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ABSTRACT: Evolution of Exotic Terranes and Marginal Seas, Western North America

K. M. Wilson, W. W. Hay, C. N. Wold

A new suite of Mesozoic plate tectonic reconstruction for North America has been produced as part of a major global synthesis. Revised continental boundaries and suspect terranes are included in the analysis, which is based on detailed tectonic interpretation using relative reliability weighting of all data sets. Maps for western North America are presented

for the period 250-90 Ma at 20-m.y. intervals.

Examination of the maps suggests that North American marginal seas and terranes coevolved through the Mesozoic. For example, Terrane I may have been assembled in the interval 250-210 Ma in a mid-latitude position some 3000 km from the mainland. This amalgamation of terranes involved the closing of several small marginal seas. A large marginal sea, Klamathia, separated the newly assembled Terrane I and smaller inboard terranes from the mainland in the Late Triassic, this sea did not close until 150 Ma.

The continental margin south of Cape Mendocino was rimmed with small terranes throughout the Mesozoic. Many of these interacted with or were the result of marginal sea-opening events. Subsequent late Mesozoic oblique convergence closed most of these basins in conjunction with terrane collisions. There is strong evidence to support a model that places Terrane II in South America in the Triassic, with rapid northward motion occurring from 210-120 Ma. The Paleocaribbea marginal sea and associated terranes developed in the interval 130-90 Ma as a result of capture of a probable oceanic plateau.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990