Paleomagnetic evidence for rapid vertical-axis rotation in the Peruvian Cordillera ca. 8 Ma
- 1Institut de Physique du Globe de Paris, Laboratoire de Paléomagnétisme, 4 place Jussieu, 75252 Paris Cedex 05, France
- 2Lawrence Livermore National Laboratory, Livermore, California 94550, USA
- 3Department of Earth Sciences, California State University, Dominguez Hills, Carson, California 90747, USA
- 4Instituto de Geológico Minero y Metalurgico, 1470 Avenida Canadá, San Borja, Lima 41, Peru
Abstract
Paleomagnetic results from 31 Neogene sites in the Peruvian Andes yield primary magnetizations, as demonstrated by positive fold and reversal tests. Strata dated as 18–9 Ma record a significant counterclockwise rotation (−11° ± 5°), whereas unconformably overlying younger strata (7–6 Ma) are not rotated. The age of rotation thus is between 9 and 7 Ma, a period that coincides with the widespread Quechua 2 deformation phase. Moreover, eight independent studies on 107–9 Ma rocks from Peru between 9°S and 15°S reveal similar and significant rotations (−15° ± 6°). This suggests that the region rotated during a 2 m.y. period of deformation ca. 8 Ma, when the Andes underwent rapid uplift and important deformation commenced in the Subandean zone.
Footnotes
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↵*rousseipgp.jussieu.fr.
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↵GSA Data Repository item 2002007, Table A— Site mean directions, is available on request from Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA, editing@geosociety.org, or at www.geosociety.org/pubs/ft2002.htm.
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- Accepted October 1, 2001.
- Received July 5, 2001.
- Revision received September 26, 2001.
- Geological Society of America
