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

构造侵蚀在增生棱柱形成中的作用——以南部秩父带和四万十带为例

基本信息

批准号：
14540428
负责人：
KIMINAMI Kazuo
金额：
$ 2.18万
依托单位：
Yamaguchi University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540428/
关键词：
Chichibu Belt Shimanto Belt seamount collision greenstone volcaniclastics tectonic erosion accretionary prism 砂岩メランジ

项目摘要

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

为了阐明地形高位俯冲的地质后果以及可能与构造侵蚀密切相关的增积棱柱中年代学缺失的含义，我们进行了以下工作：来自Ashio带Kuzuu杂岩的石灰岩鹅卵石的年龄，来自南部七步带Yukagi组的绿岩的岩石学，四国西部Shimanto带南北边界地区的地质和放射虫年龄，以及来自西四国西部Shimanto带南部的火山碎屑岩的产状和岩石学。主要结果如下：1.在苦津杂岩的灰岩砾岩中发现了早期的托阿尔西期菊石，并对其意义进行了讨论。2.玄武岩的岩石学和Yukagi组的放射虫年龄指示了九州会聚边缘晚侏罗世-早白垩世海山的碰撞。3.根据岩相和沉积年龄，四国西部岛曼都超群可划分为12个构造地层单位，时代范围为桑托纪至渐新世晚期-中新世早期。晚寒武世以后，含卵石的页岩和大量砂岩碎屑以及斜坡失稳成因的页岩开始增加。上古新统砂岩主要来源于三巴川变质带。4、在四国西部Hata Pensura东岸地区的岛曼多超群中，火山角砾岩、火山砾岩、火山砂岩、泥岩等火山碎屑岩呈小块状分布，零星分布。在某些判别图上，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，使用了一些抗蚀变元素。这些数据暗示了四国西部会聚边缘晚渐新世-早中新世海山的碰撞。