Paleomagnetism and Tectonics of Northern Munessa, Ethiopia

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Addis Ababa Universty


The paleomagnetic investigation is carried out in the eastern part of lake langano-ziway, Main Ethiopian Rift. The aim of this paleomagnetic study is to quantify vertical axis rotation.A total of 11 paleomagnetic samples were sampled from outcrop of basalt, ignimbrites and rhyolite flows ranging in age from 2ma to 0.1ma. The paleomagnetic specimens are subjected to progressive alternating field demagnetization, thermal demagnetization and impulse magnetization. In general, the directional analysis showed either one or two components of Natural Remanent Magnetization (NRM) to characterize the wholemeasurements. The low stability components are removed by alternating fields up to 15mt or by heating up to 300oC. The high stability components are isolated above those steps and vector is directed towards origin, and it represented by Characteristic Remanent Magnetization (ChRM). The principal component analysis and site mean directions calculation yielded normal and reversed polarities. An overall mean direction calculated from individual site mean directions are Ds=354.1o, Is=8.3o, N=11, K =22, α95=10o, with an angular difference of -7.8 ± 8.24 and the negative value indicate the rotation is counter clock wise.The comparison of this result with the mean expected reference dipole geomagnetic field direction (Ds=1.9, Is=13.5, N=32, K=105.6, andα95 =2.5), from the apparent polar wander path reference curve for Africa at 1.5 ma (Besse&Courtillot 2003), found to be statistically different. This would imply that the area is at the contact of central and rift margins with small rotation. These results indicate that the late Pliocene-Pleistocene rocks of the MER in the study area show small vertical axis rotation, argue transtensional and seafloorspreading- transform kinematic models. It is therefore, suggested that large offset faults, produce the right stepping, en echelon magmatic segments of the MER, which is at the transition from continental to oceanic extensionrather thanmagma intrusion.



Paleomagnetism and Tectonics