Shelf 10 km Ross Ice 5mi I ,Cam I \\ \ \ 1Cornp 2

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amp 1/ t. Fairweather - \\\ S\8f /&Jf —, Duncan Mountains location -- / map. This research was supported by National Science Foundation grant opp 74-04897.

Reference

McGregor, V. R. 1965. Geology of the area between the Axel S. Heiberg and Shackleton glaciers, Queen Maud Range, Ant- arctica. N.Z. Journal of Geology and Geophysics, 8: 314-343. S -.

Structural and petrologic studies .l4JI;I .,: •:.:;.- in the .7 "of W,. 4t1::

IAN W. D. DALZIEL, MAARTEN J . DE WIT, and CHARLES R. STERN Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964

Geologic studies in the Scotia Arc tectonics project were made in several geographic areas during the 1974-1975 austral summer, from De- cember 20, 1974, to March 11, 1975 (figure 1).

(1) and . Dr. de Wit, accompanied by Steven Dutch and Roy Figure 2. The northwest-southeast lineament formed by the Kligfield, both of the Department of Geological Strait of Magellan, Seno Almirantazgo, and Lago Fagnano. Sciences, Columbia University, and by Richardson Bottom: view northwest toward the Strait of Magellan; from Allen, Columbia College, studied Gibbs Island and the head of Seno Almirantazgo note how high cliffs in back- western Livingston Island in the South Shetland ground continue into recent fault scarp in bottom right corner. Top: view northward from the same location; note Islands group, and various localities along the Ant- how recent fault scarp is visible through the forest and sepa- arctic Peninsula as far south as Marguerite Bay. rates the forest from the marshy valley floor. Topographic The party was supported by WV Hero.. relief Is approximately 1 kilometer.

180 ANTARCTIC JOURNAL 80W CP

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pt BC BEAGLE CHANNEL 4) CD CORDILLERA DARWIN CP CERRO PAINE ANTARCTiC E ELEPHANT ISLAND M PENINSULA F LAGO FAGNANO SOUTH 6 GIBBS ISLAND SANDWICH L LIVINGSTON ISLAND ISLANDS M MARGUERITE BAY MB MONTE BIJRNEY P PALMER STATION j SA SEND ALMIRANTAZGO Figure 1.

Gibbs Island is significant as the only known 1- Mesozoic deformation had been believed to be very cation of outcropping uitramaflc rocks in the Scotia mild on the southern limb of the Scotia Arc (Dal- Arc. The party mapped all of Gibbs Island and ziel and Cortés, 1972; Dalziel, 1974). determined chat the ultramafics (massive and schistose serpentinite) structurally overlie a belt of low-grade metasediments, and that the emplace- (2) Cordillera Darwin, Tierra del Fuego. Work in ment preceded the late Mesozoic Andean orogeny. this area included a geologic traverse by Dr. Daiziel, The results can be tied to earlier work on Elephant accompanied by Ronald Bruhn and Margaret Wins- Island and in the South Orkney Islands (Dalziel low, both of the Department of Geological Sciences, et aL, 1970; Dalziei, 1971). Columbia University, from the Beagle Channel Significant results from the Antarctic Peninsula northward across the Chilean part of the range to include the recognition of the Marguerite Bay Seno Almirantazgo, and detailed mapping by Mr. "basement" complex as the probable roots of an Bruhn in the Argentine sector. There was evidence early Mesozoic caic-alkaline volcanic chain or arc, of recent faulting along the northwest-southeast and the discovery of zones of intense late Mesozoic trending Strait of Magellan-Seno Almirantazgo- deformation, as manifested by large-scale folding Lago Fagnano lineament (figure 2). The Upper and a strong cleavage in Lemaire Channel. Late Jurassic volcanic rocks along the northern part of

July/August 1975 181 the range contain more rocks of intermediate com- Geological investigations position than previously thought (Daiziel et al., 1974a). The volcanics thus may represent a rem- on Seymour Island, nant arc behind the Lower Cretaceous marginal Antarctic Peninsula basin recently recognized in the Southern (Daiziel et al., 1974b).

(3) Andean Precordillera. Detailed structural map- D. H. ELLIOT 1 , C. RINALDI 2 , W. J . ZINSMEISTER1, ping of the east-west trending part of the Precor- T. A. TRAUTMAN 1 , W. A. BRYANT 3 , and dillera north of Cordillera Darwin was begun by R. DEL VALLE4 Ms. Winslow, assisted by Linda Raedeke, University of Washington. Institute of Polar Studies and (4) Patagonian batholith. Dr. Stern, assisted by Department of Geology and Mineralogy Janet Stroup, Lamont-Doherty Geological Obser- The Ohio State University vatory, and by M. Alexandra Skewes, Universidad Columbus, Ohio 43210 de Chile, traversed the Patagonian batholith north of the Strait of Magellan to collect samples for 2Comisi6n Nacional de Energia Atómica later petrologic and geochemical studies. Buenos Aires, Argentina (5) Cenozoic and Recent igneous bodies. Dr. Stern Department of Geology and party also studied and collected from such late Northern Illinois University Cenozoic plutons of the Andean Precordillera as DeKalb, Illinois 60115 Cerro Paine, and the recently active volcanoes, such as Monte Burney. 4Direcc16n Nacional del Antártico Instituto Antártico Argentino We thank Captain Pieter Lenie and the crew of Buenos Aires, Argentina RIV Hero for their enthusiastic support of Dr. de Wits party. The work in Chile was supported by the Empresa Nacional del Petróleo. The assistance Seymour Island, about 100 kilometers southeast of Srs. Eduardo Gonzalez, Salvador Harambour, of the Antarctic Peninsula (figure 1), has the only Bernardo Bergman, and Raül Cortés was in- known exposed marine Lower Tertiary in Antarc- valuable. Finally, we thank the Chilean navy for tica. The island, first sighted by James Clark Ross transportation in the Beagle Channel. in 1843, has considerable historical interest. An This project is supported by National Science O expedition under Norwegian whaling captain C. A. Foundation grants pp 74-21415, Gx-34410, and Larsen visited the island in 1893 and made the first DES 75-04076. collections of Tertiary fossils (Sharman and New- ton, 1894, 1898); it was more extensively sampled by the Swedish South Polar Expedition (1901 to References 1903), which discovered fossil plants, penguins, and Cretaceous invertebrates, and also established an Daiziel, I. W. D. 1971. Structural studies in the Scotia Arc: the South Orkney Islands. WV Hero Cruise 71-I. Antarctic Jour- outline of the geologic history of the northern nal of the U.S., VI(4): 124-126. Antarctic Peninsula (Andersson, 1906; Norden- Dalziel, I. W. D. 1974. Evolution of the margins of the Scotia skjöld, 1905, 1913). Sea. In: The Geology of Continental Margins (Burk, C. A., and The island was examined briefly in 1953 and C. L. Drake, editors). New York, Springer-Verlag. 567-579. Daiziel, I. W. D., R. Caminos, K. F. Palmer, F. Nullo, and R. 1954 by members of the Falkland Islands Depen- Casanova. 1974a. Southern extremity of the Andes: geology dencies Survey (now the British Antarctic Survey) of Isla de los Estados, Argentine Tierra del Fuego. Ameri- (Adie, 1958), but no extensive studies were con- can Association of Petroleum Geologists. Bulletin, 58(12): ducted until the 1973-1974 season when geologists 2502-2512. Dalziel, I. W. D., and R. Cortés. 1972. Tectonic style of the from the Instituto Antártico Argentino mapped southernmost Andes and the Antarctandes. 24th Internaitonal most of the island. Four geologists from the Insti- Geological Congress, Montreal, August 1972. 316-327. tute of Polar Studies, The Ohio State University, Dalziel, 1. W. D., M. J . de Wit, and K. F. Palmer. 1974b. A fossil and from Northern Illinois University, were invited marginal basin in the southern Andes. Nature, 250: 291-294. Dalziel, I. W. D., David P. Price, and Gerry L. Stirewalt. 1970. Structural studies in the Scotia Arc: Elephant Island, Gibbs Island, Hope Bay, and Livingston Island. Antarctic Journal Isla Vicecomodoro Marambio is the name given on Argentine of the U.S., V(4): 100-101. maps.

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