Cenozoic range-front faulting and development of the Transantarctic Mountains near Cape Surprise, Antarctica: Thermochronologic and geomorphologic constraints

Abstract

[1] The Transantarctic Mountains (TAM) define the western flank of the West Antarctic rift system. Cape Surprise, near the Shackleton Glacier in the central TAM, is the only location along the range's >3500 km length where upper Paleozoic Beacon Supergroup strata are down-faulted to near sea level. Previous studies have inferred a range front master normal fault accommodates extension and rock uplift across the TAM front in this region. The history of rock uplift is debated, suggested as early as Mesozoic, typically Cenozoic, or even Pliocene or younger. Structural observations, apatite fission track (AFT) thermochronology, and geomorphologic mapping undertaken within the TAM front east of the Shackleton Glacier indicate extension, faulting, and denudation was mostly late Eocene–late Oligocene and likely into the early Miocene. An exhumed AFT partial annealing zone is found at the coast and traced >50 km inland. The base of that exhumed partial annealing zone indicates denudation accelerated at ∼40 Ma near the coast and at 30–35 Ma on the inland side of the TAM front. Vertically offset AFT isochrones across the TAM front reveal a step-faulted architecture rather than a single master fault. The cumulative vertical offset of the 55 Ma isochrone is 2.3–2.7 km, compared to 2.4–2.6 km offset of Beacon strata, indicating that all significant normal faulting is Cenozoic, and not related to Mesozoic extension within the West Antarctic rift system. Denudation from <26 Ma to ∼14 Ma produced a locally preserved erosion surface within the TAM front. Erosion surface remnants indicate the TAM front has undergone minimal internal deformation and only 290–790 m of surface uplift along offshore faults since the middle Miocene.