Introduction
Properties
of Magmas
Formation
of Magmas
Magma
Transport – Means of Ascension
Crystallization
of Magmas
Differentiation
Processes in Magma Systems
Volcanic
Rocks and The Rock Cycle
Classification
of Volcanic Rocks
Volcano
Anatomy 101
Volcanic
Eruptions
Tectonic
Setting of Active Volcanic Belts
Volcanic-related
Ore Deposits
Concluding
Points
Vocabulary
A.
Direct connection between magma generation, volcanism, plate tectonics
and crustal growth.
1. Oceanic crust building factory
at spreading centers
2. Continental crust building & recycling factory at
subduction zones
B.
The great importance of volcanism in shaping the Earth’s surface, and
the influence upon the climate and biosphere.
1. Influence on atmospheric
chemistry and transparency
2. Influence on communities of
plants and animals
3. Serious volcanic hazards on ecosystems and societies
A. What is a
magma? Defined: A magma consists of:
1.
Molten (liquid) rock
2.
Residual crystals
3.
Newly formed crystals
4.
Dissolved gases
5.
Xenoliths (exotic rock material)
B.
Physical Properties
1.
Temperature
2.
Viscosity
3.
Dissolved gas partial pressures
IV. Properties of Magmas - Definition
and characteristics
C. Magma Chemistry – Know these Four major types
1. Ultramafic (ultramafic) – Very
Low SiO4, V. High MgO, FeO, CaO
Very Hot, Very low
viscosity, Dry
2. Mafic (basaltic) Low SiO4, High
MgO, FeO, CaO; Hot;
Low Viscocity, Wet or Dry
3. Intermediate (andesitic) Mod SiO4, MgO, FeO, CaO,
NaO, Low K2O; Mod.T; Mod/High Viscocity, Wet
4. Felsic (rhyolitic/granitic) High SiO4, NaO, K2O,
Mod/Low CaO,
Low FeO
and MgO; Low T; Low Viscocity, Wet/dry
V. Formation of Magmas – The
Zone of Melting
A. Major Source Regions = Tectonic Plate Boundaries
1. Mantle rocks beneath
spreading centers.
2. Subducting oceanic slab,
mantle wedge, and crustal
root of a subduction zone.
3. Mantle rocks at the top
of mantle plumes (Hot spots)
4. Deep crustal rocks in
continental collision zones.
B. Conditions for Melting
1. Increasing Temperature
2. Decreasing Pressure
3. Increasing Water Pressure
4. Source Rock Composition
C. The Melting Process – Anatexis
1. Partial melting of rock
a. Source rock composition
b. Degree of partial melting (temp/heat-controlled)
c. Amount of water in rock
d. Melting of low temperature minerals first
2. Major chemical differences between parent source-rock
and resultant daughter-melt (magma) are mainly due
to partial melting mechanism (selective mineral melting)
A.
Mass Transfer Mechanisms
1.
Fault/fracture-controlled ascent of magma (typically through cold crust)
2. Diapirism
(balloon-like rising of magma bodies through hot crust)
B. Illustrations of Mechanisms
V. Crystallization of Magma --- A Complex Process
Controlled by Temperature, Pressure, and Chemistry
A. Bowen’s Reaction Series
B. Cooling History of a Magma
1.
Compositional changes
2. Textural changes
VI.
Differentiation -- Igneous Processes that Can
Change the Composition of Magmas
1.
Crystal settling
2.
Fractionation
3.
Assimilation
4.
Magma Mixing
A. What is volcanic
rock? Defined: An aggregate of
interlocking crystals formed
from the crystallization of a
magma that has reached the
Earth's surface (lava).
B. Extrusive rock: Equivalent to the term, volcanic.
C. Intrusive
rock – Form deep beneath the surface (these
rocks
are termed plutonic).
A. Volcanism’s Roll in the Endless Rock Cycle
1. Creation of primary surface crustal rocks
2. Creation of major mountain chains
3. Generation of nutrients, water, and gases to the surface
IX. Classification of Volcanic Rocks
A. Based on Texture and Composition
B.
The Major Volcanic Rock Types (composition-based)
1.
Komatiites – ultramafic mineralogy
2. Basalts – mafic mineralogy
3. Andesites – intermediate mineralogy
4. Rhyolites – felsic
mineralogy
Questions: 1) Mineralogy of each
type?
2) Plutonic
(intrusive) equivalents of above?
C. Other
Volcanic Rock Types (textural quality-based)
1. Porphyry
2. Scoria
3. Pumice
4. Obsidian
5. Tuffs,
Welded tuffs
6.
Pyroclastic Material – Loose particles (called tephra)
a.
Ash < 2 mm
b.
Lapilli > 2mm, < 64mm
c.
Bombs and Blocks > 64 mm
D. Identifying the major Volcanic Rocks in Hand
samples
1.
In-class examination of samples
2.
Internet images link - http://volcanoes.usgs.gov/Products/Pglossary/pglossary.html
1. Composite (strato)volcano
2. Shield Volcano
3. Cinder Cone
4. Caldera
5. Lava Dome
C. Types of Volcanic Eruption Hazards
1. Lava Fountains and Flows
2. Ash Flows
3. Ash Falls
4.
Mud Flows
5.
Harmonic Tremors
6.
Eruption Blast
7. Tsunami
D.
Active Volcanoes of the United States
1. Washington
2.
Oregon
3.
California
4.
Continental Interior
5.
Alaska and Hawaii
XI. Volcanic Eruptions
A. Types of Volcanic Eruptions
Classification based on Volcanic Explosivity Index - VEI
0 Hawaiian = Lava Flows; Little
explosiveness
1/2 Strombolian = Jetting lava; some
explosiveness
3/4 Vulcanian = Explosively ejected molten
lava and tephra
5/6 Plinian = High
velocity eruption of steam, tephra, & gases
7/8 Ultra Plinian = Extra massive Plinian
eruption
B.
Worldwide Examples of the Major
Volcanic Eruptions
1. Mt. Pinatubo – 1990
2. Kilauea – 1983 - Present
3. Mt. Saint Helens – 1980
4. Krakatau
- 1816
5. Mt. Mazama – 6,600 ya
6. Toba, Sumatra, 75,000 ya
C.
Volcanism Effects on World Climate
1. Cooling effect of Dust in
the Stratosphere
2. Warming Effect of Carbon
Dioxide Gases
3. Cooling/Precipitation
Effects of Sulphate particles
XII. Tectonic Setting for Volcanism
1.
Subduction Zones
2.
Spreading Centers
3.
Continental Rifts
4.
Hot Spots
B.
The Distinct Nature of Volcanoes and
Volcanic Rock
at
each Type of Tectonic Plate Boundary
1.
Subduction Zones
--- All types of Volcanoes
---- Mostly Andesites, Some Basalt and Rhyolite
2. Spreading Centers
--- Fissure eruptions and
Shield volcanoes
-- All Basalt (pillow variety common in undersea)
3. Continental Rifts
--- Fissure eruptions, All Major Types
– Predominant Mix
of Basalts and Rhyolites
4. Hot Spots
-- Shield
volcanoes, Cinder cones, and Fissures
--
Predominantly Basalts (rhyolites too in continents)
C.
San Diego County is a World-Class Example of
a Ancient
Subduction-related Volcanic Arc
1. Mesozoic-age magmatism (160-90
MYA; "heyday" of the dinosaurs)
2. Tectonic setting was
combination of island arc and continental-margin arc
3. Wide range of magma compositions
(basaltic to granitic)
4. Average magma composition
changed over time
5. Active volcanic chain
probably had a crest elevation of 8,000 meters
A. Porphyry copper deposits and related gold/silver
veins
1. Subduction-related
mineralization
2. Form from hydrothermal
fluids circulating over an active
magma chamber
3. Major source of world's
copper
4. Western U.S. has numerous
porphyry mines
B. “Black smoker” copper sulfide/metal deposits
1. Spreading
center-related mineralization
2. Form
from hydrothermal fluids circulating over an active
oceanic
magma chamber
3.
Actively mined deposits are part of bodies called "ophiolites"
XIV.
Global Influence of Volcanism
A. Importance of Volcanism in
Building & Shaping the Earth's Crust
1. Oceanic crust building factory
at spreading centers
2. Continental crust building
& recycling factory at subduction zones
B. Impact of Volcanism to our
Global Climate and Ecosystem
1. Influence on atmospheric
chemistry and transparency
2. Influence on communities of
plants and animals
3. Serious volcanic hazards on
ecosystems and societies
XV. Magma & Volcano Vocabulary -
Internet Image Glossary: http://volcanoes.usgs.gov/Products/Pglossary/pglossary.html
assimilation
aa
andesite
ash
basalt
Bowen's
reaction series
caldera
cinder
cone
circum-Pacific
belt
composite
(strato)volcano
crater
differentiation
fissure
eruption
harmonic
tremor
Hawaiian-style
eruption
lahar
lava
dome
lava
tube
magma
magma
differentiation
mantle
plume (hot spot)
nuee
ardente
ophiolite
pahoehoe
pillow
lava
Plinian-style
eruption
phreatic-style
eruption
porphyry
system
pyroclastic
sheet layers
rhyolite
shield
volcano
Strombolian-style
eruption
tephra
volcanic
explosivity index (VEI)
volcanism
volcano
Vulcanian-style
eruption