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Aeromagnetic surveys of theRoss Island and Taylor Glacier

quadranglesGERALD E. MONTGOMERYDepartment of Geology

Northern Illinois University

An aeromagnetic survey of the dry valley area wasflown during the 1971-1972 field season as part of theDry Valley Drilling Project (McGinnis et al., 1972).Approximately 50 percent of the 12,000 kilometers offlight line has been completed. Flight lines wereoriented east-west with 2-kilometer spacing and wereflown at 300 meters above the ground surface. Shadedareas on the map (fig. 1) indicate the completed sec-tion of the study.

Magnetic profiles flown in 1962 along the axes ofWright and Taylor Valleys (Robinson, 1964) indi-cated there were no magnetic anomalies exceeding 20gammas. Data from the present survey bear out thosefindings, but, as shown in fig. 2, magnetic anomalieshaving amplitudes of 1,200 gammas are present in theuplands surrounding the dry valleys. Depths to themagnetic source for the two anomalies near the pla-teau were calculated to be within 300 meters of thesurface. The anomalies are believed to be produced by

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isolated remanents of the Ferrar dolerites. The sillsof the Ferrar dolerites have sufficient susceptibilitycontrast with the Beacon sandstones (Bull et al., 1962)to produce these magnetic intensity values.

The region near the coast appears relatively free ofany anomalous magnetic field; however, steep mag-netic peaks of 1,000 gammas, which correlate withthe location of the Dailey Islands, also are associatedwith a broad magnetic high decreasing in value in thedirection of Ross Island. This broad anomaly appearsto be centered over the Dailey Islands and extends inthe northeast-southwest direction about 14 kilometers.The broad high indicates a deep magnetic source rockcapped by the volcanic cones of the Dailey Islands.The magnetic variation near Ross Island is typical ofthe data observed over the island and is related to asouthwestward extension of the Ross volcanics.

This is an incomplete analysis, and until the datahave been corrected and a magnetic contour map ofthe region constructed, only a qualitative interpreta-tion can be stated.

Thanks are due to the officers and men of AntarcticDevelopment Squadron Six who flew for us and tothe many others, including the photographic section,who aided us in making this a successful program.

This work was supported by National ScienceFoundation contract C-642.

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Figure 1. Aeromagnetic survey, 1971-1972. Shaded areas show completed section of the survey.

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Figure 2. Aeromagnetic profile (in gammas) and topographic profile and cross section taken along A-A' of fig. 1.

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References

Bull, C., E. Irving, and I. Willis. 1962. Further palaeo-magnetic results from south Victoria Land, Antarctica.Royal Astronomical Society. Geophysical Journal, 6(3):320-336.

McGinnis, L. D., T. Toni, and P. Webb. 1972. Dry ValleyDrilling Project. Antarctic Journal of the U.S., VII(3)53-56.

Robinson, E. E. 1964. Correlation of magnetic anomalieswith bedrock geology in the McMurdo Sound area, Antarc-tica. Journal of Geophysical Research, 69(20): 4319–43 26.

Seismic refraction and electricalresistivity investigations in

the dry valleysCLIFFORD C. CLARK

Department of GeologyNorthern Illinois University

Geophysical field work in the ice-free valleys ofVictoria Land, Antarci;ica, during the 1971-1972 aus-tral summer included both electrical depth sounding

and seismic refraction profiling. This ground explora-tion was conducted as part of the Dry Valley DrillingProject (McGinnis et al., 1972). Geophysical studieswere conducted to establish geologic control at bore-hole sites where drilling would provide relevant infor-mation concerning the history of the dry valleys. For adetailed description of electrical equipment and meth-ods, see McGinnis and Jensen (1971). An SIE port-able, 12-channel seismograph with an internal nickel-cadmium power supply was used for the 12 seismicstations of 366-meter geophone spread.

Some of the numerous lakes in the dry valleys aresuspected to be connected hydrologically to the sub-surface. In an area where the mean annual air tem-perature is —20° to — 25°C. (Horowitz et al., 1972),permafrost would be expected to restrict completelythe transfer of surface and subsurface water. Electricaland seismic measurements indicate that the occurrenceof "confining" permafrost (McGinnis and Jensen,1971) varies but is predictable. Temperatures at thebottom of some of these lakes are unexplicably high,and in some cases permafrost beneath the lakes is ab-sent. Drilling near these lakes will give us importantinformation concerning the hydrology of the area.

July-August 1972 91