The melting temperatures of K2CO3 were experimentally determined to be 1220 ± 20 °C (4.0 ± 0.5 GPa), 1290 ± 10 °C (9.0 ± 0.5 GPa), and 1313 ± 10 °C (11.5 ± 0.5 GPa) in a 2000 ton split–sphere apparatus and 1195 ± 15 °C (5.0 ± 0.5 GPa) in a 1000 ton uniaxial split–cylinder apparatus. The fusion curves of K2CO3 were calculated up to ~ 12.0 GPa for various K0′ (pressure dependence of bulk modulus) values of the liquid, according to the thermodynamic properties for crystalline and liquid K2CO3. On the basis of these experimental results and fusion curves of K2CO3, the K0′ for liquid K2CO3 is constrained to be ~ 14.4 ± 1.1 at pressures lower than 5.0 GPa in a third–order Birch–Murnaghan equation of state (EOS). However, the results at pressures above 9.0 GPa deviate from this trend, which suggests a possible phase transformation in either the crystalline or liquid phase of K2CO3 between 5.0 and 9.0 GPa. Determination of liquid K0′ allows the density of K2CO3 liquid to be calculated to high pressure. In comparison with other common carbonates, K2CO3 is shown to have the lowest melting temperature.
Carbon minerals in sixteen monomict ureilites which are variable in shock features in olivine were observed in situ by optical microscopy, scanning electron microscopy, X–ray powder diffraction, and Raman analyses. Euhedral blade–like shaped or amoeboid shaped graphite crystals occur in the very low–shock ureilites, not associated with diamond. In the low, medium, and high–shock ureilites, diamond occurs together with graphite. X–ray diffraction and Raman analyses reveal that crystallinity of diamond is relatively well in the low–shock ureilites, although it varies in a wide range in the high–shock ureilites. Diamond formation in the low–shock ureilites occurred as a result of solid–state catalytic transformation of graphite at a pressure lower than 10 GPa, with metallic iron as the catalyst, while diamond in the high–shock ureilites formed by spontaneous transformation of graphite together with the catalytic transformation at a pressure higher than 12 GPa. The relative crystal–axes orientations between graphite (Gr) and diamond (Di) determined by EBSD analyses in the low–shock Y–8448 ureilite is the same as that observed for graphite and diamond in a carbon grain from the high–shock Goalpara ureilite. The metallic iron catalyst promoted the sliding and puckering of the hexagonal carbon planes of graphite in the solid–state transformation processes of graphite to diamond after intercalating into its interplanar spaces. It is shown that noble gas systematics in ureilites can be matched with the shock formation origin of diamond in ureilites.
The Paleogene Mogok metamorphic belt in central Myanmar is composed mainly of high–grade metamorphic rocks from upper–amphibolite to granulite facies and younger intrusions. Ti–rich biotite grains (up to 6.9 wt% TiO2) from the Onzon and Shwe Myin Tin areas were systematically analyzed to examine the mechanisms of Ti–bearing substitutions. The Onzon and Shwe Myin Tin paragneisses are composed mainly of garnet, biotite, plagioclase, K–feldspar, quartz, ilmenite, and graphite. One of these contains cordierite porphyroblasts, which contain a spinel [Al/(Al + Fe3+ + Cr + V) = 0.97–0.99, Mg/(Mg + Fe2+) = 0.34–0.35, Zn = 0.04–0.05 atoms per formula unit (apfu) for O = 4], quartz, sillimanite, biotite, plagioclase, and ilmenite assemblage as inclusions. The Shwe Myin Tin paragneiss contains sillimanite as an inclusion in garnet. Using the garnet–biotite geothermometer and the garnet–biotite–plagioclase–quartz (GBPQ) geobarometer, the matrix assemblage indicates pressures (P) and temperatures (T) of 0.77–0.84 GPa and 780–850 °C, respectively. The coexisting spinel and quartz and the estimated P/T conditions imply a wide distribution of granulite facies metamorphic rocks in the northern part of the Mogok metamorphic belt. The high Ti content of biotite in the sillimanite–free Onzon samples is probably progressed result of the Ti□R−2 substitution, where R is the sum of divalent cations and □ represents vacancy in the octahedral sites. The biotite grains in the sillimanite–bearing Shwe Myin Tin sample showed a combination of Ti□R−2 and TiRAl−2 substitutions.
Due to a lack of rock samples from the Hadean Eon, the Hadean zircons have become an important means of understanding the Earth’s earliest history. This study reports the occurrence of a Hadean detrital zircon with a concordia U–Pb age of 4081 ± 71 Ma and 207Pb/206Pb age of 4087 ± 31 Ma from the Paleoproterozoic metasedimentary rocks in the Jiao–Liao–Ji Belt (JLJB) in the North China Craton. The analyzed zircon grain exhibits low luminescence and striped absorption and has relatively high Th/U ratio (0.37), all suggesting an igneous origin. It is euhedral with length/width ratios of 3:2, implying a short distance of transportation from its source. The Hadean age is ~ 570 million years older than the oldest zircon previously identified in the JLJB. This further demonstrates the existence of a Hadean continental crustal remnant in the North China Craton. In addition, to our knowledge, it is the first case of a Hadean zircon being recognized in the Paleoproterozoic sediments on Earth. The documentation of a 4.09 Ga detrital zircon not only provides a geochronological record of the oldest known crustal materials in the JLJB, but also identifies the geological environment for further exploration for the Hadean zircons or even the Hadean rocks.
In order to clarify cation distributions in the M1 and M2 sites of (Mg,Zn)2SiO4 olivine solid solution, 29Si MAS NMR spectroscopic measurement and first–principles NMR parameter calculation were conducted. The 29Si MAS NMR spectra of (Mg0.95Zn0.05)2SiO4 and (Mg0.90Zn0.10)2SiO4 olivine samples reveled three new peaks at relative chemical shift differences of 0.2, 1.1 and 2.3 ppm from the main peak of forsterite (−61.8 ppm). These shifts can be attributed to changes in the second–nearest–neighbors of Si due to substitution of Mg by Zn. Based on first–principles calculations, these peaks can be assigned to the following three groups of local Si environments in the order of increasing shift from the main peak of forsterite: i) Si tetrahedra with one corner–shared Zn in M1 or M2 octahedron, ii) Si tetrahedra with one edge–shared Zn in M2 octahedron, and iii) Si tetrahedra with one edge–shared Zn in M1 octahedron. Since the last two peaks are well separated from the others, the relative abundances of Zn in the M1 and M2 sites can be quantified using these peaks. Preference of Zn for M1 site over M2 site was inferred from the observed peak intensities. The present study demonstrated the usefulness of 29Si MAS NMR spectroscopy for quantitatively studying cation distributions in solid solutions.
Molecular dynamics (MD) simulations were performed to investigate the self–diffusion coefficients and density profiles of water confined between quartz (1010) surfaces at 298–573 K. The self–diffusion coefficient of water near the surface was lower than that of water far from the surface. The density profiles of H2O molecules showed several layered structures near the surface. In the thickness of 4.8 nm of H2O at 298 K, the thickness of layered structure was estimate to be 1.0 nm, and the self–diffusion coefficient was reduced in 1.0 nm distance from the surface. At 573 K, the thickness of reducing area could be larger than the thickness of layered structure of 1.5 nm. Even in higher temperature conditions such as 573 K, the self–diffusion coefficient of water near the surface was reduced.
The following is erratum for the original article entitled “Petrogenises of Triassic gabbroic and basaltic rocks from Chukotka, NE Russia: Eastern end of the ʻ arc-typeʼ Siberian LIP?” by the Daisuke Minyahl Teferi DESTA, Akira ISHIWATARI, Sumiaki MACHI, Shoji ARAI, Akihiro TAMURA, Galina V. LEDNEVA, Sergey D. SOKOLOV, Artem V. MOISEEV and Boris A. BAZYLEV (Vol. 110, no. 6, 249-275, 2015).
‘Petrogenises’ in the title should be ‘Petrogenesis’.