This document discusses igneous rock classifications and Bowen's reaction series. It begins by classifying igneous rocks based on their silica content into felsic, intermediate, mafic and ultramafic compositions. It then explains Bowen's reaction series, which showed that minerals crystallize from magma at different temperatures in a predictable order. Certain minerals tend to form together based on their crystallization temperatures. The document also discusses how igneous intrusive bodies like sills, dikes, batholiths and stocks form underground from crystallizing magma.

1. Igneous Chemistry
Felsic/acid = > 65% SiO2
– lots of Na, K, Al but little Mg, Fe, Ca
– e.g. continental crust; granite
Intermediate = 53 - 65% SiO2
– e.g. subduction zone volcanic rocks; andesite
Mafic/basic = 45 - 52% SiO2
– lots of Mg, Fe, Ca but silica poor
– e.g. oceanic crust; basalt
Ultramafic = < 45% SiO2
– e.g. mantle

2. Igneous Compositions
The type of rock that melts and/or the
composition of the parent magma
determines the chemistry of the rock
that crystallizes.
Other processes affect this too…
– Crystallization sequence of minerals
– Crystal settling
– Assimilation
– Magma mixing

3. Within the field of geology,Within the field of geology, Bowen's reaction seriesBowen's reaction series
is the work of the petrologist, Norman L. Bowen whois the work of the petrologist, Norman L. Bowen who
was able to explain why certain types of mineralswas able to explain why certain types of minerals
tend to be found together while others are almosttend to be found together while others are almost
never associated with one another. He experimentednever associated with one another. He experimented
in the early 1900s with powdered rock material thatin the early 1900s with powdered rock material that
was heated until it melted and then allowed to cool towas heated until it melted and then allowed to cool to
a target temperature whereupon he observed thea target temperature whereupon he observed the
types of minerals that formed in the rocks produced.types of minerals that formed in the rocks produced.
Bowen’s Reaction Series

4. He repeated this process withHe repeated this process with
progressively cooler temperatures andprogressively cooler temperatures and
the results he obtained led him tothe results he obtained led him to
formulate his reaction series which isformulate his reaction series which is
still accepted today as the idealizedstill accepted today as the idealized
progression of minerals produced byprogression of minerals produced by
cooling magma.cooling magma.
Bowen’s Reaction Series

5. Bowen’s Reaction Series
Helps understand how you can get intermediate and
mafic rocks from mafic magmas.
When a melt cools, different minerals crystallize at
different temperatures!
Minerals that cool at nearly the same temperatures
tend to occur together in rocks. Only certain minerals
can occur together.
If you remove the minerals that have crystallized at a
certain temperature, you change the overall chemistry
of the system…

6. Bowen’s Reaction Series
Continuous
Continuous
Discontinuous
Discontinuous

7. Bowen’s Reaction Series
Discontinuous Series
Only ferromagnesian.
One mineral changes to
next as temperature
slowly drops.
Each change is a
chemical reaction
between solids
(crystals) and fluids
(melt, water, gas)
present at the time.
Reactions not always
complete.

8. Bowen’s Reaction Series
Continuous Series
Nonferromagnesian
plagioclase feldspar (Ca
to Na)
As magma cools, Ca-
rich plagioclase reacts
with melt and
proportionally more Na-
rich plagioclase
crystallizes
Continues until all Ca
and Na is used up.
Plagioclase is often,
therefore, zoned with Ca
rich core and Na rich
rims.

9. Bowen’s Reaction Series
Felsic Minerals
Not really part of
series.
As Mg, Fe, Ca, and
Na are used up, left
over magma has
more and more
SiO2, K, Al, water,
and other exotic
stuff (U).
Form K feldspars,
muscovite, quartz,
accessory
minerals.
Increasing
Si
content

10. Minerals of Low SilicationMinerals of Low Silication
If there is a considerably deficiency of silica in magma, elementsIf there is a considerably deficiency of silica in magma, elements
may not be able to combine with sufficient silica to formmay not be able to combine with sufficient silica to form
minerals. This type of minerals are called minerals of lowminerals. This type of minerals are called minerals of low
silication. Example: K and Na form Leucite and Nephelinesilication. Example: K and Na form Leucite and Nepheline
instead of orthoclase and albite.instead of orthoclase and albite.
Minerals of High SilicationMinerals of High Silication
In magma, when there is an adequate amount of silica, elementsIn magma, when there is an adequate amount of silica, elements
form the minerals which are rich in silica contents. Theseform the minerals which are rich in silica contents. These
minerals are termed as minerals of high silication.minerals are termed as minerals of high silication.
Mineral of Low silication+silicaMineral of Low silication+silica Mineral of High silicationMineral of High silication

11. Minerals of Low Silication Minerals of High Silication
Leucite Orthoclase
Nepheline Albite
Analcite Anorthoclase
Olivine Orthorhombic pyroxene
Biotite Augite
Hornblende

12. Quartz(SiOQuartz(SiO22) doesn’t exist with minerlas of low silication) doesn’t exist with minerlas of low silication
Any excess of silica which may be left over after the bases areAny excess of silica which may be left over after the bases are
fully satisfied crystallizes out as quartz. The inter relationship offully satisfied crystallizes out as quartz. The inter relationship of
minerals of low and high silication shows that minerals of lowminerals of low and high silication shows that minerals of low
silication and SiOsilication and SiO22 combinedly forms minerals of high silication.combinedly forms minerals of high silication.
Hence, quartz can’t co-exists with minerals of low silication.Hence, quartz can’t co-exists with minerals of low silication.
NaAl(SiONaAl(SiO44) + 2(SiO) + 2(SiO22) = NaAl.Si) = NaAl.Si33OO88
Nepheline Quartz AlbiteNepheline Quartz Albite

13. Essential Igneous rock forming mineralsEssential Igneous rock forming minerals
Felsic/Silicic/Light coloredFelsic/Silicic/Light colored
mineralsminerals
 QuartzQuartz
 Potash FeldsperPotash Feldsper
 Mica(muscovite)Mica(muscovite)
Mafic/Ultramafic/DMafic/Ultramafic/D
ark colored mineralsark colored minerals
 OlivineOlivine
 PyroxenePyroxene
 AmphibolesAmphiboles
 BiotiteBiotite
Plagioclase feldsparPlagioclase feldspar

14. Intrusive Igneous Rock Bodies
Magmas crystallized beneath the Earth's
surface form intrusive bodies of igneous rock
known as plutons.
The term pluton (after the Greek god Pluto)
refers to any igneous intrusion regardless of
size, shape or composition of the magma.
Classification of plutons is based on:
1. Geometry of intrusion: size and shape
2. Relationship to surrounding rocks:
– concordant or boundaries parallel to layering in surrounding rocks
– discordant or boundaries cut across layering in surrounding rocks

15. Intrusive Igneous Rock Bodies

16. Intrusive Igneous Rock Bodies

17. Concordant Igneous Bodies
Sill: A sill is a
concordant body, few
cm to >1 km thick,
produced when
magma is injected
between layers of
older sedimentary or
volcanic rock, and
are generally
composed of
intermediate to basic
composition magma.

19. Concordant Igneous Bodies
Laccolith: A laccolith
represents magma
that pushes overlying
rock layers upward to
form a condordant,
mushroom-shaped,
sill-like body,
typically comprising
magma of
intermediate to
granitic composition.
It causes folding of the overlyingIt causes folding of the overlying
rock layersrock layers
Flat bottom and convex upwardFlat bottom and convex upward
dome shaped igneous bodydome shaped igneous body

20. Concordant Igneous Bodies
Lopolith: A lopolith is a
spoon-like shaped
concordant body
similar to a sill except
the floor and roof sag
downward. The
intrusions are generally
magma of intermediate
to basic composition.
These are basin or saucer shaped concordant bodies with topThese are basin or saucer shaped concordant bodies with top
nearly flat and convex bottom.nearly flat and convex bottom.

21. PhacolithsPhacoliths
These are concordantThese are concordant
bodies that occurs along thebodies that occurs along the
crests and troughs of thecrests and troughs of the
folded sedimentary strata.folded sedimentary strata.
In folding, the crest andIn folding, the crest and
trough are regions oftrough are regions of
weakness and tension,weakness and tension,
magma often intruded intomagma often intruded into
these trough and crest.these trough and crest.
Southern Patagonia Phacoliths, ChileSouthern Patagonia Phacoliths, Chile

22. Discordant Igneous Bodies
Dike:Dike: A dike is a discordant body, fewA dike is a discordant body, few
cm to >100 m thick, produced whencm to >100 m thick, produced when
magma is injected along fractures inmagma is injected along fractures in
surrounding rock layers. Dikes ftypicallysurrounding rock layers. Dikes ftypically
form from magmas of basic to graniticform from magmas of basic to granitic
composition. Ring and Radial dikes arecomposition. Ring and Radial dikes are
discordant bodies having either adiscordant bodies having either a
concentric (circular) or radialconcentric (circular) or radial
distribution; develop above a largedistribution; develop above a large
subsurface intrusive body (batholith orsubsurface intrusive body (batholith or
stock) or adjacent to volcanic pipes orstock) or adjacent to volcanic pipes or

23. Discordant Igneous Bodies
Batholith:Batholith: A batholith is a discordant magma body withA batholith is a discordant magma body with
exposed surface area of more than 100 square kilometers;exposed surface area of more than 100 square kilometers;
typically consists of multiple intrusions. Batholith aretypically consists of multiple intrusions. Batholith are
usually magma of granitic composition with minorusually magma of granitic composition with minor
intermediate varieties.intermediate varieties.
BatholithsBatholiths
are the largest bodies ofare the largest bodies of
Igneous rock, irregular inIgneous rock, irregular in
shape and occupies largeshape and occupies large
area. Their occurrence isarea. Their occurrence is
commonly associated withcommonly associated with
the mountain-buildingthe mountain-building
process.process.

24. Discordant Igneous Bodies
Stock:Stock: A stock is a discordant magma body with exposedA stock is a discordant magma body with exposed
surface area of less than 100 square kilometers; maysurface area of less than 100 square kilometers; may
represent exposed portion of a much larger intrusion. It isrepresent exposed portion of a much larger intrusion. It is
usually magma of granitic composition with minor intermediateusually magma of granitic composition with minor intermediate
varieties.varieties.
StocksStocks
Are irregularAre irregular
masses ofmasses of
batholiths habit ofbatholiths habit of
smaller dimension.smaller dimension.

25. Discordant Igneous Bodies
Volcanic pipes and Volcanic pipes and
necks:necks: are discordantare discordant
bodies that representbodies that represent
the upper part of thethe upper part of the
conduit that connectsconduit that connects
the volcanic ventthe volcanic vent
(crater) with an(crater) with an
underlying magmaunderlying magma
source (magmasource (magma
chamber or reservoir).chamber or reservoir).
Volcanic necks areVolcanic necks are
erosional remnants oferosional remnants of
magma that solidified inmagma that solidified in
the pipe or conduit.the pipe or conduit.

26. Intrusive Igneous Rock Bodies