what is a plume? by julian winter alexandra witze (2003)
TRANSCRIPT
What is a plume?By Julian Winter
Alexandra Witze (2003)
IntroductionAims• Primarily to confuse you; see
conclusion
• Briefly look at modeling
• Understand their characteristics & evolution
• Conclusion; confused?
Birth of Plumes -Morgan 1971
• Intra plate volcanism – failure of plate tectonics
• Fixed upward rise of hot, buoyant mantle
• Comes from the deep mantle
• Downward flow dispersed uniformly
• Column shape inferred from swell
Radiating Dykes
• Centrally located source• Outward injection of
magma• Plume provides point
source• Found on Venus – no
tectonics here• But not all intraplate
volcanism has such dykes!
Richard E. Ernst 2004
Plume Modelling- Whitehead & Luther 1975
• Liquids heated from below - TBL
• TBL less dense & less viscous
• Head and tail structure & entrainment
Griffiths & Campbell 1990
Plumes Refined: Flood basalts - Campbell & Griffiths 1990
• A plumes head can:-– Produce 500m-1000m uplift but later subsidence – Spread > 2000-2500km – Melt – Flood basalts– Evolution to plume tail melts
• But wait, flood basalts not found at all hotspots e.g. Hawaii!!!
Geochemistry
• Typically have enrichment in incompatible elements
• Higher concentrations of He3 (high RA)
• Typically HIMU, EM-1 & 2 & FOZO
• Isotopic ratio distinguished from DM
Angelo Peccerillo
Subduction derived plumes 1.
• Suducted slabs drive convection
• Slabs reheated in lower mantle; bouyant
• Accounts for geochemistry
Subduction derived plumes 2.
• Slab sinks to a 1600km deep TBL
• Slab creates high spot Plume
• Interface of TBL irregular
• Depth of plume can therefore be irregular thus plume can be both deep & shallow?
Subduction derived plumes 2.
Kellogg et al 1999
Supersrwells e.g. Polynesia
• Anomalously shallow seafloor several 1000km in extent
• Unusually dense concentrations of hotspots
• SUPERPLUMES
• Doming of Superplume Plumes
Superswells
Davaille (1999)
Plumes: a summary
• Plumes from CMB
• Shallower origins & subduction driven
• Superswells & Superplumes
• ‘Top down’ models & shallow plumes– Function of plate related stresses– Shallow mantle upwelling
Conclusion
Jules’ criteria for plume recognition:• LIP but no worries if not.• Monotic age progression; if it suits you.• A DEEP source but a shallow source will do.• A superswell e.g. Polynesia & Africa- they’re
just showing off.• Low seismic velocity? not if you don’t want.• Dare I say ‘radial dykes’?
So a plume is…….?
Morgan 1971
Griffiths & Campbell 1990
Kellogg 1999
Ivanov 2004 Daville (1999)
Anderson, Foulger 2004
Questions?
Condie 2003
The plate tectonic paradigm
• Intra plate volcanism – failure of plate tectonics
• Hotspots– Linear tracks – age progression– Fixed position
• Why a hot mantle? Unrealistic!