Plate Motion from Island Ages

Lava erupted from volcanoes can be dated. And many oceanic islands began their lives as undersea volcanoes.  Also, an interesting pattern was observed for many of the dates of oceanic islands that lie along a line, called “Island Chains.”  Dates get progressively older along the chain.  The “spots” are very young at one end of the line, while the “spots” are older on the other end.  Thus, the “Hot Spot” theory was formulated to explain this pattern.

The picture below shows a diagram that explains the Hot Spot theory. There are 4 islands dated at 0, 10, 20, 30 Ma. They are 300km apart. A heat source, represented by the candle, is the source of the magma that rises to the surface and erupts as lava. The overlying lithosphere moves along at a constant rate for long periods of time, and every so often, a blob of magma rises and makes a volcano. These are pretty big blobs, because there must be enough magma to make an entire oceanic island.

 

Plot the Age vs. the distance from the island with 0 (zero) age in the figure.  Does the plot indicate a pattern? What pattern?  Also, can you tell from the data the direction in which the lithosphere is moving?

 

What is the rate of motion of the lithosphere relative to the underlying magma source?