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The origin of the rotations detected paleomagnetically in the Central Andes is controversial. Tectonic models proposed to explain it involve Late Cenozoic oroclinal bending (the Bolivian Orocline), and/or small‐block rotations driven by oblique subduction. In this paper, we report paleomagnetic data from upper Miocene ignimbrites from the Puna, in the presumed southern limb of the orocline. These rocks showed high unblocking temperature and high coercivity magnetization. The resulting pole position (latitude 85.7°S, longitude 80.5°E, A95 = 7.9°, K = 22, N = 17) indicates that the study area has not been significantly affected by vertical‐axis rotation since late Miocene onward. This implies that the whole Puna has not undergone significant regional rigid‐body rotation during the same time span. A farther analysis based on Neogene paleomagnetic data from 31 Andean localities distributed from 11°S to 31°S shows the presence of rotated and unrotated areas. Systematic counterclockwise rotations in Perü and northern Bolivia are observed, whereas clockwise rotations are present in southern Bolivia, northern Chile, and perhaps northwestern Argentina. No systematic rotations are found farther south. The overall time‐spatial distributions of these Neogene paleomagnetic data suggest that if orogenic bending occurred, it must have taken place before the middle Miocene. Thus the oroclinal hypothesis cannot explain the rotations observed in middle Miocene rocks or younger ones, which also show orocline‐like declination anomalies. We suggest that small‐block rotations driven by distributed shear may be a single process that can account for the whole rotations in the Central Andes. It is hypothesized that horizontal shear in the Andean crust could be controlled by ancient structures.

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Abstract. Paleomagnetic studies in the southern Central Andes have shown the widespread presence of clockwise vertical-axis rotations. Rock units sampled in these studies, however, are heterogeneously distributed in stratigraphic age with most palcomagnetic data from northern Chile being from Mesozoic and lower Tertiary rocks, whereas most data in the southern Altiplano, Puna, and Cordillera Oriental are from upper Tertiary rocks. In this paper we present the results of a palcomagnetic study on upper Miocene sedimentary rocks and ignimbrites from the Precordillera of northern Chile (at 22øS). These rocks are coeval with the initiation of crustal shortening in the eastern foreland fold-thnmt belt which some teetome models relate to oroclinal rotation of northern Chile. Primary magnetizations in rocks from widely distributed sites in two ignimbrites indicate that no relative rotations have occurred between sites, suggesting the study area has acted as a single coherent block with respect to vertical-axis rotational deformation. Although minor inadequate sampling of palcosecular variation can affect our data set, its time-averaged palcomagnetic direction is indistinguishable from the expected late Miocene reference direction indicating no palcomagnetically significant rotation of the study area since circa 11 Ma. This suggests that late Miocene-R•nt oroclmal rotation of the northern Chilean forearc, if present, must be either very low or nonuniform. A direct implication of this restfit is that much of the unquestionable teetome rotations detected from upper Miocene rocks in the southern Central Andes is of local origin. Available structural data permit us to relate several of these rotations with shear in dextral transfer zones in the foreland thrust belt on the east side of the Andes.

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