Antarctica has long been considered to consist simply of a large Precambrian shield, flanked on one side by the circum-Pacific belt of Mesozoic and Cenozoic orogeny. The great amount of geologic information obtained during recent years, however, indicates that between shield and circum- Pacific belt are belts of Paleozoic orogeny.
The continent is probably crossed by a late Precambrian and Early Cambrian miogeosyncline, whose contents were metamorphosed and intruded by granodioritic batholiths during later Cambrian or Ordovician time. This orogen crosses the Antarctic coast between 145° and 160° E., and flanks the Ross Sea, Ross Ice Shelf, Filchner Ice Shelf, and possibly Weddell Sea, as a continuous system of high mountains. Rocks of the orogen are overlain by little-deformed Devonian to Triassic sedimentary rocks, which are intruded by sills of diabase.
Northeastern Victoria Land, west of the Ross Sea, is composed of metasedimentary rocks, striking generally east-southeastward, whose metamorphism and intrusion by granites probably occurred during Silurian or Devonian time. On strike across the Ross Sea, and trending toward the Weddell Sea at least to the region of 90° W., 82° S., are metasedimentary rocks intruded by petrographically and chemically distinctive quartz monzonites and allied granitic rocks; this terrane is considered to be of middle to late Paleozoic age.
Palmer Peninsula is composed largely of a Cretaceous batholith of quartz diorite, intrusive into metavolcanic rocks, and clearly belongs to the circum-Pacific orogen. The tectonic belt is connected to the South American Andes by way of the Scotia arc, an island-sprinkled submarine ridge; the belt is probably connected to New Zealand by way of Thurston Peninsula and the coastal region of the Amundsen Sea, and thence by way of a submarine ridge that passes near the mouth of the Ross Sea.
The Antarctic coastal region between 35° and 160° E. is characterized by charnockites, granulites, gneisses, and by varied younger crystalline rocks. As has long been recognized, this is part of a Precambrian shield, which may extend farther toward the Weddell Sea, and which presumably extends far toward the south pole in the ice-buried interior. The rocks of the shield were widely metamorphosed about 500 million years ago.
This revised pattern of Antarctic tectonics is essentially that required by Du Toit’s reassembly of the southern hemisphere continents before post-Paleozoic continental drift.
Figures & Tables
The first article in this book is the address that introduced the technical program of the 46th Annual Meeting of the AAPG. The organization and presentation of this symposium volume was developed in an orderly geographic continuity. Modern concepts of structural form and the sequence of tectonic events are carefully reported all along the mountainous western margins of the American continents. The relationship of this structural knowledge to the accumulation of oil and gas is constantly emphasized in the 26 papers contained herein.