Rock weathering process and its relationship with the structure of the critical zone of gneiss in Yanshan mountain
The structure and evolution of the critical zones in the mountain were controlled by weathering on different spatial scales.In this paper,finer-grained hornblende-plagioclase gneisses and coarser-grained biotite-plagioclase gneisses have been taken as the research objects to study the evolution process of the critical zones in gneiss distributions and to identify the key factors influencing their vertical structures.It was manifested that physi-cal weathering was the dominating type in gneisses,whose chemical weathering intensity of the soils was mainly low.In general,fine-grained hornblende-plagioclase gneiss was stronger weathered than coarse-grained biotite-plagioclase gneiss.According to strain factor,soils developed from gneisses were isovolumetric.Besides,CDF was mainly less than 0.5.Weathering intensities were remarkably influenced by biotite contents and grains size of gneisses,so that controlled the structures of the critical zones.Expansion of biotite via Fe oxidation and interlayer replacement of K with other hydrated cations causes destabilization of rock.Microfractures develop both within and between mineral grains and the permeability increases.In addition,as the grain size of the materials resulting from weathering is coarser,the specific surface area of the minerals is smaller.These characteristics proceed their par-ent rocks'high degree of physical disintegration and increased porosity and permeability.In conclusion,it was attributed to the more abundant biotite contents in biotite-plagioclase gneiss and its coarser grain size,so that the weathering front extended to 5 m below the surface,accompanied by strong-weathered layers being 1 m and soil thickness being over 20 cm.However,the weathering front of fine-grained hornblende-plagioclase gneiss is limited to 1.5 m below the surface,accompanied by soil thickness of less than 20 cm.This research is conducive to our understand about the soil formation process in mountainous areas and provides scientific basis for territorial spatial planning.
NETL
NSTL
万方数据
