Sampling an active continental paleo-margin: a LA-ICP-MS U-Pb zircon study from the Adrar des Iforas (Mali) - Archive ouverte HAL
Communication Dans Un Congrès Année : 2008

Sampling an active continental paleo-margin: a LA-ICP-MS U-Pb zircon study from the Adrar des Iforas (Mali)

Olivier Bruguier
Delphine Bosch
Renaud Caby
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Beatrice Galland
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Résumé

The Tuareg Shield results from the amalgamation, during the Pan-African orogeny, of more than twenty terranes comprising Neoproterozoic juvenile oceanic terranes and reworked or well-preserved Archean and Paleoproterozoic crustal blocks. All these amalgamated terranes are limited by trans-continental N–S shear-zones. Their main relative movements resulted from a Northern transpressional tectonic escape due to their squeezing between the West African craton (WAC) to the west and the East Saharan craton to the East. This configuration hampers tectonic correlations through the shield, but gives rise to major issues including the way along which amalgamation of the terranes occurred, their respective tectonometamorphic evolution and their origin. In order to help unravel the tectonometamorphic evolution of the westernmost part of the shield, we performed LA-ICPMS UPb zircon geochronology on samples from key lithologies collected through the Adrar des Iforas area (Mali). Samples were selected in order to represent a Neoproterozoic Andeantype active margin developed during subduction of the WAC beneath the Iforas terrane of the Tuareg Shield. In the Central Iforas Belt, arc-related calc-alkaline magmatism occurred as early as 716±6 Ma and was coeval with the 710-730 Ma old Tilemsi intraoceanic arc. Subduction-related magmatism persisted until 634±8 Ma and possibly down to 623±6 Ma, the age of the Tafeliant metadacite. Calc-alkaline batholiths were emplaced into a pre-Panafrican gneissic basement containing Paleoproterozoic units (such as the Tafeliant syenitic gneiss dated at 1966±9 Ma) and Archean components (inheritance in granitoids at c. 2.4-2.5 Ga and up to 2.8 Ga). Emplacement of syn-kinematic granitic plutons, associated to collision with the WAC, occurred at 604±5 Ma, whereas late-kinematic emplacement of the central batholith is dated at 599±3 Ma. East of the Adrar fault, the basement of the Eastern Iforas Belt contains Paleoproterozoic granitoids (Tin Essako orthogneiss dated at 2020±5 Ma), which were intruded by pre-kinematic granitoids such as the 630±6 Ma Tamaradant metadiorite. This suggests a possible synchronism of ante-collisional events on either sides of the Iforas Granulitic Unit.
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Dates et versions

hal-03945256 , version 1 (18-01-2023)

Identifiants

  • HAL Id : hal-03945256 , version 1

Citer

Olivier Bruguier, Delphine Bosch, Renaud Caby, Beatrice Galland, Dalila Hammor. Sampling an active continental paleo-margin: a LA-ICP-MS U-Pb zircon study from the Adrar des Iforas (Mali). Goldschmidt 2008: “From SEA to SKY”, Pacific Centre for Isotopic and Geochemical Research, Jul 2008, Vancouver (BC), Canada. pp.78. ⟨hal-03945256⟩
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