Pliocene–Pleistocene Paleomagnetic Secular Variation and Time‐Averaged Field From the Northern Volcanic Zone of the Andes, Colombia

• Published in: Earth and space science (Hoboken, N.J.) N.J.), 2024-06, Vol.11 (6), p.n/a
• Main Authors: Sánchez‐Duque, A., Mejia, V., Torres, M. P., Pinilla, A.
• Format: Article
• Language: English
• Subjects: andes; Data analysis; Lava; lava flows; Paleomagnetism; paleosecular variation; Pleistocene; Pliocene; rhyolitic ignimbrites; south Atlantic anomaly; time averaged field; Volcanoes
• ISSN: 2333-5084; 2333-5084
• DOI: 10.1029/2023EA003251

Paleomagnetic results obtained from 38 Pliocene—Pleistocene volcanic flows from the Knot of the Pastos and surroundings of Puracé volcano and Popayán (southwestern Colombia) are presented. Using stringent quality criteria and excluding sites that classify as representatives of transitional states of Earth's field, a selected group of 27 sites (16 with normal polarity and 11 with reversed polarity) was obtained with a mean direction (Dec = 357.8°, Inc = 6.4°, α95 = 7.5° and κ = 15) that coincides with the geocentric axial dipole field (GAD: Dec = 0o, Inc = 3.2o) and, unlike similar studies at similar latitudes, does not coincide with the GAD plus a 5% axial quadrupolar component (Dec = 0°, Inc = −1.08°). However, when serial correlation (SC) among several sites with high inclination anomalies is taken into consideration, the mean direction of two resulting groups of sites shows greater consistency with a field that includes a quadrupolar component. It is interpreted that the sites treated for SC record states of the field similar to today's field in the area of study, which is being affected by the South Atlantic Anomaly. Plain Language Summary The only way to study Earth's magnetic field in the geologic past from experimental data is by studying the magnetization of rocks that record Earth's field in a way comparable to the way compasses point close to the geographic north. Earth's magnetic field changes are significant in relatively short time‐scales like years or centuries. In this study the paleomagnetic directions recorded in volcanic products from extinct volcanoes of the Colombian Andes were obtained. Most of the volcanic flows record paleomagnetic directions consistent with the ones obtained from previous studies, which in general differ from the present magnetic directions in the area by being less inclined downwards. However, some of the volcanic flows did record paleomagnetic directions that are similar to the present magnetic directions in the area, which have been linked to an ample low magnetic intensity area in the Atlantic Ocean called the South Atlantic Anomaly. So, as it has been pointed out in other studies, it is possible that this anomaly has acted recurrently during the geologic past. Key Points The mean paleomagnetic direction among the selected sites from Colombia shows consistency with a geocentric axial dipole (GAD) field Consistency with a GAD field with a 5% quadrupolar component is obtained when serial correlation is applied Ser