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Convection modeling of the postperovskite transition and constraints on the thermal conditions near the core mantle boundary Arie van den Berg, Utrecht University David Yuen, University of Minnesota

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Outline Seismic observations of irregular D” old and new Interpretation related to Pv/PPv transition > estimate thermal conditions near CMB Modelling results of slab interaction with Pv/PPv feasibility of heat flow estimates and thermal conductivity Conclusions

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Cleary and Haddon, 1972

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Van den Berg, Cloetingh and Doornbos, 1978

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Hirose, 2007 Pv/PPv Slope 11 MPa/K, CMB intercept ~3550 K

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Boehler, Annu. Rev. Earth Planet. Sci. 1996

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Van den Berg, Rainey and Yuen, 2005

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Mantel profiles based on a modified Hofmeister (1999) model

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model of subducting slab interacting with the PV/PPv zone of D” Extended Boussinesq – ppv phase boundary T,P dep.visc. dv_T=1000, dv_P=100 Layered piecewise uniform thermal conductivity 2D domain 3000X3000km - element resolution down to 5 km near CMB Crustal (100) marker chain

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Crustal markers Spinel/Pv Pv PPv

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K_cmb=5 W/(mK)

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K_cmb=15 W/(mK)

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Single tracer T-depth paths Crustal markers in bottom PV (high k case)

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Some conclusions - Precursors to PKP from small scale scatterers near CMB can be related to heterogeneity in the Pv/PPv region due to complex phase distribution and/or crustal remnants - PPv linked to D” allows temperature estimates near CMB from seismic mapping of PPv > Pv in the thermal boundary layer - Heatflow estimates based on simple linear T profiles are feasible but require better constraints of k_cmb

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