BH250-184
Title
Subject
Description
Minor Mineral: chlorite
Olduvai Gorge (Tanzania) lies within the East African Rift System, a tectonically active zone characterized by widespread volcanic activity. The volcanic rocks in this area range from basaltic to more evolved intermediate to alkaline compositions, including trachytes and phonolites associated with late-stage rift volcanism.
The mineralogy of BH250-184 is dominated by alkali feldspar (sanidine or orthoclase), nepheline, and sodic pyroxene. The texture is typically aphanitic to porphyritic, with feldspar phenocrysts set in a fine-grained groundmass, displaying a trachytic texture.
The chemistry of BH250-184 includes (see the table):
Moderate to high SiO₂ content (~60–65 wt%)
High alkali content (Na₂O + K₂O typically 7–9 wt%)
Low to moderate MgO and FeO
Enrichment in incompatible elements such as Rb, Ba, and Sr
These characteristics are typical of potassic to ultrapotassic compositions commonly found in rift-related alkaline magmatism.
Olduvai Gorge, located in northern Tanzania within the East African Rift Valley, is one of the most important paleoanthropological sites globally and is often called the "Cradle of Mankind." Fossil deposits here span from about 2 million to 15,000 years ago, covering crucial periods of human evolution. Key early hominid fossils discovered at Olduvai include Homo habilis, considered one of the first members of the genus Homo and associated with early tool use; Paranthropus boisei, a robust australopithecine species adapted to heavy chewing with strong jaws and large teeth; and Homo erectus, linked to more advanced tools and possibly the early use of fire. The site is also famous for the Oldowan tool industry—some of the earliest known stone tools dating back around 2.6 million years—which includes simple flakes and choppers that reflect early technological innovation. Additionally, volcanic ash layers (tuffs) found at Olduvai provide precise dating of fossils, while sediment records preserve evidence of ancient landscapes, climates, and fauna, offering valuable insight into the environments inhabited by early hominids.
Coverage
Nearby Geographic Feature: Olduvai Gorge
GPS Coordinates: 2°59'31.72"S, 35°21'7.81"E