HR: 15:15h
AN: GP23A-06 INVITED     [Abstracts]
TI: Contributions and Lessons of Paleomagnetic Studies in the Northern (tropical) Andes: Examples from Mesozoic and Cenozoic rocks in Colombia, South America
AU: * Bayona, G
EM: gbayona@cgares.org
AF: Corporacion Geologica ARES, Calle 57 N. 23-09 Of. 202, Bogota, Colombia
AU: * Bayona, G
EM: gbayona@cgares.org
AF: Smithsonian Tropical Research Institute, Balboa, Ancon, Panama
AB: In the last 50 years few paleomagnetic studies have been carried out in the Colombian Andes. The first attempts were in Triassic and Jurassic igneous rocks and red beds (1960-1980), which results yielded: (1) an idea of complex vertical-axis rotations in blocks near to strike-slip faults, and (2) the difficulty of identifying Jurassic and younger magnetization components due to the same paleolatitudinal position of the South America plate since Jurassic. Paleomagnetism in Cretaceous volcanic and volcaniclastic rocks and Cenozoic intrusives to the west of the Romeral paleosuture have allowed to constrain paleolatitudinal translations of oceanic terranes and rotations associated to the complex array of strike-slip faults in the Romeral fault system. These works have been carried out by William MacDonald and co-workers in Colombia. In the last decade, paleomagnetic studies moved eastward of the Romeral paleosuture. The integration of paleomagnetic, magmatic, and stratigraphic constrains data have allowed (1) the proposition of along-margin northward translations of continental-affinity terranes along the northern margin of the South America plate during the Jurassic and (2) constrain rotation of fault-bounded blocks related to syn-extensional tectonism. These interpretations are supported by components of magnetization uncovered in Jurassic and Cretaceous rocks that passes several field tests to verify the near post-depositional age of magnetization. These rocks should be used for further paleomagnetic analyses. Magnetostratigraphy studies of sedimentary Paleogene rocks have been more challenging than in older rocks. Even though several of the sites collected have red beds or Fe-rich nodules and cementation, magnetization intensity is very low, the direction of uncovered component is parallel to the present magnetic field (with negative field tests), or new mineralization occur during heating of the sample. However, other demagnetizations techniques and rock magnetic studies should be applied in these rocks. Magnetostratigraphic studies need to be carried out in basins with volcaniclastic strata of Miocene or younger age to better constrain the uplift the Andes.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1520 Magnetostratigraphy
DE: 1522 Paleomagnetic secular variation
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly