DAVID H. ELLIOT, THOMAS H. FLEMING, CHRISTOPHER CONAWAY, and PETER BRADDOCK, Byrd Polar Research Center and Department of Geological Sciences, Ohio State University, Columbus, Ohio 43210
As part of a continuing program of investigations into the Jurassic magmatic rocks associated with Gondwanaland breakup, the Mawson Formation, Kirkpatrick Basalt, and Ferrar Dolerite were examined in the Prince Albert Mountains (figure) between 13 January and 4 February 1997. Put-in and pick-up were by LC-130, and the field investigations were aided by 2 days of helicopter support. This region was initially investigated by Skinner and Ricker (1968) and later more detailed observations and sample collections were made by Kyle (1979) and Wörner (1992).
The pyroclastic rocks of the Mawson Formation were examined at Ambalada Peak, at Thomas Rock and outcrops to its east and north, and at Sheppard Rocks. Although referred to as the "Exposure Hill Formation" by Wörner (1992), Kyle (1979) first noted the occurrence of these rocks and referred them to the "Mawson Formation"; his terminology is followed here. The pyroclastic rocks include breccias, lapilli tuffs, and tuffs. Armored lapilli, cored bombs, and fluidal basalt fragments are sparsely distributed in the breccias; outsize clasts are locally common, and in some outcrops, sedimentary rock fragments are an important component of the breccias. These and other features are indicative of hydrovolcanic processes having a role in the formation of these breccias, as has been documented for the correlative rocks in the central Transantarctic Mountains (Hanson and Elliot 1996). Thin sequences of lapilli tuff and tuff also occur and appear to include both airfall and base surge deposits. Two short sections consist of volcaniclastic strata with interbedded accretionary lapilli tuff: these rocks have similarities to the Carapace Sandstone (Ballance and Watters 1971). The upper and lower contacts of the formation are exposed at Thomas Rock, but the geologic relations are unclear because of apparent tilting of the Mawson Formation strata. Rocks similar to the lapilli tuffs and tuffs of the Mawson Formation are interbedded in the lower part of the basalt sequence at Thomas Rock. A short visit to Reckling Peak revealed the presence of Triassic strata cut by dolerite intrusions and intrusion breccias. The possible ignimbrite mentioned by Wörner (1992) was not located, and pumice fragments were not observed at Thomas Rock. The exposed and measured section at Ambalada Peak was only 70 meters thick, compared with the 200 meters reported by Kyle (1979); it is possible that additional unexamined or unexposed strata make up the difference.
The Kirkpatrick Basalt at Brimstone Peak was examined and collected in detail for geochemistry and radiometric age dating. Collections of secondary minerals were made at Brimstone Peak and Tent Rock to study the postmagmatic hydrothermal circulation systems. Sills at Thumb Point, The Mitten, Richards Nunatak, Beckett Nunatak, and Shultz Peak were also examined, and detailed collections were made for geochemical and isotopic study.
Inclement conditions curtailed the last week of fieldwork and prevented some objectives in the Ambalada Peak-Griffin Nunatak region from being met.
Thanks are given for the logistic support provided by U.S. Navy VXE-6 Squadron and Petroleum Helicopters, Inc. This field research was supported by National Science Foundation grant OPP 94-20498 to the Ohio State University.
Ballance, P.F., and W.A. Watters. 1971. The Mawson Diamictite and Carapace Sandstone, formations of the Ferrar Group at Allan Hills and Carapace Nunatak, Victoria Land, Antarctica. New Zealand Journal of Geology and Geophysics , 14(3), 512-527.
Hanson, R.H., and D.H. Elliot. 1996. Rift-related Jurassic basaltic phreatomagmatic volcanism in the central Transantarctic Mountains: Precursory stage to flood basalt effusion. Bulletin of Volcanology , 58(5), 327-347.
Kyle, P.R. 1979. Geochemical studies of Ferrar Group rocks from southern Victoria Land. Antarctic Journal of the U.S. , 14(5), 25-26.
Skinner, D.B., and J. Ricker. 1968. The geology of the region between the Mawson and Priestley Glaciers, north Victoria Land, Part II—Upper Paleozoic to Quaternary Geology. New Zealand Journal of Geology and Geophysics , 11(5), 1041-1075.
Wörner, G. 1992. Kirkpatrick Lavas, Exposure Hill Formation and Ferrar Sills in the Prince Albert Mountains, Victoria Land, Antarctica. Polarforschung , 60(2), 87-90.