The story of double spreading centers formed during continental rifting in 2D

It is common wisdom, based on many years of published simulations of continental rifting followed by spreading that in 2D when a mid-oceanic ridge form in a numerical simulation of continental rifting, extension stops and spreading take over the extension. This is generally due to the complete loss of strength of the mantle lithosphere that cannot transmit forces horizontally across the spreading zone anymore. Actually, in general even the onset of mantle lithosphere necking in a simulation can cause the end of the extension and for many years, I actually claimed very load in the past that two active necking system must be the signature of some obliquity causing 3D extensional conditions. However, recently, a whole series of 2D simulations produced systematically two spreading centers active at the same time. These results surprised me a lot. These simulations were very complex, including a lot of inheritance, the first easy conclusion could have been to say that inheritance causes multiple spreading… But we spent some time and effort to understand if this behavior was due to inheritance or something else. Simplifying our model set-up to the strict minimum, we found it was not inheritance, but a quite cold mantle temperature which permitted a larger shear coupling between the upper mantle dynamics and the mantle lithosphere.  A 50°C difference in mantle temperature radically change the results of the simulation and thanks to our failure, we have found the embryo of an alternative explanation to 3D interactions for the occurrence multiple active necking zones.