GEO401 - Chapter 4: Igneous Rocks
Felsic
- more feldspar/silica
What are the two basic compositional groups of igneous rocks?
Felsic and mafic
partial melting of rocks are
ALWAYS more felsic than their parent rocks
What are rock properties controlled by?
Composition + physical conditions > Mineralogy + texture > Rock type
Granite (igneous)
Contains feldspar and silica FELSIC
Peridotite (Igneous)
Contains olivine and pyroxene Mg (magnesium) and Fe (iron) ULTRAMAFIC
What are the four compositional groups of igneous rocks?
Felsic igneous rocks Intermediate igneous rocks Mafic igneous rocks Ultramafic igneous rocks
How do magmas form?
When rocks melt (or partially melt) -pressure decreases -Fluids are added that reduce the melting temperature of the rocks -temp increases
How do igneous rocks form?
by crystallization from magmas below melting temperatures of constituent minerals
intrusive rock
coarse-grained igneous rock that is formed when molten rock cools slowly and solidifies inside Earth's crust - large interlocking crystals
What are igneous rocks classified by?
composition and texture
what is the melting temp of rocks determined by?
composition, temperature, pressure, and the presence or absence of fluids
divergent boundaries
decrease in pressure from hot air rising due to spreading plates causes ultramafic peridotite to partially melt, forming MAFIC magma and eventually basalt or gabbro
rock texture
describes grain size, shape, and orientation
Each mineral has
different melting temp
In what types of tectonic settings will we find these different melting processes?
divergent (mafic), convergent(mafic + intermed + felsic), hot spot(mafic)
Extrusive rock
fine-grained igneous rock that is formed when molten rock cools quickly and solidifies on Earth's surface ***Under a microscope will look like a bunch of tiny crystals
Subduction zones
fluid-induced melting
What are common minerals in ultramafic/ mafic rocks?
gabbro, basalt, peridotite, olivine
Why do rocks melt?
heat, pressure, water
Mafic
more magnesium/ferric
continental convergent boundaries
most rocks melt by decompression OR addition of H2O SOMETIMES crustal thickening during mountain building can heat the lower crust enough to result in crustal melting
What is the most abundant rock in the upper mantle?
peridotite
fractional crystallization
process in which different minerals crystallize from magma at different temperatures, removing elements from magma
magmatic differentiation (fractional crystallization)
the formation of one or more secondary magmas from a single parent magma