New evidence for long‐distance fluid migration within the Earth's crust

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Abstract
During the past decade, geologists have come to appreciate the interconnectedness of hydrologic, tectonic, thermal, and geochemical processes operating within the Earth's continental crust [Oliver, 1992]. This has led to a new geologically‐based conceptual model of hydrology which is crustal‐scale and is centered in plate tectonics theory (Fig. 1). From a geological perspective, the tectonic and thermal processes which drive plate motion are also responsible, either directly or indirectly, for inducing fluid motion across and through the continents. Supporting evidence for this emerging paradigm is based on observations of pervasive rock‐water interactions associated with geologic processes as diverse as the chemical alteration of crustal rocks [Shelton et al, 1992; Elliott and Aronson, 1993; McManus and Hanor, 1993; Ague, 1991, 1994], devolatilization of minerals during burial and consequent metamorphism [Cox and Etheridge, 1989], the formation of energy and mineral deposits [Garven et al, 1993; and Cathles et al, 1993], remagnitization of ancient sedimentary rocks [McCabe and Elmore, 1989], the tectonic deformation of sedimentary basins [Oliver 1992, Ge and Garven, 1992], and the regulation of global climate [Caldeira et al, 1993, Kerrick and Caldeira, 1993, 1994]. This paper summarizes the many recent lines of theoretical, laboratory, and field evidence from diverse disciplines within the Earth Sciences supporting this emerging view of crustal‐scale hydrology. Evidence for two types of long‐distance fluid migration are highlighted: vertical pore water movement through crystalline rocks to depths greater than six km and lateral groundwater movement through sedimentary basins over hundereds of km. Also emphasized are the many driving mechanisms on fluid motion which are not typically considered in water quality and water supply investigations. Some geologic terms used in this paper, which may be unfamiliar to the reader, are defined in geologic dictionaries [American Geologic Institute, 1976].