10 research outputs found
Grandidierite and pseudomorphs of high quartz in \u27\u27nanogranite\u27\u27 and \u27\u27felsite inclusion\u27\u27 enclosed in garnet in granulite of the Highland Complex, central Sri Lanka
第6回極域科学シンポジウム[OG] 地圏11月16日(月) 国立極地研究所3階セミナー
Arrested charnockite formation in Southern India and Sri Lanka
Arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high-grade terrains of southern India and Sri Lanka. Two major kinds of orthopyroxene-producing reactions are recognized. Breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic/granitic "gray gneiss" produced the regional orthopyroxene isograd, manifest in charnockitic mottling and veining of "mixed-facies" exposures, as at Kabbal, Karnataka, and in the Kurunegala District of the Sri Lanka Central Highlands. Chemical and modal analyses of carefully chosen immediately-adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of CaO, MgO and FeO and gains of SiO 2 and Na 2 O. Rb and Y are depleted in the charnockite. Another kind of charnockitization is found in paragneisses throughout the southern high-grade area, and involves the reaction of biotite and quartz±garnet to produce orthopyroxene and K-feldspar. Although charnockite formation along shears and other deformation zones at such localities as Ponmudi, Kerala is highly reminiscent of Kabbal, close pair analyses are not as suggestive of open-system behavior. This type of charnockite formation is found in granulite facies areas where no prograde amphibole-bearing gneisses exist and connotes a higher-grade reaction than that of the orthopyroxene isograd. Metamorphic conditions of both Kabbaltype and Ponmudi-type localities were 700°-800° C and 5-6 kbar. Lower P(H 2 O) in the Ponmudi-type metamorphism was probably the definitive factor. CO 2 -rich fluid inclusions in quartz from the Kabbaltype localities support the concept that this type of charnockite formation was driven by influx of CO 2 from some deep-seated source. The open-system behavior and high oxidation states of the metamorphism are in accord with the CO 2 -streaming hypothesis. CO 2 -rich inclusions in graphitebearing charnockites of the Ponmudi type, however, commonly have low densities and compositions not predictable by vapor-mineral equilibrium calculations. These inclusions may have suffered post-metamorphic H 2 leakage or some systematic contamination. Neither the close-pair analyses nor the fluid inclusions strongly suggest an influx of CO 2 drove charnockite formation of the Ponmudi type. The possibility remains that orthopyroxene and CO 2 -rich fluids were produced by reaction of biotite with graphite without intervention of fluids of external origin. Further evidence, such as oxygen isotopes, is necessary to test the CO 2 -streaming hypothesis for the Ponmudi-type localities. © 1987 Springer-Verlag
Deficiency of dietary fiber modulates gut microbiota composition, neutrophil recruitment and worsens experimental colitis
Ulcerative colitis is an inflammatory disease of the colon that is associated with colonic neutrophil accumulation. Recent evidence indicates that diet alters the composition of the gut microbiota and influences host–pathogen interactions. Specifically, bacterial fermentation of dietary fiber produces metabolites called short-chain fatty acids (SCFAs), which have been shown to protect against various inflammatory diseases. However, the effect of fiber deficiency on the key initial steps of inflammation, such as leukocyte–endothelial cell interactions, is unknown. Moreover, the impact of fiber deficiency on neutrophil recruitment under basal conditions and during inflammation in vivo is unknown. Herein, we hypothesized that a fiber-deficient diet promotes an inflammatory state in the colon at baseline and predisposes the host to more severe colitis pathology. Mice fed a no-fiber diet for 14 days showed significant changes in the gut microbiota and exhibited increased neutrophil-endothelial interactions in the colonic microvasculature. Although mice fed a no-fiber diet alone did not have observable colitis-associated symptoms, these animals were highly susceptible to low dose (0.5%) dextran sodium sulphate (DSS)-induced model of colitis. Supplementation of the most abundant SCFA, acetate, prevented no-fiber diet-mediated enrichment of colonic neutrophils and colitis pathology. Therefore, dietary fiber, possibly through the actions of acetate, plays an important role in regulating neutrophil recruitment and host protection against inflammatory colonic damage in an experimental model of colitis