Download INTRODUCTION TO PETROLOGY

INTRODUCTION TO
PETROLOGY
WHAT IS PETROLOGY???
WHAT IS PETROLOGY???
Study of rocks (“petros”)
igneous & metamorphic
chiefly in the lithosphere
WHAT IS PETROLOGY???
Study of rocks (“petros”)
igneous & metamorphic
chiefly in the lithosphere
We will be dealing with hot rocks
tell us about composition & history of lithosphere
origin of rocks involves:
transfer of heat (energy)
movement of material
WHAT IS PETROLOGY???
Study of rocks (“petros”)
igneous & metamorphic
chiefly in the lithosphere
We will be dealing with hot rocks
tell us about composition & history of lithosphere
origin of rocks involves:
transfer of heat (energy)
movement of material
LITHOSPHERE
THINK LIKE A PETROLOGIST
what criteria do we use to distinguish rocks?
what do we want to know?
how do we answer these questions?
WHAT DO WE WANT TO KNOW?
how do we make melts?
what is melted, and where? what is the role of water?
how do melts behave during solidification?
what causes metamorphism?
how are metamorphism & deformation related?
how to rocks flow in the interior of mountain belts?
how do tectonic rates compare to heat conduction rates?
in what tectonic settings do these rocks form?
BASIS FOR UNDERSTANDING
field methods & sample study (observation)
theory, experiment & modeling (analytical)
THINGS TO CONSIDER
THINGS TO CONSIDER
materials of earth
THINGS TO CONSIDER
materials of earth
physical conditions
energy
pressure
temperature & heat
THINGS TO CONSIDER
materials of earth
physical conditions
energy
pressure
temperature & heat
relationship to tectonics
THINGS TO CONSIDER
materials of earth
physical conditions
energy
pressure
temperature & heat
relationship to tectonics
EgyPT
Fe-rich
Si-rich
EARTH INTERIOR
Fe-rich
Structure of Earth:
Si-rich
EARTH INTERIOR
Structure of Earth:
Si-rich
EARTH INTERIOR
core, mantle & crust
Fe-rich
chemical divisions
Structure of Earth:
Si-rich
EARTH INTERIOR
core, mantle & crust
mechanical divisions
mesosphere, asthenosphere & lithosphere
Fe-rich
chemical divisions
Fe-rich
Si-rich
EARTH INTERIOR
Fe-rich
Core:
Si-rich
EARTH INTERIOR
Si-rich
EARTH INTERIOR
Core:
Fe-Ni metallic alloy
inner core is solid
Fe-rich
outer core is liquid (no S-waves)
Si-rich
EARTH INTERIOR
Core:
Fe-Ni metallic alloy
inner core is solid
differentiation at work!
compositional separation within the planet
(fractionation)
Fe-rich
outer core is liquid (no S-waves)
Fe-rich
Si-rich
EARTH INTERIOR
Fe-rich
Mantle:
Si-rich
EARTH INTERIOR
peridotite (ultramafic)
greatest V, m & E
(moves & carries heat)
Fe-rich
Mantle:
Si-rich
EARTH INTERIOR
Mantle:
peridotite (ultramafic)
greatest V, m & E
(moves & carries heat)
Si-rich
EARTH INTERIOR
contains low velocity layer 60-220 km
Fe-rich
upper layer to 410 km (olivine to spinel)
Mantle:
peridotite (ultramafic)
greatest V, m & E
(moves & carries heat)
Si-rich
EARTH INTERIOR
contains low velocity layer 60-220 km
transition zone between 410-660 km
(spinel to perovskite)
SiIV to SiVI
Fe-rich
upper layer to 410 km (olivine to spinel)
Mantle:
peridotite (ultramafic)
greatest V, m & E
(moves & carries heat)
Si-rich
EARTH INTERIOR
contains low velocity layer 60-220 km
transition zone between 410-660 km
(spinel to perovskite)
SiIV to SiVI
lower mantle has more gradual velocity
increase
Fe-rich
upper layer to 410 km (olivine to spinel)
Fe-rich
Si-rich
EARTH INTERIOR
Fe-rich
Crust:
Si-rich
EARTH INTERIOR
mafic (magnesium + ferric)
to felsic (feldspar + silica)
rich in Si, Al, K, Na, Ca
Fe-rich
Crust:
Si-rich
EARTH INTERIOR
mafic (magnesium + ferric)
to felsic (feldspar + silica)
rich in Si, Al, K, Na, Ca
two main types:
oceanic
continental
+ “transitional”
Fe-rich
Crust:
Si-rich
EARTH INTERIOR
EARTH INTERIOR
EARTH INTERIOR
Oceanic crust:
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
sediments
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
sediments
pillow basalt
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
sediments
pillow basalt
sheeted dikes
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
sediments
pillow basalt
sheeted dikes
massive gabbro
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
sediments
pillow basalt
sheeted dikes
massive gabbro
ultramafic rocks (mantle)
EARTH INTERIOR
Oceanic crust:
thin: ~10 km on average
dense: ρavg = 3.0 g/cm3
relatively uniform stratigraphy
(= ophiolite suite)
sediments
pillow basalt
sheeted dikes
massive gabbro
ultramafic rocks (mantle)
mafic rocks
CONTINENTAL
OCEANIC
EARTH INTERIOR
EARTH INTERIOR
Continental crust:
thicker: 20-90 km (avg = 35 km)
less dense: ρavg = 2.7 g/cm3
highly variable composition
average = granodiorite
CHEMICAL DIVISIONS
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
later, continued differentiation was (and is) mostly a result of melting
and igneous process
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
later, continued differentiation was (and is) mostly a result of melting
and igneous process
how do we know these things???
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
later, continued differentiation was (and is) mostly a result of melting
and igneous process
how do we know these things???
seismic velocity structure
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
later, continued differentiation was (and is) mostly a result of melting
and igneous process
how do we know these things???
seismic velocity structure
meteorites
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
later, continued differentiation was (and is) mostly a result of melting
and igneous process
how do we know these things???
seismic velocity structure
meteorites
xenoliths in volcanics
CHEMICAL DIVISIONS
divisions separate Earth into Si-rich and Fe-rich spheres, largely a result
of early chemical differentiation based on a redistribution of matter,
prior to major solidification, by density
later, continued differentiation was (and is) mostly a result of melting
and igneous process
how do we know these things???
seismic velocity structure
meteorites
xenoliths in volcanics
experimental petrology
MECHANICAL DIVISIONS
Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left,
rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.
MECHANICAL DIVISIONS
Velocity structure (v)
Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left,
rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.
MECHANICAL DIVISIONS
Velocity structure (v)
v increases with density (ρ)
v = f (ρ)
Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left,
rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.
MECHANICAL DIVISIONS
Velocity structure (v)
v increases with density (ρ)
v = f (ρ)
ρ dependent on physical
properties & compositions
ρ = f (X, T)
Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left,
rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.
MECHANICAL DIVISIONS
Velocity structure (v)
v increases with density (ρ)
v = f (ρ)
ρ dependent on physical
properties & compositions
ρ = f (X, T)
v increases with depth (z) —
mostly!
Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left,
rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.
MECHANICAL DIVISIONS
Velocity structure (v)
v increases with density (ρ)
v = f (ρ)
ρ dependent on physical
properties & compositions
ρ = f (X, T)
v increases with depth (z) —
mostly!
v discontinuities indicate a
change in material composition
± properties
Figure 1-3.Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left,
rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.
MECHANICAL DIVISIONS
composition
property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
source of LVZ?
CMB
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
source of LVZ?
warmer? liquid?
CMB
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
source of LVZ?
warmer? liquid?
source of CMB?
CMB
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
source of LVZ?
warmer? liquid?
source of CMB?
CMB
change in composition
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
source of LVZ?
warmer? liquid?
source of CMB?
CMB
change in composition
source of OC-IC?
OC-IC
MECHANICAL DIVISIONS
composition
property
Velocity boundaries
LVZ
source of LVZ?
warmer? liquid?
source of CMB?
CMB
change in composition
source of OC-IC?
phase change (S to L)
OC-IC
MECHANICAL DIVISIONS
composition
Velocity boundaries
source of LVZ?
warmer? liquid?
source of CMB?
property
LVZ
LET’S LOOK IN
MORE DETAIL
CMB
change in composition
source of OC-IC?
phase change (S to L)
OC-IC
PETROLOGY & TECTONICS
major mineral transformations occur at ~410 and ~660 km
result from isochemical phase changes due to increased P
marked by seismic velocity discontinuities
Mineral
Structure
olivine
tetrahedral
spinel
perovskite
dense
tetrahedral
octahedral
Depth
Density
low
~410 km
~660 km
high
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
LO
HI
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
LO
HI
LO
HI
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
LO
HI
LO
HI
MG-SILICATES
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
LO
LO
.
H
SP
O
N
HE
T
S
A
T.Z.
HI
H
P
S
HI
E
R
E
O
S
E
M
MG-SILICATES
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
PETROLOGY & TECTONICS
Resulting divisions
lithosphere
asthenosphere
mesosphere
PETROLOGY & TECTONICS
Resulting divisions
lithosphere
asthenosphere
mesosphere
properties?
PETROLOGY & TECTONICS
Resulting divisions
lithosphere
asthenosphere
mesosphere
properties?
connections?
PETROLOGY & TECTONICS
Resulting divisions
lithosphere
asthenosphere
mesosphere
properties?
connections?
is the mantle solid everywhere?
MANTLE GEOTHERM
MANTLE GEOTHERM
compare continental,
oceanic & ridge
MANTLE GEOTHERM
compare continental,
oceanic & ridge
typical continental
geotherm = 25 °C/km
MANTLE GEOTHERM
compare continental,
oceanic & ridge
typical continental
geotherm = 25 °C/km
T @ 100 km = 1000 °C
(enough to melt rocks!)
MANTLE GEOTHERM
compare continental,
oceanic & ridge
typical continental
geotherm = 25 °C/km
T @ 100 km = 1000 °C
(enough to melt rocks!)
are they molten? P too
high? where?
CAN MELTING OCCUR?
compare geotherm to
petrologic solidus for mantle
rocks (peridotite)
if “dry” conditions, no melting
possible (geotherm below
solidus)
solid lherzolite is stable at
T above geotherm
CAN MELTING OCCUR?
under “wet” conditions (with
H2O or CO2), solidus shifts to
lower T
melting can occur where T >
solidus
low seismic velocities indicate
partial melting between
100-250 km (the LVZ)
the LVZ marks the base of
“plates” formed by rigid
lithosphere
CAN MELTING OCCUR?
under “wet” conditions (with
H2O or CO2), solidus shifts to
lower T
melting can occur where T >
solidus
low seismic velocities indicate
partial melting between
100-250 km (the LVZ)
the LVZ marks the base of
“plates” formed by rigid
lithosphere
LITHOSPHERE
LITHOSPHERE
LITHOSPHERE
lithosphere includes crust + upper mantle
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
largely solid material (silicates)
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
largely solid material (silicates)
lowest densities (2.7-3.0 g/cm3)
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
largely solid material (silicates)
lowest densities (2.7-3.0 g/cm3)
slowest seismic velocities (6-8 km/sec)
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
largely solid material (silicates)
lowest densities (2.7-3.0 g/cm3)
slowest seismic velocities (6-8 km/sec)
internal boundary is the Moho (density boundary)
LITHOSPHERE
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
largely solid material (silicates)
lowest densities (2.7-3.0 g/cm3)
slowest seismic velocities (6-8 km/sec)
internal boundary is the Moho (density boundary)
base of lithosphere is the low-velocity zone (LVZ)
LITHOSPHERE
lithosphere = plate
lithosphere includes crust + upper mantle
can be oceanic, continental, or both
typical lithosphere is 100 km
(70-125 km)
largely solid material (silicates)
lowest densities (2.7-3.0 g/cm3)
slowest seismic velocities (6-8 km/sec)
internal boundary is the Moho (density boundary)
base of lithosphere is the low-velocity zone (LVZ)
EgyPT
Physical conditions of Earth necessary to understand petrologic process:
1. pressure
2. temperature
3. energy & heat
PRESSURE GRADIENT
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE GRADIENT
P = ρgh
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE GRADIENT
P = ρgh
P increases with depth
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE GRADIENT
P = ρgh
P increases with depth
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE GRADIENT
P = ρgh
P increases with depth
Mantle: nearly linear through mantle
~ 30 MPa/km
≈ 1 GPa at base of avg crust
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE GRADIENT
P = ρgh
P increases with depth
Mantle: nearly linear through mantle
~ 30 MPa/km
≈ 1 GPa at base of avg crust
slope (ΔP/Δz) depends on density
(composition & compressibility) of material
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE GRADIENT
H
IG
H
Y
IT
S
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
N
slope (ΔP/Δz) depends on density
(composition & compressibility) of material
DE
~ 30 MPa/km
≈ 1 GPa at base of avg crust
Y
SIT
Mantle: nearly linear through mantle
DEN
P increases with depth
LOW
P = ρgh
PRESSURE GRADIENT
P = ρgh
P increases with depth
Core: ρ increases more rapidly since alloy
is more dense
smaller increase in P with depth suggests
inner core is more uniform, solid, and has
decreasing compressibility
Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25,
297-356. © Elsevier Science.
PRESSURE IN THE CRUST
h
ρgh
PRESSURE IN THE CRUST
in the crust, rocks “feel” a lithostatic
pressure
like a submarine feels hydrostatic
pressure on its hull
implies equal pressure in all directions
when materials can flow
h
ρgh
PRESSURE IN THE CRUST
in the crust, rocks “feel” a lithostatic
pressure
like a submarine feels hydrostatic
pressure on its hull
implies equal pressure in all directions
when materials can flow
h
for shallow rocks, can have differential
pressure (where horizontal stress ≠
vertical stress), causing rocks to deform
ρgh
PRESSURE IN THE CRUST
in the crust, rocks “feel” a lithostatic
pressure
like a submarine feels hydrostatic
pressure on its hull
implies equal pressure in all directions
when materials can flow
h
for shallow rocks, can have differential
pressure (where horizontal stress ≠
vertical stress), causing rocks to deform
ρgh
PRESSURE IN THE CRUST
in the crust, rocks “feel” a lithostatic
pressure
like a submarine feels hydrostatic
pressure on its hull
implies equal pressure in all directions
when materials can flow
h
for shallow rocks, can have differential
pressure (where horizontal stress ≠
vertical stress), causing rocks to deform
based on normal crustal densities,
1 kbar = 3.3 km
ρgh
ENERGY
ENERGY
Energy is the capacity to do work (subatomic, to mountain, to mantle scale)
ENERGY
Energy is the capacity to do work (subatomic, to mountain, to mantle scale)
1. kinetic energy: EK = 1/2mv2
•
motion of a body
ENERGY
Energy is the capacity to do work (subatomic, to mountain, to mantle scale)
1. kinetic energy: EK = 1/2mv2
•
motion of a body
2. potential energy: EP = mgz
•
energy of position; can be converted to Ek
ENERGY
Energy is the capacity to do work (subatomic, to mountain, to mantle scale)
1. kinetic energy: EK = 1/2mv2
•
motion of a body
2. potential energy: EP = mgz
•
energy of position; can be converted to Ek
3. thermal energy: ET = EK + EP
•
motions & attractions in a body (subatomic and larger)
•
ET ≠ heat (transferred energy)
HEAT SOURCES IN THE EARTH
HEAT SOURCES IN THE EARTH
1. Heat from the early accretion and differentiation of the Earth
•
“original heat” of early core separation (PV work of compression)
•
still slowly reaching surface as geotherm decays
HEAT SOURCES IN THE EARTH
1. Heat from the early accretion and differentiation of the Earth
•
“original heat” of early core separation (PV work of compression)
•
still slowly reaching surface as geotherm decays
2. Heat released by the radioactive breakdown of unstable nuclides
•
heat production (A) from decay of U, Th & K
•
mostly in crustal rocks
HEAT SOURCES IN THE EARTH
1. Heat from the early accretion and differentiation of the Earth
•
“original heat” of early core separation (PV work of compression)
•
still slowly reaching surface as geotherm decays
2. Heat released by the radioactive breakdown of unstable nuclides
•
heat production (A) from decay of U, Th & K
•
mostly in crustal rocks
3. Latent heat associated with outer core crystallization
•
continues today!
HEAT PRODUCTION
Rock
Abundance of radioactive element
Heat
produced
(joules/kg/yr)
U
Th
K
A
Granite
4
13
4
0.03
Basalt
0.5
2
1.5
0.005
Peridotite
0.02
0.06
0.02
0.0001
from Decker & Decker (1981)
HEAT PRODUCTION
Rock
Abundance of radioactive element
Heat
produced
(joules/kg/yr)
U
Th
K
A
Granite
4
13
4
0.03
Basalt
0.5
2
1.5
0.005
0.02
0.06
0.02
0.0001
If more heat-producing elements in
continental crust, why are T’s lower??
Peridotite
from Decker & Decker (1981)
HEAT PRODUCTION
Crustal T’s are lower because of:
1. less of it compared to mantle
2. continental crust is a good insulator
3. it’s thicker
4. it suffers from surface cooling
HEAT TRANSFER
1. radiation
•
conversion of IR energy from hot body; travels as a wave
•
efficient in a vacuum or transparent material; not efficient in rocks!
HEAT TRANSFER
2. conduction
•
transfer of EK by vibration & contact, one molecule to another
•
does not occur in a vacuum
•
greatest transfer with greatest ΔT (thermal gradient)
•
conduction increases with increasing surface area
•
depends on thermal conductivity (k) of material, given by:
q = kΔT/Δz
HEAT TRANSFER
3. convection
•
movement of material with contrasting T, which changes density
•
gravity acts on Δρ, in which less dense material (ie, hotter) rises
•
movement of solid can occur in viscous mantle rocks, including rise
of plumes
HEAT TRANSFER
4. advection
•
heat “carried” by flowing liquids or viscous bodies (e.g., water,
magma) to cooler surroundings
LAVA FLOW
MAGMA
WHAT FORMS OF HEAT TRANSFER?
GEOTHERMAL GRADIENT
Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower
limits based on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.
GEOTHERMAL GRADIENT
ΔT/Δz is the slope of T variation
with depth
Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower
limits based on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.
GEOTHERMAL GRADIENT
ΔT/Δz is the slope of T variation
with depth
gradient drives conductive cooling
toward the surface
Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower
limits based on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.
GEOTHERMAL GRADIENT
ΔT/Δz is the slope of T variation
with depth
gradient drives conductive cooling
toward the surface
why steeper curve at depth?
Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower
limits based on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.
GEOTHERMAL GRADIENT
ΔT/Δz is the slope of T variation
with depth
gradient drives conductive cooling
toward the surface
why steeper curve at depth?
more heat production in crust
Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower
limits based on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.
GEOTHERMAL GRADIENT
ΔT/Δz is the slope of T variation
with depth
gradient drives conductive cooling
toward the surface
why steeper curve at depth?
more heat production in crust
more efficient convective
mixing of heat in the mantle
Figure 1-9. Estimated ranges of oceanic and continental steadystate geotherms to a depth of 100 km using upper and lower
limits based on heat flows measured near the surface. After
Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.
IGNEOUS TECTONIC SETTINGS
1. mid-ocean ridge
5. back-arc basin
2. continental rift
6. oceanic hotspot
3. oceanic island arc
7. continental hotspot
4. continental-margin arc
IGNEOUS TECTONIC SETTINGS
1. mid-ocean ridge
5. back-arc basin
2. continental rift
6. oceanic hotspot
3. oceanic island arc
7. continental hotspot
4. continental-margin arc
WHAT’S MELTING? HOW? WHERE DOES IT GO?
IGNEOUS ROCKS
next week we’ll begin igneous rocks!