# The rotation of a plate can be represented as angular

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Unformatted text preview: s/year (mm/yr). • The rotation of a plate can be represented as angular velocity ω about a fixed axis originating at the center of the sphere. The about Euler pole is the intersection of the Euler vector ω and the surface of the sphere. OCE 661 The following figure illustrates how the rotation speed The increases from the pole of rotation, and that transform faults offsetting both ridges and trenches are small circles about the rotation pole. The first figure shows a counterclockwise rotation of plate B relative to plate A, separated by a ridge, whereas the figure on the right shows a counterclockwise rotation, separated by a subduction zone. Notice the difference in the sense of the rotation. difference OCE 661 Approximating a pole of rotation using ridge Approximating and transform orientation and • The relative motion of two plates sharing a mid-ocean ridge is assumed to be parallel to the transform faults, because assumed the arcs of the faults are expected to be small circles. (What if the this is not the case, is this possible?) this • This would imply that the rotation pole must lie somewhere on the great circle perpendicular to the small circles defined by the transform faults. Hence, if two or more transform faults between transform a plate pair are used, the intersection of the great circles plate approximates the position of the rotation pole. approximates OCE 661 OCE 661 Stage rotations: Finite rotation poles, but based on the assumption that an instantaneous rotation can be extrapolated to a finite time. They approximate the plate motion during a geological stage, and are computed by adding two (total) finite rotations to each other, one with its (total) sign reversed. sign OCE 661 OCE 661 • Stage poles represent extensions of the concept of Stage instantaneous rotation poles to the geological past. Since we cannot measure real instantaneous plate rotations for the past, we make the assumption that a particular instantaneous pole of motion has been constant fo...
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