Amalgamation process of geological units in the Hida Belt-inferred from paleomagnetism and fission-track chronology.

1.下野本型花岗岩的裂变径迹年龄为：磷灰石39~49Ma，锆石99~172Ma，辉石121~146Ma。结合全岩等时线Rb-Sr年龄和角闪石、黑云母K-Ar年龄，表明花岗岩类在200~150 Ma时从侵入年龄开始快速冷却至300 ℃，在150 Ma时以恒定速率缓慢冷却至现今.本文测定了被认为与美浓带上希达推覆体的逆冲运动有关的横山逆冲断层规角砾岩的磷灰石和锆石裂变径迹年龄。花岗岩块体的磷灰石年龄约为40Ma。花岗岩和砂岩角砾岩的锆石年龄分别为118~125Ma和140~180Ma。这些年龄表明，逆冲断层形成时，温度上升到110 ℃和240 ℃以下，逆冲运动一直持续到古近纪中期。Simonomoto型花岗岩的古地磁方向表现为浅倾角（30 °~40 °）和不同的倾角。它们的VGP分布在一个围绕北极的小圆圈上，这意味着希达地区在它们的入侵或早期冷却阶段位于北纬20度左右。对希达边缘带及其附近晚白垩世至早第三纪火山岩的古地磁研究表明，大部分火山岩为偏东的下降流，而美浓带火山岩则为小的偏东的下降流。这些数据表明，希达带和美浓带在白垩纪以后沿希达边缘带发生了相对运动。

1. Fission-track ages of the Jurassic Shimonomoto-type granitoids are determined as follows ; apatite : 39 to 49 Ma, zircon : 99 to 172 Ma, sphene : 121 to 146 Ma. These age data conbined with whole rock isochron Rb-Sr ages and hornblende and biotite K-Ar ages imply that the granitoids were rapidly cooled to 300ﾟC from their intrusion ages at about 200 Ma to 150 Ma and were slowly cooled from 150 Ma to the present in a constant rate.2. Apatite and zircon fission-track ages of fault gauge breccia of the Yokoyama thrust which has been considered to be related to the thrust movement of the Hida Nappe on the Mino Belt, were determined. The apatite ages of granite blocks show about 40 Ma. The zircon ages of granite and sandstone breccia are 118 to 125 Ma and mixed ages from 140 to 180 Ma, respectively. These ages imply that temperatrue rised up to 110ﾟC and blow 240ﾟC during the thrust formation, and suggest that the thrust movement was continued was continued until the middle paleogene.Paleomagnetic directions of the Simonomoto-type granitoids show shallow inclination (30ﾟ to 40ﾟ) and diverse declination. Their VGP distributes on a small circle around the North Pole to imply that the Hida area was situated at around 20ﾟ N in latitude during their intrusion or early cooling stages.4. Paleomagnetic studies of Lat Crataceous to Early Paleogene volcanic rocks in and near the Hida Marginal Belt show largely easterly deflected declination, while those in the Mino Belt show that small easterly deflected declination. These data imply that ralative motion between the Hida Belt and Mino Belt occurred along the Hida Marginal Belt after the Cretaceous.