A Geophysical Survey of Subglacial Geology Around the Deep-Drilling Site at Dye 3, Greenland

  1. C.C. Langway Jr.,
  2. H. Oeschger and
  3. W. Dansgaard
  1. K. C. Jezek,
  2. E. A. Roeloffs and
  3. L. L. Greischar

Published Online: 18 MAR 2013

DOI: 10.1029/GM033p0105

Greenland Ice Core: Geophysics, Geochemistry, and the Environment

Greenland Ice Core: Geophysics, Geochemistry, and the Environment

How to Cite

Jezek, K. C., Roeloffs, E. A. and Greischar, L. L. (1985) A Geophysical Survey of Subglacial Geology Around the Deep-Drilling Site at Dye 3, Greenland, in Greenland Ice Core: Geophysics, Geochemistry, and the Environment (eds C.C. Langway, H. Oeschger and W. Dansgaard), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM033p0105

Author Information

  1. Geophysical and Polar Research Center, University of Wisconsin-Madison, Madison, Wisconsin

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900575

Online ISBN: 9781118664155

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Keywords:

  • Ice sheets—Greenland—Addresses, essays, lectures;
  • Greenland Ice Sheet Program

Summary

A geophysical survey of subglacial geology was carried out upstream of the Dye 3 borehole in order to characterize bedrock morphology and near-surface crustal structure in an area believed to be close to the boundary between the Archaean craton and the Nagssugtoqidian mobile belt. The survey consisted of radar determinations of bedrock elevation and gravity measurements to be used in estimating near-surface densities.

Free-air anomalies are strongly positive (about + 80 mgal) and are about 50 mgal higher than the 1° × 1° mean free-air anomalies determined by satellite measurements. Results of our gravity surveys west of Dye 3, as well as along the EGIG line, suggest the positive anomalies are indicative of an eastward increasing trend in gravity across southern Greenland, perhaps due to regional structure in the crust and mantle rather than to glacial isostasy.

The complex bedrock topography in the Dye 3 area was mapped using radar operated from the surface. The effect of bedrock topography on the free-air gravity was modeled in three dimensions using a program based on the method of Talwani and Ewing. The uniform density model of bottom structure that gives the best fit to the gravity data has a density of 2.7 g/cc and is morphologically similar to the bedforms found in the more extensive survey presented by Overgaard and Gundestrup. The bedrock topography map we show represents our best estimate after combining the radar data with our 2.7 g/cc gravity model. We find a rugged, at times precipitous, terrain whose features have a wavelength of about 8 km, an amplitude of 350 m and a roughly north-south strike. Although the terrain suggests that this area has been structurally altered, perhaps by tectonic forces, the data provide no direct means of distinguishing between the Archaean block and the mobile belt. Morphological differences between our middle site and Dye 3 weakly suggest a geologic boundary may lie between the sites.