Physical properties of 61 rock sample collected from 22 outcrops of the Miyamori ultramafic complex in the Kitakami Mountains are reported in this paper. Their density, P-wave velocity, magnetic susceptibility, Curie temperature, and natural remanent magnetization were newly measured and discussed based on the petrographic data. The western part of the Miyamori ultramafic complex was intruded by an early Cretaceous granite, which thermally affected one-third of this complex.
     The characteristics of data are summarized as follows. Rock density varies from 2.56 to 3.15 g/cm³ with an average of 2.76 g/cm³ (gabroic rocks are excluded). P-wave velocity varies from 4.26 to 6.76 km/s with an average of 5.83 km/s. Magnetic susceptibility varies from 1.2 to 14.4×10⁻³ (cgsemu) and the Köigsberger ratio varies widely from 0.3 to 4.9, with ratio less than 1.1 for most of the strongly metamorphosd rocks. Curie temperature is approximately 578°C in 65 percent of the rock samples, indicating the presence of magnetite, whereas many strongly metamorphosed rocks have two Curie temperatures for hematite, magnetite and titanomagnetite. One sample have three Curie temperatures for hematite, magnetite and titanomagnetite. The declination of natural remanent magnetization of the rocks are mostly plotted in the northwest and all the inclinations plot downward. The average of inclination and declination are 50°N and 35°W, respectively. In preliminary palaeomagnetic observations by AC demagnetizations, the mean direction of 18 outcrops show the results similar to that of natural remanent magnetization (51°N, 39°W). Significant difference was not recognized between the strongly metamorphosed and the less metamorphosed rocks.
     It is evident that the decreasing tendency of rock density and P-wave velocity with increasing magnetic susceptibility was caused by serpentinization. But it is not clear when serpentinization occurred before and/or after the tectonic emplacement to the shallower level or late stage tectonic disturbance (about 500°C; Shibata et al., 1992) of the Miyamori ultramafic complex.

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The northern Shimanto belt in southeastern Tokushima prefecture contains many in-situ basaltic to andesitic greenstones which were intruded into and extruded onto Cretaceous terrigenous clastic sediments. The greenstones show varying degrees of alteration, with a range from weakly to strongly altered samples observed at single outcrops. Analyses of major and trace elements in 25 samples show that although K₂O, Rb and Ba in the more altered greenstones are strongly depleted, original abundances of total alkalis (Na₂O+K₂O) and the remaining elements are retained. The greenstones are classified into three groups: (1) high-P₂O₅ alkaline rocks, (2) high-Ce alkaline rocks and (3) low-Ce alkaline rocks and high-alkali tholeiites. On MORB-normalized spidergrams all samples show the high LILE/HFSE ratios and distinct negative Nb anomalies characteristic of subduction related magmas.
     Cretaceous in-situ greenstones also occur in the Naze Formation on Amami Island. They consist of both intraplate and subduction-zone alkaline types, along with high-alkali tholeiites (Yoshida et al., 1994). These magmatic suites are similar to Miocene igneous complexes located in the southernmost part of the outer zone of Southwest Japan which formed on a structural high in a forearc basin. High alkali contents of the greenstones indicate that the primitive magma from which they were derived were segregated from relatively deep mantle (>50-70 km) in a subduction-zone. Our results suggest that the in-situ greenstones were formed by igneous activity on the Cretaceous forearc structural high in a Ryukyu-type subduction zone.

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