The S₁ foliation is displayed by the greywacke, BIF, sillimanite-bearing paragneisses and amphibolite layers. It is sub- to vertical and oriented NNW-SSE to east-west on both sides of the Adzap fault (Fig. 2). It defines two average values, 62 067 and 42 302, predicting F₂ cartographic folds [Fig. 2a, 2d; 5(b)/(a)], different from the east-west S₁ foliation orientation described in literature (Feybesse et al., 1987; Maurizot et al., 1986). The foliation is folded in mega folds F₂, tight to open sub-north-south cartographic synclines, with A₂ fold axes oriented mainly NNW-SSE. They form circular or “dome” structures in the Abodveng window inside the NyC (Fig. 2). The best-fit great circle for poles of S₁ corresponds to F₂ folds oriented 60 085 (Fig. 2d). Other mega folds F₂ inferred from the equal area stereogram projections along great circles of poles foliations S₁ [Fig. 2, 5(b)/(a)]. The L₁ stretching lineation is oriented SE-NW to west-east in the NC. Its trajectories are locally reoriented west-east in the western side of Adzap fault. Its average value of 353 36 underlines its submeridian character, parallel to secant to fold axis A₂. Generally, L₁ and A₂ support the displacement top-to the NNW and ENE (Fig. 3a, d). Normal dip-slip fault types oriented NNE-SSW, NNW-SSE, WNW-ESE and ENE-WSW generated by various stress fields, define deep valleys and guide hydrographical patterns (Fig. 4a, d; Angelier, 1994; Angelier and Mechiel, 1977). The Adzap fault oriented NNW-SSE seems to be a major fault, responsible for geometric difference on both its sides. For the whole NC, reconstructed paleostresses reveal a σ₁ vertical and a σ₃ horizontal sub-east-west (Fig. 4 g). This result supports that NC faults happened under a crustal shortening and sub-east-west extension tectonics. The cross sections parallel to hinges of F₂ folds and L₁ complete the geometry of the NC (a) and its relationships with the Nyc and OC. The NC compressed in east-west during it ductile phase, is thrusted in west-east and north-south by the Nyong (b) and Yaounde (c) nappes, respectively [Fig. 5(c)/(a), (b)/(a) and (c)/(b)].

The S₂ typified foliations is the most striking structure in the NyC. It is represented, by in BIF, meta-granodiorite, meta-syenite and paragneiss layers and oriented WSW-ENE to north-south, sub-parallel to magmatic and metamorphic layering sheared by blastomylonitic S/C shear zones structures (Fig. 2). Its undulations define F₃ asymmetrical cartographic folds designed type [Fig. 2, 5 (b)/(a) and (c)/(b)]. These F₃ folds form north-east and south-west anticlines and synclines with A₃ fold axes oriented mainly NE-SW. Other F₃ mega folds inferred from equal area stereogram projections along great circles of poles S₂ foliations with average values that correspond to northern and southern sides oriented 29 037 and 71 166 (Fig. 2e). The L₂ include stretching and amphibole lineations, parallel, oriented WSW-ENE to WNW-ESE nearer to 084 21, the axes A₃ average value (Fig. 3b, e). Faults are normal, inverse dip-slip and vertical strike-slip fault types, oriented east-west, NE-SW, NNE-SSW and ENE-WSW (Fig. 4b). Akongo, Kama and Mefembe faults are major faults guiding rivers of the same names and individualising deep valleys. They were generated by the σ₁ vertical and σ₃ horizontal NW-SE (Fig. 4b, e, g). This result predicts that the NyC faults occurred under the crustal shortening and NW-SE horizontal extension regime. The cross sections parallel to hinges of F₃ folds and L₂ stretching lineation represent the geometry and the middle position of the NyC (b) on the NC (a) and under the OC (c). The NyC is compressed in NW-SE during it ductile stage. In its relationships with the NC and the OC, the NyC thrusted as the Nyong nappe (b) in west-east the NC (a) [Fig. 5 (b)/(a)] and, is thrusted in north-south by Yaounde (c) nappes [Fig. 5(c)/(b)].

Two main S_0/1/2 and S₂ foliations have been identified in metapelites and metadiorites, respectively (Mvondo et al., 2003, 2007; Owona, 2008; Owona et al., 2011). Both are treated here as S₃ foliations for comparison with S₁ and S₂ in the Ntem and Nyong complexes, respectively. The S₃ foliation in metapelites is perturbed and folded in the Yaounde area with north, north-east, north-west, south-west, west and east dip becoming homogenous and generally east-west in the contact zone with NC and NyC (Fig. 2). In the south-east of Yaounde, its average did-dip direction value is 12 358 (Fig. 3 g). The S₃ foliation in metadiorites defines “dome and basin” structures with average values 13 060, 04 346 and 79 048 in Binguela, Ngoa-Ekele and Afamba metadiorites, respectively (Fig. 2f, g). The S₃ foliations form the most striking structural feature with a southward verging Yaounde tectonic nappe transported top-to-the SSE onto the NC and NyC (Mvondo et al., 2003, 2007a; Mvondo Ondoa et al., 2009; Owona, 2008; Owona et al., 2011). The undulations of the S₃ foliations draw F₄ cartographic folds corresponding to northward and southward anticlines and synclines with A₄ fold axes oriented mainly north-south to NNE-SSW [Fig. 2, 5(c)/(a), (c)/(b))]. Other F₄ mega cartographic folds are inferred from equal area stereographic projections along great circles of poles the S₃ foliation (Fig. 2f, g, h). On the contrary to the foliation, metapelites and metadiorites display a common L₂ lineation typified L₃. L₃ includes the stretched, mineral and boudinated varieties in the OC (Fig. 2c, f). The L₃ stretching lineation plunges in north-west, north-east, south-east and south-west, as in the Yaounde area, suggesting the foliation undulation and folding. Its overall orientation is 005 11 (Fig. 3f). Locally, it is reoriented around N090 and N270 because of the refolding. The L₃ crenulated lineation is oriented 008 11 (Fig. 3 g). The kyanite, biotite, amphibole, clinopyroxene and quartzo-feldspathic aggregates form the L₃ mineral lineation oriented N009 06 in metapelites (Fig. 3 h). The biotite, amphibole, clinopyroxene and quartzo-feldspathic aggregates L₃ lineation oriented 015 15 in the metadiorites. The overall submeridian and parallelism character of L₃ lineation types represent a proof of the transport top-to-the south of the Yaounde nappe onto the Ntem and Nyong complexes. Faults are the NW-SE to north-south normal dip-slip and sinistral and dextral vertical strike-slip types (Angelier, 1994; Angelier and Mechiel, 1977). The Mefou, Akono, So’o and Ossoé Kobock Rivers are guided by most of them, constituting the proof of the structural control of the hydrographical patterns (Owona et al., 2003). The lack of cartographic offsets suggests their postorogenic stress relaxation or neotectonic event emplacement. The paleostress reconstructed reveals that these faults were generated by an overall σ₁ subvertical and σ₃ horizontal NNE-SSW (Fig. 4c, f, g). They suggest a crustal shortening and NNE-SSW extension phase established in the OC. The cross sections parallel to hinges of F₄ folds, L₃ stretching and mineral lineations represent the OC (c) and its relationships with the NC (a) and the NyC (b). The OC as the Yaounde nappe, is transported top-to the south onto the NC [Fig. 5 (c)/(a)] and, the NyC [Fig. 5(c)/(b)].

The S₁ foliation is emplaced by a granulitc D₁ tectonothermal event (? Saamian orogeny; Elmi and Babin., 2002) dated at ca. 3100 ± 100 Ma (Sm/Nd whole rock isochron, Toteu et al., 1994b) under a nonrotational deformation (Caen-Vachette et al., 1988; Lasserre and Soba, 1976). Its two average values of 62 067 and 42 302 (Fig. 2a, d) different from the east-west strike known in literature (Shang et al., 2004b; Tchameni et al., 2001) attested of an east-west D₂ Archean compression tectonic stage that peaked between 2950–2850 Ma [(Rb/Sr whole rock, Caen-Vachette et al., 1988; U/Pb, zircon, Toteu et al., 1994b) the? Ouzzalian orogeny (Elmi and Babin., 2002). D₂ that has folded the S₁ foliation in north-south F₂ cartographic folds or syncline did not generate a new foliation but induced the charnockitization of the Ntem complex (Caen-Vachette et al., 1988; Toteu et al., 1994). The L₁ stretching lineation is oriented 353 36 with overall SE-NW trajectory, parallel to A₂ main fold axis, oriented 355 30 (Fig. 2d; 3a; d). That west-east local reorientation is linked to the Adzap fault offsets (Fig. 2). The normal dip-slip faults have been emplaced by σ₁ sub-vertical paleostress and σ₃ sub-east-west horizontal paleostress (Fig. 4a, d, g). They corroborate the crustal thinning of the D₃ brittle stage according the statistical treatment of the faults slickenside and scratching attitudes (Sperner et al., 1993; Sperner and Ratschbacher, 1994) and their classification and stress orientations (Angelier and Mechiel, 1977; Angelier, 1994). These Archean faults can be younger than 2700 Ma and are considered as the earliest riftings stage in the Ntem complex (Feybesse et al., 1998).

The S₂ foliation is oriented 029 37 and 166 71 (Fig. 2b, e). It characterized the Eburnean amphibolite to granulitic tectonothermal event that peaked at ca 2050 Ma (U/Pb-Zr, Feybesse et al., 1998; Penaye et al., 2004). It is folded in asymmetric F₃ cartographic folds type with the best fit attitude oriented 21 084 under a NW-SE to north-south compression tectonic stage (Fig. 2b, e). They form the Nyong tectonic nappe transported top to the east onto the Congo craton (Feybesse et al., 1998; Tack et al., 2001; Penaye et al., 2004) as attested by the sub- to parallel A₃ fold axial oriented 084 21, the stretching and amphibole L₂ lineations types oriented 070 30 (Fig. 2b, e; Fig. 3b, e). The L₂ lineations confirm in the SW Cameroon, the eastwards transport of the Nyong nappe onto the NC or/and the WCAFB onto the CC concordant to previous results available in the literature (Feybesse et al., 1987, 1998; Ledru et al., 1994; Maurizot et al., 1986; Penaye et al., 2004; Shang et al., 2004a; Tchameni et al., 2001). According to the TURBO PASCAL program (Sperner et al., 1993; Sperner and Ratschbacher, 1994) and their classification and stress orientations (Angelier and Mechiel, 1977; Angelier, 1994) normal, inverse dip-slip and vertical strike-slip faults in the NyC happened under an overall crustal thinning and NW-SE extension regime according to the sub-vertical σ1 and the sub-horizontal σ3 determined paleostresses (Fig. 4b, e, g). Some of these faults correspond to transcurent faults, coeval to the Pan-African Yaounde tectonic nappe (Miyem, 1994; Penaye et al., 2004; Toteu et al., 1994).

The S₃ foliations in metapelites and metadiorites occurred during the Pan-African tectonothermal event that ranged between 650–540 Ma and peaked between 616 Ma (Sm/Nd-Grt; Toteu et al., 1994b) and 613–586 Ma, U/Th/Pb-Mnz, Owona, 2008) under mainly the simple shear regime (Fig. 2c, f, g, h). These S₃ foliations are inconstant in comparison with S₁ and S₂. They vary in the north on high- to medium-grade metapelites and metadiorites and become sub-east-west in low-grade chlorite schist in the south and contact zone with the NC and NyC, contradicting or discrediting their statistical overall average value 11 353. Consequently, the F₄ cartographic folds are closed to compressed anticlines, synclines and dome and basin confined in high- to medium grade metapelites (Fig. 2a). Above F₄ mega folds that form the Yaounde nappe suggests a variable east-west compressive tectonic phase confined in the north maintained or becoming north-south in the south. The similarity of elongated quartzo-feldspathic, amphibolitic aggregates and stretched L₃ lineations, and boudins are confirmed in metagranitoids and metapelites as demonstrated in literature in the OC (Mvondo et al., 2003, 2007; Owona, 2008). They plunge north-west, north-east, south-east and south-west and suggest foliation undulation and folding with 005 11 as overall orientation (Fig. 3c, f, g, h, i). Kyanite and biotite mineral L₃ lineations are oriented 009 06 (Fig. 3f), parallel to the main A₄ fold axis, oriented 346 09 (Fig. 3 g). These results confirm the transport top to the south of the Yaounde nappe onto the NC and NyC (Mvondo et al., 2003, 2007; Mvondo Ondoa et al., 2009; Owona, 2008). However, the L₃ lineations are locally reoriented N090 and N270 (Fig. 3c) suggesting the refolding and/or faulting (Mvondo et al., 2003, 2007; Owona, 2008). The normal dip-slip, sinistral and dextral vertical strike-slip faults in the OC attributed to post-orogenic stress relaxation or neotectonic events (Mvondo et al., 2007a), at ca. < 545 Ma are characterized by overall subvertical σ₁ and north-south subhorizontal σ₃ suggests a crustal thinning environment (Fig. 4c, f, g).

The NC, NyC and OC represent three lithostructural units in their boundary zone, which varies from one complex to another, with respect to their lithology, mineralogy, geothermobarometry, structural geology and geochronology (Owona, 2008). The S₁ foliations, L₁ lineation, F₂ mega folds, A₂ fold axes and faults are related to the Saamain and Ouzzalian orogeny for the Archean NC. The S₂ foliations, L₂ lineation, F₃ mega folds, A₃ fold axes and faults are inferred to the Eburnean tectonothermal event for the Paleoproterozoic NyC. The S₃ foliations, L₃ lineation, F₄ mega folds, A₄ fold axes and faults have been generated by the Panafrican orogeny. These structural imprints define the geometry and relationships of the NC, NyC and OC (Figs. 2–5). The NC, compressed in east-west, defined F₂ mega folds with hinges oriented sub-north-south parallel to A₂ axes and L₁ stretching lineation during its ductile stage. It is thrusted in west-east by the Nyong nappe and in north-south, by the Yaounde nappe (Feybesse et al., 1998; Mvondo et al., 2007; Mvondo Ondoa et al., 2009; Owona, 2008; Penaye et al., 2004). The NyC compressed during the ductile phase in NW-SE, formed F₃ asymmetrical mega folds with west-east hinges parallel to A₃ axis and L₂ mineral and stretching lineations, and was transported top-to the east onto the NC under amphibolitic conditions (Owona, 2008; Penaye et al., 2004). It is thrusted in north-south by the OC or Yaounde nappe and located stratigraphycally between the NC and OC. The OC compressed mainly in east-west during the ductile phase, defined F₄ mega folds with north-south hinges parallel to the A₄ fold axis and L₃ stretching and mineral lineations. During its transport top-to the south onto the NC and OC (Mvondo et al., 2003, 2007; Owona, 2008; Toteu et al., 2006b), the Yaounde nappe has defined the Mbalmayo shear zone under amphibolitic to green schist metamorphic conditions (Mvondo Ondoa et al., 2009). The geometry and relationships define litho-chrono-structural- and angular discordance between the NC, NyC and OC associated to an overall crustal thinning during their brittle stage.