Hypogene Caves and Karst of South America
This chapter discusses the notion of hypogene karst, reviews its diversity and further develops the hydrogeological approach to classifying hypogene karst and its settings. Since an understanding of hypogene karst requires much deeper and broader hydrogeological and geodynamic context as compared to more familiar epigene karst, this chapter provides an overview of basic concepts about fluid dynamics and hydrodynamic zoning of the upper crust and about the influence of the mantle processes on crustal fluids. The relationships of hypogene karstification with metasomatism and other processes of fluid-induced transformations of rocks are examined. It is argued that the phenomena of the so-called ghost-rock karstification (commonly attributed to epigene settings) and cavernous decay (commonly attributed to external weathering) are manifestations of hypogene karstification and related alteration of rocks around conduits. Genetic categorization and discrimination of characteristic settings of hypogene karst are based on consideration of driving forces and conditions for fluid circulation and ascending flow in the upper crust in the context of tectonic/geodynamic positions and history of regions. Development and distribution of hypogene karst of the artesian type in gravitational flow systems of cratons are governed by the basin’s configuration, topography and hydrostratigraphy. Hypogene karst of the endogenous type is governed by the geodynamic regimes and intimately related to cross-formational fluid-conducting systems. Hypogene karst is a significant component of fluid-induced lithogenesis and plays an important role in the porosity and permeability development in many sedimentary rocks and some metamorphic rocks.