geol 4700 multi-anvil pressruby.colorado.edu/~smyth/g4700/interior.pdf · • cosmochemistry:...
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GEOL 4700 ‘Field’ Mineralogy
Earth’s Interior
http://ruby.colorado.edu/~smyth/G4700.html
GEOL 4700 ‘Field’ Mineralogy
Earth’s Interior
http://ruby.colorado.edu/~smyth/G4700.html
Earth’sInterior
Multi-anvil Press
5000 ton
(Bayerisches Geoinstitut)
Earth’sInterior
The Core is MetalThe Mantle is oxygen minerals
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There could be significant hydration in the Transition Zone
How do we know what is inside the Earth?
• Seismology: Earthquake waves
• Cosmochemistry: Meteorites
• Experiments: Laboratory synthesis
• Xenoliths
Review Mantle MineralogyMantle Mineralogy: Modal Fraction
Water Storage Capacity in Ocean Units
• Nominally Anhydrous Minerals (NAMs) can incorporate up to 10 times the total Ocean mass if saturated.
Major Parts• Ocean water 0.025% of mass• Crust (Above the Moho) 0.5% of mass
– Oceanic (7 to 10 km of basalt & gabbro)– Continental (30 to 60 km of granite)
• Mantle - Moho to 2900 km - Solid Rock– 65% of total mass– Upper (Moho to 410km) (Olivine + pyroxene)– Transition Zone (410 -670 km) (Silicate Spinels)– Lower 670 to 2900 km (Perovskite + periclase)
• Core (2900 to 6367km) 35% of mass– Outer Core (Liquid Metal)– Inner Core (Solid Metal)
Crust• Oceanic Crust (Basalt and Gabbro)
– Thin (7 - 10 km)– Dense (2.9 - 3.1 g/cm3)– Young (< 250 my)
• Continental Crust (Granite + Diorite + Seds)– Thick (30 - 60 km)– Light (2.7 - 2.8 g/cm3)– Old (250 - 4000 my)
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Mantle• Upper Mantle (Moho to 410 km)
– Peridotite (Olivine + pyroxene)– Eclogite (Pyroxene + Garnet)
• Transition Zone (410 - 670 km)– Spinels and Spinelloids
• Lower Mantle (670 - 2900 km)– MgSiO3 - Perovskite – MgO - Periclase
Core• Outer Core (2900 to 5150km)
– Molten iron metal (+ ~10% lighter element)
– No S-wave transmission• Inner Core (5150 - 6378 km)
– Solid Iron Metal– May slowly rotate relative to
mantle
How do we know what’s there?
• Seismology– S-wave shadow– P and S reflections and conversions
• Meteorites:– Earth formed from primitive meteorites
• Xenoliths from kimberlites & basalts• Experiments
Seismology• S-wave shadow
– No S-waves opposite-side earthquakes
– Core (outer) must be molten• P and S reflections
– Discontinuities at 410 and 670 km– Phase Changes
• P and S travel time anomalies– Tomography– Hot and cold regions
Ringwoodite
• Formula (Mg,Fe)2SiO4
• Up to 2.4 %H2O by weight
• Stable at depths of 525 to 660 km.
• Third most abundant mineral in Earth
Wadsleyite
• Formula (Mg,Fe)2SiO4
• Up to 3.2 %H2O by weight
• Stable at depths of 410 to 525 km.
• Fourth most abundant mineral in Earth
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SeismologyP-waves S-waves
Velocity Structure and Earthquakes at N. Tonga(VanderHilst, Nature (1995)Red = slow = hot green = fast = cold
Xenoliths• Xenoliths are ‘strange rocks’• Xenoliths are inclusions in
kimberlites and basalts• Xenoliths provide natural high
pressure rocks.– Kimberlites bring diamonds and other
rock samples from as deep as 670 km.– Basalts are derived from the lithospheric
mantle
Xenoliths
Xenoliths
Xenolith-Peridotite
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Breaking Xenoliths at a Diamond Mine in South Africa
Meteorites• Meteorites tell us of Earth’s bulk
composition– Chondrites are primitive meteorites– Earth is “chondritic” in composition.
• Composition is similar to sun minus H, He and other volatiles.
Meteorites
Meteorites
Experiments• Multi-Anvil Press
– Synthesis experiments to 1000 km depth– Samples 1-5 mm3
• Diamond Anvil Cell– Spectroscopy– Ultrasound– X-ray diffraction
Multi-anvil Press
5000 ton
(Bayerisches Geoinstitut)
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Multi-anvil Press Sample Assembly
Multi-anvil Press Sample Assembly
Carbide cubes retain a lot of strain
Experiments• Multi-Anvil Press
– Synthesis experiments to 1000 km depth– Samples 1-5 mm3
• Diamond Anvil Cell– Spectroscopy– Ultrasound– X-ray diffraction
Experiments• Multi-Anvil Press
– Synthesis experiments to 1000 km depth– Samples 1-5 mm3
• Diamond Anvil Cell– Spectroscopy– Ultrasound– X-ray diffraction
Multi-anvil Press Octahedral Assembly:
After and Before
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Multi-Anvil Press Octahedron
Diamond-anvil Cell
Interior Terms
Interior Terms
Interior Terms
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Interior Terms
Interior Terms
Interior Terms
DAC on Diffractometer
Mica Crystal with Quartz @ 5GPa
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410km:Olivine Wadsleyite
Density 3.2 3.5 g/cm3
410km:Olivine Wadsleyite
Wadsleyite
Olivine
525 kmWadsleyite Ringwoodite
Ringwoodite Crystal
Ringwoodite Crystal with Quartz
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660 kmRingwoodite Perovskite + MgO
Density 3.6 4.2 g/cm3
660 kmRingwoodite Perovskite + MgOTetrahedral Si Octahedral Si
Mantle Density vs Depth
3000
3200
3400
3600
3800
4000
4200
4400
4600
4800
0 200 400 600 800 1000 1200
Lower Mantle
Transition Zone
Upper Mantle
Convection in solid mantle
• Driven by U, Th, K decay (internal engine)
• Moves about 2 cm/yr• Causes earthquakes• Moves plates• Splits and rejoins continents• One Cell or two?
Convection in solid mantle
Magnetic Field• Due to electrical currents from
Earth’s dynamo.• Convection in liquid metal outer core.• Convection is coupled to Earth’s
rotation.• Field is subject to sporadic reversals.
– Last reversal was 30,000 years ago.• Field holds ozone layer (UV shield) in
place.
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Magnetic Field
Reversals