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

RocksRocks• A rock is a naturally occurring, solid aggregate

of minerals.

Fig 4.1

How Rocks are Made and Recycled:How Rocks are Made and Recycled:

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.

Three Classes of RocksThree Classes of Rocks

Fig 4.2

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”

Igneous RocksIgneous Rocks

Common in volcanic areas & plate boundaries

Fig 4.3

Igneous

Silicates predominate

-High melting temperatures

- Abundance of silicon

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

Sedimentary

Silicates(esp. Clays)

CarbonatesSulfates

& Halides(Precipitates)

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 RocksMetamorphic RocksFig 4.6

Common at collisional plate

boundaries

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

Fig 4.8

Fig 4.8

Fig 4.8

Fig 4.8

Fig 4.8

Fig 4.8

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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

(a) The Rock Cycle(a) The Rock Cycle

Fig 4.9

Convergent Plate Boundary

-Subducting slab-Mantle melting

-Bouyant rise of melt