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Reconnaissance potassium–argon geochronology of the Suregei–Asille district, northern Kenya

Published online by Cambridge University Press:  01 May 2009

F. J. Fitch ,
P. J. Hooker ,
J. A. Miller ,
J. G. Mitchell  and
R. T. Watkins
F. J. Fitch
Affiliation:
Department of Geology, Birkbeck College, University of London, 7/15 Gresse St, London WIP 1PA
P. J. Hooker
Affiliation:
Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ
J. A. Miller
Affiliation:
Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Rise, Madingley Road, Cambridge, CB3 0EZ
J. G. Mitchell
Affiliation:
School of Physics, The University, Newcastle-upon-Tyne, NE1 7RU
R. T. Watkins
Affiliation:
Department of Geology, University of St Andrews, College Gate, St Andrews, Fife, KY16 9ST
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Abstract

Potassium–argon dating of 44 samples of basalt lavas and pantelleritic ignimbrites provides a provisional chronology for the 1900-metre thick Cenozoic succession of the Suregei–Asille district, northeast of Lake Turkana. Volcanic rocks of the Asille Group range in age from late Oligocene (Chattian) to late Miocene (Tortonian). Data obtained from conventional K–Ar total-rock analysis of basalt samples are appraised statistically to indicate the presence of three periods of enhanced volcanism centred around 27, 17 and 11.5 Ma. Equivalent ages obtained from the pyroclastic pantellerites by conventional K–Ar total-rock analysis and 40Ar/39Ar analysis of sanidine concentrates indicate that basic and acid eruptions were closely spaced in time. Continental tholeiite flood lavas belonging to the Gombe Group are of Pliocene age, but are difficult to date precisely because of their young ages and relatively high atmospheric contamination occurring as a result of the secondary alteration in the ubiquitous glass mesostasis. Those ages involving least atmospheric correction are considered most reliable, and are closely similar for the Chen Alia and Harr formations at around 4.85 Ma, although later flood eruptions may have occurred to the south and west of the Suregei–Asille district at about 3.85 Ma.

Type
Articles
Information
Geological Magazine , Volume 122 , Issue 6 , November 1985 , pp. 609 - 622
Copyright
Copyright © Cambridge University Press 1985

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