温湿气候区结晶岩与碎屑岩腐岩特征及其发育过程

发育于斜坡非饱和带的结晶岩与碎屑岩腐岩多夹于残坡积土层和风化岩带之间,保留有裂隙及层理等构造,但质地松软。腐岩结构体与母岩色差显著,保留原岩结构和构造特征,矿物成分以次生粘土矿物、次生石英及褐铁矿最为常见。腐岩次生微孔隙发育,具有低密度、高孔隙度、高渗透率、高容水度及高持水度特征。腐岩发育是通过低渗透岩石结构体风化前锋的渐进性扩展实现的,非饱和带高湿度空气形成的凝结水和降水入渗形成的非饱和渗流是该过程的核心动力。气态水分子能够扩散到低渗透岩石结构体表面内侧一定宽度范围内的孔隙系统之中凝结为液态水并溶蚀造岩矿物。雨季入渗降水在结构体表面形成的薄膜水流通过分子扩散机制接受其内侧结构体粒间溶液中的溶出组分并将其携入饱水带,同时恢复粒间溶液的侵蚀动力。当上述过程循环到一定程度时,结构面内侧便形成一定厚度的腐岩壳。腐岩壳在雨季直接吸收、贮存流经其表面的液态渗入水,在核心石外侧形成富水结构层并在旱季向包气带或其内侧的风化前锋提供水汽。随着时间推移,腐岩壳越来越厚,核心石最终消失;当某一范围内的岩石结构体全部演变为腐岩结构体时,该范围内的岩体也就完成了向腐岩体的转变。

Characteristics of saprolites formed from crystalline rock and clasolite in humid climatic regions and their development process

Abstract: The saprolites derived from crystalline rock and clasolite and developed in slope unsaturated zones are usually sandwiched between residual or colluvial soil and weathered bedrock, and retained large structures such as bedding or fractures from their parent rocks. The color difference between saprolite blocks and their parent rocks is obvious and the texture and structure of the parent rock can be preserved in saprolites. Secondary clay minerals, quartz and ferrohydrite are most common in saprolites. Saprolites have spongy micro texture and are characterized by high porosity, high intrinsic permeability, high specific water capacity, low specific yield and low density. The development of saprolite is realized by the progressive propagation of the weathering front of low permeable rock blocks, and the condensate from the moisture and the unsaturated seepage flow are the key agents of the propagation process. The gaseous water molecules in unsaturated zones spread into the pore system of rock blocks at some depth and condense into liquid water which can dissolve rock forming minerals. In rainy season, the thin water film derived from precipitation on the surface of rock blocks in unsaturated zones absorbs the dissolution components of the rock block solution and carries them into saturated zones. At the same time, the dissolving capacity of solution between mineral grains in rock blocks is also restored. When the above process circulates to some extent, saprolitic crusts will be formed inside structural planes. Saprolitic crusts may absorb and store the liquid water flowing on their surfaces, and in dry season these saprolitic crusts provide unsaturated zones and weathering fronts of rock blocks with moisture. With the lapse of time, saprolitic crusts get thicker and thicker, core stones become smaller and smaller, and finally rock blocks evolve into saprolitic blocks. When all rock blocks within the research area have developed into saprolitic blocks, the rock mass turns into saprolite.