First evidence of early Birimian (2.21 Ga) volcanic activity in Upper Guinea: the volcanics and associated rocks of the Niani suite

During the 1:200,000-scale mapping of northeastern Guinea, a suite of volcanic rocks comprising porphyritic lavas, pyroclastics and pyroclastic breccias, was identified in the Niani area in the northeast of the Siguiri Basin. The texture of the rocks, the abundance of pyroclastic deposits and the di...

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Bibliographic Details
Published in:	Journal of African earth sciences (1994) 2002-10, Vol.35 (3), p.417-431
Main Authors:	Lahondère, Didier, Thiéblemont, Denis, Tegyey, Monique, Guerrot, Catherine, Diabate, Bakari
Format:	Article
Language:	eng
Subjects:	Birimian Guinea Volcanic rocks
Online Access:	Get full text
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Summary:	During the 1:200,000-scale mapping of northeastern Guinea, a suite of volcanic rocks comprising porphyritic lavas, pyroclastics and pyroclastic breccias, was identified in the Niani area in the northeast of the Siguiri Basin. The texture of the rocks, the abundance of pyroclastic deposits and the diversity of lapilli they contain all point to explosive eruptive mechanisms. A Pb–Pb zircon evaporation age of 2212±6 Ma obtained from a sample of rhyodacite has yielded the first evidence of early Birimian volcanic activity in Guinea. Most of the volcanic rocks of the Niani volcanic suite may be defined as intermediate to acidic medium-K calc-alkaline igneous rocks. Some of them show HREE fractionation comparable to the one of high-Al/low-Yb TTGs and recent adakites. It seems probable that these lavas were emplaced in relation with the subduction of a young and hot oceanic plate.
ISSN:	1464-343X 1879-1956