Kourim, FatnaBodinier, Jean-LouisAlard, OlivierBendaoud, AbderrahmaneVauchez, AlainDautria, Jean-Marie2026-01-012026-01-010022-3530WOS:000345833900006https://hdl.handle.net/1885/733799461Peridotite xenoliths exhumed by Quaternary alkaline magmatism in the Tahalgha district, southern Hoggar, represent fragments of the subcontinental lithospheric mantle beneath the boundary between the two major structural domains of the Tuareg Shield: the 'Polycyclic Central Hoggar' to the east and the 'Western Hoggar', or 'Pharusian Belt', to the west. Samples were collected from volcanic centres located on both sides of a major lithospheric shear zone at 4°35' separating these two domains. Although showing substantial variations in their deformation microstructures, equilibrium temperatures and modal and chemical compositions, the studied samples do not display any systematic changes of these features across the 4°35'fault.The observed variations rather record small-scale heterogeneities distributed throughout the study area and reflecting the widespread occurrence of vein conduits and metasomatized wallrocks related to trans-lithospheric melt circulation during the Cenozoic. These features include partial annealing of pre-existing deformation microstructures, post-deformation metasomatic reactions, and trace-element enrichment, coupled with heating from 750-900°C (low-temperature lherzolites) to 900-1150°C (intermediate- T lherzolites and high-T harzburgites and wehrlites). Trace-element modelling confirms that the range of rare earth element (REE) variations observed in theTahalgha clinopyroxenes may be accounted for by reactive porous flow involving a single stage of basaltic melt infiltration into a light REE (LREE)-depleted protolith. Whole-rock compositions record the final entrapment of disequilibrium metasomatic melts upon thermal relaxation of the veins-wall-rock system. The striking correlations between equilibrium temperatures and trace-element enrichment favor a scenario in which the high-temperature peridotites record advective heat transport along melt conduits, whereas the intermediate- and lowtemperature lherzolites reflect conductive heating of the host Mechanical Boundary Layer. This indicates that the lithosphere did not reach thermal equilibrium, suggesting that the inferred heating event was transient and was rapidly erased by thermal relaxation down to the relatively low-temperature present-day geotherm. The low-T (< 900°C) deformed lherzolites (porphyroclastic to equigranular) are characterized by only incipient annealing and LREEdepleted clinopyroxene compositions.They were only weakly affected by the Cenozoic events and could represent relatively well-preserved samples from rejuvenated Pan-African lithosphere. Extensive lithospheric rejuvenation occurred either regionally during the Pan-African orogeny, as a result of lithospheric delamination or thermomechanical erosion after thickening, or more locally along the meridional shear zones.The low-TTahalgha lherzolites are comparable with lherzolites from Etang de Lherz, southern France, interpreted as lithospheric mantle rejuvenated by melt-induced refertilization during a late stage of theVariscan orogeny.This study was performed as part of a collaborative multidisciplinary research project on the Hoggar region chiefly involving the Facultedes Sciences de la Terre, de Geographie et d'Amenagement du Territoire (FSTGAT, USTHB, Algiers) and Geosciences Montpellier, funded by the Centre National de la Recherche Scientifique (CNRS, France: INSU and DERCI), the Direction de la Post-Graduation Recherche-Formation (DPGRF, Algeria), and the French Ministry of Foreign Affairs (MAE), through a CNRS (BDI-PED) PhD grant to F.K. (2010-2013), a CNRS-DPGRF PICS co-operation project (2008-2010), and an MAE bilateral co-operation project in the frame of the Tassili Hubert Curien program (2009 2012). Several INSU research grants (SEDIT 2007, Actions Coordonnees 2008, and SYSTER 2010-2011 programs) and the FP7-PEOPLE-IRSES project MEDYNA 2014-2017 (Maghreb-EU research staff exchange on geoDYnamics, geohazards, and applied geology in Northwest Africa, Work Package #3: Deep structures and mantle processes).32enPublisher Copyright: © The Author 2014. Published by Oxford University Press. All rights reserved.Hoggar swellPan-African orogenyTuareg ShieldLithosphere rejuvenationMantle metasomatismMantle xenolithPeridotiteRare earth elements201410.1093/petrology/egu05610.1093/petrology/egu05684987897185