the pre-late Mesozoic Greywacke-Shale Formation to theeast. Those on the Robertson Islands and eastern Corona-tion Island were derived mainly from the metamorphicbasement rocks to the west. The alluvial fans probably arerelated to Mesozoic fault block tectonics, in which inferrednorth-south trending graben faults would have been impor-tant.

Field observations have allowed some slight revision to thepreviously published geologic maps, and these changes areincorporated in figure 3. New localities at which the un-conformity below the conglomeratic beds is exposed wereobserved on several islands south of Matthews Island and atEast Cape. A new outcrop of the Gibbon Bay Shale wasfound just west of East Cape.

Dating of the sequences is important, but it is not possiblefrom field observations alone to improve on the presentrather imprecise age assignments based on limited fossilevidence (Thomson, 1975; Thomson and Willey, 1975).Laboratory studies of fossil plants from two localities onsouthern Powell Island (figure 3), and rare ammonites andbelemnites from Matthews Island may clarify the ages ofthese rocks. In addition, new collections were made offossiliferous "calcareous grit" boulders that occur in the con-glomerates at Rayner Point, and of the invertebrates fromthe Gibbon Bay Shale which underlies the conglomerate.The discovery of ammonites and belemnites in the shaleshould, it is hoped, provide a more accurate age assessmentthan has hitherto been possible. Bulk samples were alsotaken for processing for microfossils.

Acknowledgments. We are grateful for the efforts of Cap-tain Lenie and the crew of R/V Hero in helping us gain ac-cess to areas of the South Orkney Islands highly unfavorableto mariners. The scientific work was supported by NationalScience Foundation grants DPP 74-21415 to Dalziel atLamont-Doherty Geological Observatory, ColumbiaUniversity, and DPP 74-21509 to Elliot at Ohio StateUniversity and by the British Antarctic Survey.

References

Daiziel, I.W.D. 1971. Structural studies in the Scotia Arc: the SouthOrkney Islands. A ntarcticJournal of the U. S., VI(4): 124-126.

Daiziel, I.W.D. 1975. The Scotia Arc tectonics project, 1969-1975.AntarcticJournal of the U. S., X(3): 70-81.

Dalziel, I.W.D. 1976. Structural studies in the Scotia Arc: "base-ment" rocks of the South Shetland Islands. Antarctic Journal ofthe U.S., X1(2): 75-77.

Daiziel, I.W.D., M.J. de Wit, and C.R. Stern. 1975. Structural andpetrologic studies in the Scotia Arc. AntarcticJournal of the U.S.,X(4): 180-182,

Daiziel, I.W.D., and D.H. Elliot. 1973. The Scotia Arc and antarc-tic margins. In: The Ocean Basins and Margins: 1, The SouthAtlantic (A.E.M. Nairn and F.G. Stehli, editors). New York,Plenum Press, p. 171-245.

Elliot, D.H., C. Rinaldi, W.J. Zinsmeister, T.A. Trautman, W.A.Bryant, and R. del Valle. 1975. Geological investigations onSeymour Island, Antarctic Peninsula. Antarctic Journal of theU.S., X(4): 182-188.

Thomson, J.W. 1968. The geology of the South Orkney Islands: II.The petrology of Signy Island. British Antarctic Survey. ScientificReport, 62: 30.

Thomson, J.W. 1971. The geology of Matthews Island, SouthOrkney Islands. British Antarctic Survey. Bulletin, 26: 51-57.

Thomson, J.W. 1973. The geology of Powell, Christoffersen, andMichelsen Islands, South Orkney Islands. British AntarcticSurvey. Bulletin, 33 and 34: 137-167.

Thomson, J.W. 1974. The geology of South Orkney Islands: III.Coronation Island. British Antarctic Survey. Scientific Report,86. 39p.

Thomson, M.R.A. 1975. Fossils from the South Orkney Islands: II.Matthews Island. British Antarctic Survey. Bulletin, 40: 75-79.

Thomson, M.R.A. and L.E. Willey. 1975. Fossils from the SouthOrkney Islands: 1. Coronation Island. British Antarctic Survey.Bulletin, 40: 15-21.

Marie Byrd Land volcanology

WESLEY E. LEMASURIER

Natural and Physical Sciences DivisionUniversity of Colorado at Denver

Denver, Colorado 80202

Project activities during 1976-1977 centered on comple-tion of a year of study and research in New Zealand and onplanning for the 1977-1978 field season in Marie ByrdLand. These activities were related to the three parts of theproject, which are (1) studies of intraglacial volcanoes inMarie Byrd Land, (2) the tectonic relationships of vol-canism, and (3) origins of the lavas that make up the MarieByrd Land volcanoes.

The intraglacial volcanoes in Marie Byrd Land are largestructures with flat summits, a low ratio of height to basediameter, and very gently sloping flanks, similar to manysubmarine volcanoes (guyots) but unlike the classic in-traglacial volcanoes (or tablemountains) of Iceland. Theyappear to be composed entirely of hyaloclastite, which is aglassy fragmental deposit produced when lava is abruptlychilled and fragmented during eruptions beneath water orice. These deposits provide a record of the history of the icesheet in Marie Byrd Land, including information about pastthicknesses and, perhaps, former ice surface levels(LeMasurier 1972a, 1972b, 1976). To read the volcanicrecord with confidence, one needs to know which individualtextural, structural, and morphologic characteristics ofthese volcanoes are related to the subglacial environment oferuption, which features are related to characteristics of themagma, which characteristics record deep-water (thick ice)as compared to shallow water eruptions, and whether anycharacteristics distinguish between submarine and intra-glacial eruptions. In view of these problems, it has beenespecially valuable to compare the Marie Byrd Landvolcanoes with volcanoes formed by lava-water interactionselsewhere in the world, in order to better understand how touse the volcanic deposits to interpret glacial and tectonichistory.

In the last year, most progress has been in field studies ofstructures found in a variety of pyroclastic rock types thatmight be analogous to Marie Byrd Land examples. Theseinclude studies of base surge and laharic deposits in the cen-

October1977 101

tral North Island volcanic region of New Zealand andstudies of phreatomagmatic tuff cones in the Hawaiianislands (e.g., Diamond Head). These studies will be helpfulbackground for renewed field studies of the Marie ByrdLand intraglacial volcanoes scheduled for the 1977-1978austral summer season.

The remaining topics in this project, the tectonic andpetrogenetic relationships of Marie Byrd Land volcanism,are unusually interesting, because it appears that virtuallyall post-Paleozoic rocks in the region are igneous. TheCenozoic rocks are almost entirely volcanic, and Mesozoicrocks are predominantly intrusive. Interpretations ofgeologic history over the last 200 million years, therefore,rest heavily on interpretations of igneous environments.Petrologic characteristics that seem to have important tec-tonic significance in this region are (1) the change from caic-alkaline intermediate rocks to a bimodal alkaline volcanicassemblage in early Cenozoic time, (2) the K 20/Si02 ratiosof the caic-alkaline rocks, particularly with respect to thepresent continental margin, (3) the oceanic geochemicalcharacter of the alkaline rocks, together with the abundanceand diversity of acid rock types, and (4) the systematicmigrations of volcanic activity along the lengths of severallinear volcanic ranges. These characteristics have been usedto help interpret relationships between the Marie Byrd Landregion, the Pacific-Antarctic ridge system, and the NewZealand-Campbell Plateau continental block (LeMasurierand Wade, 1976; LeMasurier, in press).

I hope in the coming season to study the relations be-tween the intrusive and extrusive Mesozoic calc-alkaline ig-neous rocks, and thereby to get a clearer picture of igneousand tectonic activity along the Mesozoic continental marginof Marie Byrd Land. New Zealand geophysicists plan tocooperate in future efforts to locate magnetic anomaly pat-terns over the Marie Byrd Land coast and continental shelf,which might confirm sea floor spreading reconstructionslinking this region to magnetically distinctive portions ofNew Zealand and the Campbell Plateau. New Zealandgeologists are planning to study potential geologic andpaleomagnetic links between New Zealand and Marie ByrdLand during the coming field season. Several papersscheduled for presentation at the Third Symposium on Ant-arctic Geology and Geophysics, 22-27 August 1977, presentnew data and ideas that form the basis for these future proj-ects.

References

LeMasurier, W.E. 1972a Volcanic record of Cenzoic glacial historyof Marie Byrd Land. In: Antarctic Geology and Geophysics(Adie, R.J., ed.). Oslo, Universitetsforlaget.

LeMasurier, W.E. 1972b. Volcanic record of antarctic glacialhistory: implications with regard to Cenozoic sea levels. In: PolarGeomorphology (Price, R.J. and D.E. Sugden, compilers). In-stitute of British Geographers Special Publication, 4: 59-74.

LeMasurier, W.E. 1976. Intraglacial volcanoes in Marie ByrdLand. AntarcticJournal of the U.S., XI(4): 269-270.

LeMasurier, W.E. and F.A. Wade. 1976. Volcanic history in MarieByrd Land: implications with regard to southern hemisphere tec-tonic reconstructions. In: Proceedings of the Symposium on An-dean and Antarctic Volcanology Problems, Santiago, Chile(0. Gonzalez-Ferran, ed.). Rome: International Association of

Volcanology and Chemistry of Earth's Interior, 400-424.LeMasurier, W.E. In press. Rift valley volcanism in Marie Byrd

Land, West Antarctica. In: Volcanoes and Volcanology, Series ofEarth Sciences, volume XVI (Jack Green, ed.). Dowden,Hutchinson, and Ross.

Geothermal studies in Antarctica

EDWARD R. DECKER and GERALDJ. BUCHER

Department of GeologyUniversity of Wyoming

Laramie, Wyoming 82071

This report summarizes some of our geothermal studieswith Dry Valley Drilling Project drill holes. Data includesubsurface temperatures, thermal conductivities, and threepreliminary heat flow values. The research was done underNational Science Foundation grant OPP 72-05804.

Temperatures. Subsurface temperatures were measuredat discrete points in the holes with thermistor probes in com-bination with three-lead cables, Wheatstone-type bridges,and electronic null-detectors. When the data for hole 6 areneglected, the recent measurements of temperature in thestable portions of all relogged holes were very precise. Forexample, the temperatures measured on 20-meter intervalsbelow 50 meters in hole 3 were reproduced to within± 0.01 °C, based on logs with different probes in November1975 and January 1976. Similarly, temperatures below 40meters in holes 11 and 12 were reproduced to within± 0.02°C, when measurements were made on 20-meter in-tervals with different probes during the 1975-1976 fieldseason.

We have not been able to reproduce temperatures in allintervals of hole 6. Here, the most recent logs for the120-250 meter interval differ by as much as 0.11°C, Below250 meters, temperatures were reproduced to within± 0.03°C, and the gradient of temperature between 250 and300 meters was reproduced to within ± 10 percent.

Temperature data for selected drill holes on land are plot-ted in figure 1. If perennially frozen ground is assumed tooccur in regions with temperatures below 0°C, these dataimply the permafrost thicknesses listed below.

Site Permafrost thickness, metersHole 3 (McMurdo station) 440-500Hole 6 (Lake Vida) 800-970Holes 8 and 10 (New Harbor) 240-310Hole 11 (Commonwealth Glacier) 405Hole 12 ("Lake Leon" — unofficial 360

name)Hole 14 (North Fork) 350-360

Bucher and Decker (1976), Decker et al. (1975), and Prusset al. (1974) discuss the gradients used to determine per-mafrost thicknesses.

Figure 2 shows two temperature-depth profiles for hole 15in McMurdo Sound. Both sets of measurements were madeafter drilling had been stopped for about 8 hours. Although

102 ANTARCTIC JOURNAL