[GPlates-discuss] Flow lines and ridge jumps

Mark Brandon mark.brandon at yale.edu
Mon Dec 17 11:43:39 AEDT 2018

I have been trying out GPlates' flow-line calculation to represent the evolution of the Juan de Fuca spreading center and adjacent plates over the last 40 Ma. As you might know, the JdF spreading center has had some ridge-jump events, one at 20 Ma and another at 5 Ma. My issue here concerns how to represent a change in the spreading center with respect to the flow-line calculation. 

I document this situation here in two ways, as shown in the two attached movies. The data sources for the reconstructions are: Mueller et al 2016 AREPS Isochrons (Reconstructed Geometries), Matthews et al 2016 GPC, Mesozoic-Cenozoic Plate Topologies (Reconstructed Geometries). The reference frame for the reconstructions is North America fixed, and the time interval is from 40 Ma to present.

Note that the Yale email server strips out movie attachments, so the attachments here have extensions of .4pm to avoid this problem. Save the files and then convert the extensions to .mp4, and all will be good. 

The two reconstructions are:

1)  Movie: "flowlines Pacific-Vancouver 40-0 Ma"
The 40.1 Ma anomaly on the Pacific plate is set as the left-side endpoint for all flow lines, with the Vancouver plate on the "right side". 

2) Movie: "flowlines Pacific-JdF 40-0 Ma.mp4"
The modern Pacific/Juan de Fuca boundary is set as a "spreading center", with the flow lines calculated symmetric relative to that reference. (As an aside, I don't know why the flow-line calculation does not work in this case for the time interval between 40 and 29 Ma.) 

The first reconstruction provides a clear correspondence between the seed points and the coeval spreading center during the early part of the reconstruction. This relationship breaks down after the ridge jumps at 20 and 5 Ma. 

The second reconstruction shows a poor correspondence between seed point and the coeval spreading center during the early part of the reconstruction. That situation switches to a good correspondence during the later part of the reconstruction. 

For course, this is all expected given that the seed points for the first case are based on the initial configuration of the spreading center, and the second case, on the final configuration of the spreading center. 

The first case does a good job representing the motion of the bounding 40.1 Ma isochrons move away from the spreading center. The second case does a good job representing the age distribution near the final spreading center. Both calculations seem to give the same estimate of the displacement field relative to the coeval plate boundary (aka active spreading center). This last point is important, but difficult to precisely verify from these examples. 

>> It would be useful to hear from the GPlates programmers about this last statement. 

My objective is not the displacement field, but rather the plate age around the spreading center. My thought at this point is that the plate age might be represented by the minimum of the two age fields. In other words, a ridge jump operates to introducing younger lithosphere in the area around the new ridge. That said, I think there may be some ridge-jump situations that can defeat this simple view.

I am hoping to get feedback from others, especially those who have already thought through this situation...


-------------- next part --------------
A non-text attachment was scrubbed...
Name: flowlines Pacific-Vancouver 40-0 Ma.4pm
Type: application/octet-stream
Size: 1812976 bytes
Desc: not available
URL: <http://mailman.sydney.edu.au/pipermail/gplates-discuss/attachments/20181216/e2d0037d/attachment-0002.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: flowlines Pacific-JdF 40-0 Ma.4pm
Type: application/octet-stream
Size: 849392 bytes
Desc: not available
URL: <http://mailman.sydney.edu.au/pipermail/gplates-discuss/attachments/20181216/e2d0037d/attachment-0003.obj>
-------------- next part --------------

More information about the GPlates-discuss mailing list