Intraplate Volcanism Induced by Shear-Driven Upwelling! Beneath the Lithosphere-Asthenospere Boundary!!Clint Conrad!University of Hawaii at Manoa! Todd Bianco!Univ. Hawaii (now @Brown)! Maxim Ballmer!Univ. Hawaii!!!Gene Smith!UNLV! Benjun Wu!Johns Hopkins (now @Yale)!!!Paul Wessel!Univ. Hawaii! [Taneda,1979]
Shear-Driven Cavity Flow A classic engineering problem Industrial Applications: Spin Coating Liquid cooling by melt spinning Mixing Processes Benchmark for computational schemes [Taneda,1979]
Shear-Driven Cavity Flow Application to the LAB? Can Shear-Driven Cavity Flow induce melting and volcanism? [Taneda,1979]
Mechanisms for Intraplate Volcanism Depth Temperature Mantle Upwelling Induces Melting V Small-Scale Convection [Ballmer et al., 2007] Solidus Mantle Temperature Edge-Driven Convection [King & Anderson, 1998] Lithospheric Drips [Elkins-Tanton & Hager, 2000] For these mechanisms, upwelling flow is driven by localized mantle density heterogeneity.
Can asthenospheric shear drive upwelling and volcanism? The Shear-Driven Upwelling (SDU) Ingredients:!" Rapid Asthenospheric Shear!" Viscosity Heterogeneity Density Heterogeneity not required Conrad et al. [PEPI, 2010] Conrad et al. [Nat. Geosci., 2011] Bianco et al. [JGR, 2011] Asthenospheric Pocket Lithospheric Cavity King [News & Views, Nature Geoscience,2011]
Shear-Driven Upwelling within an Low-Viscosity Pocket " An unstudied variation of shear-driven cavity flow: " Vary the dimensions and viscosity of the pocket " Measure maximum upwelling W Low-Viscosity Pocket (! LV ) D Stationary Lithosphere Shearing Asthenosphere V = 5 cm/yr Conrad et al. [PEPI, 2010] Flowing Upper Mantle
Shear-Driven Upwelling within an Low-Viscosity Pocket " An unstudied variation of shear-driven cavity flow: " Vary the dimensions and viscosity of the pocket " Measure maximum upwelling Conrad et al. [PEPI, 2010]
Shear-Driven Upwelling within an Low-Viscosity Pocket " An unstudied variation of shear-driven cavity flow: " Vary the dimensions and viscosity of the pocket " Measure maximum upwelling Shear-Driven Upwelling Conrad et al. [PEPI, 2010]
Flow patterns within a low-viscosity!pocket" A) Thick pocket: Shear develops within the pocket B) Shallow & wide pocket: Circulation within the pocket C) Shallow & narrow pocket: Pocket rides along with flow Conrad et al. [PEPI, 2010]
SDU in 3 Dimensions: A Movie by Maxim Ballmer
Bianco Movie Snapshots: SDU evolution with time Bianco et al. [in press at JGR]
An Example Simulation!Volcano-gram" Frames from the movie 5.0 Myr 0.1 Myr Bianco et al. [in press at JGR]
Volcanism Rates Around the World Hawaiian Presheild: Hawaiian Shield: ~ 2.5 km/myr! ~ 15 km/myr Hawaiian Postshield: ~ 0.5 km/myr (Frey et al., 1990) Hawaiian Rejuvenation: < 0.05 km/myr (Mike Garcia) Neo-Volcanic Zone, Iceland: ~ 4 km/myr Rebound Iceland: ~ 20-80 km/myr (Saemendsson & Kroflukerfisins, 1991) Crater Flat, Nevada: ~ 0.03-0.3 km/myr (Valentine et al., 2006) Shear-Driven Upwelling:!less than ~0.2 km/myr!
Crater Flat, Southern Nevada Volcanic History [Valentine et al., GSA Bull., 2006] 10 Ma 1.5 Myr of basalt flows 4 Ma smaller basalt flows 1 Ma 5 volcanoes 80 ka Lanthrop Wells
Can SDU explain patterns of intra-plate volcanism? Seamounts: Global database of Wessel [2001] Intraplate Volcanoes: Basalts from www.earthchem.org:! younger than 10 Ma " " " "! >300 km from plate boundary
Can SDU explain patterns of intra-plate volcanism? Requirements for Shear-Driven Upwelling: 1. Viscosity heterogeneity with the proper geometry 2. Asthenospheric mantle near the solidus 3. Rapid asthenospheric shear
Where is asthenospheric shear largest? Surface Plate Motions
Where is asthenospheric shear largest? Surface Plate Motions and Mantle Flow at 300 km Mantle flow field from Conrad and Behn [2010]
Where is asthenospheric shear largest?
Asthenospheric Shear Beneath Continents Conrad et al. [Nature Geoscience, 2011]
Asthenospheric Shear and Continental Volcanism Conrad et al. [Nature Geoscience, 2011]
Asthenospheric Shear and Continental Volcanism Conrad et al. [Nature Geoscience, 2011]
Asthenospheric Shear and Continental Volcanism Western North America Conrad et al. [Nature Geoscience, 2011]
Asthenospheric Shear beneath the Western US About 5 cm/yr shear within the asthenosphere Westward Plate Motion
Recent Volcanic fields [Tibbetts et al., Sp. AGU, 2009] Tomographic Cross Section [Yang et al., JGR, 2008] and Melting Depths [Lee et al., EPSL 2009]
The Newer Volcanic Province (South Australia) Approx. Craton Edge Plate Motion Mt. Gambier, Erupted 4500 yrs ago Demidjuk et al., EPSL 2007 SDU-like model
Seamount Locations [Wessel, 2001] and Asthenospheric Shear Beneath Seafloor Conrad et al. [Nature Geoscience, 2011]
Seamount Locations [Wessel, 2001] and Asthenospheric Shear Beneath Seafloor Conrad et al. [Nature Geoscience, 2011]
Seamount Locations and Asthenospheric Shear Beneath Seafloor Conrad et al. [Nature Geoscience, 2011]
East Pacific Rise (West Flank) Seamount Locations and Asthenospheric Shear Beneath Seafloor Conrad et al. [Nature Geoscience, 2011]
Shearing asymmetry across the East Pacific Rise Rapid shear beneath western flank EPR Spreading
Older Seamounts on the Pacific Plate: Seamount ages estimated by Hillier [2007] using flexure of seafloor
Volume Density of Seamounts on the Pacific Plate Conrad et al. [Nat. Geosci., 2011]
Conclusions! Asthenospheric shear and lateral viscosity variations can drive!!!shear-driven Upwelling (SDU)! SDU can induce melting at the LAB! Can induce volcanism: surface expression is not hotspot-like! Rapid asthenospheric shear correlates with intraplate volcanism:!!!pacific Seamounts, Western US, Eastern Australia! Asthenospheric Pocket Lithospheric Cavity King [News & Views, Nature Geoscience,2011]