LAERCISE 2.6 Comparing Seafloor Spreading Rates of Different Mid-Ocean Ridges Name: Course: Section: Date: Map view of magnetic anomaly stripes in two oceans. Mid-Atlantic Ridge East Pacific Rise 1,500 Magnetic reversals are found worldwide, so magnetic anomaly stripes should be the same width in every ocean if the rate of seafloor spreading were the same at all mid-ocean ridges. If a particular anomaly stripe is wider in one ocean than in another, however, the difference must result from faster spreading. The figure on the right shows sim- plified magnetic anomaly stripes from the South Atlantic and South Pacific oceans, the ages of the rocks in the stripes, and their distance from the spreading center (the red line). For simplicity, only the most recent 80 million years of data are shown for the two oceans, and we will estimate the spreading rate only for that time span. (a) Provide the width of the South Atlantic Ocean, as given in km the nearer figure on the right. - (b) Estimate the average rate at which the South Atlantic Ocean has been opening over the 80 million years for which data are provided. - cm/yr km per million years Age of magnetic anomaly stripe (millions of years) Distance from spreading center (km) Age of magnetic anomaly stripe (millions of years) Distance from spreading center (km) TI .500 Ridge axis crest © Now look at the data for the South Pacific Ocean and its spreading center, the East Pacific Rise. Considering the width of this ocean, spreading rate is the same, greater, or less than that of the South Atlantic? Explain 500 500 -1,000 1,500 - 1,000 (d) Now get the details. Provide the width of the South Pacific Ocean, as given in the farther figure on the right km 2,000 - 1,500 609 _ km per (e) What is the spreading rate of the East Pacific Rise? cm/yr- million years These spreading rates are typical of the range measured through- out the world's oceans and represent "fast spreaders" and "slow 2,500 701 Red line axis of mid-ocean ridge, black positive anomaly white - negative anomaly. spreaders." 37 AIER RY EARTH FEATURES