The Study of Olivine Inclusions in Diamonds from Liaoning, China and the Evaluation of Related Thermometers

At a Glance

Metadata	Details
Publication Date	2024-08-23
Journal	Minerals
Authors	Linli Qin, Guanghai Shi, Xin Zhao, Zhenyu Chen
Institutions	Chinese Academy of Geological Sciences, China University of Geosciences (Beijing)
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Geothermobarometry and High-Precision Spectroscopy

Executive Summary

This research paper, focusing on olivine inclusions (OlDia) in natural diamonds from the North China Craton (NCC), underscores the critical role of high-ppurity diamond material in deep Earth science and high-precision analytical techniques.

Application: Utilized diamond as a robust, protective host and optical window for in situ analysis of mineral inclusions (OlDia) to constrain mantle conditions.
Analytical Requirements: Success hinged on ultra-precise sample preparation (polishing to expose inclusions) and high-sensitivity trace element analysis (Al, Cr, Ti) using LA-ICP-MS and EPMA.
Key Geochemical Findings: OlDia compositions (Mg# 92.8-93.2, high Cr#) confirm a refractory, depleted lithospheric mantle source beneath the NCC.
P-T Constraints: Established diamond formation conditions within a temperature range of 1080-1380 °C and a conductive geotherm of 39-42 mW/m².
Metasomatism Evidence: Raman spectroscopy confirmed the presence of silica fluid (non-crystalline phase) trapped within the host diamond, indicating fluid/melt metasomatism at the lower lithospheric roots (161-178 km).
Methodology Validation: The study validated the use of Al-in-olivine thermometers (T [Al-Ol, BW17]) combined with LA-ICP-MS data for the highest accuracy in geothermobarometry.

Technical Specifications

The following hard data points were extracted from the analysis, defining the extreme conditions and precision required for this type of deep Earth research.

Parameter	Value	Unit	Context
Temperature Range (T)	1080-1380	°C	Overall range for diamondiferous lithosphere (LA-ICP-MS & EPMA)
Geotherm Model	39-42	mW/m²	Conductive model geotherm beneath the North China Craton (NCC)
Depth of Enrichment	161-178	km	Corresponds to 1360-1400 °C and 55-58 kbar
Olivine Inclusion Size	20 x 20 to 100 x 50	µm	Target size for in situ analysis
LA-ICP-MS Spot Size	25-30	µm	Required precision for trace element spot analysis
EPMA Accelerating Voltage	15	kV	Used for Electron Probe Micro-Analysis
Olivine Mg# (Median)	93.1	N/A	Molar ratio (100Mg/(Mg + Fe)), indicating depleted mantle
Al Content (LA-ICP-MS)	52.8-72.3	ppm	Trace element concentration in OlDia
Cr Content (LA-ICP-MS)	268-571	ppm	Trace element concentration in OlDia
Raman Excitation Wavelength	532	nm	Used for phase confirmation (silica fluid detection)

Key Methodologies

The research relied on advanced material preparation and high-resolution spectroscopic and elemental analysis, emphasizing the need for robust, optically transparent diamond hosts.

Sample Preparation: Four diamond crystals containing olivine inclusions (OlDia) were selected. The host diamonds were precisely polished along the crystal surface to expose the inclusions for in situ analysis.
Phase Confirmation (Raman Spectroscopy):
- Used an HR-Evolution Raman spectrometer.
- Excitation Wavelength: 532 nm.
- Testing Power: 50 to 100 mW.
- Key Result: Detected sharp olivine peaks (824 and 855 cm^-1) and wide, non-crystalline peaks (679 cm^-1 and 780 cm^-1) attributed to trapped silica fluid.
Major and Trace Element Analysis (EPMA):
- Used a JEOL JXA-8230 Electron Probe Micro-Analyzer.
- Accelerating Voltage: 15 kV.
- Beam Current: 20 nA.
- Spot Size: 1-5 µm.
- Trace Elements Measured: Al, Cr (50-100 s counting time for precision).
- Sample Coating: 20 nm thin conductive carbon film.
High-Precision Trace Element Analysis (LA-ICP-MS):
- Used an IRIDIA Laser Ablation System coupled with an Agilent 7900 ICP-MS.
- Spot Size: 25-30 µm (chosen to avoid penetration of small inclusions).
- Energy Density: ~2-4 J/cm².
- Repetition Rate: 7 Hz.
- Elements Measured: Al, Ti, Cr (LODs as low as 1.7 ppm for Al).
Geothermobarometry: Applied three olivine thermometers (T [Al-Ol, dH10-Dia], T [Al-Ol, BW17], T [Cr-Ol, dH10]) using LA-ICP-MS and EPMA data, combined with iterative P-T calculations to constrain the geotherm.

6CCVD Solutions & Capabilities

The successful execution of this geothermobarometry study relies on materials science capabilities that 6CCVD provides directly to the research community. Our MPCVD diamond products offer superior purity, thermal stability, and customization necessary to replicate and advance high P-T inclusion studies.

Applicable Materials for Replication and Extension

To replicate the function of the natural diamond host—acting as an ultra-pure, high-pressure optical window for in situ spectroscopy and trace element analysis—6CCVD recommends Optical Grade Single Crystal Diamond (SCD).

6CCVD Material	Key Specification	Application Relevance
Optical Grade SCD	High Purity (low N, B content)	Essential for minimizing background noise during Raman and LA-ICP-MS analysis.
SCD Substrates	Thickness: 0.1 µm - 500 µm	Provides robust, thin windows for high-pressure cells or thick substrates for thermal management in analytical equipment.
Polycrystalline Diamond (PCD)	Plates up to 125 mm diameter	Ideal for large-area diamond anvil cell (DAC) gaskets or high-wear components in sample preparation equipment.
Boron-Doped Diamond (BDD)	Custom Doping Levels	For related electrochemical or sensing experiments requiring conductive diamond electrodes (e.g., studying redox reactions in metasomatic fluids).

Customization Potential for High-Precision Research

The paper highlights the critical need for precise sample preparation (polishing to expose inclusions) and the use of small analytical spots (25-30 µm). 6CCVD excels in providing materials tailored for these demanding requirements:

Ultra-Precision Polishing: 6CCVD guarantees surface roughness Ra < 1nm for SCD and Ra < 5nm for inch-size PCD. This ultra-flatness is crucial for minimizing optical scattering and ensuring accurate focusing for in situ Raman and LA-ICP-MS measurements.
Custom Dimensions and Geometry: We provide plates and wafers up to 125 mm (PCD) and substrates up to 10 mm thick. Our advanced laser cutting services allow for the creation of custom geometries, apertures, and micro-machined features necessary for DAC experiments or specialized sample holders.
Custom Metalization Services: While the researchers used a carbon film for EPMA conductivity, 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu). This is vital for researchers developing integrated diamond sensors, thermal heat spreaders, or electrical contacts for high P-T experiments.

Engineering Support

The complex use of trace element thermometers (Al-in-olivine, Cr-in-olivine) demonstrates the deep material science expertise required for geothermobarometry.

6CCVD’s in-house PhD team specializes in the growth and characterization of MPCVD diamond. We offer consultation services to assist researchers in selecting the optimal diamond material (SCD vs. PCD, specific doping, orientation) for similar High P-T Geothermobarometry and Metasomatism projects, ensuring the diamond substrate itself does not interfere with sensitive trace element or spectroscopic measurements.

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

View Original Abstract

Olivine is the most abundant mineral in mantle peridotite and a typical inclusion in diamonds, providing essential evidence for the characterization of the diamondiferous lithospheric mantle. Three olivine inclusions in diamonds (OlDia) from Liaoning in the North China Craton (NCC) were exposed for in situ measurements, and the compositional data of 62 other OlDia from Liaoning were collected based on previous reports. The enrichment of TiO2 (>0.1 wt.%) with high Cr# (>50; Cr# = 100Cr/(Cr + Al) by atom) was revealed, despite the predominance of depleted TiO2 contents and high Mg# (92.8-93.2; Mg# =100Mg/(Mg + Fe) by atom) for OlDia. Silica fluid accompanying olivine still trapped in the host diamond was recognized using Raman spectroscopy. Three thermometers were applied to the OlDia, based on the data from Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Electron Probe Micro-Analysis (EPMA), and a temperature range (TLA and TEPMA) of 1080-1380 °C was yielded. With respect to the TLA, Al-in-olivine thermometers were preferred, although there was a smaller deviation between TEPMA and TLA when using the Cr-in-olivine thermometer. The results of these thermometers show a high correlation with TEPMA, enabling their application based on EPMA data. Projections onto 39-42 mW/m2 model geotherms underline a diamondiferous base of the lithospheric mantle beneath the NCC. The lithospheric mantle is characterized by refractory and depleted sections, where enrichment metasomatism may have occurred at the lower roots (161-178 km).

Tech Support

Original Source

DOI: https://doi.org/10.3390/min14090850

References

2020 - Fo and Ni Relations in Olivine Differentiate between Crystallization and Diffusion Trends
2022 - Temperature and oxygen state of kimberlite magma from the North China Craton and their implication for diamond survival [Crossref]
2020 - Study of kimberlite type diamond deposit and its metallogenic model—An example of the primary diamond deposit in the Wafangdian area of Liaoning province (In Chinese with English Abstract)
2001 - Metasomatic clinopyroxene inclusions in diamonds from the Liaoning Province, China [Crossref]
1999 - Typomorphic peculiarities and significance of mineral inclusions in diamond in Liaoning province, China
1998 - Formation of diamond with mineral inclusions of “mixed” eclogite and peridotite paragenesis [Crossref]
1994 - Characteristics of inclusions from diamond in No.50 pipe at Wafangdian, south Liaoning
2008 - The origin of cratonic diamonds—Constraints from mineral inclusions [Crossref]
2010 - Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry [Crossref]