Transformation textures in post-perovskite: Understanding mantle flow in the D '' layer of the Earth

Deformation and texture formation in (Mg, Fe)SiO3 post perovskite (ppv) is a potential explanation for the strong seismic anisotropy that is found in the D '' layer of the Earth. However, different experimental approaches have resulted in different lattice preferred orientations (LPO) in deformed ppv that have led to ambiguity in the interpretation of deformation in the lowermost mantle. Here, we show that deformation of the analogue substance CaIrO3 during a phase transformation from perovskite to ppv leads to a transformation texture that differs from the CaIrO3 ppv deformation texture but resembles the results from ppv deformation experiments in diamond anvil cells. Assuming material spreading parallel to the core-mantle boundary, our results predict a widespread shear wave splitting with fast horizontal S-waves, which is compatible with seismic studies. Downwelling material that undergoes a phase transformation may develop a transformation texture that would locally result in vertically polarized fast S-waves. Citation: Walte, N. P., F. Heidelbach, N. Miyajima, D. J. Frost, D. C. Rubie, and D. P. Dobson (2009), Transformation textures in post-perovskite: Understanding mantle flow in the D '' layer of the Earth, Geophys. Res. Lett., 36, L04302, doi: 10.1029/2008GL036840

Quantitative characterization of plastic deformation of single diamond crystals: A high pressure high temperature (HPHT) experimental deformation study combined with electron backscatter diffraction (EBSD)

We report the results of a high-pressure high-temperature (HPHT) experimental investigation into the deformation of diamonds using the D-DIA apparatus. Electron backscatter diffraction (EBSD) data confirm that well-defined 300–700 nm wide {111} slip lamellae are in fact deformation micro-twins with a 60° rotation around a axis. Such twins formed at high confining pressures even without any apparatus-induced differential stress; mechanical anisotropy within the cell assembly was sufficient for their formation with very little subsequent lattice bending ( slip system dominates as expected for the face-centred cubic (FCC) structure of diamond. Slip occurs on multiple {111} planes resulting in rotation around axes. Deformation microstructure characteristics depend on the orientation of the principal stress axes and finite strain but are independent of confining pressure and nitrogen content. All of the uniaxially deformed samples took on a brown colour, irrespective of their initial nitrogen characteristics. This is in contrast to the two quasi-hydrostatic experiments, which retained their original colour (colourless for nitrogen free diamond, yellow for single substitutional nitrogen, Type Ib diamond) despite the formation of {111} twin lamellae. Comparison of our experimental data with those from two natural brown diamonds from Finsch mine (South Africa) shows the same activation of the dominant slip system. However, no deformation twin lamellae are present in the natural samples. This difference may be due to the lower strain rates experienced by the natural samples investigated. Our study shows the applicability and potential of this type of analysis to the investigation of plastic deformation of diamonds under mantle conditions

A dual specificity kinase, DYRK1A, as a potential therapeutic target for head and neck squamous cell carcinoma

Despite advances in clinical management, 5-year survival rate in patients with late-stage head and neck squamous cell carcinoma (HNSCC) has not improved significantly over the past decade. Targeted therapies have emerged as one of the most promising approaches to treat several malignancies. Though tyrosine phosphorylation accounts for a minority of total phosphorylation, it is critical for activation of signaling pathways and plays a significant role in driving cancers. To identify activated tyrosine kinase signaling pathways in HNSCC, we compared the phosphotyrosine profiles of a panel of HNSCC cell lines to a normal oral keratinocyte cell line. Dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) was one of the kinases hyperphosphorylated at Tyr-321 in all HNSCC cell lines. Inhibition of DYRK1A resulted in an increased apoptosis and decrease in invasion and colony formation ability of HNSCC cell lines. Further, administration of the small molecular inhibitor against DYRK1A in mice bearing HNSCC xenograft tumors induced regression of tumor growth. Immunohistochemical labeling of DYRK1A in primary tumor tissues using tissue microarrays revealed strong to moderate staining of DYRK1A in 97.5% (39/40) of HNSCC tissues analyzed. Taken together our results suggest that DYRK1A could be a novel therapeutic target in HNSCC

Real-time observation of crystallization and textural evolution in magmatic systems with the moissanite cell

International audienceWe have developed a new experimental technique that allows real-time in-situ investigation of crystallization and melting processes up to 1250°C. The method uses a moissanite cell specifically designed for long-term direct observation under an optical microscope. The method was tested at moderate temperatures (300-850°C) by observing the crystallization and textural coarsening of polycrystalline salt aggregates that are analogues for silicate systems with a low to moderate surface energy anisotropy (i.e. olivine-melt, quartz-melt). The experiments show that the technique is particularly suitable for the direct investigation of processes occurring along grain boundaries on the micro-scale. A major result is the first detailed in-situ observation of coalescence between two chloride grains during static grain growth in the presence of melt. The moissanite cell also allowed for the first time the real-time observation of crystallization of a melt with basaltic-andesitic composition at both temperatures near the liquidus (ca. 1250°C) and just above the glass-transition (900°C). In these experiments the growth history of individual crystals was observed, and direct measurements of crystal growth and dissolution rates were performed. The formation of crystal clusters, and the interaction between crystals, magmatic flow and bubbles during nucleation, growth and dissolution processes were studied. Detailed texture analysis and crystal size distribution (CSD) measurements on the basaltic andesite crystallizing at 900°C provided insight on the effect of texture-modifying processes on the evolution of the CSD. In particular overgrowth and coalescence of plagioclase crystals at 900°C were observed and appear to be important in controlling the evolution of CSD. Our results show that optical in-situ observations reveal insights that are not accessible by conventional methods; thus it emphasizes the importance of in-situ experimental investigations for a correct interpretation of rock textures, and for better understanding growth and dissolution kinetics. The final textures of igneous rocks do not necessarily record the early stages of texture evolution and current models for the interpretation of CSD curves require revision

A moissanite cell apparatus for optical in situ observation of crystallizing melts at high temperature

International audienc

In-situ observations of crystal growth in a basalt melt and the development of crystal size distribution (CSD) in igneous rocks.

Igneous rocks are formed by the solidification of silicate melts. From a microscopic perspective, melt solidification is known to involve a series of physico-chemical processes, including crystal nucleation, crystal growth, Ostwald ripening, and others. A good understanding of these processes and their collective operation is therefore fundamental in deciphering magma history from rock texture. To understand the solidification processes of natural magma and the texture evolution of igneous rocks, we have studied the crystallization of a high-K basaltic melt cooling from ~1240 °C by in-situ observation in a moissanite cell. In a series of experiments with different thermal history, olivine or clinopyroxene (cpx) appeared as the liquidus phase before the formation of plagioclase. Nucleation of olivine occurred only in a narrow temperature and time interval below the liquidus. During cooling at 100 °C/hr, the morphology of olivine and cpx transited from tabular to hopper habit. To first order approximation, crystal grow rate is proportional to crystal size. This causes a counterclockwise rotation of the crystal size distribution (CSD) curves, whereas Ostwald ripening reduces the population density of the smaller crystals. Our experiments provide the first observation of proportionate crystal growth and suggest that conventional analyses of crystal size distributions of igneous rocks may be in error – the slope of the CSD cannot be interpreted in terms of a uniform growth rate and the intercept with the vertical axis does not correspond to a nucleation density. In reality, nucleation of each mineral is probably limited to a short event, which is followed by a long period of crystal growth (with growth rates proportional to crystal size) and annealing