Cretaceous Uplift of the Transantarctic Mountains-Not Due to Rift-Flank Uplift

The Transantarctic Mountains (TAM) form a >3000 km-long boundary between East and West Antarctica with extreme relief reaching to >4500 m in elevation. Proximity of the TAM to the Cretaceous/Paleogene West Antarctic Rift System (WARS) suggests a genetic relationship between development of the TAM and extension of West Antarctica. However, the details of this relationship remain elusive.Here we present the results of a low-temperature thermochronology study in the central TAM combined with numerical modelling of the thermal-kinematic crustal evolution. Sampling was undertaken along the ~100 km long, ~40 km wide Byrd Outlet that cuts through the TAM. We focus on the results of apatite fission track (AFT) analysis of seventeen samples collected along two near-vertical transects. All of these samples yield AFT ages of ~80 Ma. Transect A, located 45 km from the mountain front, has nine ~80 Ma samples along >1500 m of near-vertical relief (580-2140 m asl). Transect B is located 70 km from the mountain front, with eight ~80 Ma old samples along 700 m of near-vertical relief (450 m to 1150 m asl).These ~identical ages typically would be interpreted to indicate rapid cooling through the AFT partial annealing zone (PAZ; 120°C-60°C). However, inverse modeling (HeFTy) shows that the samples experienced slow cooling (~4°C/m.y.), with samples remaining within the AFT PAZ for 30-60 my. Thus, there appears to be an inherent contradiction between the instantaneous cooling at ~80 Ma and the very slow cooling. To explore this apparent contradiction we designed a finite-difference thermal-kinematic model to reconstruct the erosional/cooling history of the crust of the Byrd Outlet region. Successful simulations must predict three things: 1) a coherent 1500 m thick crustal section that passes through the AFT closure temperature (110°C) ± simultaneously (± 5my), 2) this crustal section then must remain in the AFT PAZ for greater than 15 my, and 3) the top of this crustal section is currently located 1300 m below the adjacent surface of the earth (below the current peak of Mt McClintock at 3490 asl).Modeling results confirm that successful simulations must include rapid incision of a km’s-deep gorge and the associated ± instantaneous cooling of the crustal section, followed by 10’s of millions of years of regional erosion and slow cooling through the AFT PAZ.These results provide constraints on the timing and mechanisms responsible for the uplift of the central TAM. Firstly, the region-wide 80 Ma ages reveals incision of high topography in the Cretaceous, ~coeval with development of the West Antarctic Rift System. Secondly, this development of high topography far inland from the mountain front is inconsistent with rift-flank uplift. Additionally, the deep incision indicates > 5 km of uplift, which exceeds the amount that could be reasonably assigned to just flexure plus crustal thickening or just flexure plus lithospheric