7/28/2019 82280616 Bowen s Reaction Series
1/11
Silicon-
OxygenTetrahedron
(SiO4)
Isolated Tetrahedrons
(Olivine)
7/28/2019 82280616 Bowen s Reaction Series
2/11
Tetrahedron Arrangement
S ingle-Chain Double-Chain S heet
Pyroxene Amphibole Mica
7/28/2019 82280616 Bowen s Reaction Series
3/11
Common silicate minerals
7/28/2019 82280616 Bowen s Reaction Series
4/11
Igneous Rock Textures
Igneous Rock Textures
T extureT exture refers to the size, shape andrefers to the size, shape andarrangement of grains or other constituentsarrangement of grains or other constituentswithin a rock within a rock
Texture of igneous rocks is primarilyTexture of igneous rocks is primarilycontrolled bycontrolled by cooling ratecooling rateE xtrusive igneous rocksE xtrusive igneous rocks cool quickly at or cool quickly at or near E arths surface and are typicallynear E arths surface and are typically f f ineine--
grained grained (most crystals 1 mm)
Coarse-grained igneous rock
Fine-grained igneous rock
7/28/2019 82280616 Bowen s Reaction Series
5/11
I gneous rocksClassification is based on the rock's textureand mineral constituents
Texture
Size and arrangement of crystalsTypes
Fine-grained fast rate of coolingCoarse-grained slow rate of cooling
Porphyritic (two crystal sizes) two rates of coolingGlassy very fast rate of cooling
7/28/2019 82280616 Bowen s Reaction Series
6/11
I gneous Rock I dentificationI gneous Rock I dentificationI gneous rock names are based onI gneous rock names are based on texturetexture (grain size) and(grain size) andmineralogicmineralogic compositioncompositionT extural classi f icationT extural classi f ication
P lutonic P lutonic rocksrocks ((gabbrogabbro--dioritediorite--granite) are coarsegranite) are coarse- -grained and cooledgrained and cooledslowly at depthslowly at depth
VolcanicVolcanic rocksrocks (basalt(basalt--andesiteandesite--rhyoliterhyolite) are typically fine) are typically fine- -grained andgrained andcooled rapidly at the E arths surfacecooled rapidly at the E arths surface
Compositional classi f icationCompositional classi f ication M a f ic M a f ic rocksrocks ((gabbrogabbro--basalt) contain abundant dark basalt) contain abundant dark- -coloredcolored
ferromagnesian mineralsferromagnesian minerals I ntermediate I ntermediate rocksrocks (diorite(diorite--andesiteandesite) contain roughly equal amounts of ) contain roughly equal amounts of
dark dark-- and lightand light--colored mineralscolored minerals Felsic Felsic rocksrocks (granite(granite--rhyoliterhyolite) contain abundant light) contain abundant light- -colored mineralscolored minerals
7/28/2019 82280616 Bowen s Reaction Series
7/11
I gneous Rock ChemistryI gneous Rock ChemistryRock chemistry, particularlyRock chemistry, particularly silica silica (SiO(SiO 22) content, determines) content, determines
mineral content and general color of igneous rocksmineral content and general color of igneous rocks Ultrama f icUltrama f ic //UltrabasicUltrabasic rocks have 63% silica, by weight, and containlightlight--colored minerals that are abundant in silica, aluminum, sodiumcolored minerals that are abundant in silica, aluminum, sodiumand potassiumand potassium------------------ Oversaturated rocksOversaturated rocks
Intrusive/extrusiveIntrusive/extrusive felsicfelsic rocksrocks -- granite/granite/rhyoliterhyolite
7/28/2019 82280616 Bowen s Reaction Series
8/11
B owens Reaction SeriesB owens Reaction SeriesM
inerals crystallize in a predictable order, over a largeM
inerals crystallize in a predictable order, over a largetemperature rangetemperature rangeE arly f ormed mineral + remaining melt = new mineral E arly f ormed mineral + remaining melt = new mineral
Discontinuous branch Discontinuous branch Ferromagnesian minerals (olivine, pyroxene, amphibole,Ferromagnesian minerals (olivine, pyroxene, amphibole, biotite biotite))
crystallize in sequence with decreasing temperaturecrystallize in sequence with decreasing temperature As one mineral becomes chemically unstable in the remainingAs one mineral becomes chemically unstable in the remaining
magma, another begins to formmagma, another begins to form
Continuous branchContinuous branch Plagioclase feldspar forms with a chemical composition that evolvesPlagioclase feldspar forms with a chemical composition that evolves
(from Ca(from Ca--rich to Narich to Na--rich) with decreasing temperaturerich) with decreasing temperature
7/28/2019 82280616 Bowen s Reaction Series
9/11
7/28/2019 82280616 Bowen s Reaction Series
10/11
Observations from B owensObservations from B owensLarge variety of igneous rocks is produced byLarge variety of igneous rocks is produced by
diversification of diversification of magma compositionsmagma compositions
M a f ic M a f ic magmasmagmas will crystallize intowill crystallize into basalt basalt or or gabbro gabbro if if earlyearly--formed minerals are not removed from the magmaformed minerals are not removed from the magma
I ntermediate magmas I ntermediate magmas will similarly crystallize intowill similarly crystallize intodioritediorite or or andesiteandesite if minerals are not removedif minerals are not removed
Separation of earlySeparation of early- -formed ferromagnesian mineralsformed ferromagnesian minerals
from a magma body increases the silica content of thefrom a magma body increases the silica content of theremaining magmaremaining magma
M inerals melt in the reverse order of that in which theyM inerals melt in the reverse order of that in which theycrystallize from a magmacrystallize from a magma
7/28/2019 82280616 Bowen s Reaction Series
11/11