The debate regarding whether or not melting anomalies are fuelled by hot diapirs from the deep mantle – the Plume hypothesis – or whether they arise from shallow processes ltimately related to plate tectonics – the Plate hypothesis  – is an extraordinarily rich cross - disciplinary subject with seemingly endless ramifi cations. Relevant material is scattered far and wide, and because of this, over the last decade, scientists have come together and tried to address this problem using the website www.mantleplumes.org.

The turn of the twenty-first century ushered in an upsurge of questioning of then-current views of the links between mantle convection and surface kinematics and volcanism. Since the early 1970s the mantle plume hypothesis had been the most popular explanation for volcanism apparently not explained by plate tectonics, including both large-volume magmatism and volcanism in regions distant from plate boundaries.

Written by two geologists with a field-based research approach, this overview of plate tectonics hinges on observations and processes that help explain the natural world. We describe the many different features and processes involved in plate tectonics, fusing them into themes such as ocean spreading, subduction, and orogeny.We teach plate tectonics not only through words but also through maps, cross sections, three-dimensional diagrams, and photographs – as those familiar with Structural Geology, a previous text by one of the authors, will have come to expect.

Plate tectonics is the unifying theory of the solid Earth that describes the surface of our planet as being fragmented into rigid plates that move in relation to each other. Many fundamental geological processes, such as earthquakes, volcanism, and the formation of mountains, occur at the plates’ boundaries. In its initial formulation, plate tectonics was a kinematic theory that described and quantified these movements and associated deformation. Plate tectonics evolved into a dynamic theory, describing the forces driving the surface deformation and the internal dynamics of our planet. We also came to realize that plate tectonics is only one of the possible tectono-magmatic styles in which a planet can operate and that these can change over time. In the past years, the geosciences community has started to develop a theory that integrates plate tectonics and mantle convection as part of a single system. This was possible because of the ever-increasing high-quality imaging of Earth’s interior and our computational capabilities. But while the progress has been enormous, there are still many uncertainties and challenges ahead. <...>

This book is a collection of papers on an aspect of plate tectonics of which our understanding is at present limited. In the mid-1970s, prior to the recent phase of IPOD active margin drilling, few geologists would have anticipated that at the start of the 1980s so many new questions concerning the nature of tectonic and sedimentary processes in forearc regions would have come to light.

Plate tectonics, as it operates in the modern earth, represents in a fundamental sense a mechanism by which excess thermal energy from the mantle is dissipated (Sclater et ai., 1980). A substantial data base now exists concerning the operation of plate tectonics during Phanerozoic time, and evidence for similar tectonic activity during Proterozoic time appears to be steadily growing, both in quantity and quality.

Fifty years ago, Tuzo Wilson published his paper asking ‘Did the Atlantic close and then re-open?’. This led to the ‘Wilson Cycle’ concept in which the repeated opening and closing of ocean basins along old orogenic belts is a key process in the assembly and breakup of supercontinents.

Throughout the history of the study of the Earth, geologists have attempted to understand the factors and forces which shape the surface of our globe. In this book, we shall attempt to summarise the current theories of how the gross surface layer of the Earth evolves tectonically.

Forty years ago when plate tectonics was first discovered, there was a major shift in thinking in the Earth Sciences. Little was known at that time about the deep mantle because of the lack of knowledge about material properties, the absence of any seismic tomography or concepts such as mantle convection. Thus the theory of plate tectonics was built on surface observations and kinematic constraints. The theory of plate tectonics is not independent but consists of several assumptions. Examples are the origin of arc magma, MORB or OIB, and the distribution of earthquakes and the plate margin processes are all part of plate tectonics theory. <...>

All aspects of the Earth’s history and structure, including its majestic mountains, giant rift valleys, and deep ocean basins, were fashioned by mobile crustal plates.The Earth’s outer shell is made up of a dozen or o plates composed of the upper mantle, or lithosphere, and the overlying continental and oceanic crust.The plates ride on the semimolten rocks of the upper mantle and carry the continents along with them.The movement of the plates accounts for all geologic activity taking place on the planet’s surface. In this manner, plate tectonics is continously changing and rearranging the face of the Earth.