Tertiary remagnetization of Paleozoic rocks from the Eastern Cordillera and sub‐Andean Belt of Bolivia

Abstract

Paleomagnetic samples were collected from 98 sedimentary horizons in eight different Devonian to Permian sedimentary units at eight localities in the Eastern Cordillera and the sub‐Andean Belt of Bolivia. For 77 sites, thermal demagnetization allowed determination of a characteristic magnetization (ChRM) with site‐mean 95% confidence limit, α95, ≤15°. The ChRM is carried predominantly or entirely by hematite. Fold and reversal tests from two of the sampled localities indicate that the characteristic magnetization is synfolding, likely acquired during the earliest stages of deformation. Additionally, a modified conglomerate test at one locality and the nearly uniform direction of ChRM across the Devonian to Permian age units clearly reveals the secondary nature of the characteristic magnetization. Finally, the ChRM directions are discordant from any expected Paleozoic directions. Paleomagnetic poles calculated from the ChRM directions fall near the Cenozoic portion of the apparent polar wander path for South America. We interpret these observations to indicate widespread chemical remagnetization of these Paleozoic strata during, but prior to completion of, Cenozoic Andean folding.