Diagenetic transformation of clinoptilolite to analcime in silicic tuffs of Hokkaido, Japan |
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Authors: | S Ogihara |
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Institution: | (1) Fossil Fuels and Environmental Geochemistry, Newcastle Research Group (NRG), University of Newcastle, NE1 7RU Newcastle upon Tyne, UK;(2) Present address: Geological Institute, University of Tokyo, 7-3-1-Hongo Bunkyo-ku, 113 Tokyo, Japan |
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Abstract: | Diagenetic clinoptilolite and analcime are present in the diagenesis of Tertiary marine silicic tuffs in the MITI-Toyokoro borehole, Hokkaido, Japan. Chemical analysis, SEM and petrographic observations show the mechanism of clinoptilolite to analcime transformation. Na-K clinoptilolite (Na K=6:4), an alteration product of volcanic glass, is detected at depths of 1230 to 2710m. A more Na-rich clinoptilolite (Na: K = 9:1) discovered at depths between 2590 and 2710 m is a result of a cation exchange mechanism. The formation of analcime at greater depths is due to a microdissolution-precipitation mechanism, that is Na-rich clinoptilolite dissolved and analcime precipitated as a result of increasing burial. At 2710 m analcime occurs next to the Na-rich clinoptilolite and it is assumed that the Na-rich clinoptilolite is an intermediate phase. |
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