Petrofabrics of Bedded Cherts

层状燧石是汇聚板块边界造山带特征增生杂岩的组成岩之一。它主要由放射虫和海绵针状物等硅质骨架组成，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。在层状燧石岩组构的基础上，重点研究了沉积、成岩作用、俯冲作用、区域变质作用等与吸积构造有关的地质过程。利用普通偏光显微镜、能量色散和微探针分析、x射线衍射分析等方法对原始成分和二次沉淀物质进行了鉴别。层状燧石形成过程中的各种事件记录在其岩组构中，这些岩组构由硅质有机残留物、伊利石和绿泥石以及石英和锰绿泥石等次生沉淀填充空隙或裂缝形成。指示沉积环境的岩组有平行层状、重铸状构造、切填构造等。成岩岩组构为间质充填的隐晶石英和因压力溶解作用而形成的花柱状结构。与吸积过程有关的岩组构包括：沟填体中的角化或塌缩沉积结构和高压条件下裂缝中注入的泥质物质。变质岩组构表现为重结晶结构，包括变质矿物，如静辉石和丽辉石。隆升过程中的岩构反映在石英脉充填的张拉解理或裂缝中，可能是深部超高压的释放。

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.