1. Chemical consequences of perovskite fractionation from an ultramafic liquid with application to the dynamics of a basal magma ocean Leah Ziegler, Hongluo Zhang, Colin Jackson, Matt Jackson, Dave Stegman Team BMO:

2. What is a basal magma ocean? Labrosse et al., 2007 - a dense melt layer that forms at the bottom of the mantle – likely linked to a whole mantle magma ocean

3. Why a basal magma ocean? -poorly understood lower mantle structures: -missing geochemical reservoirs: Garnero and McNamara, 2008 Labrosse et al., 2007

4. How would a basal magma ocean form? Figures: Stixrude et al., 2009 -Density crossover between liquid and solid at mid-mantle depths is possible – depends on Kd-Fe -Curvature of mantle liquidus can lead to crystallization initiating at mid-mantle depths w/ Fe w/o Fe

5. Density of liquid and solid with crystallization -f(X liq, X sol, X U+Th+K, time) Concentration of REE and heat producers (U+Th) associated with BMO products -Both Require: - major element partition coefficients (Kd) - trace element partition coefficients Key parameters for evaluating BMO:

6. Step 1: Compile Kd database for Mg-Pv, Ca-Pv, & Fe-MgO -Database compiled at CIDER 2012 -Details of database: Total number of studies: 19 Experiments including -- Mg-Pv: 31 -- Ca-Pv: 10 – Fe-MgO:12 Pressure Range: 23 – 86 GPa Temperature Range: 2300 – 3500°C Database will be published with initial reporting of findings

7. Effect of Al content on the solubility of Fe in MgPv & Kd-TE Importance of charge coupled substitutions right: Frost and Langenhorst, 2002 left: Liebske et al., 2005

8. Step 2: Parameterize Kds for Mg-Pv Models for Mg-Pv major elements: Observed Predicted Equal weight, multiple linear regression

9. Step 2: Parameterize Kds for Mg-Pv Models for Mg-Pv trace elements: Observed Predicted Similar TE substitutions as pyroxene

10. Team BMO met in October at BU: - Refined Kd parameterizations -Developed stoichiometric Mg-Pv crystallization model -Quantified uncertainties in crystallization model predictions using monte carlo approach -Accounts for covariation in model parameters -Thank you Don Forsyth Step 3: Apply Kds for Mg-Pv BMO crystallization

11. Model Results Liquid evolution with crystallization (batch): Majors: cation mol fraction, Trace: PPM* Bulk: McDonough & Sun BSE, 40 GPa

12. Al-free Al-bearing Model Results K d Fe with crystallization (BSE bulk, 40 GPa): Results from 78.5 GPa: Andrault et al., 2012 Al + Si causing offset between Nomura and Andrault ?

13. Model Results Removal of heat producing elements and REE from liquid (batch): High Al in MgPv makes it significant reservoir for TEs Still working to incorporate full uncertainties into TE Kds

14. -Al partitions equally between MgPV and liquid -REE+U+Th have similar substitutions into pyx and MgPv - Al AND Ca are important -Fe is a moderately incompatible element – Fe is strongly controlled by Al, but other effects appear significant (Si liq ?) Preliminary Findings

15. Post-AGU Team BMO Meet up: - Develop new crystallization model - Weaver and Langmuir (1990) -Working with Stephane Escrig to implement his code - stoichiometry - self-consistent saturation of phases - Predict past Fe-MgO or Ca-Pv saturation - Couple chemical model to dynamical model Current Directions

16. System of Equations: Crystallization Model -Maintains stoichiometry on Si and Mg site

17. Effect of Al content on Kd-Fe at high P & T Al-free Al-bearing Andrault et al., 2012

18. Kds

19. Solid Evolution