Studies in the South 77.1, January 1977

Table 2. Initial data on meteorites found during 1976-1977 field season. Field collection nos. a Typeb Wt.(g) Latitude Longitude MB-i Chond. 4,108 7703502S 16001935E MB-2 Chond. 13,782 7703902S 16002225E AH-i Chond. 20,151 76°3927 Sc 15903315 Ec AH-2 Iron 1,510 76°3927 c 159°3316 E AH-3 Chond. 10,495 7604729S 15902644E AH-4 Chond. 305 7604516S 15902012E AH-5 Achond. 1,425 7603702S 159°2146E AH-6 Chond. 1,137 7603847S 15902257 E AH-7 Chond. 410 7604008S 15902146E AH-8 Chond. 1,150 7603927S 15901814E AH-9 Chond. 407,041 7604314S 159°1739 S AH = Allan Hills. MB = Mount Baldr. bAchond = Achondrite. Chond. = Chondrite. cAH. 1 and AH. 2 were found 80 meters apart and were therefore assigned the same geographic coordinates. During the coming field season we hope to investigate studies in the South blue ice patches somewhat farther north along the interface zone between the polar ice plateau and the Transantarctic Orkney Islands: R/V Hero Cruise Mountains. This research was supported by National Science Founda- 77.1, January 1977 tion grant DPP 76-10800. IANW.D. DALZIEL, DAVID H. ELLIoT,23 JANET W. THOMSON, 4 MICHAEL R.A. THOMSON,5 NEIL A. WELLS, 2'3 and WILLIAMJ. ZINSMEISTER24 Lamont-Doherty Geological Observatory Columbia University References Palisades, New York 10964 21nstitute of Polar Studies Ohio State University Duke, M. 1965. Discovery of the Neptune Mountains iron meteorite, Columbus, Ohio 43210 Antarctica. Meteoritical Bulletin, 34: 2.3. Ford, A.B., and R.W. Tabor. 1971. The Thiel Mountains pallasite 3Department of Geology and Mineralogy of Antarctica. U.S. Geological Survey Professional Paper, 750-D: Ohio State University D56-D60. Columbus, Ohio 43210 Mawson, D. 1915. In: The Home of the Blizzard. Heinemanns, British Antarctic Survey London, Vol. 2, p. 11. 417ormerly of the Shiraishi, K., R. Naruse, and K. Kusunoki. 1976. Collection of 5British Antarctic Survey Antarctic Yamato meteorites, Antarctica, in December 1973. Madingley Road Record, 55: 49-60. Cambridge CB3 OET, England Tolstikov, E. 1961. Discovery of Lazarev iron meteorite, Antarctica. Meteoritical Bulletin, 20: 1. Yanai, K. 1976. Search and collection of Yamato meteorites, Ant- R/V Hero departed Puerto Beigrano, Argentina, on 5 arctica, in October and November 1974, Antarctic Record, 56: January 1977, bound for the South Orkney Islands. Geologic 70.81. work was performed 12 through 31 January 1977 on Corona - Yoshida, M., H. Ando, K. Omoto, R. Naruse, and Y. Ageta. 1971, Discovery of meteorites near Yamato Mountains, East Antarctica, Antarctic Record, 39: 62-65. Alphabetical order, 98 ANTARCTIC JOURNAL tion, Powell, Fredriksen, Michelsen, and Laurie Islands, as Graywacke-Shale Formation in the South Orkney Islands well as the Robertson, Saddle, Weddell, and Inaccessible (see Dalziel and Elliot, 1973). The graywacke and shale Islands (figure 1). The ship returned to Ushuaia, Argentina, complex is here taken together with the metamorphic com- via Palmer Station on 10 February 1977. plex to constitute the geologic "basement" of the region. The purposes of the voyage were (1) to conclude structural This is in keeping with usage in southern South America. investigations of the so-called "basement" (i.e., probable Prior to 1971, knowledge of the "basement" rocks of the pre-Jurassic) rocks of the South Shetland and South Orkney South Orkneys was based on the extensive, but primarily Islands initiated by Dalziel in 1968-1969 as part of the U.S. lithologic, observations by members of the British Antarctic Scotia Arc Tectonics Project (see Dalziel, 1975, 1976, and Survey on Signy, Coronation, Powell, and Fredriksen Dalziel et al., 1975); (2) to augment the collections of Islands (see Thomson, 1968, 1973, 1974). The present in- metamorphic and igneous rock from Coronation and other vestigations, taken with work on Laurie, Fredriksen, Powell, islands available for petrologic study (Thomson, 1971, 1973 and Signy Islands in the course of R/V Hero cruise 71-1 and 1974); (3) to investigate the Mesozoic rocks of the South (Dalziel, 1971), enables the completion of a lithologic and Orkneys as part of a program initiated by Elliot in structural map of the "basement" of the entire South 1974-1975 to study the late Mesozoic and Cenozoic evolution Orkneys group. It is now clear that the South Orkney of the Antarctic Cordillera by means of sedimentary deposits Islands, including the Inaccessible Islands, all have geologic of that age (Elliot et al., 1975); and (4) to augment the affinities with Livingston, southern Elephant, and Gibbs somewhat meager collections of fossils from the South Islands of the South Shetlands, rather than with the Orkney Islands (Thomson, 1975; Thomson and Willey, blueschist terrain of Smith, northern Elephant, and 1975). Clarence Islands (Dalziel, 1976; see figure 2). A major step "Basement" rocks. Two tectono-stratigraphic units of forward in the understanding of Antarctic Peninsula-South possible pre-Jurassic age are exposed along the Antarctic Scotia Ridge geology was made during the present cruise Peninsula and on the islands of the South Scotia Ridge, a with the recognition of a lithologic and structural transition metamorphic complex and a highly deformed but otherwise along the west coast of Powell Island between the overlying unmetamorphosed sedimentary complex consisting predom- Greywacke-Shale Formation of Laurie, Fredriksen, Powell, inantly of greywacke and shale. The latter is known as the and the Saddle and Weddell Islands, and the underlying Trinity Peninsula "Series" in the Peninsula, the Miers Bluff metamorphic complex of Coronation and Signy Islands. Formation in the South Shetland Islands, and the Collections were made from the mafic dikes cutting the -60°30S 46000W 45 6 30W 4500W 44°30W o 0 , Inaccessible N Islands 0 (b Saddle Islands - 60040S Powell Weddell Islands 1.0 Cb 0I 20 30 Figure 1. Location map of the South Orkney KM Island Islands. -600501S .00 50 Coronation Island 600$ Elephant Island South Laurie \C . Clarence Island Orkney Is. Island Gibbs Island Q\ 7 Livingston Island Smith Island 0 Antarctica 50 Figure 2. Location map of the northern Antarctic KM. Peninsula, South Shetland Peninsula Islands and South Orkney 650$ Islands. October 1977 GB M 45010W 45°00 W he kEast Cape \ Rayner (i •- Point Powell Gibbon . Soy L ewthwa/Ie (1 Position $0 0 40S : approximate t I / I G c (M—G I Island •• J Coronation C- • I Island L ) 9 / John G—i:d reaics Strait Michel sen : Matthews Island Robertson, 4 Ii 60048S _A! Island Grey Island Conglomeratic rocks Greywacke-Shale Formation Figure 3. Geologic Metamorphic coimplex sketch map of the P Plant locality Lewthwaite Strait area, Islands South Orkney Islands. On GB Gibbon Bay Sha Ic Powell Island the letter Dikes symbols M--G and G-.-M are used to represent - -- Conglomerate-me tamorphic complex contact rocks transitional from the -- Greywacke- Shale - metamorphic complex contact metamorphic complex to the Graywacke•Shale For- f--- Fault mation and vice versa; see text for explanation. metamorphic rocks of Coronation Island for paleomagnetic Mesozoic rocks. The primary objective was to establish the study, as well as from the "basement" complexes as a whole relations of the Mesozoic strata (see Thomson, 1971, 1973, for petrologic, structural, and radiometric work. Outcrops 1974) which crop out adjacent to Lewthwaite Strait (figure visited for the first time along the northern and western 3) to the evolution of the Antarctic Codillera and its exten- coasts of Coronation Island consist of metamorphic rocks sion in the South Orkneys. Investigation of the sedimen- comparable with those occurring elsewhere on the island tology of the Mesozoic conglomeratic strata showed that at (Thomson, 1974). At most of the new localities the typical least five sedimentary facies are present and allows the rock-type is a grey micaceous schist. However, marbles and recognition of the sequences as alluvial fan deposits. Those interlayered garnetiferous rocks were noted at three of the on Powell and adjacent islands were derived from the north localities and hornblende-garnet schists at a fourth. and east, and in their composition reflect the occurrence of 100 ANTARCTIC JOURNAL the pre-late Mesozoic Greywacke-Shale Formation to the Thomson, J.W. 1971. The geology of Matthews Island, South east. Those on the Robertson Islands and eastern Corona- Orkney Islands. British Antarctic Survey. Bulletin, 26: 51-57. tion Island were derived mainly from the metamorphic Thomson, J.W. 1973. The geology of Powell, Christoffersen, and basement rocks to the west. The alluvial fans probably are Michelsen Islands, South Orkney Islands. British Antarctic related to Mesozoic fault block tectonics, in which inferred Survey. Bulletin, 33 and 34: 137-167. north-south trending graben faults would have been impor- Thomson, J.W. 1974. The geology of South Orkney Islands: III. tant. Coronation Island. British Antarctic Survey. Scientific Report, Field observations have allowed some slight revision to the 86. 39p. previously published geologic maps, and these changes are Thomson, M.R.A. 1975. Fossils from the South Orkney Islands: II. incorporated in figure 3. New localities at which the un- Matthews Island. British Antarctic Survey. Bulletin, 40: 75-79. conformity below the conglomeratic beds is exposed were Thomson, M.R.A. and L.E. Willey. 1975. Fossils from the South observed on several islands south of Matthews Island and at Orkney Islands: 1. Coronation Island. British Antarctic Survey. 40: 15-21. East Cape. A new outcrop of the Gibbon Bay Shale was Bulletin, found just west of East Cape. Dating of the sequences is important, but it is not possible from field observations alone to improve on the present rather imprecise age assignments based on limited fossil Marie Byrd Land volcanology evidence (Thomson, 1975; Thomson and Willey, 1975). Laboratory studies of fossil plants from two localities on southern Powell Island (figure 3), and rare ammonites and WESLEY E.

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