# The Djourdé-Sinassi magmatic-migmatitic complex, Northern Cameroon: a record of vertical extrusion of the Pan-African partially molten orogenic root

Suzanne Tiani Djuimou, Merlain Bouyo Houketchang, Olivier Vanderhaeghe, Ludovic Achu Megnemo, Loïque Rodolph Azefack Mbounou, Michel Grégoire, Armand Kagou Dongmo, Olivier Vanderhaeghe

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Suzanne Tiani Djuimou, Merlain Bouyo Houketchang, Olivier Vanderhaeghe, Ludovic Achu Megnemo, Loïque Rodolph Azefack Mbounou, et al.. The Djourdé-Sinassi magmatic-migmatitic complex, Northern Cameroon: a record of vertical extrusion of the Pan-African partially molten orogenic root. Bulletin de la Société Géologique de France, 2025, 196, pp.11. 10.1051/bsgf/2025014. hal-05381649

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# The Djourdé-Sinassi magmatic-migmatitic complex, Northern Cameroon: a record of vertical extrusion of the Pan-African partially molten orogenic root

Suzanne Tiani Djuimou<fnref n="1" />,*, Merlain Bouyo Houketchang<fnref n="2" />, Olivier Vanderhaeghe<fnref n="3" />, Ludovic Achu Megnemo<fnref n="1" />, Loïque Rodolph Azefack Mbounou<fnref n="1" />, Michel Gregoire<fnref n="3" /> and Armand Kagou Dongmo<fnref n="1" />

Received: 27 December 2024 / Accepted: 21 April 2025 / Publishing online: 13 June 2025

**Abstract** – The Djourdé-Sinassi magmatic-migmatitic complex is part of the juvenile Neoproterozoic Garoua Domain located in Northern Cameroon. It is surrounded by the Zalbi, Poli and Rey-Bouba greenstone belts, limited to the east by the sinistral Tcholliré-Banyo Shear zone and to the south by the Poli Thrust System. The Djourdé-Sinassi magmatic-migmatitic complex is subdivided into a western magmatic domain made of diorite, tonalite, granodiorite, with numerous enclaves of mafic and ultramafic rocks, and an eastern domain dominated by metatexite migmatites enclosing ubiquitous mafic to ultramafic rafts. The plutonic rocks of the western domain display a gently dipping to vertical magmatic fabric with variable trends. Locally, trains of hornblendite enclaves with lobate boundaries and dismembered into a network of felsic veins points to injection of mafic magma that mingled with a host magmatic mush and/or partially molten rocks. The migmatites display a foliation delineated by the alternation of leucosome and mesosome layers, that are mainly subvertical and wrapped around the metric to kilometric size rafts of mafic and ultramafic rocks. A texturally continuous network of leucosome veins concordant to discordant relative to the syn-migmatitic foliation and the mineral assemblage attests for syntectonic melt segregation under granulite facies conditions (Hbl + Pl ± Bt ± Grt ± Opx ± Cpx; peak: ≥800 °C/8–10 kbar). The magmatic fabric of plutonic rocks and the syn-migmatitic foliation are locally transposed into subvertical shear zones with a steeply plunging mineral and stretching lineation. Kinematic criteria are identified in the subhorizontal plane perpendicular to the lineation, which indicates that deformation was not plane strain and occurred in 3D. N-S to NE-SW striking shear zones are sinistral whereas E-W to WNW-ESE trending ones are dextral. These shear zones first developed in the presence of melt but then under solid-state during progressive retrogression from amphibolite to greenschist facies (Ab+Qtz + Ep ± Op ± Chl + Ser + Ep). These data suggest that the Djourdé-Sinassi magmatic-migmatitic complex corresponds to the former root of the Central African Orogenic Belt originating from partial melting of a juvenile mafic crust. This root has been vertically extruded under a pure-shear dominated constrictional regime with vertical stretching in the presence of melt coeval with the injection of mantle-derived mafic magmas and was then progressively exhumed towards the surface. This deformation pattern is consistent with the position of the Sinassi complex surrounded by greenstone belts and on a larger scale, confined in between the West African – Congo craton and Saharan metacraton.

**Keywords:** Djourdé-Sinassi magmatic-migmatitic complex / mafic-ultramafic rocks / migmatites / Central African Orogenic Belt / vertical constriction / Cameroon

<footnote n="1">¹ University of Dschang, Faculty of Science, Department of Earth Sciences, P.O. Box. 67, Dschang, Cameroon</footnote>

<footnote n="2">² Centre for Geological and Mining Research, PO Box 333, Garoua, Cameroon</footnote>

<footnote n="3">³ GET, University of Toulouse, UPS, CNRS, IRD, CNES, 14 av. E. Belin, 31400, Toulouse, France</footnote>

<footnote>*Corresponding author: suzanne.tiani@univ-dschang.org</footnote>
**Résumé** – Complexe magmatique-migmatitique de Djourdé-Sinassi, Nord – Cameroun : témoin de l'extrusion verticale de la racine orogénique Pan-Africaine partiellement fondue. Le complexe magmatique-migmatitique de Djourdé-Sinassi fait partie du domaine Néoproterozoïque juvénile de Garoua, situé dans le Nord du Cameroun, entouré par les ceintures de roches vertes de Zalbi, Poli et Rey-Bouba, limité à l'est par la zone de cisaillement senestre de Tcholiré-Banyo et au sud par le système de faille de Poli. Le complexe magmatique-migmatitique de Djourdé-Sinassi est subdivisé en un domaine magmatique à l'ouest composée de diorite, tonalite, granodiorite et granite avec de nombreuses enclaves de roches mafiques et ultramafiques, et une partie à l'est dominée par des migmatites métatexitiques contenant des enclaves mafiques à ultramafiques omniprésentes. Les roches plutoniques à l'est présentent une fabrique magmatique légèrement pentée à verticale à orientation variable. Localement, des trains d'enclaves de hornblendite aux contours lobés et disloqués par un réseau de veines felsiques indiquent l'injection de magma mafique qui s'est mélangé avec une masse magmatique hôte et/ou des roches partiellement fondues. Les migmatites affichent une foliation définie par l'alternance de niveaux de leucosome et de mésosome, principalement subverticale suivant une direction parallèle à l'alignement des enclaves de roches mafiques et ultramafiques de taille métrique à kilométrique. Un réseau continu de veines de leucosome, concordant et discordant par rapport à la foliation syn-migmatitique, atteste d'une ségrégation syntenique du magma sous des conditions de faciès granulite (pic : ≥800°C/8–10 kbar). La texture magmatique des roches plutoniques et la foliation syn-migmatitique sont localement transposées en zones de cisaillement subverticales avec une linéation minérale et d'étirement à plongement fort. Des critères cinématiques sont identifiés dans le plan subhorizontal perpendiculaire à la linéation, ce qui indique que la déformation n'était pas plane et s'est produite en 3D. Les zones de cisaillement orientées N-S à NE-SW affichent des critères cinématiques senestres, tandis que celles orientées E-W à WNW-ESE sont dextres. Ces zones de cisaillement se sont d'abord développées en présence de magma, puis à l'état solide lors de la rétrogression progressive du faciès amphibolite au faciès schiste vert (Ab+Qtz + Ep ± Op ± Chl+Ser+Ep). Ces données suggèrent que le complexe magmatique-migmatitique de Djourdé-Sinassi représente un témoin de la racine de la Ceinture Orogénique d'Afrique Centrale, issue de la fusion partielle d'une croûte mafique juvénile. Cette racine a ensuite été extrudée verticalement sous un régime dominé par le cisaillement pur avec un étirement vertical en présence de magma, coïncidant avec l'injection de magmas mafiques dérivés du manteau, et a été progressivement exhumée vers la surface. Ce schéma de déformation est cohérent avec la position du complexe de Sinassi, entouré de ceintures de roches vertes et, à une échelle plus large, confiné entre les cratons Ouest-Africain – Congo et le métacraton du Sahara.

**Mots-clés** : complexe magmatique-migmatitique de Djourdé-Sinassi / roches mafiques-ultramafiques / migmatites / ceinture orogénique d' / Afrique centrale / constriction verticale / Cameroun

## Highlights

* Djourdé-Sinassi magmatic-migmatitic complex has recorded reworking of a juvenile mafic crust into migmatites and plutonic rocks that formed the root of the Central African Orogenic Belt.

* This root has then been vertically extruded under a pure-shear dominated constrictional regime with vertical stretching in the presence of melt.

* The shear zones which is located at the Djourdé-Sinassi magmatic-migmatitic complex has developed in the presence of melt but then under solid-state during progressive retrogression from amphibolite to greenschist facies.

# 1 Introduction

The Central African Orogenic Belt (CAfOB) also known as Central African Fold Belt (Fig. 1), lies between the West African Craton, Congo Craton and Saharan Metacraton (Bessoles and Trompette, 1980; Nzenti et al., 1988; Castaing et al., 1994; Abdelsalam et al., 2002; Toteu et al., 2004; Van Schmus et al., 2008; Liégeois et al., 2013; Jackson and

Ramsay, 1980; Kröner and Stern, 2004). It formed during the Pan-African orogeny as a result of the assembly of Gondwana Supercontinent during late Precambrian time (Trompette, 1997; Trompette, 2000). The Sinassi – Mayo Kebbi region marks the transition between the Adamawa-Yadé Domain with Paleoproterozoic and Archean inheritances, and the Western Cameroon Domain (Toteu et al., 2004) or North-Western Cameroon Domain (Bouyo Houketchang et al., 2009) dominated by juvenile Neoproterozoic rocks. It has been interpreted as a major batholith owing to the predominance of plutonic rocks with a calc-alkaline signature dated from ca. 750 to 580 Ma and to their locally intrusive contact into the low to medium grade greenstone belts (Penaye et al., 2006; Pouclet et al., 2006; Toteu et al., 2006; Isseini et al., 2012; Bouyo Houketchang et al., 2015, 2016). However, plutonic rocks of the Sinassi – Mayo Kebbi batholith are associated with migmatitic gneisses hosting a series of mafic to ultramafic rocks that were not fully considered in previous works. What is the timing of emplacement of the mafic to ultramafic magmas relative to the emplacement of intermediate to felsic plutons? Does partial melting occur as a consequence of magma intrusion or does it respond to crustal thickening? What is the significance of the structural record of these plutonic and metamorphic rocks? The goal of this paper is to address these questions by documenting the petro-structural and microstruc-
<figure><img src="image_2.png" /><figcaption>**Fig. 1.** (a) Geological map of the Pan-African belt north of the Congo craton (after Toteu et al., 2022) showing the Sinassi location with yellow star and the main lithotectonic domains. CCSZ: Central Cameroonian Shear Zone; TBSZ: Tibati-Banyo Shear Zone; NBSZ: Ngoro-Belabo Shear Zone; CC: Congo Craton; AYD: Adamawa-Yade Domain; YD: Yaoundé Domain; WCD: Western Cameroon Domain. (b) Cameroon Domain Geological sketch map of Northern Cameroon and Southwestern Chad (modified after Toteu et al., 2001; Pinna et al., 1994; Toteu et al., 2004; Bouyo Houketchang et al., 2015, 2016). TBF: Tchollire-Banyo Fault; NP: Neoproterozoic; PP: Paleoproterozoic. Inset: location of the study area within the network of the Pan-African belts of West and Central Africa. Solid Square: Central African Fold Belt (CAfOB); polygon: study area (Fig. 2).</figcaption></figure>

tural record of the metamorphic and plutonic rocks in order to characterize PT conditions and kinematic of deformation, and discuss the relative timing of magmatism, deformation and metamorphism within the Sinassi batholith that we name, in the following, the Djourdé-Sinassi magmatic-migmatitic complex.

## 2 Geological background

### 2.1 Central african orogenic belt

In Cameroon, the CAfOB had been originally subdivided into (1) the West Cameroon Domain, (2) the Adamawa-Yadé Domain and (3) the South Cameroon Domain (Ngnotué et al., 2000; Toteu et al., 2001, 2004). More recent geological mapping supported by new geochronological and geophysical data allowed to refine the geotectonic domains (into (1) the

Garoua Domain (GD); (2) the Bamenda-Tignère Domain (BTD); (3) the Nyong Bayomen Domain (NBD); and (4) the Extended Congo Craton Domain (ECCD) subdivided into the Adamawa-Yadé, Yaoundé, Ntem and Moloundou Sembé-Ouesso subdomains (Fig. 1a; Toteu et al., 2022).

The GD, including the Djourdé-Sinassi magmatic-migmatitic complex, extending to SW Chad into the Mayo Kebbi Domain (Penaye et al., 2006; Pouclet et al., 2006; Isseini, 2011) (Fig. 1b), is limited eastwards by the Tcholliré-Banyo Shear Zone (TBSZ) and southwards by the Poli Thrust System (PTS). The GD includes the Poli-Bibémi Greenstone Belt made-up of low to high grade schists and gneisses with a protolith age dated at ~830 Ma (Toteu et al., 1987, 2006) thrusting southward onto the BTD, and the Rey Bouba Greenstone Belt with a protolith age of ~670 Ma (Bouyo Houketchang et al., 2015) consisting of low to medium grade
schists located along the TBSZ. The Rey Bouba Greenstone Belt, composed of metapelite and metagrauwacke with a protolith that was deposited approximately between ~645 and ~630 Ma, underwent low-grade metamorphism around ~600 Ma. This belt has been interpreted as a basin supplied by a continental arc (Toteu et al., 1987, 2006; Pinna et al., 1994; Bouyo Houketchang et al., 2015; Mbanga et al., 2023). The BTD, extending to the SW of the GD, is in contrast, characterized by Paleo- to Mesoproterozoic basement including orthogneisses, micaschists, quartzites and high grade pelitic paragneisses and metabasites dated from ~2180 to <1400 Ma. This period marks the emplacement of a magmatic protolith occurring with granulitic metamorphism and the source of sediments respectively (Toteu et al., 2001; Penaye et al., 2004; Bouyo Houketchang et al., 2009, 2013; Delor et al., 2021). Both domains comprise pre- to post-tectonic calc-alkaline granitoid plutons dated from ~686 to ~563 Ma (e.g. Toteu et al., 2001, 2006; Penaye et al., 2006; Kwékam et al., 2010, 2020; Bouyo Houketchang et al., 2016; Tchameni et al., 2016; Nomo Negue et al., 2017), and post-tectonic alkaline granites and syenites forming small plutons dated between ~600–550 Ma (Dawaï et al., 2013, 2022; Noudiédié and Tcheumenak, 2023; Bello et al., 2024). These plutons have been interpreted as part of a magmatic arc formed in a subduction context. At the regional scale, they are aligned parallel to the NNE-SSW to NE-SW trending regional schistosity and include numerous mafic to ultramafic enclaves (e.g. Njanko et al., 2010; Fozing et al., 2015, 2021; Bouyo Houketchang et al., 2016; Njiki Chatué et al., 2020).

The structural record of the GD and BTD encompasses a low-grade amphibolite facies flat-lying foliation associated with isoclinal folds and a NW-SE trending stretching lineation attributed to a D₁ deformation phase of crustal thickening (Ngako et al., 1992; Nzenti et al., 1992). This foliation is transposed into sinistral strike slip shear zones, attributed to a D₂ deformation phase, marked by isoclinal folds with a vertical axial planar schistosity bearing an NNE-SSW to NE-SW trending mineral lineation developed under high grade amphibolite to granulite facies prograde metamorphism (Nzenti et al., 2007; Bouyo Houketchang et al., 2013) synchronous of intensive migmatization (Ngako, 1986). The D₂ is attributed to a regime of transpression with sinistral shear zones such as TBSZ. Subvertical dextral shear zones trending WSW-ENE, which are parallel to the Central Cameroon Shear Zone, are associated with the formation of mylonitic foliation under medium to low-grade amphibolite retrograde metamorphism. These zones also localize the emplacement of the syntectonic leucocratic granite veins, interpreted as related to D₃ deformation (Bouyo Houketchang et al., 2013; Dawaï, 2014; Fozing et al., 2015; Saha-Fouotsa et al., 2019). A last deformation phase D₄ has been invoked based on transposition of previous structures into regional-scale N-S and E-W trending ductile sinistral shear zones that controlled the emplacement of felsic veins (Fozing et al., 2015; 2021; Mbanga et al., 2023).

## 2.2 Tcholliré-banyo shear zone

The TBSZ is a NE-SW trending crust-scale shear zone initially interpreted as a dextral shear zone (Dumont, 1986) but

revised as a sinistral shear zone (Penaye et al., 1989; Ngako et al., 2008; Nomo Negue et al., 2017; Saha-Fouotsa et al., 2018). The TBSZ corresponds to the transposition of a shallowly dipping S₂ foliation/schistosity bearing a subhorizontal mineral stretching lineation, into a subvertical NE-SW striking mylonitic foliation (Ngako et al., 2008; Nomo Negue et al., 2017; Saha Fouotsa et al., 2018) and is considered to be the major boundary between the GD – BTD (former Western Cameroon Domain) and the Adamawa-Yadé Domain (Fig. 1, Toteu et al., 2001, 2004; Ganwa et al., 2008, 2016; Bouyo Houketchang et al., 2009; Nomo Negue et al., 2017; Tchakounté et al., 2017; Saha-Fouotsa et al., 2019; Delor et al., 2021). Deformation along the TBSZ was potentially active from ~650 to ~580 Ma on the basis of U/Pb zircon dating of syn-tectonic plutons (Penaye et al., 1989; Toteu et al., 2001; Saha-Fouotsa et al., 2019) which contain also zircon grains as old as ~719 Ma (Nomo Negue et al., 2017), which might be inherited from the source of the magma.

## 2.3 Geology of the djourdé-sinassi area

The first geological surveys in the study area were carried out by Koch (1959) and Schwoerer (1965). Subsequent works by Pinna et al. (1994), Penaye et al. (2006) and (Bouyo Houketchang et al. 2013, 2015, 2016) enabled to identify the main geological formations in the Djourdé-Sinassi area (Fig. 2):

- the Sinassi batholith, composed of granitoids described as a tonalite-trondhjemite-granodiorite suite associated with diorite and granite that contains enclaves of amphibolite/ultramafic rocks, is cross-cut by dykes of rhyolite and syenite and locally contain sulfur and gold (Penaye et al., 2006; Bouyo Houketchang et al., 2016);

- the Rey Bouba Neoproterozoic greenstone belt (RBGB; Pinna et al., 1994; Bouyo Houketchang et al., 2015; Mbanga et al., 2023), which marks the eastern edge of the Sinassi batholith and is intruded by the post-collisional Vaïmba granite;

- the Palaeozoic Mangbaï formations (Bea, 1987; Bea et al., 1990) and the Cretaceous Benoué sandstones, deposited in basins controlled by E-W and ESE-WNW trending faults, respectively and representing the post- Pan-African cover.

The granitoids of the Sinassi batholith exhibit a moderately to highly potassic calc-alkaline affinity with I-type metaluminous signature and moderate to weak negative Nb-Ta, Ti and Eu anomalies interpreted to reflect emplacement in a continental magmatic arc setting (Bouyo Houketchang et al., 2016). These granitoids have recorded P-T emplacement conditions of 4.04–5.82 kbar/698–728 °C and 4.23–5.76 kbar/667–720 °C using geothermobarometric calculations hornblende-plagioclase thermometry and aluminum-in hornblende barometry, in the Djourdé and Sinassi areas, respectively (Bouyo Houketchang et al., 2016). U/Pb geochronology on zircon grains from these magmatic rocks points to (i) sources with ages at ~746 Ma, ~722 Ma, ~713 Ma and ~692 Ma; (ii) emplacement ages at ~686–670 Ma (orthogneiss group), ~666–661 Ma (synchronous emplacement of the Djourdé and Sinassi granodiorites groups) and ~644 Ma (emplacement age of quartz-eyed diorites in the Sinassi group); and
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** A hillshade map with outcrop station highlights geological structures such as folds and faults by emphasizing variations in elevation. We use it by making geological contours visible.</figcaption></figure>

(iii) post-magmatic alteration or metamorphism at ~600 Ma (Bouyo Houketchang *et al.*, 2016).

Bouyo Houketchang *et al.* (2016) reported the presence of mafic and ultramafic rocks exposed as enclaves in the Sinassi batholith and that display foliation, lineation, folds, shear zones and fractures. The present work focusses on new petrographic data of mafic-ultramafic rocks and migmatitic gneisses, as well as the structural and microstructural characteristics of the Sinassi rocks, in order to update the available geological map from Bouyo Houketchang *et al.* (2016) (Fig. 2), and to unravel the kinematic evolution and the tectonic significance of the so-called Djourdé-Sinassi magmatic-migmatitic complex in the deformation history of CAfOB in Cameroon.

# 3 Methodology

## 3.1 Field data collection and processing

Several field campaigns enabled to map about 932 stations ((Fig. 2) in the study area. Structures were measured in the field and the projection of the poles of foliations, lineations and fold axes (directions and dips/plunge) was carried out using Stereonet v.11 software (Cardozo and

Allmendinger, 2013), in the lower hemisphere of the Schmidt diagram (Ragan, 1973).

## 3.2 Sample collection and processing for microstructural study

Fresh rock samples were collected in the field for microstructural analysis. The thin sections were made at the Geosciences Environnement Toulouse (GET) laboratory (Observatoire Midi-Pyrénées, France) and at the SARM Nancy (France) laboratory. A total of 55 thin sections were obtained from the selected rock samples, distributed as follows: migmatitic gneisses (02), amphibolites (17), pyroxenites (05), metahornblendites (07), metagabbros (03), hornblendites (03), diorites (07), tonalites (03), granodiorites (03) and mylonitic (grano)diorites (05) were observed using a polarizing optical microscope.

# 4 New geological map and lithological units

A refined geological map (Fig. 3) and tentative cross section (Fig. 3) are presented for the Djourdé-Sinassi complex based on new field observations, which highlights its
<figure><img src="image_4.png" /><figcaption>**Fig. 3.** New geological map of the study area (modified after Bouyo Houketchang et al., 2016) and tentative cross-sections NNW-SSE show the interpreted structures and possible lithological contacts respectively.</figcaption></figure>

subdivision into an eastern domain dominated by migmatitic rocks and a western domain made of plutonic rocks. The eastern domain of the Djourdé-Sinassi complex, exposes hectometer to kilometer thick mafic-ultramafic rafts that are parallel to the syn-migmatitic foliation of the host migmatitic gneiss and are more or less continuous over tens of kilometers at Sinassi, Tokormaye, Warkla, Koindéri, Vaimba 2, Bamboro, Mayo Sinassi, Mayo Warkla, New Warkla-Koindéri quarter district and eastwards of Laoubou. The plutonic rocks of the western domain encompass diorite, tonalite, granodiorite and granite in which mafic-ultramafic rocks are present as boudinaged or folded enclaves.

## 4.1 Mafic-ultramafic rocks

Mafic-ultramafic rocks comprise interlayered pyroxenite, metahornblendite, metagabbro and amphibolite that are exposed as more or less continuous and boudinaged rafts within the host migmatitic gneiss and are crosscut by a network of felsic veins. Boudins are angular to rounded, display a $S_{0/n}$ foliation, and are wrapped into the $S_{mgm}$ syn-migmatitic foliation (Fig. 4a, b and c) and the mylonitic foliation as well (Fig. 4d). The syn-migmatitic foliation is also affected by isoclinal folds with folded leucosomes (Fig. 4e). Asymmetrically folded and sigmoid-shape mafic boudins provide
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** Outcrop of mafic-ultramafic rocks. (a) Sigmoid-shaped pyroxenite boudins in migmatitic pyroxenite. (b) Sigmoid-shaped amphibolite boudins in migmatitic amphibolite. (c) Ovoid-shaped metahornblendite enclave rimmed by amphibolite bands concordant to the S<sub>mgm</sub> foliation. (d) Amphibolite enclaves hosted in mylonitic diorite. (e) F<sub>n+2</sub> isoclinal folded granitic vein in metahornblendite. (f) F<sub>n+3</sub> disharmonic folds of amphibolite showing sinistral motion within mylonitic granodiorite. (g) δ-type marker showing a dextral kinematic movement. (h) S<sub>0/n</sub> compositional banding developed in the banded garnet amphibolite. The illustrations were observed on subhorizontal planes.</figcaption></figure>
kinematic criteria (Fig. 4f and g). These features indicate that deformation occurred in the presence of melt that migrated into dilatation sites. Locally, all these structures are crosscut and transposed with a relic gneissic foliation that is subparallel (Fig. 4h).

Pyroxenite is made of subrhombic clino- and orthopyroxenes with a symplectic or poikiloblastic texture highlighted by hornblende inclusions (Fig. 5a). Quartz forms ocelli inclusions trapped within plagioclase or hornblende blasts. Pyroxenite locally alternates with metahornblendite and metagabbro. Metahornblendite displays a nematogranoblastic to porphyronematoblastic texture indicating the retromorphosis of clinopyroxene into hornblende and the overgrowth of sphene grains on opaque minerals (Fig. 5b). Metahornblendite locally contains leucite or quartz (Fig. 5c). Metagabbro shows a granonematoblastic texture with subrectangular or subrhombic green hornblende, clinopyroxene and zoned plagioclase blasts associated with scarce orthoclase and microcline blasts (Fig. 5d). Quartz generally appears as small grains at the edge or as ocelli inclusions within hornblende blasts. The preferred orientation of hornblende, clinopyroxene and plagioclase define a foliation that is locally mylonitic (Fig. 5e). Symplectite growths are noticed along mylonitic shear bands. Metagabbro is locally rimmed by amphibolite (Fig. 5f), which attests for the superposition of metamorphism and deformation on a former magmatic protolith. Amphibolites are mainly made of plagioclase blasts, and porphyroblastic hornblende (Fig. 5g) with a composition that falls within the ranges of edenite, magnesio-hornblende, magnesiorpargasite, ferro-hornblende, pargasite and actinolite. At Bamboro, a migmatitic amphibolite is characterized by alternation of mesosome and leucosome with subglobular garnet poikiloblasts that contain quartz, plagioclase and biotite inclusions, preferentially in the mesosome (Fig. 5h). Overall accessory mineral phases in these mafic-ultramafic rocks include apatite, zircon and opaque minerals; secondary phases encompass epidote, calcite, chlorite, prehnite, pumpelleyite and sericite.

The primary mineral assemblage in amphibolites is represented by Hbl±Grt + Bt + Pl. Relics of early assemblage (Cpx + Opx + Pl) from the low-pressure granulite facies (8-10 kbar/800-850 °C; Bucher and Frey, 2002; *Bucher and Grapes, 2011*) are found in pyroxenite and pyroxene metahornblendite (Fig. 5a and b). These relic assemblages show destabilization phases around the pyroxenes, indicating a retrograde metamorphism (Fig. 5a and b). In metagabbro, the metamorphic peak is defined by the mineral assemblage Cpx + Hbl + Pl, while the assemblage Grt + Hbl + Bt + Pl is developed in the garnet-bearing migmatitic amphibolite, characteristic of regional metamorphism in the high-grade amphibolite facies at high pressure (7-9 kbar/650-700 °C; *Bucher and Grapes, 2011*). Leucosome veins of tonalitic/dioritic/granodioritic composition in the migmatitic amphibolite point to partial melting, which requires a temperature of ~750 °C in anhydrous condition (*Rapp et al.*, 1991; *Wyllie and Wolf*, 1993; *Wolf and Wyllie*, 1994) or 650 °C in hydrous condition (*Green et al.*, 2016; *Palin et al.*, 2016). The presence of ubiquitous green hornblende porphyroblasts in these mafic-ultramafic rocks (Fig. 5), suggests pervasive amphibolite facies conditions reached at $T > 500-550°C$ (Pons, 2001;

*Bucher and Grapes, 2011*). Retrogression of pyroxene into actinolite and actinolitic hornblende is symptomatic of greenschist facies conditions at about 3–5 kbar/350–500 °C (Pons, 2001; *Bucher and Grapes, 2011*).

## 4.2 Migmatitic gneisses

Migmatitic gneisses derive mainly from mafic rocks (Fig. 6a). They grade from metatexite to diatexite and display diffuse contacts with granodioritic and granitic plutonic rocks (Fig. 6b). Migmatitic gneisses exhibit a syn-migmatitic foliation characterized by alternation of centimeters to decimeter thick mesosome layers made of hornblende and biotite, and leucosome layers made of plagioclase and quartz. (Fig. 6c and d). The mesosome and leucosome display a coarse grained texture. In the mesosome, the preferred orientation of hornblende and biotite defines a planar fabric. Interstitial plagioclase and quartz display only limited evidences for solid state deformation (Fig. 6e). This suggests that deformation occurred in the presence of a melt fraction that segregated to form a film in between residual crystals (Fig. 6f).

The syn-migmatitic foliation is transposed into a gneissic foliation defined by the preferred orientation of biotite/amphibole blasts in the mesosome and by quartz ribbons and feldspar blasts in the leucosome (Fig. 6g). The syn-migmatitic foliation displays a steeply-plunging $Le_{n+1}$ mineral stretching lineation defined by the alignment and preferred stretching of biotite/amphibole blasts in the melanosomes, or quartz ribbons and feldspar blasts in the leucosomes (Fig. 6h). The syn-migmatitic foliation is affected by isoclinal folds (Fig. 7a) and leucosome concordant veins are boudinaged (Fig. 7b). In the migmatitic gneiss, amphibole is magnesio-hastingsite and plagioclase is andesine. Accessory mineral phases are represented by sphene, apatite, zircon and opaque minerals, whilst secondary phases include epidote, chlorite, damourite and sericite.

The main mineral paragenesis in the migmatitic gneiss is Hbl + Bt + Pl + Qtz ± Kfs, which is diagnostic of amphibolite facies regional metamorphism (Fig. 6f). The absence of garnet and pyroxene in the mesosome indicates a pressure < 7–8 kbar (Wyllie and Wolf, 1993; Bucher and Frey, 1994). Widespread quartzofeldspathic leucosome veins associated with biotite-hornblende mesosome (Fig. 6e and f) point to *in situ* partial melting potentially in presence of water possibly followed by progressive dehydration-melting of biotite and hornblende (Le Breton and Thompson, 1988; *Rapp et al.*, 1991; *White et al.*, 2005; Weinberg and Hasalová, 2015). Rare potassium feldspar is observed in the mesosome or leucosome layers (Fig. 7c), thus evidencing *in situ* melting of a plagioclase-rich protolith at a temperature above 650 °C (Green *et al.*, 2016). Nevertheless, hornblende destabilizes into Bt + Qtz + Op ± Ep (Fig. 7d) and Qtz + Ep ± Op ± Chl (Fig. 7c). The persistency of epidote in these secondary mineral assemblages suggests a retrogression of hornblende under transition conditions from low-grade amphibolite facies to green schist facies (4–6 kbar/500–600 °C; *Bucher and Grapes, 2011*). Biotite stability suggests a temperature around ~600 °C (Bucher and Grapes, 2011). Hornblende and biotite are retrogressed in epidote and chlorite.
<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Microphotographs of mafic-ultramafic rocks. (a) Destabilization of pyroxene into amphibole + quartz + opaque. (b) Overgrown sphene grains around opaque minerals. (c) Leucite in metahornblendite. (d) Microcline blasts in metagabbro. (e) Granonematoblastic texture of metagabbro showing concordant fabric to the mylonitic foliation in the adjacent shear band. (f) Outcrop photographs showing contact between metagabbro, amphibolite and metahornblendite. (g) Porphyroblastic green hornblende in biotite amphibolite. (h) Poikiloblastic garnet showing inclusion of plagioclase-quartz-biotite in garnet amphibolite.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Fig. 6.** Outcrop photographs of migmatitic gneisses (a, b, d, g and h), (b): exposure showing migmatitic gneiss with a shallow dipping foliation delineated by concordant granitic veins, (c): sample of migmatitic gneiss showing the melanosome, leucosome and mesosome layers, (d) $S_{mgm}$ foliation affected by asymmetrical folds $F_{n+1}$, (e): quartzofeldspathic leucosome layers including biotite flakes, (f): Interstitial plagioclase between residual hornbelnde crystals, (h): Migmatites with a foliation transposed into the shear zone with a down-dip stretching lineation marking the transition from the Sinassi to the Djourdé domains.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>**Fig. 7.** Field structures and microphotographs in migmatitic gneiss: (a) sheath-like or isoclinal folds $F_{n+2}$ showing elliptical sections, (b) $B_{n+1}$ asymmetrical boudins, (c) Mesosome with hornblende, retrogressed into quartz, epidote, and opaques, and interstitial microcline and quartz, (d) Hornblende retrogressed into biotite+quartz+opaque.</figcaption></figure>

## 4.3 Plutonic rocks

Plutonic rocks comprise diorite, tonalite, granodiorite and granite, and display a magmatic planar fabric $S_m$. In the western domain of the studied area, the predominant plutonic rock is a heterogeneous granodiorite characterized by a coarse-grained dominantly magmatic texture. It is made of plagioclase, green hornblende, potassium feldspar, quartz and biotite flakes. The granodiorite contains angular enclaves of diorite made of plagioclase, quartz, potassium feldspar and green hornblende crystals (Fig. 8e). The granodiorite is cross-cut by shallow-dipping granitic sills (Fig. 8d) and by felsic veins with sharp contacts (Fig. 8c). At the regional scale, the granodiorite is in gradational contact with circular plutonic bodies of tonalite and granite. Tonalite is made of plagioclase, quartz and green hornblende phenocrysts, and biotite lamellas as well. Granite is made of quartz, potassium feldspar, plagioclase and green hornblende phenocrysts, and biotite lamellas as well. Accessory mineral phases include sphene, zircon, apatite and opaque crystals. In the eastern domain of the study area, granite dykes either concordant to the $S_{0/n}$ foliation in amphibolite wall rock (Fig. 8a) or discordant to the $S_{mgm}$ and $S_{0/n}$ foliations of their metamorphic host rocks (Fig. 8b).

Amphibolite and metagabbro are present as sub-rounded enclaves with straight boundaries in diorite, granodiorite and granite and are interpreted as equivalent of the mafic-ultramafic rafts of the eastern domain of the Djourdé-Sinassi complex (Fig. 8f). In contrast, the granitoids also contain trains of hornblendite enclaves dispersed into the granitic host and displaying lobate/diffuse magmatic contacts (Fig. 9a). Locally plagioclase crystals are incorporated into the hornblendite (Fig. 9b). The network of felsic veins that invades the hornblendite ranges from millimeter to centimeter in thickness, and are predominantly composed of plagioclase, quartz, hornblende and opaque crystals (Fig. 9c and d). These relationships point to magma mingling and mixing. Hornblendite outcrops are also cross-cut by bands of pyroxene metahornblendite that show straight boundaries (Fig. 9e).

In granitoid a $S_m$ magmatic fabric is marked by the preferred orientation of feldspar phenocrysts, amphibole needles or biotite flakes but also of schlieren and mafic-ultramafic enclaves distributed within the rock volume. $S_m$ magmatic fabric is cross-cut by $C_{n+1}$ syn-magmatic shear planes defined by the reorientation of biotite schlieren and feldspar phenocrysts obliquely to the main direction of the magmatic fabric (Fig. 10a). Textures range from medium- to
<figure><img src="image_9.png" /><figcaption>**Fig. 8.** Contact between the mafic-ultramafic rocks and the granitoids in the Sinassi area. (a): dyke of granite into mafic rocks, (b): Migmatitic amphibolite with steep dipping synmigmatitic foliation crosscut by granodioritic veins. (c): Granodiorite with shallow-dipping granitic vein. (d): Granodiorite with shallow-dipping granitic vein. (e): enclave of diorite with diffuse boundary in the host granodiorite, (f): Granodiorite with enclave that has preserved the contact between a metagabbro and an amphibolite.</figcaption></figure>

coarse-grained, with development of magmatic, submagmatic to solid-state microstructures. Euhedral feldspar and amphibole crystals, and biotite flakes are devoid of intracrystalline deformation (Fig. 10b). Plagioclase forms synneusis aggre-

gates with local zoning and with the development of magmatic myrmekite buds on the edges of feldspars (Fig. 10c), associated with microfractures affecting feldspar crystals and sealed by plagioclase or quartz late melts. Quartz mostly
<figure><img src="image_10.png" /><figcaption>**Fig. 9.** Relationships of hornblendites and metahornblendites with felsic rocks (a, b, c and e). (a) lobate or diffuse magmatic contacts (b): magmatic contact between hornblendite and granodiorite, (c): magmatic contact between hornblendite and host diorite, (d): Felsic vein in diffuse contact with host hornblendite. (e): interlayered pyroxene metahornblendite and hornblendite.</figcaption></figure>

displays a homogeneous extinction but is locally marked by a chessboard texture and lobate grain boundaries indicative of high-temperature dynamic recrystallization (Fig. 10d). High-temperature solid state deformation is also attested by bended

feldspar twins and kink bands in plagioclase. Feldspar crystals are intensely transformed into sericite or damourite whilst biotite flakes are locally recrystallized into chlorite and hornblende into epidote, which marks retrogression and
<figure><img src="image_11.png" /><figcaption>**Fig. 10.** Field structures and microstructures in the granitoids. (a): S<sub>m</sub> magmatic fabric reoriented by C<sub>n+1</sub> synmagmatic sinistral shear zone, (b): magmatic texture with euhedral feldspar crystals, (c): myrmekitic buds along plagioclase rim, (d): chessboard pattern of quartz crystal, (e): plagioclase affected by kink band and damouritization, (f): mylonite fabric defined by quartz ribbons, (g): anticlockwise bookshelf structure, (h): asymmetric porphyroclasts of feldspars describing the sinistral motion.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Fig. 11.** Litho-structural map showing field foliation and planar fluidity with lower hemisphere equal area projection stereograms (contour intervals = 1σ) of the metamorphic, migmatitic, mylonitic and planar fluidity rocks.</figcaption></figure>

hydrothermal alteration (Fig. 10e). S<sub>m</sub> magmatic fabric is transposed into mylonite fabric along localized sinistral or dextral shear zones (Fig. 10f). This mylonite fabric is associated with asymmetric quartz ribbons and feldspar porphyroclasts. (Fig. 10g and h).

**5 Regional structural trends**

The Djourdé-Sinassi magmatic-migmatitic complex displays a complex polyphased structure. The S<sub>0/n</sub> foliation preserved in the mafic-ultramafic rafts, as illustrated at Mayo Sinassi and Mayo Tokormaye stations, is E-W striking and is steeply dipping, parallel to the preferred orientation of the rafts (Fig. 11). The strike of this S<sub>0/n</sub> foliation is subparallel to the foliation in the adjacent Rey Bouba greenstone belt, except that the latter is shallowly dipping (Fig. 2). The mafic-ultramafic rafts are wrapped into the S<sub>mgm</sub> syn-migmatitic foliation that is ENE-WSW striking and is steeply dipping (Fig. 11). This S<sub>mgm</sub> syn-migmatitic foliation is parallel to the S<sub>2</sub> foliation

trajectories in the Rey Bouba greenstone belt and to the trend of the TBSZ. All structures are transposed into NE-SW striking steeply dipping sinistral and E-W dextral shear zones bearing a subvertical L<sub>n+1</sub> mineral and stretching lineation (Fig. 12).

In the plutonic domain of the Djourdé-Sinassi complex, the structure is mostly characterized by a gently to steeply dipping (21°-90°) magmatic planar fabric S<sub>m</sub> in tonalite, granodiorite, granite and diorite with variable strikes (Fig. 11). This magmatic fabric is locally transposed into the sinistral and dextral shear zones identified in the migmatitic domain. Indeed, this S<sub>m</sub> magmatic fabric is transposed into NE-SW striking steeply dipping S<sub>n+2</sub> foliation bearing a steeply SW plunging L<sub>n+2</sub> mineral and stretching lineation with a mean of N033°E/74°SW (Fig. 12). This transposition is marked by asymmetric folds with axes with a mean orientation N067°E/52°SW (Fig. 12) and by sigmoid-shape boudins consistent with a sinistral sense of shear.

The contact between the migmatitic domain and the plutonic domain of the Djourdé-Sinassi complex, is marked, in
<figure><img src="image_13.png" /><figcaption>**Fig. 12.** Litho-structural map showing mineral stretching lineation and fold axes with lower hemisphere equal area projection stereograms (contour intervals = 1σ) of the metamorphic, migmatitic, mylonitic and magmatic rocks.</figcaption></figure>

the southern domain of the studied area, by a NE-SW trending subvertical sinistral mylonitic shear zone characterized by sheath folds with a steeply dipping axis, subparallel to the stretching lineation. This mylonitic shear zone is parallel to the sinistral TBSZ (Fig. 6d, g, h). In the northern domain of the studied area, the contact between the migmatitic domain and the plutonic domain is marked by a E-W trending subvertical dextral mylonitic shear zone. No crosscutting relationships have been identified between these shear zones.

# 6 Discussion

## 6.1 Significance of the relationships between mafic-ultramafic rocks, migmatites and granitoid plutons

Based on mineralogical, geochemical and geochronological data, Bouyo Houketchang et al. (2016) proposed that the Sinassi batholith is the Cameroonian extension of the Mayo Kebbi batholith in south-eastern Chad (e.g. Penaye et al., 2006; Pouclet et al., 2006; Isseini et al., 2012), both recording an identical tectonic-magmatic evolution during Neoproterozoic times. Considering these previous studies, recent petrographic observations, including migmatitic gneisses and mafic-ultramafic rocks that locally form migmatites with various meso-scale field relationships reflecting different structural

levels, indicate a need to reinterpret the regional significance of the Djourdé-Sinassi magmatic-migmatitic complex.

Migmatitic gneisses of the Djourdé-Sinassi complex, especially in the eastern domain of the studied area, correspond to metatexites that represent former partially-molten rock, in agreement with criteria based on the continuity of the syn-migmatitic foliation (Sawyer, 1994; Vanderhaeghe, 2001, 2009). Pyroxenite, metahornblendite and metagabbro are surrounded by amphibolite, which attest for deformation and metamorphism of the mafic-ultramafic rafts (see Figs. 4c, 5f). The diffuse contact of these rafts with the mesosome of the host migmatites suggests that these rocks represent, at least in part, the protoliths of the migmatites. Partial melting of a mafic rock leaves a residue rich in plagioclase and pyroxene and produces a tonalitic/dioritic/granodioritic melt (Bonzi et al., 2021). Expected peritectic phases (e.g. pyroxene, garnet) from amphibole-consuming dehydration melting reactions are absent in tonalite/diorite/granodiorite, but are present in pyroxenites and migmatitic amphibolite. The network of texturally continuous felsic veins concordant to discordant relative to the syn-migmatitic foliation of migmatitic amphibolite and metatexite migmatite (see Fig. 8a) is interpreted to represent channels for migration of granitic melt (see Fig. 8b). Mafic-ultramafic rocks contain patches, felsic veins that might reflect evidences of *in situ* partial
melting or infiltration of the nearby generated melt into residual solids (see Figs. 4a, b, g and 5f). Overall, the distribution of leucosome veins within foliation, boudins necks, fold axial planes and shear planes, suggests that deformation played a key role in the segregation and migration of magma (Brown and Rushmer, 1997; Vanderhaeghe, 2001; Toé et al., 2013).

Heterogeneous granodiorite/diorite/tonalite, exposed in the western domain of the studied area, characterized by their richness in mafic-ultramafic enclaves (see Fig. 9a), are consistent with diatexite migmatite representing a deeper structural level compared to the metatexite migmatite. This is consistent with the estimated PT conditions using geo-thermobarometric calculations (hornblende-plagioclase thermometry and aluminum-in hornblende barometry) pointing to a depth of ~16–18 km documented by magmatic petrology (Bouyo Houketchang et al., 2016). Nevertheless, this proposition of an origin of plutonic rocks by *in situ* partial melting of mafic rocks does not preclude an intrusion of mantle-derived magmas. Indeed, the diffuse and cuspate contacts between some hornblendite and diorite to granodioritic magmatic rocks points to mingling associated with some mixing (Chappell, 1996). Furthermore, the dismembered aspect of some hornblendite enclaves (Fig. 5b) and round-to ovoid-shaped hornblendite enclaves, suggests that they formed by injection of ultramafic melt in a host granodioritic/tonalitic magma and/or partially molten rock (Dorais et al., 1990; Blundy and Sparks, 1992; Bonin, 2004). Some hornblendite enclaves have included feldspar crystals originating from their dioritic/granodioritic host (Fig. 5a, b). Their presence reveals that they have been mechanically included in the enclave when it was not completely crystallized (Didier, 1984; Solgadi et al., 2007; Nédélec and Bouchez, 2011). Similar field relationships between mafic-ultramafic enclaves and their host rocks have been also described in the Mbe – Sassa-Mbersi granitoids (Saha-Fouotsa, 2018), the Numba pluton (Njiki Chatué, 2021), the Pitoa pluton (Happi Djofna, 2024) and in a worldwide review (e.g. Weinberg et al., 2021).

## 6.2 Tectonic significance of the fabric of plutonic rocks and migmatites of the Djourdé-Sinassi complex: constriction with vertical stretching in the core of the CAFOB

The structural and petrological features presented above indicate that deformation of the Djourdé-Sinassi magmatic-migmatitic complex was dominated by a vertical direction of stretching coeval with NE-SW trending sinistral shearing and WNW-ESE dextral shearing in the horizontal plane, perpendicular to the stretching lineation. The resulting finite strain ellipsoid is in the constriction field. This deformation started in the presence of melt and continued during progressive retrogression. At the lowest structural level, the magmatic fabric of the tonalite and granodiorite delineates kilometer scale domes. Local constriction might be localized in triple points between domes such as described in the east Pilbara craton (Western Australia) where the formation of domes and constriction have been attributed to partial convective overturn (Collins et al., 1998). At higher structural, constriction is rather

evidenced by mutual crosscutting relationships between dextral and sinistral shear zones. The overall subvertical foliation and strike-slip shear zones with a down-dip lineation reflects a vertically elongated finite deformation ellipsoid within the constriction field with strain accommodation alongside subvertical strike-slip shear zones marked by vertical flattening and stretching (Gapais et al., 2008; Cagnard et al., 2007; Fueten and Robin, 1989). This is consistent with the vertical orogen-parallel flow mode of Chardon et al. (2009) but with a vertical direction of stretching. The steep plunge of lineation points to a pure-shear dominated transpression (Fossen and Tikoff, 1993) and the parallelism between lineation and axes of isoclinal folds are diagnostic of a shear-component at a low-angle to fold axes, as illustrated by the model of Tikoff and Peterson (1998). This deformation regime was coeval to injection of mafic magmas and was then recorded during progressive retrogression from granulite to amphibolite facies and even greenschist facies, which suggests progressive exhumation of these rocks. From a regional overview, this subvertical constrictional strain has never been described wherever in the GD and BTD. However, similar observation of steeply-plunging streaks and lineation were made in the neighboring Mbé – Sassa-Mbersi region by Saha-Fouotsa (2018) and Saha-Fouotsa et al., (2019).

## 7 Conclusion and perspectives

- The Djourdé-Sinassi magmatic-migmatitic complex comprises an eastern domain made of a heterogeneous assemblage of migmatitic gneisses including rafts and enclaves of mafic-ultramafic rocks (pyroxenites, metahornblendites metagabbros and amphibolites), and a western domain made of diorite, tonalite and granodiorite plutons mingled with ultramafic magmas (hornblendites) and containing numerous mafic enclaves.

- The polyphase structure of the Djourdé-Sinassi complex is characterized by a $S_{0/n}$ foliation preserved in the mafic-ultramafic rocks that is wrapped into the syn-migmatitic foliation of the host migmatites. Deformation, partial melting and melt segregation-migration were coeval as attested by a texturally continuous network of leucosome veins concordant to discordant relative to the syn-migmatitic $S_{mgm}$ foliation is boudinaged, affected by isoclinal folds and transposed into subvertical NE-SW and WSW-ENE striking shear zones bearing a subvertical mineral and stretching lineation and associated with sinistral and dextral kinematic criteria, respectively. At the lowest structural level exposed in the western domain of the studied area, plutonic rocks are characterized by a gently to steeply dipping planar magmatic fabric locally transposed into sinistral and dextral shear zones parallel to the ones identified in the eastern migmatitic domain.

- Mineral parageneses, textures and microstructures highlight a metamorphism under granulite facies (peak: ≥ 800 °C/8–10 kbar) associated to partial melting, melt segregation and migration to form migmatites and plutons, followed by retrogression in the greenschist facies conditions (≤ 500 °C/3–5 kbar) along shear zones.
- The Djourdé-Sinassi magmatic-migmatitic complex represents the exhumed mid- to lower structural level of the orogenic root of the Central African Orogenic Belt deformed in a non-plane strain 3D regime with a vertical stretching direction associated with non-coaxial deformation in the horizontal plane, resulting in a finite strain ellipsoid in the constriction field. Persistence of this regime from high-grade metamorphism in the presence of melt to retrogression under greenschist facies is consistent with progressive vertical extrusion and exhumation of these rocks. This peculiar tectonic pattern might be related to the position of the Djourdé-Sinassi magmatic-migmatitic complex, surrounded by greenstone belts and confined between the West African Craton, the Congo Craton and the Sahara Metacraton.

## Acknowledgments

This manuscript is part of the first author's PhD thesis. Dr. Ngassam Mbianya Ghislain is highly acknowledged for constructive discussions during field works. We would like to thank Mr. Tchikri Koi for invaluable support during field works. Mr. Ouing Michelle is acknowledge for his hospitality and the facilities allowed during field trips. We also want to thank Dr. Kamguia Woguia Brice and Mr. Tchouandom Eric who significantly contributed to improve the language quality of first version of the present paper. Fabienne De Parseval at GET and the SARM team at the CRPG Nancy are thanked for the very nice thin sections. This project was financially supported by the CNRS LithoCOAC project and IRN FALCoL as well as the French Embassy in collaboration with the Agence Universitaire de la Francophonie (AUF), which covered analytical costs and the travel and daily expenses of the first author in Toulouse, France.

## Conflicts of interest

The authors declare that they have no competing interests or personal relationships that could have influenced the data presented in this manuscript.

## Data availability statement

The data used to support the findings of this study are available from the corresponding author upon request.

## References

- Abdelsalam MG, Liégeois JP, Stern RJ. 2002. The Saharan metacraton. J Afr Earth Sci 34: 119-136.

- Bea A. 1987. Grabens et volcanisme tholéitique continental associé, d'âge Ordovicien-Dévonien probable, dans la région de Garoua, au Nord-Cameroun. These Doctorat 3ème Cycle, Universite Aix-Marseille III, 170p.

- Bea A, Cochemé JJ, Trompette R, Affaton P, Soba D, Sougy J. 1990. Grabens d'âge Paléozoïque inférieur et volcanisme tholéitique associé dans la région de Garoua, Nord Cameroun. J Afr Earth Sci 10: 657-667.

- Bello A, Dawaï D, Antonio PYJ, Laurent O, Dopico CIM, Tchameni R, Vanderhaeghe O. 2024. The deformed alkaline Balda granite (Northern Cameroon): a witness of back-arc basin in the northern part of Central African Orogenic Belt. Precambrian Res 410: 107490.

- Bessoles B, Trompette R. 1980. Geologie de l'Afrique. La chaîne Pan-Africaine: "zone mobile d'Afrique Centrale (partie sud) et zone mobile soudanaise". Memoire. BRGM France, 92, 396.

- Blundy JD, Sparks RSJ. 1992. Petrogenesis of mafic inclusions in granitoids of the Adamelo Massif, Italy. J Petrol 33: 1039-1104.

- Bonin B. 2004. The coeval mafic and felsic magmas in postcollisional to within plate regimes necessarily imply two constrasting, mantle and crustal sources? A review. Lithos 78: 1-24.

- Bonzi WME, Vanderhaeghe O, Van Lichtervelde M, Wenmenga U, André-Mayer AS, Salvi S, Poujol M. 2021. Petrogenetic links between rare metal-bearing pegmatites and TTG gneisses in the West African Craton: The Mangodara district of SW Burkina Faso. Precambrian Res 364: 106359.

- Bouyo Houketchang M, Toteu SF, Deloule E, Penaye J, Van Schmus WR 2009. U-Pb and Sm-Nd dating of high-pressure granulites from Tcholliré and Banyo regions: evidence for a Pan-African granulite faciès metamorphism in north-central Cameroun. J Afr Earth Sci 54: 144-154.

- Bouyo Houketchang M, Penaye J, Barbey P, Toteu SF, Wandji P. 2013. Petrology of high-pressure granulite facies metapelites and metabasites from Tcholliré and Banyo regions: Geodynamic implication for the Central African Fold Belt (CAFB) of north central Cameroon. Precambrian Res 224: 412-433.

- Bouyo Houketchang M, Zhao Y, Penaye J, Zhanga SH, Njelb UO. 2015. Neoproterozoic subduction-related metavolcanic and meta-sedimentary rocks from the Rey Bouba Greenstone Belt of north-central Cameroon in the Central African Fold Belt: New insights into a continental arc geodynamic setting. Precambrian Res 261: 40-53.

- Bouyo Houketchang M, Penaye J, Njelb UO, Moussango API, Sep JPN, Nyama BA, Wassouo, WJ, Abat JME, Yaya F, Mahamat A, Ye H, Wu F. 2016. Geochronological, geochemical and mineralogical constraints of emplacement depth of TTG suite from the Sinassi Batholith in the Central African Fold Belt (CAFB) of northern Cameroon: Implications for tectonomagmatic evolution. J Afr Earth Sci 116: 9-41.

- Brown M, Rushmer T. 1997. The role of deformation in the movement of granitic melt: views from the laboratory and the field. In: Holness, M.B. (Ed.), Deformation enhanced fluid transport in the Earth's crust and mantle. The Mineralogical Series. Chapman & Hall pp. 111-144.

- Bucher K, Frey M. 1994. Petrogenesis of metamorphic rocks. Springer-Verlag, Berlin, Heidelberg, 318p.

- Bucher K, Grapes R. 2011. Petrogenesis of metamorphic rocks. Springer Science & Business Media. https://doi.org/10.1007/978-3-540-74169-5

- Cagnard F, Gapais D, Barbey P. 2007. Collision tectonics involving juvenile crust: the example of the southern Finnish Svecofennides. Precambrian Res 154: 125-141.

- Cardozo N, and Allmendinger RW. 2013. Spherical projections with OSXStereonet. Comput Geosci 51: 193-205.

- Castaing C, Feybesse JL, Thieblemont D, Triboulet C, Chevremont P. 1994. Paleogeographical reconstructions of the Pan-African/Brasiliano orogen: closure of an oceanic domain or intra-continental convergence between major blocks. Precambrian Res 69: 327-344.

- Chardon D, Gapais, D, Cagnard F. 2009. Flow of ultra-hot orogens: a view from the Precambrian, clues for the Phanerozoic. Tectono-physics 477: 105-118.
Chappell BW. 1996. Magma Mixing and the Production of Compositional Variation within Granite Suites: evidence from the Granites of Southeastern Australia. J Petrol 37: 449–470.

Collins WJ, Van Kranendonk MJ, Teyssier C. 1998. Partial convective overturn of Archaean crust in the East Pilbara craton, Western Australia: driving mechanisms and tectonic implications. J Struct Geol 20: 1405–1424.

Dawaï D. 2014. Les plutons de Guider et de Bossou-Pologozom (chaîne Pan-Africaine au Nord Cameroun) : analyses pétrographique, structural, magnétique, géochronologique et implications géodynamiques. [Ph.D. Thesis, University of Toulouse]. 208p.

Dawaï D, Bouchez JL, Paquette, JL, Tchameni R. 2013. The Pan-African quartzsyenite of Guider (North-Cameroon): magnetic fabric and U-Pb dating of a late-orogenic emplacement. Precambrian Res 236: 132–144.

Dawaï D, Saha Fouotsa NA, Bello A, Tchameni R, Nédélec A, Bouchez J-C. 2022. Petrology of the late Pan-African Guider syenite pluton (Cameroon): implications for magma genesis and emplacement. J Afr Earth Sci 190: 104519.

Delor C, Bernard J, Tucker RD, Roig J-Y., Bouyo Houketchang M, Couëffé R, Blein O. 2021. Carte géologique du Cameroun à 1/1 000 000. Ministère des Mines de l'Industrie et du Développement Technologique, 2ème édition.

Didier J. 1984. The problem of enclaves in granitic rocks, a review of recent ideas on their origin. In: Xu, K., Tu, G. (eds) Geology of Granites and Their Metallogenic Relations. Beijing: Science Press, pp. 137–144.

Dorais MJ, Whitney JA, Roden MF. 1990. Origin of mafic enclaves in the Dinkey Creek Pluton, Central Sierra Neveda Batholith, California. J Petrol 31: 853–881.

Dumont JF. 1986. Identification par télédétection de l'accident de la Sanaga (Cameroun) : Sa position dans le contexte des grands accidents d'Afrique Centrale et la limite nord du craton congolais. Géodynamic 1: 13–19.

Fossen H, Tikoff B. 1993. The deformation matrix for simultaneous simple shearing, pure shearing and volume change, and its application to transpression-transtension tectonics. J Struct Geol 15: 413–422.

Fozing EM, Njanko T, Seta N, Kwékam M, Njonfang E, Rochette P. 2015. Structural characterization of the Misajé granitic pluton (NW Cameroon): constraints from magnetic and field observations. Int J Afr Earth Sci. https://doi.org/10.1007/s00531-015-1288-6.

Fozing EM, Kwékam M, Tcheumenak Kouémo J, Njanko T, Njonfang E. 2021. Kinematic analysis of the Dschang granitic pluton (West-Cameroon): implications to the Pan-African deformation of the Central African fold belt in Cameroon during the post-collisional history of western Gondwana. Precambrian Res 359: 106231.

Fueten F, Robin PY. 1989. Structural petrology along a transect across the Thompson Nickel Belt, Manitoba: dip slip at the western Churchill-Superior boundary. Can J Earth Sci 26: 1976–1989.

Ganwa A, Frisch W, Siebel W, Shang KC, Ondoa MJ, Satir M, Numbem TJ. 2008. Zircon $^{207}$Pb/$^{206}$Pb evaporation ages of Panafrican metasedimentary rocks in the Kombé-II area (Bafia Group, Cameroon): Constraints on protolith age and provenance. J Afr Earth Sci 51: 77–88.

Ganwa AA, Klötzli US, Hauzenberger C. 2016. Evidence for Archean inheritance in the pre-Panafrican crust of Central Cameroon: insight from zircon internal structure and LA-MC-ICP-MS U-Pb ages. J Afr Earth Scis 120: 12–22.

Gapais D, Pelletier A, Ménot R-P., Peucat J-J. 2008. Paleoproterozoic tectonics in the Terre Adélie craton (East Antarctica). Precambrian Res 162: 531–539.

Green ECR, White RW, Diener JFA, Powell R, Holland TJB, Palin RM. 2016. Activity-composition relations for the calculation of partial melting equilibria in metabasic rocks. J Metamorph Geol 34: 845–869.

Happi Djofna CR. 2024. Pétrologie et analyse structural des formations métamorphiques et plutoniques du secteur Est de Pitoa : implication géodynamique de la Chaîne Panafricaine au Nord Cameroun. [Ph.D. Thesis, University of Ngaoundéré], 240p.

Isseini M. 2011. Croissance et différenciation crustale au Néo-protérozoïque: Exemple du domaine panafricain du Mayo Kébbi au Sud-Ouest du Tchad. [Thèse de Doctorat/Ph.D., Université Henri Poincaré-Nancy 1], 345p.

Isseini M, André-Mayer AS, Vanderhaeghe O, Barbey P, Deloule E. 2012. A type granite from the Pan-African orogenic belt in southwestern Chad constrained using geochemistry, Sr-Nd isotopes and U-Pb geochronology. Lithos 153: 39–52.

Jackson NJ, Ramsay CR. 1980. What is the “Pan-African”? A consensus is needed. Geology 8: 210–211.

Kröner A, and Stern RJ. 2004. Pan-African Orogeny. Encyclopedia Geol 1: 1–12.

Koch P. 1959. Carte géologique de reconnaissance du Cameroun à l'échelle du 1/500 000, feuille Garoua-Ouest avec notice explicative. Direction des Mines et de la Géologie du Cameroun, 48p.

Kwékam M, Liégeois JP, Njonfang E, Affaton P, Hartmann G, Tchoua FM. 2010. Nature, origin and significance of the Fomépéa Pan-Africain high-K calc-alkaline plutonic complex in the Central Africa Fold Belt (Cameroon). J Afr Earth Sci 57: 79–95.

Kwékam M, Dunkl I, Fozing EM, Hartmann, G, Njanko T, Tcheumenak KJ, Njonfang E. 2020. Syn-kinematic ferroan high-K I-type granites from Dschang in southwestern Cameroon: U-Pb age, geochemistry and implications for crustal growth in the late Pan-African orogeny. Geolog Soc London, Special Publ 502 https://doi.org/10.1144/SP502-2019-19.

Le Breton N, Thompson AB. 1988. Fluid-absent (dehydration) melting of biotite in metapelites in the early stages of crustal anatexis. Contrib Mineralog Petrol 99: 226–237.

Liégeois JP, Abdelsalam MG, Ennih N, Ouabadi A. 2013. Metacraton: nature, genesis and behavior. Gondwana Res 23: 220–237.

Mbanga FA, Moussango Ibohn PA, Nlomngan Sep JP, Mahamat A, Wadjou Wassouo J, Fodoué Y, Essi Abaté JM, Liou Guedala A, Mounoumeck VP, Njel OU. 2023. Structures and petrography of the Neoproterozoic Rey Bouba Greenstone Belt in the Northern Cameroon: implications for deformational characterization. Arab J Geosci 16: 67.

Nédélec A, Bouchez JL. 2011. Pétrologie des granites, structure, cadre géologique. Collection Interaction, Vuibert, 320 p.

Ngako V. 1986. Evolution métamorphique et structurale de la bordure Sud-Ouest de la « série de Poli » (segment Camerounais de la chaîne Pan-Africaine). Mémoires et Documents du Centre Armoricain d'Etude Structurale des Socles 5: 185p.

Ngako V, Jégouzo P, Nzenti JP. 1992. Champ de raccourcissement et de cratonisation du Nord Cameroun du Paléozoïque supérieur au Paléozoïque moyen. Compte Rendu de l'Académie des Sciences de Paris 315: 371–377.

Ngako V, Affaton P, Njonfang E. 2008. Pan-African tectonics in northwestern Cameroon: Implication for the history of western Gondwana. Gondwana Res. 14: 509–522.
Ngnotué T, Nzenti JP, Barbey P, Tchoua FM. 2000. The Ntui-Bétamba highgrade gneisses: a northward extension of the Pan-African Yaoundé gneisses in Cameroon. *J Afr Earth Sci* 31: 369–381.

Njanko T, Nédélec A, Kwékam M, Siqueira R, Esteban L. 2010. Emplacement and deformation of the Fomopéa pluton: Implication for the Pan-African history of Western Cameroon. *J Struct Geol* 3: 306–320.

Njiki Chatué C. 2021. Évolution structurale et pétrogenèse du pluton granitique de Numba (SW- Cameroun) : Implication géodynamique. [Ph.D. Thesis, University of Dschang], 274p.

Njiki Chatué C, Njanko T, Fozing EM, Bella Nké BE, Séta N, Njonfang E. 2020. Field observations, magnetic fabrics and microstructures evidences of syn-kinematic emplacement of the Numba granitic pluton (western Cameroon domain). *J Afr Earth Sci* 172: 104009.

Nomo Negue E, Tchameni R, Vanderhaeghe O, Fengyue S, Barbey P, Tekoum Lé Fosso, PM, Eglinger A, Saha Fouotsa NA. 2017. Structure and LA-ICP-MS zircon U-Pb dating of syn-tectonic plutons emplaced in the Pan-African Banyo-Tcholliré shear zone (central north Cameroun). *J Afr Earth Sci* 131: 251–271.

Noudiédié Kamgang JA, and Tcheumenak Kouemo J. 2023. Structural analysis of the Banyo syenitic pluton: Implication for its synkinematic emplacement and correlations to Gode Gormaya and Rocher du Loup shear zones – Related Pan-African N-S syenites. Solid Earth Sci. https://doi.org/10.1016/j.sesci.2023.05.003

Nzenti JP, Barbey P, Macaudiere JP, Soba D. 1988. Origin and evolution of the late Precambrian high grade Yaounde gneisses (Cameroon). Precambrian Res 38: 91–109.

Nzenti JP, Ngako V, Kambou R, Penaye J, Bassahak & Njel OV. 1992. Structures régionales de la chaîne Pan-Africaine au Nord-Cameroun. Compt Rend Acad Sci, Paris 611 : 115-119.

Nzenti JP, Njiosseu TEL, & Nzina Nchare A. 2007. The metamorphic evolution of the Paleoproterozoic high grade Banyo gneisses (Adamawa, Cameroon, Central Africa). *J Cameroon Acad Sci* 7: 95–109.

Palin RM, White RW, Green ECR. 2016. Partial melting of metabasic rocks and the generation of tonalitic-trondhjemitic-granodioritic (TTG) crust in the Archaean: constraints from phase equilibrium modelling. Precambrian Res 287: 73–90.

Penaye J, Toteu SF, Michard A, Bertrand JM, Dautel D. 1989. Reliques granulitiques d'âges protérozoïque inférieur dans la zone mobile panafricaine d'Afrique centrale au Cameroun; géochronologie U-Pb sur zircon au Cameroun. Compte Rendu de l'Académie des Sciences de Paris 309: 315-318.

Penaye J, Toteu SF, Tchameni R, Van Schmus WR, Tchakounté J, Ganwa A, Minyem D, Nsifa EN. 2004. The 2.1 Ga West Central African belt in Cameroon: extension and evolution. *J Afr Earth Sci* 39: 159–164.

Penaye J, Kröner A, Toteu SF, Van Schmus WR, Doumnang JC. 2006. Evolution of the Mayo Kébbi region as revealed by zircon dating: an early (ca. 740 Ma) Pan-African magmatic arc in southwestern Chad. *J Afr Earth Sci* 44: 530–542.

Pinna P, Calvez JY, Abessolo A, Angel JM, Mekoulou Mekoulou T, Mananga G, Vernhet Y. 1994. Neoproterozoic events in the Tcholliré area: Pan-African crustal growth and geodynamics in central-northern Cameroon (Adamawa and North Provinces). *J Afr Earth Sci* 18: 347–353.

Pons JC. 2001. La petro sans peine –2. Minéraux et roches métamorphiques. C.P.D.P. Académie de Grenoble 228p.

Pouclet A, Vidal M, Doumnang JC, Vicat JP, Tchameni R. 2006. Neoproterozoic crustal evolution in Southern Chad: Pan-African

ocean basin closing, arc accretion and late- to post-orogenic granitic intrusion. *J Afr Earth Sci* 44: 543–560.

Ragan DM. 1973. Structural geology, an introduction to geometrical techniques. 2nd edn. Wiley, 222p.

Rapp RP, Watson EB, Miller CF. 1991. Partial melting of amphibolite/ eclogite and the origin of Archean trondhjemites and tonalites. Precambrian Res 51: 1–25.

Saha-Fouotsa. 2018. Croissance et remobilisation crustale au Néo-protérozoïque : magmatisme, métamorphisme et déformation le long de la zone de cisaillement de Tcholliré – Banyo (région de Mbé – Sassa-Mbersi). [Ph.D. Thesis, University of Ngaoundéré], 245p.

Saha-Fouotsa AN, Tchameni R, Zeh A, Nomo Negue E, Dawaï D, Penaye J, Fosso Tchunte P.M. 2018. Polyphase deformation in the Mbé – Sassa-Bersi area: implications on the tectono-magmatic history of the area and the tectonic evolution of the Tcholliré-Banyo and Central Cameroon Shear Zones (Central North Cameroon). *J Geosci Geomatic* 6: 41–54.

Saha-Fouotsa AN, Vanderhaeghe O, Barbey P, Eglinger A, Tchameni R, Zeh A, Fosso Tchunte P, Nomo Negue E. 2019. The geologic record of exhumed root of the Central African Orogenic Belt in the Central Cameroon domain (Mbé-Sassa-Mbersi region). *J Afr Earth Sci* 151: 286–314.

Sawyer EW. 1994. Melt segregation in the continental crust. *Geology* 22: 1019–1022.

Schwoerer P. 1965. Carte géologique de la reconnaissance au 1/500 000 et notice explicative sur la feuille de Garoua-Est. Direction des Mines et de la Géologie du Cameroun.

Solgadi F, Moyen JF, Vanderhaeghe O, Sawyer, EW, Reisberg L. 2007. The role of crustal anatexis and mantle-derived magmas in the genesis of synorogenic Hercynian granites of the Livradois area, French Massif Central. Canadian Mineralogist 45: 581–606.

Tchakounté J, Eglinger A, Toteu SF, Zeh A, Nkoumbou C, Mvondo-Ondoa J, Penaye J, de Wit M, Barbey P. 2017. The Adamawa-Yadé domain, a piece of Archaean crust in the Neoproterozoic Central African Orogenic Belt (Bafia area, Cameroon). Precambrian Res 299: 210–229.

Tchameni R, Sun F, Dawaï D, Danra G, Tékoum L, Nomo Negue E, Vanderhaeghe O, Nzolang, C, Dagwaï Nguidama. 2016. Zircon dating and mineralogy of the Mokong Pan-African magmatic epidote-bearing granite (North Cameroon). *Int J Earth Sci* 105: 1811–1830.

Tikoff B, Peterson K. 1998. Physical experiments of transpressional folding. *J Struct Geol* 20: 661–672.

Toé W, Vanderhaeghe O, André-Mayer AS, Feybesse JL, & Milési JP, (2013). Frommigmatites to granites in the Pan-African Damara orogenic belt, Namibia. *J Afr Earth Sci* 85: 62–74.

Toteu SF, Michard A, Bertrand J-M., Rocci G. 1987. U/Pb dating of Precambrian rocks from northern Cameroon, orogenic evolution and chronology of the pan-African belt of central Africa. Precambrian Res 37: 71–87.

Toteu SF, Van Schmus RW, Penaye J, Micharda 2001. New U-Pb and Sm-Nd data from North-Central Cameroon and its bearing on the Pre-Pan-African history of Central Africa. Precambrian Res 108: 45–73.

Toteu SF, Penaye J, Djomani YP. 2004. Geodynamic evolution of the Pan-African belt in central Africa with special reference to Cameroon. Can. *J Afr Earth Sci* 41: 73–85.

Toteu SF, Penaye J, Deloule E, Van Schmus WR, Tchameni R. 2006. Diachronous evolution of volcano-sedimentary basins north of the Congo craton: insights from U-Pb ion microprobe dating of zircons
from the Poli, Lom and Yaounde Series (Cameroon). J Afr Earth Sci 44: 428–442.

Toteu SF, Wit MD, Penaye J, Drost K, Tait AJ, Bouyo Houketchang M, Van Schmus WR, Jelsma H, Moloto-A-Kenguemba GR, Filho AFS, Lerouge C, Doucouré M. 2022. Geochronology and correlations in the Central African Fold Belt along the northern edge of the Congo Craton: new insights from U-Pb dating of zircons from Cameroon, Central African Republic, and southwestern Chad. Gondwana Res 107: 296–324.

Trompette R. 1997. Neoproterozoic (600 Ma) aggregation of Western Gondwana: a tentative scenario. Precambrian Res 82: 101–112.

Trompette R. 2000. Gondwana evolution; its assembly at around 600 Ma. Comptes Rendus de l'Académie des Sciences, Sciences de la Terre et des Planètes 330: 305–315.

Vanderhaeghe O. 2001. Melt segregation, pervasive melt migration and magma mobility in the continental crust: the structural record from pores to orogens. Phys Chem Earth Part Solid Earth Geodesy 26: 213–223.

Vanderhaeghe O. 2009. Migmatites, granites and orogeny: Flow modes of partially molten rocks and magmas associated with melt/

solid segregation in orogenic belts. Tectonophysics, Hot orogens 477: 119–134.

Van Schmus, WR, Oliveira EP, da Silva Filho AF, Toteu SF, Penaye J, Guimarães IP. 2008. Proterozoic links between the Borborema Province, NE Brazil, and the Central African Fold Belt. Geology Society London Special Publication 294: 69–99.

Weinberg RF, Hasalová P. 2015. Water-fluxed melting of the continental crust: a review. Lithos 212-215: 158–188.

Weinberg RF, Vernon Ron H, Schmeling H. 2021. Processes in mushes and their role in the differentiation of granitic rocks. Earth-Sci Rev 220: 103665.

White R, Pomroy N, Powell R. 2005. An in situ metatexite-diatexite transition in upper amphibolite facies rocks from Broken Hill, Australia. J Metamorphic Geol 23: 579–602.

Wolf MB, Wyllie PJ. 1994. Dehydration-melting of amphibolite at 10 kbar: the effects of temperature and time. Contrib Mineral Petrol 115: 369–383.

Wyllie PJ, Wolf MB. 1993. Amphibolite dehydration-melting: sorting out the solidus. Geolology Society London Special Publication 76: 405–416.

**Cite this article as:** Djuimou ST, Houketchang MB, Vanderhaeghe O, Megnemo LA, Mbounou LRA, Gregoire M, Dongmo AK. 2025. The Djourdé-Sinassi magmatic-migmatitic complex, Northern Cameroon: a record of vertical extrusion of the Pan-African partially molten orogenic root, BSGF - *Earth Sciences Bulletin* 196: 11. https://doi.org/10.1051/bsgf/2025014