Uniform TitlePetrochemistry and geochronology of Ngorongoro Volcanic Highland Complex (NVHC) and its relationship to Laetoli and Olduvai Gorge, Tanzania
NameMollel, Godwin F. (author), Swisher III, Carl (chair), Carr, Michael (internal member), Feigenson, Mark (internal member), Furman, Tanya (outside member), Rutgers University, Graduate School - New Brunswick,
Laetoli Site (Tanzania),
Olduvai Gorge (Tanzania),
Great Rift Valley
DescriptionThe Ngorongoro Volcanic Highland Complex (NVHC) of northern Tanzania is situated at the southern divergence of the Gregory Rift, part of the East African Rift System. The NVHC consists of at least nine major volcanic centers that erupted lavas, ash flows, and other pyroclastic materials from Pliocene to Present. These volcanoes are considered the source of lavas and other volcaniclastic material found interbedded in the adjacent anthropological sites of Olduvai Gorge and Laetoli.
This dissertation focuses on the petrochemistry and geochronology of six major NVHC centers: Satiman, Lemagurut, Oldeani, Ngorongoro caldera, Olmoti, and Embagai, as well as Laetoli Ogol lava flows, Olduvai Gorge Bed I lava and the isolated cone of Engelosin. The overall intent is to provide a geochemical and geochronological framework for the NVHC and refine correlations of the NVHC volcanoes with Olduvai and Laetoli.
Interpretation of petrographic and x-ray fluorescence data (major element) indicate that the studied volcanoes produced magmas that vary in composition from foidite to phonolite and basalt to rhyolite. Laser ablation data (trace element) from all lavas support an origination from a K-rich peridotite. The Sr-Nd-Pb isotopes (TIMs data) show wide variation in all centers that is considered to indicate crust-magma interaction, an interpretation supported by Ce/Pb ratios ([less than] 25 [plus/minus] 5) lower than expected for mantle derived melts. Lava samples with mantle values (Ce/Pb) have Sr-Nd-Pb isotope ratios that can be explained by mixing between high-µ and enriched mantle reservoirs.
40Ar/39Ar dating of matrix and anorthoclase from the sampled NVHC volcanoes indicates a range in activity from 4.65 Ma to ~ 0.60 Ma. Satiman is the oldest, followed by Engelosin 2.97 Ma, Lemagurut 2.40 Ma, Ngorongoro 2.28 Ma, Olmoti 2.01 Ma, Oldeani 1.61 Ma and Embagai ~1.20 Ma. Overlapping activity is recorded between Lemagurut, Ogol and Ngorongoro as well as between Ngorongoro and Olmoti. Correlation of ages and mineral assemblages from these volcanoes and that of the tephra from Olduvai and Laetoli, confirm a Satiman and Ngorongoro source for the Laetolil and Naibadad Beds in the Laetoli area respectively, whereas, that of Olmoti upper section correlates with Olduvai Bed I lava, confirming an Olmoti source.
NoteIncludes bibliographical references (p. 219-232).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.