Geo-electromagnetic deep structure of old plate boundary-the Hidaka and Kamuikotan belts-

沿着日中变质带和日本神山变质带、老板块边界的3条剖面进行了宽带大地电磁研究，获得了以下结果：东中-神东变质带南段(东中剖面)I-1。浅层电阻率结构与地表地质关系良好：导电的Sorachi-Yezo地层(10欧姆)和电阻性东高变质带(1000欧米)。I-2。古大洋板块(侏罗纪圈闭的大洋板块)被检测为索拉奇-耶佐组的阻性基底。I-3。Kamuikotan带以西的沉积物比Shibetsu剖面的沉积物厚得多，前者厚10公里，后者厚3公里。这一差异表明，北海道与千岛弧自中新世以来的碰撞形成了东高-龟山带南部的深部前渊。I-4。东高山脉下方有向东倾斜的导体和俯冲的楔形阻尼器。倾斜导线与地震低速、低Q异常相吻合。II.东高-神木带北段(石贝图剖面)II-1。浅层电阻率结构一般与日中剖面的电阻率结构相同。II-2。在该剖面下观察到了向西倾斜的导电层，表明库拉板块存在大洋沉积层。III.什贝图剖面(鲁贝希贝剖面)向东延伸的部分，尽管即使在本区地壳更深的地方，电阻率结构也是复杂的，但结构有向东倾斜的趋势。因此，可以对库拉板块向东俯冲鄂霍次克地块的白垩纪进行成像。

Broad-band magnetotelluric investigations were made along 3 profiles across the Hidaka and Kamuikotan metamorphic belts, old plate boundary, and the following results were obtained.I. Southern part of the Hidaka-Kamuikotan belts (Hidaka profile) I-1. Shallow resistivity structure is well collerated with the surface geology: the conductive Sorachi-Yezo formations ((] SY.simeq.[) 10 ohm m) and the resistive Hidaka metamorphic belt ((] SY.simeq.[) 1000 ohm m). I-2. Old oceanic plate (trapped oceanic plate in the Jurassic) was detected as a resistive basements of the Sorachi-Yezo formations. I-3. The sediment to the west of the Kamuikotan belt is significantly thicker ((] SY.simeq.[)10 km) than that of the Shibetsu profile ((] SY.simeq.[) 3 km). This difference implies that the deep foredeep is created in the southern part of the Hidaka-Kamuikotan belts by the collision of Hokkaido and the Kurile arc since the Miocene time. I-4. There is eastward dipping conductor and overriding wedge-shape resister beneath the Hidaka mountains. The dipping conductor is consistent with the seismic low velocity and low Q anomaly.II. Northern part of the Hidaka-Kamuikotan belts (Shibetsu profile) II-1. Resistivity structure at shallow depth is generally common with that of Hidaka profile. II-2. Beneath this profile, westward dipping conductive layer was observed, suggesting the existence of the oceanic sedimentary lyer on the Kula plate.III. Eastwardly extended part of the Shibetsu profile (Rubeshibe profile) Although the resistivity structure is complex even at deeper crust of this region, the structure is tend to dip eastwardly. Therefore, the Cretaceous eastward subduction of the Kula plate against the Okhotsk block can be imaged.