| Titre : |
Le batholite composite de l'Adrar des Iforas (Mali) : et géochronologie d'une succession magmatique du calco-alcalin à l'alcalin dans le cadre de l'orogenèse pan-africaine |
| Type de document : |
texte imprimé |
| Auteurs : |
Liegeois, Jean Paul, Auteur |
| Editeur : |
Bruxelles - Belgique : Académie royale des Sciences de l'Outre-mer (ARSOM) |
| Année de publication : |
1988 |
| Collection : |
Mémoires in-8° |
| Sous-collection : |
Sciences naturelles et médicales num. n.s., t.22, fasc.2 |
| Importance : |
1 v. (xii, 231 p.) |
| Présentation : |
ill., cartes |
| Note générale : |
Thèse de doctorat révisée, Université Libre de Bruxelles, 1987
Réf. bibl. p. 167-185 |
| Langues : |
Français (fre) |
| Catégories : |
Géochimie -- Adrar des Iforas (Mali et Algérie) ; Géologie -- Adrar des Iforas (Mali and Algérie) ; Géologie et minéralogie
|
| Index. décimale : |
556.7 |
| Note de contenu : |
The Adrar des Iforas has essentially been built in the Pan-African epoch lato sensu (730-550 Ma) during the subduction and subsequent collision between the Tuareg shield and the West African craton of Eburnean age (2000 Ma). In the Iforas, the oblique and docking nature of the collision has preserved both the units linked to pre-tectonic magmatic and volcano-sedimentary events and a huge composite talc alkaline batholith which is finally intruded by alkaline magmas. The intrusion of the different plutons of the Iforas composite batholith have been related to successive steps of oceanic closure: subduction, collision and post-collision events. The different phases of the Pan-African orogeny have then been dated. We conclude that the Pan-African in the Iforas, as in Hoggar, has its climax around 600 Ma and that the magmatic activity of the batholith has lasted about 100 Ma. The isotopic (Sr, Nd, Pb, O) and geochemical (major, traces and rare earth elements) studies have demonstrated a mantle origin for both talc-alkaline and alkaline groups. Modelling has followed composition evolution of the mantle-source during the collision, based on the definition of representative source-areas found in the Iforas. The synthesis has led to a geodynamical model in which subduction and collision magmas are both derived from the lithospheric mantle modified by the fluids rising from the dehydration of the oceanic subducted plate. In this model, the alkaline group is the result of the conjugated effects of the reactivation of lithospheric shear-zones and the rise of the asthenosphere during the break-up of the plunging oceanic plate. Both groups have suffered contamination from the granulitic lower crust (5 to 20%). This study shows the importance of crustal accretion during Pan-African orogeny, defines and interprets the characteristics of magmas linked to late Precambrian subduction and collision and advances some ideas on alkaline magma genesis in a post-tectonic context |
Le batholite composite de l'Adrar des Iforas (Mali) : et géochronologie d'une succession magmatique du calco-alcalin à l'alcalin dans le cadre de l'orogenèse pan-africaine [texte imprimé] / Liegeois, Jean Paul, Auteur . - Bruxelles - Belgique (Brusselles - Belgique) : Académie royale des Sciences de l'Outre-mer (ARSOM), 1988 . - 1 v. (xii, 231 p.) : ill., cartes. - ( Mémoires in-8°. Sciences naturelles et médicales; n.s., t.22, fasc.2) . Thèse de doctorat révisée, Université Libre de Bruxelles, 1987
Réf. bibl. p. 167-185 Langues : Français ( fre)
| Catégories : |
Géochimie -- Adrar des Iforas (Mali et Algérie) ; Géologie -- Adrar des Iforas (Mali and Algérie) ; Géologie et minéralogie
|
| Index. décimale : |
556.7 |
| Note de contenu : |
The Adrar des Iforas has essentially been built in the Pan-African epoch lato sensu (730-550 Ma) during the subduction and subsequent collision between the Tuareg shield and the West African craton of Eburnean age (2000 Ma). In the Iforas, the oblique and docking nature of the collision has preserved both the units linked to pre-tectonic magmatic and volcano-sedimentary events and a huge composite talc alkaline batholith which is finally intruded by alkaline magmas. The intrusion of the different plutons of the Iforas composite batholith have been related to successive steps of oceanic closure: subduction, collision and post-collision events. The different phases of the Pan-African orogeny have then been dated. We conclude that the Pan-African in the Iforas, as in Hoggar, has its climax around 600 Ma and that the magmatic activity of the batholith has lasted about 100 Ma. The isotopic (Sr, Nd, Pb, O) and geochemical (major, traces and rare earth elements) studies have demonstrated a mantle origin for both talc-alkaline and alkaline groups. Modelling has followed composition evolution of the mantle-source during the collision, based on the definition of representative source-areas found in the Iforas. The synthesis has led to a geodynamical model in which subduction and collision magmas are both derived from the lithospheric mantle modified by the fluids rising from the dehydration of the oceanic subducted plate. In this model, the alkaline group is the result of the conjugated effects of the reactivation of lithospheric shear-zones and the rise of the asthenosphere during the break-up of the plunging oceanic plate. Both groups have suffered contamination from the granulitic lower crust (5 to 20%). This study shows the importance of crustal accretion during Pan-African orogeny, defines and interprets the characteristics of magmas linked to late Precambrian subduction and collision and advances some ideas on alkaline magma genesis in a post-tectonic context |
|
Accueil
Ajouter le résultat dans votre panier Faire une suggestion Affiner la recherche
