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

Vertical‐axis rotations determined from paleomagnetism of Mesozoic and Cenozoic strata of the Bolivian Andes

“… Roperch et al [2000] then used these directions to determine Tertiary vertical‐axis rotations of the Subandean zone. Following exclusion of results from one locality of Libarkin et al [1998], Roperch et al [2000] and Gilder et al [2003] correctly observed that maximum clustering of paleomagnetic directions from Paleozoic rocks in the southern Subandean zone occurs at 100% unfolding. This indicates that the Paleozoic strata acquired the characteristic magnetization prior to folding.…”

“…Ages of the sampled formations are Mississippian and Late Permian, preceding and following the Permo‐Carboniferous Reversed‐Polarity Superchron. Indeed Libarkin et al [1998] observed normal‐polarity magnetization in the Mississippian Tupambi and Taiguati formations. Thus assigning the age of (re)magnetization to the reversed‐polarity superchron is at best highly speculative.…”

“… Libarkin et al [1998] argued that paleomagnetic data from Devonian through Late Permian strata of the Eastern Cordillera and Subandean zone were best grouped at 80% unfolding indicating remagnetization during Tertiary folding. While accepting a Tertiary origin for magnetization of the Devonian Vila Vila Formation at Pongo, Roperch et al [2000] reinterpreted the paleomagnetic directions of Libarkin et al [1998] as acquired during the Permo‐Carboniferous Reversed‐Polarity Superchron. Roperch et al [2000] then used these directions to determine Tertiary vertical‐axis rotations of the Subandean zone.…”

“…The discordant inclination from the Ravelo Formation could also indicate an age of magnetization much younger than the Jurassic age of the sampled rocks (Figure 5c). As demonstrated by paleomagnetic results from red sedimentary strata of the Devonian Vila Vila Formation at Pongo in the Eastern Cordillera, Tertiary remagnetization of older strata has occurred during Andean deformation at some locations [ Libarkin et al , 1998]. Taken together with results from the inclination‐only fold test, these problems indicate that the primary origin of magnetization for Mesozoic strata at a number of locations is in doubt.…”

Tectonic rotations within the Bolivian Altiplano: Implications for the geodynamic evolution of the central Andes during the late Tertiary

“…In contrast, data from five sub-Andean localities are better clustered after full bedding correction (k=-72) than with 80% unfolding (k=-25) (Figure 15). We did not use results from the Abra Tapecua and Saimapata east localities because of inconsistensies in the published data [Libarkin et al, 1998, 13c and 13d). There is also a lack of geological evidence for a bending of the forearc by an amount equivalent to the relative rotations recorded east of the Western Cordillera.…”