燕山山地片麻岩风化过程与地球关键带结构耦合关系研究

Rock weathering process and its relationship with the structure of the critical zone of gneiss in Yanshan mountain

山地地球关键带的形成和演化在不同空间尺度上受风化过程的控制。本文以细粒角闪斜长片麻岩和粗粒黑云斜长片麻岩为例,研究片麻岩地球关键带结构的演化过程,识别影响地球关键带垂向结构的主控因素。结果表明片麻岩的物理风化程度较高,化学风化程度低且细粒角闪斜长片麻岩化学风化程度相对较高,发育等体积风化,化学损耗低于0.5。在风化成土过程中黑云母含量和矿物粒径影响风化程度,从而影响其地球关键带结构,风化初始阶段黑云母通过铁氧化和层间钾被其他水合阳离子替代而扩张,岩石破碎,形成大量裂隙,渗透率提高。粗矿物颗粒导致母岩比表面积较低,物理崩解程度较高,促进孔隙度和渗透率提高,因此粗粒黑云斜长片麻岩风化前锋可达到5 m,强风化层可达1 m,土壤平均厚度多大于20 cm,而角闪斜长片麻岩风化前锋深度减至1.5 m以内,平均土壤厚度多小于20 cm。该研究成果有助于认识山区土壤形成过程,为国土空间规划提供科学依据。

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 biotiteplagioclase 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 biotiteplagioclase 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.