Paleomagnetic and paleosecular variation study of the Mt. Cameroon volcanics (0.0–0.25 Ma), Cameroon, West Africa

Abstract

Mt. Cameroon (4075 m) is a large volcanic horst and is presently the only active volcano on the Cameroon Volcanic Line (eight eruptions during the last century). This location belongs to the famous Bangui magnetic anomaly and is thus of particular interest for the investigation of the persistence and the evolution of the anomaly with time. We have conducted a paleomagnetic study of 94 samples drilled from 13 lavas flow on Mount Cameroon (0.0–0.25 Ma). Low-field susceptibility versus temperature ( k– T) and SIRM experiments indicated that magnetite (575 °C) was the dominant magnetic carrier and that several sites were characterized by low-temperature mineral phases (e.g. 100–200 °C and 300–400 °C), reflecting the presence of titanomagnetite with low Titanium content. At least eight samples from each site were demagnetized using both thermal treatment and alternating fields (a.f.). One contemporaneous site provided inconsistent and scattered directions and was rejected. Successful mean paleomagnetic directions were obtained for 12 sites but two sites exhibited inclinations which were significantly away from the inclination of the geocentric axial dipole (GAD) and VGP latitudes lower than 60°. Their age indicates that they were likely recorded during a period of reduced dipole intensity and they were thus discarded. The time-averaged direction derived from this final selection has a mean declination of 354.2° and a mean inclination of 5.1°, which is 3° lower than the GAD inclination. The corresponding VGP position is slightly far sided but contains the north geographic pole. The angular standard deviation (13.7°) of the VGPs is also not significantly different from the predictions of model G at this latitude. Thus we found no evidence for a long-term anomaly in this area but additional sites are needed to provide more conclusive indications.