Archaean stromatolites from the Ngesi Group,Belingwe greenstone belt,Zimbabwe; preservation and stable isotopes — preliminary results |
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| Authors: | PI Abell J McClory A Martin EG Nisbet |
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| Institution: | 1. Chemistry Department, University of Rhode Island, Kingston, R.I. 02881 U.S.A.;2. Geology Department, Anglo—American Corporation, P.O. Box 1108, Harare Zimbabwe;3. Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada |
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| Abstract: | The petrology and stable isotope chemistry of cyanobacterial stromatolites of Archaean age (2.7 Ga) from the Cheshire and Manjeri Formations of the Belingwe greenstone belt in Zimbabwe have been examined. Palaeomagnetic data suggest that the stromatolites formed in tropical to subtropical latitudes. The Cheshire Formation shows little evidence of either anion or cation exchange during metamorphism, and the stable carbon and oxygen isotope ratios suggest a formation at temperatures perhaps considerably below 80°C. The Manjeri Formation, only slightly older, but overlain by a thick volcanic sequence, shows a low grade of metamorphism, and isotope ratios that are consistent with a metamorphic temperature of around 200°C. |
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