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

Vincent, NGAKO; Emmanuel, Njonfang; Julien, Bernard; Jean Marcel, Abate Essi; Mero, Yannah; Augustin Patrice, Moussango Ibohn; Sylvestre, Ntomba; Yaya, Fodoue; Z&eacute;non, Itiga

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

Document Type : Original Article

Authors

NGAKO Vincent ¹

Njonfang Emmanuel ²

Bernard Julien ³

Abate Essi Jean Marcel ⁴

Yannah Mero ⁴

Moussango Ibohn Augustin Patrice ⁴

Ntomba Sylvestre ⁵

Fodoue Yaya ⁴

Itiga Zénon ⁶

¹ Institute of Geology and Mining Researches, yaoundé, Cameroon

² High Teacher Training School, University of Yaound&amp;eacute; I, Yaound&amp;eacute;, Cameroon

³ Bureau of Geology and Mining Researches, 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

Abstract

Analogue upright folds in the Sao Francisco Congo craton (SFCC) northern margin overprint an early flat–lying to moderate dipping XY deformation plane outlined by an S1–2 foliation. They display steep 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 boundaries 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 granitoid massifs and veins. 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 reconstruct the first and second order fold profiles from the geometry of regional S1–2 foliation trends. The resulting finite strain pattern materializes a global–scale D1–2 and D3 interference. Two main stress directions are inferred from XY planes and layer parallel shortening: the N020oE direction correlates with E–W foliation trends marking the earlier nappes stacking episodes upon the SFCC between 680 and 620 Ma (orogeny 1); and the N120oE direction correlates with meridian–directed nappes stacking episodes upon the West African Craton and F3 fold nappes overprints in CAFB between 600 and 580 Ma (orogen 2).

Keywords

Finite– strain pattern

High Strain Zone

Neoproterozoic fold belts

Plates’ collision

Orogens 1 and 2