Published using Google Docs
Tutorial 2.7: Introduction to the Kinematics Tool
Updated automatically every 5 minutes

Introduction to the Kinematics Tool

Author: Samantha Ross

Updated for GPlates 2.2 and the reconstruction of Müller et al. (2019) by Behnam Sadeghi and Christopher Alfonso

EarthByte Research Group, School of Geosciences, The University of Sydney, Australia

Introduction to the Kinematics Tool

Aim

Included Files

Background

Exercise 1 - Using the Kinematics Tool

Exercise 2 - Looking at relative and absolute motion

References

Aim

This tutorial is designed to introduce the user to the features of the Kinematics Tool and teach the user how to compare absolute and relative plate kinematics.

Included Files

Click here to download the data bundle for this tutorial.

The tutorial dataset includes the following files:

Background

Kinematics describes the motion of objects and in a GPlates context, we can look at the kinematics of various features to understand their magnitude and direction of motion over time. In GPlates, the Kinematics Tool renders 2D plots of velocity (and velocity-related quantities) over time.

Exercise 1 - Using the Kinematics Tool

Introduction to the features of the Kinematics Tool and learn how to export data

  1. Open GPlates and load the following files using Open Feature Collection.

  1. Making sure that the Muller_etal_2019_CombinedRotations.rot rotation model is selected, rotate the globe so that it is centred on India and select it using the Feature Inspection tool (Figure 1).

Figure 1: View of India (Step 2)

  1. Go to Utilities → Open Kinematics Tool… (or Ctrl/Cmd+Shift+K)

A new window will open (Figure 2), however you will notice that it is blank (Figure 2)

Figure 2: Kinematics Tool Window

  1. Click the ‘Use focussed feature’ button in the top left corner of the box. Data should now appear in the window that corresponds to the focussed feature (Figure 3).

Figure 3: Kinematics Tool describing the motions of the Indian Craton (Plate ID 501)

Note that this tool specifies the Latitude, Longitude and Plate ID of a point on the feature in focus (Figure 4). In this example, we note that the point we are calculating kinematics for has a Plate ID of 501, which corresponds to the Indian craton. Note that the Anchor Plate ID is set at 0. This means that we are calculating the absolute motion of this point. If we want to compute relative motion, we need to specify the plate we want to calculate relative motion with respect to (we will do this in Exercise 2).

If there is a specific point you wish to calculate kinematics for, you can manually type in the Latitude, Longitude and corresponding Plate ID into these fields and click Update. This is an alternate method of specifying the point you wish to calculate kinematics for, rather than using the focussed feature method.

Figure 4: Kinematics Tool highlighting Latitude, Longitude and Plate ID specifications

The table in the top half of this window describes a variety of parameters over a specified time period with specific time steps, as defined in the top right corner of the window (Figure 5). In this example, kinematics have been calculated between 200-0 Ma in steps of 5 Myr.

Figure 5: Kinematics Window highlighting calculation specifications

The Begin, End and Step fields can also be determined by how your animation is configured. To calculate kinematics for the same time period and timesteps as the animation, click the ‘Use animation values’ option (Figure 6). Unless you have already specified values, GPlates will use the default Begin, End and Step values.

Figure 6: Kinematics Tool window highlighting the ‘Use animation values’ button

If you want to configure the animation values, go to Reconstruction → Configure Animation… and specify values there (Figure 7).

Figure 7: Configure Animation window

Returning to the Kinematics Tool, the data in the table is plotted in the bottom part of the window, one variable at a time. To change the variable that is displayed, we can use the buttons to the left of the graph (Figure 8). At the moment, we can see how latitude has changed from 200-0 Ma.

Figure 8: Kinematics Tool with Display panel highlighted

  1. Change the graph so that it displays Longitude vs time.

The y-axis of the graph (Longitude) shows all possible values (-180–180°), which compresses the graph a little and makes it difficult to detect changes in motion. We can use the tools to the right of the graph (Figure 9) to zoom in and out to see more detailed longitudinal changes.

Figure 9: Kinematics Tool with view controls highlighted

The 4 controls can be used to change the way the graph is presented as follows:

 Autoscale y-axis: automatically scales to the extent of the y-axis - useful for detecting minor changes in motion.

 Stretch y-axis: zoom in

 Compress y-axis: zoom out

 Flip horizontal axis: flips time axis (x-axis) - useful to see motion backwards from present day or motion forwards from the specified time.

  1. Experiment with these tools to see how they change the presentation of the graph so it is easier to see how the longitude changed over time (Figure 10).

N.B. When you have finished using the ‘Autoscale y-axis’ tool, you must deselect it to make the other tools available.

a)

b)

Figure 10: Longitude vs time with: a) ‘Autoscale y-axis’ b) ‘Autoscale y-axis’ and ‘Flip horizontal axis’

  1. Change the graph so that it displays Velocity magnitude vs time (Figure 11).

 

Figure 11: Kinematics Tool showing India’s velocity magnitude through time

  1. To further customise the Kinematics Tool outputs, click ‘Settings’ in the bottom left corner, which will open up a new window.

In the Settings window, you can change the method for calculating velocities, as well as changing the velocity magnitude thresholds for displaying warnings. For example, try changing the “Yellow velocity warning” to 15 cm/yr. This will highlight any rows in the table which have a velocity magnitude greater than 15 cm/yr – useful for determining if and when plate velocities exceed physically plausible values.

Figure 12: The Configure Velocity Calculations window (Step 8)

  1. After changing the yellow velocity warning value to 15 cm/yr, click ‘Apply’, then ‘Close’ and click ‘Update’ in the main Kinematic Tool window.

If you now inspect the table, you will notice that one of the rows (60 Ma) has been highlighted in yellow, indicating that the velocity at this time step is greater than 15 cm/yr (Figure 13).

Figure 13: After updating the Kinematics Tool, the row entry for 60 Ma has been highlighted in yellow.

  1. To demonstrate how the Kinematics Tool can be used to find problems in plate models, switch to the 2.7_demo.rot rotation file using the Layers window, then click Update in the Kinematics Tool window.

This rotation file contains an error in India’s rotations at 125 Ma, resulting in anomalous velocities which can be easily identified using the Kinematics Tool (Figure 14). To see the result of this error, reconstruct the period 130–120 Ma in the main window.

Figure 14: Using the Kinematics Tool, errors in plate reconstructions are easy to spot, such as this incorrect rotation at 125 Ma in 2.7_demo.rot.

Afterwards, switch back to the Muller_etal_2019_CombinedRotations.rot rotation model using the Layers window, and Update the Kinematics Tool again.

The values calculated by the Kinematics Tool and shown in the table can also be exported to a file (e.g. CSV, TSV) for later use.

  1. In the main kinematic Tool window, click ‘Export Table’ (Figure 15). Navigate to where you would like to save your file and click ‘Save’.

Figure 15: Kinematics Tool showing the ‘Export table’ option (Step 11).

The exported file can be used by any tool capable of processing CSV or TSSV files (e.g. Excel, Python, GMT). This will allow you to perform more advanced operations using this data, such as plotting multiple values on one graph. For example, you could use this method to compare the motion of a single point across several different reconstruction models.

Exercise 2 - Looking at relative and absolute motion

Compare the absolute kinematics of Australia with its kinematics relative to Antarctica.

In Exercise 1, we looked at the absolute motion of a point over time. We can also use the Kinematics Tool to investigate the motion of a point relative to another plate. This can be useful to determine when different plates are moving as one and when they start to move independently.

In this exercise, we will investigate the motion of the Australian plate since 200 Ma, both in absolute terms and relative to the Antarctic plate.

  1. If coming from Exercise 1, unload the 2.7_demo.rot rotation model using the File → Manage Feature Collections window.

  1. Load the following rotation and coastline files into GPlates (if coming from Exercise 1, these files will already be loaded):

  1. Rotate the globe so that Australia and Antarctica are in view (Figure 16)

Figure 16: View of Australia and Antarctica (Step 2)

  1. Using the Feature Inspection Tool, select Australia.

  1. Click Utilities → Open Kinematics Tool… (or Ctrl/Cmd+Shift+K)

  1. Select ‘Use focussed feature’ to fill the Lat, Lon, and Plate ID fields automatically. Notice that the given Lat and Lon values (-10.7492, 142.6121) correspond to a point at the far northern tip of Australia (Figure 17). This is because when used with a polygon or polyline feature, the ‘Use focussed feature’ option simply uses the location of the first point in the list which makes up the feature’s geometry.

Since we will be looking at the motion of Australia relative to Antarctica, we want to choose a point closer to Antarctica, ideally somewhere along the southern coast (Figure 17).

Figure 17: Automatically selected point for kinematic calculations in yellow, manually selected point in red

  1. Manually change the Latitude and Longitude in the top left corner of the Kinematics Tool window to -32.0295, 132.1987. Make sure the Plate ID is 801 (Australian plate) and the Anchored Plate ID is 0. We will also set the Begin and End times to 200 Ma and 0 Ma, respectively, and use 5 My timesteps. Then click ‘Update’.

  1. Change the display of the graph and look at the absolute Latitude, Longitude, Velocity Magnitude and Velocity Azimuth of southern Australia over time (Figure 18)

Figure 18: Absolute kinematics for a point on the southern Australian coastline.

We will now compute the motion of this same point relative to Antarctica.

  1. In the Kinematics Tool window, specify the Anchor Plate ID as 802 (Antarctica) and click ‘Update’

  1. Change the display of the graph and look at the absolute Latitude, Longitude, Velocity Magnitude and Velocity Azimuth of Australia over time (Figure 19).

Figure 18: Kinematics for a point on the southern Australian coastline, relative to the Antarctic plate.

Notice that for the period 200–160 Ma, the four parameters we are looking at do not change. This indicates that there is no relative motion between Australia and Antarctica at this time, but this does not mean that the point is stationary. Rather, this indicates that Australia and Antarctica were moving as one during this period, and when the graphs begin to show changes in these parameters, Australia and Antarctica are starting to move independently.

If we were to look at the absolute motion of a corresponding point in Antarctica, we would expect identical kinematics during 200–160 Ma, as indicated by the lack of relative motion. We can also check this by playing the animation in the main GPlates window.

Note: Be careful when comparing graphs if you have used the ‘Autoscale y-axis’ tool - some changes will be magnified so they appear greater than they are. The y-axis extents of different graphs may also differ and become a problem when comparing Latitude and Longitude.

References

Müller, R. D., Zahirovic, S., Williams, S. E., Cannon, J., Seton, M., Bower, D. J., Tetley, M. G., Heine, C., Le Breton, E., Liu, S., Russell, S. H. J., Yang, T., Leonard, J., and Gurnis, M., 2019, A Global Plate Model Including Lithospheric Deformation Along Major Rifts and Orogens Since the Triassic: Tectonics, v. 38, no. 6, p. 1884-1907. doi: 10.1029/2018tc005462.