Clockwise Rotation of the Gedemsa Magmatic Segment during the Early Pleistocene, Main Ethiopian Rift, Ethiopia

The Main Ethiopian Rift (MER) is characterized by left-lateral transtension due to an oblique divergence between Somalia and Nubia plates. The present study area, Gedemsa Magmatic Segment, is located where several segments (Yerrer Tullu Wellel Volcano-tectonic Lineament, central and northern MER) interact. We conduct a detailed paleomagnetic survey in order to fully understand the kinematics of the segment. We collect a total of one-hundred-seventy oriented paleomagnetic core samples from 23 sites were collected from the Nazareth Group (1.7-1.9 Ma) and the Wonji group (≤0.3 Ma) rock units. Combined thermal (Th) and Alternating Field (AF) demagnetization revealed two components of Natural Remanent Magnetizations (NRM): a low stability component, which is removed by AF of 20-30mT or heating up to 200oC and a second and high stability component isolated above these steps is directed toward the origin and considered as Characteristic Remanent Magnetization (ChRM). All the studied specimens show normal geomagnetic polarity. The overall mean direction for the Wonji group is Decs=0.60, Incs=5.10 (α95 =6.50, K =35.8, N=14) while for the Nazareth group is Decs=18.90, Incs=13.40 (α95=10.30, K=35.6, N=7). Comparing the mean directions with respective reference geomagnetic dipole fields indicates a 170±3.40 clockwise rotation for the Nazreth group units. On the contrary, the Wonji group units show no statistically significant vertical axis rotation. Our results indicate that deformation due to the opening of DebreZeit-Butajira (DzB) and Yerer - Tullu Wellel Volcano-tectonic Lineament (YTVL) segments affected the deformation of the Gedemsa magmatic segment. This shows oblique rifting kinematics are more complex than previously known and it calls for a detailed paleomagnetic studies all along the strike of the MER.