Non-Destructive In Situ Study of Plastic Deformations in Diamonds: X-ray Diffraction Topography and µFTIR Mapping of Two Super Deep Diamond Crystals from São Luiz (Juina, Brazil)

Abstract

Diamonds from Juina, Brazil, are well-known examples of superdeep diamond crystals formed under sublithospheric conditions and evidence would indicate their origins lie as deep as the Earth's mantle transition zone and the Lower Mantle. Detailed characterization of these minerals and of inclusions trapped within them may thus provide precious minero-petrogenetic information on their growth history in these inaccessible environments. With the aim of studying non-destructively the structural defects in the entire crystalline volume, two diamond samples from this locality, labelled JUc4 and BZ270, respectively, were studied in transmission mode by means of X-ray Diffraction Topography (XRDT) and micro Fourier Transform InfraRed Spectroscopy (µFTIR). The combined use of these methods shows a good fit between the mapping of spatial distribution of extended defects observed on the topographic images and the µFTIR maps corresponding to the concentration of N and H point defects. The results obtained show that both samples are affected by plastic deformation. In particular, BZ270 shows a lower content of nitrogen and higher deformation, and actually consists of different, slightly misoriented grains that contain sub-grains with a rounded-elongated shape. These features are commonly associated with deformation processes by solid-state diffusion creep under high pressure and high temperature.

Deformation Features of Super-Deep Diamonds

“…Various zones of the crystals have traces of plastic deformations as a series of thin lines (deformation lamellae) intersecting different growth zones of the crystals. These features of the internal structure have also been detected in many previously described super-deep diamonds derived from different depth regimes [10,12,15,20,56,[64][65][66].…”

“…There is little data regarding the internal structure of super-deep diamonds. Agrosi et al [20] studied the internal structures of two super-deep diamond samples non-destructively by X-ray diffraction topography (XRDT) and micro Fourier transform infra-red spectroscopy (µFTIR). Results showed that both samples are affected by complex plastic deformation.…”

“…For sublithospheric diamonds, deformation is assumed to be much stronger than that observed in lithospheric diamonds due to greater pressure and temperature. Hence plastic deformation features of diamonds in the sublithospheric mantle may be much more complex and perhaps only distinguished by applying a combination of techniques [20]. In this work, we have studied the internal structures and deformation features of sublithospheric diamonds using multiple specific methods.…”

The Many Facets of Diamond Crystals

“…Recently, numerous investigations have been undertaken to extract and decipher this diamond message. In their contribution, Giovanna Agrosi, Gioacchino Tempesta, Giancarlo Della Ventura, Mariangella Cestelli Guidi, Mark Hutchison, Paolo Nimis, and Fabrizio Nestola studied diamond crystals from Sao Luiz (Juina, Brazil) [6]. Diamonds from Juina, Brazil, are well-known examples of superdeep diamond crystals formed under sublithospheric conditions at depths greater than 400 km [7].…”

Tracking hidden organic carbon in rocks using chemometrics and hyperspectral imaging

“…Spectroscopic techniques and especially Synchrotron-based Fourier-Transform Infrared microspectroscopy (S-FTIR) have been used in geosciences for decades 1 – 3 . S-FTIR has notably been proven efficient for determining at the micrometer scale the mineral, fluid and organic phases contained in interplanetary dust particles, meteorites and terrestrial material 4 – 10 . When characterizing samples at micrometer scale, user is tracking phases with a very limited spatial distribution and more or less low concentrations.…”