Abstract

One of the most conspicuous tectonic features of southern Chile is a 1000-km-long, N-S trending lineament known as the Liquiñe-Ofqui fault. Although generally regarded as a strike-slip fault, the amount and timing of strike-slip motion are unknown, and even the full extent and exact geometry of the feature remain in doubt. As part of ongoing investigations by Chilean and U.S. scientists we undertook a paleomagnetic study of Neocomian volcanosedimentary (Alto Palena Formation) and intrusive (North Patagonian batholith) rocks located just east of the main trace of the fault. All sites have normal polarity and form a common circular cluster. Indirect evidence strongly suggests extensive remagnetization of the Alto Palena rocks by intrusion of the batholith during the mid-Cretaceous long normal period. A paleomagnetic pole calculated from combined Alto Palena and North Patagonian batholith sites lies at 84.2°S, 159.9°E (α95 = 5.5°; k = 50). when compared with Cretaceous reference poles for the South American craton this suggests a small but significant amount of clockwise rotation but little or no poleward transport. These results are consistent with other paleomagnetic data for the Chilean Andes and point to widespread rotational shear associated with the Liquiñe-Ofqui fault. © 1992.