Activity 1: Ridges, Isochrons, and Oceanic Crust
New oceanic crust is generated at a midocean ridge as magma wells up from the mantle, intrudes along the axis of the ridge system, and solidifies (Fig. 1). At any instant, the magma/crust along the ridge crest is of the same age (0). As this band of new crust moves away from the midocean ridge, it becomes progressively older. Lines drawn parallel to the ridge and connecting oceanic crust of equal age are isochrons. The age of an isochron and its distance from the ridge allow us to calculate the rate of seafloor spreading (rate = distance/time) along different parts of the midocean ridge system.
Fig. 1. Creation of oceanic crust at the midocean ridge and aging of oceanic crust as it moves away from the ridge. The red line represents an isochron, i.e., a line connecting rocks of equal age. An individual isochron ages as it moves away from the midocean ridge.
A simple paper model elegantly illustrates important concepts of sea floor spreading, including the creation of oceanic crust and isochrons.  More...
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