Geological Framework of Lake Vostok, East Antarctica


M. Studinger1, R.E. Bell1, G. Karner1, V. Levin2, C. Raymond3, A. Tikku1, A. Lerner-
Lam1

1 Lamont-Doherty Earth Observatory
2 Rutgers University
3 Jet Propulsion Laboratory


The existing picture of East Antarctica as an aseismic, stable cratonic unit is 
largely based on the geological record preserved in sparse rock outcrops along the 
perimeter of the continent and isolated geophysical reconnaisance traverses in the 
interior. Lake Vostok is situated in the middle of the East Antarctic craton. We postulate 
that the topographic depression that provides the space for Lake Vostok was formed 
along a major geologic and tectonic boundary. This boundary is expressed as an abrupt 
change in the roughness of the subglacial topography across the lake. The rugged 
topography west of the lake changes to a smooth, downward bending topography east of 
the lake. The regional magnetic field changes its character across the lake supporting the 
idea of different subglacial lithologies east and west of the lake. In order to develop 
geological models for the nature of this boundary, we tested a range of gravity and 
magnetic models and compared the predicted gravity from a kinematic and flexural 
model with the observed gravity. From this analysis, we can rule out the possibility that 
the boundary represents a simple variation in crustal thickness. Similarly, we also 
concluded that the boundary was not formed as a simple extensional structure. Our 
kinematic and flexural gravity modeling supports the idea that the boundary represents 
the hinge zone of a former passive continental margin across which thrust sheets were 
emplaced. A deep asymmetric structure in the magnetic basement mapped by Werner 
deconvolution suggests the presence of a ~400 km wide, ~10 km deep sedimentary basin 
west of the lake. This basin coincides with the conceptual tectonic model derived from 
the gravity data. The velocity and density model derived from receiver functions of 14 
teleseismic events provides an independent constraint of the crustal structure and is 
consistent with the gravity modeling and magnetic inversion. We explain the line of 5 
recent earthquakes along the tectonic boundary as the minor, normal reactivation of the 
basal thrust sheets that in turn, produced the depression representing Lake Vostok. The 
presence of deeply penetrating-crustal faults beneath Lake Vostok is supported by the 
He3/He4 ratio in the Vostok ice core (J.R. Petit, pers. comm.).