The investigation of multiphase inclusions trapped within super-deep diamonds provides extremely important petrogenetic information from depths into the lower mantle (e.g., Palot et al., 2016, Smith et al., 2016). Methods commonly used to investigate these inclusions require cutting, crushing or ion/laser ablating the diamond host to expose inclusions for conventional and/or non-conventional geochemical analyses. These methods, however, can introduce significant artefacts and contaminations, especially on metallic inclusions or iron carbides. Non-destructive, in situ investigation of inclusions still trapped in their diamond host, is thus the only way to obtain, without ambiguities, information about diamond formation. With this aim, we studied a sample (JUc4) of inferred super-deep origin from São Luiz (Juina, Brazil) by using a multi-methodological approach. The inclusions still trapped within the diamond host were investigated by micro-computed X-ray tomography (mCXRT), micro X-ray fluorescence (mXRF), micro-Raman and Infrared (FTIR) spectroscopies. The structural defects were also investigated by X-ray topography (XRDT) (Agrosì et al., 2016). The diamond sample exhibits an irregular morphology, a light-brown colour and five optically opaque large inclusions from 100 to 300 μm in diameter. XRDT images show a clear plastic deformation. Micro-chemical maps, obtained by mXRF, show a high Fe content for all the inclusions; the identification of ferropericlase as a constituent was later confirmed by micro-destructive Laser Induced Breakdown Spectroscopy (μLIBS). One inclusion is different from the others because it exhibits a flask shape and a clear multiphase nature, as indicated by detailed mCXRT reconstruction. FTIR maps show a concentric zoning of N defects and this inclusion appears to be located near the center of diamond growth. Part of this inclusion consists of ferropericlase, as confirmed by non-destructive micro- X-Ray Diffraction. μ-Raman and FTIR investigations on this inclusion reveal also the presence of carbonates and pseudo-amorphous carbon. In particular, μ-Raman maps obtained reveal the typical large D and G bands corresponding to pseudo-amorphous graphite. The FTIR spectra show a doublet at 1430-1440 cm-1 corresponding to the presence of carbonates, suggesting a genesis of this diamond in a carbonate-rich system. No Raman or FTIR evidences for OH- or CH4 were observed.
Non-destructive in situ analysis of multiphase inclusions in a super-deep diamond
Agrosì G.
;Tempesta G.;Mele D.;Della Ventura G.;Mangone A.;Caggiani M. C.;Allegretta I.;
2017-01-01
Abstract
The investigation of multiphase inclusions trapped within super-deep diamonds provides extremely important petrogenetic information from depths into the lower mantle (e.g., Palot et al., 2016, Smith et al., 2016). Methods commonly used to investigate these inclusions require cutting, crushing or ion/laser ablating the diamond host to expose inclusions for conventional and/or non-conventional geochemical analyses. These methods, however, can introduce significant artefacts and contaminations, especially on metallic inclusions or iron carbides. Non-destructive, in situ investigation of inclusions still trapped in their diamond host, is thus the only way to obtain, without ambiguities, information about diamond formation. With this aim, we studied a sample (JUc4) of inferred super-deep origin from São Luiz (Juina, Brazil) by using a multi-methodological approach. The inclusions still trapped within the diamond host were investigated by micro-computed X-ray tomography (mCXRT), micro X-ray fluorescence (mXRF), micro-Raman and Infrared (FTIR) spectroscopies. The structural defects were also investigated by X-ray topography (XRDT) (Agrosì et al., 2016). The diamond sample exhibits an irregular morphology, a light-brown colour and five optically opaque large inclusions from 100 to 300 μm in diameter. XRDT images show a clear plastic deformation. Micro-chemical maps, obtained by mXRF, show a high Fe content for all the inclusions; the identification of ferropericlase as a constituent was later confirmed by micro-destructive Laser Induced Breakdown Spectroscopy (μLIBS). One inclusion is different from the others because it exhibits a flask shape and a clear multiphase nature, as indicated by detailed mCXRT reconstruction. FTIR maps show a concentric zoning of N defects and this inclusion appears to be located near the center of diamond growth. Part of this inclusion consists of ferropericlase, as confirmed by non-destructive micro- X-Ray Diffraction. μ-Raman and FTIR investigations on this inclusion reveal also the presence of carbonates and pseudo-amorphous carbon. In particular, μ-Raman maps obtained reveal the typical large D and G bands corresponding to pseudo-amorphous graphite. The FTIR spectra show a doublet at 1430-1440 cm-1 corresponding to the presence of carbonates, suggesting a genesis of this diamond in a carbonate-rich system. No Raman or FTIR evidences for OH- or CH4 were observed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
