| Sumario: | Preliminary paleomagnetic data for rocks from the Choiyoi Formation, exposed at the Cerro Chachil and Sierra de Catan-Lil (39.1°S, 70.5°W, Cordillera Principal, Argentina), assigned sensu lato to the Permo-Triassic, are discussed. The directions of the stable remanent magnetization (SRM) for these rocks have been submitted to the fold test. This analysis indicates that most of the Choiyoi Formation rocks are carriers of a prefolding SRM. The mean prefolding SRM for samples of normal and reversed polarity (within 40° of the mean; 277°, +54°, A95 = 8°, N = 21, K = 15.2, R = 19.683) yields a mean pole at 18°S, 126°W, 95 = 10°. The paleomagnetic data indicate two preliminary interpretations. One interpretation suggests that the sampling site rotated 90° clockwise around a vertical axis since Permian times. The other interpretation suggests that the sampling site integrates the allochthonous microplate suggested by Vilas and Valencio (1982) and Valencio and Vilas (1985). This microplate was situated in the Pacific at tropical latitudes in the late Paleozoic. © 1988.
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