Chemical Weathering, Regolith and Climate in Metamorphic and Igneous Terrains

Abstract

In this chapter, the phrase ‘chemical weathering’ is used in its broadest sense, and concerns chemical forms of rock disintegration as diverse as late magmatic alteration and meteoric weathering processes stricto sensu. The products of weathering occur in a wide spectrum of chemical and grain size categories, ranging from clays to coarse sand or gravel (grus, or arènes). Though a conventional distinction is usually made between this particular category of saprolite on the one hand, and mantles of debris produced by mechanical processes (frost action, for instance) on the other, the frequent interaction between the two groups of processes, especially in the temperate zone, cannot be emphasised enough. Indeed, while a mechanical disintegration of the rock material into small units facilitates chemical decay by increasing the total area of particle surfaces that are in contact with the reactive solutions, antecedent chemical alteration can also increase the efficiency of certain mechanical processes (see Chapter 6). Chemical weathering also acts as a prelude to soil development, which in turn, through the interference of vegetation, may profoundly modify the structure and composition of the weathering mantle. Geomorphologists have usually focused more on the status of saprolite as parent material for soils rather than on the soils themselves, and this tendency is reflected in the research presented in this chapter.