Paleomagnetic evidence for rapid vertical-axis rotation in the Peruvian Cordillera ca. 8 Ma

Quechua II contraction in the Ayacucho intermontane basin: Evidence for rapid and episodic Neogene deformation in the Andes of central Perú

“…The apparent rotation may therefore reflect the well-known secular variation of the earth's magnetic field that many workers have used to fingerprint regional ash-flow sheets (e.g., Grommé et al, 1972). Moreover, half of the data reported as being from the Huanta Formation were obtained from the newly recognized Huayllapata Formation (Wise, 2004), and therefore are older than previously reported in the literature cited by Rousse et al (2002). Similarly, the paleomagnetic samples from the Mayocc Member used in the interpretation by Rousse et al (2002) are younger than reported by Mégard et al (1984).…”

“…Similarly, the paleomagnetic samples from the Mayocc Member used in the interpretation by Rousse et al (2002) are younger than reported by Mégard et al (1984). Finally, the very short span of the Quechua II event precludes the interpretation by Rousse et al (2002) of counterclockwise rotation of the entire Peruvian Andes between the end of deposition of the Huanta and the deposition of Ayacucho Formations because this would require unreasonably rapid plate convergence rates and rotation of a significant portion of a continental mass.…”

“…Rousse et al (2002) used new paleomagnetic data from rocks of the Ayacucho basin to conclude that most of this rotation took place during the period of Quechua II deformation. This model should be accepted with considerable caution, in particular with the timing of rotation outside of the basin.…”

“…The data given by Rousse et al (2002) are sparse, and most of their measurements on post-rotation rocks were from the thick ash-flow unit within the Ayacucho Formation. The apparent rotation may therefore reflect the well-known secular variation of the earth's magnetic field that many workers have used to fingerprint regional ash-flow sheets (e.g., Grommé et al, 1972).…”

Undulatory Silver-Rich Polymetallic Veins of the Castrovirreyna District, Central Peru: Fault Growth and Mineralization in a Perturbed Local Stress Field

“…To evaluate the paleostress direction, it is useful to reconstruct the late Miocene counterclockwise rotation of about 15°to 20°along the Peruvian Andes to correctly orient the veins at Castrovirreyna with respect to the regional stress field (Kono et al, 1985;Macedo-Sánchez et al, 1992;Mac-Fadden et al, 1995;Rousse et al, 2002). This correction places the Castrovirreyna veins oblique to the principal compressive paleostress direction, consistent with the left-lateral shearing in the district (Fig.…”