Geochemistry%20and%20Mantle%20Plumes

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Geochemistry and Mantle Plumes

• Chris Hawkesworth
• University of Bristol

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Intraplate Basalts

• Mantle components (origins)
• Reservoirs in the mantle (spatial)
• Tracers of mantle convection (dynamics)
• Melt generation and differentiation

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Geochemistry and Mantle Plumes

• Physical anomaly
• Volume anomaly (rates)
• Intraplate geochemistry
• Elevated temperatures and/or source composition
• Depths of origin

Not on its own evidence for plumes
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Contrast Auckland and Hawaii
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Eruptive Volumes
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Depths of chemical variations in the mantle

• Mineral stability
• Core contributions
• 3/4He and deep mantle
• Young, and therefore shallow
• Buoyancy flux?

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Cape Verdes
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Buoyancy flux
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Melt Generation

• Degrees of melting melt volumes
• Rates of melting- U series isotopes
• Buoyancy flux

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buoyancy flux k(upwelling velcocity)2
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Continental Flood Basalts

• 150-200km thick continental lithosphere
• Delaminate and/or erode
• Melt the lithosphere until lithospheric thinning
  allows melting of the plume
• Melt more fertile material - ?eclogite

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Summary

• Improved melt generation models
• Buoyancy flux
• Dipping reflectors
• Continental Flood Basalts

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Towards a definition of plumes

• Narrow column of buoyant material
• Linked to a thermal boundary layer (but suggest
  we leave that general)
• elevated temperatures?
• Appears difficult to model the Earth without
  having plumes, but only a few!
• Important that any definition is amenable to
  observations from different subject areas

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