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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
EARTH INTERIOR
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Structure of Earth:
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Structure of Earth:
chemical divisions
core, mantle & crust
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Structure of Earth:
chemical divisions
core, mantle & crust
mechanical divisions
mesosphere, asthenosphere & lithosphere
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Core:
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Core:
Fe-Ni metallic alloy
outer core is liquid (no S-waves)
inner core is solid
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Core:
Fe-Ni metallic alloy
outer core is liquid (no S-waves)
inner core is solid
differentiation at work!
compositional separation within the planet (fractionation)
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Mantle:
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Mantle:
peridotite (ultramafic)
greatest V, m & E (moves & carries heat)
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Mantle:
peridotite (ultramafic)
greatest V, m & E (moves & carries heat)
upper layer to 410 km (olivine to spinel)
contains low velocity layer 60-220 km
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Mantle:
peridotite (ultramafic)
greatest V, m & E (moves & carries heat)
upper layer to 410 km (olivine to spinel)
contains low velocity layer 60-220 km
transition zone between 410-660 km (spinel to perovskite)
SiIV to SiVI
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Mantle:
peridotite (ultramafic)
greatest V, m & E (moves & carries heat)
upper layer to 410 km (olivine to spinel)
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
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Crust:
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Crust:
mafic (magnesium + ferric)to felsic (feldspar + silica)
rich in Si, Al, K, Na, Ca
Si-r
ich
Fe-r
ich
EARTH INTERIOR
Crust:
mafic (magnesium + ferric)to felsic (feldspar + silica)
rich in Si, Al, K, Na, Ca
two main types:
oceanic
continental
+ “transitional”
Si-r
ich
Fe-r
ich
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
mafic rocks
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)
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
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
CHEMICAL DIVISIONS
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
Velocity boundaries
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
warmer? liquid?
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
warmer? liquid?
source of CMB?
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
warmer? liquid?
source of CMB?
change in composition
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
warmer? liquid?
source of CMB?
change in composition
source of OC-IC?
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
warmer? liquid?
source of CMB?
change in composition
source of OC-IC?
phase change (S to L)
composition property
LVZ
CMB
OC-IC
MECHANICAL DIVISIONS
Velocity boundaries
source of LVZ?
warmer? liquid?
source of CMB?
change in composition
source of OC-IC?
phase change (S to L)
composition property
LVZ
CMB
OC-IC
LET’S LOOK IN MORE DETAIL
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 Depth Density
olivine tetrahedral low
spinel dense tetrahedral
perovskite octahedral high
~410 km
~660 km
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
HI
LO
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
HI
LO
HI
LO
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
MG-SILICATES
HI
LO
HI
LO
VARIATION IN SEISMIC VELOCITY, DENSITY & MINERAL STRUCTURE
MG-SILICATES
HI
LO
HI
LO
ASTHENOSPH.
MESOSPHERE
T.Z.
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?
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
CAN MELTING OCCUR?
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 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 = plate
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
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.
LO
W D
EN
SIT
Y
HIG
H DEN
SITY
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 hullimplies 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 hullimplies equal pressure in all directions when materials can flow
for shallow rocks, can have differential pressure (where horizontal stress ≠ vertical stress), causing rocks to deform
h
ρgh
PRESSURE IN THE CRUST
in the crust, rocks “feel” a lithostatic pressure
like a submarine feels hydrostatic pressure on its hullimplies equal pressure in all directions when materials can flow
for shallow rocks, can have differential pressure (where horizontal stress ≠ vertical stress), causing rocks to deform
h
ρgh
PRESSURE IN THE CRUST
in the crust, rocks “feel” a lithostatic pressure
like a submarine feels hydrostatic pressure on its hullimplies equal pressure in all directions when materials can flow
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
h
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 elementHeat
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 elementHeat
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)
If more heat-producing elements in continental crust, why are T’s lower??
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
MAGMA
LAVA FLOW
WHAT FORMS OF HEAT TRANSFER?
GEOTHERMAL GRADIENT
Figure 1-9. 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. 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 steady-state 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 steady-state 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 steady-state 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 steady-state 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.
more heat production in crust
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 steady-state 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.
more heat production in crust
more efficient convective mixing of heat in the mantle
IGNEOUS TECTONIC SETTINGS
1. mid-ocean ridge
2. continental rift
3. oceanic island arc
4. continental-margin arc
5. back-arc basin
6. oceanic hotspot
7. continental hotspot
IGNEOUS TECTONIC SETTINGS
1. mid-ocean ridge
2. continental rift
3. oceanic island arc
4. continental-margin arc
5. back-arc basin
6. oceanic hotspot
7. continental hotspot
WHAT’S MELTING? HOW? WHERE DOES IT GO?
IGNEOUS ROCKS
next week we’ll begin igneous rocks!