Looking into the Earth An Introduction to Geological Geophysics

In the 1960s the theories of continental drift and sea floor spreading (hitherto largely regarded with scepticism) fused to give birth to plate tectonics, the idea that the surface of the Earth consists of huge rigid pieces that move independently, with most tectonic and igneous activity taking place at their margins as a consequence of their relative movements. Plate tectonics provides a framework for much of geology, being relevant to topics as diverse as continent formation, orogenesis, earthquakes, volcanoes, past climates, and palaeontology. It has been particularly successful when applied to oceans and their margins, but less so at explaining tectonic processes within continents, where deformation extends far from the plate margins.

The success of plate tectonics posed further questions: How deep do plates extend, and what moves them? How does intracontinental tectonics relate to plate collisions? What causes the volcanism – sometimes very extensive – found far from plate margins? This has led enquiry deeper within the earth, particularly to convective flows within the mantle, and this larger framework can be termed global tectonics.

This chapter is mainly concerned with the basic concepts of plate tectonics, which were established largely by geophysical evidence, and geophysics, with its ability to investigate the deep Earth, continues to play a major part in extending our understanding of its processes.

Geophysical techniques employed: Many geophysical techniques have played a part, but seismology, seismicity, magnetics, palaeomagnetism, gravity, radiometric dating, and heat flow have had the major roles.