K-Ar, Rb-Sr and fission-track age determinations were carried out on rocks along the Median Tectonic Line (MTL) in the Kayumi area, Mie Prefecture. K-Ar ages on the Ryoke granitic rocks range from 44.1 to 84.3 Ma. Within about 1000m of MTL, the ages for K-feldspars and biotites decrease toward MTL, probably caused by the hydrothermal alteration associated with cataclasis, whereas the ages for homblendes increase toward MTL. The cooling rate of the granitic rocks, calculated from K-Ar ages and closure temperatures of minerals, is 31-56°C/Ma.
K-Ar ages for muscovites from pelitic schists in the Sanbagawa belt are 73.6-75.6 Ma; decrease in age is not observed even near MTL. Rb-Sr ages for muscovites from the schists are 72.2-77.5 Ma, nearly the same as the K-Ar ages. These age data are assumed to indicate the time of maximum temperature for the Sanbagawa schists in this area.
Fission track ages for zircons from the Ryoke granitic rocks range from 52.4 to 59.5 Ma, approximating to K-Ar ages of K-feldspars for the same rocks. Fission-track ages for zircons from the Sanbagawa schists are 59.0 and 61.2 Ma, nearly 15 Ma younger than the K-Ar ages of muscovite for the same rocks.
The fine fractions (<2μm) separated from MTL fault gouges at the Nishitani River and Kayumi give K-Ar ages of 41.8 and 51.4 Ma, respectively. The former age probably represents the time of hydrothermal alteration following the major fault movement of MTL associated with cataclasis.

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Carbonaceous material in pelitic rocks and limestones of the Ayukawa and the Daioin Formations in the Hitachi metamorphic rocks was investigated by means of X-ray powder diffraction technique. Carbonaceous material in these metasediments was graphitized under the conditions of greenschist facies. rystallite thickness L_c (002) ranges from 29 to 170 Å in the Ayukawa Formation and that from 120 to 300 Å in the Daioin Formation.
L_c (002) of carbonaceous material in pelitic rocks containing biotite is more than 60 Å and increases with increasing metamorphic grade. L_c (002) value at a boundary between greenschist and epidote-amphibolite facies may be estimated 260-300 Å from the data of L_c (002) of the lower part of the Daioin Formation.
L_c (002) of the Ayukawa Formation surrounding the sheared granite is above 200 Å. As compared with the general value of the Daioin Formation, L_c (002) of the Daioin Formation around the sheared granite is not so high. Thermal effect of the sheared granite was not marked, which suggests that the sheared granite intruded under low temperature condition.

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Accretionary lapilli show two types of occurrence in pyroclastic flow deposits-those fill steam pipes (INSIDE PIPE) and those occurring in the pyroclastic flow deposits not containing pipes (OUTSIDE PIPE). The host pyroclastic flow deposits with pipes contain much less lapilli than those without having pipes. The measurements of diameter, porosity and bulk density of lapilli, as well as the observation of the internal structure revealed no difference between accretionary lapilli of INSIDE PIPE and OUTSIDE PIPE. Thus lapilli of both occurrences were formed by the same process, i.e. by volcanic hailstone.
Whereas pyroclastic materials including pumice and lithic fragments are found in all the directions from the Aira caldera, accretionary lapilli are found only in the southeast region of the caldera. This difference results from different modes of transportation; the pumice and lithic fragments were controlled by the flows, whereas accretionary lapilli were strongly affected by the wind, as they form in high-altitude.

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