In a new paper to appear in Physics of the Earth and Planetary Interiors , Magali Billen and Katrina Arredondo (PhD 2016) show that during episodes of slab folding in the transition zone the overriding plate and the underlying asthenosphere can flow in opposite directions. This occurs as rapid sinking of the slab in the transition zone causes the viscosity to drop to less than 10^19 Pa-s around the slab and beneath the overriding plate. Such low viscosity allows the asthenosphere to be pulled toward the slab, while the overriding plate is pushed by the advancing motion of the subducting plate and shallow slab.
Strangely, I have never been to GSA before, but this year I am making up for this and presenting 3 talks and 1 poster at GSA.
Numerical models of subduction show that spontaneous rifting of the arc or forearc may occur due to an in situ instability in the mantle wedge corner. This new mode of arc/forearc rifting is explained in a journal article by Dr. Billen, that is now in press at Geophysical Research Letters.