Regional geologic constraints including crustal architecture, combined with observations made by Ford and Barrett (1975) on core from DSDP-site 270 in the central Ross Sea, indicate Cretaceous extension between East and West Antarctica was accommodated largely by detachment faulting. Structures in the basement rock and sedimentary breccia cored at site 270 have characteristics consistent with rocks that have undergone progressive deformation during exhumation along low-angle detachments. Metamorphic rocks recovered are both ductilely and brittlely deformed. Sedimentary breccia cored just above basement rock is locally derived, formed by erosion of previously brecciated ductilely deformed metamorphic and igneous rock. Angular clasts within the syn-tectonic breccia contain ductile fabric which have been subsequently overprinted by brittle deformation. The breccia itself has also undergone brittle deformation. Apatite fission track data from calc-silicate gneiss recovered from site 270 gives a mean age of 103+ or -11 Ma, with two components of single grain ages; 187+ or -22 Ma and 90+ or -6 Ma. We suggest the older component reflects initial cooling due to transtension between East and West Antarctica in the Jurassic. The younger (and more prevalent) group of single grain ages is indicative of Cretaceous extension (105-85 Ma). Cenozoic extension and magmatism occurred within the Victoria Land Basin, coeval with uplift of the present day Transantarctic Mountains.