Included are some workflows that use continent contouring from GPlately. This essentially amounts to creating a ContinentContouring object using rotation files, some continent/craton features (polygons), a contour resolution to determine how finely tessellated the contour outlines should be, a buffer/gap threshold to expand continents outward, and two area thresholds to separately exclude small continental islands and small oceanic islands. It will then reconstruct the polygons to an age and contour them into continents. This will output the continent contours (as polyline continental-oceanic boundaries) and/or continent masks (a 2D NumPy boolean array of continental crust at each age):
from gplately.ptt.continent_contours import ContinentContouring
continent_contouring = ContinentContouring(...)
...
contoured_continents = continent_contouring.get_contoured_continents(age)
continent_mask = continent_contouring.get_continent_mask(age)
The workflows then use these contours and masks in different ways.
The following Python packages are required:
You can install these with conda:
conda create -n <conda-environment> -c conda-forge gplately numpy pygplates
conda activate <conda-environment>
...where <conda-environment> should be replaced with the name of your conda environment.
Current workflows include:
Creates passive margins through time by excluding those parts of contours that are considered to be active margins (that are within a threshold distance from subduction zones).
To run the workflow you'll first need to copy the Merdith et al (2021) 1Ga plate model files into models/Merdith_etal_2021_Published/.
Note: You can use a different plate model by changing the parameters
rotation_features,topology_featuresandcontinent_featuresto refer to files that you provide. And you can change the time range.
You can then run the workflow with python create_passive_margins.py. You should end up with a files output/passive_margin_features.gpmlz containing the passive margin features, output/subduction_zone_features.gpmlz containing the subduction zones, output/continent_contour_features.gpmlz containing the continental-oceanic boundaries (COBs) as polylines (these are all the contours around continental crust), and a NetCDF grid at each time output/continent_mask_<time>.nc representing the mask of continental crust at that time.
Parameters at the top of create_passive_margins.py control its behaviour. The time range is specified with start_time, end_time and time_interval. The maximum distance of an active margin from a subduction zone (in kms) is specified with max_distance_of_subduction_zone_from_active_margin_kms. The grid spacing (in degrees) between points in the grid used for contouring/aggregrating blocks of continental polygons is specified with continent_contouring_point_spacing_degrees. The parameter continent_contouring_area_threshold_steradians (which can also be a function of time continent_contouring_area_threshold_steradians(time)) determines if contoured continents smaller than this will be excluded. The parameter continent_exclusion_area_threshold_steradians (which can also be a function of time) determines if oceanic holes (in continents) smaller than this will be excluded. The parameter continent_contouring_buffer_and_gap_distance_radians (which can also be either a function of time or a function of both time and a specific contoured continent) will expand continents ocean-ward by a buffer of this distance. The parameter continent_separation_distance_threshold_radians (which can also be a function of time) determines the distance above which continents become separated. And finally, the use_all_cpus parameter controls CPU usage (whether to use multiple CPUs and how many).
All the passive margins found for all times end up in a single file (similarly for subduction zones and continent contours). Each passive margin feature only exists at its reconstruction time (+/- 0.5 * time_interval). And you don’t need a rotation file to view these through time (they don’t have plate IDs) since they are meant to be reconstructed snapshots (from 0Ma to 1000Ma).
Note: When running the script you’ll get lots of temporary files, but they’ll get cleaned up when the script finishes (provided it’s not interrupted).
This workflow does not actually use continent contouring. Instead it's a version of create_passive_margins.py that reconstructs continent boundaries (instead of contouring reconstructed continental polygons). Because of this, the continent features should be continent boundaries (otherwise anything inside a continent will mistakenly get picked up as a passive margin).
However, the only output files are output/passive_margin_features.gpmlz containing the passive margin features and output/subduction_zone_features.gpmlz containing the subduction zones. But, like create_passive_margins.py, all the passive margins found for all times end up in a single file (similarly for subduction zones), and these are snapshots (ie, don't need a rotation model to view).