igneous processes glg 101 - physical geology bob leighty
TRANSCRIPT
Igneous ProcessesIgneous Processes
GLG 101 - Physical GeologyGLG 101 - Physical Geology Bob LeightyBob Leighty
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!Explore and have fun!
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.
higher T &
P
lower T &
P
The Earth has a lot of trapped heat (from
radioactive decay)
deep
shallow
hottercolder Temperature
Depth
X
Increasing pressure downward typically keeps rocks from melting
Temperature increaseswith depth
Heat Within the EarthHeat Within the EarthIgneousIgneous
ProcessesProcesses
Depth(km)
50
0Temperature (°C) 10000
1000C / 50 km = 20C/km
Lower gradients (“cold”) <20C/km (continental interiors)
Some areas have different geothermal gradients
Higher gradients (“hot”) >40C/km (active volcanic areas)
1000C / 25 km = 40C/km
Heat Within the EarthHeat Within the EarthIgneousIgneous
ProcessesProcesses
Depth(km)
50
0
Temperature (°C) 10000
solid rocks
Solid rock melts (become magma) when it is heated above a certain temperature
magma
melting temperature (increases with depth)
How Does Solid Rock Melt?How Does Solid Rock Melt?IgneousIgneous
ProcessesProcesses
geothermalgradient
Depth(km)
50
0Temp (°C) 10000
Melting temperature is controlled by the composition of the rock
solid rocks
magmageothermalgradient
basalt melting T
granite melting T(lower)
How Does Solid Rock Melt?How Does Solid Rock Melt?IgneousIgneous
ProcessesProcesses
“dry” basalt melting T
(water lowers the melting T – makes it easier to melt)
Depth(km)
50
0Temp (°C) 10000
solid rocks
magmageothermalgradient
“wet” basalt melting T(lower)
How Does Solid Rock Melt?How Does Solid Rock Melt?IgneousIgneous
ProcessesProcesses
Melting temperature is also controlled by the presence of water
solid rocks
magmaDepth(km)
50
0Temp (°C) 10000
geothermalgradient
Rocks can melt by:
1) increasing T 2) decreasing P 3) adding water
Partial melting: only part of the rock melts
Different Ways Rocks Can MeltDifferent Ways Rocks Can MeltIgneousIgneous
ProcessesProcesses
Divergent Margins Divergent Margins
(mid-ocean ridges, continental rifts)(mid-ocean ridges, continental rifts)
Plates pull apart, lets mantle rocks rise & melt
(decompression melting)
Magmatism & Plate TectonicsMagmatism & Plate TectonicsIgneousIgneous
ProcessesProcesses
Forms oceanic crust
Example: Mid-Atlantic Ridge, Red Sea,
East Pacific Rise
Intense heating melts overlying
lithosphere
Rocks in a mantle plume rise &
melt (decompression melting)
Magmatism & Plate TectonicsMagmatism & Plate TectonicsIgneousIgneous
ProcessesProcesses
Intraplate “Hot spots”Intraplate “Hot spots”
Example: Hawaiian Islands (oceanic crust),
Yellowstone (continental crust)
Most continental crust forms
in this way
Hydrous (“wet’) melting above
down-going slab
Magmatism & Plate TectonicsMagmatism & Plate TectonicsIgneousIgneous
ProcessesProcesses
Convergent MarginsConvergent Margins
(subduction zones)(subduction zones)
Example: Andes, Cascades
Volcanic arcs
Differentiation: magmas may change as they rise
Rising MagmaRising MagmaIgneousIgneous
ProcessesProcesses
Magma will start to rise due to a buoyancy contrast with
surrounding rock
Magma forms diapirs (magma balloons)
Magma DifferentiationMagma DifferentiationIgneousIgneous
ProcessesProcesses
Magma mixing - magmas may mix & contaminate each
other
Assimilation - contamination of a magma by wall rock
Magma DifferentiationMagma DifferentiationIgneousIgneous
ProcessesProcesses
Assimilation - contamination of a magma by wall rock
Magma DifferentiationMagma DifferentiationIgneousIgneous
ProcessesProcesses
Assimilation - contamination of a magma by wall rock
Magma DifferentiationMagma DifferentiationIgneousIgneous
ProcessesProcesses
Crystallization – Depending on a magma’s composition,
certain minerals will begin to crystallize as the magma
cools
Mafic minerals
Magma DifferentiationMagma DifferentiationIgneousIgneous
ProcessesProcesses
Crystal settling – Heavy, early-formed crystals (like
olivine, rich in Fe, Mg, & Ca) sink & form layers
Magma DifferentiationMagma DifferentiationIgneousIgneous
ProcessesProcesses
WWW Links in this LectureWWW Links in this Lecture
> Radioactive decay - http://en.wikipedia.org/wiki/Radioactive_decay
> Geothermal gradient - http://science.enotes.com/earth-science/geothermal-gradient
> Magma - http://en.wikipedia.org/wiki/Magma
> Partial melting - http://en.wikipedia.org/wiki/Magma#Partial_melting
> Oceanic crust - http://en.wikipedia.org/wiki/Oceanic_crust
> Mid-Atlantic Ridge - http://en.wikipedia.org/wiki/Mid-Atlantic_Ridge
> Red Sea - http://en.wikipedia.org/wiki/Red_Sea
> East Pacific Rise - http://en.wikipedia.org/wiki/East_Pacific_Rise
> Divergent boundary - http://en.wikipedia.org/wiki/Divergent_boundary
> Hot spot - http://en.wikipedia.org/wiki/Hotspot_%28geology%29
> Mantle plume - http://en.wikipedia.org/wiki/Mantle_plume
> Hawaiian Islands - http://en.wikipedia.org/wiki/Hawaiian_Islands
> Yellowstone - http://en.wikipedia.org/wiki/Yellowstone_Caldera
> Convergent boundary - http://en.wikipedia.org/wiki/Convergent_boundary
> Volcanic arc - http://en.wikipedia.org/wiki/Volcanic_arc
> Continental Crust - http://en.wikipedia.org/wiki/Continental_crust
> Andes - http://en.wikipedia.org/wiki/Andes
> Cascades - http://en.wikipedia.org/wiki/Cascade_Range
IgneousIgneous
ProcessesProcesses
WWW Links in this LectureWWW Links in this Lecture
> Buoyancy - http://en.wikipedia.org/wiki/Buoyancy
> Magma differentiation - http://en.wikipedia.org/wiki/Igneous_differentiation
> Magma mixing -
http://en.wikipedia.org/wiki/Igneous_differentiation#Magma_mixing
> Magma assimilation -
http://en.wikipedia.org/wiki/Igneous_differentiation#Assimilation
> Crystallization - http://en.wikipedia.org/wiki/Igneous_differentiation#Fractional_crystallization_of_igneous_rocks
IgneousIgneous
ProcessesProcesses