Abstract
The chemical nature and composition of the growth medium of monocrystalline (MC) diamonds is still a matter of debate, partially because carbonate-bearing high-density fluids (HDFs) that are common in fibrous diamonds have not been found in MC diamonds. Here we report the first finding of HDF microinclusions in a MC octahedral diamond from Finsch, South Africa and in the MC octahedral core of a coated diamond from Kankan, Guinea; both diamonds carry nitrogen in B-centers.Numerous microinclusions in diamond Finsch_2a_cap1 are restricted to two thin layers parallel to the (1. 1. 1) face, ~20 and 200. μm from the diamond rim. Low-Mg carbonatitic HDFs are found along the inner layer while the outer layer trapped saline compositions. The major and trace element compositions of the inclusions and their infrared spectra are highly similar to those of microinclusions found in fibrous diamonds. A few isolated microinclusions of saline compositions are scattered around a sulfide inclusion in the center of the octahedral core of diamond ON-KAN-383.This evidence for the involvement of oxidized fluids in the formation of MC diamonds adds to previous reports on the antiquity of HDFs in fibrous diamonds, the presence of carbonate and halide phases in inclusions in MC diamonds and the similarity of trace element pattern of a MC diamond to those of low-Mg carbonatitic HDF in fibrous diamonds. In addition, we show that the interaction of HDFs with depleted garnets can produce sinusoidal REE patterns which are one of the primary features of lherzolitic and harzburgitic garnet inclusions in MC diamonds. Together, these observations suggest that HDFs are involved in the formation of many types of diamonds from the Archaean to the Phanerozoic. HDFs are trapped in large quantities during rapid, fibrous growth, but must also be present during the growth of many MC diamonds.
| Original language | English |
|---|---|
| Pages (from-to) | 145-159 |
| Number of pages | 15 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 141 |
| DOIs | |
| State | Published - 15 Sep 2014 |
| Externally published | Yes |
Bibliographical note
Funding Information:We thank Judith Millage and Bill Griffin for the Finsch sample and Jeff Harris and DeBeers for the Kankan diamond, the associate editor Chris Herd, Graham Pearson and two anonymous reviewers for their helpful comments and Bill Griffin for discussions and suggestions. ON thanks Debora Araugo, Norm Pearson and Bill Griffin for their help with the LA-ICP-MS analyses. ND thanks David Fisher and Mike Gaukroger for their help with the X-ray topography analysis. This research was supported by THE ISRAEL SCIENCE FOUNDATION (grant No. 435/12 to Oded Navon). This is LDEO contribution number 7810. Our good friend Dr. Itzhak Kiflawi was a major contributor in all aspects of this research, he died on the 12th of February 2013.
