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Plate tectonic theory has profoundly changed the way geoscientists view Earth and provides an important theoretical and conceptual framework for understanding the origin and global distribution of igneous, sedimentary, and metamorphic rocks (Chapters 7–18). It also helps to explain the distribution of diverse phenomena that include faults, earthquakes, volcanoes, mountain belts, mineral deposits, and even the evolution of life and the evolving composition of the atmosphere.

The fundamental tenet of plate tectonics (Le Pichon 1968; Isacks et al. 1968) is that the lithosphere is broken along major fault systems into large, relatively rigid pieces called plates that move relative to one another. The existence of the strong, breakable lithosphere permits plates to form. Most plates are huge, with areas of 10⁵–10⁸ km² and thicknesses that average ~10³ km; some plates are smaller and microplates are smaller still. The fact that they overlie a weaker, slowly flowing asthenosphere permits them to move very slowly. Each plate is separated from adjacent plates by plate boundary segments that end in triple junctions (McKenzie and Morgan 1969) where three plates are in contact (Figure 1.3).

The relative movement of plates with respect to the boundary that separates them defines three major types of plate boundary segments (Figure 1.4) and two hybrids: (1) divergent plate (2) convergent, (3) transform, (4) divergent‐transform hybrid, and (5) convergent‐transform hybrid.

Each type of plate boundary produces a characteristic suite of features and Earth materials. This relationship between the kinds of Earth materials formed and the plate tectonic settings in which they are produced provides a major theme of the chapters that follow.