浙江江郎山丹霞地貌区岩性特征

Experimental Study on Lothological Characteristic with Danxia Landform,Jianglang Mountain,Zhejiang Province

对浙江江郎山丹霞地貌区主要岩层方岩组(K1f)的22块岩石标本进行常量元素、氧化物含量的X荧光和薄片偏光显微镜鉴定,分析了江郎山丹霞地貌发育的岩性特征与地貌成因的关系:(1)方岩组(K1f)砾岩中的火山岩砾石和岩屑含量普遍较高,SiO2含量普遍也很高(在44.90%～75.80%之间),表明岩性总体上抗风化能力强,这使江郎山丹霞地貌最具特色的"三爿石"历经沧桑仍能巍然屹立,江郎山也因此成为丹霞地貌发育晚年时期的典型代表。(2)方岩组(K1f)的砂岩抗风化能力相对较弱,其胶结物的主要成分为方解石,粒间孔隙约占20%～25%,局部可见方解石胶结物的溶蚀现象。岩石薄片鉴定可看出,其粒间孔隙很可能是方解石胶结物被溶蚀后的结果,而且构成砂岩的岩体的流纹岩岩屑等其本身就具有气孔构造,这些岩屑在显微镜下可见已经强烈泥化,岩体抗风化程度较低,这是构成该区地貌岩性之一的砂岩被侵蚀和风化程度较高的主要原因。(3)在江郎山丹霞地貌发育过程中方岩组(K1f)岩性对地貌的形成起了基础和决定性的作用。这种岩性的特征及抗风化能力的不同导致的差异风化现象,对该区丹霞地貌后期的微地貌发育具有重要的影响,岩性差异风化是江郎山山体崩塌、扁平状洞穴的形成的重要因素,这也为研究江郎山等丹霞地貌山区地质灾害的岩性特征奠定了基础。

22 block of rock specimens were collected from Fangyan major rock group （K1f） on Jianglang Mountain,Zhejiang Province.X-ray fluorescence analysis on macroelement and oxidate content,thin-section polarizing microscope identification were carried out.The causes of the relationship between the development of Jianglang Mountain Danxia lithology and topographic features was analyzed：（1）Volcanic gravel and debris content of conglomerate on Fangyan Group （K1f） is relatively high. The content of SiO2 is also high （44.90%~75.80% in between）,It indicated that its ability of resistance to weathering is strong.It is the reasons that ＂Three Stone＂ on Jianglang Mountain can still stand tall through the vicissitudes. Jianglang Mountain became Danxia a typical representative of old age period of developmental. （2） The ability of resistance to weathering of Fangyan Group （K1f） sandstone is relatively weak,its main component of cement is the calcite,intergranular apertuer gapporosity about 20%~25%,partial visibility of the dissolution of calcite cement phenomenon. Identification of thin-section polarizing microscope on rock also can be seen,the intergranular porosity is likely to be calcite cement has been the result of corrosion,but also constitute a sandstone rock rhyolite debris,such as its pore structure itself,these cuttings at can be seen under the microscope has a strong clay,and rock of less wind resistance,which constitutes one of the area lithology sandstone landform erosion and the main reason for the higher degree of weathering. （3） Fangyan Group （K1f） lithology played a decisive role on the process of development of Danxia landform on Jianglang Mountain.This lithological characteristics and resistance to weathering of the difference in ability lead to differences in weathering phenomenon in the area. It is the foundation that the mountain collapsed,flat cave formation and ＂Three Stone＂ standing on Jianglang Mountain because of the lithologic differences.