Testing Tectonic Rotations in the Southern Central Andes

MILANESE, FLORENCIA NIDIA

Seminario; Lectures of the China University of Geosciences, Beijing; 2022

A paleomagnetic study performed in Plio-Pleistocene volcanic rocks of two localities inthe Southern Central Andes is presented. The region corresponds to the transitionzone between the Central and the Patagonian Andes. In the latter, deformation isalmost exclusively controlled by the dextral-strike slip Liquiñe-Ofqui Fault Zone, thatextends from ~ 47 °S to ~ 38 °S and accommodates the deformation generated by theoblique subduction of the Nazca Plate below South America. To the north of ~ 36 °S,deformation is mainly contractional. Our study was carried out in the transition zonebetween both tectonic regimes. Sampling consisted of 31 paleomagnetic sitesdistributed in two localities: the Loncopué (~ 38.0 °S, 70.7 °W) and Andacollo (~ 37.2°S, 70.8 °W) areas. We sampled Pliocene and Pleistocene volcanic rocks with agesyounger than 5 Ma. After stepwise demagnetization and principal component analysis,site mean remanence directions were computed. Both localities show non-significantclockwise rotations of 1.7° ± 14.4° (Loncopué) and 8.1° ± 8.4° (Andacollo). Althoughthe presently available database does not support significant tectonic rotation of theAndacollo lavas, preliminary results obtained from upper Miocene volcanics in anearby area indicating ~ 20° of clockwise rotation, encourage further studies toimprove the resolution of the paleomagnetic data to determine if crustal block rotationshave been, or still are, part of the Andean deformational processes.