The fate of carbonate in oceanic crust subducted into earth's lower mantle

At a Glance

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	Geophysical Laboratory, University of Science and Technology of China
Citations	34
Analysis	Full AI Review Included

6CCVD Technical Documentation: Analysis of Deep Earth Carbon Sequestration via Diamond Anvil Cell Experiments

Reference: Drewitt et al. (2019). The fate of carbonate in oceanic crust subducted into earth’s lower mantle. Earth and Planetary Science Letters, 511, 213-222.

Executive Summary

This research utilizes advanced high-pressure/high-temperature techniques—specifically the Laser-Heated Diamond Anvil Cell (LHDAC)—to simulate conditions in the Earth’s lower mantle and determine the fate of subducted oceanic carbonate. The key findings and their technical implications underscore the essential role of high-quality Single Crystal Diamond (SCD) in extreme physical science:

Diamond is the Ultimate Carbon Sink: Experimental results in the FeO-MgO-SiO₂-CO₂ (FMSC) and CaO-MgO-SiO₂-CO₂ (CMSC) systems demonstrate that carbonate materials react with silica between 40 and 70 GPa to form silicate phases and CO₂-V.
Decarbonation Barrier: This reaction creates an “impenetrable barrier” to carbonate subduction beyond ~1500 km deep, ensuring carbon is transformed into refractory phases rather than transported as liquid carbonate.
In-Situ Diamond Synthesis: Crucially, CO₂-V, stable over a narrow depth range, eventually breaks down via dissociation reactions at temperatures above 1800 K to form immobile, refractory diamond (C) plus oxygen (O₂).
Extreme P-T Capability Validation: The entire study validates the ability of highly pure SCD to serve as anvils in achieving and sustaining pressures up to 90 GPa and temperatures up to 2200 K, conditions essential for replicating deep Earth dynamics.
Analytical Reliance on Diamond: Identification of newly formed diamond within the quenched run products relied on highly sensitive micro-Raman spectroscopy centered on the characteristic 1332 cm^-1 diamond vibration peak.
MPCVD Material Applicability: Replication and extension of this fundamental deep Earth physics research requires the precisely cut and polished SCD and PCD components that 6CCVD specializes in.

Technical Specifications

The following hard data points were extracted, primarily defining the extreme experimental conditions achieved using the LHDAC setup:

Parameter	Value	Unit	Context
Pressure Range (Synthesis)	35 to 90	GPa	Lower mantle simulation, FMSC/CMSC systems.
Pressure Range (Theory/Prediction)	40 to 140	GPa	Predicted range for decarbonation.
Temperature Range	1600 to 2200	K	Achieved via double-sided YAG laser heating.
Diamond Anvil Culet Diameter	200 to 250	µm	Size constraints for achieving maximum pressure.
Sample Chamber Diameter	50 to 70	µm	Laser-drilled into Re gasket, defining sample volume.
Sample Foil Thickness	10 to 15	µm	Dimensions of material compressed between anvils.
Thermal Insulation Layer (NaCl)	15 to 20	µm	Thickness used to minimize heat loss to anvils.
Decarbonation Reaction Range	40 to 70	GPa	Pressure range where carbonate reacts with SiO₂.
Diamond Formation Temperature	1800 to 1900	K	Minimum temperature required for CO₂ dissociation.
Raman Shift (Diamond Signature)	1332	cm^-1	Fundamental vibration used for detection.
X-ray Wavelengths	0.4246, 0.37388	Å	Wavelengths used at Diamond Light Source/ESRF synchrotron.
Temperature Measurement Method	Standardized Radiometric	N/A	Error determined by standard deviation from mean.

Key Methodologies

The LHDAC experiments required highly specialized preparation and diagnostics, demonstrating the necessity of ultra-precision diamond components.

Starting Composition Synthesis:
- Ternary bulk compositions (FMSC and CMSC systems) were created by mixing specific ratios of carbonates (MgCO₃, CaCO₃, FeCO₃) with SiO₂ glass.
- Platinum black (Pt-black, ~10 wt.%) was added to the Fe-free CMSC samples to act as a laser absorption coupler.
- Mixtures were ground under acetone for 2-4 hours to achieve a homogeneous, fine powder with a grain size mode of 1-3 µm.
Diamond Anvil Cell (DAC) Assembly:
- Princeton-type symmetric DACs employing 200-250 µm culet diameter SCD anvils were used.
- Rhenium (Re) gaskets, pre-indented to ~50 µm, were laser-drilled to create 50-70 µm diameter sample chambers.
- A ~30 to 50 µm chip of starting material was loaded, flanked by 15-20 µm thick laser-cut NaCl discs used for thermal insulation.
Laser Heating and Temperature Measurement:
- High temperatures were achieved using a double-sided heating system employing two 100 W Yb-doped YAG fiber lasers.
- Beam shaping optics provided a ‘flat top’ beam profile (20 µm spot) to ensure minimal radial temperature gradients.
- Temperature was measured using standardized radiometric techniques, with experiments held for up to one hour between 1600 and 2200 K.
Pressure Measurement:
- Pressure was determined before and after heating via the Raman shift of the SCD anvil’s singlet peak, calibrated relative to the ruby scale. Measurement precision was 0.1 GPa (accuracy ±2 GPa).
Diagnostic Analysis (Quenched Products):
- Synchrotron X-ray Diffraction (XRD): Angle-dispersive XRD was performed at high pressure (in-situ) or on quenched samples (post-experiment) using micro-focused beams (3 x 4 µm²) to identify non-ternary phases (bridgmanite, Ca-perovskite, stishovite, dolomite III).
- Micro-Raman Spectroscopy: Utilized in confocal mode (532 nm laser) for pressure confirmation and, critically, for identifying reaction products. Raman mapping (3-5 µm steps) focused specifically on the 1332 cm^-1 peak for definitive diamond detection.

6CCVD Solutions & Capabilities

Replicating and extending deep Earth physics experiments—such as those involving LHDAC—requires materials that can withstand and transmit light under extreme conditions. 6CCVD provides the necessary high-purity MPCVD diamond components, ensuring reliable data acquisition and experimental integrity.

Applicable Materials

Research Requirement	6CCVD Recommended Material	Technical Advantage
Diamond Anvils (Optical Access)	Optical Grade Single Crystal Diamond (SCD)	Exceptional transparency across visible/IR spectra required for laser heating and radiometric temperature measurement. Highest purity ensures minimal background noise during Raman spectroscopy.
Gasket Support / High P-T Containment	Thermal Grade Polycrystalline Diamond (PCD)	High mechanical strength and thermal stability (500 µm thickness capability) suitable for backing plates or support in critical DAC components, ensuring minimal thermal expansion/stress effects.
Conductive / Metal Targets (Couplers)	Custom Metalized Diamond Wafers	SCD or PCD substrates coated with Au, Pt, or Pd (internal capability) can serve as integrated laser couplers, offering superior geometric control compared to loose Pt-black powder.

Customization Potential

The success of LHDAC relies heavily on the precision engineering of the SCD anvils and sample environment. 6CCVD’s core capabilities are directly applicable to optimizing this demanding research field:

Precision Culet Machining: The experiments required SCDs with culet diameters in the 200-250 µm range. 6CCVD specializes in the precise polishing (Ra < 1 nm) and laser cutting of SCD wafers up to 500 µm thickness, ensuring the strict tolerances required for optimal pressure generation and alignment.
Advanced Metalization Services: The use of Pt-black as a laser coupler is necessary but can introduce complexities. 6CCVD offers in-house Ti/Pt/Au or Pt/Pd metalization services. Applying a precise, thin metal film directly to the SCD culet or an insert plate provides a cleaner, more controlled coupling mechanism for uniform sample heating.
Large Substrates for Tooling: 6CCVD produces SCD and PCD substrates up to 125mm (PCD) and 10mm thickness, ideal for creating specialized backing disks, inserts, or supporting structures required for DAC preparation and alignment.

Engineering Support & Logistics

6CCVD’s in-house PhD engineering team is available to assist researchers in high-pressure geophysics and materials science with material selection. We provide expertise in choosing the optimal SCD orientation and quality needed to achieve maximum transparency and mechanical stability for lower mantle simulation projects like deep carbon cycle studies or high-pressure mineral synthesis.

We support global research efforts with reliable, timely delivery. Standard global shipping (DDU) is provided, with DDP options available upon request, ensuring sensitive diamond components arrive ready for immediate experimental use.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We 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 ∼35 to 90 GPa at temperatures of ∼1600 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 ±Ca-perovskite +CO2at pressures in the range of ∼40 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 ∼1500 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

Original Source

DOI: https://doi.org/10.1016/j.epsl.2019.01.041

References

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 Earth’s 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]