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Petrology Quiz 2

Terms in this set (47)

basalt silica content
43-52%
Basalt aluminum concentration
13-18%
Basalt iron concentration
9-12%
Basalt magnesium concentration
5-12%
Basalt calcium concentration
9-12%
Basalt potassium concentration
0.1-1%
Basalt sodium concentration
2-4%
Basalt minerals
plagioclase (ca-rich)
Augite (ca-rich cpx)
Hyperstene (ca-poor, opx)
Pidgeonite (Ca-poor, cpx)
Olivine
Magnetite/ illmenite
Diopside
Hornblende
Sulfides
Quartz
Alkali-olivine basalts
-olivine (abundant)
-augite
Tholeiitic Basalts
-little to no olivine
-calcium poor pyroxene (pidgeonite or OPX)
-Hawaiian basalts are olivine tholeiitic
ropy lava
Pahoehoe
steep gradient of lava
aha
Flood/Plateau Basalt
Covers hundreds of km's and thousands of feet thick
crust sinks due to it
see on the moon
puts lots of volatiles into the air
Significant flood basalts
keweenaw (middle to late Proterozoic)
Parana Basin - Brazil (Late Jurassic - early Cretaceous)
Deccan Traps - India (Cenozoic)
Columbia Plateau - N.W. US (Miocene)
Rift volcanism
location of basalt
caused by:
tensional forces
Mid ocean ridge basalts -most common
Spreading centers
Usually tholeiitic basalts
Subduction Zone
location of basalt
caused by:
Compressional forces
oceanic arcs - aleutions
continental arcs. / margins - andes and pacific N.W.
Melting of subtracting slab
generally alkali olivine, but some tholeiitic
associated with strato or composite volcanos
granitic compositions due to partial melting of continental crust.
Intraplate volcanism
location of basalt
Mantle Hot-spot - mystery
Hawaii-mona kaya- largest geological structure
dominated by tholeiites with some olivine tholeiites
pyroclastic rocks
explosive and violent eruptions break up rocks
oatmeal heating
categorized based on fragment size
bombs
>64 mm
form agglomerate
blocks
>64mm
form volcanic breccia
Lapillus
2-64mm
form lapilli tuff
Ash
<2mm
form ash tuff
Lapilli
peles hair = glass strands
Peles tears = glass droplets
individual crystals with a glass jacket
Ash types
vitric
crystal
lithic
scoria
black frothy 80% vesicular and floats
Pumice
felsic fibrous si-rich
Pyroclastic flows
fast moving cloud of ash and lava that comes from a directed blast out of a volcano
accelerates from gas expansion in rapid heating
Ignimbrite
Ash flow tuff
fine grain ash compacted and welded together by residual tuff
fiami
welded look
turbulent flow region= top
uncompressed pumice lumps made of sanidine+quartz+glass
Laminar flow structures
High viscosity and friction
"flow banding" - colored bamnds caused by concentration of crystals/ inclusions and separation due to high viscosity flow
Middle area of flow
welded and compacted pumice
mix of lithic and glassy crystals
rhyolite silica
69-77%
rhyolite titanium
0-0.3%
rhyolite aluminum
10-16%
rhyolite iron
.5%-5%
rhyolite manganese
0-.1%
rhyolite magnesium
0-1%
rhyolite calcium
.1-1%
rhyolite sodium
.5-6%
rhyolite potassium
4-11%
rhyolite phosphorous
0-.5%
Rhyolite water
0-2%
Rhyolite common minerals
quartz
sanidine
plagioclase
anorthoclase
magnetite
rhyolite uncommon minerals
Hornblende
Hypersthene
oxides
zircon
sphene
apatite
characteristics of rhyolites
phenocrysts are cracked
usually feldspar crystals are more cracked than quartz crystals.
cracking happens in late stage cooling
deformed biotities and hornblendes. usually reddish to black in color due to hydrothermal alteration
tephra
anything blasted into the air and rains down
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