Transcript Geodynamics
Dynamics of Mantle Plumes • Methods for modeling basic thermal plumes (with and without tracers) • Plumes interacting with plates (and ridges) • Plumes in thermo-chemical convection • More elaborate proposals for plumes Dynamics of the mantle… Global scale: mantle contains both well-mixed regions and heterogeneity Fine scale heterogeneity Fine-scale variations in the (from Harpp and White, Galapagos 2001, G-cubed) Galapagos Islands Harpp and White, G-cubed 2001 Hawaiian emperor track (Steinberger et al. Nature 04) From Garnero, Annual Reviews of Earth & Planetary Sciences, 2000 Figure courtesy of E. Garnero, ASU Farnetani et al. 2002: Model 1: uniform mantle, low viscosity plume Farnetani et al. 2002: Model 3: viscosity jump in transition zone Thin dense layer at base Low viscosity in plume Farnetani et al: EPSL, 2002 Detail of mixing in plume: black tracers are from basal b.l. grey are from transition zone Courtesy of Shijie Zhong, U. Colorado (see: Entrainment of a dense layer by thermal plumes Zhong and Hager, Geophysical Journal International September 2003) Courtesy of Shijie Zhong, U. Colorado Double Diffusive Convection Model of D” B=1 Ra = 107 Earth’s surface Core-mantle boundary Color indicates Temperature N. Montague and L. Kellogg, JGR, 2000 time N. Montague and L. Kellogg, JGR, 2000 time horizontal distance N. Montague and L. Kellogg, JGR, 2000 A dense layer stabilizes the flow With a dense layer in D” No dense layer time More temperature-dependent viscosity B= 1 Kellogg and Montague, in preparation Hansen & Yuen Varying properties with depth allows layering Layered convection experiments by Anne Davaille, (Nature 402, 756, Dec. 1999) Davaille experiments + several numerical models (redrawn from Davaille, 1999; color points are numerical models from various sources) Courtillot, V., Davaille, A., Besse, J., Stock, J., Earth and Planetary Science Letters, 2003. Courtillot, V., Davaille, A., Besse, J., Stock, J., Earth and Planetary Science Letters, 2003. Olympus Mons (Mars)-Hawaii Comparison 0 km Hunt and Kellogg, 2000 Depth 670 km Mixing in 2-D with particles •Added at subduction zones •Removed at mid-ocean ridges 2900 km 1 10 100 Normalized viscosity Hunt & Kellogg, 2000 - effect of viscosity on mixing Constant viscosity viscosity 1 10 100 1 10 100 1 10 100 Pressure-dependent viscosity: smooth increase Transition zone viscosity: Jump at 670 km D. L. Hunt & L. H. Kellogg, 2000 Distribution of heterogeneities Heat budget of the Earth (all values given in terawatts) various sources Total global heat flow: 44 TW Total BSE Heat production: 20 TW + (from cosmochemistry) Continental crust produces: 4.6 to 10 TW A uniform, depleted mantle could produce: 5 – 7 TW Requires (AT LEAST) 3 to 10.4 TW produced elsewhere (mantle or core) Comparisons of mantle cooling regimes Lithospheric Conduction Moon Mercury Mars? Venus? Earth Plate recycling Io Hotspot Volcanism Kellogg et al., 1999 After a figure in E. M. Moores, L. H. Kellogg, and Y. Dilek, Ophiolites, Tectonics, and Mantle Convection: a contribution to the "Ophiolite Conundrum", in Optiolites and the Oceanic Crust, GSA Special Paper 349, 3-12, 2000. After a figure in E. M. Moores, L. H. Kellogg, and Y. Dilek, Ophiolites, Tectonics, and Mantle Convection: a contribution to the "Ophiolite Conundrum", in Optiolites and the Oceanic Crust, GSA Special Paper 349, 3-12, 2000. http://www.nsf.gov/pubs/2004/nsf04593/nsf04593.htm or link to this from: http://www.csedi.org National Science Foundation Cooperative Studies Of The Earth's Deep Interior (CSEDI) NSF 04-593 Full Proposal Deadline(s) (due by 5 p.m. proposer's local time): September 20, 2004 August 25, 2005 and annually thereafter Synopsis of Program: The Division of Earth Sciences (EAR) invites the submission of proposals for collaborative, interdisciplinary studies of the Earth's interior within the framework of the community-based initiative known as Cooperative Studies of the Earth's Deep Interior (CSEDI). Funding will support basic research on the character and dynamics of the Earth's mantle and core, their influence on the evolution of the Earth as a whole, and on processes operating within the deep interior that affect or are expressed on the Earth's surface. Projects may employ any combination of field, laboratory, and computational studies with observational, theoretical, or experimental approaches. Support is available for research and research infrastructure through grants and cooperative agreements awarded in response to investigator-initiated proposals from U.S. universities and other eligible institutions. Multidisciplinary work is required. EAR will consider co-funding of projects with other agencies and supports international work and collaborations.