Sonia Rousse, Stuart Gilder, Daniel Farber, Brendan McNulty, Victor R. Torres; Paleomagnetic evidence for rapid vertical-axis rotation in the Peruvian Cordillera ca. 8 Ma. Geology ; 30 (1): 75–78. doi: https://doi.org/10.1130/0091-7613(2002)030<0075:PEFRVA>2.0.CO;2
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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.