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Igneous Rocks
… rocks formed by the
solidification (cooling or
freezing) of melt or molten rock
Igneous Rocks
… melt or molten rock is commonly
referred to as
magma
… much like ice forms by the freezing of water at 0° (32°F)
…igneous rocks form by the cooling / freezing of magma,
only at much higher temperatures,
…between 650° and 1100°C
Magma that cool at or near
Earth’s surface are termed
Extrusive
or Volcanic rocks
Magma that cool beneath
Earth’s surface are termed
Intrusive or
Igneous rocks
What is magma made of?
The composition of the magma depends on:
•
Original Composition of the melt
•
Partial melting (fractionation) of source rock
•
Contamination of “country rock” and/or
•
Fractional crystallization
What is magma made of?
•
All magmas contain Si and O
•
Magmas also contain varying proportions of
elements
such as Al, Ca, Na, K, Fe, Mg
•
Water and Volatiles
•
Wet magmas include up to 15% volatiles
such as CO
2
, N
2
, H
2
, SO
2
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How / where do igneous rocks originate ?
Melting and
extruding of
molten rock
Heat transfer…
Addition of volatiles…
Decompression…
Melting
Partial Melting / Fractionation
Decompression Melting
Partial Melting / Fractionation
Fractional (partial) melting
since materials melt at different temperatures,
raising temperatures high enough to melt silicates
can result in those materials with higher melting
temperatures to fall out of solution..thus the melt is
now fractionated or different in compostion from the
total composition of the orignal rock
When this melt cools, it will form a rock of different
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- Spring '11
- Swisher
- Geology, Igneous rocks, Bowen, pyroxene, Volcanic rocks
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