【摘要】 在扬子地台通过对晚震旦世－古生代地层中许多硅岩层的主元素和微量元素含量及组合关系的研究，总结了硅岩的地球化学特征，进而讨论硅质的来源和硅岩形成的地质背景及其有利的地球化学条件．更多还原

【Abstract】 Silicolite strata with different thickness and shapes are developed in most horizons of Sinian to Upper Palaeozoic in the Yangtze Platform.Most of the siliceousrocks are located in the anoxic melanocratic rock-series,while some of them aredirectly deposited between volcanic rocks and tuffs.The siliceous rocks mainly consist of tiny a-quartze.The main geochemical features of siliceous rocks in this area are as follows:l)Host elements are simple and concentric,beside SiO2,only Al2O3,CaO,FeO,organic carbon,and K2O of some samples can reach more than 1 % in content;2) Theratio of Al/(Al + Fe+Mn) of all the samples are greater than 0.1,most of themare 0.2-0.6; They show obvious tendency change towards different times,differentsections or different layers at the same section;3) Most of K2O/Na3O ratio arelarger than 1,only same sections which related to the volcanic activity have theratio less than 1;4) Mn contents are low generally, most of the MnO/TiO2 ratioare smaller than 0.1,only a small amount of samples have the ratio greater than1:5) Generally,the content of trace elements in siliceous rocks is low having a positive correlation to the content of clay and organic matter,and it has an obviousnegative correlation to the crystallization degree of minerals; 6) P, Ba, V, Cr andMn in siliceous rocks vary greatly in content,Ba,V have a positive correlation toCr and a negative one to Mn; 7) Rich in organic matter;and 8) The mean 8 30Siof siliceous rocks in this area ranges from +0.3‰to + 0.4‰.The formation of primary bedded siliceous rocks since Late Proterozoic in theYangtze Platform is the products of particular sedimentary environment under particular geotectonic setting at definite geohistorical stage.The silicon in this area has acomplicated source being accumulated by multiple manners.Long term surface weathering,erosion and halmyrolysis,including large-scale glacial erosion and miclobial action made a large amount of silicon freed into sea-water and become the principle source of silicon for forming silicolites. Locally,especially in active zone,large-scale volcanic eruption and hot spring up-welling may abruptly release a largeamount of SiO2, which will be the important source of silicon.In addition to the function of silicon-concentration,the abrupt increase of living beings and organic matter can constantly change the medium condition so thatthe medium become favourable for the concentration,preservation,saturation anddeposition of silicon.Submarine volcanism is another important factor for silicoliteformation.It not only can enlarge local silicon concentration rapidly,but also canchange water temperature,increase nutrient for microbes,promote the reproductionof bacteria and microbes,raise the content of anions such as S2- obviously,andconstantly change local medium condition of sea-water to form local geochemicaldomain more favourable for silicolite formation.In one word,the formation process of silicolites in this area is very complicated.It can be concluded as follows:Under particular geological setting and on thebasis of abundant material source,biochemical process can concentrate and preservesilicon,and constantly improve the medium condition favourable to the saturationand deposition of silicon so that silicon can deposit steadily.Then,after diagenesis.and a series of epigenetic changes as well as reworking,the existing bedded silicolites are formed.更多还原