Paleomagnetic investigations of the Sledgers Group, Bowers ...
This research was supported by National Science Foundation grant DPP 80-19527. Sandiford was supported by an Australian Commonwealth Postgraduate Research Award.
References Dow, J. A. S., and Neall, V. E. 1974. Geology of the lower Rennick Glacier, northern Victoria land, Antarctica. New Zealand Journal of Geology and Geophysics, 17(3), 659-714. Gair, H. S. 1967. The geology from the upper Rennick Glacier to the coast, northern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 10(2), 309-344.
Kleinschmidt, G. 1981. Regional metamorphism in the Robertson Bay Group area and in the southern Daniels Range, north Victoria Land, Antarctica—A preliminary comparison. Geologisches Jahrbuch, B41, 201-228. Laird, M. G., Bradshaw, J. D., and Wodzicki, A. 1982. Stratigraphy of the Upper Precambrian and Lower Paleozoic Bowers Supergroup, northern Victoria Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Tessensohn, F., Duphorn, K., Jordan, H., Kleinschmidt, G., Skinner, D. N. B., Vetter, U., Wright, T. 0., and Wyborn, D. 1981. Geological comparison of basement units in north Victoria Land, Antarctica. Geologisches Jahrbuch, B41, 31-88. Wodzicki, A., Bradshaw, J. D., and Laird, M. G. 1982. Petrology of the Wilson and Robertson Bay Groups and Bower Supergroup, northern Victoria Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press.
Paleomagnetic investigations of the Sledgers Group, Bowers Mountains, northern Victoria Land KURT
E. SCHMIERER, RUSSELL F. BURMESTER, \ ';\
and ANTONI WoDzIcKI Department of Geology Western Washington University Bellingham, Washington 98225
Structural mapping and sampling of the Sledgers Group for paleomagnetic analysis was conducted during the 1981-82 field season in the Lanterman and Explorers Ranges of the Bowers Mountains, northern Victoria Land. Approximately 400 paleomagnetic drill cores were taken at 44 volcanic and sedimentary drill sites in the vicinity of the Alt and Carryer Glaciers, tributaries of the lower Rennick Glacier, and 113 oriented hand samples were taken at 12 volcanic sites. Of these 56 sites, 42 are from subaerial and submarine flows of the Vendian to Lower Cambrian (Adams et al. 1982) Glasgow Volcanics, which attain their greatest thickness between the Alt and Carryer Glaciers. These predominantly basaltic to andesitic volcanics contain minor younger rhyolitic subaerial flows and breccias and epizonal plutons. The remaining 14 sites are from breccias and con glomerates of the Glasgow Volcanics and consanguinous sediments of the Molar Formation, and from mudstones, dikes, and sills of overlying Carryer Conglomerate (Laird, Bradshaw, and Wodzicki 1976). Figure 1 gives locations of these 56 sites. Drill sites were located to either side of the northwest-trend ing fold axes of major folds in the Sledgers Group (figure 1), allowing application of the fold test (Graham 1949; McElhinny 1964) to assist in the isolation and identification of primary magnetization and later components. Breccia and conglomerate clasts of the Glasgow and Molar Formations were sampled for application of the conglomerate test (Graham 1949; Starkey and Palmer 1970) to evaluate magnetic stability. In addition to constraining various pre-Cretaceous recon structions of Australia and Antarctica, determination of the
N w::: E S
FOLD AXES
0 PALE0000NETIC
DRILL SITE
LOCATIONS
£ CAMPS
TO
or
Figure 1. Map of primary field area.
precise apparent polar wandering path from northern Victoria Land will provide information bearing on other salient tectonic issues, including the relative motion between East and West Antarctica during the Tertiary proposed by Cox and Gordon (1978). Paleomagnetic analysis of all samples is under way. Paleomagnetic samples also were obtained from plutonic rocks of the Admiralty and Granite Harbor Intrusives; a total of 103 drill cores were taken at six sites in the Salamander and ANTARCTIC JOURNAL
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Freezing point depression in degrees Celsius
Figure 2. Freezing point depression curve for ethanol/water mixtures.
Alamein Ranges of the Freyberg Mountains, northern Victoria Land. Drilling of the McMurdo Volcanics on Ross Island during equipment checkouts yielded 40 cores from three sites. Drill cores were obtained using a modified two-stroke, chainsaw-drive unit with a tubular diamond bit. A pressurized plastic pump can with a volume of 6 liters provided drill fluid to the bit, using a specially designed chuck. All drill equipment and fluid was backpacked to the drill sites, since virtually all sites were inaccessible by motor toboggan; good outcrop was confined to areas of high relief. All drill equipment performed flawlessly throughout the season. Keeping the drill fluid in a liquid state in freezing temperatures was a primary concern. Ethanol was combined with a water/snow mixture to depress the freezing point of the drill fluid. We varied the mixture of ethanol to water according to the ambient temperature. Figure 2 shows a freezing point depression curve for ethanol/water mixtures. When possible, the ethanol was mixed with snow at the drill sites and allowed to melt in the sun overnight, minimizing the total weight of fluid carried into the sites. The ethanol/water fluid proved to be superior to ethylene glycol mixtures used on previous expeditions (Burmester and Sheriff 1980), for several reasons. Ethanol has a lower density and freezing point, reducing the weight of loads carried in to
Geology of the Bowers Trough and its possible correlation with the Dundas Trough, Tasmania A. W0DzIcK1, R. F. BuRMESTER, and K. E. ScHMIERER Department of Geology Western Washington University Bellingham, Washington 98225
1982 REVIEW
drill sites, and a lower boiling point, resulting in dry cores instead of the wet, slippery cores obtained using ethylene glycol/water drill fluids. In addition, the ethanol mixture did not cover the driller with slimy fluid. Water-soluble oil was added to the drill fluid as a bit lubricant, in a 50:1 fluid-to-oil ratio for mafic volcanic and sedimentary rocks, and in a 30:1 ratio for granitic rocks. The addition of water-soluble oil further depressed the freezing point of the drill fluid. All drill cores were oriented in the field by means of simultaneous sun compass and magnetic compass readings. The orientation data were reduced in the field by means of a programed calculator. The liquid crystal display on our calculator had the advantage of long battery life, with no recharging capability required in the field, but it could not operate in temperatures below freezing and thus had to be kept warm. This research was supported by National Science Foundation grant DPP 80-20728.
References Adams, C. J. D., Gabites, J . E., Wodzicki A., Laird, M. C., and Bradshaw, J. D. 1982. Potassium-argon geochronology of the Precambrian-Cambrian Wilson and Robertson Bay Groups and Bowers Supergroup, north Victoria Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Burmester, R. F., and Sheriff, S. D. 1980. Paleomagnetism of the Dufek intrusion, Pensacola Mountains, Antarctica. Antarctic Journal of the U.S., 15(5), 43-45. Cox, A., and Gordon, R. G. 1978. Paleomagnetic evidence for large Tertiary motion of Marie Byrd Land (West Antarctica) relative to East Antarctica. EOS, Transactions of the American Geophysical Union, 59, 1059. (Abstract) Graham, J . W. 1949. The stability and significance of magnetism in sedimentary rocks. Journal of Geophysical Research, 54, 131-167. Laird, M. G., Bradshaw, J . D., and Wodzicki, A. 1976. Re-examination of the Bowers Group (Cambrian), northern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 19(2), 275-282. McElhinny, M. W. 1964. Statistical significance in the fold test in paleomagnetism. Geophysical Journal of the Royal Astronomical Society, 8, 338-340. Starkey, J . , and Palmer, H. C. 1970. The sensitivity of the conglomerate test in paleomagnetism. Geophysical Journal of the Royal Astronomical Society, 22, 235-240.
Field mapping of the Bowers Supergroup has been carried out near the Alt, Carryer, and Sledgers Glaciers in the Bowers Mountains (figure 1). The study area lies near the coast facing Australia and thus occupies an important position for preCretaceous plate reconstruction of Gondwanaland. This article compares the geology of the Bowers and Dundas Troughs and discusses their possible correlation. The geology of the Bowers Mountains was studied in detail during the 1974-75 NZARP (New Zealand Antarctic Research Program) expedition (Adams et al. 1982; Bradshaw, Laird, and Wodzicki 1982; Cooper et al. 1982; Laird, Bradshaw, and
References Dow, J. A. S., and Neall, V. E. 1974. Geology of the lower Rennick Glacier, northern Victoria land, Antarctica. New Zealand Journal of Geology and Geophysics, 17(3), 659-714. Gair, H. S. 1967. The geology from the upper Rennick Glacier to the coast, northern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 10(2), 309-344.
Kleinschmidt, G. 1981. Regional metamorphism in the Robertson Bay Group area and in the southern Daniels Range, north Victoria Land, Antarctica—A preliminary comparison. Geologisches Jahrbuch, B41, 201-228. Laird, M. G., Bradshaw, J. D., and Wodzicki, A. 1982. Stratigraphy of the Upper Precambrian and Lower Paleozoic Bowers Supergroup, northern Victoria Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Tessensohn, F., Duphorn, K., Jordan, H., Kleinschmidt, G., Skinner, D. N. B., Vetter, U., Wright, T. 0., and Wyborn, D. 1981. Geological comparison of basement units in north Victoria Land, Antarctica. Geologisches Jahrbuch, B41, 31-88. Wodzicki, A., Bradshaw, J. D., and Laird, M. G. 1982. Petrology of the Wilson and Robertson Bay Groups and Bower Supergroup, northern Victoria Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press.
Paleomagnetic investigations of the Sledgers Group, Bowers Mountains, northern Victoria Land KURT
E. SCHMIERER, RUSSELL F. BURMESTER, \ ';\
and ANTONI WoDzIcKI Department of Geology Western Washington University Bellingham, Washington 98225
Structural mapping and sampling of the Sledgers Group for paleomagnetic analysis was conducted during the 1981-82 field season in the Lanterman and Explorers Ranges of the Bowers Mountains, northern Victoria Land. Approximately 400 paleomagnetic drill cores were taken at 44 volcanic and sedimentary drill sites in the vicinity of the Alt and Carryer Glaciers, tributaries of the lower Rennick Glacier, and 113 oriented hand samples were taken at 12 volcanic sites. Of these 56 sites, 42 are from subaerial and submarine flows of the Vendian to Lower Cambrian (Adams et al. 1982) Glasgow Volcanics, which attain their greatest thickness between the Alt and Carryer Glaciers. These predominantly basaltic to andesitic volcanics contain minor younger rhyolitic subaerial flows and breccias and epizonal plutons. The remaining 14 sites are from breccias and con glomerates of the Glasgow Volcanics and consanguinous sediments of the Molar Formation, and from mudstones, dikes, and sills of overlying Carryer Conglomerate (Laird, Bradshaw, and Wodzicki 1976). Figure 1 gives locations of these 56 sites. Drill sites were located to either side of the northwest-trend ing fold axes of major folds in the Sledgers Group (figure 1), allowing application of the fold test (Graham 1949; McElhinny 1964) to assist in the isolation and identification of primary magnetization and later components. Breccia and conglomerate clasts of the Glasgow and Molar Formations were sampled for application of the conglomerate test (Graham 1949; Starkey and Palmer 1970) to evaluate magnetic stability. In addition to constraining various pre-Cretaceous recon structions of Australia and Antarctica, determination of the
N w::: E S
FOLD AXES
0 PALE0000NETIC
DRILL SITE
LOCATIONS
£ CAMPS
TO
or
Figure 1. Map of primary field area.
precise apparent polar wandering path from northern Victoria Land will provide information bearing on other salient tectonic issues, including the relative motion between East and West Antarctica during the Tertiary proposed by Cox and Gordon (1978). Paleomagnetic analysis of all samples is under way. Paleomagnetic samples also were obtained from plutonic rocks of the Admiralty and Granite Harbor Intrusives; a total of 103 drill cores were taken at six sites in the Salamander and ANTARCTIC JOURNAL
400 CD
350 E
300 250 200 150 CD
100 50
0
—3
—6
—9
—12
-in
Freezing point depression in degrees Celsius
Figure 2. Freezing point depression curve for ethanol/water mixtures.
Alamein Ranges of the Freyberg Mountains, northern Victoria Land. Drilling of the McMurdo Volcanics on Ross Island during equipment checkouts yielded 40 cores from three sites. Drill cores were obtained using a modified two-stroke, chainsaw-drive unit with a tubular diamond bit. A pressurized plastic pump can with a volume of 6 liters provided drill fluid to the bit, using a specially designed chuck. All drill equipment and fluid was backpacked to the drill sites, since virtually all sites were inaccessible by motor toboggan; good outcrop was confined to areas of high relief. All drill equipment performed flawlessly throughout the season. Keeping the drill fluid in a liquid state in freezing temperatures was a primary concern. Ethanol was combined with a water/snow mixture to depress the freezing point of the drill fluid. We varied the mixture of ethanol to water according to the ambient temperature. Figure 2 shows a freezing point depression curve for ethanol/water mixtures. When possible, the ethanol was mixed with snow at the drill sites and allowed to melt in the sun overnight, minimizing the total weight of fluid carried into the sites. The ethanol/water fluid proved to be superior to ethylene glycol mixtures used on previous expeditions (Burmester and Sheriff 1980), for several reasons. Ethanol has a lower density and freezing point, reducing the weight of loads carried in to
Geology of the Bowers Trough and its possible correlation with the Dundas Trough, Tasmania A. W0DzIcK1, R. F. BuRMESTER, and K. E. ScHMIERER Department of Geology Western Washington University Bellingham, Washington 98225
1982 REVIEW
drill sites, and a lower boiling point, resulting in dry cores instead of the wet, slippery cores obtained using ethylene glycol/water drill fluids. In addition, the ethanol mixture did not cover the driller with slimy fluid. Water-soluble oil was added to the drill fluid as a bit lubricant, in a 50:1 fluid-to-oil ratio for mafic volcanic and sedimentary rocks, and in a 30:1 ratio for granitic rocks. The addition of water-soluble oil further depressed the freezing point of the drill fluid. All drill cores were oriented in the field by means of simultaneous sun compass and magnetic compass readings. The orientation data were reduced in the field by means of a programed calculator. The liquid crystal display on our calculator had the advantage of long battery life, with no recharging capability required in the field, but it could not operate in temperatures below freezing and thus had to be kept warm. This research was supported by National Science Foundation grant DPP 80-20728.
References Adams, C. J. D., Gabites, J . E., Wodzicki A., Laird, M. C., and Bradshaw, J. D. 1982. Potassium-argon geochronology of the Precambrian-Cambrian Wilson and Robertson Bay Groups and Bowers Supergroup, north Victoria Land, Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Burmester, R. F., and Sheriff, S. D. 1980. Paleomagnetism of the Dufek intrusion, Pensacola Mountains, Antarctica. Antarctic Journal of the U.S., 15(5), 43-45. Cox, A., and Gordon, R. G. 1978. Paleomagnetic evidence for large Tertiary motion of Marie Byrd Land (West Antarctica) relative to East Antarctica. EOS, Transactions of the American Geophysical Union, 59, 1059. (Abstract) Graham, J . W. 1949. The stability and significance of magnetism in sedimentary rocks. Journal of Geophysical Research, 54, 131-167. Laird, M. G., Bradshaw, J . D., and Wodzicki, A. 1976. Re-examination of the Bowers Group (Cambrian), northern Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics, 19(2), 275-282. McElhinny, M. W. 1964. Statistical significance in the fold test in paleomagnetism. Geophysical Journal of the Royal Astronomical Society, 8, 338-340. Starkey, J . , and Palmer, H. C. 1970. The sensitivity of the conglomerate test in paleomagnetism. Geophysical Journal of the Royal Astronomical Society, 22, 235-240.
Field mapping of the Bowers Supergroup has been carried out near the Alt, Carryer, and Sledgers Glaciers in the Bowers Mountains (figure 1). The study area lies near the coast facing Australia and thus occupies an important position for preCretaceous plate reconstruction of Gondwanaland. This article compares the geology of the Bowers and Dundas Troughs and discusses their possible correlation. The geology of the Bowers Mountains was studied in detail during the 1974-75 NZARP (New Zealand Antarctic Research Program) expedition (Adams et al. 1982; Bradshaw, Laird, and Wodzicki 1982; Cooper et al. 1982; Laird, Bradshaw, and
