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

By Emmanuel Nsifa Nkonguin, Rigobert Tchameni, Anne Nédélec, Roberto Siqueira, André Pouclet and Jerôme Bascou

Abstract

International audienceThree 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

Topics: Nepheline syenite, Southwest Cameroon, AMS, Pan-African, Shear zone, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, [SDE.MCG]Environmental Sciences/Global Changes
Publisher: 'Elsevier BV'
Year: 2013
DOI identifier: 10.1016/j.jafrearsci.2013.07.008
OAI identifier: oai:HAL:insu-00852181v1
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