Archaean greenstone belt from the Central African Republic (Equatorial Africa) |
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| Authors: | JL Poidevin J Dostal C Dupuy |
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| Institution: | Département de Géologie, Université de Republic Centrafricain, B.P. 1450, Bangui Central African Republic;Department of Geology, Saint Mary''s University, Halifax, Nova Scotia Canada;Centre Geologique et Geophysique, U.S.T.L., 34060 Montpellier France |
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| Abstract: | The Bandas belt, one of two prominent Archaean greenstone belts in the Central African Republic (Equatorial Africa), is ca. 250 km long. At the southernmost part of the belt, a metasedimentary—metavolcanic rock suite is preserved only in brachysynclines. The suite can be divided into two lithostratigraphic units. The lower unit is composed predominantly of volcanic rocks, while the upper one contains mainly metasedimentary rocks. The volcanic rocks, which are part of a sequence ca. 3600 m thick, can be sub-divided according to stratigraphic position, lithology and geochemistry into three groups. The lowermost group includes low-K tholeiitic basalts depleted in light REE. The second group consists of tholeiitic basalts with light REE-enriched patterns and the third, uppermost, group includes andesites, which are similar in several respects to Recent calc-alkaline andesites.The tholeiitic basalts of the first two groups are probably related to different upper mantle sources. The andesites of the third group were produced either by fractional crystallization from a basaltic magma enriched in light REE or equilibrium melting of eclogite or garnet amphibolite. |
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