Structural studies in the Scotia Arc: Dr. Horacio J. Harrington on an Argentine expedi- tion 30 years ago. Harringtons work (1943) showed Isla de los Estados, the island to consist almost entirely of probable Upper R/V Hero Cruise 72-2 Jurassic acidic volcanic rocks comparable to those of the Serie Tobifera (or Serie Porphyritica) that crops IAN W. D. DALZIEL out extensively in the Andean Cordillera. The north- Lamont-Doherty Geological Observatory ernmost part of Isla de los Estados (including the Columbia University offshore islets) Harrington found to consist of black shales and other sedimentary rocks of supposed Lower The objective of R/V Hero Cruise 72-2 was to Cretaceous age (fig. 1). study the geology of Isla de los Estados, Argentina, and adjacent areas of Isla Grande, the main island of The scientists participating in the present work . The cruise formed part of a con- were: Ian Daiziel and Keith Palmer of Lamont- tinuing study of the tectonics of the Scotia Arc under Doherty Geological Observatory, Roberto Caminos National Science Foundation grant GV-19541 (Dal- and Francisco Nollo of the Direccion Nacional de ziel, 1969, 1970, 1971a and b; Daiziel et al., 1970; Geologia y Mineria, Buenos Aires, and Riccardo Palmer and Daiziel, in press), and was undertaken Casanova of the Departamento de Geologia, Univer- jointly with Argentine scientists. sidad de Buenos Aires. The vessel sailed from Punta Isla de los Estados is situated on the northern limb Arenas, Chile, on April 25, 1972, and returned to of the Scotia Arc off the eastern tip of Isla Grande (fig. 1) and is the termination of the Andean Cordil- lera. The island trends east-west. It is approximately 60 kilometers long, up to 20 kilometers wide. It is $ extremely rugged, and the coastline is deeply indented A1 by numerous fjords (fig. 2). Accounts of the topog- 4f raphy, history of exploration, plants and animals can k be found in the reports of R/V Hero Cruises 71-2 and 71-5 (Flint, 1971; Imshaug, 1972). s 2

Apart from collections made on early voyages ¶. (Hyades, 1887), previous knowledge of the geology of Isla de los Estados is entirely due to the work of

Dr. Dalziel was senior scientist, Cruise 72-2. .y,..

660 I. 64 Figure 2 (above). The mountainous interior of Isla de los Estados, consisting entirely of massive A PLANT/C OCEA N volcanic rocks of probable Late Jurassic age. 540 30 - . .

1 .k TIERA DEL FUEGO Vp !.} SLA D( LOS ESTADOS Figure 1 (left). Easternmost Isla Granda (Tierra del Fuego) and DRAKE Isla de los Estados. Areas of outcrop of volcanic rocks are PASSAGE shown in black. Landing sites on Isla Grande are shown as black 0 40 dots. l—Isla Observatorio. KMS

66o 65 4.

September-October 1972 151 Rio Gallegos, Argentina, on June 1, 1972. Twenty- References nine days were spent working on Isla de los Estados Daiziel, I. W. D. 1969. Structural studies in the Scotia and four at the eastern end of Isla Grande in an at- Arc: . Journal of the U.S., tempt to correlate the lithic units and geologic struc- IV(4): 137. ture across the Strait of Le Maire. Daiziel, I. W. D. 1970. Structural studies in the Scotia Arc: the Patagonian and Fuegian . Antarctic Journal of Over 200 landings were made around the coast of the U.S., V(4): 99-100. Isla de los Estados and on Isla Observatorio to the Daiziel, I. W. D. 1971a. Structural studies in the Scotia Arc: Canal Beagle, Tierra del Fuego. Antarctic Journal north (fig. 1). Extensive collecting was undertaken, of the U.S.,VI(4): 122-124. and lithologic and structural maps were prepared. A Dalziel, I. W. D. 1971b. Structural studies in the Scotia joint preliminary scientific report will be published Arc: the South Orkney Islands. RJV Hero Cruise 71-1. in the near future. Antarctic Journal of the U.S., VI(4): 124-126. Daiziel, I. W. D., Price, D. J . and Stirewalt, G. 1970. Struc- Thanks are due to numerous individuals in Argen- tural studies in the Scotia Arc: Elephant Island, Gibbs tina for their help in making arrangements for the Island, Hope Bay, and Livingston Island. Antarctic Journal cruise, notably Dr. R. Muller, Director Nacional de of the U.S.,V(4): 100-101. Imshaug, Henry A. 1972. K/V Hero Cruise 71-5 to Isla de Geologia y Mineria, Professors H. Harrington, J . Tur- los Estados. Antarctic Journal of the U.S., VII (2): 42-44. ner, and D. Valencio of the Universidad de Buenos Flint, 0. S. 1971. R/V Hero Cruise 71-2 to Isla de los Aires, Dr. N. Fourcade of the Instituto Antartico Estados. Antarctic Journal of the U.S., VI (6): 263-265. Argentino, Dr. A. Lonardi of the Instituto Oceano- Harrington, H. J . 1943. Observaciones geologicas en la Isla de los Estados. An. Mus. Arg. Cien. Nat., Geol. Publ. 29, graphico Argentino, and Mr. M. B. Kratzer, scientific p. 29-52. attaché at the U.S. Embassy. Hyades, J. 1887. Mission scientifique du Cap Horn (1882- 1883). Geologie, Paris, IV, 242 p. The enthusiasm and skill with which Captain Pieter Palmer, K. F., and Daiziel, I. W. D. In press. Structural Lenie operated his vessel in uncharted waters con- studies in the Scotia Arc: Andean Cordillera, Tierra del tributed immeasurably to the success of the cruise. Fuego. Antarctic Journal of the U.S., VII (1).

Petrology of Deception Island volcano C.I.P.W. norms have been computer calculated. In- terpretation of these data indicates that Deception CHARLES H. SHULTZ rocks belong to the oceanic basalt-trachyte associa- Department of Geology tion, although the match is imperfect. The parent Slippery Rock State College magma is probably similar to Kunos low-potassium, high-aluminum basalt (Kuno, 1960). Chemical vari- Two years have passed since the August 1970 vol- ations of recent pyroclastics were probably caused by canic eruption at Deception Island. Perhaps, con- liquid-crystal fractionation related to the separation trary to my expectations, this most recent eruptive of diopsidic augite and titaniferous magnetite. cycle has come to an end. Assuming this to be the Very welcome support of the project has been lent case, field work on the project is essentially complete. by Prof. Bernard M. Gunn of the University of During the past year I have continued to evaluate Montreal. Prof. Gunn has been investigating low- field observations, petrographic data, and chemical potassium andesites and tholeiites of oceanic islands analysis. I have concentrated my petrographic work worldwide. He is currently analyzing my materials, on the pre-1967 pyroclastics, tuffs, and breccias, including the oldest rocks on the island, for such trace which have never been investigated satisfactorily. elements as chromium, nickel, cobalt, barium, zinc, Universal stage work on rock samples that have been copper, strontium, and rubidium. On the basis of chemically analyzed is continuing. I was fortunate preliminary results he has concluded that Deception in receiving a generous sample of the volcanic ash rocks and pyroclastics are primarily ". . . low-potas- and dust that fell on the Soviet Bellingauzen Station sium basaltic andesite typical of island arcs" (personal shortly after the eruption of August 12, 1970. Petro- communication). graphically, this material compares favorably with During the past year I presented a paper on the mechanically analyzed tephra collected on Deception volcanology and petrology of the recent eruptions Island. (Shultz, 1971) and published a paper giving details Much of my effort has been concentrated on eval- of the 1970 eruptions (Shultz, in press). uation of the chemistry of recent pyroclastics and the This work was supported by National Science relationship of the island to other volcanoes of the Foundation grant GA-4146 to The Ohio State Uni- world. The chemical data have been normalized, and sity.

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