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ABSTRACT: The Nature and Origin of Thrust-and-Fold Belts

PRICE, RAYMOND A., Queen's University, Kingston, Ontario, Canada

Thrust-and-fold belts have been enigmatic ever since large-scale overthrusting was first convincingly documented in the Swiss Alps, some 150 years ago. In spite of some impressive recent advances in our understanding of their nature, origin and evolution, many fundamental observations require further elucidation. These include:

--the pattern of distribution of displacements among the array of faults that forms the structural skeleton of most thrust-and-fold belts, and that characteristically appears to involve the concentration of the greater part of the total displacement of the entire belt on a very few large faults, and the dispersion of the remaining lesser part of the total displacement over a very large number of smaller faults.
--reconciliation of the assumption of mechanical homogeneity and isotropy in the very successful critical-taper model explanation for the vertical cross section shape and orientation of thrust-and-fold belts with the common occurrence within critically Previous HittaperedTop wedges of individual overthrust thrust faults along which coherent sheets of rock 5-10 km thick have been displaced >50 km.
--the relative lack of heating in rocks that have been buried beneath thrust sheets that are 5-10 km thick.
--the common occurrence of very extensive (>100 sq. kilometers) bedding-parallel detachments that lie within strong homogeneous formations, such as massive carbonate rocks, or within the crystalline basement.
--curved thrust-and-fold belts that bear clear evidence of radial, outward-directed overthrusting.
--thrust-and-fold belts, like the Carpathians and Apennines, in which the hinterland is an area of lower elevation in which there has been back-arc spreading, extension, and subsidence during critical-taper overthrusting along the foreland.


AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)