Abstract: Unusual Orogenic Mechanisms and Related Displacements

ZOLNAI, GREG

Several mechanisms may be present simultaneously within the same orogenic belt. These can be understood and the amount of corresponding movements can be estimated only if the composition and heritage of the basement is taken into account. - Orogeny is not compressive folding only.

The amount of compression assigned to each of the folded structures often varies, depending of the interpretation-scheme accepted "ante".

The typical, and overhelmingly used "West Canadian Rockies" mechanism (duplexes) dominates, in fact, in only part of the North American Cordillera; i.e., between the Peace River Arch (N) and the Uinta Ranges (S); beyond these limits more open folds and diverging polarities prevail.

Only part of the Alpine realm is a true fold (overthrust) belt. Large areas within consist of internal, relatively stable masses, devoid of large-scale compressions. "Tectonic units" (rather than "nappe units") reflect thick skin (rather than thin skin) mechanisms, involving basement control.

Important folded areas can be interpreted without much shortening. Some flysch belts reflect structural inversion and gravity tectonics. Foreland foldbelts (folded Jura, Wyoming province, North Franklin Mountains, South Atlas, Indonesia) and passive margins (Franklinian and Innuitian belts in Canada) exhibit basement adjustments, with wrenching.

Hydrocarbon history and habitat are to be considered differently in each of the cases, and working hypotheses have to be tested accordingly. Exploration may need to be reoriented, but new leads can be found, even in mature areas, if the deep mechanisms are well understood and applied.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria