Diamond-inclusion system recording old deep lithosphere conditions at Udachnaya (Siberia)

Diamonds and their inclusions are unique fragments of deep Earth, which provide rare samples from inaccessible portions of our planet. Inclusion-free diamonds cannot provide information on depth of formation, which could be crucial to understand how the carbon cycle operated in the past. Inclusions in diamonds, which remain uncorrupted over geological times, may instead provide direct records of deep Earth’s evolution. Here, we applied elastic geothermobarometry to a diamond-magnesiochromite (mchr) host-inclusion pair from the Udachnaya kimberlite (Siberia, Russia), one of the most important sources of natural diamonds. By combining X-ray diffraction and Fourier-transform infrared spectroscopy data with a new elastic model, we obtained entrapment conditions, Ptrap = 6.5(2) GPa and Ttrap = 1125(32)–1140(33) °C, for the mchr inclusion. These conditions fall on a ca. 35 mW/m2 geotherm and are colder than the great majority of mantle xenoliths from similar depth in the same kimberlite. Our results indicate that cold cratonic conditions persisted for billions of years to at least 200 km in the local lithosphere. The composition of the mchr also indicates that at this depth the lithosphere was, at least locally, ultra-depleted at the time of diamond formation, as opposed to the melt-metasomatized, enriched composition of most xenoliths

Ecological phytochemistry of Cerrado (Brazilian savanna) plants

The Cerrado (the Brazilian savanna) is one of the vegetation formations of great biodiversity in Brazil and it has experienced strong deforestation and fragmentation. The Cerrado must contain at least 12,000 higher plant species.We discuss the ecological relevance of phytochemical studies carried out on plants from the Cerrado, including examples of phytotoxicity, antifungal, insecticidal and antibacterial activities. The results have been classified according to activity and plant family. The most active compounds have been highlighted and other activities are discussed. A large number of complex biochemical interactions occur in this system. However, only a small fraction of the species has been studied from the phytochemical viewpoint to identify the metabolites responsible for these interactions

Pressure-volume equation of state for chromite and magnesiochromite: A single-crystal X-ray diffraction investigation

The pressure-volume equation of state for the two spinel end-member compositions chromite FeCr2O4 and magnesiochromite MgCr2O4 was determined for flux-grown synthetic single crystals at room temperature up to 8.2 and 9.2 GPa, respectively, by single-crystal X-ray diffraction using a diamondanvil cell. The pressure-volume data show that the linear volume compressibility (here used only for purpose of comparison), calculated as beta(V) = vertical bar[Delta V/V-0)/Delta P]vertical bar, is 0.00468 and 0.00470 GPa(-1), for chromite and magnesiochromite, respectively, with a negligible difference below 0.5%. The experimental data were fitted to a third-order Birch-Murnaghan equation of state (BM3) allowing a simultaneous refining of the following coefficients: V-0 = 588.47(4) angstrom(3), K-T0 = 184.8(1.7) GPa, and K' = 6.1(5) for chromite and V-0 = 579.30(4) angstrom(3), K-T0 = 182.5(1.4) GPa, and K' = 5.8(4) for magnesiochromite. The difference in K-T0 is reduced to <1.5% going from Fe to Mg end-member composition, whereas the first pressure derivative seems not to be affected by the chemical variability. The limited difference in the equation of state coefficients recorded for FeCr2O4 and MgCr2O4 allowed us to fit the pressure-volume data of both to a single BM3 equation, resulting in a K-T0 = 184.4(2.2) GPa and K' = 5.7(6)