26. Contrasts in Tectonic History Along the Eastern Pacific Rim

  1. George H. Sutton,
  2. Murli H. Manghnani,
  3. Ralph Moberly and
  4. Ethel U. Mcafee
  1. R. H. Dott Jr.

Published Online: 17 MAR 2013

DOI: 10.1029/GM019p0299

The Geophysics of the Pacific Ocean Basin and Its Margin

The Geophysics of the Pacific Ocean Basin and Its Margin

How to Cite

Dott, R. H. (1976) Contrasts in Tectonic History Along the Eastern Pacific Rim, in The Geophysics of the Pacific Ocean Basin and Its Margin (eds G. H. Sutton, M. H. Manghnani, R. Moberly and E. U. Mcafee), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM019p0299

Author Information

  1. Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706

Publication History

  1. Published Online: 17 MAR 2013
  2. Published Print: 1 JAN 1976

ISBN Information

Print ISBN: 9780875900193

Online ISBN: 9781118663592

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Keywords:

  • Geophysics—Pacific area—Congresses;
  • Woollard, George Prior, 1908

Summary

The histories of ocean basins prior to the Jurassic must be sought in their old convergent margins, but such margins are extremely complex due to compressional and transcurrent deformation, metamorphism, uplift, and erosion. Commonly several important tectonic events have been superimposed. Some events, however, have been more widespread and profound, in which case these serve to punctuate an otherwise rather chaotic record. The mobile eastern Pacific rim, while superficially homogeneous- appearing, is in fact a collage of many tectonic elements and segments that differ significantly in detail from their neighbors. Successions of dismemberments by extensional and transform motions and telescoping by convergence have left important marks. In early Paleozoic time, both western North and South America had tranquil, trailing-edge shelf-slope margins presumably rifted from some other, unknown continent(s). Subduction accompanied by calc-alkaline igneous activity began along the entire eastern Pacific margin at least by Permian time, and has continued along most of the margin to the present. Evidence for subduction is clearest for Mesozoic and early Cenozoic time; ophiolites, melanges, and blue schists of the Franciscan complex providing especially compelling evidence in addition to calc-alkaline magmatism. Opening of a late Paleozoic marginal basin in western North America, a late Mesozoic one in Tierra del Fuego, and doubtless others, accompanied subduction. But other areas are almost totally lacking in ophiolites, melanges, and blue schists. Moreover, late Mesozoic-early Cenozoic granitic batholiths, which are almost universal along the entire Pacific rim, lie inland in many places, but on the coast in others. Even more puzzling, in western Peru and Chile, an old Paleozoic or Precambrian metamorphic crystalline complex lies at the coast and extends offshore beneath the continental shelf almost to the trench. In mid-Cenozoic (Oligocene-Miocene) time, almost the entire circum-Pacific rim underwent profound tectonic changes, but of different sorts in different regions. Although by no means precisely synchronous, those changes do seem to be related somehow. Collision of North America with the East Pacific ridge resulted in the replacement of subduction by transform and accompanying block-fault deformation. The Cascade and Aleutian arcs were born, as was the volcanic Isthmus of Panama. In the central Andes, great vertical uplift was accompanied by block faulting and formation of the modern Andean volcanoes. In the Scotia Sea region, final dismemberment of South America from Antarctica occurred as here, too, the continent collided with an old ridge system. The South Georgia microcontinent separated from Tierra del Fuego and soon thereafter the South Sandwich arc formed. These events around the Pacific margin correlate in a very general way with a major ridge jump in the east-central Pacific beginning about 25–30 m.y. ago, the slightly earlier bend in the Hawaiian- Emperor chain, and the upheaval of the Indonesian-Himalayan-Alpine orogenic belt.