[ Evolution des paragenèses métamorphiques dans les formations panafricaines du Sud Maradi (Sud Niger) ]
Volume 34, Issue 2, November 2021, Pages 380–395
Baraou Souley Idi1 and Moussa Konaté2
1 Université d’Agadez, Faculté des Sciences et Techniques, Département de Géologie, P.O. Box 199, Agadez, Niger
2 Université Abdou Moumouni de Niamey, Faculté des Sciences et Techniques, Laboratoire de Géologie: Eaux Souterraines et Géoressources, BP 10662, Niamey, Niger
Original language: French
Copyright © 2021 ISSR Journals. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The Pan-African province of South Maradi represents the northern part of Benin-Nigerian Shield, corresponding to the Pan-African mobile zone located in the East of West African Craton. In this basement zone, the distribution of metamorphic formations is marked by gradual transitions: from schists to gneiss and then to migmatites. The schists outcrop in a NE-SW bands, alternating parallely with gneiss bands, limited by the shear zones. The alternation of schists and gneiss bands, associated to ductile shear zones and the existence of a gradual transition from schists to migmatite, raises questions about the geodynamic context of crustal evolution. The study of metamorphic paragenesis (aim of this study), allows to specify the geodynamic context that prevailed in this portion of the pan-African mobile zone of South Maradi. The methodological approach combines petrostructural analysis and determination of mineral assemblages by using the petrographic microscope. The chronology of the metamorphic mineral assemblages and their relationship with the deformation structures made it possible to highlight a prograde phase of metamorphic evolution (green schist facies- amphibolite facies, granulite facies) then retrograde, synchronous with a tangential tectonic and then transcurrent one. Further south in the contiguous Pan-African province of Nigeria, pressure elevation from 6.8 kbars to 9-10 kbars associated with a prograde metamorphism have been related to burial then to a crustal thickening by pile-ups.
Author Keywords: South Maradi, Pan-African mobile zone, Schists and Gneiss bands, Shear zone, Mineral paragenesis.
Volume 34, Issue 2, November 2021, Pages 380–395
Baraou Souley Idi1 and Moussa Konaté2
1 Université d’Agadez, Faculté des Sciences et Techniques, Département de Géologie, P.O. Box 199, Agadez, Niger
2 Université Abdou Moumouni de Niamey, Faculté des Sciences et Techniques, Laboratoire de Géologie: Eaux Souterraines et Géoressources, BP 10662, Niamey, Niger
Original language: French
Copyright © 2021 ISSR Journals. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
The Pan-African province of South Maradi represents the northern part of Benin-Nigerian Shield, corresponding to the Pan-African mobile zone located in the East of West African Craton. In this basement zone, the distribution of metamorphic formations is marked by gradual transitions: from schists to gneiss and then to migmatites. The schists outcrop in a NE-SW bands, alternating parallely with gneiss bands, limited by the shear zones. The alternation of schists and gneiss bands, associated to ductile shear zones and the existence of a gradual transition from schists to migmatite, raises questions about the geodynamic context of crustal evolution. The study of metamorphic paragenesis (aim of this study), allows to specify the geodynamic context that prevailed in this portion of the pan-African mobile zone of South Maradi. The methodological approach combines petrostructural analysis and determination of mineral assemblages by using the petrographic microscope. The chronology of the metamorphic mineral assemblages and their relationship with the deformation structures made it possible to highlight a prograde phase of metamorphic evolution (green schist facies- amphibolite facies, granulite facies) then retrograde, synchronous with a tangential tectonic and then transcurrent one. Further south in the contiguous Pan-African province of Nigeria, pressure elevation from 6.8 kbars to 9-10 kbars associated with a prograde metamorphism have been related to burial then to a crustal thickening by pile-ups.
Author Keywords: South Maradi, Pan-African mobile zone, Schists and Gneiss bands, Shear zone, Mineral paragenesis.
Abstract: (french)
La province panafricaine du Sud Maradi représente l’extrémité septentrionale du Bouclier Bénino-Nigérian, correspondant à la portion de la zone mobile panafricaine située à l’Est du Craton Ouest Africain. Dans cette zone de socle, la distribution des formations métamorphiques est marquée par des passages graduels: des schistes à des gneiss puis à des migmatites. Les schistes forment des lanières d’orientation NE-SW, en alternance avec des bandes de gneiss, de même orientation, limitées par des couloirs de cisaillement (Shear Zone). L’alternance des bandes de schistes et de gneiss, associée à des couloirs de cisaillements ductiles et l’existence d’un passage graduel des schistes à des migmatites, conduit à se poser des questions sur le contexte géodynamique de l’édification de la croûte. L’étude des paragenèses métamorphiques, objet de la présente étude, permet de préciser le contexte géodynamique qui a prévalu, dans cette portion de la zone mobile panafricaine du Sud Maradi. L’approche méthodologique associe l’analyse pétrostructurale et la détermination des paragenèses minérales au microscope polarisant. La chronologie des assemblages métamorphiques et leurs calages par rapport aux structures de déformations a permis de mettre en évidence une phase prograde de l’évolution métamorphique (faciès schiste vert-faciès apmhibolite, faciès granulite) puis rétrograde, synchrone d’une tectonique tangentielle puis transcurrente. Plus au Sud dans la province panafricaine contiguë du Nigéria, les élévations de pression de 6.8 kbars à 9-10 kbars associées au métamorphisme prograde a été relié à un enfouissement, lié à un épaississement crustal par empilements de nappes.
Author Keywords: Sud Maradi, zone mobile panafricaine, bandes de schistes et de gneiss, couloir de cisaillement, paragenèse minérale.
How to Cite this Article
Baraou Souley Idi and Moussa Konaté, “Evolution of metamorphic paragenesis in the South Maradi Pan-African formations (South Niger),” International Journal of Innovation and Applied Studies, vol. 34, no. 2, pp. 380–395, November 2021.
