Download Lecture 5B / Igneous Rocks

Igneous Rocks
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Igneous
Rocks
The Life of Magma
 Most magma initially rises because of its greater buoyancy
>
cool and crystallize at depth as intrusions
>
migrate to the surface and erupt as extrusions
Igneous
Rocks
Composition & Texture
 Composition (mineralogy) - mostly related to what was melted
 Texture (crystal size) - mostly related to the cooling rate
(largely controlled by where the magma cools)
rhyolite
fine-grained texture
Cool slowly
at depth
Crustal melting
felsic magmas
granite
coarse-grained texture
Igneous
Rocks
Naming Igneous Rocks
click on the chart
Igneous
Rocks
Igneous Compositions
Mafic
 Mafic magmas are rich in Fe, Mg, & Ca, but poor in Si, Na, & K
O
O
Ca
Si O
Ca
O
Mg
O
Fe
magma
O
Fe
O
Si
O
Mg
Igneous
Rocks
Igneous Compositions
Mafic
 Upon cooling, mafic magmas crystallize mafic minerals…
…which compose most mafic igneous rocks
olivine
basalt
pyroxene
Ca-feldspar
gabbro
Igneous
Rocks
Igneous Compositions
Mafic & Ultramafic
 Abundant in the oceanic crust & mantle
basalt
gabbro
peridotite
Igneous
Rocks
Igneous Compositions
Mafic & Ultramafic
 Mafic rocks form by partial melting of ultramafic mantle
basalt
gabbro
peridotite
Igneous
Rocks
Igneous Compositions
Felsic
 Felsic magmas are poor in Fe, Mg, & Ca, but rich in Si, Na, & K
O
K
Si O
O
K
O
Na
O
Si
magma
O
Si
O
Si
O
Na
Igneous
Rocks
Igneous Compositions
Felsic
 Upon cooling, felsic magmas crystallize felsic minerals…
…which compose most felsic igneous rocks
mica
NaFeldspar
rhyolite
K-feldspar
quartz
granite
Igneous
Rocks
Igneous Compositions
Felsic
 Abundant in the continental crust
rhyolite
pumice
granite
Igneous
Rocks
Igneous Compositions
Felsic
 Form by melting continental crust
rhyolite
pumice
granite
Igneous
Rocks
Igneous Compositions
Intermediate
 “Combo deal” includes some mafic & felsic elements
O
Ca
Si O
O
K
O
Na
O
Fe
magma
O
Si
O
Si
O
Mg
Igneous
Rocks
Igneous Compositions
Intermediate
 Upon cooling, intermediate magmas crystallize int. minerals…
…which compose intermediate igneous rocks
amphibole
andesite
Ca/Na
Feldspar
diorite
Igneous
Rocks
Igneous Compositions
Intermediate
 Abundant in the continental crust
andesite
diorite
Igneous
Rocks
Igneous Compositions
Intermediate
 Form by “wet” melting of the mantle and crust
andesite
diorite
Igneous
Rocks
Igneous Textures
 Big crystals (coarse-grained texture)
> slow cooling at depth (intrusive)
microscope view
granite
Igneous
Rocks
Igneous Textures
 Small crystals (fine-grained texture)
> fast cooling on the surface (extrusive)
rhyolite
basalt
Igneous
Rocks
Igneous Textures
 No crystals (glassy texture)
> ultra-fast to cool (quenching) on the surface (extrusive)
obsidian
Igneous
Rocks
Igneous Textures
 Big & small crystals (porphyritic texture)
> two stages of cooling: slower & faster cooling (int & ext)
microscope view
porphyritic andesite
Igneous
Rocks
Igneous Textures
 Holes or vesicles (vesicular texture)
> gas bubbles escaping the magma (extrusive)
scoria
Igneous
Rocks
Igneous Textures
 Pieces of rock (pyroclastic texture)
> explosive eruption (extrusive)
Volcanic breccia, lapilli, & tuff
increasing
explosiveness
Igneous
Processes
WWW Links in this Lecture
> Magma - http://en.wikipedia.org/wiki/Magma
> Buoyancy - http://en.wikipedia.org/wiki/Buoyancy
> Intrusions - http://en.wikipedia.org/wiki/Intrusion
> Extrusions - http://en.wikipedia.org/wiki/Extrusive
> Mafic - http://en.wikipedia.org/wiki/Mafic
> Basalt - http://en.wikipedia.org/wiki/Basalt
> Gabbro - http://en.wikipedia.org/wiki/Gabbro
> Oceanic crust - http://en.wikipedia.org/wiki/Oceanic_crust
> Mantle - http://en.wikipedia.org/wiki/Mantle_%28geology%29
> Peridotite - http://en.wikipedia.org/wiki/Peridotite
> Felsic - http://en.wikipedia.org/wiki/Felsic
> Rhyolite - http://en.wikipedia.org/wiki/Rhyolite
> Granite - http://en.wikipedia.org/wiki/Granite
> Continental Crust - http://en.wikipedia.org/wiki/Continental_crust
> Pumice - http://en.wikipedia.org/wiki/Pumice
> Andesite - http://en.wikipedia.org/wiki/Andesite
> Diorite - http://en.wikipedia.org/wiki/Diorite
> Obsidian - http://en.wikipedia.org/wiki/Obsidian
> Scoria - http://en.wikipedia.org/wiki/Scoria
> Tuff - http://en.wikipedia.org/wiki/Tuff