Shikoku Karst, the mountainous limestone plateau extending from west to east in central Shikoku, is one of Upper Paleozoic limestone plateau in the southwest Japan outer belt. Basal greenstones, overlain by the limestone bed are composed of weakly porous pillow to massive lavas and hyaloclastites which are intercalated with thin chert and clastic sediments. Petrochemical affinity of the greenstones from Shikoku Karst with arc basalt is well exhibited by MORB normalized Nb-depleted spidergram. The greenstones from Akiyoshi-dai and Taishaku-dai, the coeval limestone plateaus in the southwest Japan inner belt, have the similar petrochemistry to seamounts or oceanic islands of intra-oceanic plate. REE abundance of the greenstones from
Shikoku Karst is evidently lower than that of Taishaku-dai and Akiyoshi-dai. Chondrite normalized patterns of the rocks from Shikoku Karst characterized by low and mild downward inclination from LREE to HREE or mild upward convex of intermediate REE are similar to that of N-MORB and/or island-arc tholeiites. Chondrite normalized patterns of the greenstones from Akiyoshi-dai and Taishaku-dai represent tholeiitic and alkaline basalts patterns of within oceanic plate. Ce_N/Yb_N to CeN relation supports the same magmatic and geotectonic interpretation mentioned above.
It is concluded that the greenstones from Shikoku Karst represent island arc related origin, and the greenstones from Taishaku-dai and Akiyoshi-dai express intra-plate seamounts or oceanic islands.

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The Kakkonda geothermal field is one of the most prominent liquid-dominated geothermal systems belong to the Sengan geothermal area in Northeast Japan. A granite pluton is confirmed at the bore holes of 1, 950-2, 770m depth, which is considered to be a possible heat source of the area. The pluton is named the Kakkonda granite. The samples examined were obtained bore holes in which temperatures over 350°C were measured. K-Ar ages of minerals of the pluton have the range from 0.068 to 0.34 Ma, which may indicate the ages subsequent passing the closure temperature of each mineral. The intrusive age of the pluton might have been older than the obtained data because of high temperatures, and might have been slightly younger than 0.7-1.0 Ma, from the relation between the ages of the adjacent Tamagawa Welded Tuffs. At any rate, obtained ages are the youngest of all the plutons heretofore reported.
Chemical composition of the Kakkonda Granite ranges from quartz diorite and tonalite of SiO₂, 65% to granite of SiO₂ 75%, and is similar to that of rocks of the adjacent older volcanoes of the age 0.5-1 Ma, but shows slight differences from that of the Tamagawa Welded Tuffs ; i. e., the former two are lower in A1₂O₃, P₂O₅ and higher in MgO contents than the Tamagawa Welded Tuffs. Major and trace element chemistry of the pluton also shows similar characteristics of that of the Pleistocene dacitic and rhyolitic pyroclastic flows from southern part of northeast Honshu, Japan.
The genetic relation between the pluton and the Tamagawa Welded Tuffs or the older volcanoes should be further studied in detail.

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