Igneous Rocks Flashcards
How are igneous rocks formed
by the cooling of magma
what are the three types of magma
Mafic/Basaltic magma, intermediate magma and felsic/basaltic magma
how is mafic magma formed
two methods: decompression melting and flux melting
what is decompression melting
convection currents in the mantle can take chunks of the mantle with them. As the mantle rises the pressure drops, allowing the molecules to move faster resulting in the melting of that chunk. this process has minimal temperature change and is the largest source of mafic magma
what is flux melting
when two tectonic plates collide, the heavier plate is driven down into the mantle. the increased pressure and temperature drives out volatiles in the crust and when they come into contact with the mantle they lower the melting temperature of mantle.
what is heat transfer
rising basaltic magma if unable to rise to the earths surface pools underneath the crust. the heat generated by the pool melts the surrounding crust
what is the dominant component of lava
silica
what are properties of mafic/basaltic magma
low silica, dark coloured, low viscosity, high temp, volatile poor. mafic minerals dominate
what are the properties of andesitic magma
as a mix of basaltic and felsic magma, properties are in between
what are the properties of rhyolitic magma
formed from crustal material, high silica, light coloured, high viscosity, low temp, volatile rich, very sticky
what can mafic magma form
olivine and pyroxene
what can andesitic magma form
pyroxene, amphibole, biotite
what can rhyolitic magma form
biotite, quartz, muscovite and feldspars
how are igneous rocks classified
based on the rock texture, mineral composition
how many igneous rock textures are there and what are they
3, aphantic, phaneritic and porhyritic
how are intrusive igneous rocks formed
slow cooled in the earths crust e.g. gabbro and granite
how are extrusive igneous rocks formed
fast cooling after reaching the earths surface e.g. basalts and obsidian
why are unaltered intrusive and extrusive igneous rocks suitable for engineering applications
strength due to interlocking crystals, stable overall at most dip angles and have little water flow
why aren’t volcaniclastic rocks suitable for engineering purposes
weathers easily and decreases strength
what are the two main groups of igneous rocks
volcanic/extrusive and plutonic/intrusive
what is hot spot volcanism
when a moving tectonic plate moves over a stationary hotspot. creating intrusive and extrusive basalt
what is plate divergence
when 2 plates move away from each other and rising magma fills the gap forming both intrusive or extrusive basalt
what is island arc plate subduction
when an oceanic plate is subducted beneath another oceanic plate. creating mafic to intermediate extrusives and intrusives
what is continental plate subduction
when an oceanic plate collides with a continental plate with the oceanic plate being subducted. creating mafic to felsic intrusives and extrusives
what are the properties of basalts
extrusive, dark coloured and aphanitic, silica content 47-53%
what are the properties of andesites
intermediate extrusive rock, medium grey colour, porphyritic with phenocrysts normally feldspars, proxene. silica content 53-63%
what are the properties of dacite
intermediate extrusive rock, colour medium grey, with phenocrysts normally feldspars. silica content 63-70%
what are the properties of rhyolite
extrusive rock, light colour due to high silica content of 70-78%. porphyritic with phenocrysts normally feldspar
what are the properties of gabbro
intrusive rock, dark in colour, dense with a phanertic texture with crystals feldspar, pyroxene silica content 47-53%
what are the properties of diorite
intrusive intermediate rock, speckled black and white with a phaneritic texture crystals normally feldspar, silica content ranging from 53-70%
what are the properties of granite
intrusive rock with pinkish white colour, phaneritic texture with crystals of feldspar and quartz, silica content 70-78%
