ESCI 101: Lecture Rocks February 16, 2007 Copy of this lecture will be found at: With Some Graphics from Press et al., Understanding Earth, 4th Ed. (Copyright © 2004 by W. H. Freeman & Company) From bl/images/blbif.htm Banded Iron Formation

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.cemented togethercalciteminerals –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

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

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

Metamorphic Rocks Fig 4.6 Common at collisional plate boundaries

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

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

Fig 4.8

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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 & spreading - convergent - hot spots Continents - San Andreas Fault - Chelungpu Fault - Hawaii

(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 Fig 4.9 Convergent Plate Boundary -Solidification of melt 3. Mountain building

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

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

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

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