Christian Teyssier Christine Siddoway Michael A. Cosca C. Mark Fanning Rory McFadden 2015 <p id="sp0005">In Marie Byrd Land, West Antarctica, the Fosdick Mountains migmatite-cored gneiss dome was exhumed from mid- to lower middle crustal depths during the incipient stage of the West Antarctic Rift system in the mid-Cretaceous. Prior to and during exhumation, major crustal melting and deformation included transfer and emplacement of voluminous granitic material and numerous intrusions of mantle-derived diorite in dikes. A succession of melt- and magma-related structures formed at temperatures in excess of 665&nbsp;±&nbsp;50&nbsp;°C based on Ti-in-zircon thermometry. These record a transition from wrench to oblique extensional deformation that culminated in the development of the oblique South Fosdick Detachment zone. Solid-state fabrics within the detachment zone and overprinting brittle structures record translation of the detachment zone and dome to shallow levels.</p><p id="sp0010">To determine the duration of exhumation and cooling, we sampled granite and gneisses at high spatial resolution for U–Pb zircon geochronology and ⁴⁰Ar/³⁹Ar hornblende and biotite thermochronology. U–Pb zircon crystallization ages for the youngest granites are 102&nbsp;Ma. Three hornblende ages are 103 to 100&nbsp;Ma and 12 biotite ages are 101 to 99&nbsp;Ma. All overlap within uncertainty. The coincidence of zircon crystallization ages with ⁴⁰Ar/³⁹Ar cooling ages indicates cooling rates &gt;&nbsp;100&nbsp;°C/m.y. that, when considered together with overprinting structures, indicates rapid exhumation of granite and migmatite from deep to shallow crustal levels within a transcurrent setting. Orientations of structures and age-constrained crosscutting relationships indicate counterclockwise rotation of stretching axes from oblique extension into nearly orthogonal extension with respect to the Marie Byrd Land margin. The rotation may be a result of localized extension arising from unroofing and arching of the Fosdick dome, extensional opening within a pull-apart zone, or changes in plate boundary configuration.</p><p id="sp0015">The rapid tectonic and temperature evolution of the Fosdick Mountains dome lends support to recently developed numerical models of crustal flow and cooling in orogenic crust undergoing extension/transtension, and accords with numerous studies of migmatite-cored gneiss domes in transcurrent settings.</p> application/pdf 10.1016/j.lithos.2015.07.005 en Elsevier Mid-Cretaceous oblique rifting of West Antarctica: Emplacement and rapid cooling of the Fosdick Mountains migmatite-cored gneiss dome article