The West Antarctic rift system (WARS) is the product of
multiple stages of intracontinental deformation from Jurassic to Present. The Cretaceous rifting phase accomplished
>100 percent extension across the Ross Sea and central West
Antarctica, and is widely perceived as a product of pure shear
extension orthogonal to the Transantarctic Mountains that led
to breakup and opening of the Southern Ocean between West
Antarctica and New Zealand. New structural, petrological,
and geochronological data from Marie Byrd Land reveal
aspects of the kinematics, thermal history, and chronology of
the Cretaceous intracontinental extension phase that cannot
be readily explained by a single progressive event. Elevated
temperatures in "Lachlan-type" crust caused extensive
crustal melting and mid-crustal flow within a dextral transcurrent strain environment, leading to rapid extension and
locally to exhumation and rapid cooling of a migmatite dome
and detachment footwall structures. Peak metamorphism and
onset of crustal flow that brought about WARS extension
between 105 Ma and 90 Ma is kinematically, temporally,
and spatially linked to the active convergent margin system
of East Gondwana. West Antarctica-New Zealand breakup
is distinguished as a separate event at 83-70 Ma, from the
standpoint of kinematics and thermal evolution
