Transcript Rock Cycle and Structure of the Earth

Structure of the
Earth and
the Rock Cycle
Lithosphere composed of
minerals
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Definition of “Mineral” ?
Silicate minerals
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92% of crust
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silicon and oxygen
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A rock is a natural solid substance made
up of minerals
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rocks classified by origin : 3 types
Types of Rocks
1. IGNEOUS
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molten rock that has cooled and solidified
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molten rock is magma or lava
a) INTRUSIVE
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cools below surface; big crystals; coarse
b) EXTRUSIVE
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cools at surface; fine
Fine-textured extrusive
Coarse-textured intrusive
Glassy; rapid cooling
Basalt with vesicles
extrusive
intrusive
Mafic and felsic igneous rock
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Felsic: mostly felsic minerals
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Mafic: mostly mafic minerals
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High in feldspar and silicate minerals
Lighter
Less dense
High in magnesium and iron
Darker
Denser
Ultramafic: all mafic minerals
2. SEDIMENTARY
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made up of sediments that have been
compacted and cemented.
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sediments: all solid particles transported by
water, ice, wind, gravity
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mud, sand, shells, debris, dust, rock fragments
mudstone, sandstone, limestone, conglomerate,
shale
accumulate in strata (layers)
mudstone
sandstone
limestone
conglomerate
strata
3. METAMORPHIC
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altered from original rock by heat,
pressure or chemical activity
began as igneous, sedimentary, or
metamorphic rock
shale --> slate
 slate --> schist
 granite --> gneiss
 limestone --> marble
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gneiss
schist
slate
Rock Cycle
Structure of Earth
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Core
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Mantle
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Crust
Core
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Inner
5150 – 6370 km (below surface)
 Solid iron
 5400 – 9000 degrees F
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Outer
2900 – 5150 km
 Molten iron
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Core
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Mantle
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Crust
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Lower mantle
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Upper
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Uppermost
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Lower mantle
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Upper mantle
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very dense; iron and
magnesium
670 – 2900 km
rigid at lower end
“plastic” toward
crust: asthenosphere
250 -670 km
Uppermost mantle
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Rigid
“Moho” to 70 km
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“Moho”
Mohorovičić discontinuity
 Boundary between crust and mantle
 Change in seismic waves here
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Core
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Mantle
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Crust
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Crust
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continental : 25 miles thick
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oceanic: 5-6 miles thick
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Lower mafic; upper felsic (granite)
Less dense
Mafic (basalt)
More dense
Lithosphere = uppermost mantle and crust
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Rigid
ultramafic
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Lithosphere is divided into large plates
rigid plates “float” on the plastic
asthenosphere, just deep enough to
support their own weight:
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Isostasy
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Isostatic adjustment of crust:
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add weight (sediment, glacial ice): crust will
sink
remove weight (erosion, glacial ice melts):
crust will rebound
ice
Duluth
Crust sank
Northeast
“drowned “ St. Louis River