Analogue upright folds in the Sao Francisco Congo Craton deformed margin, Central African Fold Belt (CAFB). Inferences to the Western Gondwana tectonic evolution

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نوع مقاله : مقاله پژوهشی

نویسندگان

1 Institute of Geology and mining Researches, Yaoundé, Cameroon

2 High Teacher Training School, University of Yaoundé I, Yaoundé, Cameroon

3 Bureau de Recherches Géologiques et Minières (BRGM), Orléans Cedex 1, France

4 Institute of geology and Mining Researches, Yaoundé, Cameroon

5 Institute of Geology and Mining Researches, Yaoundé, Cameroon

6 Department of Earth Sciences, Faculty of Sciences, University of Douala, Douala, Cameroon

چکیده

Analogue upright folds in the Sao Francisco Congo Craton (SFCC) northern margin overprint an early flat–lying to E–W–directed moderate dipping XY deformation plane outlined by an S1–2 foliation. They display steeply dipping high strain zones (HSZ) parallel to the axial planes of first to fourth–order analogue folds. The HSZ widths are scaled to the fold order: discrete crenulation boundary HSZ scaled to the third and fourth–order folds, thick crenulation boundary HSZ scaled to the first and second ones. The HSZ morphology varies with the structural levels: in the shallow and medium–crustal levels, disjunctive and gradational–type cleavages prevail, whereas discrete and zonal–type mylonitic cleavages are ubiquitous in deeper levels where they interact with the emplacement of granitoids. Z– and S–types crenulation showing boundaries cleavages or HSZ characterize analogue fold limbs, and M–type ones, analogue fold hinges. These structural markers enable to reconstruct the first and second–order fold profiles from the geometry of regional S1–2 foliation trends. The resulting finite–strain pattern materializes D1–2 and D3 interference at global–scale. Two main stress directions are inferred from XY planes and layer–parallel shortening: 1) the N20oE direction correlates with roughly E–W foliation trends marking the earlier nappes stacking episodes upon the SFCC (orogeny 1: 680–620 Ma), and 2) the N120oE direction correlates with meridian–directed nappes stacking episodes upon the West African Craton and F3 fold nappes overprints in CAFB (orogen 2: 600–580 Ma).

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انتشار آنلاین از تاریخ 31 مرداد 1403

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