Download Remote Sensing of the Earth`s Interior

Remote Sensing of the Earth’s Interior
• Earth’s interior is largely inaccessible
Origin and Layering of the Earth: Geochemical Perspectives
• Composition of Earth cannot be understood in isolation
– Sun and meteorites are closely linked
• Solar system formed in Milky Way galaxy @ Big Bang 15 Ma
– Nucleosynthesis in stars, H+He ejected > rotating gas/dust cloud
– Material in compressed disk heats, volatilizes, cools
• Most refractory dust particles cooled first
– Accretion in several stages:
• Planetesimals 10 m to 1000 km diameter form (10 kyr time scale)
• Planetesimals gow by collisions/intersecting orbits (106 yr scale)
• Planetary “embryos” form (108 yr time scale)
– Embryos collided to form planets
– Earth-Moon system may reflect such a collision
– Sun’s composition gives best estimate for that of Solar Nebula
• Mainly H + He
• Relative abundances of other elements nearly identical to meteorites
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Remote Sensing of the Earth’s Interior
• Geophysics:
– Tools
• seismic waves (velocity, tomography)
• gravity
• heat flow/temperature distribution
• magnetic field past and present
• satellite (GPS) geodesy
– Inferences
• gross composition of crust, mantle, core
• boundaries of property-specific regions
• scale of convection/tectonics
• structure & dynamics of mantle & crust
Remote Sensing of the Earth’s Interior
• Geochemistry
– Tools:
• Major, trace & volatile element distribution
– melts vs. residua
• Mineralogy
• Experimental petrology
• “Memory” of past events in radioisotopic systems
– Inferences:
• composition of crust, mantle, core
• mechanisms and depth of mantle melting
• quantitative history from radioisotopic dating
• signatures of tectonic processes present and past
• structure & dynamics of mantle & crust
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Earth’s Internal Structure
• Established using seismic reflection, refraction
• Crust
– Continental
• Less dense
• 20-70 km thick
– Oceanic
• more dense
• 5-10 km thick
• Mohorovicic discontinuity
– Boundary separating crust from mantle
– defined by increase in P-wave velocity (to 8 km/sec)
Earth’s Internal Structure
• The Mantle
– Ultramafic Rock
– Lithosphere
• Crust & uppermost mantle
– Asthenosphere
• Low velocity zone
• lubrication for plate tectonics
– Lower mantle
• boundaries at 400 & 670 km
• Pressure increases with depth
• more dense mineral structures
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Plate Tectonics Paradigm
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Consequence of heat loss
Convection transfers heat effectively
Mantle flows on geologic timescales
Lithospheric plates meet along 3 boundaries
– Divergent
– Convergent
– Transform
• Melting, volcanism coincide with plate boundaries
– Exception: “Hot spot” or intraplate magmatism
• Plate tectonics influences magma generation
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From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
Plate Tectonics Paradigm
• Plate tectonics influences magma generation
– Decompression melting
• active upwelling of buoyant mantle plumes
• passive upwelling associated with removal of lithospheric lid at
divergent boundary (MOR)
– Hydrous (fluxed) melting
• subduction zones
– Relative volumes
– Chemical & isotopic “fingerprinting” of lavas
• provides information about mantle that has melted
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From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
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Mid-Ocean Ridge System
8 km
From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
Subduction Zones
From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
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Subduction Zones: Seismic
Tomographic Image
From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
Plume magmatism
Fate of subducted slabs
From: Perfit and Davidson (2000) in Encyclopedia of Volcanoes, H. Sigurdsson, ed.
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•Magma erupted at
•mid-ocean ridges (MORB)
•plumes (OIB)
•subduction zones (IAB)
•Sample mantle from which they come
•Chemical “fingerprinting”
•Trace elements
•Isotopes
•Clues to origin & history of mantle
From: Perfit and Davidson (2000)
in Encyclopedia of Volcanoes, H.
Sigurdsson, ed.
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