Projects per year
Abstract
Fluid inclusions trapped in fast-growing diamonds provide a unique
opportunity to examine the origin of diamonds, and the conditions under
which they formed. Eclogitic to websteritic diamondites from southern
Africa show 13C-depletion and 15N-enrichment relative to mantle values (δ13C = -4.3 to -22.2 ‰ and δ15N = -4.9 to +23.2 ‰). In contrast the 3He/4He
of the trapped fluids have a strong mantle signature, one sample has
the highest value so far recorded for African diamonds (8.5 ± 0.4 Ra).
We find no evidence for deep mantle He in these diamondites, or indeed
in any diamonds from southern Africa. A correlation between 3He/4He ratios and 3He concentration suggests that the low 3He/4He are largely the result of ingrowth of radiogenic 4He
in the trapped fluids since diamond formation. The He-C-N isotope
systematics can be best described by mixing between fluid released from
subducted altered oceanic crust and mantle volatiles. The high 3He/4He of low δ13C diamondites reflects the high 3He concentration in the mantle fluids relative to the slab-derived fluids. The presence of post-crystallisation 4He in the fluids means that all 3He/4He
are minima, which in turn implies that the slab-derived carbon has a
sedimentary organic origin. In short, although carbon and nitrogen
stable isotope data show strong evidence for crustal sources for
diamond-formation, helium isotopes reveal an unambiguous mantle
component hidden within a strongly 13C-depleted system.
Original language | English |
---|---|
Pages (from-to) | 39-43 |
Journal | Geochemical Perspectives Letters |
Volume | 11 |
DOIs | |
Publication status | Published - 10 Oct 2019 |
Keywords
- Diamond
- Volatiles
- Nobel gases
- Stable isotopes
- Deep carbon cycle
Fingerprint
Dive into the research topics of 'A secretive mechanical exchange between mantle and crustal volatiles revealed by helium isotopes in 13C-depleted diamonds'. Together they form a unique fingerprint.Projects
- 1 Finished
-
The Nature of the Deep Nitrogen Cycle: The nature of the deep nitrogen cycle
Mikhail, S. (PI)
1/06/17 → 4/09/20
Project: Standard
Profiles
-
Sami Mikhail
- School of Earth & Environmental Sciences - Reader
- St Andrews Centre for Exoplanet Science - Board Member
- St Andrews Isotope Geochemistry
Person: Academic
-
A genetic metasomatic link between eclogitic and peridotitic diamond inclusions
Mikhail, S., Rinaldi, M., Mare, E. R. & Sverjensky, D., 24 Mar 2021, In: Geochemical Perspectives Letters. 17, p. 33-38Research output: Contribution to journal › Article › peer-review
Open AccessFile -
Deep Earth carbon reactions through time and space
McCammon, C., Bureau, H., Cleaves II, H. J., Cottrell, E., Dorfman, S. M., Kellogg, L. H., Li, J., Mikhail, S., Moussallam, Y., Sanloup, C., Thomson, A. R. & Brovarone, A. V., 2 Jan 2020, In: American Mineralogist. 105, 1, p. 22-27 6 p.Research output: Contribution to journal › Special issue › peer-review
Open AccessFile -
Editorial: deep carbon science
Cardace, D., Bower, D., Daniel, I., Ionescu, A., Mikhail, S., Pistone, M. & Zahirovic, S., 12 Nov 2020, In: Frontiers in Earth Science. 8, 611295.Research output: Contribution to journal › Editorial › peer-review
Open AccessFile