This figure is a schematic map of two lithospheric plates with a boundary betwee

Question

This figure is a schematic map of two lithospheric plates with a boundary between them. Teeth on the boundary indicate a convergent plate boundary, and the teeth are on the upper plate at the boundary. Plate C is considered to be attached to the screen and is not moving. Plate D, however, is free to move. The figure has a map scale in kilometers. A red linear reference line shown on the figure is attached to Plate C and will not move. Plate C is continental lithosphere, and Plate D is oceanic lithosphere. An autonomous (robotic) observatory is built on the seafloor (indicated by a blue polygon). The observatory is built to last indefinitely. The convergence rate between the two plates is 5 mm/yr (millimeters per year). In 20 million years from now, where on the red number line will the observatory be?

Explanation / Answer

The motion of the observatory can be described as : it will first move along a linear path till it reaches the subduction zone,after that it will move at angle of 25-45°(considering 45° as the subducting plate is dense oceanic plate and overriding plate is continental plate)

Distance travelled in 20million years= 20×10^6 × 5×10^(-6)=100Km.

Hence ,the observatory would be present at the 100Km mark.

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