Background

2004 ◽  
Author(s):  
William H. Kimbel ◽  
Yoel Rak ◽  
Donald C. Johanson ◽  
Ralph L. Holloway ◽  
Michael S. Yuan
Keyword(s):  
Fossil Record ◽  
Eastern Africa ◽  
Northern Ethiopia ◽  
East African ◽  
Afar Depression ◽  
The North ◽  
Time Period ◽  
African Rift ◽  
The One ◽  
Fossil Hominin

Australopithecus afarensis is a fossil hominin species known from at least four East African Rift Valley sites ranging from northern Ethiopia in the north to northern Tanzania in the south and bridging the time period between approximately 3.6 and 3.0 million years ago (Ma). First identified in the late 1970s as the bipedal but craniodentally apelike rootstock from which later Australopithecus and Homo evolved (Johanson et al., 1978; Johanson and White, 1979), A. afarensis constituted the first substantial record of unequivocal human ancestors older than 3.0 million years (Myr). An array of more recently made discoveries have placed A. afarensis in a pivotal position in early hominin phylogeny, bracketed in time between, on the one hand, two temporally successive species, A. anamensis and Ardipithecus ramidus, that jointly extend the hominin record back to 4.4 Ma (M. Leakey et al., 1995, 1998; White et al., 1994, 1995), and, on the other hand, the earliest strong (stratigraphic) evidence for hominin lineage diversification, with the first known records of A. africanus (ca. 2.7 Ma) in southern Africa, and of A. aethiopicus (ca. 2.7 Ma) and A. garhi (2.5 Ma) in eastern Africa (Walker et al., 1986; Asfaw et al., 1999).2 The task of sorting out the relationships among all of these species hinges on the interpretation of A. afarensis itself, from its alpha taxonomy and phylogenetic role to its pattern of evolution over time. A prerequisite to achieving this goal is a more complete knowledge of the A. afarensis fossil record, narrowing gaps in our knowledge of anatomy and variation, as well as of distributions in space and time. On sample size alone, A. afarensis is the best-known hominin species in the eastern African fossil record. The vast majority of fossils in the A. afarensis hypodigm, some 360 specimens, or approximately 90% of the total, have been recovered at the Hadar site, from the 200+ meter sequence of silts, sands, and clays that comprise the Hadar Formation, which is exposed along the drainages of the Awash River in the Afar Depression of northern Ethiopia (Johanson et al., 1982a; Kimbel et al., 1994).

scholarly journals Tectono-magmatic evolution of the younger Gardar southern rift, South Greenland

2013 ◽  
Vol 29 ◽  
pp. 1-24 ◽  
Author(s):  
Brian G.J. Upton
Keyword(s):  
Mafic Magma ◽  
Dyke Swarm ◽  
Small Scale ◽  
Alkaline Magmatism ◽  
East African ◽  
The North ◽  
Intrusive Rocks ◽  
Alkali Granites ◽  
African Rift ◽  
Very High

The 1300–1140 Ma Gardar period in South Greenland involved continental rifting, sedimentation and alkaline magmatism. The latest magmatism was located along two parallel rift zones, Isortoq–Nunarsuit in the north and the Tuttutooq–Ilimmaasaq–Narsarsuaq zone in the south addressed here. The intrusive rocks crystallised at a depth of troctolitic gabbros. These relatively reduced magmas evolved through marked iron enrichment to alkaline salic differentiates. In the Older giant dyke complex, undersaturated augite syenites grade into sodalite foyaite. The larger, c . 1163 Ma Younger giant dyke complex (YGDC) mainly consists of structureless troctolite with localised developments of layered cumulates. A layered pluton (Klokken) is considered to be coeval and presumably comagmatic with the YGDC. At the unconformity between the Ketilidian basement and Gardar rift deposits, the YGDC expanded into a gabbroic lopolith. Its magma may represent a sample from a great, underplated mafic magma reservoir, parental to all the salic alkaline rocks in the southern rift. The bulk of these are silica undersaturated; oversaturated differentiates are probably products of combined fractional crystallisation and crustal assimilation. A major dyke swarm 1–15 km broad was intruded during declining crustal extension, with decreasing dyke widths and increasing differentiation over time. Intersection of the dyke swarm and E–W-trending sinistral faults controlled the emplacement of at least three central complexes (Narssaq, South Qôroq and early Igdlerfigssalik). Three post-extensional complexes (Tugtutôq, Ilímaussaq and late Igdlerfigssalik) along the former rift mark the end of magmatism at c . 1140 Ma. The latter two complexes have oblate plans reflecting ductile, fault-related strain. The Tugtutôq complex comprises quartz syenites and alkali granites. The Ilímaussaq complex mainly consists of nepheline syenite crystallised from highly reduced, Fe-rich phonolitic peralkaline (agpaitic) magma, and resulted in rocks with very high incompatible element concentrations. Abundant anorthositic xenoliths in the mafic and intermediate intrusions point to a large anorthosite protolith at depth which is considered of critical importance in the petrogenesis of the salic rocks. Small intrusions of aillikite and carbonatite may represent remobilised mantle metasomites. The petrological similarity between Older and Younger Gardar suites implies strong lithospheric control of their petrogenesis. The parental magmas are inferred to have been derived from restitic Ketilidian lithospheric mantle, metasomatised by melts from subducting Ketilidian oceanic crust and by small-scale melt fractions associated with Gardar rifting. There are numerous analogies between the southern Gardar rift and the Palaeogene East African rift.

Legacies of Slavery in North-West Uganda: The Story of the ‘one-Elevens’

Africa ◽  
2006 ◽  
Vol 76 (2) ◽  
pp. 180-199 ◽  
Author(s):  
Mark Leopold
Keyword(s):  
Northern Uganda ◽  
East African ◽  
Southern Sudan ◽  
North West ◽  
The Core ◽  
The North ◽  
Rebel Groups ◽  
The Face ◽  
History Of ◽  
The One

AbstractThis article outlines the history of a people known as ‘Nubi’ or ‘Nubians’, northern Ugandan Muslims who were closely associated with Idi Amin's rule, and a group to which he himself belonged. They were supposed to be the descendants of former slave soldiers from southern Sudan, who in the late 1880s at the time of the Mahdi's Islamic uprising came into what is now Uganda under the command of a German officer named Emin Pasha. In reality, the identity became an elective one, open to Muslim males from the northern Uganda/southern Sudan borderlands, as well as descendants of the original soldiers. These soldiers, taken on by Frederick Lugard of the Imperial British East Africa Company, formed the core of the forces used to carve out much of Britain's East African Empire. From the days of Emin Pasha to those of Idi Amin, some Nubi men were identified by a marking of three vertical lines on the face – the ‘One-Elevens’. Although since Amin's overthrow many Muslims from the north of the country prefer to identify themselves as members of local Ugandan ethnic groups rather than as ‘Nubis’, aspects of Nubi identity live on among Ugandan rebel groups, as well as in cyberspace.

Geochemical and petrophysical characterization of mantle metasomatism beneath the North Tanzanian Divergence, East African rift.

2021 ◽  
Author(s):  
Adeline Clutier ◽  
Fleurice Parat ◽  
Michel Gregoire ◽  
Benoit Gibert ◽  
Stéphanie Gautier ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Lithospheric Mantle ◽  
East African Rift ◽  
Mantle Xenoliths ◽  
P Wave ◽  
S Wave ◽  
East African ◽  
The North ◽  
Alkaline Magmas ◽  
African Rift

<p>The North Tanzanian Divergence (NTD) is the prolongation of the eastern branch of the East African Rift and is a place of intense volcanism. Numerous volcanoes erupted deep subalkaline to highly alkaline magmas, including the particular active natrocarbonatite Oldoinyo Lengai. On the North-South axis (Natron to Manyara basins), three highly alkaline volcanoes, Pello Hills, Lashaine and Labait, erupted melilite magmas that originated from low degree of partial melting of asthenospheric mantle (depth > 120 km). The particularity of these volcanoes is that they sampled numerous mantle xenoliths during ascent. This represents a unique opportunity to study the composition and the rheology of lithospheric mantle. Mantle xenoliths are deep garnet-bearing peridotites (120 km depth), amphibole and phlogopite peridotites and phlogopitites. They contain abundant hydrous minerals as isolated crystals or veins that attest to an important metasomatism beneath the NTD. Previous geochemical and petrological studies have highlighted interactions of alkaline magmas and the thick cratonic lithosphere as metasomatic agent. However, the presence and composition of magmas, the degree of metasomatism, and the role of metasomatism on mantle rheology below the NTD is still debated.</p><p>To characterize these previous parameters, in this study we performed geochemical and petrophysical analyses on metasomatized, fertile and refractory mantle xenoliths from Labait (on-craton volcano) and Pello Hills (in-rift volcano). Using mineral compositions and thermobarometer calibrations, we estimated the depth of mantle xenoliths between 40 and 140 km (14 to 47 kbar) and temperatures from 930 to 1340°C. EBSD analysis on thin sections indicate that peridotites and amphibole/phlogopite-bearing mantle xenoliths display a moderate to strong deformation induced crystal preferred orientation. In contrast, weak mineral orientations have been observed in phlogopite-amphibole-clinopyroxene-bearing veins. Calculation of seismic properties using MTEX program show that peridotites are seismically anisotropic, up to 12.4% for P-wave velocity (Vp) and 6.8% for S-wave velocity (Vs). The Vp and Vs in hydrous veins are lower than in peridotites (Vp: 7.5-7.9 and 8.3-9.6 km/s; Vs: 4.4-4.6 and 5.0-5.3 km/s respectively) and therefore the Vp and Vs velocities decrease with the increasing proportion of metasomatic minerals. We estimate that a peridotite with 20 vol.% metasomatic vein has a velocity decrease of 3.5% for Vp and 2.9% for Vs, compared to a fertile peridotite.</p><p>These geochemical and petrophysical approaches are important to understand P- and S-wave propagation in the lithospheric mantle beneath the NTD and more specifically in metasomatized lithospheric mantle. The new in situ data and models from mantle xenoliths will be compared to tomographic acquisition and discussed in term of temperature, presence of melt or metasomatism processes. Both petrophysical and geophysical data will help to precisely determine the structure and rheology of the lithospheric mantle, which may control the propagation of the rift at early stage rifting between the Tanzanian craton and the mobile Proterozoic belts.</p>

The Aquatic Civilization of Middle Africa

1974 ◽  
Vol 15 (4) ◽  
pp. 527-546 ◽  
Author(s):  
J. E. G. Sutton
Keyword(s):  
Lake Victoria ◽  
Eastern Africa ◽  
Cultural Tradition ◽  
Main Stage ◽  
African Culture ◽  
Way Of Life ◽  
East African ◽  
Aquatic Life ◽  
Kenya Rift ◽  
African Rift

Between the ninth and third millennia B.C. wetter conditions prevailed over most of Africa. Lakes and rivers were fuller and some of the internal basins were temporarily linked, especially in the ‘Middle African’ belt. This comprises the southern Sahara and Sahel, stretching from the Upper Niger to the Middle Nile, with a south-easterly extension into the Upper Nile basin and the East African rift valleys. This situation was exploited by people who developed a decidedly aquatic economy and culture. From their waterside camps and settlements archaeologists have recovered bones of fish and aquatic animals which these people ate, as well as the distinctive harpoon-heads carved from bone with which they obtained them, and also pottery, bearing peculiar decoration executed with fish-bones and water-shells, made in imitation of (fishing-) baskets. Boating and other cultural developments are deducible. The harpoons date back to 7,000 b.c. at least; the pottery dates back to more than 6,000 b.c. and was clearly an African invention. It reflects important developments in gastronomy and home life.In the Kenya rift valley the main stage of Leakey's ‘Kenya Capsian’ culture is essentially the local manifestation of this far-flung ‘aquatic civilization’.Its greatest extent was achieved during the wettest times of the seventh millennium b.c., and probably involved the expansion of Negroid peoples across this continent-wide savanna belt. Also explained perhaps is the extensive, though now fragmented, distribution of languages which Greenberg combines in his ‘Nilo-Saharan’ super-family. It is suspected that aspects of this ancient aquatic way of life may be maintained or reflected by latter-day isolated or ‘unclean’ lake or swamp communities. This subject has been largely neglected by African culture-historians.Drier conditions in the late sixth and fifth millennia b.c. signalled a decline of this aquatic civilization and, in particular, broke its geographical continuity. Nevertheless, there was a qualified revival in many parts in the fourth and third millennia. In the Kenya rift this later phase seems to equate with the first stage of the ‘stone bowl cultures’. Around Lake Victoria a devolved relic survived until the eve of Bantu expansion about two thousand years ago. Other late or modified examples are known on the Nile and in the western Sudan. Generally, however, the viability and prestige of an aquatic way of life were undermined by the second millennium b.c. In the Sahara and Sahel as well as in the northerly parts of eastern Africa this decline was paralleled by the spread of pastoralism as a new basis of subsistence and prestige. Those who introduced cattle to Kenya from Ethiopia were Cushitic-speakers maintaining, significantly, a fish-taboo.This subject should prove of considerable historiographical interest. The aquatic way of life flourished through Middle Africa at the very time when grain-agriculture and stock-raising were being pioneered in the Near East; and the slow spread of agriculture in Africa, sometimes considered an indication of ‘backwardness’, may be partly explicable by the very success of the aquatic life and of its distinct cultural tradition which was ascendant for a while across the widest part of the continent.

Seismic wave attenuation in the lithosphere of the North Tanzanian divergence zone (East African rift system)

2017 ◽  
Vol 58 (2) ◽  
pp. 253-265 ◽  
Author(s):  
A.A. Dobrynina ◽  
J. Albaric ◽  
A. Deschamps ◽  
J. Perrot ◽  
R.W. Ferdinand ◽  
...  
Keyword(s):  
Seismic Wave ◽  
Wave Attenuation ◽  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
East African ◽  
Seismic Wave Attenuation ◽  
The North ◽  
African Rift
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