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
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
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
and transform orientation
• The relative motion of two plates sharing a mid-ocean ridge is
assumed to be parallel to the transform faults, because
the arcs of the faults are expected to be small circles. (What if
this is not the case, is this possible?)
• 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
a plate pair are used, the intersection of the great circles
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
sign OCE 661 OCE 661 • Stage poles represent extensions of the concept of
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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