This preview shows page 1. Sign up to view the full content.
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 midocean 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...
View
Full
Document
This document was uploaded on 01/26/2014.
 Winter '14

Click to edit the document details