ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

A.K. KERR 1, DAVID E. SUGDEN 1,
HERMIONE A.P. COCKBURN\ RODERICK W. BROWN 2
& MICHAEL A. SUMMERFIELD1
Tectonics and landscape development in a passive
margin setting: the Transantarctic Mountains
1Department of Geography, University of Edinburgh,
Edinburgh ER8 9XP, U.K.
2 Victorian Institute of Earth and Planetary Sciences, School of Earth
Sciences, La Trobe University, Bundoora, Victoria 3083, Australia
Two contrasting approaches have generally been applied
to the problem of long-term landscape development in
passive continental margin settings. One involves the modelling
of tectonic mechanisms on the basis of geophysical
data on internal processes and lithospheric properties to
yield coarse-scale predictions of changes in topography through
time. The other approach utilises predominantly
geomorphological data to reconstruct histories of landscape
development without any explicit attempt to explain
the tectonic events that have necessarily contributed to the
inferred sequences of landscape change. The first strategy
involves forward modelling in which the aim is to identify
the particular combination of lithospheric properties and
tectonic proceses responsible for creating the present large-scale
topography. The second approach uses reverse
modelling which starts with the present landscape and
aims to reconstruct its history by identifying age relationships
between different landscape elements. Over the past
decade it has been increasingly appreciated that the internally-driven,
tectonic mechanisms operating on passive
margins do not operate independently, but rather interact
with surface processes which re-distribute material through
denudation and deposition. It is also becoming evident
that the effective analysis of such interactions between the
Earth's internal and external systems requires inputs from
both the forward and reverse modelling strategies. Geomorphological
evidence of landscape change, as well as
geophysical data and tectonic models, are therefore necessary
components of any comprehensive explanation of large-scale,
long-term landscape evolution on passive margins.
We assess the utility of these forward and reverse modelling
approaches to landscape analysis in the context of the
high-elevation passive margin represented by Transantarctic
Mountains. Rising to elevations in excess of 4000 m and
extending for more than 3000 km, the Transantarctic
Mountains provide a particularly valuable case study for
the assessment of the relative role of tectonic and surface
processes in landscape development. This is because the
persistence of a frigid polar environment throughout a significant
part of the late Cenozoic has led to the detailed
preservation of a range of ancient landscape features and
associated terrestrial deposits to an extent that has not occurred
elsewhere. It is likely that ice has been present as a
geomorphic agent in Antarctica since at least the Oligocene,
and the present-day dry, polar environment of the
Transantarctic Mountains appears to have existed with lit-
tle change since the Miocene. In constrast to virtually all
other terrestrial environments, the role of running water as
a geomorphic agent has been very largely surpressed for
millions of years and consequently the Transantarctic
Mountains also provide a setting within which to investigate
the relationships between tectonics and an unusually limited
suite of surface geomorphic processes. This region
therefore constitutes a valuable benchmark against which
to compare the morphotectonic evolution of other glaciated
passive margins, notably those fringing the North
Atlantic Ocean.
Morphological mapping combined with apatite fissiontrack
analysis on outcrop samples (including near-vertical
profiles) and in-situ produced cosmogenic isotope measurements
on bedrock surfaces provide constraints on the
long-term landscape history of specific sections of the the
Transantarctic Mountains and allow some provisional conclusions
to be drawn about long-term landscape development
in these areas and its interaction with rift and postrift
tectonics:
1. A wedge of crustal section over 4 km thick at the coast
and thinning inland has been removed from the coastal
margin of the mountains.
2. Most of this erosion was accomplished under fluvial
conditions before a full Antarctic ice sheet built up.
3. Dissection of the passive margin upwarp now represented
by the Transantarctic Mountains was largely accomplished
before the mid-Miocene. There is no firm geomorphological
evidence for Plio-Pleistocene uplift, as envisaged
by some researchers.
4. Glacial modification of the mountains has occurred selectively
and generally only to a moderate degree with the
main exception of the primary outlet glaciers and valley
glaciers of northern Victoria Land.
5. Except at low altitudes, where there has been significant
summer melting, rates of rock weathering under existing
conditions are close to zero and have remained so for
over 15 Ma.
A.R. KERR\ P. HUYBRECHTS 2
, DAVID E. SUGDEN 1
& MICHAEL A. SUMMERFIELD 1
Continental morphology and East Antarctic Ice Sheet
sensitivity
1Department of Geography, University of Edinburgh,
Edinburgh ER8 9XP, UK
2 Department of Geography, Free University of Brussels, Belgium
This paper investigates the sensitivity of the East Antarctic
Ice Sheet to the tectonic history of the Transantarctic
Mountains. For some years there has been a debate as to
whether during the Pliocene East Antarctica was largely
deglaciated or whether the East Antarctic Ice Sheet remained
in a similar state to that of today. The debate has fo-
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