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What is a plume? By Julian Winter

What is a plume? By Julian Winter. Alexandra Witze (2003). Introduction. Aims Primarily to confuse you; see conclusion Briefly look at modeling Understand their characteristics & evolution Conclusion; confused?. Birth of Plumes - Morgan 1971.

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What is a plume? By Julian Winter

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  1. What is a plume?By Julian Winter Alexandra Witze (2003)

  2. Introduction Aims • Primarily to confuse you; see conclusion • Briefly look at modeling • Understand their characteristics & evolution • Conclusion; confused?

  3. Birth of Plumes -Morgan 1971 • Intra plate volcanism – failure of plate tectonics • Fixedupward rise of hot, buoyant mantle • Comes from the deep mantle • Downward flow dispersed uniformly • Column shape inferred from swell

  4. 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

  5. Plume Modelling- Whitehead & Luther 1975 • Liquids heated from below - TBL • TBL less dense & less viscous • Head and tail structure & entrainment Griffiths & Campbell 1990

  6. 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!!!

  7. Geochemistry • Typically have enrichment in incompatible elements • Higher concentrations of He3 (high RA) • Typically HIMU, EM-1 & 2 & FOZO • Isotopic ratio distinguished from DM

  8. Angelo Peccerillo

  9. Subduction derived plumes 1. • Suducted slabs drive convection • Slabs reheated in lower mantle; bouyant • Accounts for geochemistry

  10. 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?

  11. Subduction derived plumes 2. Kellogg et al 1999

  12. Supersrwells e.g. Polynesia • Anomalously shallow seafloor several 1000km in extent • Unusually dense concentrations of hotspots • SUPERPLUMES • Doming of Superplume  Plumes

  13. Davaille (1999) Superswells

  14. 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

  15. 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’?

  16. Morgan 1971 Griffiths & Campbell 1990 Kellogg 1999 Ivanov 2004 Daville (1999) Anderson, Foulger 2004 So a plume is…….?

  17. Questions?

  18. Condie 2003

  19. The plate tectonic paradigm • Intra plate volcanism – failure of plate tectonics • Hotspots • Linear tracks • age progression • Fixed position • Why a hot mantle? Unrealistic!

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