International Geologiical Congress - Oslo 2008

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MPM-10 Fluids and melts in the Earth?s mantle: From natural observation to HT-HP experiment

 

Comprehension syngenetic inclusions in carbonados

 

Alexander Sukharev, Institute of geology (Russian Federation)
Maximiliano Martins, Federal University (Brazil)
Vitaly Petrovsky, Institute of geology (Russian Federation)
Valery Silaev, Institute of geology (Russian Federation)
Vasily Khitynin, Institute of geology (Russian Federation)
 

 

The urgency of researches of micropolycrystalline diamonds is defined by that, as now not only the opposite opinions on genesis carbonados are kept in all acuteness, but sometimes in general filogenetic identity and genetic affinity with monocrystalline diamonds calls into question. The object of our researches is carbonados from recent and neogene-quaternary alluvial placers of basic diamond territories of Brazil.
Gas-fluid phase of carbonado and associated minerals were studied with pyrochromatograph technique using chromatograph, equipped by pyrolytic add-on device. Gas composition was determined in the mode of two-stage (20-500 and 500-1000°C) and multi-step (20-300 and further at 100 °C) heating. In pyrolyzate carbonados obtained as a result of multistage heating, are found out (in sequence of reduction of the contents) H2O, CO, CO2, N2, H2, CH4, C4, C3, C2. During heating the structure allocated from carbonados of gases changes from CO2-water up to ÑO2-H2O-wastegaseous.
In carbonados we established more than 100 kinds of mineral inclusions. We attributed the most part of xenomineral impurities attributed to epigenetic inclusion type, among those we distinguish products of condensation of mantle-magmatic fluids (epigenetic inclusions of the first type) and exogenic mineralization, which developed during diagenesis of the diamond object on the terrestrial surface (epigenetic inclusions of the second type). We attributed syngenetic inclusions of phase-homogeneous solid solutions to those based on zircon, which prototype is possible to consider inclusion Ti-Fe-Si-Zr-Al oxides solid solutions we established earlier in the Uralian monocrystalline diamonds. Besides in carbonados us have been revealed micro-nanoscale mineral and fluid inclusions in individuals of actually diamond phase: cerianite, rutile, zircon, α-Fe (Cr), quartz, apatite, mica, Pb-Zn, communities of liquid and gas phases of not established structure, KCl, Al2O3, S, Ca-K-Fe-Ti-aluminosilicate.
The data received allow refusing from rough genetic opposition between polycrystalline and monocrystalline diamonds. It is possible, that these minerals represent only variations of products of uniform process mantle diamonformation. Researches were carried out with use SEM, TEM, spectral semiquantative and instrumental neutron-activated analyses, photoroentgenostructure, Raman spectroscopy and photo-FIB-methods (Focus ion Beam, GeoForschungsZentrum, Potsdam, Germany), gas mass-spectrometry, ESP, photo-, roentgenoluminescence and gas pirochromotography.
This work was supported by the RFBR (project 105-5-64615).

 

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