Mineral Inclusions in Lithospheric Diamonds

Stachel, Thomas; Aulbach, Sonja; Harris, Jeffrey W.

doi:10.2138/rmg.2022.88.06

Cited by 49 publications

(29 citation statements)

References 315 publications

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“…Irrespective of the nature of the inclusions and the thermobarometric methods used, the frequency distribution of pressures for lithospheric diamond is essentially unimodal, with a mode at ~6 GPa, corresponding to depths around ~190 km (Fig. 8; see also Stachel andHarris 2008 andStachel 2014 for broadly similar distributions obtained using different thermobarometers and partly different datasets). The slight differences between the pressure distributions obtained for clinopyroxene and orthopyroxene-garnet inclusions may largely be ascribed to recognized inconsistencies between the different thermobarometer combinations used and, perhaps, to sampling bias.…”

Section: Lithospheric Diamondsmentioning

confidence: 88%

“…Early reviews of P-T distributions for lithospheric diamonds were made by Nimis (2002), based on thermobarometry of chromian diopside inclusions, and by Stachel and Harris (2008) and Stachel (2014), using a more comprehensive set of thermobarometers. More recently, Nimis et al (2020) investigated diamond depth distributions for a set of South African kimberlites and provided evidence for systematic trends of likely global significance.…”

Section: Introductionmentioning

confidence: 99%

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Pressure and Temperature Data for Diamonds

Nimis

2022

Reviews in Mineralogy and Geochemistry

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Section: Lithospheric Diamondsmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Pressure and Temperature Data for Diamonds

Nimis

2022

Reviews in Mineralogy and Geochemistry

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“…The major geological varieties defined by inclusion mineralogy are shown in table 1. These represent diamonds from the lithospheric mantle, formed at approximately 150-200 km, and exclude the rarer (<2%) sublithospheric or "superdeep" varieties of diamonds (Smith et al, 2017;Stachel et al, 2022a).…”

Section: Diamond Formation and Its Geological Frameworkmentioning

confidence: 99%

“…The most common geological varieties of diamond on the basis of mineral inclusions, modified fromStachel et al (2022a).…”

mentioning

confidence: 99%

Methods and Challenges of Establishing the Geographic Origin of Diamonds

Smith¹,

Smit²,

Shirey³

2022

G&G

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ome famous diamonds, such as the Hope, the Cullinan, and the 404.2 ct "4 de Fevereiro" diamond in figure 1, have high-profile histories that include their geographic provenance. Other dia-monds with a known origin can occasionally be sourced in the marketplace or directly from miners. But for the majority of diamonds, this information is not preserved, instead becoming obscured as they move through the supply chain. To some extent, diamond provenance has not been seen as a valuable piece of information and is not presented as a relevant pricing factor the way it sometimes is for some other gemstones. Rough diamonds are typically bought and sold in lots or parcels based on physical characteristics, including color, clarity, size, and morphology. In assembling these parcels, it is common practice to mix diamonds of similar character from different mines. Faceted diamonds are sold mainly on the basis of the 4Cs (color, cut, clarity, and carat weight) and may be mixed further.Beyond the historical or scientific interest in provenance, several recent developments have put dia mond origin at the forefront of conversations in the industry and among consumers. Initially, this was driven by a need to track conflict diamonds and prevent their entrance into the trade. Now, with mount-

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“…sub-lithospheric) (e.g. Kaminsky et al, 2001;Stachel and Harris, 2008;Shirey et al, 2013;Stachel et al, 2022). Once trapped in their diamond hosts, these inclusions remain uncorrupted over geological time and represent key geological samples from otherwise inaccessible regions of our planet.…”

Section: Introductionmentioning

confidence: 99%

Relatively oxidized conditions for diamond formation at Udachnaya (Siberia)

et al. 2022

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Abstract. Thanks to the physical strength of diamonds and their relatively unreactive chemical nature, their mineral inclusions may remain exceptionally preserved from alteration processes and chemical exchanges with surrounding minerals, fluids and/or melts following diamond formation. Cr-bearing spinels are relatively common inclusions found in peridotitic diamonds and important oxybarometers providing information about the oxygen fugacity (fO2) of their source mantle rocks. Here, we investigated a magnesiochromite–olivine touching pair in a diamond from the Udachnaya kimberlite (Siberia) by in situ single-crystal X-ray diffraction and energy-domain synchrotron Mössbauer spectroscopy, aiming to constrain the physical–chemical conditions of diamond formation and to explore the redox state of this portion of the Siberian craton when the diamond was formed. The P–T–fO2 entrapment conditions of the inclusion pair, determined by thermo- and oxybarometric analyses, are ∼ 5.7(0.4) GPa and ∼ 1015(50) ∘C (although entrapment at higher T and re-equilibration during subsequent mantle storage are also possible) and fO2 near the enstatite–magnesite–olivine–diamond (EMOD) buffer. The determined fO2 is similar to, or slightly more oxidized than, those of xenoliths from Udachnaya, but whilst the xenoliths last equilibrated with the surrounding mantle just prior to their entrainment in the kimberlite at ∼ 360 Ma, the last equilibration of the inclusion pair is much older, occurring at 3.5–3.1, ∼ 2 or ∼ 1.8 Ga before final encapsulation in its host diamond. Hence, the similarity between xenoliths and inclusion fO2 values indicates that the modern redox state of this portion of the Siberian lithosphere was likely attained relatively early after its formation and may have persisted for billions of years after diamond formation, at least at the local scale. Moreover, the oxygen fugacity determination for the inclusion pair provides direct evidence of diamond formation near the EMOD buffer and is consistent with recent models suggesting relatively oxidized, water-rich CHO fluids as the most likely parents for lithospheric diamonds.

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Mineral Inclusions in Lithospheric Diamonds

Abstract: Notes: * Refers to a mineral inclusion where an original structure is inferred. See text for most of the epigenetic mineralogy.

Cited by 49 publications

References 315 publications

Pressure and Temperature Data for Diamonds

Pressure and Temperature Data for Diamonds

Methods and Challenges of Establishing the Geographic Origin of Diamonds

Relatively oxidized conditions for diamond formation at Udachnaya (Siberia)

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