浙江江山市江郎山岩石岩性特征及其对丹霞地貌形成的影响

The Contribution of Lithological Characteristics to Danxia Landform Genesis in Jianglang Mountain,Zhejiang Province

岩性特征的量化研究对分析丹霞地貌的成因具重要意义。江郎山岩石岩性标本的X射线荧光光谱分析和偏光显微镜鉴定发现,江郎山方岩组砂岩、砾岩中SiO2含量高达55.5%-75.8%,火山岩碎屑含量高,石英晶屑多已被高温熔蚀,三爿石中多处贯穿有辉绿岩和橄榄玄武岩的岩脉和岩墙,其辉绿-间粒结构和斜长石与暗色矿物的组合,构成了抗风化能力强的岩体,使三爿石得以长期保存。洞穴岩石CaO含量百分比的平均值是崖壁的三倍,且洞穴中岩石的胶结物多为方解石,其含量超过总胶结物的50%以上,使岩石结构的稳定性受到影响,会发生类似石灰岩地区的溶蚀作用,从而导致岩体的破碎和崩塌,有可能形成诸如会仙岩、天宫洞等大型洞穴和凹槽。

Quantitive lithological study is significant for analyzing the genesis of Danxia Landform. Polariscope thin section and X fluorescence spectroscopy analyses results indicates that volcanic gravel and rock clastic are major components of Fangyan Formation （K1 f） , and that SiO2 content is commonly as high as 55.7 % - 75.8 %. The volcanic gravels are very hard and highly inert because of their experience of high temperature activities, like quenching course and because of the peculiar dolerite space-grained structure, plagioclase and dark minerals form hard rock body. The average CaO content of stones in caves is about 6.07 %, which is three times higher than those of cliffs. Rock cements in caves are mainly calcite, accounting for more than 50%. Carbon dioxide from air dissolved into the infiltrating water to form ions like CO3^2- and HCO3^- , which can dissolve calcite component and can modify the stability of stone＇s structure. Thereby, stones crash and dilapidation phenomenon happens. These processes result in some caves like Huixianyan Cave, Tiangongdong Cave, Jingxinshishi Cave and Zhonggudong Cave.