Genesis of Diamond in Metal–Carbon and Metal–Sulfur–Carbon Melts: Evidence from Experimental Data

Doklady Earth Sciences - The experimental data on diamond growth in the Fe–Ni–S–C and Fe–S–C systems with a sulfur content of 5–14 wt % at 5.5 GPa and...     

Morphological Features of Diamond Crystals Dissolved in Fe<Subscript>0.7</Subscript>S<Subscript>0.3</Subscript> Melt at 4 GPa and 1400°C

An experimental study of the dissolution of natural and synthetic diamonds in a sulfur-bearing iron melt (Fe_0.7S_0.3) with high P–T parameters (4 GPa, 1400°С) was performed. The results demonstrated that under these conditions, octahedral crystals with flat faces and rounded tetrahexahedral diamond crystals are transformed into rounded octahedroids, which have morphological characteristics similar to those of natural diamonds from kimberlite. It was suggested that, taking into account the complex history of individual natural diamond crystals, including the dissolution stages, sulfur-bearing metal melts up to sulfide melts were not only diamond-forming media during the early evolution of the Earth, but also natural solvents of diamond in the mantle environment before the formation of kimberlitic melts.     

Morphology of Crystals Growing in Impact Diamonds of the Popigai Astrobleme (Experimental Data)

Doklady Earth Sciences - Experimental results on the growth of cubic diamond on lonsdaleite-bearing diamonds from the Popigai astrobleme at 5.5 GPa and 1450°C in the Fe–Ni–C system...     

Inclusions of metal solvent and color of boron-bearing monocrystals of synthetic diamond

Cuboctahedral diamond monocrystals of physical classification type IIb weighing from 0.1 to 2 carats and with minor faces {110}, {311}, and {511} have been synthesized. The crystals are characterized by various hues of blue and dark blue depending on the amount of B in the system. A characteristic feature of these diamonds is a sectorial structure expressed in a nonuniform color distribution. The following types of metallic inclusions in the crystals have been recognized: faceted isometric, lamellar, and extended inclusions; unfaceted irregular and drop-shaped inclusions; and microinclusions. These inclusions are related to the chemical composition of the metal solvent.     

Problem of water in the upper mantle: Antigorite breakdown

Doklady Earth Sciences -     

Late Precambrian Metamorphic Complexes of the Ulutau Massif (Central Kazakhstan): Age,Composition, and Formation Settings of Protoliths

Geotectonics - This work presents the results of a study of metamorphic rocks of the Bekturgan and Balazhezdy groups of the Precambrian Ulutau massif (Central Kazakhstan), which have been...     

On the formation of element carbon during decomposition of CaCO3 at High P-T parameters under reducing conditions

This work presents data on the experimental study of CaCO₃ stability (3.0–5.5 GPa; 1300–1400°C) under reducing conditions modeling the presence of metallic iron. It is established that CaCO₃ is stable at the above P-T parameters under reducing conditions (in the presence of metallic Ti). CaCO₃ decomposed only when it chemically interacted with iron, forming Ca-ferrites and releasing solid carbon in the form of graphite in the closed system (in sealed Pt-ampoules).     

The stability of ortho- and clinopyroxenes,olivine, and garnet in kimberlitic magma

It is generally accepted that the composition of ultrabasic nodules and their quantitative proportions do not significantly change during their transportation with kimberlitic magma to the Earth’s surface. We performed an experimental study of the relative stability of olivine, garnet, and pyroxenes in kimberlite melt at high pressure and temperatures (4 GPa, 1300–1500 °C). The study has shown that the loss in weight of minerals and, correspondingly, the rate of their dissolution in kimberlite melt differ considerably. The following sequence of the dissolution rates of minerals has been established: Cpx ≥ Opx > Gar > Ol. Pyroxenes are characterized by the most rapid dissolution, and olivine is the most stable mineral. The assumption is made that clinopyroxenites and websterites disintegrate more rapidly than dunites and lherzolites in kimberlitic magma.