Structural Studies in the Scotia Arc: Elephant Island ...
MADRE QUATENAP Y AND DE DIOS
Eli
ANDEAN IGNEOUS COUPLED
CRETACEOUS SEDIMENTS
JURASSIC AND CRETACEOUS VOLCANIC ROCKS U. PALEOZOIC SEDIMENTS
Simplified geologic map of southern South America. The black arrows show the general location of the traverses made during Hero Cruise 69-6.
MFIAMORPHIC
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phism or basement reactivation (apart from cleancut thrusting) at this time. At least two fold episodes affected the Pennsylvanian-Permian marine succession of the Madre de Dios basin on the west coast of the continent. However, there is no direct evidence of the age relationship between the polyphase deformation recognizable in the pre-late Jurassic metamorphic complex to the east and that observed in these sediments. Pebbles of granitic rocks were found in the sediments. The large granitic (and earlier basic) intrusives seen to cut the Pennsylvanian-Permian sediments, the metamorphic basement, and the Mesozoic cover rocks are mainly post-tectonic. There is no structural evidence that any of these igneous rocks are older than latest Mesozoic-Tertiary. Their foliation is primary. A large number of specimens were collected for microscopic studies. It is hoped that these will shed further light on the nature of the various deformational events for which field evidence was observed. The specimens of the metamorphic rocks will make it possible to establish the relationship in time between deformation and metamorphism. Over 100 oriented specimens were collected for paleomagnetic analysis. References Cortés, R. and I. W. D. Dalziel. 1970. The tectonic history of the Patagonian Andes (abstract). American Geophysical Union. Transactions, 51:421. Katz, H. R. In press. Some new concepts on geosynclinal development and mountain building at the southern end of South America. International Geological Congress, New Delhi, 1964.
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Structural Studies in the Scotia Arc: Elephant Island, Gibbs Island, Hope Bay, and Livingston Island D. DALZIEL, DAVID P. PRICE, and GERRY L. STIREWALT
IAN W.
Lamont-Doherty Geological Observatory Columbia University During January and February 1970, the authors carried out geologic studies at a number of localities in the South Shetland Islands and the Antarctic Peninsula (see map). Ten days were spent on the west coast of Elephant Island, ten days at the northeastern end of the Antarctic Peninsula (Hope Bay), and a brief landing was made on Gibbs Island. In addition, one of us (D.P.P.) worked with geologists from the Instituto Antártico Chileno (Francisco Hervé and Eduardo Valenzuela) on western Livingston Island for two weeks in early February. The rocks seen on western Elephant Island consisted of metasedimentary schists similar to those reported from elsewhere on the island (Wordie, 1921; Tilley, 1930; Tyrrell, 1945; Araya and Hervé, 1966). However, the authors were able to establish a history of polyphase deformation, which had not previously been recognized in the metamorphic rocks of the islands in the Scotia Arc. The visit to Hope Bay was improvised when logistic problems prevented the establishment of another camp on Elephant Island. Hope Bay is the "type" locality for studying the relationship between ANTARCTIC JOURNAL
principal investigator in the Miers Bluff Formation of eastern Livingston Island during the 1968-1969 season (Dalziel, 1969). The Jurassic volcanics and sediments which crop out at a higher topographic level (and have a basal conglomerate containing clasts from the Trinity Peninsula Series), on the other hand, show no signs of having been affected by more than a mild regional tilting to the southwest. Thus, although it is not possible to prove unequivocally that an unconformable relationship exists between the two sequences, as the actual contact is covered by a scree slope (Adie, 1957; Bibby, 1966; Schopf, in press), there is little room for doubt that such an unconformity exists, as Adie (1957) has long maintained. On western Livingston Island, Price examined the sedimentary and volcanic sequence of the Byers Peninsula previously assigned to the Miocene (Hobbs, 1968), but now recognized as Mesozoic (Araya and Hervé, 1966; 0. Gonzalez, personal communication). The rocks are much less intensely deformed than the sediments of the Miers Bluff Formation (? Trinity Peninsula Series) of eastern Livingston Island (Daiziel, 1969). On Gibbs Island, time was available only for collecting. A helicopter reconnaissance indicated, however, that ultramafic rocks are not confined to the eastern end of the island (Narrow Isle) as previously reported (Tyrrell, 1945). Material was collected for petrologic, paleontologic, paleomagnetic, and geochronologic study.
ELIPHANY ISIAND
50 W
OINVILLE
KING =GE
LIVINGSTON ISLAND
References
BEEN QUATERNARY AND TERTIARY ANDEAN IGNEOUS COMPLEX CRETACEOUS AND JURASSIC SEDIMENTS JURASSIC VOICANIC ROCKS
.;5 TRINITY PENINSULA SERIES AND EQUIVALENTS METAMORPHIC BASEMENT(?) COMPLEX
Geological map of the South Shetland Islands and the northern Antarctic Peninsula (modified, with permission, from a British Antarctic Survey map compiled by R. J. Adie). Localities visited are indicated by black arrows.
two of the most important lithostratigraphic units of the Antarctic Peninsula area, namely the Trinity Peninsula Series (? late Paleozoic) and the volcanic and sedimentary Jurassic sequence (Adie, 1957). While the details of their structural history could not be established within the limited area studied, the northwesterly dipping sediments of the Trinity Peninsula Series have clearly been affected by a number of episodes of folding and faulting. Their structural style is similar to that observed by the July—August 1970
Adie, R. J . 1957. The petrology of Graham Land, ITT: Metamorphic rocks of the Trinity Peninsula Series. Falkland Islands Dependencies Survey. Scientific Report No. 20. 26 p. Araya, Roberto and Francisco Hervé. 1966. Estudio geomorfológico y geológico en ]as Islas Shetland del Sur, Antártica. Instituto Antdrtico Chileno. Publicación No. 8, p. 1-15. Bibby, J . S. 1966. The stratigraphy of part of north-east Graham Land and the James Ross Island Group. British Antarctic Survey. Scientific Report No. 53. 37 p. Daiziel, I. W. D. 1969. Structural studies in the Scotia Arc: Livingston Island. Antarctic Journal of the U.S., IV (4) 137. Hobbs, G. J . 1968. The geology of the South Shetland Islands: IV, The geology of Livingston Island. British Antarctic Survey. Scientific Report, No. 47. 34 p. Schopf, J . M. In press. Plant material from the Miers Bluff Formation of the South Shetland Islands. Tilley, C. E. 1930. Petrographical notes on rocks from Elepliant Island, South Shetlands. In: Report on the Geo-
logical Collections made during the Voya'e of the Quest.
British Museum of Natural History, p. 55-62. Tyrrell, G. W. 1945. Report on rocks from West Antarctica and the Scotia Arc. Discovery Reports, 23: 76-88. Wordie, J . M. 1921. Shackleton Antarctic Expedition, 19141917. Geological observations in the Weddell Sea area. Royal Society of Edinburgh. Transactions, 53 (pt. I, no. 2): 17-27.
101
Eli
ANDEAN IGNEOUS COUPLED
CRETACEOUS SEDIMENTS
JURASSIC AND CRETACEOUS VOLCANIC ROCKS U. PALEOZOIC SEDIMENTS
Simplified geologic map of southern South America. The black arrows show the general location of the traverses made during Hero Cruise 69-6.
MFIAMORPHIC
ca I
I
7U
phism or basement reactivation (apart from cleancut thrusting) at this time. At least two fold episodes affected the Pennsylvanian-Permian marine succession of the Madre de Dios basin on the west coast of the continent. However, there is no direct evidence of the age relationship between the polyphase deformation recognizable in the pre-late Jurassic metamorphic complex to the east and that observed in these sediments. Pebbles of granitic rocks were found in the sediments. The large granitic (and earlier basic) intrusives seen to cut the Pennsylvanian-Permian sediments, the metamorphic basement, and the Mesozoic cover rocks are mainly post-tectonic. There is no structural evidence that any of these igneous rocks are older than latest Mesozoic-Tertiary. Their foliation is primary. A large number of specimens were collected for microscopic studies. It is hoped that these will shed further light on the nature of the various deformational events for which field evidence was observed. The specimens of the metamorphic rocks will make it possible to establish the relationship in time between deformation and metamorphism. Over 100 oriented specimens were collected for paleomagnetic analysis. References Cortés, R. and I. W. D. Dalziel. 1970. The tectonic history of the Patagonian Andes (abstract). American Geophysical Union. Transactions, 51:421. Katz, H. R. In press. Some new concepts on geosynclinal development and mountain building at the southern end of South America. International Geological Congress, New Delhi, 1964.
100
Structural Studies in the Scotia Arc: Elephant Island, Gibbs Island, Hope Bay, and Livingston Island D. DALZIEL, DAVID P. PRICE, and GERRY L. STIREWALT
IAN W.
Lamont-Doherty Geological Observatory Columbia University During January and February 1970, the authors carried out geologic studies at a number of localities in the South Shetland Islands and the Antarctic Peninsula (see map). Ten days were spent on the west coast of Elephant Island, ten days at the northeastern end of the Antarctic Peninsula (Hope Bay), and a brief landing was made on Gibbs Island. In addition, one of us (D.P.P.) worked with geologists from the Instituto Antártico Chileno (Francisco Hervé and Eduardo Valenzuela) on western Livingston Island for two weeks in early February. The rocks seen on western Elephant Island consisted of metasedimentary schists similar to those reported from elsewhere on the island (Wordie, 1921; Tilley, 1930; Tyrrell, 1945; Araya and Hervé, 1966). However, the authors were able to establish a history of polyphase deformation, which had not previously been recognized in the metamorphic rocks of the islands in the Scotia Arc. The visit to Hope Bay was improvised when logistic problems prevented the establishment of another camp on Elephant Island. Hope Bay is the "type" locality for studying the relationship between ANTARCTIC JOURNAL
principal investigator in the Miers Bluff Formation of eastern Livingston Island during the 1968-1969 season (Dalziel, 1969). The Jurassic volcanics and sediments which crop out at a higher topographic level (and have a basal conglomerate containing clasts from the Trinity Peninsula Series), on the other hand, show no signs of having been affected by more than a mild regional tilting to the southwest. Thus, although it is not possible to prove unequivocally that an unconformable relationship exists between the two sequences, as the actual contact is covered by a scree slope (Adie, 1957; Bibby, 1966; Schopf, in press), there is little room for doubt that such an unconformity exists, as Adie (1957) has long maintained. On western Livingston Island, Price examined the sedimentary and volcanic sequence of the Byers Peninsula previously assigned to the Miocene (Hobbs, 1968), but now recognized as Mesozoic (Araya and Hervé, 1966; 0. Gonzalez, personal communication). The rocks are much less intensely deformed than the sediments of the Miers Bluff Formation (? Trinity Peninsula Series) of eastern Livingston Island (Daiziel, 1969). On Gibbs Island, time was available only for collecting. A helicopter reconnaissance indicated, however, that ultramafic rocks are not confined to the eastern end of the island (Narrow Isle) as previously reported (Tyrrell, 1945). Material was collected for petrologic, paleontologic, paleomagnetic, and geochronologic study.
ELIPHANY ISIAND
50 W
OINVILLE
KING =GE
LIVINGSTON ISLAND
References
BEEN QUATERNARY AND TERTIARY ANDEAN IGNEOUS COMPLEX CRETACEOUS AND JURASSIC SEDIMENTS JURASSIC VOICANIC ROCKS
.;5 TRINITY PENINSULA SERIES AND EQUIVALENTS METAMORPHIC BASEMENT(?) COMPLEX
Geological map of the South Shetland Islands and the northern Antarctic Peninsula (modified, with permission, from a British Antarctic Survey map compiled by R. J. Adie). Localities visited are indicated by black arrows.
two of the most important lithostratigraphic units of the Antarctic Peninsula area, namely the Trinity Peninsula Series (? late Paleozoic) and the volcanic and sedimentary Jurassic sequence (Adie, 1957). While the details of their structural history could not be established within the limited area studied, the northwesterly dipping sediments of the Trinity Peninsula Series have clearly been affected by a number of episodes of folding and faulting. Their structural style is similar to that observed by the July—August 1970
Adie, R. J . 1957. The petrology of Graham Land, ITT: Metamorphic rocks of the Trinity Peninsula Series. Falkland Islands Dependencies Survey. Scientific Report No. 20. 26 p. Araya, Roberto and Francisco Hervé. 1966. Estudio geomorfológico y geológico en ]as Islas Shetland del Sur, Antártica. Instituto Antdrtico Chileno. Publicación No. 8, p. 1-15. Bibby, J . S. 1966. The stratigraphy of part of north-east Graham Land and the James Ross Island Group. British Antarctic Survey. Scientific Report No. 53. 37 p. Daiziel, I. W. D. 1969. Structural studies in the Scotia Arc: Livingston Island. Antarctic Journal of the U.S., IV (4) 137. Hobbs, G. J . 1968. The geology of the South Shetland Islands: IV, The geology of Livingston Island. British Antarctic Survey. Scientific Report, No. 47. 34 p. Schopf, J . M. In press. Plant material from the Miers Bluff Formation of the South Shetland Islands. Tilley, C. E. 1930. Petrographical notes on rocks from Elepliant Island, South Shetlands. In: Report on the Geo-
logical Collections made during the Voya'e of the Quest.
British Museum of Natural History, p. 55-62. Tyrrell, G. W. 1945. Report on rocks from West Antarctica and the Scotia Arc. Discovery Reports, 23: 76-88. Wordie, J . M. 1921. Shackleton Antarctic Expedition, 19141917. Geological observations in the Weddell Sea area. Royal Society of Edinburgh. Transactions, 53 (pt. I, no. 2): 17-27.
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