It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth’s major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions in conjunction with analytical and numerical modelling.
We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Our models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength–velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. This mechanism offers new insights into the balance of plate driving forces through time.
The images illustrate the plate speed-up of South America, Australia, and North America during the fragmentation of Pangea. The process is linked to the rift-induced damage of the breaking continent, as illustrated in the lower right image. (click to enlarge)
Brune, S., Williams, S.E., Butterworth, N.P., Müller, R.D.: Abrupt plate accelerations shape rifted continental margins: Nature, 536 (7615), 201–204, doi:10.1038/nature18319.
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The video is taken from the free webinterface of the rift velocity database (linked here). Follow this link to view and download rift velocities during Pangea break-up.
Rift velocity evolution during separation of South America from Africa. The abrupt speed-up of South America is due to a cross-scale effect: the non-linear decay of rift strength. The abrupt rift weakening results from non-Newtonian rheology and brittle failure of the materials that constitute Earth's lithosphere.