Origin of the DUPAL anomaly in mantle xenoliths of Patagonia (Argentina) and geodynamic consequences
Résumé
The sub-continental lithospheric mantle of South America has been known for some time to carry the DUPAL isotope anomaly as seen in volcanics from the Paraná volcanic province. However, this has not allowed discriminating whether the DUPAL anomaly is a primary feature of the mantle source or acquired during the upwelling and emplacement of the primary magmas. We discovered mantle xenoliths from the Tres Lagos location in Patagonia that carry evidence of percolation by metasomatic melts that imparted the DUPAL isotope anomaly signature. We discuss a model that requires four isotope components (LCC, EM2, HIMU and DM) to account for the Sr, Nd and Pb isotope variability of our samples. We propose that upwelling of hot astenosphere during the Miocene could have triggered the melting of the LCC and EM2 components carrying the DUPAL anomaly, previously entrained in the subcontinental mantle by subduction. These ascending melts would have then metasomatised the local SCLM characterised by DMM and HIMU geochemical affinity generating the hybrid DUPAL-bearing mantle sampled by the Tres Lagos xenoliths.