Download Mantle - Geology Rocks

Earth Structure
Earth Structure
CONTINENTAL CRUST
OCEANIC CRUST
Continental crust -“Granitic”
CRUST
CRUST
MANTLE
Mohorovivic Discontinuity
(Moho)
MANTLE
Oceanic crust - “Basaltic”
Peridotite (olivine & augite)
Gutenberg Discontinuity
CORE
CORE
Iron & Nickel
This is a compositional layering of the Earth i.e. by what material the
layers are made of.
Earth Structure
solid (cool, brittle & rocky)
CRUST
LITHOSPHERE
partially molten (only 1-5% molten)
ASTHENOSPHERE
MANTLE
CORE
MESOSPHERE
OUTER
CORE
INNER
CORE
solid (solid-state convection)
liquid
solid
This is a mechanical layering of the Earth i.e. by what properties the layers
have.
Earth Structure
Crust
Mantle
Core
Compositional
Earth Structure
Crust
Seismic wave velocities
Lithosphere
Asthenosphere
Mantle
Core
Compositional
6km/s
Continental crust
7km/s
8km/s
7.8km/s
Oceanic crust
Upper mantle
Upper mantle
Mesosphere
13km/s
Outer Core
8km/s
Outer core
Inner Core
11km/s
Inner core
Mechanical
Mantle
Continental crust
Lithosphere
2.7
Granitic
>65%
Oceanic crust
(solid/brittle)
3.0
Basaltic
45-52%
(weak / 150km
Asthenosphere ductile)
250km
3.3
Mesosphere
Mantle
(solid)
5.5
Peridotite
<45%
[solid-state
convection due to
high pressures &
temperatures over
long periods of time]
2,900km
Outer core
Core
8.0
10
(liquid)
Metallic
0%
(Fe , Ni , S)
5,100km
Inner core
(solid)
14
6,300km
Metallic
(Fe & Ni)
0%
Mid-oceanic ridge
Lithosphere
Continental
crust
MOHO
Granitic
Basaltic
Peridotite
Asthenosphere
Upper
mantle
Oceanic crust
Temperature Variation within Earth’s Interior
Depth (km)
Geotherm (°C)
Melting point of Peridotite (°C)
0
50
200
500
1000
2000
3000
4000
5000
6000
15
1250
1450
1900
2500
3250
4000
4250
4250
4250
1200
1350
1600
2100
3000
3600
3850
4050
4200
4500
1.
2.
3.
4.
5.
6.
Plot the data onto
graph paper, with
depth on the vertical
axis.
Describe how the
geotherm varies with
depth.
Define the geotherm.
Locate the Earth’s
internal layers on the
graph.
Describe the physical
state of the Earth’s
interior in relation to
the melting point curve.
Calculate the average
geothermal gradient
for the first 50km into
the Earth.
Temperature Variation within Earth’s Interior
Temperature (°C)
Asthenosphere
(semi-solid)
Depth
(km)
Mesosphere
(solid)
Outer Core
(liquid)
Inner Core
(solid)
Temperature Variation within Earth’s Interior
Temperature (°C)
Lithosphere
(solid)
Asthenosphere
(semi-solid)
Geotherm
Depth
(km)
Melting curve
Mesosphere
(solid)
Outer Core
(liquid)
Where does this heat
come from?
• Radiogenic heat
Inner Core
(solid)
• Primordial heat
Age
Oceanic
Continental
<200 million years
<4000 million
years
35km (rift valleys) –
70km (mountains)
Thickness
6-10km
Density
3.0g/cm3
2.6 – 2.7g/cm3
Composition
Basaltic
Granitic
Structure
Sediments, Pillow lavas,
Sheeted dykes, Gabbro
Upper crust, lower crust
Formation
Sea-floor spreading
Subduction
Continental collision
Evidence for Earth Structure
• Seismic Waves
• Density of Earth
• Earth’s Magnetic Field
• Meteorites
Seismic Waves
1. Surface Waves
i). L-Waves (long waves)
2. Body Waves
i). P-Waves (push waves)
•
travel through liquids & solids
•
fastest waves (4 – 7km/s)
ii). S-waves (shake waves)
•
travel through solids only
•
slower than P-waves (2 - 5km/s)
both travel faster as material gets
more rigid & less compressible
Seismic Waves Velocity
3
2
4
Inner Core
Mesosphere
Outer Core
5
1
Lithosphere
Asthenosphere
7
6
Mid-oceanic ridge
Lithosphere
Continental
crust
MOHO
Granitic
Basaltic
Peridotite
Asthenosphere
Upper
mantle
Oceanic crust
Continental crust
Lithosphere
6
2.7
Granitic
>65%
Oceanic crust
(solid/brittle)
7
8
3.0
Basaltic
45-52%
(weak / 150km
Asthenosphere ductile)
250km
7.8
3.3
Mesosphere
Mantle
(solid)
5.5
[solid-state
convection due to
high pressures &
temperatures over
long periods of time]
<45%
13
8.0
2,900km
Outer core
Core
Peridotite
8
10
(liquid)
Metallic
0%
(Fe , Ni , S)
5,100km
Inner core
(solid)
11
6,300km
14
Metallic
(Fe & Ni)
0%
Seismic Waves Refraction
Seismograph
Station 2
•Direct
•Reflected
•Refracted
Focus
Boundary between
layer 1 & 2
(Moho)
Epicentre
Seismograph
Station
Layer 1
(Crust)
Layer 2
(Mantle)
h = depth
Хd = distance from epicentre where all seismic waves arrive at same time
V1 = velocity of P waves in layer 1
V2 = velocity of P waves in layer 2
Suppose the shadow zone for P waves was located
between 120 and 160º rather than 103 and 142º.
What would this indicate about the size of the
core?
Why is there a S-wave shadow zone?
There is a S-wave shadow zone from where the Swaves cannot reach the other side of the Earth as
they are stopped by the liquid outer core. Liquids
cannot transmit shear waves due to the weak
bonding between particles.
Meteorites
Meteorites
Stony Meteorites
Iron Meteorites
Density
Earth’s Magnetic Field