Basic Geology

1
Earth Materials Images from Strahler and
Strahler, 2005

• The Crust and its Composition
• Igneous Rocks
• Sediments and Sedimentary Rocks
• Metamorphic Rocks
• The Cycle of Rock Change

2
The Crust and its Composition

• oxygen and silicon account for about 75 of the
  earth's crust
• metallic elements iron, aluminum and the base
  elements account for most of the rest

Figure11.1, p. 399
3
The Crust and its Composition

• the elements of the crust are combined in
  inorganic chemical compounds called minerals
• these minerals are mixed together in various
  proportions to form different rock classes
• rocks of the Earth's crust are grouped into three
  major classes igneous, sedimentary and
  metamorphic rocks

4
Igneous Rocks

• igneous rocks consist mainly of silicate minerals
  containing silicon, oxygen and metallic elements
• less dense felsic minerals (from feldspar and
  silica) dominate the igneous rocks of the upper
  crust while more dense mafic and ultramafic (iron
  and magnesium) minerals dominate those of the
  lower crust
• magma that solidifies below the Earths surface
  and remains surrounded by older, preexisting rock
  is called intrusive igneous rock
• where magma reaches the surface, it emerges as
  lava, which solidifies to form extrusive igneous
  rock

5
Igneous Rocks

• intrusive igneous rocks solidify below the
  Earths surface, they cool slowly and therefore
  develop larger mineral crystals visible to the
  eye
• extrusive igneous rocks cool very rapidly on the
  land surface or ocean bottom and thus develop
  smaller, microscopic size crystals

6
Igneous Rocks

• Igneous rocks consist mainly of silicate minerals
  containing silicon, oxygen and metallic elements
• less dense felsic minerals dominate the igneous
  rocks of the upper crust while more dense mafic
  and ultramafic minerals dominate those of the
  lower crust

Figure11.4, p. 401
7
Igneous Rocks

• Intrusive (plutonic) igneous rocks
• granite felsic intrusive igneous rock (same
  minerals as rhyolite)
• diorite intermediate intrusive igneous rock
• (same minerals as andesite)
• gabbro mafic extrusive igneous rock (same
  minerals as basalt)
• peridotite ultramafic (olivine rich)

Figure11.4, p. 401
8
Igneous Rocks

• Extrusive (volcanic) igneous rocks
• rhyolite felsic extrusive igneous rock (same
  minerals as granite)
• andesite intermediate extrusive igneous rock
• (same minerals as diorite)
• basalt mafic extrusive igneous rock (same
  minerals as gabbro)

Figure11.4, p. 401
9
Plutonic Rock in N. America
http//upload.wikimedia.org/wikipedia/commons/1/1a
/North_america_rock_plutonic.jpg
10
Volcanic Rock in N. America
http//upload.wikimedia.org/wikipedia/commons/f/fa
/North_america_rock_volcanic.jpg
11
Igneous Rocks
a body of intrusive igneous rock is called a
pluton (granite typically accumulates in enormous
plutons, called batholiths extending down several
kilometers and occupying an area of several
thousand square kilometers) a sill is a
plate-like pluton formed when magma forces its
way between two preexisting (usually sedimentary)
rock layers
Figure 11.9, p. 404
12
Igneous Rocks
a dike is a wall-like pluton formed when a
vertical rock fracture is forced open by
magma magma entering small, irregular, branching
fractures in the surrounding rock solidifies in a
branching network of thin veins
Figure 11.9, p. 404
13
Sediments and Sedimentary Rocks

• mineral alteration occurs when the minerals in
  igneous rocks are transformed chemically into new
  minerals that are more stable at or near the
  Earths surface
• processes of mineral alteration include
  oxidation, hydrolysis, and solution
• in the process of mineral alteration, solid rock
  is weakened, softened, and fragmented, yielding
  particles of many sizes and mineral compositions
• when transported by a fluid mediumair, water, or
  glacial icethese particles are known
  collectively as sediment
• three major classes of sediment clastic (from
  pre-existing rocks), chemically precipitated
  sediment and organic sediment

14
Sediments and Sedimentary Rocks
sediment accumulates in more-or less horizontal
layers, called strata (beds) - individual strata
are separated from those below and above by
surfaces called stratification planes or bedding
planes
Figure 11.15, p. 410
15
Sediments and Sedimentary Rocks
Clastic sediment consists of inorganic rock and
mineral fragments, called clasts
Figure 11.14, p. 410
16
Sediments and Sedimentary Rocks

• chemically precipitated sediment consists of
  inorganic
• mineral compounds precipitated from a saltwater
• solution or as hard parts of organisms
• in the process of chemical precipitation, ions in
  solution combine to form solid mineral matter
  separate from the solution (e.g. limestone,
  gypsum, chert)
• organic sediment consists of the tissues of
  plants and animals, accumulated and preserved
  after the death of the organism (e.g. a layer of
  peat in a bog or marsh)

17
Sediments and Sedimentary Rocks

• Hydrocarbons in sedimentary rocks are compounds
  of carbon, hydrogen and oxygen solid fuels such
  as coal, liquids such as petroleum, and gas as
  natural gas

Figure 11.18, p. 412
18
Metamorphic Rocks
metamorphic rocks are formed from preexisting
rocks by intense heat and pressure, which alter
rock structure and chemical composition Heat and
pressure are produced by various processes,
including but not limited to tectonic activity,
deep burial, and contact with magma. shale is
transformed to slate or schist, sandstone to
quartzite, and limestone to marble gneiss forms
when an intrusive magma cools next to igneous or
sedimentary rocks
19
Metamorphic Rocks
example of a schist
Figure 11.19, p. 412
20
Metamorphic Rocks
some metamorphic changes
21
The Cycle of Rock Change
the cycle of rock change describes how Earth
materials are cycled and recycled by Earth
processes over geologic time in the surface
environment, rocks weather into sediment in the
deep environment, heat and pressure transform
sediment into rock that is eventually exposed at
the surface
Figure 11.21, p. 416