Role of tectonic erosion in formation of accretionary prism - examples from the Southern Chichibu Belt and the Shimanto Belt

为了阐明地形高俯冲的地质后果和可能与构造侵蚀密切相关的增生棱柱年代性缺失的含义，本文进行了以下工作：石尾带Kuzuu杂岩的石灰岩卵石年龄，南部Chichibu带Yukagi组绿岩的岩石学，西部Shimanto带南北边界地区的地质和放射虫年龄，以及西部Shimanto带南部火山碎屑岩的产状和岩石学。主要研究结果如下：在库祖杂岩灰岩砾岩中发现了早陶塔世的菊石，并对其意义进行了讨论。龙城组玄武岩岩石学和放射虫年龄表明晚侏罗世-早白垩世在九州辐合边缘发生了海山碰撞。四国西部石满托超群根据岩相和沉积时代可划分为12个构造地层单元，年龄范围为三东统至晚渐新世-早中新世。晚坎帕纪以后，以斜坡破坏成因的砂岩和页岩为主要碎屑的含砾页岩开始增多。上古新世砂岩主要来自三八川变质带。火山碎屑岩，如火山角砾岩、火山砾岩、火山砂岩和泥岩等，零星分布在四国西部哈塔半岛东岸的岛满托超群中。在一些抗蚀变元素的判别图上，大多数火山岩具有海山成因的板内碱性玄武岩的地球化学亲和性。这些资料暗示了晚渐新世-早中新世在四国西部辐合边缘发生过海山碰撞

The followings have been performed to clarify geologic consequences of subduction of topographic high and implication of chronological absence in accretionary prism which may have close association with tectonic erosion : age of limestone pebble from the Kuzuu Complex of the Ashio Belt, petrography of greenstones from the Yukagi Formation in the Southern Chichibu Belt, geology and radiolarian ages of the boundary area of the Northern and Southern Shimanto belts in western Shikoku, and occurrence and petrography of volcaniclastic rocks from the southern Shimanto Belt of western Shikoku. The main results are as follows.1.Early Toarcian ammonite was found from limestone conglomerate in the Kuzuu Complex, and its implication was discussed.2.Petrography of basaltic rocks and radiolarian age of the Yukagi Formation are indicative of a collision of seamount during the late Jurassic-Early Cretaceous at the convergent margin of Kyushu.3.The Shimanto Supergroup, western Shikoku, can be divided into twelve tectonostratigraphic units on the basis of lithofacies and depositional ages, and ranges in age from the Santonian to the late Oligocene-Early Miocene. Pebbly shales with large rubbles of sandstone and shale of slope-failure origin begin to increace after the Late Campanian. The sandstones from the Upper Paleocene were mainly derived from the Sanbagawa Metamorphic Belt.4.Volcaniclastic rocks such as volcanic breccia, volcanic conglomerate, volcanic sandstone and mudstone with volcanic rock gravels are found in small bodies sporadically scattered in the Shimanto Supergroup in east coast area of the Hata Peninsura, western Shikoku. Most volcanic rocks have a geochemical affinity of within-plate alkaline basalts of seamount origin on some discrimination diagrams using some alteration-resistant elements. The data are suggestive of a collision of seamount during the Late Oligocene-Early Miocene at the convergent margin of western Shikoku