Structure of the Transantarctic Mountains Determined From Geophysical Surveys

  1. Mort D. Turner and
  2. John E. Splettstoesser
  1. Edwin S. Robinson1 and
  2. John F. Splettstoesser2

Published Online: 16 MAR 2013

DOI: 10.1029/AR036p0119

Geology of the Central Transantarctic Mountains

Geology of the Central Transantarctic Mountains

How to Cite

Robinson, E. S. and Splettstoesser, J. F. (1986) Structure of the Transantarctic Mountains Determined From Geophysical Surveys, in Geology of the Central Transantarctic Mountains (eds M. D. Turner and J. E. Splettstoesser), American Geophysical Union, Washington, D. C.. doi: 10.1029/AR036p0119

Author Information

  1. 1

    Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061

  2. 2

    Minnesota Geological Survey, University of Minnesota, St. Paul, Minnesota 55114

Publication History

  1. Published Online: 16 MAR 2013
  2. Published Print: 1 JAN 1986

ISBN Information

Print ISBN: 9780875901848

Online ISBN: 9781118664797

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Keywords:

  • Bedrock geology;
  • Bouguer gravity anomalies;
  • Geophysical surveys;
  • Isostasy;
  • Roosevelt island;
  • Seismic velocity structure;
  • Topography

Summary

Seismic and gravimetric survey results outline the extent of the Transantarctic Mountain system beneath the ice cover, provide information about the upper crustal geology, and indicate gross variations in crustal thickness. The stratigraphic section is exposed from sea level to elevations in excess of 4 km along the western coast of the Ross Sea. The Beacon Supergroup, ranging in age from Devonian to Jurassic, consists mainly of nearly flat-lying nonmarine and shallow marine sediments. The Beacon overlies unconformably a complex of Precambrian and lower Paleozoic metamorphosed geosynclinal rocks and granitic intrusions. Diabase sills of Jurassic age intrude the basement complex and the sedimentary section. Late Tertiary and Quaternary volcanics are widespread in the area bordering the Ross Sea. The mountain system appears to be a block-faulted structure. Topographic data from seismic surveys show it to be of asymmetrical cross section, steeper on the West Antarctic side. Subglacial bedrock elevation profiles determined from seismic and gravimetric measurements compare well with more recent airborne radio echo-sounding results in the same area. The system is approximately 200 km wide in the Victoria Land area and widens to about 400 km in the region of the Horlick Mountains. Seismic refraction data indicate that if the Beacon Supergroup exists beneath the ice cover, it is much thinner than the exposed sections. Reflection results point to a thin layer of unconsolidated sediment beneath the ice in many areas. In general, East and West Antarctica are characterized by similar upper crustal velocity structure. Bouguer gravity anomalies indicate that crustal thickness along the East Antarctic margin, including the mountains, is at least 10 km thicker than in the adjacent Ross Sea area. A gradient exceeding 3 mGal/km perpendicular to the ranges and extending along the western coast of the Ross Sea, the Horlick Mountains front, and the border of the Weddell Sea and the Pensacola Mountains indicates an abrupt change in crustal thickness as demonstrated by twodimensional model studies. Bouguer anomalies more negative than −100 mGal characterize the East Antarctic sector, compared to values of about +30 mGal in the Ross Sea area. These facts suggest that a major crustal fault zone extends along the coast of the Ross Sea and the border of the Horlick Mountains. No such fault zone was indicated along the East Antarctic margin of the mountain system. This leads to a modification of the “Great Antarctic Horst” concept to that of a block-faulted mountain system bordered on the West Antarctic side by a crustal fault. The ice-covered area west of the ranges in northern Victoria Land is characterized by an isostatic anomaly more negative than −30 mGal. This anomaly is difficult to explain in terms of delayed rebound associated with a thinning ice cover or of regional compensation of the mountain ranges. Therefore additional stresses in the mantle appear to be required to maintain the observed state of isostatic imbalance. The existence of a spectacular intracontinental mountain system devoid of folds and thrust faults, and bordered by a fault zone across which crustal thickness changes by 10 km or more, is unique in modern global continental geology. Speculations suggest that the structural origin of the present Transantarctic Mountains is related to nonconvergent movements of West Antarctic plate fragments along the margin of an East Antarctic plate. Now the mountains are essentially aseismic, and volcanic activity is diminished. These considerations suggest that an episode of intensive tectonism may be drawing to a close and that formerly mobile fragments may have fused into the present Antarctic plate.