TRANSANTARCTIC BASIN: NEWINSIGHTS FROM FISSION TRACKAND STRUCTURAL DATA FROM THE USARP MOUNTAINS AND ADJACENT AREAS (NORTHERN VICTORIA LAND,ANTARCTICA)

The USARP Mountains comprise two N-S-aligned mountain ranges (Daniels Range, Pomerantz Tableland) located along the western margin of the RennickGlacier inNorthernVictoria Land (NVL). Four zircon and titanite ¢ssion track (FT) ages fromgranitic samples from the PomerantzTableland fall in a common range of 369^392Ma.The apatite FTages from20GraniteHarbour Intrusive rocks sampled throughout theUSARPMountains are distinctively younger (86^270Ma); their mean track lengths (MTL) vary between11.0 and13.9mm. Six samples fromRenirie Rocks and the Kavrayskiy Hills east of theUSARPMountains have even younger, concordant apatiteFTages of 43^71Ma, andMTL of 12.2^14.0 mm.Thermal history modelling of the thermochronological data indicate that both the Daniels Range and PomerantzTableland experienced a common Phanerozoic geologic history consisting of a mid-Devonian pulse of rapid denudation, followed by a protracted denudation stage between the Carboniferous and Jurassic.This latter period of denudationwas contemporaneous with the formation of theTransantarctic Basin to the east.We consequently suggest that theUSARP Mountains were one of the major source areas for the Beacon Supergroup that formed the ¢ll of the Transantarctic Basin.Subsequent to the deposition of the Beacon sequence, the now-outcropping rocks of theUSARPMountains were buried to a maximum depth of 4.2km. A palaeogeothermal gradient of 25 8 1Ckm1was inferred at the time of maximumburial. Inversion of theTransantarctic Basin due to the breakup of Gondwana, and in response to Cenozoic rifting and uplift of theTransantarctic Mountains, has triggered the ¢nal denudation stages recorded inNVL since the Cretaceous.Thereby, the amounts of denudation increase eastward.Whereas 2.4^4.2 km of crustal unloading are recognized for theUSARPMountains since the Cretaceous,more than 4 km of denudation has occurred towards the RennickGraben alone since the Eocene.This denudationwas associatedwith major fault activities involving earlyENE^WSWtoE^W-directed extension.Related structureswere reactivated bydominant NW^SEtoNNW^SSE-oriented right-lateral shear genetically linked to the formation and inversion of the structural depression of the RennickGraben in Cenozoic times.