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Microstructures and temperature variability during the Eburnean deformations in the Daléma area, Eastern Senegal

Abstract : In the Dal¨¦ma area, the eastern part of theK¨¦dougou-K¨¦ni¨¦ba inlier, the petrographic study of feldsparand quartz microstructures revealed the variability of temperaturesrelated to partitioned D2 Eburnean deformation andretrograde metamorphism from the superimposed D3Eburnean deformation. Two major thermal events, Q1 andQ2, related to D2 and D3 Eburnean deformation phases, wereidentified in intracrystalline microstructures in the Dal¨¦maarea. The first identified thermal event called Q1, which wouldhave created the largest heat flow, was recorded especially inthe shear zones. The microstructure features of this thermalevent are syntectonic to the emplacement of granitoids around2,100 Ma, during the D2 Eburnean deformation phase. ThisD2 Eburnean deformation phase is characterized by thepartitioning of sinistral transpressive deformation betweenpure shear to simple shear-dominated domains. The thermalgradient associated with this event is very important in theinner shear zones (¡Ý750 ¡ãC) and decreases towards theirborders, where it would be estimated at ¡«450 ¡ãC. Outsidethe shear zones, the metamorphic temperature peaks are lessimportant with thermal gradients lower than 400 ¡ãC. Theywould be very low (¡Ü250 ¡ãC) in undeformed rocks with wellpreserved primary beddings. The intensity of the second thermalevent is weaker than in the first one, with temperatures notexceeding 500 ¡ãC. The intracrystalline microstructures whichcharacterize this second thermal event are closely connectedto those of the D3 Eburnean deformation phase, and cross-cutor are superimposed on those of the first thermal event relatedto the D2 Eburnean deformation phase. This second thermalevent is then subsequent to the late D3 Eburnean deformationphase. The intracrystalline microstructures related to the D1Eburnean deformation phase were not identified, and theirabsence is interpreted in various ways.
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Submitted on : Monday, March 2, 2015 - 1:52:29 PM
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Tahar Aifa, Moussa Dabo. Microstructures and temperature variability during the Eburnean deformations in the Daléma area, Eastern Senegal. Arabian Journal of Geosciences, Springer, 2015, 8 (2), pp.677-689. ⟨10.1007/s12517-013-1254-1⟩. ⟨insu-01121682⟩



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