Computer Science
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56.3561h&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 56, Issue 9, pp.3561-3570
Computer Science
3
Scientific paper
Measurement of 18 O / 16 O ratios of pyroxene phenocrysts in the 179-Ma Lebombo rhyolites of the Karoo Volcanic Province provides a means of estimating 18 O values of the original magmas. Results show that the inferred magma 18 O values were generally lower than those of normal rhyolites. The average magmatic 18 O value for a Lebombo rhyolite is calculated to be about 5.6 , with lowest value being about 4.4 The presence of large volumes (>30,000 km 3 ) of low- 18 O rhyolite in the Lebombo monocline is attributed to large-scale interaction between the source(s) of the rhyolite and meteoric water. Deep penetration (> 10 km) and extensive circulation of meteoric water could have been facilitated by brittle fracturing which must have accompanied the initial rifting of southern Africa and Antarctica. Radiogenic isotope data indicate that the most likely source for the rhyolites was underplated Karoo-age gabbro having a high component of asthenospheric material.
Erlank Anthony J.
Harris Chris
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