Skip to Content


No results


No results


No results

Search Results


No results
Search events using: keywords, sponsors, locations or event type
When / Where

Presented By: Earth and Environmental Sciences

Smith Lecture - Dr. Tesfaye Kidane, Wayne State University

Geomagnetic Significance of the Paleomagnetic analysis on the Plio-Pleistocene Volcanic Rocks, Afar Depression, Ethiopia

Northwest-southeast orieted prominent faults in the Afar depression expose thick sequences of ~2Myr old trap-like basalt known as Stratoid. Over the years, sixty two successive lava flows; thirty-three from Gamarri, and twenty-nine from Dobi cliffs respectively were sampled for paleomagnetism. The study at Gamarri revealed reverse-normal-reverse (R-N-R) polarity intervals with anomalous directions at the base. Paleointensity experiments showed two successive periods of low field intensity (<15μT lowest part of the section and ~20μT from upper flows with full normal polarity direction) separated by a brief period of field recovery. Original unspiked K/Ar age experiments made at five levels had given a mean age of 2.07±0.05 Ma for the entire section, while a follow-up 40Ar/39Ar experiments gave ages ranging from 2.118±0.057 to 2.063±0.044 Ma for the normal polarity interval while an older age 2.34±0.092Ma for the bottom. Along the Dobi cliff, ~50 Km NE of Gamarri, only second volcanic record to compare with, showed R-N-R-N polarity sequences from bottom to top with a striking similar anomalous direction at the base. K/Ar age determination of the normal polarity interval showed a mean age of 2.18±0.06 Ma for the top normal interval and attempts of K/Ar at the base was not successful. A “W” shaped paleointensity variations with unique extreme low mean value of 6.4μT and 3.6μT at the onset and end of the lower normal polarity interval was detected. 40Ar/39Ar experiments along a third section in Norhern Dobi (Iso-Dedai) gave a N-R sequence with a paleointensity mean values of 6.83±0.04μT,and 40Ar/39Ar experiments on the sequence gave a mean 40Ar/39Ar age of 2.15±0.031Ma. The radio-isotopis ages in the three localities indicate the normal polarities identified have statistically different ages, a result not supported by field geology and paleomagnetism. Hence the normal polarity identified at the three sections could be correlated with the Reunion event(s) using the available Geomagnetic Polarity Time Sclae (GPTS). This notion is supported by the independent magnetostratigraphic study at Omo Valley (southwest Ethiopia), where the well-dated Shungura Formations, revealed the two Reunion events.

Explore Similar Events

  •  Loading Similar Events...

Back to Main Content