DIFFERENTIAL MOVEMENT ACROSS BYRD GLACIER, ANTARCTICA, AS INDICATED BY GEOMORPHOLOGICAL ANALYSIS AND APATITE (U-TH)/HE THERMOCHRONOLOGY

The Transantarctic Mountains (TAM) are a continental-scale rift shoulder separating cratonic East Antarctica from the West Antarctic rift system. At a number of locations along the TAM, ice from the East Antarctic ice sheet pours across the mountains through major outlet glaciers. The greatest volume of ice of any of the outlet glaciers is carried by Byrd Glacier, which also marks a major discontinuity in the Neoproterozoic-early Paleozoic Ross orogen, the so-called basement of the TAM. Based on no geological evidence, early geologists inferred faults down the axes of a number of the outlet glaciers. The objective of this study was to assess possible differential movement across the inferred fault beneath Byrd Glacier. Two complementary approaches were taken, one geomorphological, the other thermochronological. The geomorphological part of the study relied on the presence of the Kukri erosion surface, an unconformity on the Ross basement rocks overlain by subhorizontal, sedimentary rocks of the Devonian to Triassic Beacon Supergroup. A Landsat image of the Byrd Glacier area was overlain on Aster Global DEM data and spot elevations of the Kukri erosion surface to the north and south of Byrd Glacier were mapped. The difference in elevation of the erosion surface across Byrd Glacier showed an offset of ~1km with the south side up relative to the north. The geochronological part of the study utilized single-crystal, (U-Th)/He analysis of apatite from samples of known elevations collected on both the north and south sides of Byrd Glacier. When plotted on an age vs. elevation diagram, the data indicate an overall denudation rate of ~0.04 mm/yr between 180 – 40 Ma. When the data are separated geographically, they show an offset of ~1 km across Byrd Glacier with the south side displaced up relative to the north. The complementary results from this study demonstrate the utility of our dual approach to this tectonic problem.