The fate of carbonate in oceanic crust subducted into earth's lower mantle
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2019-02-10 |
| Journal | Earth and Planetary Science Letters |
| Authors | James W. E. Drewitt, Michael J. Walter, Hongluo Zhang, S. C. McMahon, David Edwards |
| Institutions | Diamond Light Source, University of Science and Technology of China |
| Citations | 34 |
Abstract
Section titled āAbstractāWe report on laser-heated diamond anvil cell (LHDAC) experiments in the FeO-MgO-SiO2-CO2(FMSC) and CaO-MgO-SiO2-CO2(CMSC) systems at lower mantle pressures designed to test for decarbonation and diamond forming reactions. Sub-solidus phase relations based on synthesis experiments are reported in the pressure range of ā¼35 to 90 GPa at temperatures of ā¼1600 to 2200 K. Ternary bulk compositions comprised of mixtures of carbonate and silica are constructed such that decarbonation reactions produce non-ternary phases (e.g. bridgmanite, Ca-perovskite, diamond, CO2-V), and synchrotron X-ray diffraction and micro-Raman spectroscopy are used to identify the appearance of reaction products. We find that carbonate phases in these two systems react with silica to form bridgmanite Ā±Ca-perovskite +CO2at pressures in the range of ā¼40 to 70 GPa and 1600 to 1900 K in decarbonation reactions with negative Clapeyron slopes. Our results show that decarbonation reactions form an impenetrable barrier to subduction of carbonate in oceanic crust to depths in the mantle greater than ā¼1500 km. We also identify carbonate and CO2-V dissociation reactions that form diamond plus oxygen. On the basis of the observed decarbonation reactions we predict that the ultimate fate of carbonate in oceanic crust subducted into the deep lower mantle is in the form of refractory diamond in the deepest lower mantle along a slab geotherm and throughout the lower mantle along a mantle geotherm. Diamond produced in oceanic crust by subsolidus decarbonation is refractory and immobile and can be stored at the base of the mantle over long timescales, potentially returning to the surface in OIB magmas associated with deep mantle plumes.
Tech Support
Section titled āTech SupportāOriginal Source
Section titled āOriginal SourceāReferences
Section titled āReferencesā- 2018 - CaCO3 phase diagram studied with Raman spectroscopy at pressures up to 50 GPa and high temperatures and DFT modeling [Crossref]
- 1997 - A simulation study of induced failure and recrystallization of a perfect MgO crystal under non-hydrostatic compression: application to melting in the diamond-anvil cell [Crossref]
- 1993 - Experimental-evidence for carbonate stability in the earths lower mantle [Crossref]
- 2007 - Carbonates from the lower part of transition zone or even the lower mantle [Crossref]
- 2010 - Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism [Crossref]
- 2006 - Experiments on CaCO3-MgCO3 solid solutions at high pressure and temperature [Crossref]
- 2015 - Stable isotope evidence for crustal recycling as recorded by superdeep diamonds [Crossref]
- 2014 - Hidden carbon in Earthās inner core revealed by shear softening in dense Fe7C3 [Crossref]
- 2015 - Alteration of ocean crust provides a strong temperature dependent feedback on the geological carbon cycle and is a primary driver of the Sr-isotopic composition of seawater [Crossref]
- 2013 - Evidence that low-temperature oceanic hydrothermal systems play an important role in the silicate-carbonate weathering cycle and long-term climate regulation [Crossref]