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Hydrogen isotopic composition of diamond-hosted silicates from the lithospheric mantle of the Guiana Shield
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DOI：10.1180/mgm.2026.10191.png)
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Abstract
En 中文
The hydrogen isotope composition of the mantle provides insight into the advection; melting and metasomatism of the mantle; and the Earth’s water cycle. Because of sampling challenges; most estimates for the hydrogen composition of the mantle have been derived from basaltic glasses rather than from direct samples of the mantle. We present the first direct measurement of D/H ratios in nominally anhydrous orthopyroxene and olivine inclusions hosted within diamonds. The diamond hosts were recovered from placer deposits in Guyana; South America. The diamond-hosted inclusions preserve a population with δD of –31 ± 59‰ (normalised to Vienna Standard Mean Ocean Water). This value is D-enriched relative to that expected for a homogeneous upper mantle and is similar to values measured for arc basalts. We introduce three explanations for the observed D-enrichment in the anhydrous silicate inclusions. The hydrogen isotopic composition of the mantle might simply be heterogeneous in space and/or time. The measured D-enrichment could instead preserve local heterogeneity produced by fluids genetically related to the crystallisation of the diamond hosts. Local and mantle-wide processes might also have operated in concert; and overprint each other. Diamond-hosted silicate inclusions preserve an underexplored record of Earth’s water cycle.
Keywords:
diamonds
inclusions
hydrogen isotopes
Guyana
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