Post-Aragonite Phases of CaCO3 at Lower Mantle Pressures

ORAL

Abstract

The properties of carbonate minerals at mantle conditions have significant impact on our understanding of the carbon cycle and the composition of the Earth interior. In recent years, there has been interest in the behavior of carbonates at lower mantle conditions, specifically in their C hybridization. Using high-pressure synchrotron X-ray diffraction in a diamond anvil cell coupled with direct laser heating using a CO2 laser, we identify a crystalline phase of CaCO3 above 40 GPa - corresponding to a lower mantle depth of ∼1,000 km - which is predicted by ab initio random structure search (AIRSS). The observed sp2 C-hybridized species at 40 GPa is monoclinic (P21/c) and is stable up to 50 GPa, above which its structure cannot be indexed by existing CaCO3 phases. We investigate with nudged elastic band calculations the reaction mechanisms between relevant phases of CaCO3 and postulate that the mineral is capable of undergoing sp2-sp3 hybridization change purely in the P21/c structure - forgoing the accepted post-aragonite Pmmn structure.

*National Nuclear Security Administration / Stewardship Science Academic Alliances program / DOE Co-operative Agreement #DE-NA0001982. DOE-NNSA Award No. DE-NA0001974 and DOE-BES Award No. DE-FG02-99ER45775. DOE-BES Contract No. DE-AC02-06CH11357.

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Presenters

  • Dean Smith

    • Department of Physics and Astronomy and HiPSEC, University of Nevada, Las Vegas

Authors

  • Dean Smith

    • Department of Physics and Astronomy and HiPSEC, University of Nevada, Las Vegas

  • Keith Lawler

    • Department of Chemistry and Biochemistry and HiPSEC, University of Nevada, Las Vegas

  • Miguel Martinez-Canales

    • School of Physics and Astronomy and CSEC, University of Edinburgh

  • Austin Daykin

    • Department of Physics and Astronomy and HiPSEC, University of Nevada, Las Vegas

  • Zachary Fussell

    • Department of Physics and Astronomy and HiPSEC, University of Nevada, Las Vegas

  • G Alexander Smith

    • Department of Chemistry and Biochemistry and HiPSEC, University of Nevada, Las Vegas

  • Christian Childs

    • Department of Physics and Astronomy and HiPSEC, University of Nevada, Las Vegas

  • Jesse Smith

    • High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institute of Washington
    • High Pressure Collaborative Access Team, Geophysical Laboratory,Carnegie Institution of Washington

  • Chris Pickard

    • Department of Materials Science and Metallurgy, University of Cambridge

  • Ashkan Salamat

    • Department of Physics and Astronomy and HiPSEC, University of Nevada, Las Vegas
    • Physics and Astronomy, University of Nevada, Las Vegas