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Deep carbon: carbonates etc

Deep carbon: carbonates etc. University College London: Adrian P Jones and coworkers Judith Milledge (Emeritus), UCL APJ Postgrads: Emma Tomlinson, Su Trickett, Dan Howell, Sami Mikhail, (Emma Bowden, Rachel Hazael, Gianluigi Rosatelli, Matt Genge, Dave Dobson)

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Deep carbon: carbonates etc

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  1. Deep carbon: carbonates etc University College London: Adrian P Jones and coworkers Judith Milledge (Emeritus), UCL APJ Postgrads: Emma Tomlinson, Su Trickett, Dan Howell, Sami Mikhail, (Emma Bowden, Rachel Hazael, Gianluigi Rosatelli, Matt Genge, Dave Dobson) OPEN UNIVERSITY: Alex Verchovsky, Monica Grady..

  2. DEEP CARBON CYCLE Rosetta CO2 Mt Erebus effect (Eruption?) Model of CO2 Pacific atmospheric distribution Volcanic eruptions outgas CO2 What is the bulk C of the Earth? What is the volcanic flux of CO2? -Steady state vs catastrophic -Eurocarb…. 4.6 Ga Protoearth 4.56 Moon Diamond + O2 = CO2 core Geodynamicinterior C delivery meteorites Diamond as a major C reservoir

  3. Deep carbon APJ perspective • Carbon-rich volcanism • Degassing • Mantle Carbonate • Where, why • Planetary perspective • Venus, Earth, the beginning. • Mantle Diamond • Reservoir and age • Impact behaviour of carbonate, diamond..

  4. Carbonatite volcanism • Oldoinyo Lengai • CO2 degassing • Mantle carbon • 1966, 2007 events, plus continuously active • Regional carbon footprint

  5. Natrocarbonatite to carbonatite in ~1 year at <43oC.: density 2006 Zaitsev and Keller, Lithos 91, 191-207 2007 UCL unpublished data*

  6. Observational tools • Geology, rocks and minerals • Meteorites, rocks and minerals • Mineralogy, petrology, geochemistry • Carbon inorganic vs organic • Field observations • Laboratory Experiments

  7. Carbonate melt mantle: Canary • Direct observation of carbonate in mantle xenoliths is becoming more widely recognised • Cryptic metasomatism of mantle xenoliths from transient carbonatites often leaves a distinctive geochemical “smell” Carbonatite*

  8. Carbonate melt mantle: Tanzania(Rudnick ~1999,2000)

  9. ~100 km

  10. Transition zone ULM • Martinez et al 1998 (JGR 103) • suggested carbonate minerals and melts in the transition zone • Superdeep diamond inclusions provide precious samples (akin to meteorites but smaller, rarer and arguably much more valuable) • Carbonate is very rare (maybe 2 grains worldwide) • New data on metal carbide inclusions maybe from ~20 GPa • Some doubt about pressure = depth

  11. Jagersfontein c-type (chondritic relics) diamonds?32 out of 148 diamonds contained dark inclusions; 13 have native siderophile metal/carbide

  12. ~3000 km (no samples) Isshiki et al Nature 2003 High PT exeriments Ono et al Am Mineral 2005 calcite post aragonite Also Seto et al 2007 subduction reactions To ~2000 km 3000K (Phys Chem Mineral)

  13. Modelling (Oganov): stable structure of CaCO3 at 150 GPa

  14. Is carbon oxidised or reducedin the lower mantle? (Oganov)

  15. Modelling: Oganov et al

  16. Modelling cont:

  17. So, carbonate reservoirs are plentiful • But reservoirs are hypothetical, where are the deepest, and oldest samples? • Carbonate as a carbon reservoir is almost certainly dynamic, and involved in the convective cycle; hinges on oxygen and T • How much is really subducted (<2%?) • Carbonate may be so dynamic that the carbon cycle in the upper mantle is isolated from the lower mantle.

  18. Carbon bottleneck • No consensus on bulk Earth carbon • Cosmochemical the best? • Need more information from meteorites • And it is rapidly evolving • Did the moon-forming event change everything? • Carbon isotopes • We can construct a mass balance model for the whole Earth, but major assumptions

  19. Deep carbon: Europe • European Eurocores proposal (link from previous ESF Eurocarb) 2009? • NASA Orbiting carbon observatory; volcanic 16 km footprint (eg Etna) • ?UK consortium of volcano CO2 monitors • NERC, ESF

  20. Meteoritic carbon • Evolving view of carbon chemistry from meteorites (see figure) • New hypothesis for bulk Earth (Grady, Open University) – APJ separate short presentation? El Goresy et al 2005

  21. 1: Carbon: planetary perspective • M.M. Grady, Verchovsky, A. B., & Wright, I. P. Magmatic carbon in Martian meteorites: attempts to constrain the carbon cycle on Mars.Int J Astrobiol 3, 117-124 (2004) • Abstract…”[Mars meteorites] show that the magmatic component has a very variable abundance of 1-100 ppm, with d13C ~-20+/-4%0. This value is close to magmatic carbon determined for Moon and for Vesta (parent body of HED basaltic meteorites), but very different from that of the Earth.” • Conclusions…(4) ..perhaps the d13C of -5%0 on Earth does not represent the bulk planet.

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