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Book Chapter

Map-view models for correcting and calculating shortening estimates in rotated thrust fronts using paleomagnetic data

By
E.L Pueyo
E.L Pueyo
Departamento Ciencias de la Tierra, Universidad de Zaragoza, c/Pedro Cerbuna 12, Zaragoza 50009, Spain, and Lab. Paleomagnetismo, I.C.T. “Jaume Almera” CSIC, c/Solé i Sabarís s/n, Barcelona 08028, Spain
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A Pocoví
A Pocoví
Departamento Ciencias de la Tierra, Universidad de Zaragoza, c/Pedro Cerbuna 12, Zaragoza 50009, Spain
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H Millán
H Millán
Departamento Ciencias de la Tierra, Universidad de Zaragoza, c/Pedro Cerbuna 12, Zaragoza 50009, Spain
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A.J Sussman
A.J Sussman
Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
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Published:
January 01, 2004

The application of classic geometric techniques in cross section balancing and restoration has restricted our understanding of rotational kinematics. Vertical-axis rotations are common in most curved orogenic systems, and the presence of such rotations provides valuable information that can be integrated with other geologic constraints. If paleomagnetic data are available in an area and reliable rotation values can be determined, then those shortening values obtained using traditional methods of restoration can be corrected by removing the deflection (error) due to rotation. This paper presents two trigonometric map-view methods (corrected shortening and realistic shortening) that allow for more accurate shortening estimates in areas that have undergone rigid-body rotations about a vertical-axis. In order to use these models, paleomagnetic data should record similar rotation magnitudes along strike, structural analysis should indicate a generally continuous shortening gradient, the location of the rotation axis (tip line of the fault) should be identified, and apparent/spurious rotations should be removed from any rotation values used in the models.

The curved, frontal portion of the External Sierras fold-thrust belt in the Southern Pyrenean orogenic system is an area in which vertical-axis rotations have been documented. By applying our map-view trigonometric models to this region, we recalculated the shortening from four existing cross sections. Shortening estimates from traditional methods and our corrected shortening values differ up to 20%. In addition, realistic shortening values are up to 25% higher than traditionally determined shortening estimates. The realistic shortening values, which are independently calculated, permit preliminary reconstruction of eroded hanging wall cutoff lines. The limitations of our methods, sources of errors, and possible improvements are also presented.

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GSA Special Papers

Orogenic curvature: Integrating paleomagnetic and structural analyses

Aviva J. Sussman
Aviva J. Sussman
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Arlo B. Weil
Arlo B. Weil
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Geological Society of America
Volume
383
ISBN print:
9780813723839
Publication date:
January 01, 2004

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