Understanding rotations
Ádám T. Kocsis 
The duration of features
Geometric vector features on their own do not say much about plate tectonic evolution, they just represent the spatial extent of units as points, lines or polygons. In themselves they only have durations.
Load in the plate polygons by going to File->Open Feature Collection…, navigate to GeoData/FeatureCollections/ContinentalPolygons and open Global_EarthByte_GPlates_PresentDay_ContinentalPolygons.gpmlz!
Note that after you load in the feature collection, if the time is set to 0, you can see all polygons: (view set to Mollweide projection, and polygons are filled)
If you move the time slider back (e.g. to 200Ma), you will note that some polygons are disappearing.
Note where this happens, and go back to the present day to see these polygons. You can use the Inspect features tool to see the attributes of such polygons:
If you lookat the right-hand side panel, you will see that there are entries for Valid time that range from a value to another value. In the case of the selected Lesser Antilles Arc, the from value is set to 40 (Ma), and the to is set to future, which means that this feature starts to exist only at 40Ma, and it will not disappear in the future. If the reconstruction time moves beyond the interval outlined by these two values, the feature will not be included in that reconstruction.
These values set whether features exist or not at a time, but they do not move them around. For that we need rotation files. You can go ahead and unload/eject the Continental Polygons feature now.
Rotations
Download example
To better understand what is actually happening in such a model, we need to simplify a complete plate tectonic reconstruction to the elemental baseics. For this exercise, go on and download these example files
and put them in a convenient folder (in this case they will be in the Downloads folder).
Example Coastlines
You can open the coastlines file with the Open Feature Collection tool.
You can use the inspect tool to confirm that the following features have these Plate IDs:
| Feature | Plate ID |
|---|---|
| Africa | 701 |
| Australia | 801 |
| Antarctica | 802 |
| Tasmania | 850 |
The rotation file
To see how rotations work, we are going to implement a single rotation, and add it to an already structured file. The rotation file has .rot extension. It is a plain text file that can be opened by any text or code editor.
Opening the rotation file in Notepad
Go on an open this file in notepad (Windows’ default text editor), by 1. navigating to the file in Windows Explorer, 2. right click on the file, and select Open with:
In the dialog box, that appears, select More apps,
and then Notepad
The structure of the rotation file
The rotation file s a “whitespace-delimited” file, it has a table-like structure.