Chapter 3

Evolution of Triple Junctions, McKenzie and Morgan 1969

McKenzie and MorganMorganJason Morgan (1935-present) took his PhD at Princeton where he spent most of his career. His work on plate tectonics, published 1968, focused on magnetic anomaly data, in contrast to McKenzie’s application of fault slip directions; they are fundamentally the same theory. Morgan went on to apply and refine Tuzo Wilson’s ideas about hot spots and mantle plumes, together with mantle convection. together built on the geometric framework that they had independently put forward in 1967 and 1968. They use vectors to describe the relative movements of plates and assess the stability of triple junctions, where three plates meet. They test the evolution of triple junctions in the North Pacific, using the history of the plate boundaries off western North America derived from the magnetic stripes in the ocean floor combined with the bathymetry. The newly-determined ages of the periods of normal and reversed magnetism make McKenzie and Morgan’s quantitative analysis possible and plausible.