Download Fundamental Concepts in Igneous Petrology

Fundamental Concepts in Igneous
Petrology (Chapter 1)
Ash-Rich Strombolian Activity, Stromboli Volcano, Italy
Image source: www.photovolcanica.com
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A Observational criteria (general)
A.
i. Field Criteria
cross-cut the
countryy rocks
and truncate
structures
image source: Barb Dutrow,
Dutrow
2005
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A. Observational criteria (general)
i. Field Criteria Contact effects: chilled margins
or contact metamorphic effects
(
(above)
) Salsburyy Crags,
g , Teschenite Sill
(Edinburgh)
(right) Hutton’s step – contact
Image source: Barb Dutrow and Darrell Henry (2002)
metamorphism of sandstone
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A. Observational criteria (general)
i. Field Criteria
Geological forms
directly observed
as igneous
events:
• cinder cones
cones,
stratovolcanoes,
flows, etc.
Ash-Rich Strombolian Activity, Stromboli Volcano, Italy
Image source: www.photovolcanica.com
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A. Observational criteria (general)
ii. Textural Criteria
Gabbro - Rustenberg layered suite,Bushveld Complex:
Image source:
http://web.uct.ac.za/depts/geolsci/dlr/bv_thin.html
Macroscopic/
microscopic
development of
interlocking texture.
• first-crystallizing minerals
are most euhedral and later
minerals are less euhedral
(paragenetic sequence)
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A. Observational criteria (general)
ii. Textural Criteria
Osidian from a flow
Image source: Hamblin and Christiansen (2001)
glassy textures
Ash grain from
pyroclastic
p
eruption:
e.g. Mt. St. Helens
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A. Observational criteria (general)
ii. Textural Criteria random orientation of
crystals
• except where there is crystal
settling
g or magmatic
g
flow
Granite (above) and Gabbro (right)
Image source: Darrell Henry, 2007
1. How do we know we are dealing
with
i h iigneous rocks?
k ?
A. Observational criteria (general)
ii. Textural Criteria development of pyroclastic
p
((explosive
p
eruptive
p
deposits
materials)
• rapidly cooled/partly sedimentary
Rapidly cooled fragments
Rapidly-cooled
of rock and ash extruded as
a hot volcanic ash deposit welded tuff
Image source: Hamblin and
Christiansen (2001)
2. What does a igneous petrologist try
to assess:
•
•
•
•
generation
i off melts
l – [how
[h many?]
?]
source of melting – [where?]
material that is melted – [what?]
processes that modifyy melts during
p
g
crystallization, etc.? [how changed?]
3. How does a petrologist assess this?
A. Experience at looking at rocks and
interpreting
p
g textures
Tokachi Volcano, Hokkaido, Japan (2006) Walter Maresch (Ruhr Univ.), Barb Dutrow
(LSU) and Dan Dunkley (Univ. Tokyo). Image source: Darrell Henry
3. How does a petrologist assess this?
B. Experimental data to simulate the
conditions at depth
p
Piston cylinder apparatus and experimental assembly from Ruhr Univ.. Image source: Barb
Dutrow, 1987
3. How does a petrologist assess this?
C. Theoretical models to extend experimental
data to other conditions i.e. thermodynamics
y
Theoretical melting models to relate decompression melting and the types of melts to
rocks. Image source: Ed Stolper (CalTech).
3. How does a petrologist assess this?
D. Knowledge of the interior of the Earth –
direct samples
p of the mantle
Mantle xenolith in alkali basalt.
Image source: Barb Dutrow, 2006
Seiad Ultramafic Complex, northern
California Image source: Darrell Henry
California.
Henry, 1973
3. How does a petrologist assess this?
D. Knowledge of interior of the Earth –
indirect samples
p - meteorites
Meteorites - arrested early
stages of development of
solar nebula with no
subsequent alteration or
differentiation
• clues to the development
of the planets
Meteor
M
t r Crater,
Cr t r Arizona.
Ariz n The
Th explosive
pl i
impact of a meteorite about 25,000 ybp.
Image source: Press and Siever, 2001
3. How does a petrologist assess this?
D. Knowledge of interior of the Earth –
indirect samples
p - meteorites
Irons (Fe-Ni alloy) - planetary
cores?
• 5% of falls
[Iron meteorite MALTAHOHE, Namibia Image
source: http://www.meteoriteman.com/]
Stony-irons (Metal and silicate
minerals) - partial differentiation
• 1% of falls
[Stony-iron meteorite – palllasite, Dora, New Mexico.
Image source: Smithsonian Institution]
3. How does a petrologist assess this?
D. Knowledge of interior of the Earth –
indirect samples
p - meteorites
Stones (Achondrites) –
differentiated – also SNC g
group
p
• 8% of falls
[Achondrite – Martian meteorite, Nakhla, Egypt,
Image
g source: http://www.meteoriteman.com/]
p //
/]
Stones (Carbonaceous chondrite)
– primitive/undifferentiated
/
• 86% of falls
[Chondrite – Allende meteorite: Chihuahua, Mexico.
Image source: http://www.meteoriteman.com/]
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
y
Earth has layered
structure:
• crust (oceanic and
continental)
• mantle
• core (inner and outer)
image source: Press and Siever, 2001
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
Internal structure is
largely established by
variations in P- and Sseismic waves.
• The Mohorovicic (Moho)
discontinuity at interface
of crust and upper
mantle is compositional
discontinuity.
image source: Winter (2001)
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
Low velocity zones in upper
mantle is zone of 1-10%
melting
• forms the asthenosphere
• serves as interface of
lithospheric plates and
mesophere.
image source: Winter (2001)
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
Damping of S waves in the
outer core signals presence
of liquid outer core.
Sharp increase in SS and P
Pwave velocities indicate
solid metallic inner core.
image source: Winter (2001)
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
Continental crust vs. ocean crust
Thicker: 25-60 km vs. 0-10 km
Older: some >4 Ga vs. <160 Ma.
Si-richer: 52-75% SiO2 vs. 50-52% SiO2.
Crust/upper mantle are coupled
as lithospheric
p
p
plate to depths
p
of
initial low velocity zones.
image source: Press and Siever (2001)
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
Within mantle there are
additional discontinuities that
mark polymorphic transitions of
olivine:
• 410 km olivine converts to
spinel-type
spinel
type structures
• 660 km there is a transition to
a perovskite-type structure.
image source: Press and Siever (2001)
4. What do we think we know about
Earth’s
Earth s interior?
A. The Earth is layered
New player: Post-perovskite high-pressure
g p
p
phase of MgSiO
g
3
• P and T stability at lowermost
Earth'ss mantle.
Earth
mantle
p
derives from
• “Post-perovskite"
name of stable phase of MgSiO3
throughout most of Earth's
mantle, i.e. perovskite.
image source: Press and Siever (2001)
5. Hypothesis for origin of Earth?
A Early differentiation (first few 10s of
A.
millions of years?)
image source: Press and Siever (2001)
Differentiation process
likelyy results from
heating due to
combinations of
• gravitational
i i
l collapse
ll
• accretion of
planetismals
• Sinking of iron to form
core
• radioactive decay
Renewed interest in the Early Earth
Possible early evolution of solar system (4.57 Ga)
Alternate Early Earth scenarios
P ibl events
Possible
nt
• Moon-forming
i
impactor
( 4 54 Ga)
(~4.54
G )
• Magma vs. watery
oceans (4.4-4.0 Ga)
Artist: Ron Miller
The Most Ancient Earth Materials Known
Detrital Zircons from a
conglomerate at Jack Hills,
Australia
False
F
l color
l CL image
i
off ancient
i t
zircon. (Wilde et al. 2001)
Alternate Early Earth timeline
Places of Other Ancient Earth Materials
5. Hypothesis for origin of Earth?
B Resulting heterogeneous Earth composition
B.
Differentiation
produced chemical
zonation in the Earth
Defines nature of rock
types that will develop.
image source: Press and Siever (2001)
6. P
P--T-depth relation in the Earth?
Relationship between
depth and pressure
a function of weight of
the overlying column of
material.
image source: Winter (2001)
5. P
P--T-depth relation in the Earth?
In systems that flow
(ductile), P is equal in all
directions i.e. lithostatic
P = ρgh
• ρ = density
• g = acceleration of
gravity
• h = height of rock
column
image source: Winter (2001)
5. P
P--T-depth relation in the Earth?
Near surface, rocks
behave brittly
• can accommodate small
amount of differential P
(a few kbars) before
fracturing.
density changes primarily
with composition e.g.
crust ~ 2.8 g/cm3 and
mantle ~ 3.3 g/cm3.
image source: Winter (2001)
5. P
P--depthdepth-T relation in the Earth?
Variation of T with
depth is geothermal
gradient.
gradient
Related to factors
including cooling
initiated in the early
Earth and radioactive
decay.
decay
image source: Winter (2001)
Estimated ranges of oceanic and
continental steady-state geotherms to a
depth of 100 km using upper and lower
limits based on heat flows measured
near the surface.
5. P
P--depthdepth-T relation in the Earth?
Heat is transferred by:
p
• radiation to space
(minor)
• conduction (thermal
(
vibration)
(
y
• convection (density
differences
associated with T))
• advection (transfer of
heat with rocks).
)
image source: Winter (2001)
7. Where are magmas from? – where
it is hot enough – plate tectonics
5
3
1
6
7
4
2
200 km
Continental Crust
400
Oceanic Crust
Lithospheric Mantle
?
600 km
Source of Melts
?
Sub-lithospheric Mantle
?
?
image source: Winter (2001)
1. Mid
Mid--ocean Ridges
5. BackBack-arc Basins
2 Intracontinental
2.
I
i
l Rifts
Rif
6 Ocean
6.
O
Island
I l d Basalts
B l
3. Island Arcs
7. Miscellaneous Intra
Intra-Continental
C i
lA
Activity
i i
4 Active
4.
A i C
Continental
i
lM
Margins
i
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kimberlites, carbonatites,
kimberlites,
carbonatites,
anorthosites...
anorthosites
...