Abstract

RODRIGUEZ-CHAVAIRO, Santiago; JIMENEZ, Giovanny  and  GOYES-PENAFIEL, Paul. Flattening factor estimation of the magnetic inclination and its implications in the Jurassic tectonic models in the NW margin of South America. Bol. geol. [online]. 2024, vol.46, n.2, pp.13-30.  Epub June 14, 2024. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v46n2-2024001.

Paleogeographic reconstructions and tectonic models are complemented by paleomagnetism, since vertical axis rotations are calculated using magnetic declination, and paleolatitudes are derived from magnetic inclination. In siliciclastic rocks, the flattening process may cause inclination shallowing and, therefore, an underestimation of paleolatitudes. Different techniques have been proposed to calculate the flattening factor, however, some require massive databases and demanding or specialized laboratory processes. A less-used method that combines the Anisotropy of Magnetic Susceptibility and Paleomagnetism allows us to calculate the flattening factor. Results of Anisotropy of Magnetic Susceptibility in samples of the Girón Group and the results of inclination shallowing are reported for a total of 103 sites in rocks from the Triassic to the Cenozoic distributed in the Eastern Cordillera, Santander Massif and Catatumbo. Four filters were applied to the data set and four curve fit models were run, the mean flattening value calculated is 1.04 ± 0.6, suggesting that the magnetic inclination has not been affected by inclination shallowing, therefore, the paleolatitude values do not vary significantly. However, such a high error is due to a mixture of two groups of data, one with shallow inclinations and latitudes close to its current position and another group with greater inclinations and latitudes in the southern hemisphere. Based on this premise, we applied a new filter of very high and shallow inclinations, leaving the intermediate ones, to obtain a flattening factor of 0.93 ± 0.22. The correction method using the new filter in the Eastern Cordillera data set is effective in correcting medium to high inclinations in Lower Jurassic rocks.

Keywords : Eastern Cordillera; Magnetic susceptibility; Correction; Curve fit; Paleolatitude.

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