The occurrence and distribution of Mo and molybdenite in unaltered peralkaline rhyolites from Pantelleria, Italy
Article Abstract:
Molybdenite platelets in phenocrysts and matrix glass in unchanged felsic volcanic rocks often occur in pantellerites (peralkaline rhyolites), seldom occur in pantelleritic trachytes, and are absent in trachytes. The presence of MoS2 platelets in phenocryst phases, in matrix glass and in some melt inclusions implies the direct precipitation of MoS2 from the peralkaline melt. The presence of Molybdenum (Mo) is lower than in matrix glass, and its variation is in proportion to the presence of phenocryst. A decrease in the temperature during magmatic differentiation results in the precipitation of MoS2. The high Mo content and low redox state in the pantellerites corresponding to metaluminous magmas results in MoS2 saturation at magmatic temperatures.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1993
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Volatile characteristics of peralkaline rhyolites from Kenya: an ion microprobe, infrared spectroscopic and hydrogen isotope study
Article Abstract:
The examination of the pre-eruptive and the post-eruptive water content of mildly peralkaline rhyolites of the Greater Olkaria Volcanic Complex, Kenya Rift Valley, reveals the amounts of degassing, the closed versus open system of degassing behavior and the role of flourine in influencing the speciation of water dissolved in the magma. The pre-eruptive and the post eruptive water contents shows low degassing before and during eruption. With the increase in flourine content and peralkalinity, there is an increase in the amount of molecular water, which reveals a competition between fluoride ions and hydroxyl groups for sites which are alike within the melt structure.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1993
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FTIR micro-reflectance measurements of the CO(super 2-)(sub 3) ion content in basanite and leucitite glasses
Article Abstract:
Fourier transform infrared (FTIR) micro-reflectance spectroscopy is an accurate, rapid and non-destructive method for the determination of the carbonate content of basanite and leucitite glasses. The method requires a single polished glass surface, while sample thickness measurements are unnecessary. The contribution of the IR beam resonance, due to the carbonate molecules, to the total IR reflectance is a measure of the carbonate content. Secondary ion mass spectrometry is used to calibrate the results. The results are similar to those obtained from transmission studies.
Publication Name: Contributions to Mineralogy and Petrology
Subject: Earth sciences
ISSN: 0010-7999
Year: 1996
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