New Paleomagnetic data from the Northern Argentine Puna: Central Andes Rotation Pattern Reanalysed

PREZZI, CLAUDIA BEATRIZ; ALONSO, RICARDO

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Año: 2002 vol. 107 p. 1 - 18

0148-0227

Along the central Andes a pattern of vertical axis rotations (CARP) has been paleomagnetically identified. These rotations, which are counterclockwise north of Arica and clockwise to the south, have been detected in Mesozoic and Cenozoic rocks cropping out in the Andean forearc and the Altiplano-Puna. Different models have been proposed to explain the geodynamic evolution of the central Andes, but the origin of these rotations remains controversial. Such models involve oroclinal bending and/or local block rotations. This lack of agreement is partly due to the scarce paleomagnetic database, particularly for the Argentine Puna.Here we report new paleomagnetic data obtained in the northern Argentine Puna from 57 sites drilled from Miocene volcaniclastic rocks and 12 sites from the Cretaceous-Eocene Salta Group.It was determined that (1) the Morro Blanco area did not undergo significant vertical axis rotation since at least the middle Miocene; (2) the Loma Blanca mine area underwent a clockwise vertical axis rotation of 10 later than the late Miocene; and (3) the Coranzulı´ area underwent a clockwise vertical axis rotation of 40 later than the Cretaceous-Eocene. The central Andes database was analyzed, and some features of the CARP were determined. These features were explained considering ‘‘domino’’-style models for the forearc and a local block rotation model in response to penetrative shear for the Altiplano-Puna. Penetrative shear would occur along a high electrical conductivity zone. However, the possibility of the existence of an oroclinal bending of