Paleosecular variation record from Pleistocene-Holocene lava flows in southern Colombia.

Improvements in the spatial and temporal coverage of paleomagnetic data are essential to better evaluate paleofield behaviour over the past 10 Myr, especially due to data scarcity at low latitudes in the South American region. Here, we provide new Pleistocene-Holocene (0–2 Ma age interval) paleodirectional data from three volcanic systems (Doña Juana Volcanic Complex, Galeras Volcanic Complex and Morasurco Volcano) in southwestern Colombia between latitudes 1.2 and 1.4°N. A total of 38 paleodirectional sites were studied using progressive alternating field and thermal demagnetization treatments. After excluding transitional data, we obtain thirty site-mean directions for analysis of paleosecular variation (PSV) and the time-averaged field (TAF) in the study area. The mean direction (Dec = 351.2°, Inc = −3.4°, α₉₅ = 6.2°, k = 20.0) and the paleomagnetic pole (Plat = 80.7°N, Plon = 173.1°E, A₉₅ = 5.2°, K = 29.1) of these sites are not statistically compatible with the expected geocentric axial dipole (GAD) field direction and geographic north pole, respectively. Virtual geomagnetic pole dispersion (S_B) for our filtered dataset (S_B(2Ma) = 15.2_12.0^17.6°) and the Brunhes chron (S_B(Bru) = 16.0_11.6^19.1°) are consistent at the 95% confidence level with South American studies at equatorial latitudes and recent PSV models for the 0–10 Ma and Brunhes intervals. Likewise, the corresponding inclination anomaly (ΔI) for two age groups ΔI_2Ma =  − 5.9_−12.1^0.3° and ΔI_Bru =  − 5.3_−13.7^3.1° suggests large deviations relative to the GAD model, in accordance with predictions from zonal TAF models. The high VGP dispersion could be linked to strong longitudinal variability of the magnetic equator position over South America. This feature reflects the presence of significant non-dipole field components in this region that have been detected in geomagnetic field models for the most recent centuries and millennia, probably associated with the presence of the South Atlantic Magnetic Anomaly in the South American region.