Structure and petrology of Pan-African nepheline syenites from the South West Cameroon; Implications for their emplacement mode, petrogenesis and geodynamic significance

Emmanuel Nsifa Nkonguin 1 Rigobert Tchameni 2 Anne Nédélec 3 Roberto Siqueira 3, 4 André Pouclet 5 Jerôme Bascou 6
1 Département des Sciences de la Terre
2 Département des Sciences de la Terre
3 GET - Géosciences Environnement Toulouse
4 Instituto de Geociências [São Paulo]
5 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
6 LMV - Laboratoire Magmas et Volcans
Abstract : Three late-Neoproterozoic nepheline syenite intrusions crop out close to the late-Pan-African SW Cameroon shear zone, namely the Mont des Eléphants, Eboundja and Rocher du Loup intrusions. They are characterized by magmatic to solid-state deformation structures and microstructures. Their magmas were mainly derived from partial melting of the subcontinental lithospheric mantle. Magmatic differentiation may have occurred through fractionation of clinopyroxene, amphibole, plagioclase and accessory minerals (apatite, sphene, magnetite and zircon). Bulk magnetic susceptibilities are variable in intensity depending of the magnetite content. Their magnetic anisotropies are unusally high, especially in the Rocher du Loup intrusion. The trajectories of magnetic foliations and lineations display an arcuate shape from an E-W direction in the easternmost Mont des Eléphants to a N-S direction in the Rocher du Loup intrusion. These features are consistent with a synkinematic emplacement in relation with the sinistral motion along the SW Cameroon shear zone, whose age is therefore dated by the age of the syenites, i.e. 590 Ma. Magma genesis and ascent was likely favored by a large gradient in lithospheric thickness along the western margin of the Congo craton.
Keywords : Nepheline syenite Southwest Cameroon AMS Pan-African Shear zone
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Journal articles
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Submitted on : Tuesday, August 20, 2013 - 10:51:27 AM
Last modification on : Friday, January 10, 2020 - 9:09:55 PM

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Emmanuel Nsifa Nkonguin, Rigobert Tchameni, Anne Nédélec, Roberto Siqueira, André Pouclet, et al.. Structure and petrology of Pan-African nepheline syenites from the South West Cameroon; Implications for their emplacement mode, petrogenesis and geodynamic significance. Journal of Southeast Asian earth sciences, Elsevier, 2013, 87, pp.44-58. ⟨10.1016/j.jafrearsci.2013.07.008⟩. ⟨insu-00852181⟩

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