1 / 25

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.

alka
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related