Abstract:
Separate regions within the Transantarctic Mountains, the uplifted flank of the
West Antarctic rift system, appear to have distinct Neogene histories of
glaciation and valley downcutting. Incision of deep glacial outlet valleys
occurred at different times throughout central and northern Victoria Land. This
is corroborated by measurements of cosmogenic nuclides 21Ne, 10Be and 26Al of
glacial
... erosion surfaces and high-elevated moraines. 21Ne ages of two summit
plateaus, at elevations of 1650 m in central Victoria Land and ~2800 m in
northern Victoria Land, range from 3.84 to 11.2 Ma, respectively. The latter
date indicates that these glacial erosion surfaces are the oldest known
exposure dated surfaces on Earth. Glacial erosion terraces, remnants of early
phases of valley downcutting, have 21Ne ages of 1.27 and 6.45 Ma for central
Victoria Land and northern Victoria Land, respectively. Therefore, deglaciation
of summit plateaus, valley downcutting and topographic uplift occurred during
the mid Miocene in northern Victoria Land and not earlier than the mid Pliocene
in central Victoria Land. In northern Victoria Land ice flow directions changed
markedly from the time a regional ice sheet occupied the level of the highest
summits to the present condition with summits rising up to 800 above the valley
glaciers. In central Victoria Land the oldest documented ice flow direction
occupying the summit erosion surface prior to incision was SW-NE, draining the
East Antarctic Ice Sheet along an outlet glacier at least ten times as wide as
the present E-W flowing David Glacier. This great variation in denudation
histories probably results from differential tectonic uplift of various regions
within the presently active rift flank. Three tectonic processes contribute to
late Neogene uplift, (1) ongoing extension in adjacent Ross Sea rift basins,
(2) regional dextral transtension following SE trending Precambrian and
Palaeozoic structural trends which offsets the ~N-S trending grain of the rift
and reactivates earlier faults, and (3) isostatic response to valley
downcutting and related denudation.
INVESTIGATORS
Dr F.M. Van der Wateren
A.L.L.M. Verbers (M. Sc)
Dr T.J. Dunai
Dr. S. Passchier 
