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The Ongoing and the Early Differentiation of the Earth: the Role of Volatiles

The Ongoing and the Early Differentiation of the Earth: the Role of Volatiles. Rajdeep Dasgupta. June 26, 2008. COMPRES. Volatiles and Solid Earth Science. Short-Term Carbon Cycle. http://earthobservatory.nasa.gov/Library/CarbonCycle. Long-Term Carbon Cycle.

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The Ongoing and the Early Differentiation of the Earth: the Role of Volatiles

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  1. The Ongoing and the Early Differentiation of the Earth: the Role of Volatiles Rajdeep Dasgupta June 26, 2008 COMPRES

  2. Volatiles and Solid Earth Science

  3. Short-Term Carbon Cycle http://earthobservatory.nasa.gov/Library/CarbonCycle

  4. Long-Term Carbon Cycle

  5. C Fluxes – IN and OUT (How uncertain?) (Marty and Tolstikhin, 1998; Plank and Langmuir, 1998; Sleep and Zahnle, 2001; Jarrard, 2003; Resing et al., 2004; Hayes and Waldbauer, 2006)

  6. Release of Subducted Carbon – how, where ? Partial melting of carbonated eclogite (eclogite + CO2) is likely to control the depth of release of crustal carbon in the mantle

  7. Deep Cycling of Carbon Dasgupta et al. (2004) - EPSL

  8. Fate of Carbonated Eclogite in the Upwelling Mantle Deep Melting of Carbonated Eclogite in the Earth’s upper mantle and generation of carbonatitic melt Dasgupta et al. (2004) - EPSL

  9. If carbonated eclogite melts very deep, solidus of peridotite+CO2 controls loci of carbon storage and release

  10. 6.6 GPa, 1300 °C Experiments with Peridotite+CO2 6.6 GPa, 1250 °C Dasgupta and Hirschmann (2006) - Nature

  11. Solidus of Peridotite with trace CO2 Deep Melting of Carbonated peridotite in the Earth’s upper mantle and generation of carbonatitic melt (with ~40 wt.% CO2) For 30-350 ppm C, this melting generates 0.03-0.3 wt.% carbonatitic melt eclogite + CO2 Falloon and Green (1989) Dasgupta and Hirschmann (2006) - Nature

  12. Geochemical Consequence of Deep Melting 25% of the mantle/ Ga • Release of highly incompatible tracers and volatiles • U-Th-Pb-He and K-Ar, Rb-Sr, Sm-Nd may be strongly fractionated in the depleted residual peridotite and in small-degree carbonatitic melt • If stored for long, both carbonatite extracted residue and carbonatite implanted metasomatized mantle lithology may evolve as geochemical reservoirs with distinct isotopic signatures. 1  1018 g of mantle/ yr Dasgupta & Hirschmann (2006) - Nature

  13. Carbon in the Core?

  14. C Behavior of Carbon during magma ocean differentiation? Behavior of C during early Earth differentiation (metal-silicate equilibration)? Partitioning of C during core-mantle equilibration

  15. Solubility of Carbon in core melts? Carbon solubility determinations at 2 GPa at 1300-2500 °C Starting mix – Fe or Fe-5.2 wt.% Ni in graphite capsule Electron microprobe analysis of carbon content using LPC2 crystal and experimentally synthesized Fe3C and Fe7C3 crystals as standards Dasgupta and Walker (2008) - GCA

  16. Solubility of Carbon in core melts? Texture of quenched Fe±Ni-C melt Dasgupta and Walker (2008) - GCA

  17. Carbon solubility in core melts Dasgupta and Walker (2008) - GCA

  18. Constraint on DC (silicate-metal) from solubility Dasgupta and Walker (2008) - GCA

  19. Constraint on DC (silicate-metal) from mantle carbon content Carbon content of the mantle? • Direct measurement of CO2 in mantle derived melts/ glasses (MORB, OIB, Arc Lavas and melt inclusions) (e.g., Dixon et al., 1997; Bureau et al., 1998) • Direct measurement of CO2 in mantle-derived fluids (trapped gas bubbles in basalts, hydrothermal vent fluids, plumes) and gases (e.g., Aubaud et al., 2005) ￭ Measurement of CO2/Incompatible species ratio in glasses, fluids, gases and independent estimate of mantle He or Nb etc. CO2/3He, CO2/4He (e.g., Trull et al., 1993; Marty and Tolstikhin, 1998; Shaw et al., 2003; Resing et al., 2004) CO2/Ar (e.g., Tingle, 1998; Cartigny et al., 2001) CO2/Nb (e.g., Saal et al., 2002; Cartigny et al., 2008) CO2/Cl (e.g., Saal et al., 2002)

  20. Constraint on DC (silicate-metal) from mantle carbon content Batch segregation of core melt Dasgupta and Walker (2008) - GCA

  21. Constraint on DC (silicate-metal) from mantle carbon content + metal solubility Fractional segregation of core melt Batch segregation of core melt Dasgupta and Walker (2008) - GCA

  22. 0.25 ± 0.15 wt.% C Carbon in the Core? Core is likely to be the most enriched deep Earth reservoir of carbon ~48 x 1024 g C in the core Dasgupta and Walker (2008) - GCA

  23. Summary

  24. The Road Ahead Interested in the role of volatiles…? Rajdeep.Dasgupta@rice.edu

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