Petrology, geochemistry and age of satiman, lemagurut and oldeani: Sources of the volcanic deposits of the laetoli area

Godwin F. Mollel, Carl C. Swisher, Mark D. Feigenson, Michael J. Carr

Research output: Chapter in Book/Report/Conference proceedingChapter

33 Scopus citations


We report on the petrochemistry and geochronology of lavas from Satiman, Lemagurut and Oldeani volcanoes, as well as from isolated Ogol flows. Comparisons of their age and mineral compositions are made with those of the Laetolil Beds to confirm the sources for these latter volcaniclastic deposits. A comparison with other volcanic centers in the region and an attempt to constrain the depth at which melting occurs is also made. Lava compositions vary between centers, with Satiman composed of foidite and phonolite. Lemagurut ranges from basalt through benmorite, whereas Oldeani is basalt and trachyandesite, and Ogol is basaltic. The Sr-Nd isotopes of these lavas are characterized by relative unradiogenic Nd (143Nd/144Nd =0.512056 – 0.512610), but with radiogenic Sr (87Sr/86Sr = 0.70371 – 0.70609), suggesting a source explained by mixing between high-μ and enriched mantle reservoirs. These isotope ratios, together with trace elements patterns and ratios (e.g., Tb/Yb), indicate melting in the lithospheric mantle consistent with other studies in the region. 40Ar/39Ar dating indicates an age range for Satiman of 4.63 ± 0.05 to 4.02 ± 0.02 Ma, Lemagurut and Ogol from 2.40 ± 0.01 to 2.22 ± 0.10 Ma and Oldeani from 1.61 ± 0.01 to 1.52 ± 0.02 Ma. The age of Satiman and its silica undersaturated composition make it the likely source of the > 4.3 – 3.5 Ma Laetolil Beds. The age and composition of Naibadad Beds that overlie the Laetoli Beds are consistent with the composition and revised ages of 2.28 ± 0.02 – 2.04 ± 0.01 Ma for Ngorongoro. The Olpiro Beds, which are fine-grained and of phonolitic composition, may correlate best with the more distal Olmoti Crater.

Original languageEnglish (US)
Title of host publicationVertebrate Paleobiology and Paleoanthropology
Number of pages21
StatePublished - 2011

Publication series

NameVertebrate Paleobiology and Paleoanthropology
ISSN (Print)1877-9077

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Palaeontology


  • Ar/Ar dating
  • Geochemistry
  • Ogol
  • Petrology
  • Tanzania


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