Two episodes of deformation atMt. Madison, Antarctica

general they strike to the northeast and dip steeply north-west or southeast. In rare instances fold closures can be seenin the S foliation (figure 2). They are tight to isoclinal inprofile and suggest that much of S 1 is transposed fromoriginal bedding.

EDMUND STUMP

Department of GeologyArizona State University

Tempe, Arizona 85281

During 10-12 January 1979 a party from Arizona StateUniversity, consisting of S. G. Borg, P. V. Colbert, P. H.Lowry, and the author visited Mt. Madison, as a satellite ofthe helicopter-supported Darwin Glacier camp (Stump,Sheridan, Borg, Lowry, and Colbert 1979). The field partyworked only 1 day on the second spur from the west(figure 1) and sat out a fog the remainder of the time.

Mt. Madison had been visited in 1960-61 by a New Zea-land party working between the Byrd and Starshot Gla-ciers. Skinner (1965) describes the rocks there as "coarse,sugary, gray to cream and white marbles interbedded withoccasional slate, schist, and hornfels". Mineral assemblagesare compatible with the amphibolite hornfels facies of met-amorphism. Of note is the presence of scapolite. Northwestand northeast trending folds were mapped (Skinner 1964,1965).

The field party found two phases of folding present inthe study area. The rocks on the lower portion of the spurare caic-schists which pass up into marbles about halfwayto the top. Foliation (S 1 ) appears as discontinuous bands orstreaks with greater or lesser amounts of biotite. Orienta-tions are quite variable depending upon the degree of de-velopment of the second generation of deformation, but in

Figure 1. Location map, Mt. Madison area.

Figure 2. Selborne Marble, Mt. Madison. S 1 folded by S2. Arrowindicates fold closures in S1.

This foliation is overprinted by a discontinuous or crenu-lation cleavage (52) which produces folding of S 1 . Openfolds or chevron folds plunge approximately 45° to thewest (figures 2 and 3). The extent to which this style isdeveloped throughout the Mt. Madison massif remains tobe seen.

Several authors have reported multiple folding north ofByrd Glacier (Smithson, Fikkan, and Toogood 1970; Findlay1978; Skinner in press). Burgess (in press) has observed twofold orientations in the Shackleton Limestone throughoutthe region south of Byrd Glacier. The Shackleton Limestoneis unmetamorphosed and folding style is more open, withcleavage occurring only in axial regions of the folds. Thiscontrasts to the relationship at Mt. Madison where S 1 andS2 foliations are penetrative throughout the exposure. The

Figure 3. Selborne Marble, Mt. Madison. S 1 folded by S2.

1980 REVIEW 13

relationship between the folds reported by Burgess (inpress) and those described here cannot be determined frompresent evidence.

Skinner (1964, 1965) named the rocks at Mt. Madison theSelborne Marble and distinguished them from the Shack-leton Limestone due to their higher metamorphic grade. Hesuggested that they may be Precambrian in age, correlativewith the Nimrod Group in the Miller Range (Grindley,McGregor, and Walcott 1964). If this is the case, deforma-tion at Mt. Madison is probably not related to the Shackle-ton Limestone south of Byrd Glacier.

To me, lithologies at Mt. Madison appear similar to thoseof the Shackleton Limestone and pelitic Dick Formation(Skinner 1965), and I would suggest that the Selborne Mar-ble is a metamorphosed equivalent of those two formations.The metamorphic grade suggests an adjacent granitic plutonnorth of Mt. Madison removed and buried by Byrd Glacier.

This work was supported by National Science Founda-tion grant DPP 76-82040.

References

Burgess, C.J. In press. Geology of the Shackleton Limestone (Cam-brian) in the Byrd Glacier area. New Zealand Antarctic Record.

Findlay, R. H. 1978. Provisional report on the geology of the regionbetween the Renegar and Blue Glaciers, Antarctica. New ZealandAntarctic Record, 1, 39-44.

Grindley, G. W., McGregor, V. R., and Walcott, R. I. 1964. Outlineof the geology of the Nimrod-Beardmore-Axel Heiberg Glaciersregion, Ross dependency. In R. J . Adie (Ed.), Antarctic geology.Amsterdam: North-Holland Publishing.

Skinner, D. N. B. 1964, A summary of the geology of the regionbetween Byrd and Starshot glaciers, south Victoria Land, InR. J. Adie (Ed.), Antarctic geology. Amsterdam: North-HollandPublishing.

Skinner, D. N. B. 1965. Petrographic criteria of the rock unitsbetween the Byrd and Starshot Glaciers, south Victoria Land,Antarctica. New Zealand Journal of Geology and Geophysics, 8,292-303.

Skinner, D. N. B. In press. Stratigraphy and structure of lowergrade metasediments of Skelton Group, McMurdo Sound—DoesTeall Graywacke really exist? In C. Craddock (Ed.), AntarcticGeoscience. Madison: University of Wisconsin Press.

Smithson, S. B., Fikkan, P. R., and Toogood, D. J . 1970. Early geo-logic events in the icefree valleys, Antarctica. Geological Society ofAmerica Bulletin, 81, 207-210.

Stump, E., Sheridan, M. F., Borg, S. G., Lowry, P. H., and Colbert,P. V. 1980. Geological investigations in the Scott and Byrd Glacierareas. Antarctic Journal of the U.S., 14(5), 39-40.

Microclimate and weatheringprocesses in the area of Darwin

Mountains and Bull Pass,Dry Valleys

FRANTZ-DIETER MIOTKE

Geographisches InstitutUniversitat Hannover

Hannover, West Germany

During December 1978 and January 19791 studied micro-climate, weathering processes, and antarctic landforms inthe area of Darwin Mountains (80°S) and Bull Pass, DryValleys (77°30'S).

Antarctic rocks disintegrate by the combined action ofseveral different processes. Joints existing due to endogenicactivity (Gerber and Scheidegger 1969) open primarily be-cause of temperature-caused tension, frost cracking, andsalt fretting. Chemical weathering processes are limited tothe short summer period when temperatures of rock sur-faces can reach as high as 30°C and reflect daily tempera-ture variations and moisture in rocks and soil.

Daily temperatures were recorded by thermistorsinstalled:

1. Into dark dolorites, light sandstones, and granites hav-ing different albedos;

2. Into small rocks, large boulders, and bedrock;3. Immediately below the rock surface, into the rock cen-

ter, and under rocks;4. Into rocks with different exposures to sun radiation;5. Into soils down to 100 centimeters;6. Into snow down to 70 centimeters; and7. Along snow margins.

Figure 1 illustrates the variations in temperature in rocksand soil in the Darwin Mountains.

Microclimatic differences were of special interest andthese proved to be considerable within very limited envi-ronments. Temperature variations within soils and rocksand their daily changes affect the existence of algae, lichens,and other microforms of life in Antarctica. Not too much isknown so far about the microclimate of ice-free areas inVictoria Land.

Moisture in soils is normally very low at the upper sur-face (to 5 centimeters deep), mostly below 0.1 percent, butit can be higher where meltwater infiltrates along the mar-gin of snowfields. Soil moisture can be as high as 20 percentwhere locally existing ice (up to 20 centimeters deep, as inthe Darwin Mountains) melts somewhat during summer.Due to differences in heat conductivity, daily heat flow into

14 ANTARCTIC JOURNAL