Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XX, Nos.2-3


Rodingites from the Kamuikotan Tectonic Belt, Hokkaido

Katoh, Takayuki;Niida, Kiyoaki

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A large number of rodingites were found in and around serpentinite masses of the Kamuikotan Tectonic Belt. The original rocks of the rodingite were also found. They are microdiorite-microgabbro, olivine clinopyroxenite, and slate. Reaction zones between the serpentinite and the original rock are divided into two zones; one is rodingite zone composed mainly of diopside, hydrogrossular, wollastonite, chlorite, prehnite, and tremolite, and the other is chlorite zone which contains large amounts of chlorite. The rodingites are characterized by the higher contents of CaO, Al2O3, TiO2, and H2O and the lower contents of SiO2, Na2O and K2O than those in the original rocks. Compositional variation observed in the reaction zones suggests that the rodingites were formed through the following metasomatic process; (1) Ca, Al, Ti, and H2O migrated from serpentinite into the reaction zone, (2) Si and alkali moved from the original rock towards serpentinite through the reaction zone, and (3) a considerable amount of Mg, Fe, and Mn as well as Ca, Al, Ti, and H2O fixed within the chlorite zone. On the basis of hydrothermal experiments on stability ranges of xonotlite-wollastonite, vesuvianite, diopside, and hydrogrossular, most of the rodingites from the Kamuikotan Tectonic Belt are considered to have been formed at the temperature higher than 350℃.