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Effects of ridge collision on accretionary complex - An example of eastern Shikoku

山脊碰撞对增生杂岩的影响——以四国东部为例

基本信息

批准号：
06640584
负责人：
KIMINAMI Kazuo
金额：
$ 1.34万
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：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

The research was performed on the Upper Cretaceous Shimanto Supergroup from Ryukyu Islands to eastern Shikoku. The following summary of the research results is obtained.1. Instrusion of basaltic rocks into unconsolidated terrigenous sediments induceced enrichment of SiO2 and CaO,and decrease of K2O in the altered part of sediments.2. Organic metamorphism in the makimine Formation, eastern Kyushu, was studied by means of vitrinite refrectance. This study has revealed that intrusion of basaltic rock has affected thermal effects on argillaceous sediments in a trench area.3. Tectono-stratigraphic variations in chemical compositions of the sandstones in eastern Shikoku define three petrofacies (I,II and III) arranged from north to south.4. The Cretaceous Shimanto sandstones in eastern Shikoku become more acidic with time. This trend is in harmony with that of the Cretaceous volcanic rocks in the western Chugoku District.5. During the latest Cretaceous, the western Chugoku District was widely covered by rhyolitic rocks and supplied a large amount of coarse-grained clastic sediment into the trench area just before ridge collision, resulting in the accretion of tectonically-repeated thick sequences of turbidites such as Hiwasa Formation in eastern Shikoku.6. The Oboke psammitic schists are inferred to be metamorphic equivalent of sandstones in the Hiwasa Formation, deposited in a trench area during the Campanian, in eastern Shikoku.7. Accumulation of a large amount of coarse-grained clastic sediment in the trench area during the Campanian induced offscraping and underplating in the subduction zone, forming the Hiwasa Fomastion and Oboke unit, respectively.

研究对象为琉球群岛至四国群岛东部上白垩统岛曼都超群。以下是研究成果的总结。玄武岩向松散陆源沉积物的侵入导致蚀变部位SiO_2和CaO的富集，K_2O的减少。用镜质组折射率法研究了九州东部马基明组的有机变质作用。这项研究揭示了玄武岩侵入对海沟区泥质沉积物的热效应。四国东部砂岩化学成分的构造地层变化确定了从北向南排列的三种岩相(I、II、III)。四国东部白垩纪岛曼托砂岩随时间的推移而变得更加酸性。这一趋势与中部地区西部白垩纪火山岩的趋势是一致的。在晚白垩世，楚国地区西部广泛被流纹岩覆盖，并在隆起碰撞前向海沟地区提供了大量粗粒碎屑沉积物，导致了构造重复的厚层浊积岩的沉积，如四国东部的Hiwa组。奥博克砂质片岩被推断为与四国东部坎帕尼亚纪海沟地区的Hiwaa组中砂岩相当的变质岩。寒武纪期间，海沟地区堆积了大量粗粒碎屑沉积物，引起俯冲带的剥离和底侵，分别形成了Hiwaa造山带和Oboke单元。