Download Rock cycle and Igneous rocks

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Igneous Rocks
and Intrusive
Igneous Activity
The 3 types of rocks: !  Sedimentary !  Igneous !  Metamorphic Marble
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SEDIMENTARY ROCKS
Come from rocks sediments (rock fragments, sand, silt, etc.)
Fossils
Siltstone
IGENEOUS ROCKS
Are made of volcanic material (lava or magma)
Extrusive Igneous
(or volcanic)
rock formation
Intrusive
IntrusiveIgneous
Igneous
(or
( plutonic)
plutonic)
rock
rockformation
formation
Basalt
Granite
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METAMORPHIC ROCKS
Rocks have been changed from a pre-existing rock,
by high-pressure/high-temperature
Marble
Sedimentary
Sedimentary
Metamorphic
Igneous
The Rock Cycle Igneous
Rock
High Temp. Sediments Pressure and
Metamorphic
Rock
Sedimentary
Rock
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Igneous rocks "  Igneous rocks make up large parts of the continents and all the oceanic crust -­‐ indicate plate boundaries 4
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Composition of Magma "  Silica is the primary constituent of magmas "  Magmas are differentiated based on the relative proportions of silica, iron, and magnesium.   Felsic – silica rich, iron and magnesium poor   Intermediate – intermediate between felsic and mafic   Mafic – silica poor, iron and magnesium rich Bowen’s reaction series "  Bowen’s reaction series describes the sequence of mineral crystallization in a cooling magma. "  There are two branches in the reaction series:   Discontinuous series. -­‐ produces ferromagnesian minerals   Continuous series -­‐ produces a variety of plagioclase feldspars 5
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Igneous Rock Textures "  Minerals begin to crystallize from magma and lava after small crystal nuclei form and grow. Intrusive (plutonic) Extrusive (or volcanic) Igneous Rock Textures "  Minerals begin to crystallize from magma and lava after small crystal nuclei form and grow. "  Two broad groups of igneous rocks are:   Extrusive (or volcanic) Form in the exterior of the earth. Rapid cooling = Aphanitic texture =mineral grains are not easily visible   Intrusive (plutonic) Form in underground. Slow cooling = Phaneritic texture: mineral grains that are easily visible Also we have:   Rocks with more complex cooling histories are characterized by porphyritic textures. Mineral grains with different sizes. 6
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Examples Igneous Extrusive Rocks
Obsidian is usually black in color though it can also be
red or have a greenish tint. It is a dense volcanic glass,
usually composed of rhyolite, rich in iron and
magnesium. Obsidian is formed when the lava cools so
quickly that crystals do not have time to grow. Obsidian
fractures with very sharp edges. It was used by Stone
Age cultures for making knives, arrowheads, and other
tools where sharp edges are important.
Basalt is a dark-colored, fine-grained rock composed
mainly of plagioclase and pyroxene minerals. It most
commonly forms as an extrusive rock, such as a lava
flow, but can also form in small intrusive bodies, such
as an igneous dike or a thin sill.
Pumice is light and porous. It forms during explosive
eruptions. Pumice is full of holes caused by expanding
volcanic gases. It is composed of volcanic glass and
minerals, and can form in all types of magma: basalt,
andesite, dacite, and rhyolite.
Examples Igneous Intrusive Rocks
Granit is a light-colored rock with grains large enough
to be visible with the unaided eye. It forms from the
slow crystallization of magma below Earth’s surface.
Granite is composed mainly of quartz and feldspar with
minor amounts of mica, amphiboles and other minerals.
This mineral composition usually gives granite a red,
pink, gray or white color with dark mineral grains visible
throughout the rock.
Diorite is a coarse-grained, intrusive igneous rock that
contains a mixture of feldspar, pyroxene, hornblende
and sometimes
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Crystals vs. Sediments (Granit = Igneous intrusive) (Conglomerate = sedimentary) Intrusive Igneous Bodies -­‐ Plutons "  Plutons are bodies of igneous rock which have been intruded in country rock or have formed in place far beneath the surface. 8
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Volcanic pipes and necks
"  Volcanic pipes are magma-­‐filled, cylindrical feeder channels beneath volcanoes. "  Pipes can become volcanic necks with deep erosion. Geo-inSight 3., p. 100
Laccoliths
Geo-inSight 6. and 7., p. 101
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Dikes and sills
"  Dikes are discordant features (meaning they cut across layering in the country rock) "  Sills are concordant (parallel to the rock layers). Batholiths and Stocks
"  Batholiths are plutons that have more than 100 km² in area of exposure. "  Stocks are somewhat smaller plutonic bodies. 10