Structural studies in the Scotia Arc: Isla de los Estados, Argentina R/V ...
Dr. Horacio J . Harrington on an Argentine expedition 30 years ago. Harrington's work (1943) showed the island to consist almost entirely of probable Upper Jurassic acidic volcanic rocks comparable to those of the Serie Tobifera (or Serie Porphyritica) that crops out extensively in the Andean Cordillera. The northernmost part of Isla de los Estados (including the offshore islets) Harrington found to consist of black shales and other sedimentary rocks of supposed Lower Cretaceous age (fig. 1). The scientists participating in the present work were: Ian Daiziel and Keith Palmer of LamontDoherty Geological Observatory, Roberto Caminos and Francisco Nollo of the Direccion Nacional de Geologia y Mineria, Buenos Aires, and Riccardo Casanova of the Departamento de Geologia, Universidad de Buenos Aires. The vessel sailed from Punta Arenas, Chile, on April 25, 1972, and returned to
Structural studies in the Scotia Arc: Isla de los Estados, Argentina R/V Hero Cruise 72-2 IAN W. D. DALZIEL
Lamont-Doherty Geological Observatory Columbia University The objective of R/V Hero Cruise 72-2 was to study the geology of Isla de los Estados, Argentina, and adjacent areas of Isla Grande, the main island of Tierra del Fuego. The cruise formed part of a continuing study of the tectonics of the Scotia Arc under National Science Foundation grant GV-19541 (Dalziel, 1969, 1970, 1971a and b; Daiziel et al., 1970; Palmer and Daiziel, in press), and was undertaken jointly with Argentine scientists. Isla de los Estados is situated on the northern limb of the Scotia Arc off the eastern tip of Isla Grande (fig. 1) and is the termination of the Andean Cordillera. 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 by numerous fjords (fig. 2). Accounts of the topography, history of exploration, plants and animals can be found in the reports of R/V Hero Cruises 71-2 and 71-5 (Flint, 1971; Imshaug, 1972). 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
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Dr. Dalziel was senior scientist, Cruise 72-2.
660
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A PLANT/C 540 30'
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A1'
64
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Figure 2 (above). The mountainous interior of Isla de los Estados, consisting entirely of massive volcanic rocks of probable Late Jurassic age.
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TIERA DEL FUEGO
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SLA D( LOS ESTADOS Figure 1 (left). Easternmost Isla Granda (Tierra del Fuego) and Isla de los Estados. Areas of outcrop of volcanic rocks are shown in black. Landing sites on Isla Grande are shown as black dots. l—Isla Observatorio.
DRAKE PASSAGE 0 40 KMS 66o
September-October 1972
65
'4. 151
Rio Gallegos, Argentina, on June 1, 1972. Twentynine days were spent working on Isla de los Estados and four at the eastern end of Isla Grande in an attempt to correlate the lithic units and geologic structure across the Strait of Le Maire. Over 200 landings were made around the coast of Isla de los Estados and on Isla Observatorio to the north (fig. 1). Extensive collecting was undertaken, and lithologic and structural maps were prepared. A joint preliminary scientific report will be published in the near future. Thanks are due to numerous individuals in Argentina for their help in making arrangements for the cruise, notably Dr. R. Muller, Director Nacional de Geologia y Mineria, Professors H. Harrington, J . Turner, and D. Valencio of the Universidad de Buenos Aires, Dr. N. Fourcade of the Instituto Antartico Argentino, Dr. A. Lonardi of the Instituto Oceanographico Argentino, and Mr. M. B. Kratzer, scientific attaché at the U.S. Embassy. The enthusiasm and skill with which Captain Pieter Lenie operated his vessel in uncharted waters contributed immeasurably to the success of the cruise.
Petrology of Deception Island volcano CHARLES H. SHULTZ Department of Geology Slippery Rock State College
Two years have passed since the August 1970 volcanic eruption at Deception Island. Perhaps, contrary to my expectations, this most recent eruptive cycle has come to an end. Assuming this to be the case, field work on the project is essentially complete. During the past year I have continued to evaluate field observations, petrographic data, and chemical analysis. I have concentrated my petrographic work on the pre-1967 pyroclastics, tuffs, and breccias, which have never been investigated satisfactorily. Universal stage work on rock samples that have been chemically analyzed is continuing. I was fortunate in receiving a generous sample of the volcanic ash and dust that fell on the Soviet Bellingauzen Station shortly after the eruption of August 12, 1970. Petrographically, this material compares favorably with mechanically analyzed tephra collected on Deception Island. Much of my effort has been concentrated on evaluation of the chemistry of recent pyroclastics and the relationship of the island to other volcanoes of the world. The chemical data have been normalized, and 152
References Daiziel, I. W. D. 1969. Structural studies in the Scotia Arc: Livingston Island. Antarctic Journal of the U.S.,
IV(4): 137. Daiziel, I. W. D. 1970. Structural studies in the Scotia Arc: the Patagonian and Fuegian Andes. Antarctic Journal of the U.S., V(4): 99-100. Daiziel, I. W. D. 1971a. Structural studies in the Scotia Arc: Canal Beagle, Tierra del Fuego. Antarctic Journal of the U.S.,VI(4): 122-124. Dalziel, I. W. D. 1971b. Structural studies in the Scotia Arc: the South Orkney Islands. RJV Hero Cruise 71-1. Antarctic Journal of the U.S., VI(4): 124-126. Daiziel, I. W. D., Price, D. J . and Stirewalt, G. 1970. Structural studies in the Scotia Arc: Elephant Island, Gibbs Island, Hope Bay, and Livingston Island. Antarctic Journal of the U.S.,V(4): 100-101. Imshaug, Henry A. 1972. K/V Hero Cruise 71-5 to Isla de los Estados. Antarctic Journal of the U.S., VII (2): 42-44. Flint, 0. S. 1971. R/V Hero Cruise 71-2 to Isla de los Estados. Antarctic Journal of the U.S., VI (6): 263-265. Harrington, H. J . 1943. Observaciones geologicas en la Isla de los Estados. An. Mus. Arg. Cien. Nat., Geol. Publ. 29, p. 29-52. Hyades, J . 1887. Mission scientifique du Cap Horn (18821883). Geologie, Paris, IV, 242 p. Palmer, K. F., and Daiziel, I. W. D. In press. Structural studies in the Scotia Arc: Andean Cordillera, Tierra del Fuego. Antarctic Journal of the U.S., VII (1).
C.I.P.W. norms have been computer calculated. Interpretation of these data indicates that Deception rocks belong to the oceanic basalt-trachyte association, although the match is imperfect. The parent magma is probably similar to Kuno's low-potassium, high-aluminum basalt (Kuno, 1960). Chemical variations of recent pyroclastics were probably caused by liquid-crystal fractionation related to the separation of diopsidic augite and titaniferous magnetite. Very welcome support of the project has been lent by Prof. Bernard M. Gunn of the University of Montreal. Prof. Gunn has been investigating lowpotassium andesites and tholeiites of oceanic islands worldwide. He is currently analyzing my materials, including the oldest rocks on the island, for such trace elements as chromium, nickel, cobalt, barium, zinc, copper, strontium, and rubidium. On the basis of preliminary results he has concluded that Deception rocks and pyroclastics are primarily ". . . low-potassium basaltic andesite typical of island arcs" (personal communication). During the past year I presented a paper on the volcanology and petrology of the recent eruptions (Shultz, 1971) and published a paper giving details of the 1970 eruptions (Shultz, in press). This work was supported by National Science Foundation grant GA-4146 to The Ohio State Unisity. ANTARCTIC JOURNAL
Structural studies in the Scotia Arc: Isla de los Estados, Argentina R/V Hero Cruise 72-2 IAN W. D. DALZIEL
Lamont-Doherty Geological Observatory Columbia University The objective of R/V Hero Cruise 72-2 was to study the geology of Isla de los Estados, Argentina, and adjacent areas of Isla Grande, the main island of Tierra del Fuego. The cruise formed part of a continuing study of the tectonics of the Scotia Arc under National Science Foundation grant GV-19541 (Dalziel, 1969, 1970, 1971a and b; Daiziel et al., 1970; Palmer and Daiziel, in press), and was undertaken jointly with Argentine scientists. Isla de los Estados is situated on the northern limb of the Scotia Arc off the eastern tip of Isla Grande (fig. 1) and is the termination of the Andean Cordillera. 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 by numerous fjords (fig. 2). Accounts of the topography, history of exploration, plants and animals can be found in the reports of R/V Hero Cruises 71-2 and 71-5 (Flint, 1971; Imshaug, 1972). 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
$
'k 4f s* 2 ¶.
Dr. Dalziel was senior scientist, Cruise 72-2.
660
'I.
A PLANT/C 540 30'
.y,..
A1'
64
OCEA N
Figure 2 (above). The mountainous interior of Isla de los Estados, consisting entirely of massive volcanic rocks of probable Late Jurassic age.
- . . 1
.k
TIERA DEL FUEGO
Vp
} !'.
SLA D( LOS ESTADOS Figure 1 (left). Easternmost Isla Granda (Tierra del Fuego) and Isla de los Estados. Areas of outcrop of volcanic rocks are shown in black. Landing sites on Isla Grande are shown as black dots. l—Isla Observatorio.
DRAKE PASSAGE 0 40 KMS 66o
September-October 1972
65
'4. 151
Rio Gallegos, Argentina, on June 1, 1972. Twentynine days were spent working on Isla de los Estados and four at the eastern end of Isla Grande in an attempt to correlate the lithic units and geologic structure across the Strait of Le Maire. Over 200 landings were made around the coast of Isla de los Estados and on Isla Observatorio to the north (fig. 1). Extensive collecting was undertaken, and lithologic and structural maps were prepared. A joint preliminary scientific report will be published in the near future. Thanks are due to numerous individuals in Argentina for their help in making arrangements for the cruise, notably Dr. R. Muller, Director Nacional de Geologia y Mineria, Professors H. Harrington, J . Turner, and D. Valencio of the Universidad de Buenos Aires, Dr. N. Fourcade of the Instituto Antartico Argentino, Dr. A. Lonardi of the Instituto Oceanographico Argentino, and Mr. M. B. Kratzer, scientific attaché at the U.S. Embassy. The enthusiasm and skill with which Captain Pieter Lenie operated his vessel in uncharted waters contributed immeasurably to the success of the cruise.
Petrology of Deception Island volcano CHARLES H. SHULTZ Department of Geology Slippery Rock State College
Two years have passed since the August 1970 volcanic eruption at Deception Island. Perhaps, contrary to my expectations, this most recent eruptive cycle has come to an end. Assuming this to be the case, field work on the project is essentially complete. During the past year I have continued to evaluate field observations, petrographic data, and chemical analysis. I have concentrated my petrographic work on the pre-1967 pyroclastics, tuffs, and breccias, which have never been investigated satisfactorily. Universal stage work on rock samples that have been chemically analyzed is continuing. I was fortunate in receiving a generous sample of the volcanic ash and dust that fell on the Soviet Bellingauzen Station shortly after the eruption of August 12, 1970. Petrographically, this material compares favorably with mechanically analyzed tephra collected on Deception Island. Much of my effort has been concentrated on evaluation of the chemistry of recent pyroclastics and the relationship of the island to other volcanoes of the world. The chemical data have been normalized, and 152
References Daiziel, I. W. D. 1969. Structural studies in the Scotia Arc: Livingston Island. Antarctic Journal of the U.S.,
IV(4): 137. Daiziel, I. W. D. 1970. Structural studies in the Scotia Arc: the Patagonian and Fuegian Andes. Antarctic Journal of the U.S., V(4): 99-100. Daiziel, I. W. D. 1971a. Structural studies in the Scotia Arc: Canal Beagle, Tierra del Fuego. Antarctic Journal of the U.S.,VI(4): 122-124. Dalziel, I. W. D. 1971b. Structural studies in the Scotia Arc: the South Orkney Islands. RJV Hero Cruise 71-1. Antarctic Journal of the U.S., VI(4): 124-126. Daiziel, I. W. D., Price, D. J . and Stirewalt, G. 1970. Structural studies in the Scotia Arc: Elephant Island, Gibbs Island, Hope Bay, and Livingston Island. Antarctic Journal of the U.S.,V(4): 100-101. Imshaug, Henry A. 1972. K/V Hero Cruise 71-5 to Isla de los Estados. Antarctic Journal of the U.S., VII (2): 42-44. Flint, 0. S. 1971. R/V Hero Cruise 71-2 to Isla de los Estados. Antarctic Journal of the U.S., VI (6): 263-265. Harrington, H. J . 1943. Observaciones geologicas en la Isla de los Estados. An. Mus. Arg. Cien. Nat., Geol. Publ. 29, p. 29-52. Hyades, J . 1887. Mission scientifique du Cap Horn (18821883). Geologie, Paris, IV, 242 p. Palmer, K. F., and Daiziel, I. W. D. In press. Structural studies in the Scotia Arc: Andean Cordillera, Tierra del Fuego. Antarctic Journal of the U.S., VII (1).
C.I.P.W. norms have been computer calculated. Interpretation of these data indicates that Deception rocks belong to the oceanic basalt-trachyte association, although the match is imperfect. The parent magma is probably similar to Kuno's low-potassium, high-aluminum basalt (Kuno, 1960). Chemical variations of recent pyroclastics were probably caused by liquid-crystal fractionation related to the separation of diopsidic augite and titaniferous magnetite. Very welcome support of the project has been lent by Prof. Bernard M. Gunn of the University of Montreal. Prof. Gunn has been investigating lowpotassium andesites and tholeiites of oceanic islands worldwide. He is currently analyzing my materials, including the oldest rocks on the island, for such trace elements as chromium, nickel, cobalt, barium, zinc, copper, strontium, and rubidium. On the basis of preliminary results he has concluded that Deception rocks and pyroclastics are primarily ". . . low-potassium basaltic andesite typical of island arcs" (personal communication). During the past year I presented a paper on the volcanology and petrology of the recent eruptions (Shultz, 1971) and published a paper giving details of the 1970 eruptions (Shultz, in press). This work was supported by National Science Foundation grant GA-4146 to The Ohio State Unisity. ANTARCTIC JOURNAL
