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Plate Velocities from GPlates Reconstructions as TERRA Input

Motivation

In order to reproduce a realistic circulation structure in the mantle, adequate initial and boundary conditions are needed. The most detailed information about past mantle flow that we have are the effects that it caused to the plates at the surface.

The software GPlates is now the standard tool to combine information about past plate development. The result are linear plate boundaries that can be combined to closed plate outlines. However, TERRA does not need plate boundaries, but a velocity field. The velocities can be computed using the Euler poles - however, for each grid point the corresponding Euler pole must be known.

So this text describes how to create TERRA velocity fields (which are normal cfiles; each radial layer corresponds to one time step) out of linear plate outlines.

Instructions

Preparing the data:

  • Launch GPlates.
  • Load the plate polygons (*.gpml) and the corresponding Euler rotation file (*.rot).
  • Select "Reconstruction/Export" from the menu.
  • Select the desired time range and step width.
  • Export the "equivalent stage rotations" (CSV file containing the Euler poles).
  • Export the "resolved topologies" (GMT *.xy file containing the closed plate outlines, without intersections). (Only the "Polygons.platepolygons.*" files are needed; the others can be discarded.)

Creating TERRA plate maps:

  • You need the scripts gplates2terra_wrapper.sh and findplate.pl.
    • The findplate script does the actual work, i.e. it reads the plate outlines and assigns a plate id to each grid point (the grid is created internally).
    • The wrapper script runs the above script for each time step (if possible in parallel), converts the GPlates's absolute 3-digit plate ids to sequential numbers, and writes a rotation file suitable for TERRA. (Since these tasks require all time steps, they can only be done outside the above script that knows only about the current timestep.)
  • Wrapper script: Adjust there the variables "POLYGONPATH" and "CFILE_PATH", if necessary. Attention: Paths must be absolute!
  • Run the wrapper script, preferably on a machine with many processors; thus, several time steps can be processed in parallel.
  • Example:
    path_with_polygons$ ../Tools/gplates2terra_wrapper.sh
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