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Petrofabrics of Bedded Cherts

层状燧石岩石结构

基本信息

批准号：
06640590
负责人：
SAITO Yasuji
金额：
$ 1.09万
依托单位：
National Science Museum, Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06640590/
关键词：
bedded chert accretion complex subduction accretion tectonics

项目摘要

Bedded chert is one of consttituting rocks of accretion complex characterized orogenic belts in convergent plate boundary. It consists mainly of such siliceous skeletons as radiolarians and sponge spicules with subordinate clay material of aeolian origin and Fe-Mn minerals precipitated from sea water, and is therefore considered to be an ancient pelagic sediment. On the basis of petrofabrics of bedded chert, geologic processes in relation with accretion tectonics were studied in particular ranging from sedimentation and diagenesis to accretion and regional metamorphism due to subduction. Original constituent and secondarily precipitated materials are discriminated by methods using an ordinary polarizing microscope, energy dispersion and also microprobe analyzes, and X-ray power diffraction analysis. Various events during formation process of bedded cherts are recorded in their petrofabrics mentioned below, formed by siliceous organic remains, illite and chlorite, and secondary precipitates filling interstices or fractures such as quartz and manganoan chlorite.Petrofabrics indicating sedimentary environments are parallel lamination, load-cast like structure, cut and fill structure and etc. Diagenetic petrofabrics are existence of intersticial filling cryptocrystalline quartz and of stylolitic texture showing sutured contact among constituent grains due to pressure-sulution. Examples of petrofabrics related to accretion process are brecciated or collapse sedimentary textures in trench-fill and injection of argillaceous material into fractures under hyper-pressure condition. Metamorphic petrofabrics are shown as recrystallized textures including metamorphic minerals such as stilpnomelane and riebeckite. Petrofabrics during uplift process are reflected in quartz vein filling tension cleavages or cracks, probably meaning release of hyper-pressure under deeper condition.

层状硅质岩是汇聚板块边界造山带增生杂岩的构造岩之一。它主要由放射虫和海绵骨针等硅质骨架组成，其次是风成粘土物质和海水沉淀的铁锰矿物，因此被认为是一种古老的远洋沉积物。根据层状硅质岩的岩石组构，研究了与增生构造有关的地质作用，特别是从沉积和成岩作用到俯冲作用引起的增生和区域变质作用。通过使用普通偏光显微镜、能量色散和微探针分析以及X射线粉末衍射分析的方法来区分原始成分和二次沉淀材料。层状硅质岩的岩石组构记录了其形成过程中的各种事件，岩石组构由硅质有机质残留物、伊利石、碳酸盐岩和充填于空隙或裂隙中的次生沉淀物如石英、锰氧化物等组成，指示沉积环境的岩石组构为平行纹层、负载铸造状构造，成岩组构表现为晶体充填隐晶石英和因压力作用而呈缝合接触的缝合结构，解决方案。与加积过程有关的岩组的例子是在超高压条件下沟槽充填和泥质物质注入裂缝中的角砾化或塌陷沉积结构。变质岩组表现为重结晶结构，包括硬锰矿和钠闪石等变质矿物。隆升过程中的岩组表现为石英脉充填的张裂或裂隙，可能意味着深部超压的释放。