Topic 5 not on midterm 2 Flashcards
What is the difference between magma and lava?
Magma is composed of Molten rock and is stored in the Earth’s crust. Lava is magma that reaches the surface through a volcano vent.
How are igneous rocks classified?
Igneous rocks can be:
- Intrusive - cooling within the earth, because it cools very fast minerals are small
- Extrusive - cooling at the earth’s surface or very close to it, because it cools over a long period of time minerals grow larger
Note: color is very important in identifying different minerals in that rock as it formed in a rock by using Bowen’s reaction scale - different minerals form at different temperatures
Calcium rich minerals form at high temperatures and sodium rich rocks form with less temperature
What are the different types of intrusive igneous structures?
Dikes - a tabular igneous body that cuts across sedimentary structures or other linear features (discordant)
Sills - are formed from magmas that entered the country rock parallel to the bedding layer and are concordant with the country rock
Plutons- are discordant intrusive rock formed at great depths - are large, course grained and irregular in shape
-Batholith - a pluton that is larger than 100km2
- Stocks - a pluton that is less than 100km2
What are the three mechanisms of magmatic differentiation
Differentiation is the process by which magma evolve to give rise to a variety of magmas and rock types
- Assimilation - composition of crust is different then magma - as magma rises through the crust it can react with crystal rocks and become part of the magma
- Magma mixing - if two or magmas with different composition come in contact with one another beneath the surface of the Earth - they can mix and produce composition intermediates
- Bowen’s reaction series and crystal setting - magmas do not solidify instantaneously - there is a sequence of minerals that crystallize as a magma cools based on their melting point. The earliest formed minerals sink to the bottom of the magma chamber, Fe-Mg rich materials are highest temperature and sink first and these ions are removed leaving an increase in SiO4, Al, K and Na in the melt
Explain how partial melting results in more felsic magmas?
Mafic is made of magnesium and iron and has a higher density and is found in the oceanic crust. Felsic is made of Feldspar and silica is a low density and found in the continental crust.
In partial melting - when rock melts because it is of mixed composition it melts over a range of temperatures at various pressures and during the melting the liquid composition changes. Partial melting produces magma with more felsic because the first minerals to melt are felsic because they melt at lower temperatures then mafic
Explain the difference between mafic and felsic igneous rock
Mafic is composed of minerals rich in Magnesium and Iron, has a higher melting point, it is higher density 3.0g/cm3 and is found primarily in oceanic crust
Felsic - is composed of minerals rich in Feldspar and silica, it has a lower melting point than Mafic, lower density 2.7mg:cm3 and is found predominantly in the continental crust
How are fine grained rocks formed
When magma cools slowly and fine grained is also refered to as Aphanitic texture
How are coarse grained rocks formed
When magma cools slowly - there are l age mineral grains also called phaneritic texture
What is the origin of magma
Source of most magma is the upper crust in which generated from solid rock
- Increase temperature - there is a geothermal gradient average 25 degree Celsius/km in upper crust - is variable between oceanic and continental mantle
- peridoitite tenperaure of peridotite melt> geothermal gradient >=solid - Decrease pressure - increase depth leads to increase pressure which leads to a higher melting point
- Addition of volatiles
Water and other volatiles cause rocks to melt at lower temperatures
