The topics covered in this chapter can be summarized as follows:

Section Summary
1.1 Discovering Plate Tectonics Giant strides were made in understanding Earth during the middle decades of the 20th century, including discovering magnetic evidence of continental drift, mapping the topography of the ocean floor, describing the depth relationships of earthquakes along ocean trenches, measuring heat flow differences in various parts of the ocean floor, and mapping magnetic reversals on the sea floor. By the mid-1960s, the fundamentals of the theory of plate tectonics were in place.
1.2 Plates, Plate Motions, and Plate Boundaries Earth’s lithosphere is made up of over 20 plates that are moving in different directions at rates of between 1 cm/y and 10 cm/y. The three types of plate boundaries are divergent (plates moving apart and new crust forming), convergent (plates moving together and one being subducted), and transform (plates moving side by side). Divergent boundaries form where existing plates are rifted apart, and it is hypothesized that this is caused by a series of mantle plumes. Subduction zones are assumed to form where accumulation of sediment at a passive margin leads to separation of oceanic and continental lithosphere. Supercontinents form and break up through these processes.
Lab 1 Exercises Characteristic features of divergent, convergent, and transform plate boundaries can be explored by examining global datasets of volcanology, seismology (earthquakes), topography/bathymetry, and seafloor age displayed on a world map. Since tectonic plates move over a mantle plume that we assume to be stationary, we can use chains or tracks of hot spot volcanoes to interpret the direction of plate motion. By using the age of these hot spot volcanoes, and the distance between volcanoes in the same chain, we can estimate the rate of plate motion.


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A Practical Guide to Introductory Geology Copyright © 2020 by Siobhan McGoldrick is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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