STRUCTURAL AND GEOMORPHIC DEVELOPMENT OF THE TRANSANTARCTIC MOUNTAINS USING LOW TEMPERATURE THERMOCHRONOLOGY: A STUDY OF THE FORD NUNATAKS, REEDY GLACIER AREA, ANTARCTICA

The Transantarctic Mountains (TAM) represents the uplifted rift flank that defines the geological and morphological boundary between East and West Antarctica. The southernmost large outlet glacier through the TAM is the seldom-visited Reedy Glacier. The Ford Nunataks are situated within the Transantarctic Mountain Front (TMF) on the eastern side of the Reedy Glacier lying between the dramatic escarpment (~2500 m relief) of the Wisconsin Range and the down-dropped basins of the West Antarctic Rift System (WARS). This work represents part of a series of studies along the TAM documenting the denudation history in order to constrain the tectonic evolution of the TAM and WARS.

Samples were collected for low temperature thermochronology over a relief of 625 m. In general, apatite fission track (AFT) ages range from 48-106 Ma with mean track lengths of 10-13 mm and standard deviations of 1.4-2.0 mm. Analysis of apatite chemistry using Dpar indicates little chemical variation between samples and individual grains. Interpretation of AFT data and thermal modeling using the AFTSolve program indicate the Ford Nunataks AFT samples record two episodes of denudation; A Late Cretaceous event followed by an event initiated in the Late Eocene. Previous AFT work in the neighboring Scott Glacier 120 km northwest of the Reedy Glacier has recorded these events while the Ohio Range, 175 km southeast of the Reedy Glacier, has only recorded the Late Cretaceous event indicating the Cenozoic denudation event is lessening in magnitude as it propagates southward. The TAM in the Reedy Glacier thus mark the transition from Cenozoic dominated denudation to earlier phases (e.g. Late Cretaceous) of denudation that occur further along the TAM in the Ohio Range and Thiel Mountains.

East-west trending fault zones in the central Fords and just inboard towards the Wisconsin Range escarpment have horizontal slickenlines indicative of dextral strike-slip movement. This lack of evidence for a normal component of faulting coupled with no offset in AFT age for closely-spaced samples across fault zones, does not support the idea that this portion of the TMF is a zone of normal faulting such as seen elsewhere in the TAM. Instead, it is likely that the Ford Nunataks represent an erosional remnant formed by escarpment retreat.