Potassium—Argon Ages from the Volcanic Province of Northern Tanzania

Evans, A.G.; Fairhead, J.D.; Mitchell, J. G.

doi:10.1038/physci229019a0

Cited by 29 publications

(20 citation statements)

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“…Kilimanjaro and Mt. Meru (28) indicate that the radiation of Dendrosenecio occurred within the past million years and that D. meruensis was derived within the past 200,000 years. This result is congruent with the observed paucity of restriction-site variation among the giant sencios.…”

Section: Resultsmentioning

confidence: 99%

Chloroplast DNA variation and the recent radiation of the giant senecios (Asteraceae) on the tall mountains of eastern Africa.

Knox

Palmer

1995

Proc. Natl. Acad. Sci. U.S.A.

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Chloroplast DNA restriction-site variation was surveyed among 40 accessions representing all 11 species of giant senecios (Dendrosenecio, Asteraceae) at all but one known location, plus three outgroup species. Remarkably little variation (only 9 variable sites out of roughly 1000 sites examined) was found among the 40 giant senecio accessions, yet as a group they differ significantly (at 18 sites) from Cineraria deltoidea, the closest known relative. This pattern indicates that the giant senecios underwent a recent dramatic radiation in eastern Africa and evolved from a relatively isolated lineage within the Senecioneae. Biogeographic interpretation of the molecular phylogeny suggests that the giant senecios originated high on Mt. Kilimanjaro, with subsequent dispersion to the Aberdares, Mt. Kenya, and the Cherangani Hills, followed by dispersion westward to the Ruwenzori Mountains, and then south to the Virunga Mountains, Mt. Kahuzi, and Mt. Muhi, but with dispersion back to Mt. Elgon. Geographic radiation was an important antecedent to the diversification in eastern Africa, which primarily involved repeated altitudinal radiation, both up and down the mountains, leading to morphological parallelism in both directions. In general, the plants on a given mountain are more closely related to each other than they are to plants on other mountains, and plants on nearby mountains are more closely related to each other than they are to plants on more distant mountains. The individual steps of the geographic radiation have occurred at various altitudes, some clearly the result of intermountain dispersal. The molecular evidence suggests that two species are extant ancestors to other species on the same or nearby mountains.The giant senecios are an unusual group of plants that have diversified to occupy a range of habitats, from 2500 to 4600 m, on 10 mountains >3300 m tall within 40 of the equator in Zaire, Rwanda, Uganda, Kenya, and Tanzania (1). Now segregated as the genus Dendrosenecio (Hauman ex Hedberg) Nordenstam, the giant senecios comprise 11 species and 6 nonautonymic subspecific taxa (2). Their habitats range from upper montane forest (mist-forest) through the giant heather zone and highaltitude wet meadows and extend almost to the upper limit of the unusual afro-alpine zone, whose climate has been characterized as "summer every day and winter every night" because strong diurnal fluctuations exceed seasonal variation (3). These plants typically have a giant-rosette growth form with a massive terminal leaf rosette borne atop a thick woody stem. During reproduction, a large terminal inflorescence is produced, and two to four lateral branches are usually initiated. Old plants appear as candelabras the size of telephone poles, with each branch bearing a leaf rosette (Fig. 1). The giantrosette growth form, large pith volume, marcescent foliage, and nyctinasty have evolved independently in the montane east The giant senecios show an unusual trend of massive plants occurring at high elevations, with smaller plan...

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Section: Resultsmentioning

confidence: 99%

Chloroplast DNA variation and the recent radiation of the giant senecios (Asteraceae) on the tall mountains of eastern Africa.

Knox

Palmer

1995

Proc. Natl. Acad. Sci. U.S.A.

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“…Our new set of 40 K- 40 Ar data permits to better constrain the time framework previously established (Evernden and Curtis, 1965;Evans et al, 1971;Downie and Wilkinson,1972;Wilkinson et al,1986), with emphasis on the youngest magmatic events that are recorded by rocks largely exposed on the upper slopes of the three edifices. Three successive volcanic stages are distinguished and referred to as the main edifices of Kilimanjaro, respectively.…”

Section: Volcanic History and Implicationsmentioning

confidence: 99%

“…The arrangement of dated volcanic features in the NTD into tectono-magmatic lineaments supplies additional insights on its structural history during the onset of magmatism. The compilation of existing radiochronological ages (Evernden and Curtis, 1965;Evans et al, 1971;Bagdasaryan et al, 1973;MacIntyre et al, 1974, Wilkinson et al,1986, Dawson, 1992) reveal a rough E-W age progression which is due to a shift of magmatic activity eastwards in the time range 5.0 Ma-Present. The precursor volcanics in the NTD are nephelinites, ~8.1-7.3 Ma in age, emplaced in the Essimingor region (Bagdasaryan et al, 1973), but the main volcanic activity started at 5.0 Ma and involved three successive magmatic stages until recent times.…”

Section: Tectono-magmatic Rift Frameworkmentioning

confidence: 99%

“…The 50 x 200 km NKVB comprises numerous volcanic edifices, and their extensively distributed effusive and air-fall material, that were emplaced during the time interval 8 MaPresent (Evernden and Curtis, 1965;Evans et al, 1971;Bagdasaryan et al, 1973;Macintyre et al, 1974, Wilkinson et al,1986, Dawson, 1992 close to, or following in part, a fundamental lithospheric-scale discontinuity between Proterozoic terranes of the Mozambique Belt and Archaean cratonic blocks involving the Masai nucleus (Fig. 1).…”

Section: Tectono-magmatic Rift Frameworkmentioning

confidence: 99%

“…Paradoxally, recent radiometric dating have not been applied to Mount Kilimanjaro though forming the most prominent volcanic construction of the East African Rift. Compiling the seven published ages for the three cones (Shira, Kibo and Mawenzi) forming Kilimanjaro (Evernden and Curtis, 1965;Evans et al, 1971;Bagdasaryan et al, 1973;Wilkinson et al, 1986) shows a polyphased volcanic history over the past 2 Ma, between ~2.3 and ~0.17 Ma (Dawson,1992), but given the uncertainties about these data (for example, 2.3±0.4 Ma, Bagdasaryan et al, 1973), it is difficult to establish a genetic link between the Shira, Mawenzi and Kibo magmatic activities.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

New K–Ar age determinations of Kilimanjaro volcano in the North Tanzanian diverging rift, East Africa

Nonnotte

Guillou

Gall

et al. 2008

Journal of Volcanology and Geothermal Research

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The Kilimanjaro is the African highest mountain and culminates at 5895 m high. This huge volcanic edifice is composed of three main centres along a N110°E-striking axis (Shira, Kibo and Mawenzi from W to E), and emplaced in a key area where a major N80°E-oriented volcanic lineament intersects a first-order NW-SE basement fault-like discontinuity.Seventeen K-Ar ages (on microcrystalline groundmass) acquired on lavas and intrusive facies from the three eruptive centres confirm that the Plio-Quaternary volcanicity of Kilimanjaro is clearly polyphased. The oldest phases of volcanic activity begun at ~2.5 Ma in the Shira vent and our data suggest that the latest important phases occurred around 1.9 Ma, just before the collapse of the Northern part of the edifice. Magmatic activity then shifted eastwards in the

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The Gregory Rift

Scoon

2018

Geology of National Parks of Central/Southern Kenya and Northern Tanzania

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Potassium—Argon Ages from the Volcanic Province of Northern Tanzania

Cited by 29 publications

References 2 publications

Chloroplast DNA variation and the recent radiation of the giant senecios (Asteraceae) on the tall mountains of eastern Africa.

Chloroplast DNA variation and the recent radiation of the giant senecios (Asteraceae) on the tall mountains of eastern Africa.

New K–Ar age determinations of Kilimanjaro volcano in the North Tanzanian diverging rift, East Africa

The Gregory Rift

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