Geotraverses of the Japanese Islands

日本领土的地理导线日本群岛分为两个主要的地质省份，日本东北部和日本西南部。这两个省都是由许多构造地体组成的。如果不了解这些地体，就不能很好地了解日本群岛复杂的地质史。本研究的目的是通过在日本群岛从北海道到冲绳的许多地区的大地导线来研究这些地体的地体内部和地体间的关系以及地层、沉积学、年代学和变质特征，并概述古生代到新生代的地质演化。作为这项研究的结果，获得了以下几条新的证据。在希达地体的中部，所谓的前寒武纪灰色花岗岩以脉状和脉状产出，切割着希达片麻岩。通过对灰色闪长岩中独居石和锆石的钟声年龄进行详细的年代学研究，揭示其侵入于三叠纪早三叠世(约240 Ma)。不是在前寒武纪时代。南北卡米地体石炭纪伊利卡米花岗岩中独居石和锆石颗粒的嵌合年龄数据表明，花岗岩中许多锆石晶体的瓦缘中也记录了约250 Ma的热事件。日本东北部和西南部最近的二叠纪磁化作用似乎比人们所认为的要广泛得多。最古老的放射性年龄是Kamiaso砾岩中石英长石片麻岩的2050 Ma Rb-Sr全岩等时线年龄(最初是1985 Ma，用目前公认的衰减常数重新计算)。米诺地体中石英长片麻岩碎屑和砂岩中的独居石的钟声年龄也约为1700~1400 Ma，表明中前寒武纪岩石在经典岩石的物源中分布广泛。

Geotraverses of the Japanese IiandsThe Japanese Islands are divided into two principal geologic provinces, Northeast Japan and Southwest Japan. Both provinces are composed of many tectonostratigraphic terrenes. Without knowledge of these terrenes, the complex geological history of the Japanese Islands can not be properly understood.The purpose of this study is to examine intra- and inter-terrene relations as well as stratigraphic, sedimentological, geochronological and metamorphic characteristics of these terrenes through geotraverses in many regions in the Japanese Islands, from Hokkaido to Okinawa, and to overview the Paleozoic to Cenozoic geologic evolution.As a result of this study, the following lines of new evidence were obtained.(1). In the central part of the Hida terrene the so-called Precambrian Gray Granite occurs as veins and dikes cutting the Hida gneiss. The detailed geochronological studies on the basis of CHIME ages of monazites and zircons from the Gray, franite have revealed that it intruded into the Hida gneiss in early Triassic time (ca. 240 Ma). not in Precambrian time.(2). CHIME age data of monazite and zircon grains from the Carboniferous llikami granite in the Soutil Kitakami terrene have shown that the ca. 250 Ma thermal event is also recorded in tile rims of many zircon crystals in the granite. It seems probable that the latest Permian magnatism was much more extensive both in Northeast Japan and Southwest Japan than has been thought.(3). The oldest radiometric date is a 2050 Ma Rb-Sr whole-rock isochron age (originally 1985 Ma, it was recalculated using the currently-accepted decay constant) for quartzo-feldspathic gneisses in the Kamiaso conglomerate. CHIME ages of monazites in quartzo-feldspathic gneiss clasts and sandstones in the Mino terrene also give ca. 1700-1400 Ma, showing that the middle Precambrian rocks were widespread in the provenance of the classic rocks.