Structure and Kinematics of the Central Transantarctic Mountains: Constraints from structural geology and geomorphology near cape surprise

The transition zone between the Transantarctic Mountains (TAM) and the West Antarctic rift system is defined as the Transantarctic Mountain Front (TMF). In the vicinity of Cape Surprise (84°30'S) near the Shackleton Glacier in the central TAM, two fault sets have been mapped. Mesoscopic faults and geomorphic trends indicate that one set of normal faults within the TMF is generally dip-slip in nature and strikes parallel to the mountain range. The second fault set is oriented approximately perpendicular to this. Kinematic analysis of lineated fault surfaces reveals an extension axis oriented 020°-040°, orthogonal to the trend of the central TAM. However, asymmetric drainage patterns and a small number of lineated fault surfaces support a kinematic model of Cenozoic dextral transtension in the TMF. While age constraints on these two episodes of deformation are poor, it is likely that dextral transtension followed orthogonal extension, as suggested from other regions of the TAM. Apparent orthogonal extension in the TMF is thus consistent with early Cenozoic rift-flank uplift driven by isostatic forces. A middle to late Cenozoic period of transtension could be contemporaneous with strike-slip faulting in the Ross Sea, and could also indicate less strain partitioning between the rift system and the TMF after the uplift rate decreased.