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

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

Cleary and Haddon, 1972

Van den Berg, Cloetingh and Doornbos, 1978

Hirose, 2007

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

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

Van den Berg, Rainey and Yuen, 2005

Mantel profiles based on a modified Hofmeister (1999) model

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

Crustal markers

Spinel/Pv

Pv

PPv

K_cmb=5 W/(mK)

K_cmb=5 W/(mK)

K_cmb=5 W/(mK)

K_cmb=15 W/(mK)

K_cmb=15 W/(mK)

K_cmb=15 W/(mK)

Single tracer T-depth paths

Crustal markers in bottom PV(high k case)

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