Presentation on theme: "Do Plumes Exist? Gillian R. Foulger Durham University GEOL 4061 Frontiers of Earth Science."— Presentation transcript:
Do Plumes Exist? Gillian R. Foulger Durham University GEOL 4061 Frontiers of Earth Science
What is a plume? A plume is a bottom-heated convective upwelling that rises through its own thermal buoyancy. Plumes almost certainly must rise from a “thermal boundary layer”, i.e., from material that lies just above a hot body.
1971: Plumes were invented to explain: Morgan (1971) excess volcanism “hot spots” fixed relative to one-another linear island chains
Later the “plume-head, plume-tail” model developed Griffiths & Campbell (1990): Plumes created by injecting syrup/water mix (to be less dense) into the tank.
Problems There is little evidence that “hot spots” are hot Some have very small melt volumes They are not fixed relative to one-another Many chains not time-progressive Seismology does not reliably detect them in the lower mantle
An unfalsifiable hypothesis However, study of melting anomaly origins has not progressed because of “plume belief”
Are “hot spots” hot? What does “hot” mean? 200 - 300 K is the minimum required for a plume How hot are “hot spots”?
Current problems Origin of excess melt –source consistent with geochemistry –energy budget to melt large volumes: must either accumulate melt over long period of time and retain in the mantle, or melt very rapidly - a melt-as-erupted basis Hawaii
Student seminars 1. What is a plume? 2. Are plumes predicted by realistic convection experiments and numerical simulations? 3. What is the origin of ocean island basalt (OIB)? 4. Are the predictions of the plume hypothesis borne out by observation? 1. Temperature 5. Are the predictions of the plume hypothesis borne out by observation? 2. Uplift 6. What is the origin of high 3He/4He? 7. Have plumes been detected seismologically? 8. What alternatives are there to the plume hypothesis? 9. Can the plume hypothesis be tested, and if so how? 10. How can the Plate Tectonic Processes theory be tested?