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Download 43-48 Ma - EPSc 453 Interior of the Earth
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Hotspots Concentrated volcanic activity. Linear volcanic chains in the interiors of the plates. Age progression along chain Chemistry of erupted lavas is significantly different than MOR or IA Some hotspots have broad topographic swell ~ 1000 m [Steinberger et al., 2004] Hawaii hotspot track Yellowstone hotspot track Are hotspots fixed? A global “hotspot” reference frame 25-43 Ma 43-48 Ma Hawaiian emperor track (Steinberger et al. Nature 04) Global scale: mantle contains both well-mixed regions and heterogeneity Fine scale heterogeneity Fine-scale variations in the Galapagos (from Harpp and White, 2001, G-cubed) Galapagos Islands Harpp and White, G-cubed 2001 Large Igneous Provinces (LIPs) Figure 15.1. Map of the major large igneous provinces (LIPs) on Earth, including continental flood basalt provinces, volcanic passive margins, oceanic plateaus, aseismic submarine ridges, ocean basin flood basalts, and seamount groups. After Saunders et al. (1992) and Saunders (pers. comm.). The volcanic eruption theory Deccan Traps - India Massive outpouring of flood basalts in India – more than 1.5 vertical km visible in this photo Does Deccan Traps volcanism present an alternative theory? Evidence against a volcanic origin – shocked quartz (from Chicxulub) The difference in age between top and bottom of a 3500 m composite section, probably comprising 80% of the total Deccan volume, is statistically insignificant, with the overall mean age being 64.7±0.6 Ma. Chenet et al [2007] Mass Extinctions The real reason dinosaurs became extinct Variable extinction rate in the geological record Data from Rohde & Muller [2005] Do mantle plumes cause flood basalts? Richards et al, 1989 Reunion hotspot and Deccan Traps Duncan, 1990 Columbia River Flood Basalts Camp et al. 2013 Plumes and plume swells Hotspot Swells Measuring buoyancy flux from hotspot swells Calculating Buoyancy Flux Calculated Buoyancy Fluxes How much heat is transported by plumes? • We can sum the buoyancy flux for all the plumes • Get 41 Mg s-1 (Davies 1988); 55 Mg s-1 (Sleep, 1990); 47 Mg s-1 (King & Adam, 2014) • Heat flux of plumes H = Buoyancy * Cp/𝛂 • So given the buoyancy of the largest plume (Hawaii) is ~ 8 Mg s-1, heat flux is 0.3 TW • Total heat flux of all plumes is ~ 2 TW • Total heat flow of the earth is 46 TW, 38 TW emerges from the mantle • Plume flux is only a small part of heat transport relative to plate tectonics and large-scale convection Seismic tomography indicates plumes orginate from the core-mantle boundary French & Romanowicz 2015 Broad plumes from the core-mantle boundary Mantle plumes and CMB structure Model for LLSVPs and mantle plumes Garnero 2007 McNamara & Zhong 2005 Plumes and hotspots Rayleigh-Taylor instability Large head, thin tail Rheology Vigor of convection Compositional vs thermal buoyancy Ascent times Rheology Deflection, capture by mantle wind Compositional vs thermal buoyancy [Griffiths and Campbell, 1990] Entrainment of a dense layer by thermal plumes Zhong and Hager, Geophysical Journal International September 2003)
