Palaeomagnetism and geochronology of Oligocene and Miocene volcanic sections from Ethiopia: geomagnetic variability in the Afro-Arabian region over the past 30 Ma

Lhuillier, Florian und Gilder, Stuart A. (2019): Palaeomagnetism and geochronology of Oligocene and Miocene volcanic sections from Ethiopia: geomagnetic variability in the Afro-Arabian region over the past 30 Ma. In: Geophysical Journal International, Bd. 216, Nr. 2: S. 1466-1481

Abstract

We report palaeomagnetic and K-Ar geochronologic results of two volcanic sequences from Ethiopia. The Belessa section, dated around 29-30 Ma and spanning approximate to 1km in thickness, is related to the Oligocene Afro-Arabian traps, whereas the approximate to 700-m-thick Debre Sina section was emplaced during the Miocene in two periods around 10-11 and 14-15 Ma. We sampled 67 flows of predominantly basaltic rocks near Belessa and 59 rhyolitic to trachybasaltic flows near Debre Sina. From a geodynamic viewpoint, the magnetostratigraphy of the Belessa sequence confirms that the Ethiopian traps were emplaced at a minimum rate of onemeter per kyr, with a possible acceleration of the volume of volcanism over time. To provide insight into the evolution of the geomagnetic field in the Afro-Arabian region over the past 30Myr, we combined our results with previous studies in the same area. Recentred directional distributions were elongated in the meridian plane, in coherence with field models for a dipole-dominated field. The dispersion S of the virtual geomagnetic poles, representative of the vigour of palaeosecular variation, was approximately 50percent higher during the 10-30 Ma interval than during the past 5Myr. As the reversal frequency f was more than two times lower during the Early Oligocene than during the Plio-Pleistocene, it appears that S and f are uncorrelated in this near-equatorial region. It remains an open question whether this apparent decoupling is ascribable to a local anomaly, is only sporadic in time, or represents a general feature of the geodynamo.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 0956-540X
• Sprache: Englisch