial & lithification
-Chemical precipitation
(e) The Rock Cycle(e) The Rock Cycle
Fig 4.9
Deformation & Metamorphism-Continental collision (i.e., orogeny)
-Burial & deformation-Increased pressure & temperature