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The Role of the Core in Mantle Plumes

The Role of the Core in Mantle Plumes. Graham Smith University of Durham Dept. of Earth Sciences. How is the Core Involved?. Source of. HEAT. Origin of plumes at the Core- Mantle Boundary (CMB)?. from Ritsema et al. 1999. Why a CMB Origin?. Large Igneous Provinces.

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The Role of the Core in Mantle Plumes

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  1. The Role of the Core in Mantle Plumes Graham Smith University of Durham Dept. of Earth Sciences

  2. How is the Core Involved? Source of HEAT Origin of plumes at the Core- Mantle Boundary (CMB)? from Ritsema et al. 1999.

  3. Why a CMB Origin? Large Igneous Provinces Earth’s Geodynamo Earth’s Heat Budget “Superplume” events correlate well with patterns of magnetic reversal Size of some large igneous provinces requires an origin in the lower mantle or the CMB Mechanism of heat removal from the CMB area 50-75% increase in rate of crustal production CRETACEOUS SUPERCHRON Modified from Condie (2003) www.creaso.com

  4. OSMIUM Outer core enriched in Os by 300x mantle values High 187Os/188Os and 186Os/188Os “Plume-related” basalts carry this signal Addition of ≤1wt.% outer core material BUT, High Os ratios can also be generated in the crust

  5. Why Not the Upper Mantle? PUM = Primitive Upper Mantle From Brandon et al. 1999.

  6. OSMIUM CRUSTAL CONTAMINATION e.g. Koolau lavas, Hawaii High 187Os/188Os Low 186Os/188Os High d18O High Sr Low Nd

  7. HELIUM Core enriched in primordial He during accretion High 3He/4He ratios Modified from van Keken et al. (2002) MORB = 8±1 Ra

  8. FOZO: A common theme OIBs comprise a variety of different isotopic endmembers Geochemical signatures all point to a common component Material rising from the CMB incorporates deep mantle material FOZO But, FOZO is poor in Os

  9. Ultra-Low Velocity Zones

  10. Implications Osmium systematics suggest incorporation of outer core material at CMB Presence of recycled ancient crust suggests that slabs sink to CMB Primordial 3He points strongly to a CMB origin for plumes Less degassed lower mantle separated from degassed upper mantle points to a double-layer mantle system. Courtesy of University of Hawaii, Institute for Astronomy

  11. References Rost & Revenaugh (2001). Science 294 1911-14. Schubert et al. (2001). Mantle Convection in the Earth & Planets. Tschauner et al. (1999). Nature 398 604-7. Van Keken et al. (2002). Annu. Rev. Earth Planet. Sci. 30 493-525 Walker et al. (1995). Science 269819-22. Widom & Shirey (1996). Earth & Planetary Science Letters142 451-65. Brandon et al. (1998). Nature280 1570-73. Brandon et al. (1999). Earth & Planetary Science Letters 174 25-42. Campbell & Griffiths(1992). J.Geol. 92 497-523. Condie. (2003) Plate Tectonics and Crustal Evolution, 4th ed.. Butterworth-Heinemann. Dubrovinsky et al. (2001). Nature 412 527-29. Gurnis et al. (1998). The Core-Mantle Boundary Region. AGU Geodynamics Series 28. Jacobs (1993). Deep Interior of the Earth. Chapman & Hall. Jephcoat (1998). Nature 393 355-58. Knittle & Jeanloz (1991). Science 251 1438-43. Larson (1991). Geology 19 547-50. Li & Agee (1996). Nature 381 686-89. Macpherson et al. (2000). Earth & Planetary Science Letters 176 171-83. Marty et al. (1996). Earth & Planetary Science Letters 144223-37. McElhinny (1979). The Earth: Its Origin, Structure & Evolution. Peltier (1989). Fluid Mechanics of Astrophysics & Geophysics 4.

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