ESCI101 09 Rocks

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ESCI 101: Lecture Rocks February 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 andamp; Company) From http://geology.about.com/library/ bl/images/blbif.htm Banded Iron Formation

Rocks: 

Rocks A rock is a naturally occurring, solid aggregate of minerals. Fig 4.1

Three Classes of Rocks: 

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: 

Distinguishing Characteristics Mineralogy - Constituent minerals and their relative proportions. Texture - Sizes, shapes, and arrangements of minerals within the rock, e.g., Course-grained Fine-grained Foliated (planar fabric) All are clues to a rock’s origin and history.

Three Classes of Rocks: 

Three Classes of Rocks Fig 4.2

Igneous Rocks: 

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: Course, interlocking crystals Extrusive rocks cool rapidly at (or near) the surface of the earth: Fine-grained, often 'glassy'

Igneous Rocks: 

Igneous Rocks Common in volcanic areas andamp; plate boundaries Fig 4.3

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Igneous Silicates predominate High melting temperatures Abundance of silicon

Sedimentary Rocks: 

Sedimentary Rocks Loose particles (sand, silt, marine shells) accumulate on shorelines, basins, rivers, etc., Clastic Sediments Minerals precipitate from dissolved chemicals in water Chemical andamp; Biochemical Sediments All are the products of Weathering - that breaks up and decays rocks, and Erosion - that transports from source to point of deposition

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Weathering andamp; Erosion Transport Deposition Basement Rocks Chemical: Limestone Fig 4.4 Common along passive margins (and other basins) Clastic: Sandstone

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Sedimentary Silicates (esp. Clays) Carbonates Sulfates andamp; Halides (Precipitates)

Metamorphic Rocks: 

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° Regional Metamorphism - High pressures and temperatures derive from regional collision, deformation and mountain building. Contact Metamorphism - Locally high temperatures, adjacent to intrusions.

Metamorphic Rocks: 

Metamorphic Rocks Fig 4.6 Common at collisional plate boundaries

Metamorphic Rocks: 

Metamorphic Rocks Fig 4.6 Foliations - Planar fabric defined by Alignment of platy minerals (micas andamp; clays) Alternating bands of mineral types Indicative of high pressures and deformation during formation Pressure-Temperature-time paths Not Foliated Distinct low- pressure minerals

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Metamorphic Silicates predominate Due to silicate source rocks Distinctive mineral types indicative of solid state reactions

Characteristic Metamorphic Minerals: 

Characteristic Metamorphic Minerals For more images: http://skywalker.cochise.edu/wellerr/mineral/ kyanite andalusite sillimanite staurolite garnet

Rock Types: 

Rock 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

Outcrop Exposures: 

Outcrop Exposures Fig 4.7 Measure orientation andamp; thickness Record regional patterns on geologic maps Infer what lies below

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Fig 4.8

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Fig 4.8

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Fig 4.8

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Fig 4.8

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Fig 4.8

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Fig 4.8 ?? ?? ?? ?? ??

Rock Types: 

Rock 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 andamp; spreading convergent hot spots Continents San Andreas Fault Chelungpu Fault Hawaii

The Rock Cycle: 

The Rock Cycle Melting andamp; Intrusion Solidification of melt Mountain Building Uplift andamp; Exposure Weathering Erosion andamp; Transport Deposition andamp; Burial Metamorphism Melting andamp; Intrusion Fig 4.9

(a) The Rock Cycle: 

(a) The Rock Cycle Fig 4.9 Convergent Plate Boundary Subducting slab Mantle melting Bouyant rise of melt

(b) The Rock Cycle: 

(b) The Rock Cycle Fig 4.9 Convergent Plate Boundary Solidification of melt Mountain building

(c) The Rock Cycle: 

(c) The Rock Cycle Fig 4.9 Precipitation andamp; Weathering Moisture laden air Precipitation and run-off Freezing andamp; thawing

(d) The Rock Cycle: 

(d) The Rock Cycle Fig 4.9 Sediment Transport to Oceans Deposition Burial andamp; lithification Chemical precipitation

(e) The Rock Cycle: 

(e) The Rock Cycle Fig 4.9 Deformation andamp; Metamorphism Continental collision (i.e., orogeny) Burial andamp; deformation Increased pressure andamp; temperature

(a) The Rock Cycle: 

(a) The Rock Cycle Fig 4.9 Convergent Plate Boundary Subducting slab Mantle melting Bouyant rise of melt

Plate Tectonics & Climate: 

Plate Tectonics andamp; Climate Plate tectonics drives uplift andamp; subsidence Climatic processes weather andamp; transport sediment Interactions control the rock cycle Fig 4.9