Th-230 - U-238 series disequilibrium of the Olkaria basalts Gregory Rift Valley, Kenya: Petrogenesis

Details Th-230 - U-238 series disequilibrium of the Olkaria basalts Gregory Rift Valley, Kenya: Petrogenesis Th-230 - U-238 series disequilibrium of the Olkaria basalts Gregory Rift Valley, Kenya: Petrogenesis

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24..123b&link_type=abstract

In Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F p 123-124 (SEE N94-12015 01-91)

Other

African Rift System, Basalt, Isotopes, Kenya, Magma, Petrology, Feldspars, Inclusions, Lava, Pyroxenes, Trachyte

Scientific paper

Strong mixing trends on a (Th-230/Th-232) versus Th diagram show that the basalts are mixed magmas which have undergone interaction with the crust. Instantaneous Th/U ratios are less than time integrated ones but these exceed the Th/U ratios in the MORB and OIB sources. This indicates that the mantle may have undergone some metasomatic fluxing, crustal contamination of the basalts will also enhance these ratios. Early activity on the Akira plain is represented by early basalts and hawaiites. The early basalt samples are known to predate the earliest comendites. The most recent phase of activity is represented by another cinder cone 40-50 m high being feldspar and clinopyroxene phyric. Inclusions which occur in the comendites vary in size and distribution. The largest and most porphyritic are the trachytes (up to 40 cm) with alkali feldspar phases up to 6 mm and small pyroxenes in the ground mass. The second set of inclusions are smaller (up to 10 cm) and are largely aphyric. The distribution of the inclusions are not uniform, the Broad Acres (C5) lavas contain 2-5 percent. The size of the inclusions decrease from south to north, as does the abundance of the trachytic inclusions. The major element variations in the Naivasha basalts, hawaiites and magmatic inclusions are discussed.

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